WO2014194926A1

WO2014194926A1 - Method for controlling an operation of a multi-clutch transmission

Info

Publication number: WO2014194926A1
Application number: PCT/EP2013/001621
Authority: WO
Inventors: Anders Hedman
Original assignee: Volvo Truck Corporation
Priority date: 2013-06-04
Filing date: 2013-06-04
Publication date: 2014-12-11

Abstract

The present invention relates to a method for controlling an operation of a multi-clutch transmission (100) operatively connected to a prime mover of a vehicle. The multi-clutch transmission (100) includes a dual-clutch assembly (10), a clutch input shaft (20) drivingly connected to the prime mover and a transmission output shaft (30).The dual-clutch assembly (10) is provided with a first clutch (12) and a second clutch (14) operatively connected to the clutch input shaft (20) and configured for transmitting a rotational torque of the clutch input shaft (M_cis); the first clutch (12) is operatively connected with a first input shaft (42) of a first sub-transmission (40) having a first set of gears (70), the first clutch (12) is transmitting a first rotational torque portion (Μ₁) of the rotational torque of the clutch input shaft (M_cis) to the first input shaft (42); the second clutch (14) is operatively connected with a second input shaft (52) of a second sub-transmission (50) having a second set of gears (80), the second clutch (14) is transmitting a second rotational torque portion (M₂) of the rotational torque of the clutch input shaft (M_cis) to the second input shaft (52), the method comprising the steps of: (a) engaging the first clutch (12), or the first clutch (12) and the second clutch (14), at a launch of the vehicle for transmitting a rotational torque (M_output) to the transmission output shaft (30) while a rotational speed of the first input shaft (42) is different from a rotational speed of the clutch input shaft (20); and (b) decreasing the initial amount of the first rotational torque portion (M₁) to a decreased amount and increasing the initial amount of the second rotational torque portion (M₂) to an increased amount while the rotational speed of the first input shaft (42) is different from the rotational speed of the clutch input shaft (20). The present invention also relates to a control unit (60) for a vehicle configured for implementing a method for controlling the operation of the multi-clutch transmission (100).

Description

METHOD FOR CONTROLLING AN OPERATION OF A MULTI-CLUTCH TRANSMISSION

Field of the Invention

The present invention relates to a method for controlling an operation of a multi-clutch transmission operatively connected to a prime mover of a vehicle. The present invention is particularly suitable for heavy, on- and off-road vehicles. Moreover, the present invention relates to a control unit for a vehicle configured for implementing a method for controlling an operation of a multi-clutch transmission.

Background of the Invention

Conventionally, dual clutch transmissions are cross-breed between stepped transmissions, with power interruption at gear shifts, and powershifting, without power interruption, planetary transmissions. A dual clutch transmission uses two separate clutches for odd and even gears, which are typically provided in the form of friction clutches or dry multi-plate clutches. The two clutches are operatively connected to two input shafts, respectively, and to the output of the engine. Functionally, this is equivalent to utilizing two conventional transmissions in parallel, i.e. two parallel sub-transmissions, while operating one at a time for power transfer. The sub-transmission that is currently not in use, i.e. idling, can have a gear engaged and prepared for a subsequent shift. As a result, the shift may be carried out by simultaneously disengaging the clutch of the previously used sub-transmission and engaging the clutch of the previously idling sub-transmission.

In addition, a dual-clutch transmission has many components in common with a conventional stepped transmission, e.g. gearwheels, shafts and tooth clutches. Hence, it is likely that a properly designed dual-clutch transmission will have the potential of providing powershifts at a reasonable production cost and at low power losses. Due to the similarity in components with conventional stepped transmissions, dual-clutch transmissions and conventional stepped transmissions may be manufactured in the same production facilities and with the same production equipment. Various types of dual-clutch transmissions are known for heavy vehicles. US 5 150 628, for example, discloses a dual-clutch transmission for rear wheel drive vehicles having two separate countershafts connected to two input shafts, respectively. The countershafts are here arranged parallel to the transmission input which may lead to difficulties in installing the transmission into the vehicle since the transmission becomes somewhat wider than a conventional stepped transmission. DE 923 402 and DE 3 131 156 Al disclose further examples of dual-clutch transmissions. This type of transmission comprises only one countershaft. On the countershaft, there is arranged a couple of loose gearwheels which are capable of being selectively engaged through a plurality of mechanical tooth clutches. In this manner, it becomes possible to provide a powershiftable dual-clutch transmission nearly as slim as a corresponding conventional stepped transmission. However, the number of gears and the available speed reduction ratios are believed to be insufficient for heavy duty vehicles.

One critical component in a dual-clutch transmission is the set of clutches. A clutch has limited thermal capacity and often inadequate service life due to wear.

In addition, at the launch of the vehicle, there is a significant amount of heat generated due to slipping of the engaged clutch. This is partly due to that conventional methods for operating the dual-clutch transmission only make use of one of the clutches at the vehicle launch. Typically, the lowest gear of the available set of gears is activated by the first clutch, while a higher gear is prepared by the second clutch. The second clutch is thereafter engaged so as to activate a different gear.

Over time, the operation of the dual-clutch transmission has continuously been further developed and for heavy vehicles it has often been an aim to improve the acceleration of the vehicle at the launch. However, to launch a heavy vehicle is not always a simple operation. Above all, it is particularly demanding for the clutches since a high amplification of the torque of the prime mover is required which is partly due to a low ratio between prime mover power and vehicle weight. Several attempts to achieve this have been carried out. In WO 2004/010019, for example, a dual-clutch transmission is disclosed which utilises two clutches simultaneously at the launch of the vehicle. More specifically, each clutch of the two clutches transmits a constant and equal torque portion at the entire launch phase of the vehicle. Thereby, the operation of this dual-clutch transmission allows for a fairly equal sharing of thermal load among the two clutches.

Despite the activity in the field, exemplified by the above-cited disclosures, there remains a need for a method of controlling a multi-clutch transmission which combines high performance and functionality with an acceptable period of use in service. In particular, there is a need for an alternative solution of controlling a multi- clutch transmission enabling an improved and smooth launch of the vehicle.

It would be beneficial if it could be ensured that the launch of the vehicle can be initiated without excessive wear of the clutches.

Summary of the Invention

It is an object of the present invention to provide a method for controlling an operation of a multi-clutch transmission having improved functionalities in relation to prior art solutions.

According to a first aspect of the present invention there is provided a method for controlling an operation of a multi-clutch transmission. The multi-clutch transmission is operatively connected to a prime mover of a vehicle. The multi-clutch transmission comprises a dual-clutch assembly, a clutch input shaft drivingly connected to the prime mover and a transmission output shaft. The multi-clutch assembly is provided with a first clutch and a second clutch operatively connected to the clutch input shaft and configured for transmitting a rotational torque of the clutch input shaft M_cj_s. The first clutch is operatively connected with a first input shaft of a first sub-transmission having a first set of gears, the first clutch is transmitting a first rotational torque portion Mi of the rotational torque of the clutch input shaft M_Cj_S to the first input shaft, the first rotational torque portion

being transformed via a first gear of the first set of gears to the transmission output shaft. Analogously, the second clutch is operatively connected with a second input shaft of a second sub-transmission having a second set of gears, the second clutch is transmitting a second rotational torque portion M₂ of the rotational torque of the clutch input shaft M_cj_S to the second input shaft, the second rotational torque portion M₂ being transformed via a second gear of the second set of gears to the transmission output shaft. The method comprises the steps of:

a. engaging the first clutch, or the first clutch and the second clutch, at a launch of the vehicle for transmitting a rotational torque M_0Ut_Put to the transmission output shaft while a rotational speed of the first input shaft is different from a rotational speed of the clutch input shaft, wherein an initial amount of the first rotational torque portion M is higher than an initial amount of the second rotational torque portion M₂ such that the first clutch transmits a higher amount of the rotational torque of the clutch input shaft M_Cj_S than the second clutch; and

b. decreasing the initial amount of the first rotational torque portion Mi to a decreased amount and increasing the initial amount of the second rotational torque portion M₂ to an increased amount while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft.

In other words, the present invention relates to an optimization of the operation of the multi-clutch transmission. In particular, the present invention relates to an optimization of the operation of the multi-clutch transmission at the launch of the vehicle so as to reduce the wear of the components in the multi-clutch transmission, while maintaining a high amplification of the rotational torque of the prime mover. Thereby, it becomes possible to set the vehicle in motion in an effectual and reliable manner.

It is to be noted that in the context of the present invention, the provision while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft refers to the relation between the rotational speed of the first input shaft and the rotational speed of the clutch input shaft prior to the synchronous condition of the first input shaft and the rotational speed of the clutch input shaft. It should be generally understood that the term "synchronous condition" here refers to a condition when the first clutch is synchronized with the clutch input shaft, i.e. when the rotational speed of the first input shaft is equal to the rotational speed of the clutch input shaft. Thus, when the first clutch is in a synchronous condition with the clutch input shaft, there is no slipping of the first clutch. From the above, it can therefore be readily understood that the provision while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft may also be denoted as the slipping phase of the first clutch.

Analogously, the second clutch is in a synchronous condition when the second clutch is synchronized with the clutch input shaft, i.e. when the rotational speed of the second input shaft is equal to the rotational speed of the clutch input shaft. Thus, when the second clutch is in a synchronous condition with the clutch input shaft, there is no slipping of the second clutch.

Thus, by the provision while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft in step (a), it is meant that step (a) is initiated before the first clutch is in a synchronous condition with the clutch input shaft. Moreover, by the provision while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft in step (b), it is meant that step (b) is initiated before the first clutch is in a synchronous condition with the clutch input shaft.

By the method step (a), as described above, and the provision that the initial amount of the first rotational torque portion M is higher than the initial amount of the second rotational torque portion M₂ such that the first clutch transmits a higher amount of the rotational torque of the clutch input shaft M_cj_S than the second clutch, it becomes possible to initially provide a high amplification of the rotational torque of the prime mover so as to set the vehicle in motion without any difficulties. It addition, the vehicle can be set in motion in a reliable manner since it uses the first gear, which is typically provided with the highest transmission ratio of the available gears. Thereby, the torque on the output shaft, M_0Ut_Put, is maximised, which, in turn, will maximise the tractive effort of the driven wheels of the vehicle.

