FR3147325A1 - METHOD FOR DETERMINING AN ENGINE TORQUE SETPOINT DURING A GEAR CHANGE IN A THERMAL VEHICLE EQUIPPED WITH AN AUTOMATIC GEARBOX - Google Patents

Abstract

The method is implemented in a vehicle having a powertrain comprising a heat engine (MT) and an automatic gearbox (BVA), the method determining an engine torque setpoint (Ce) during a gear change, from an engaged gear (Re) to a target gear (Re), as a function of a wheel torque setpoint (Cw), an evaluation of an inertial torque to be taken into account for the gear change and an overall gear reduction of the powertrain. According to the invention, the evaluation of the inertial torque to be taken into account is made as a function of the target gear (Rc). Figure 1

Description

METHOD FOR DETERMINING AN ENGINE TORQUE SETPOINT DURING A GEAR CHANGE IN A THERMAL VEHICLE EQUIPPED WITH AN AUTOMATIC GEARBOX

The present invention relates generally to the field of thermal powertrains with automatic gearboxes in motor vehicles. More particularly, the invention relates to a method for determining an engine torque setpoint during a gear change in a thermal powertrain with automatic gearbox equipping a motor vehicle. The invention is applicable in particular when controlling a thermal powertrain with automatic gearbox by a radar of an advanced driver assistance system called “ADAS” (for “Advanced Driver Assist System” in English).

There schematically illustrates a conventional vehicle GMP thermal powertrain comprising an MT thermal engine and a TR transmission system.

The TR transmission system essentially comprises an automatic gearbox BVA, a differential device DI and drive shafts. The automatic gearbox BVA comprises a gearbox BV, strictly speaking, and a torque converter TC. The gearbox BV includes gear trains and actuators and synchronizers for changing transmission gears. The torque converter TC is equipped with a lock-up clutch EP. An input shaft AP of the gearbox is coupled via the torque converter TC to the drive shaft and the flywheel VL of the thermal engine MT. An output shaft AS of the gearbox is coupled to the wheels WH of the vehicle, via the differential device DI.

The torque converter TC is arranged between the thermal engine MT and the gearbox BV in order to ensure the transmission of the engine torque to the gearbox BV, the differential device DI and the wheels WH. The torque converter TC comprises in particular a pump turbine TP driven in rotation by the thermal engine MT, a receiver turbine TR secured to the primary shaft AP and a stator ST arranged between the turbines TP and TR. The EP clutch provides a bridging/unbridging function in the torque converter TC. The EP clutch is controlled to close when the pump turbine TP and the receiver turbine TR rotate at approximately the same speed. The converter TC is then said to be “bridged”, with the mechanical connection between the turbines TP and TR made integral by the closing of the EP clutch, for full transmission of the engine torque by the converter TC. When the EP clutch is open, the TC converter, which is then said to be “unclutched”, provides torque conversion via its functional means, namely, the TP, TR turbines, the ST stator and the oil.

The various operating modes and life phases of the GMP powertrain are managed primarily by an engine control unit ECU_E and a transmission control unit ECU_T which communicate with each other via a data communication bus. The ECU_E and ECU_T control units collaborate with each other to implement the various control strategies of the GMP powertrain.

When the GMP powertrain is controlled by an RD radar of an advanced driver assistance system "ADAS", for example, with the adaptive cruise control function called "ACC" (for "Adaptive Cruise Control" in English) or the level 4 automatic parking function called "CPK4" (for "City Park - level 4", the RD radar provides a torque instruction to the wheel Cw directly to the engine control computer ECU_E, for controlling the GMP powertrain.

To comply with the wheel torque setpoint Cw provided by the radar RD, the engine control computer ECU_E must provide the thermal engine MT with an engine torque setpoint Ce which takes into account the gear ratio introduced by the transmission system TR and the inertial torque of the thermal engine at the wheel. For this, the following equalities are used:

1) Cj = Jdω/dt,

2) Cw = α.Ce – Cj,

in which Cj = Jdω/dt is the inertial torque of the heat engine at the wheel and α is the overall gear ratio introduced by the transmission system TR, with J being the total inertia between the heat engine and the wheel, brought back to the level of the primary shaft AP, ω and dω/dt being respectively the angular speed and the angular acceleration of the primary shaft AP.

When the torque converter TC is unclamped, the total inertia J to be taken into account for calculating the inertial torque is given by the sum of the inertias of the differential device DI, the gearbox BV and the receiving turbine TR. When the torque converter TC is bridged, the total inertia J to be taken into account for calculating the inertial torque is given by the sum of the inertias of the differential device DI, the gearbox BV, the torque converter TC and the thermal engine MT.