By the method step (b), as described above, and the provision that decreasing the initial amount of the first rotational torque portion M] to a decreased amount and increasing the initial amount of the second rotational torque portion M₂ to an increased amount while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft, it becomes possible to enhance the flexibility in sharing thermal load (and wear) between the first clutch and second clutch. This is due to that the amount of engagement of the first clutch is decreasingly shifted such that the amount of the first rotational torque portion Mi is decreased compared to the amount in step (a), while the amount of engagement of the second clutch is progressively shifted such that the amount of the second rotational torque portion M₂ is increased compared to the amount in step (a).

Typically, but not strictly necessarily, the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion M_1? such that the second clutch transmits a higher amount of the rotational torque of the clutch input shaft M_cj_s than the first clutch

Thus, by the principle of the present invention, it becomes possible to enhance the flexibility in sharing thermal load (and wear) between the first clutch and the second clutch. As such, the torque transfer contribution from the first clutch and the second clutch is optimized at the initial phase of the vehicle launch, i.e. step (a), and subsequently shifted to another torque transfer contribution between the first clutch and the second clutch, i.e. step (b).

By allowing for an optimization of sharing thermal load between the clutches at the vehicle launch, the service life of the multi-clutch transmission can be extended avoiding costly and time-consuming maintenance work. Moreover, by controlling the operation of the multi-clutch transmission according to the above principle, the vehicle launch (i.e. moving away from rest) can be controlled in a very straightforward manner by decreasingly shifting the amount of engagement of the first clutch and progressively shifting the amount of engagement of the second clutch. To this end, the method for controlling the operation of the multi-clutch transmission allows for high comfort and fuel-efficient driving.

In the alternative above when step (a) only involves engaging the first clutch, it should be readily understood that no rotational torque of the clutch input shaft M_cj_s is transmitted by the second clutch. Hence, the second clutch may not be operated at the initial phase of the launch of the vehicle for transmitting a rotational torque M_output to the transmission output shaft while a rotational speed of the first input shaft is different from a rotational speed of the clutch input shaft. In the alternative above when step (a) involves engaging the first clutch and second clutch, the second clutch is used to share thermal load so as to keep the level of wear of the first clutch to a minimum.

In particular, it has been realised by the inventor that the clutches of a multi- clutch transmission can be thermally overloaded at the launch of the vehicle due to excessive slipping of the clutch in order to set the vehicle in motion. Even normal use of a clutch increases the wear, and decreases the lifespan, of the clutch. Therefore, at very heavy launch of a heavy vehicle, there is typically excessive slipping of the clutch causing a significant amount of heat generation in the clutch. At least for this reason, the present invention specifically relates to a method for controlling the operation of a multi-clutch transmission at the launch of the vehicle, i.e. moving away from rest.

By the term "drivingly connected" typically means that a first component is connected to a second component in a manner allowing a transfer of a rotational movement and/or rotational torque from the first component to the second component. Therefore, the term encompasses a functional construction in which two components are connected such that the rotational speed of the first component corresponds to the rotational speed of the second component. However, the term also encompasses a functional construction in which there is a ratio between the rotational movement of the first component and the rotational movement of the second component, i.e., the rotational speed of the second component is proportional to the rotational speed of the first component.

By the term "operatively connected" or "operatively driven" means that a component is in operative relation to another component, e.g. the provision that the first clutch is operatively connected to the sub-transmission means that the clutch is in operative relation with the sub-transmission.

It should be readily understood that shifting clutch engagement, e.g. shifting from an engagement of the first clutch to an engagement of the second clutch, while disengaging the first clutch, is not an immediate operation. Instead, it is typically an operation being executed under a transition phase. Similarly, shifting from step (a) to step (b) is normally not an immediate operation, but frequently a shifting, in terms of amount of engagement of the clutches, which is being executed under a transition phase.

Likewise, the step of decreasing the initial amount of the first rotational torque portion Mi to a decreased amount and increasing the initial amount of the second rotational torque portion M₂ to an increased amount is normally executed under a time period (transition phase). As an example, the step (b) may last for about 0.1 - 0.5 s. In this context of the present invention, step (b) may therefore refer to the transition phase, i.e. decreasing an amount the first rotational torque portion Mi and increasing the amount of the second rotational torque portion M₂, and the status of the amount of engagement of the first clutch and second clutch after the transition phase, i.e. the decreased amount and the increased amount.

Decreasing the amount of the rotational torque portion is carried out by decreasing the level (or amount) of engagement of the clutch. Analogously, increasing the amount of the rotational torque portion is carried out by increasing the level (or amount) of engagement of the clutch.

As mentioned above, the increased amount of the second rotational torque portion M₂ may be higher than the decreased amount of the first rotational torque portion Mi. Hereby, the second clutch transmits a higher amount of the rotational torque of the clutch input shaft M_cis than the first clutch. In this manner, the level of engagement of the first clutch is decreased. In other words, unnecessary wear of the first clutch is avoided, which will further extend the service life of the first clutch.

According to an example embodiment, the multi-clutch transmission in step (a) may be operated such that there is a significant difference between the initial amount of the first rotational torque portion and the initial amount of the second rotational torque portion. In this manner, the multi-clutch transmission is capable of providing an initial high amplification of the torque of the prime mover via the first clutch (typically transformed via the gear having the highest transmission ratio) while allowing thermal load to be shared by the two clutches. As an example, the multi- clutch transmission in step (a) may be operated such that the initial amount of the first rotational torque portion Mi amounts to preferably at least 60 % of the rotational torque of the clutch input shaft M_Cj_S. Still preferably, the multi-clutch transmission in step (a) may be operated such that the initial amount of the first rotational torque portion Mi amounts to at least 70 % of the rotational torque of the clutch input shaft M_Cj_S. Still preferably, the multi-clutch transmission in step (a) may be operated such that the initial amount of the first rotational torque portion Mi amounts to at least 80 % of the rotational torque of the clutch input shaft M_Ci_S. Still preferably, the multi- clutch transmission in step (a) may be operated such that the initial amount of the first rotational torque portion M_\ amounts to at least 95 % of the rotational torque of the clutch input shaft M_Cj_S. One advantage with this provision is that the amplification of the prime mover torque is further improved.

In the various torque ratio examples as mentioned above, it goes without saying that the initial amount of the second rotational torque portion M₂ amounts to the remaining amount of the rotational torque of the clutch input shaft M_cj_S (if neglecting torque losses from windage, oil churning, etc.). That is, the initial amount of the first rotational torque portion Mi and the initial amount of the second rotational torque portion M₂ amounts to 100 % of the rotational torque of the clutch input shaft M_ci_s. Hence, if the initial amount of the first rotational torque portion Mi amounts to 60 %, the initial amount of the second rotational torque portion M₂ amounts to 40 % (of the rotational torque of the clutch input shaft M_cj_s). Hence, various torque ratios between the initial amount of the first rotational torque portion Mi and the initial amount of the second rotational torque portion M₂ are conceivable as long as the initial amount of the first rotational torque portion Mi is higher than the initial amount of the second rotational torque portion M₂.

According to another example embodiment of the present invention, the multi- clutch transmission in step (a) may even be operated such that the initial amount of the first rotational torque portion Mi amounts to 100 % of the rotational torque of the clutch input shaft M_Cj_S, whereby the first clutch transmits all rotational torque of the clutch input shaft M_cj_S while the second clutch transmits no rotational torque of the clutch input shaft M_cj_s. One advantage with this provision is that the amplification of the prime mover torque is further improved. In this aspect of the present invention, it is realized that only the first clutch may be engaged in step (a) whilst the second clutch remains disengaged. Alternatively, the multi-clutch transmission in step (a) can initially be operated to engage both the first clutch and the second clutch, while only allowing the first clutch to transmit rotational torque of the clutch input shaft M_Cj_S. It should be readily understood that this can be realised by a pre-selection of a second gear in the second sub-transmission while operating the second clutch to transmit no rotational torque.

According to one example embodiment, the multi-clutch transmission may in step (a) only use the first gear provided with the highest transmission ratio of any of the gears in the first set of gears and the second set of gears. In this manner, it is ensured that the vehicle can be reliably launched at a very heavy launch.

In various example embodiments, the first gear of the first set of gear may be provided with a higher transmission ratio than the second gear of the second set of gears.

In addition, or alternatively, the multi-clutch transmission may in step (b) be operated such that the increased amount of the second rotational torque portion M₂ amounts to preferably at least 60 % of the rotational torque of the clutch input shaft M_Ci_S. By this operation, the first clutch will generate less slipping energy. Still preferably, the multi-clutch transmission may in step (b) be operated such that the increased amount of the second rotational torque portion M₂ amounts to at least 70 % of the rotational torque of the clutch input shaft M_cj_s. Still preferably, the multi-clutch transmission may in step (b) be operated such that the increased amount of the second rotational torque portion M₂ amounts to at least 80 % of the rotational torque of the clutch input shaft M_cj_s. Still preferably, the multi-clutch transmission may in step (b) be operated such that the increased amount of the second rotational torque portion M₂ amounts to at least 95 % of the rotational torque of the clutch input shaft M_Ci_S. It should be readily appreciated that by increasing the amount of the second rotational torque portion M₂, it becomes possible to reduce the slipping energy generated by the first clutch.

In the various torque ratio examples as mentioned above, it goes without saying that the decreased amount of the first rotational torque portion

amounts to the remaining amount of the rotational torque of the clutch input shaft M_cj_s (if neglecting torque losses from windage, oil churning, etc.). That is, if the increased amount of the second rotational torque portion M₂ amounts to 60 %, the decreased amount of the first rotational torque portion M_\ amounts to 40 % (of the rotational torque of the clutch input shaft M_Cj_S). Hence, various torque ratios between the decreased amount of the first rotational torque portion Mi and the increased amount of the second rotational torque portion M₂ are conceivable. The multi-clutch transmission may in step (b) even be operated such that the increased amount of the second rotational torque portion M₂ amounts to 100 % of the rotational torque of the clutch input shaft M_Cj_S. Hereby, the second clutch transmits all rotational torque of the clutch input shaft M_ci_s while the first clutch transmits no rotational torque of the clutch input shaft M_cj_s. By this operation, the first clutch generates less slipping energy. In this aspect of the present invention, it is to be noted that only the second clutch may be engaged in step (b) whilst the first clutch becomes disengaged. Alternatively, the multi-clutch transmission in step (b) may be operated to maintain the engagement of both the first clutch and the second clutch, while only allowing the second clutch to transmit rotational torque of the clutch input shaft M_Ci_S.