The inertia of the BV gearbox is dependent on the gear engaged. During gear changes of the BV gearbox, the total inertial torque Cj undergoes a significant variation, because the gear ratio of the BV gearbox changes and the speed of the input shaft AP varies rapidly.

In the state of the art, to determine the engine torque setpoint Ce during a gear change in the gearbox BV, from an engaged gear X to a target gear Y, the inertial torque Cj is estimated based on gear information Re=X known to the engine control computer ECU_E. Given that the gear information Re only changes from Re=X to Re=Y at the end of the gear change, it follows that the inertial torque Cj is estimated throughout the gear change with the information Re=X of the initial gear.

With an engine torque setpoint Ce determined in accordance with the aforementioned known method, the inventive entity noted, at the end of the gear change, an excess torque at the wheel when the gear change is up and a lack of torque at the wheel when the gear change is down, i.e. when downshifting. The excess torque at the wheel noted during the upshift constitutes a setpoint tracking error which is due to an overestimation of the inertial torque to be compensated. The lack of torque at the wheel noted during the downshift constitutes a setpoint tracking error which is due to an underestimation of the inertial torque to be compensated.

As an illustration, the shows a torque reading at the wheel Cw obtained during an upshift with control of the GMP powertrain by the RD radar for “ACC” regulation according to the prior art, i.e., with the inertial torque which is estimated according to the gear engaged information. The excess torque at the wheel at the end of the upshift is visible in the continuous line circle CTC1.

The present invention aims to provide a solution to the drawback set out above of the state of the art by providing a new method for determining the engine torque setpoint to be supplied to a thermal powertrain with automatic gearbox during a gear change, for satisfactory monitoring of a torque setpoint at the wheel.

According to a first aspect, the invention relates to a method for determining an engine torque setpoint during a gear change, from a gear engaged to a target gear, in a powertrain of a vehicle equipped with a heat engine and an automatic gearbox, the engine torque setpoint being determined as a function of a wheel torque setpoint, an evaluation of an inertial torque to be taken into account for the gear change and an overall gear ratio of the powertrain. According to the invention, the evaluation of the inertial torque to be taken into account is made as a function of the target gear.

According to a particular characteristic, the evaluation of the inertial torque to be taken into account is also made as a function of the gear engaged, considering an inertia of the traction chain as being equal to an interpolation between a first traction chain inertia value resulting from the gear engaged and a second traction chain inertia value resulting from the target gear.

According to another particular characteristic, the inertial torque to be taken into account is evaluated in real time during the gear change by a transition function delivering an instantaneous value of the inertial torque to be taken into account varying between a first inertial torque value resulting from the gear engaged and a first speed regime associated with said engaged gear and a second inertial torque value resulting from the target gear and a second speed regime associated with said target gear.

According to yet another special feature, the transition function is a linear function.

The invention also relates to a calculator comprising a memory storing program instructions for implementing the method as briefly described above.

According to a particular characteristic, the calculator is an engine control calculator.

The invention also relates to a vehicle having a powertrain comprising a heat engine and an automatic gearbox, and means for controlling the powertrain by a torque instruction at the wheel, in which a calculator is included as indicated above.

According to a particular feature, the vehicle's control means include a radar of an advanced driving assistance system.

Other advantages and features of the present invention will become more apparent upon reading the detailed description below of several particular embodiments of the invention, with reference to the accompanying drawings, in which:

There is a block diagram showing schematically an architecture of a thermal powertrain equipped with an automatic gearbox.

There is an example of a wheel torque reading obtained with the prior art during an upshift in the thermal powertrain of the .

There is a functional block diagram of a first embodiment of the method of the invention.

There is an example of a wheel torque reading obtained with the first embodiment of the method of the invention during an upward gear change in the thermal powertrain of the .

There is a functional block diagram of a second embodiment of the method of the invention.

There is a functional block diagram of a third embodiment of the method of the invention.

With particular reference to the , a first particular embodiment of the method according to the invention is now described. The method is implemented in a thermal powertrain, such as the GMP group of the , comprising the MT thermal engine and a TR transmission system equipped with a BVA automatic gearbox.

As visible in the , a software module SW0 is hosted in a MEM memory of the engine control computer ECU_E and implements an algorithm whose function, during a gear change, is to convert the wheel torque setpoint Cw received into an engine torque setpoint Ce for controlling the thermal engine MT.