Although, in step (b), the increased amount of the second rotational torque portion M₂ typically is higher than the decreased amount of the first rotational torque portion M_ls it is also possible that the shift of the amount of engagement of the clutches in step (b) can be executed such that the decreased amount of the first rotational torque portion Mj is higher than the increased amount of the second rotational torque portion M₂. As an example, the multi-clutch transmission may in step (b) be operated such that the increased amount of the second rotational torque portion M₂ amounts to 45 % of the rotational torque of the clutch input shaft M_cj_S, while the decreased amount of the first rotational torque portion M_\ amounts to 55 % of the rotational torque of the clutch input shaft M_Ci_S. In another example embodiment, the increased amount of the second rotational torque portion M₂ may amount to more than 30 % of the rotational torque of the clutch input shaft M_Ci_S. Still preferably, the increased amount of the second rotational torque portion M₂ may amount to more than 40 % of the rotational torque of the clutch input shaft M_Ci_S. In various example embodiments, the multi-clutch transmission may in step (a) be operated to pre-select a first gear of the first set of gears and a second gear of the second set of gears prior to engaging the first clutch and/or the second clutch.

Alternatively, the multi-clutch transmission may in step (a) be operated to pre- select a first gear of the first set of gears and a second gear of the second set of gears while engaging the first clutch and/or the second clutch.

According to an example embodiment, the method may further comprise the step of:

c. disengaging the first clutch such that the first gear is inactivated and all rotational torque of the clutch input shaft M_Ci_S is transmitted by the second clutch while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft. Hereby, no rotational torque of the clutch input shaft M_Ci_S is transmitted by the first clutch. In addition, there will be no slipping energy generated in the first clutch. Hence, the service life of the first clutch is further extended. Moreover, when the first clutch is disengaged, it becomes possible to pre-select another gear in the first sub-transmission.

d. re-engaging the first clutch for re-activating the first gear of the first set of gears while the rotational speed of the first input shaft is different from the rotational speed of the clutch input shaft, such that both the first clutch and the second clutch transmit rotational torque of the clutch input shaft M_Ci_S. By operating the multi-clutch transmission according to this step, it becomes possible for the first clutch to more rapidly establish a synchronous condition with the clutch input shaft. In addition, unnecessary slipping of the second clutch is avoided.

e. re-engaging the first clutch for re-activating the first gear of the first set of gears while the rotational speed of the first input shaft is equal to the rotational speed of the clutch input shaft, such that both the first clutch and the second clutch transmit rotational torque of the clutch input shaft M_Cj_S. By operating the multi-clutch transmission according to this step, it becomes possible to even better share thermal energy between the first clutch and the second clutch before any of the clutches is in a synchronous condition with the clutch input shaft.

f. disengaging the second clutch such that the second gear is inactivated and all rotational torque of the clutch input shaft M_ci_s is transmitted by the first clutch while the rotational speed of the first input shaft is equal to the rotational speed of the clutch input shaft. Hereby, no rotational torque of the clutch input shaft M_cj_s is transmitted by the second clutch.

Advantageously, a time period of an execution of the step (b) and step (c) may be between 0.1-0.5 s. It is believed that the above time period allows for an optimal shifting in terms of obtaining an initial amplification of the rotational torque of the prime mover while sharing the thermal load between the first clutch and the second clutch. As an example, the time period of an execution of the step (b) and step (c) may be between 0.2-0.3 s. In the context of the present invention, an execution of step (b) and step (c) corresponds to a so-called slipping phase, i.e. a shifting from the first clutch (or the first clutch and second clutch) to the second clutch. It should be readily appreciated that by a shifting from the first clutch (or the first clutch and second clutch) to the second clutch may include the step of disengaging the first clutch. Alternatively, it may include the step of controlling the operation of the first clutch such that no rotational torque Mj may be transmitted by the first clutch.

The multi-clutch transmission may be operated according to various preprogrammed parameters and/or conditions. As an example, step (b) of the method may be initiated when a threshold value corresponding to a predetermined driving resistance value is exceeded. In this context of the present invention, the term "driving resistance" may include rolling resistance as well as road inclination.

In addition, or alternatively, step (b) of the method may be initiated when a threshold value corresponding to a predetermined clutch slip energy value is exceeded. In addition, or alternatively, step (b) of the method may be initiated when a threshold value corresponding to a predetermined temperature value in the first clutch is exceeded. Furthermore, it is also envisaged to operate the multi-clutch transmission according to various combinations of the above predetermined values, and it will be within the capability of those skilled in the art to determine an appropriate combination of the values. In addition, it should be readily appreciated that the level of any of the above values is ultimately dependent and defined in view of the operation of the multi-clutch transmission and the type of vehicle.

According to an example embodiment, the first sub-transmission having the first set of gears may be configured for establishing odd-numbered shift stages; and the second sub-transmission having the second set of gears may be configured for establishing even-numbered shift stages.

The method is suitably, but not strictly necessarily, operated by a control unit. Hence, the multi-clutch transmission may further comprise a control unit configured to operate the multi-clutch transmission.

According to a second aspect of the present invention there is provided a control unit for a vehicle configured for implementing a method according to any of the aspects and/or example embodiments as mentioned above.

Effects and features of this second aspect of the present invention are largely analogous to those described above in relation to the first aspect of the present invention.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

According to a third aspect of the present invention there is provided a computer program product comprising a computer readable medium having stored thereon computer program means for causing the control unit to control the operation of the multi-clutch transmission. Moreover, the computer program product comprises code for executing the method according to any of the aspects and/or example embodiments as mentioned above.

Effects and features of this third aspect of the present invention are largely analogous to those described above in relation to the first aspect and second aspect of the present invention.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person may realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. For example, the above description of the different advantages of the present invention is only described in relation to driving the vehicle in a forward direction, the various embodiments of the invention are of course also applicable when providing the method in reversed gear, i.e. when the vehicle is moved in a rearward direction.

Brief Description of the Drawings

The various aspects of the invention, including its particular features and advantages, will be readily understood from the following illustrative and non- limiting detailed description and the accompanying drawings, in which:

Fig. 1 schematically illustrates a dual-clutch transmission according to an example embodiment of the present invention;

Fig. 2a is a graphic representation showing an example of an operation of a method according to the prior art, in which the dual-clutch transmission assembly solely engages one clutch at a launch of the vehicle;

Fig. 2b is a graphic representation showing another example of an operation of a method according to the prior art, in which the dual-clutch transmission assembly engages two clutches at a launch of the vehicle;

Fig. 3 a is a graphic representation of a method for controlling the operation of a dual-clutch transmission according to an example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition; Fig. 3b is a graphic representation of a method for controlling the operation of a multi-clutch transmission according to another example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition;

Fig. 3c is a graphic representation of a method for controlling the operation of a multi-clutch transmission according to a third example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition;

Fig. 3d is a graphic representation of a method for controlling the operation of a multi-clutch transmission according to a fourth example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition;

Fig. 4a is a graphic representation of a method for controlling the operation of a multi-clutch transmission according to yet another example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition;

Fig. 4b is a graphic representation of a method for controlling the operation of a dual-clutch transmission according to yet another example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition;

Fig. 4c is a graphic representation of a method for controlling the operation of a dual-clutch transmission according to a further example embodiment of the present invention, in which the operation of the method is illustrated from a vehicle launch until a first clutch is in a synchronous condition.

Detailed Description of Exemplary Embodiments of the Invention

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference characters refer to like elements throughout the description.

Referring now to the figures and Fig. 1 in particular, there is depicted a multi- clutch transmission 100 of a vehicle according to an example embodiment of the present invention.

The multi-clutch transmission 100 is operatively connected to a prime mover of a vehicle. The prime mover here is typically an engine, e.g. an internal combustion engine, of a heavy road vehicle such as a heavy truck or bus. However, it will be readily appreciated that other engines and/or vehicles may be contemplated.

The multi-clutch transmission 100 comprises a dual-clutch assembly 10. In this aspect of the present invention, it should be readily appreciated that the term multi-clutch transmission 100 is a wider term for a transmission system optionally including several types of sub-transmissions. The dual-clutch assembly, which may also be denoted a dual-clutch transmission (DCT) (sometimes also referred to as a twin-clutch gearbox or double-clutch transmission), is a type of semi-automatic or automated manual automotive transmission. It may be structurally described as two separate manual transmissions working as one unit. It is to be noted that the structural elements of a dual-clutch assembly are well-known to the skilled person, but typically it refers to transmission system that is configured to dispose a first clutch 12 and a second clutch 14 at the front thereof so as to continue to be selectively operated, thereby reducing the speed change time. In principle, the dual-clutch transmission 10 uses two separate clutches, i.e. the first clutch 12 and the second clutch 14 for an odd gear set 70 and an even gear set 80, respectively. The dual-clutch assembly 100 thereby splits up odd and even gears on two shafts and two clutches. Each clutch may therefore be considered as a separate torque-transmitting unit. Various clutches may be used in a multi-clutch transmission: As an example, the clutch can be provided in the form of a dry friction clutch, i.e. dry single-plate clutches. However, any type of clutch is conceivable such as wet multi-plate clutches.

Besides a dual-clutch assembly 10, the multi-clutch transmission 100 comprises a clutch input shaft 20 drivingly connected to the prime mover and a transmission output shaft 30. The clutch input shaft 20 here is drivingly connected to a crank shaft of the prime mover (not shown).

As mentioned above, the dual-clutch assembly 10 is provided with the first clutch 12 and the second clutch 14. The first clutch 12 and the second clutch 14 are operatively connected to the clutch input shaft 20 and configured for transmitting a rotational torque of the clutch input shaft M_Cj_S.

As may be seen in Fig. 1, the first clutch 12 is operatively connected with a first input shaft 42 of a first sub-transmission 40 having a first set of gears 70. In this manner, the first clutch 12 is capable of transmitting a first rotational torque portion Mi of the rotational torque of the clutch input shaft M_Cj_S to the first input shaft 42. Analogously, the second clutch 14 is operatively connected with a second input shaft 52 of a second sub-transmission 50 having a second set of gears 80. In this manner, the second clutch 14 is capable of transmitting a second rotational torque portion M₂ of the rotational torque of the clutch input shaft M_cj_s to the second input shaft 52.

Typically, but not necessarily, the first clutch 12 and the second clutch 14 may be are arranged axially in succession in a transmission housing.

By the above functional configuration, it is readily appreciated by the skilled person that the first rotational torque portion M] is being transformed via a first gear 110 of the first set of gears 70 to the transmission output shaft 30. Analogously, the second rotational torque portion M₂ is being transformed via a second gear 120 of the second set of gears 80 to the transmission output shaft 30.