The software module SW0 authorizes the implementation of the method according to the invention by the execution of program code instructions by a processor (not shown) of the engine control computer ECU_E. The engine control computer ECU_E, under the supervision of the software module SW0, cooperates in particular with the transmission control computer ECU_T for the implementation of the method according to the invention.

In general, the SW0 software module determines the engine torque setpoint Ce which corresponds to the wheel torque setpoint Cw by exploiting the equality 1) indicated above and the following equality 3) deduced from the equality 2) indicated above, namely:

1) Cj = Jdω/dt,

3) Ce = (Cw+ Cj)/ α.

Unlike the prior art which, when changing gear from an engaged gear Re=X to a target gear Rc=Y, uses the engaged gear Re=X to estimate the inertial torque Cj of the heat engine at the wheel, the invention, in this embodiment, provides for using the target gear Rc=Y instead of the engaged gear Re=X for estimating the inertial torque Cj.

The SW0 software module receives as input the wheel torque setpoint Cw, the target ratio information Rc=Y, a speed information Nap of the primary shaft AP and the overall gear ratio information α of the transmission system TR and delivers as output the engine torque setpoint Ce.

The SW0 software module essentially comprises four functions F1 to F4 to determine the engine torque setpoint Ce corresponding to the wheel torque setpoint Cw.

Function F1 is a mapping which, when changing gear from Re=X to Rc=Y, receives as input the target gear Rc=Y and outputs as output the inertia J of the thermal engine at the wheel. Function F2 receives as input the inertia J delivered by function F1 and the speed Nap and calculates the inertial torque Cj by exploiting equality 1) above. Function F3 adds the inertial torque Cj, calculated by function F2, to the torque setpoint at the wheel Cw and outputs the resulting sum Cw+Cj to function F4. The engine torque setpoint Ce is output by function F4 which determines it by dividing the sum Cw+Cj by the overall gear ratio α of the transmission system TR.

As an illustration, the shows a wheel torque reading Cw obtained during an upshift with powertrain control according to the first embodiment described above of the method of the invention, i.e., with the inertial torque which is estimated as a function of the target gear information. As visible in this reading, in the continuous line circle CTC2, the invention makes it possible to eliminate the excess wheel torque at the end of the upshift of the prior art. On the other hand, a lack of torque, visible in the broken line circle CTD, appears at the start of the upshift.

Results consistent with those illustrated in the are obtained during a downshift, with the elimination of the lack of torque at the wheel of the prior art at the end of the downshift and the appearance of an excess torque at the wheel at the start of the downshift.

The lack of wheel torque at the start of an upshift is less criticized by users than the excess wheel torque at the end of an upshift. Furthermore, downshifts under load are relatively rare when controlled by “ADAS” systems, which limits the disadvantage of excess wheel torque at the start of a downshift. From this, it follows that the first embodiment described above of the method of the invention will be suitable for certain applications.

For more precise monitoring of the torque setpoint at the wheel, the invention proposes a second mode and a third mode of implementation of the method described below with particular reference to the and to the , respectively. Increasing the number of information taken into account improves the monitoring obtained from the torque setpoint at the wheel.

In reference to the , the second embodiment of the method of the invention is implemented by means of a software module SW1. The software module SW1 receives as input the torque setpoint at the wheel Cw, the information on the engaged gear Re=X and the target gear Rc=Y, the information on the speed Nap of the primary shaft AP and the information on the overall gear ratio α of the transmission system TR and outputs the engine torque setpoint Ce.

The software module SW1 essentially comprises five functions F10, F11 and F2 to F4. In this second embodiment, the inertia J taken into account is determined by the functions F10 and F11, the functions F2 to F4 remaining identical to those of the first embodiment of the method. The function F10 is a mapping which, when changing gear from Re=X to Rc=Y, receives as input the engaged gear Re=X and the target gear Rc=Y and delivers as output the respective inertias Je and Jc of the heat engine to the wheel. The function F11 receives as input the inertias Je and Jc and calculates the inertia J to be taken into account by interpolation, for example, by determining J=(Je+Jc)/2. The inertia J is then provided as input to the function F2, together with the speed Nap, for calculating the inertial torque Cj. Function F3 receives as input the wheel torque setpoint Cw and the inertial torque Cj delivered by function F2 and calculates the sum Cw+Cj. Function F4 determines the engine torque setpoint Ce by dividing the sum Cw+Cj by the overall gear ratio α of the transmission system TR.

In reference to the , the third embodiment of the method of the invention is implemented by means of a software module SW2. The software module SW2 receives as input the torque setpoint at the wheel Cw, the information on the engaged gear Re=X and the target gear Rc=Y, information on the speed Nsb of the output shaft of the gearbox BV and the overall gear ratio information α of the transmission system TR and outputs the engine torque setpoint Ce.