Although not illustrated in Fig. 1, it is ordinary that the clutch input shaft 20 may be coaxially arranged with the first input shaft 42 and the second input shaft 52. As an example, a coaxial arrangement of the first shaft and second shaft is obtained by having a hollow second input shaft (also denoted as the outer shaft), making room for the first input shaft (also denoted the inner shaft). In this manner, the first input shaft is nested inside the second input shaft. It is thus to be noted that the clutches may be installed in several arrangements, e.g. in a concentric arrangement, where both clutches share the same plane when viewed perpendicularly from the clutch input shaft, along the same centre line as the crankshaft of the prime mover when viewed head-on along the length of the clutch input shaft. Alternatively, the clutches may be installed in a side-by-side arrangement, when viewed perpendicularly from the clutch input shaft, but again sharing the centre line of the prime mover crankshaft.

In the example embodiment illustrated in Fig. 1, the second input shaft 52 here is arranged to feed second gear 120, fourth gear 140 and sixth gear 160, while the first input shaft 42 is arranged to feed first gear 110, third gear 130 and fifth gear 150. Thereby, the second clutch 14 controls second 120, fourth 140 and sixth 160 gears, while the first clutch 12 controls first 110, third 130 and fifth 150 gears. Typically, although not required, the first sub-transmission 40 having the first set of gears 70 is configured for establishing odd-numbered shift stages; and the second sub- transmission 50 having the second set of gears 80 is configured for establishing even- numbered shift stages. That is, one clutch controls the odd gears (first, third, fifth and reverse), while the other clutch controls the even gears (second, fourth and sixth). By using this arrangement, it becomes possible to change gear without interrupting the power flow from the engine to the transmission.

The first set of gears 70 of the first sub-transmission 40 typically includes the first gear 110, third gear 130 and fifth gear 150. Likewise, the second set of gears 80 of the second sub-transmission 50 typically includes the second 120, fourth 140 and sixth 160 gears. Thus, the multi-clutch transmission has six forward gears where high power transfer to the driven wheels is enabled during shifts between consecutive gears.

Optionally, the first gear 110 of the first set of gear 70 is provided with a higher transmission ratio than the second gear 120 of the second set of gears 80. In other words, the first gear 110 here is provided with the highest transmission ratio of any of the gears in the first set of gears and the second set of gears.

The sub-transmission which is not in use for the time being, i.e. idling, can have a gear engaged and prepared for a subsequent shift. This shift may be carried out by simultaneously disengaging the clutch of the previously used sub-transmission and engaging the clutch of the previously idling sub-transmission.

Moreover, it is to be noted that each sub-transmission can be of a non- planetary type or a planetary type. However, since the construction and the function of a sub-transmission and a clutch are well-known to the skilled person, no further description is given as to the arrangement of various gearwheels and/or how the gearwheels are locked to the different shafts.

In order to obtain a thorough, but not over-constrained suspension of the shafts, the multi-clutch transmission may also include various pilot bearings (not shown).

Typically, the first sub-transmission 40 and the second sub-transmission 50 and their respective clutches 12, 14 are contained within a housing (not shown).

The operation of the multi-clutch transmission 100 may be controlled by a control unit 60 or an actuator device (not shown). Thereby, the control unit 60 here is configured to operate the multi-clutch transmission 100. Typically, the control unit comprises a computer program product. The computer program product includes a computer readable medium having stored thereon computer program means for causing the control unit to control the operation of the multi-clutch transmission. Moreover, the computer program product comprises code for executing a method according to any one of the example embodiments as described hereinafter.

In addition, the multi-clutch transmission 100 may include various valves, shift rods, shift forks, electronics and sensors as is evident to the person skilled in the art.

In prior art, such a multi-clutch transmission has for example been controlled by operating either one of the first clutch and the second clutch at a launch of the vehicle. Fig. 2a shows a diagram of a corresponding prior art embodiment utilizing only one clutch at the launch of the vehicle.

In this Figure, as well as in the Figures 2b through 4c which will be discussed further below, a bold line in the diagram represents an engaged mode of a clutch, whereby a gear is activated so as to transform a rotational torque of the prime mover. Accordingly, the reference numeral gl indicates that the first gear 110 of the first set of gears 70 is activated by the engagement of the first clutch 12. Similarly, the bold line relating to reference numeral g2 indicates that the second gear 120 of the second set of gears 80 is activated by the engagement of the second clutch 14. Moreover, a dotted line in the diagram represents a disengaged mode of a clutch, whereby a gear is inactivated such that no rotational torque of the prime mover is transformed by that gear.

In addition, in all figures showing a diagram of the operation of the method, i.e. Figs. 2a - 4c, the operation of the method is described as a function of time (x- axis) and the relationship ni_n/n_Ci_S (y-axis), wherein is the rotational speed of the first input shaft 42 and n_Ci_s is the rotational speed of the clutch input shaft. In this context of the present invention, the rotation torque of the prime mover is transmitted to the multi-clutch transmission via the clutch input shaft. It is to be noted that since the clutch input shaft is drivingly connected to the prime mover, the rotational speed of the clutch input shaft, represented by the reference numeral n_Ci_S, may correspond to the rotational speed of the prime mover. However, in some embodiments, it may be possible that there is a gear ratio between the clutch input shaft and the shaft of the prime mover.

Furthermore, the origin represents the mode of a vehicle just about to launch, i.e. when the rotational speed of the transmission output shaft 30 is equal to zero.

Turning now to Fig. 2a, a first example of a prior art method for operating a multi-clutch transmission is described. Initially, at tlO the vehicle is launched by engaging the first clutch such that the first gear gl is activated. Then, between tlO - ti l, the first clutch of first gear gl is in a slipping state due to a speed difference between the rotational speed of the first input shaft and the rotational speed of the clutch input shaft, thereby accelerating the vehicle. As such, the rotational speed difference between the rotational speed of the first input shaft and the rotational speed of the clutch input here is represented by the difference between the line "1" and the bold line representing gl. Accordingly, between tlO - ti l, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft.

Then, at ti l, the rotational speed of the first input shaft is equal to the rotational speed of the clutch input shaft, which here is represented by ni_n/n_ei_S = 1. As such, at this state of the operation, the first clutch of the first gear gl is in a synchronous condition with the clutch input shaft, i.e. there is no slipping of the first clutch. Accordingly, between ti l - tl2 the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft, but without any slipping. In Fig. 2a, a synchronous condition is illustrated by the horizontal bold line gl (between ti l- tl2). Accordingly, in this Figure, as well as in the Figures 2c through 4c which will be discussed further below a horizontal bold line of gl coinciding with the line "1" illustrates that the rotational speed of the first input shaft 42 is equal to the rotational speed of the clutch input shaft 20 (sometimes also denoted as a non-slipping state), while a horizontal bold line of g2 coinciding with the line "1" illustrates that the rotational speed of the second input shaft 52 is equal to the rotational speed of the clutch input shaft 20.

Then, at tl2 in Fig. 2a, a gear shift is initiated by disengaging the first clutch and engaging the second clutch, whereby the first gear gl is inactivated and the second gear g2 is activated, respectively. The gear shift is completed at tl3, i.e. the first gear gl is now inactive whilst the second clutch is engaged such that the second gear g2 is active. Accordingly, between tl3 - tl4, the engaged second clutch is transforming a rotational torque of the clutch input shaft to the second input shaft.

The multi-clutch transmission now utilizes the second clutch and the second gear g2 until a further shift is initiated. Meanwhile, a preselection of a new gear g3 is carried out by the multi-clutch transmission between tl4 - tl5, i.e. the preselected gear is changed from gear gl to gear g3, in order to prepare the multi-clutch transmission for a gear shift from gear g2 to gear g3. The gear shift from gear g2 to gear g3 is then executed between tl6 - tl7 in a similar manner as the gear shift from gear gl and gear g2 between tl2 - tl3, such that gear g3 becomes activated. Accordingly, from tl7 and on, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft..

The operation of the multi-clutch transmission according to above prior art method typically allows for a reliable launch of the vehicle since it uses the first gear provided with the highest transmission ratio of the available gears. However, at very heavy vehicle launches, the engaged clutch may be thermally overloaded while slipping. As a consequence, the first clutch will be exposed to excessive wear being detrimental to the function and durability of the multi-clutch transmission. Another prior art method of operating a multi-clutch transmission is shown in Fig. 2b. In this prior art embodiment, which is disclosed in WO 2004/010019, the first clutch and the second clutch are simultaneously utilized at the launch of the vehicle in order to reduce the thermal load generated in the multi-clutch transmission. Initially, at t20 the vehicle is launched by engaging the first clutch and second clutch such that the first gear gl and the second gear g2 are activated, respectively. Then, between t20 - 121, the first clutch of the first gear gl and the second clutch of second gear g2 are in a slipping state due to a speed difference between the rotational speed of the first input shaft and the rotational speed of the clutch input shaft, thereby accelerating the vehicle. As such, the rotational speed difference between the rotational speed of the first input shaft and the rotational speed of the clutch input here is represented by the differences between the line "1" and the bold lines representing gl and g2. Accordingly, between t20 - 121, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft and the engaged second clutch is transforming a rotational torque of the clutch input shaft to the second input shaft.

Then, at t21, the rotational speed of the first input shaft is equal to the rotational speed of the clutch input shaft, which here is represented by n^/rieis = 1. As such, at this state of the operation, the first clutch of the first gear gl is in a synchronous condition with the clutch input shaft, i.e. there is no slipping of the first clutch, while the engaged second clutch is maintaining a slipping state. To this end, the first clutch becomes disengaged, whereby the first gear gl is inactivated such that the engaged second clutch now transforms all rotational torque of the clutch input shaft to the second input shaft via the second gear g2, while still being in a slipping state. Accordingly, between t21 - t22 the engaged second clutch is transforming all rotational torque of the clutch input shaft to the second input shaft via the second gear g2, while slipping. At t23, the rotational speed of the second input shaft is equal to the rotational speed of the clutch input shaft, which here is represented by nj_n/n_ej_s = 1. As such, at this state of the operation, the second clutch of the second gear g2 is in a synchronous condition, i.e. there is no slipping of the second clutch. Accordingly, between t23 - t24, the engaged second clutch is transforming a rotational torque of the clutch input shaft to the second input shaft, but without any slipping.

The multi-clutch transmission now utilizes the second clutch and the second gear g2 until a further shift is initiated. Meanwhile, a preselection of a new gear g3 is carried out by the multi-clutch transmission between t24 - t25, i.e. the preselected gear is changed from gear gl to gear g3, in order to prepare the multi-clutch transmission for a gear shift from gear g2 to gear g3.

Then, at t26, a gear shift is initiated by disengaging the second clutch and reengaging the first clutch, whereby the second gear g2 is inactivated and a third gear g3 is activated, respectively. The gear shift is completed at t27, i.e. the second gear g2 is now inactive whilst the first clutch is engaged such that the third gear g3 is active. Accordingly, from t27 and onwards, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft.

The operation of the multi-clutch transmission according to above prior art method typically allows for a fairly equal sharing of thermal load among the two clutches. As such, by simultaneously slipping both clutches at the entire vehicle launch, it becomes possible to slightly increase the thermal capacity of the multi- clutch transmission.

However, it has been realised by the inventor that only a marginal improvement seems possible since the speed ratio of the second gear g2 is lower than the speed ratio of the first gear gl. Thus, by using the second clutch and the second gear g2, it is likely that the amount of rotational torque downstream of the transmission, i.e. the rotational torque transmitted to the transmission output shaft, is lower than if only the first clutch, and the first gear gl having the highest transmission ratio of the available gears, is utilized. In addition, since the second gear g2 typically has a lower transmission ratio than the first gear gl, there will be a larger slip speed when the second clutch is engaged (and the second gear is activated) at the vehicle launch. In this context of the present invention, the term slip speed refers to the rotational speed difference between the clutch input shaft and the respective input shaft. Moreover, the amplification of the prime mover torque is reduced with this launching method, since only a part of the prime mover torque is transferred to the sub-transmission where the lowest gear, having the highest speed reduction ratio, is engaged. This may become critical in a heavy vehicle with a low power to weight ratio, especially at the initial phase of a launch, where the vehicle may be immovable to the ground.

The present invention provides the possibility to control the operation of the multi-clutch transmission 100 in an improved manner, while still obtaining an effectual and reliable launch of the vehicle. In particular, by optimizing the torque transfer contribution from the first clutch and the second clutch at the launch, it becomes possible to initially provide a high amplification of the rotational torque of the prime mover so as to set the vehicle in motion without any difficulties. In addition, by the present invention, it becomes possible to enhance the flexibility in sharing thermal load (and wear) between the first clutch and second clutch.

To this extent, the operation of the multi-clutch transmission 100 is controlled by a method as will be discussed further below. The present invention provides several different possibilities for controlling the operation of the multi-clutch transmission. These possibilities will now be discussed with reference to the example embodiments shown in Figures 3 a to 4c.

Turning now to Fig. 3a, there is depicted a graphic representation of a method for controlling the operation of the multi-clutch transmission 100, as described above, according to one example embodiment of the present invention. The operation of the method here is illustrated from the vehicle launch until the first clutch is in a synchronous condition. Initially, at t30 (corresponding to method step (a)), the first clutch 12 is engaged at the launch of the vehicle for transmitting rotational torque to the first input shaft 42, while the rotational speed of the first input shaft 42 is different from a rotational speed of the clutch input shaft 20. Accordingly, between t30 - t31, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft. In addition, since only the first clutch is engaged, no rotational torque of the clutch input shaft M_Cj_S is transmitted by the second clutch. In other words, the multi-clutch transmission 100 here is operated such that the initial amount of the first rotational torque portion Mj amounts to 100 % of the rotational torque of the clutch input shaft M_Cj_S, whereby the first clutch 12 transmits all rotational torque of the clutch input shaft M_cj_s while the second clutch 14 transmits no rotational torque of the clutch input shaft M_Cj_S.

Hence, in this example embodiment, the second clutch is not operated at the launch of the vehicle for providing a rotational torque M_0Ut_Put to the transmission output shaft while a rotational speed of the first input shaft is different from a rotational speed of the clutch input shaft.

Thereby, the multi-clutch transmission 100 is operated such that an initial amount of the first rotational torque portion M] is higher than an initial amount of the second rotational torque portion M₂. In this manner, the first clutch 12 is capable of transmitting a higher amount of the rotational torque of the clutch input shaft M_ci_S than the second clutch 14. This operation is initiated before the first clutch 12 is in a synchronous condition with the clutch input shaft 20, i.e. before the relation ni_n/ _Cj_S is equal to 1. As such, the first clutch is transforming a rotational torque portion of the clutch input shaft to the first input shaft while slipping.

Then, at t31 , a shift of the amount of engagement of the first clutch and the second clutch is initiated. More specifically, between t31 - 132 (partly corresponding to method step (b)), the method is operated by decreasing the initial amount of the first rotational torque portion Mi to a decreased amount, which is illustrated by a change of the thickness of the bold line representing gl, and increasing the initial amount of the second rotational torque portion M₂ to an increased amount, which is illustrated by a change from the dotted line to a bold line representing g2. As is clear from Fig. 3 a, this operation is executed while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20 (as illustrated by line gl being below the line ni_n/n_Cj_S equal to 1). Thereby, the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion M] such that the second clutch 14 transmits a higher amount of the rotational torque of the clutch input shaft M_Ci_S than the first clutch 12. In particular, this operation is initiated before the first clutch 12 is in a synchronous condition, i.e. before the relation nj_n/n_e is equal to 1. As such, the first clutch and the second clutch are transforming a rotational torque portion of the clutch input shaft while slipping. To this end, between t31 - t32, the first clutch 12 and the second clutch 14 are capable of sharing the thermal load generated in the multi-clutch transmission while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, i.e. before the first clutch 12 is in a synchronous condition.

At t32, the above operation, i.e. shifting from the first clutch to the second clutch, is completed, and the engaged second clutch transforms all rotational torque of the clutch input shaft, while slipping. In other words, the second clutch 14 transmits the increased amount of the second rotational torque portion M₂ and the first clutch 12 transmits the decreased amount (i.e. no rotational torque) of the first rotational torque portion Mi.

That is, the first clutch 12 is disengaged such that the first gear 110 is inactivated and all rotational torque of the clutch input shaft M_Cj_S is transmitted by the second clutch 14 while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, whereby no rotational torque of the clutch input shaft M_cj_s is transmitted by the first clutch 12. This operation corresponds to step (c) of the method. It is to be noted that the shift from the first clutch to the second clutch is completed while the first clutch is slipping, and therefore before the first clutch is in a synchronous condition, i.e. before the relation ni_n/n_cj_S is equal to 1.

Then, at t33, the rotational speed of the second input shaft is equal to the rotational speed of the clutch input shaft, which here is represented by nj_n/n_ei_s = 1. As such, at this state of the operation, the second clutch of the second gear g2 is in a synchronous condition, i.e. there is no slipping of the second clutch. Accordingly, between t33 - t34, the engaged second clutch is transforming a rotational torque of the clutch input shaft to the second input shaft, but without any slipping. Then, at t36, a gear shift is initiated by disengaging the second clutch and engaging the first clutch, whereby the second gear g2 is inactivated and the third gear g3 is activated, respectively. The gear shift is completed at t37, i.e. the second gear g2 is now inactive whilst the first clutch is engaged such that the third gear g3 is active. Accordingly, from t37 and onwards, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft. It is to be noted that in all example embodiments of the present invention, as illustrated by Figs. 3a through 4c, the step of preselecting a gear of either the first set of gears or the second set of gears may be executed as an initial step in the step of engaging either of the first clutch or the second clutch. Alternatively, the step of preselecting a gear of either the first set of gears or the second set of gears may be executed prior to and separate from the step of engaging either of the first clutch or the second clutch. As an example, pre-selecting the first gear 110 of the first set of gears 70 may be executed prior to the step of engaging the first clutch 12. In addition, or alternatively, pre-selecting the second gear 120 of the second set of gears 80 may be executed prior to the step of engaging the first clutch 12. In addition, or alternatively, pre-selecting the first gear 110 of the first set of gears 70 may be executed prior to the step of engaging the second clutch 14.

Alternatively, pre-selecting the second gear 120 of the second set of gears 80 may be executed at the launch of the vehicle. Alternatively, pre-selecting the second gear 120 of the second set of gears 80 may be executed while engaging the first clutch 12. Alternatively, pre-selecting the second gear 120 of the second set of gears 80 may be executed while the first clutch 12 is engaged.

In addition, or alternatively, pre-selecting the third gear 130 of the first set of gears 70 may be executed while the second clutch 14 is engaged.

From the above, it should be readily appreciated to the skilled person that any of the available gears may be pre-selected in a similar manner before that gear is capable of being activated by the clutch. In the context of the present invention, the term "pre-select" refers to the step of selecting a certain mechanical connection in the sub-transmission in order to provide a gear ratio corresponding to the selected mechanical connection.

In order to pre-select a certain gear (corresponding to a certain mechanical connection), while any of the clutches is engaged, it may be useful to implement various synchronization rings. However, for the purpose of controlling the operation of the multi-clutch transmission according to the present invention, it is to be noted that the step of selecting a mechanical connection is apparent to the skilled person, and therefore the step will not be further explained herein. Moreover, in all example embodiments, as illustrated by Figs. 3a through 4c, the multi-clutch transmission 100 in step (a) here only uses the first gear 110 provided with the highest transmission ratio of any of the gears in the first set of gears 70 and the second set of gears 80.

Fig. 3b illustrates a graphic representation of a method for controlling the operation of the multi-clutch transmission 100, as described above, according to another example embodiment of the present invention.

One difference between the embodiment depicted in Fig. 3 a and the embodiment depicted in Fig. 3b is that both the first clutch 12 and the second clutch 14 are engaged at the launch of the vehicle for providing the rotational torque M_output to the transmission output shaft 30. In other words, at tl30 (corresponding to method step (a)), the first clutch 12 and the second clutch 14 are engaged at the launch of the vehicle for providing the rotational torque M_0Ut_Put to the transmission output shaft 30 while the rotational speed of the first input shaft 42 is different from a rotational speed of the clutch input shaft 20. As mentioned above, a difference of the bold line gl to the line "1" illustrates that the rotational speed of the first input shaft 42 is different from a rotational speed of the clutch input shaft 20 (slipping state). Analogously, a difference of the line g2 to the line "1" here illustrates that the rotational speed of the second input shaft 52 is different from a rotational speed of the clutch input shaft 20 (slipping state). Accordingly, between tl30 - tl31, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft and the engaged second clutch is transforming a rotational torque of the clutch input shaft to the second input shaft.