The software module SW3 essentially comprises eight functions F10, F12 to F16, F3 and F4. The functions F10, F3 and F4 remain identical to those of the second embodiment of the method. In this third embodiment, an inertial torque at the start of the gear change Cje and an inertial torque at the end of the gear change Cjc are calculated respectively for the engaged gear Re=X and the target gear Rc=Y, by means of the functions F10, and F12 to F15. The inertial torque Cj to be taken into account is estimated in real time during the gear change, by means of the transition function F16 which calculates the values of Cj between Cj=Cje and Cj=Cjc.

Function F10 is a mapping that, when changing gear from Re=X to Rc=Y, receives as input the engaged gear Re=X and the target gear Rc=Y and outputs the respective inertias Je and Jc of the heat engine to the wheel. Functions F12 and F13 receive as input the speed Nsb of the gearbox output shaft and output primary shaft speeds Nape and Napc corresponding to the engaged gear Re=X and the target gear Rc=Y, respectively. The speeds Nape and Napc are calculated from the speed Nsb and the gear ratios De and Dc corresponding to the ratios Re=X and Rc=Y, respectively. Function F14 calculates the inertial torque Cje from the inertia Je and the primary shaft speed Nape. Function F15 calculates the inertial torque Cjc from the inertia Jc and the primary shaft speed Napc.

During the gear change, function F16 calculates in real time the instantaneous value of the inertial torque Cj using the following transition function:

4) Cj=(1-x).Cje + x.Cjc, with x being a time variable evolving from 0 to 1 between the start and the end of the gear change.

Typically, the aforementioned transition function is a linear function.

Function F3 receives as input the wheel torque setpoint Cw and the inertial torque Cj delivered by function F16 and calculates the sum Cw+Cj. Function F4 determines the engine torque setpoint Ce by dividing the sum Cw+Cj by the overall gear ratio α of the transmission system TR.

The present invention provides low-cost, software-based solutions that improve the precision of wheel torque control during gear changes in a vehicle equipped with a thermal powertrain with automatic transmission, as well as user comfort.

The invention is not limited to the particular embodiments which have been described here by way of example. Those skilled in the art, depending on the applications of the invention, will be able to make various modifications and variations falling within the scope of protection of the invention.

Claims (8)

Method for determining an engine torque setpoint (Ce) during a gear change, from an engaged gear (Re) to a target gear (Rc), in a powertrain (GMP) of a vehicle equipped with a heat engine (MT) and an automatic gearbox (BVA), said engine torque setpoint (Ce) being determined as a function of a wheel torque setpoint (Cw), an evaluation of an inertial torque to be taken into account (Cj) for said gear change and an overall gear ratio (α) of said powertrain, characterized in that the evaluation (F1, F2) of said inertial torque to be taken into account (Cj) is made as a function of said target gear (Rc). Method according to claim 1, characterized in that the evaluation (F10, F11, F2) of said inertial torque to be taken into account (Cj) is also made as a function of said engaged ratio (Re), considering an inertia (J) of said drive chain as being equal to an interpolation (F11) between a first drive chain inertia value (F10, Je) resulting from said engaged ratio (Re) and a drive chain inertia value (F10, Jc) resulting from said target ratio (Rc). Method according to claim 1, characterized in that said inertial torque to be taken into account (Cj) is evaluated in real time during the duration of said gear ratio change by a transition function (F16) delivering an instantaneous value of said inertial torque to be taken into account (Cj) varying between a first inertial torque value (Cje) resulting from said engaged gear (Re) and a first speed regime (Nape) associated with said engaged gear (Re) and a second inertial torque value (Cjc) resulting from said target gear (Rc) and a second speed regime (Napc) associated with said target gear (Rc). Method according to claim 3, characterized in that said transition function (F16) is a linear function. Computer (ECU_E) comprising a memory (MEM) storing program instructions (SW0, SW1, SW2) for implementing the method according to any one of claims 1 to 4. Calculator according to claim 5, characterized in that said calculator is an engine control calculator (ECU_E). Vehicle having a powertrain comprising a thermal engine (MT) and an automatic gearbox (BVA), and means (RD) for controlling said powertrain (GMP) by a wheel torque instruction (Cw), characterized in that it also comprises a computer (ECU_E) according to claim 5 or 6. Vehicle according to claim 7, characterized in that said piloting means comprise a radar (RD) of an advanced driver assistance system (ADAS).