Thereby, the multi-clutch transmission 100 is operated such that an initial amount of the first rotational torque portion Mi is higher than an initial amount of the second rotational torque portion M₂. In this manner, the first clutch 12 is capable of transmitting a higher amount of the rotational torque of the clutch input shaft M_cj_s than the second clutch 14. This operation is initiated before the first clutch 12 is in a synchronous condition, i.e. before the relation ni_n/n_Ci_S is equal to 1. As such, the first clutch is transforming a rotational torque portion of the clutch input shaft to the first input shaft and the second clutch is transforming a rotational torque portion of the clutch input shaft to the second input shaft while slipping. The principle that the initial amount of the first rotational torque portion Mj is higher than the initial amount of the second rotational torque portion M₂ is illustrated by the bold line gl being thicker than the hollow line g2.

Various torque ratios between the initial amount of the first rotational torque portion Mi and the initial amount of the second rotational torque portion M₂ are conceivable as long as the initial amount of the first rotational torque portion Mi is higher than the initial amount of the second rotational torque portion M₂. In the example embodiment as illustrated in Fig. 3b, the multi-clutch transmission 10 in step (a) is operated such that the initial amount of the first rotational torque portion Mj amounts to 60 % of the rotational torque of the clutch input shaft M_cj_S, while the initial amount of the second rotational torque portion M₂ amounts to 40% of the rotational torque of the clutch input shaft M_Ci_S. In another example embodiment the ratio may be selected such that the initial amount of the first rotational torque portion M amounts to 95 % of the rotational torque of the clutch input shaft M_Ci_S, while the initial amount of the second rotational torque portion M₂ amounts to 5% of the rotational torque of the clutch input shaft M_cj_s.

Then, at tl31, a shift of the amount of engagement of the first clutch and the second clutch is initiated. More specifically, between tl31 - tl32 (partly corresponding to method step b), the method is operated by decreasing the initial amount of the first rotational torque portion Mi to a decreased amount, which is illustrated by a change of the thickness of the bold line representing gl, and increasing the initial amount of the second rotational torque portion M₂ to an increased amount, which is illustrated by a change from the hollow line to a bold line representing g2. As is clear from Fig. 3b, this operation is executed while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20 (as illustrated by the lines gl and g2 being below the line nj_n/n_Cj_s equal to 1). Thereby, the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion Mi such that the second clutch 14 transmits a higher amount of the rotational torque of the clutch input shaft M_ci_s than the first clutch 12. In particular, this operation, i.e. method step (b), is initiated before the first clutch 12 is in a synchronous condition, i.e. before the relation is equal to 1. As such, the first clutch and the second clutch are transforming a rotational torque portion of the clutch input shaft while slipping.

To this end, between tl 31 - tl32, the first clutch 12 and the second clutch 14 are capable of sharing the thermal load generated in the multi-clutch transmission while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, i.e. before the first clutch 12 is in a synchronous condition.

Various torque ratios between the decreased amount of the first rotational torque portion Mi and the increased amount of the second rotational torque portion M₂ are conceivable as long as the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion Mi. In the example embodiment as illustrated in Fig. 3b, the multi-clutch transmission 10 in step (b) is operated such that the increased amount of the second rotational torque portion M₂ amounts to 60 % of the rotational torque of the clutch input shaft M_Ci_S, while the decreased amount of the first rotational torque portion Mi amounts to 40% of the rotational torque of the clutch input shaft M_Ci_S. In another example embodiment the ratio may be selected such that the increased amount of the second rotational torque portion M₂ amounts to 95 % of the rotational torque of the clutch input shaft M_Ci_S, while the decreased amount of the first rotational torque portion Mi amounts to 5% of the rotational torque of the clutch input shaft M_Cj_S. In one example embodiment, corresponding to the operation of g2 at t32 in Fig. 3b, the multi-clutch transmission 100 in step (b) may be operated such that the increased amount of the second rotational torque portion M₂ amounts to 100 % of the rotational torque of the clutch input shaft M_Ci_S, whereby the second clutch 14 transmits all rotational torque of the clutch input shaft M_cis while the first clutch 12 transmits no rotational torque of the clutch input shaft M_Cj_S.

Turning again to Fig. 3b, the above operation, i.e. shifting from the first clutch 12 and second clutch 14 to only the second clutch 14, is completed at tl32, and thereafter the engaged second clutch transforms all rotational torque of the clutch input shaft 20, while slipping. In other words, the second clutch 14 transmits the increased amount of the second rotational torque portion M₂ and the first clutch 12 transmits the decreased amount (i.e. no rotational torque) of the first rotational torque portion Mi.

That is, the first clutch 12 is disengaged such that the first gear 110 is inactivated and all rotational torque of the clutch input shaft M_Ci_S is transmitted by the second clutch 14 while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, whereby no rotational torque of the clutch input shaft M_Cj_S is transmitted by the first clutch 12. This operation corresponds to step (c) of the method. It is to be noted that the shift from the first clutch and second clutch to only the second clutch is completed while the first clutch 12 is slipping, and therefore before the first clutch 12 is in a synchronous condition with the clutch input shaft 20, i.e. before the relation ni_n/n_Cj_S is equal to 1.

Then, at tl 33, the rotational speed of the second input shaft is equal to the rotational speed of the clutch input shaft, which here is represented by nj_n/n_ei_s = 1. As such, at this state of the operation, the second clutch of the second gear g2 is in a synchronous condition, i.e. there is no slipping of the second clutch. Accordingly, between tl 33 - tl34, the engaged second clutch is transforming a rotational torque of the clutch input shaft to the second input shaft, but without any slipping. Then, at tl36, a gear shift is initiated by disengaging the second clutch and engaging the first clutch, whereby the second gear g2 is inactivated and the third gear g3 is activated, respectively. The gear shift is completed at tl37, i.e. the second gear g2 is now inactive whilst the first clutch is engaged such that the third gear g3 is active. Accordingly, from tl 37 and onwards, the engaged first clutch is transforming a rotational torque of the clutch input shaft to the first input shaft.

Fig. 3 c illustrates a graphic representation of a method for controlling the operation of the multi-clutch transmission 100, as described above, according to another example embodiment of the present invention.

In this embodiment, the operation of the multi-clutch transmission 100 between t230 - t232 is equivalent to the operations executed between t30 - t32 as described above for the embodiment in Fig. 3 a. Hence, in this example embodiment, the second clutch is not operated at the launch of the vehicle for providing a rotational torque M_output to the transmission output shaft while a rotational speed of the first input shaft is different from a rotational speed of the clutch input shaft. However, although not shown in the Figures, it should be readily understood that the operation of the multi-clutch transmission 100 between t230 - t232 may be executed in accordance with the operations as described above for the embodiment in Fig. 3b, i.e. between tl 30 - tl 32.

One difference between the embodiment depicted in Fig. 3 a and the embodiment depicted in Fig. 3c is that the method is operated such that the first clutch 12 and the second clutch 14 are still being engaged after the shift of the amount of engagement of the first clutch 12 and the second clutch 14. More specifically, between t231 - 1232 (partly corresponding to method step (b)), the method is operated by decreasing the initial amount of the first rotational torque portion Mj to a decreased amount, which is illustrated by a change of the thickness of the bold line representing gl, and increasing the initial amount of the second rotational torque portion M₂ to an increased amount, which is illustrated by a change from the dotted line to a bold line representing g2. Similar to the condition of the operation in Fig. 3a, this operation is executed while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20 (as illustrated by line gl being below the line ni_n/n_cis equal to 1). However, instead of completely disengaging the first clutch 12 after the transition phase (t231 - t232) as described in relation to Fig. 3a (corresponding to t31 - 132), both the first clutch 12 and the second clutch 14 are still being engaged after the operation at t232. In other words, the second clutch 14 transmits the increased amount of the second rotational torque portion M₂ and the first clutch 12 transmits the decreased amount of the first rotational torque portion Mi.

That is, the first clutch 12 and the second clutch 14 are still being engaged at t232 for providing the rotational torque M_output to the transmission output shaft 30 while the rotational speed of the first input shaft 42 is different from a rotational speed of the clutch input shaft 20. In addition, since both clutches are still being operated, they are capable of sharing thermal energy generated by the multi-clutch transmission in the launch phase before the first clutch is in a synchronous condition with the clutch input shaft. The shift of amount of engagement in the transition phase corresponding to t231 - t232 can be executed in several different ways. In this example embodiment, the multi-clutch transmission 100 is operated between t232 - t233 such that the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion Mi. Thereby, the second clutch 14 transmits a higher amount of the rotational torque of the clutch input shaft M_Cj_S than the first clutch 12. The principle that the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion Mi is illustrated by the bold line g2 being thicker than the hollow line gl.

Various torque ratios between the increased amount of the second rotational torque portion M₂ and the decreased amount of the first rotational torque portion Mi are conceivable. Typically, but not strictly necessarily, the increased amount of the second rotational torque portion M₂ is higher than the decreased amount of the first rotational torque portion Mi. In the example embodiment as illustrated in Fig. 3c, the multi-clutch transmission 100 between t232 - 1233 is operated such that the increased amount of the second rotational torque portion M₂ amounts to 60 % of the rotational torque of the clutch input shaft M_Cj_S, while the decreased amount of the first rotational torque portion Mi amounts to 40% of the rotational torque of the clutch input shaft M_cj_S. In another example embodiment the ratio may be selected such that the second rotational torque portion M₂ amounts to 95 % of the rotational torque of the clutch input shaft M_Ci_S, while the decreased amount of the first rotational torque portion Mi amounts to 5% of the rotational torque of the clutch input shaft M_Cj_S.

In yet another example embodiment, as illustrated in Fig. 3d, the shift of the amount of engagement in the transition phase (corresponding to t331 - 1332) can even be executed such that the decreased amount of the first rotational torque portion Mi is higher than the increased amount of the second rotational torque portion M₂. Accordingly, in this example embodiment, the operation of the multi-clutch transmission 100 between t330 - t332 is equivalent to the operations executed between t230 - t232 as described above for the embodiment in Fig. 3c. As for the example embodiments in Fig. 3a and Fig. 3c, the second clutch is not operated at the launch of the vehicle for providing a rotational torque M_outpu_t to the transmission output shaft while a rotational speed of the first input shaft is different from a rotational speed of the clutch input shaft. However, it should be readily understood that the operation of the multi-clutch transmission 100 between t330 - t332 may be executed in accordance with the operations as described above for the embodiment in Fig. 3b, i.e. between tl30 - tl32.

More specifically, between t331 - t332 (corresponding to method step (b)), the method is operated by decreasing the initial amount of the first rotational torque portion Mj to a decreased amount, which is illustrated by a change of the thickness of the bold line representing gl, and increasing the initial amount of the second rotational torque portion M₂ to an increased amount, which is illustrated by a change from the dotted line to a bold line representing g2. Similar to the condition of the operation in Fig. 3a or Fig. 3c, this operation is executed while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20 (as illustrated by line gl being below the line nj_n/n_Ci_S equal to 1). Similar to the condition of the operation in Fig. 3c, both the first clutch 12 and the second clutch 14 are still being engaged after the operation at t332. In other words, the second clutch 14 transmits the increased amount of the second rotational torque portion M₂ and the first clutch 12 transmits the decreased amount of the first rotational torque portion Mi. Thus, both clutches are capable of sharing thermal energy generated by the multi- clutch transmission at this state of the launch phase, which is before the first clutch is in a synchronous condition with the clutch input shaft. However, in the example embodiment as shown in Fig. 3d, the multi-clutch transmission 100 here is operated between t332 - t333 such that the decreased amount of the first rotational torque portion Mj is higher than the increased amount of the second rotational torque portion M₂. Thereby, the first clutch 12 is still transmitting a higher amount of the rotational torque of the clutch input shaft M_Ci_S than the second clutch 14, which here is illustrated by the hollow line gl and the hollow line g2.

As an example, between t332 - 1333, the multi-clutch transmission 100 can be operated such that the increased amount of the second rotational torque portion M₂ amounts to 45 % of the rotational torque of the clutch input shaft M_Ci_S, while the decreased amount of the first rotational torque portion M_\ amounts to 55 % of the rotational torque of the clutch input shaft M_Cj_S. Alternatively, the increased amount of the second rotational torque portion M₂ can amount to 40 % of the rotational torque of the clutch input shaft M_cj_s, while the decreased amount of the first rotational torque portion Mi amounts to 60 % of the rotational torque of the clutch input shaft M_Cj_S. Alternatively, the increased amount of the second rotational torque portion M₂ can amount to 35 % of the rotational torque of the clutch input shaft M_Ci_S, while the decreased amount of the first rotational torque portion M_\ amounts to 65 % of the rotational torque of the clutch input shaft M_Cj_S.

Fig. 4a illustrates a graphic representation of a method for controlling the operation of the multi-clutch transmission 100 according another example embodiment of the present invention. In this embodiment, the operation of the multi- clutch transmission 100 between t40 - t42 is equivalent to the operations executed between t30 - t32 as described above for the embodiment in Fig. 3a. Alternatively, the operation of the multi-clutch transmission 100 between t40 - 142 may be executed in accordance with the operations as described above for the embodiment in Fig. 3b.

Similar to the status of the transmission at t32, the method at t42 has completed the shift from the first clutch 12 to the second clutch 14. Thereby, the engaged second clutch 14 transforms all rotational torque of the clutch input shaft, while slipping. That is, the first clutch 12 is disengaged such that the first gear 1 10 is inactivated and all rotational torque of the clutch input shaft M_Cj_S is transmitted by the second clutch 14 while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, whereby no rotational torque of the clutch input shaft M_cj_s is transmitted by the first clutch 12. This operation corresponds to step (c) of the method. More specifically, the shift from the first clutch to the second clutch is completed while the first clutch is slipping, and therefore before the first clutch is in a synchronous condition with the clutch input shaft 20, i.e. before the relation nj_n/n_Ci_S is equal to 1. The multi-clutch transmission 100 is thereafter operated according to the step (c) as mentioned above until t41b.

However, instead of using the engaged second clutch 14 until any of the first clutch and second clutch is in a synchronous condition, the method here comprises an additional step (d) at the time t41b, which is executed after the operation at t42, but before the operation at t42b. Accordingly, at t41b, the multi-clutch transmission is operated to re-engaging the first clutch 12 for re-activating the first gear 110 of the first set of gears 70 while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, such that both the first clutch 12 and the second clutch 14 transmit rotational torque of the clutch input shaft M_cj_s. This is illustrated in Fig. 4a by two thinner solid lines representing gear gl and gear g2, respectively. Hence, between t41b - t42b, the two clutches are operated together allowing them to share the thermal energy generated by the multi-clutch transmission at the launch of the vehicle. In this manner, it becomes even faster to reach the synchronous condition since gear gl having the highest transmission ratio is re-used by the multi-clutch transmission. In addition, unnecessary slipping of the second clutch is avoided since both clutches are capable of absorbing the thermal load. More specifically, the first clutch 12 and the second clutch 14 are capable of sharing the thermal load generated in the multi-clutch transmission while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, i.e. before the first clutch 12 is in a synchronous condition.

Then, at t42b, the rotational speed of the first input shaft 42 is equal to the rotational speed of the clutch input shaft 20, which here is represented by nj_n/n_ej_s = 1. As such, at this state of the operation, the first clutch 12 of the first gear gl is in a synchronous condition, i.e. there is no slipping of the first clutch 12. Further, as an additional method step, corresponding to step (f), the second clutch 14 here is disengaged such that the second gear 120 is inactivated and all rotational torque of the clutch input shaft M_Cj_S is transmitted by the first clutch 12 while the rotational speed of the first input shaft 42 is equal to the rotational speed of the clutch input shaft 20. Thereby, no rotational torque of the clutch input shaft M_Ci_S is transmitted by the second clutch 14. In other words, between t42b - t43a, the engaged first clutch is transforming a rotational torque of the clutch input shaft 20 to the first input shaft 42, but without any slipping.

Then, at t43a, an additional gear shift is initiated by progressively engaging the second clutch 14, whereby the first clutch 12 and the second clutch 14 are operated similar to the operation between t41 - t42. In other words, the first gear gl and the second gear g2 are both activated, and both the first clutch and the second clutch transform a rotational torque portion of the clutch input shaft. This operation is executed while the rotational speed of the second input shaft 52 is different from the rotational speed of the clutch input shaft 20.

At t43, the first gear gl is again inactivated while the second clutch 14 is engaged such that the second gear g2 is active. In addition, at t43, the second clutch is in a synchronous condition, there is no slipping of the second clutch 14. Accordingly, between t43 - 144, only the engaged second clutch is transforming a rotational torque of the clutch input shaft 20 to the second input shaft via the second gear g2, but without any slipping.

Fig. 4b illustrates a graphic representation of a method for controlling the operation of the multi-clutch transmission 100 according yet another example embodiment of the present invention. In this embodiment, the operation of the multi- clutch transmission 100 between t50 - t52 is equivalent to the operations executed between t30 - t32 as described above for the embodiment in Fig. 3a, and therefore equivalent to the operations executed between t40 - t42 as described above for the embodiment in Fig. 4a. Alternatively, the operation of the multi-clutch transmission 100 between t50 - t52 may be executed in accordance with the operations as described above for the embodiment in Fig. 3b.

In addition, the operation of the multi-clutch transmission 100 between t51b - t52b is initially equivalent to the operation executed at t41b. More specifically, at t51b, the multi-clutch transmission 100 is operated to re-engaging the first clutch 12 for re-activating the first gear 110 of the first set of gears 70 while the rotational speed of the first input shaft 42 is different from the rotational speed of the clutch input shaft 20, such that both the first clutch 12 and the second clutch 14 transmit rotational torque of the clutch input shaft M_Ci_S. This is illustrated in Fig. 4b by two thinner solid lines representing gear gl and gear g2, respectively. Hence, between t51b - t52b, the two clutches are operated together allowing them to share the thermal energy generated by the multi-clutch transmission at the launch of the vehicle. In this manner, it becomes even faster to reach the synchronous condition since gear gl having the highest transmission ratio is re-used by the multi-clutch transmission. In addition, unnecessary slipping of the second clutch is avoided since both clutches are capable of absorbing the thermal load.

However, instead of disengaging the first clutch 12 of the first gear gl when it is in a synchronous condition, as previously described for the embodiment in Fig. 4a with particular reference to the operation at t42b, the method according to the example embodiment as illustrated in Fig. 4b is controlled to maintain the engagement of the first clutch 12 and second clutch 14 even after the first clutch 12 is in a synchronous condition with the clutch input shaft 20. In other words, between t5 lb - t52b, the engagement of the first clutch 12 and second clutch 14 is maintained even if the rotational speed of the first input shaft 42 becomes equal to the rotational speed of the clutch input shaft 20, which here is represented by nj_n/n_ei_s = 1. As such, at this state of the operation, the first clutch of the first gear gl is in a synchronous condition, i.e. there is no slipping of the first clutch. Accordingly, between t51b - t52b, the engaged first clutch and second clutch are transforming a rotational torque of the clutch input shaft to the first input shaft and the second input shaft , but without any slipping.

Then, from t52b and onwards, the operation of the multi-clutch transmission according to the embodiment in Fig. 4b corresponds to the operation of the multi- clutch transmission according to the embodiment in Fig. 4a as mentioned above with particular reference to t42b and onwards.

Fig. 4c illustrates another graphic representation of a method for controlling the operation of the multi-clutch transmission 100 according to another example embodiment of the present invention. In this embodiment, the operation of the multi- clutch transmission 100 between t60 - t62 is equivalent to the operations executed between t30 - t32 as described above for the embodiment in Fig. 3a, and therefore equivalent to the operations executed between t40 - t42 as described above for the embodiment in Fig. 4a. Alternatively, the operation of the multi-clutch transmission 100 between t60 - t62 may be executed in accordance with the operations as described above for the embodiment in Fig. 3b.

One difference between the embodiments depicted in Fig. 4a and Fig. 4b and the embodiment depicted in Fig. 4c is that, at t61b, the method is operated according to a different step, step (e). This means that at t61b, the first clutch 12 is re-engaged for re-activating the first gear 110 of the first set of gears 70 while the rotational speed of the first input shaft 42 is equal to the rotational speed of the clutch input shaft 20, such that both the first clutch 12 and the second clutch 14 transmit rotational torque of the clutch input shaft M_Cj_S. Analogous to the situation for the above embodiments, this condition is illustrated in Fig. 4c by the horizontal thinner solid lines gl and g2 representing that ni_n/n_ei_s = 1. That is, the horizontal thinner solid line gl, coinciding with the line "1", illustrates that the rotational speed of the first input shaft 42 is equal to the rotational speed of the clutch input shaft 20 (so called non- slipping state), while the horizontal thinner solid line g2, below the line "1", illustrates that the rotational speed of the second input shaft 52 is less than the rotational speed of the clutch input shaft 20 (so called slipping state).

Accordingly, between t61b - t62b, the engaged first clutch and second clutch are transforming a rotational torque of the clutch input shaft to the first input shaft and the second input shaft, respectively. To this end, in the transition phase between t61b - t62b, the first clutch 12 and the second clutch 14 are capable of sharing the thermal load generated in the multi-clutch transmission while there is no slipping of any of the first clutch and second clutch.

As may be seen in Fig. 4c, the multi-clutch transmission 100 maintains the engagement of the first clutch 12 and second clutch 14 in the transition phase until t62b. Thereafter, from t62b and onwards, the operation of the multi-clutch transmission according to the embodiment in Fig. 4c corresponds to the operation of the multi-clutch transmission according to the embodiment in Fig. 4a as mentioned above with particular reference to t42b and onwards.

Typically, but not necessarily, the operation t31-t32, t41-t42, t51-t52 and t61- t62, corresponding to method step (b) and method step (c), is executed between 0.1- 0.5 s. Hence, a shifting from the first clutch 12 (or the first clutch and the second clutch) to only the second clutch 14 is executed between 0.1-0.5 s. Without being bound by any theory, it is believed that the above time period allows for an optimal shifting in terms of obtaining an initial amplification of the rotational torque of the prime mover while sharing the thermal load between the first clutch and the second clutch in the transition phase. However, it should be readily appreciated that the time of the transition phase is ultimately determined in view of the configuration of the clutches and desired vehicle comfort.

Optionally, but not strictly required, step (b) can be initiated when a threshold value corresponding to a predetermined driving resistance value, a predetermined clutch slip energy value or a predetermined temperature value in the first clutch 12 is exceeded.

Thanks to the method of the present invention, the operations of the multi- clutch transmission are optimized in terms of sharing thermal load between the first clutch and the second clutch. In particular, the operations of the multi-clutch transmission are optimized at the launch of the vehicle so as to reduce the wear of the components in the multi-clutch transmission, while maintaining a high amplification of the rotational torque of the prime mover. Thereby, it becomes possible to set the vehicle in motion in an effectual and reliable manner.

Although the invention has been described in relation to specific combinations of specific transmission configurations, it should be readily appreciated that a use of the different gear wheels may be combined in other configurations as well which is clear for the skilled person when studying the present application. Also, the present disclosure has mainly been made for running a vehicle in the forward direction and it should hence be readily understood that the invention is equally applicable for reverse driving as well. Thus, the above description of the example embodiment of the present invention and the accompanying drawings are to be regarded as a non- limiting example of the invention and the scope of protection is defined by the appended claims. Any reference sign in the claims should not be construed as limiting the scope.

Claims

1. A method for controlling an operation of a multi-clutch transmission (100) operatively connected to a prime mover of a vehicle, the multi-clutch transmission (100) comprising a dual-clutch assembly (10), a clutch input shaft (20) drivingly connected to the prime mover and a transmission output shaft (30), the dual-clutch assembly (10) is provided with a first clutch (12) and a second clutch (14) operatively connected to the clutch input shaft (20) and configured for transmitting a rotational torque of the clutch input shaft (M_cj_s); the first clutch (12) is operatively connected with a first input shaft (42) of a first sub-transmission (40) having a first set of gears (70), the first clutch (12) is transmitting a first rotational torque portion (M0 of the rotational torque of the clutch input shaft (M_Ci_S) to the first input shaft (42), the first rotational torque portion (M0 being transformed via a first gear (110) of the first set of gears (70) to the transmission output shaft (30); the second clutch (14) is operatively connected with a second input shaft (52) of a second sub-transmission (50) having a second set of gears (80), the second clutch (14) is transmitting a second rotational torque portion (M₂) of the rotational torque of the clutch input shaft (M_Ci_S) to the second input shaft (52), the second rotational torque portion (M₂) being transformed via a second gear (120) of the second set of gears (80) to the transmission output shaft (30), the method comprising the steps of:

(a) engaging the first clutch (12), or the first clutch (12) and the second clutch (14), at a launch of the vehicle for transmitting a rotational torque (M_0Ut_Put) to the transmission output shaft (30) while a rotational speed of the first input shaft (42) is different from a rotational speed of the clutch input shaft (20), wherein an initial amount of the first rotational torque portion (M is higher than an initial amount of the second rotational torque portion (M₂) such that the first clutch (12) transmits a higher amount of the rotational torque of the clutch input shaft (M_Ci_S) than the second clutch (14);

(b) decreasing the initial amount of the first rotational torque portion (M to a decreased amount and increasing the initial amount of the second rotational torque portion (M₂) to an increased amount while the rotational speed of the first input shaft (42) is different from the rotational speed of the clutch input shaft (20).

2. The method according to claim 1, wherein, in step (b), the increased amount of the second rotational torque portion (M₂) is higher than the decreased amount of the first rotational torque portion (M , such that the second clutch (14) transmits a higher amount of the rotational torque of the clutch input shaft (M_Cj_S) than the first clutch (12).

3. The method according to claim 1 or claim 2, wherein the multi-clutch transmission (100), in step (a), is operated such that the initial amount of the first rotational torque portion (M^ amounts to preferably at least 60 % of the rotational torque of the clutch input shaft (M_Cj_S), still preferably at least 70 % of the rotational torque of the clutch input shaft (M_Cj_S), still preferably at least 80 % of the rotational torque of the clutch input shaft (M_Ci_S), still preferably at least 95 % of the rotational torque of the clutch input shaft (M_Ci_S).

4. The method according to claim 1 or claim 2, wherein the multi-clutch transmission (100), in step (a), is operated such that the initial amount of the first rotational torque portion (M amounts to 100 % of the rotational torque of the clutch input shaft (M_Ci_S), whereby the first clutch (12) transmits all rotational torque of the clutch input shaft (M_Cj_S) while the second clutch (14) transmits no rotational torque of the clutch input shaft (M_cj_s).

5. The method according to claim 1 or claim 4, wherein the multi-clutch transmission (100), in step (a), only uses the first gear (110) provided with the highest transmission ratio of any of the gears in the first set of gears (70) and the second set of gears (80).

6. The method according to any one of the preceding claims, wherein the multi- clutch transmission (100), in step (b), is operated such that the increased amount of the second rotational torque portion (M₂) amounts to preferably at least 60 % of the rotational torque of the clutch input shaft (M_cj_s), still preferably at least 70 % of the rotational torque of the clutch input shaft (M_Ci_S), still preferably at least 80 % of the rotational torque of the clutch input shaft (M_c,_s), still preferably at least 95 % of the rotational torque of the clutch input shaft (M_cj_S).

7. The method according to claim 1 to claim 5, wherein the multi-clutch transmission (100), in step (b), is operated such that the increased amount of the second rotational torque portion (M₂) amounts to 100 % of the rotational torque of the clutch input shaft (M_Ci_S), whereby the second clutch (14) transmits all rotational torque of the clutch input shaft (M_Ci_S) while the first clutch (12) transmits no rotational torque of the clutch input shaft (M_Ci_S).

8. The method according to any one of the preceding claims, wherein the first gear (110) of the first set of gear (70) is provided with a higher transmission ratio than the second gear (120) of the second set of gears (80).

9. The method according to any one of the preceding claims, wherein step (b) is initiated before the first clutch (12) is in a synchronous condition with the clutch input shaft (20).

10. The method according to any one of the preceding claims, wherein the multi- clutch transmission (100), in step (a), is operated to pre-select a first gear (110) of the first set of gears (70) and a second gear (120) of the second set of gears (80) prior to engaging the first clutch (12) and/or the second clutch (14).

11. The method according to claim 1 to claim 9, wherein the multi-clutch transmission (100), in step (a), is operated to pre-select a first gear (110) of the first set of gears (70) and a second gear (120) of the second set of gears (80) while engaging the first clutch (12) and/or the second clutch (14).

12. The method according to any one of the preceding claims, wherein the method further comprising the step of:

(c) disengaging the first clutch (12) such that the first gear (110) is inactivated and all rotational torque of the clutch input shaft (M_Cj_S) is transmitted by the second clutch (14) while the rotational speed of the first input shaft (42) is different from the rotational speed of the clutch input shaft (20), whereby no rotational torque of the clutch input shaft (M_Cj_S) is transmitted by the first clutch (12).

13. The method according to claim 12, wherein the method further comprising the step of:

(d) re-engaging the first clutch (12) for re-activating the first gear (110) of the first set of gears (70) while the rotational speed of the first input shaft (42) is different from the rotational speed of the clutch input shaft (20), such that both the first clutch (12) and the second clutch (14) transmit rotational torque of the clutch input shaft (M_cj_s).

14. The method according to claim 12, wherein the method further comprising the step of:

(e) re-engaging the first clutch (12) for re-activating the first gear (110) of the first set of gears (70) while the rotational speed of the first input shaft (42) is equal to the rotational speed of the clutch input shaft (20), such that both the first clutch (12) and the second clutch (14) transmit rotational torque of the clutch input shaft (M_cj_s).

15. The method according to claim 13 or claim 14, wherein the method further comprising the step of:

(f) disengaging the second clutch (14) such that the second gear (120) is inactivated and all rotational torque of the clutch input shaft (M_Ci_S) is transmitted by the first clutch (12) while the rotational speed of the first input shaft (42) is equal to the rotational speed of the clutch input shaft (20), whereby no rotational torque of the clutch input shaft (M_Cj_S) is transmitted by the second clutch (14).

16. The method according to claim 12, wherein a time period of an execution of the step (b) and step (c) (t31 -t32, t41 -t42, t51 -t52 and t61 -t62) is between 0.1 -0.5 s.

17. The method according to any one of the preceding claims, wherein the step (b) is initiated when a threshold value corresponding to a predetermined driving resistance value, a predetermined clutch slip energy value or a predetermined temperature value in the first clutch (12) is exceeded.

18. The method according to any one of the preceding claims, wherein the first sub-transmission (40) having the first set of gears (70) is configured for establishing odd-numbered shift stages; and the second sub-transmission (50) having the second set of gears (80) is configured for establishing even-numbered shift stages.

19. The method according to any one of the preceding claims, wherein the multi- clutch transmission (100) further comprises a control unit (60) configured to operate the multi-clutch transmission (100).

20. A control unit (60) for a vehicle configured for implementing a method according to any one of the preceding claims.

21. Computer program product comprising a computer readable medium having stored thereon computer program means for causing a control unit to control the operation of a multi-clutch transmission, wherein the computer program product comprises:

- code for executing the method according to any one of claims 1 - 19.