GB2112100A

GB2112100A - Arrangement for blocking the engagement of a clutch of a motor vehicle

Info

Publication number: GB2112100A
Application number: GB08236416A
Authority: GB
Inventors: Schwerin Wolfgang Von; Alfred Konrad; Adalbert Litterst
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1981-12-24
Filing date: 1982-12-22
Publication date: 1983-07-13
Also published as: GB2112100B; IT8224861A0; FR2518939B1; DE3151416A1; DE3151416C2; IT1155025B; FR2518939A1; IT8224861A1

Abstract

An arrangement for blocking the engagement of a clutch (5) of a motor vehicle comprises a lock actuator (9) which can be switched over to close a valve 30 to prevent damage to the engine (3) resulting from excessive speeds occurring in the event of an incorrect gear change to too low a gear. A control device (13) is connected to a gearbox input speed sensor (12) via an inhibiting or locking circuit (17) and the connection between the control device (13) and the lock actuator (9) is maintained irrespective of the positions of the gear change box. The inhibiting circuit (17) transmits an input signal for the control device (13) only above a limiting value. Either the control device (13) is influenced solely by the gear speed and the valve 30 is bypassed by a check valve (41) for disengagement of the clutch (5) - or the control device (13) brings the lock actuator (9) into the locking position only upon the appearance of two input signals, the second input signal of which is triggered if the clutch actuator (8) is brought into its release position. The clutch may automatically re-engage through a restriction when valve 30 reopens. <IMAGE>

Description

SPECIFICATION Arrangement for blocking the engagement of a clutch of a motor vehicle The invention relates to an arrangement for blocking the engagement of a clutch which is connected to the torque transmission system between an internal combustion engine and a gear change box of a motor vehicle, comprising a clutch actuator, which can be actuated between a "disengage" or throw-out position for releasing the clutch and an "engage" position for engaging the clutch, and a lock actuator which can be switched from an inoperative neutral position into a locking position in which it is connected kinematically to the clutch actuator, comprising a control device which controls the auxiliary control power of the lock actuator and which is influenced by a gear speed through a sensor and which, upon the occurrence of critical speed values, brings the lock actuator into its locking position.

A known arrangement of this kind (German Offenlegungsschrift (Laid-Open Specification) No.

23 56 745) is used to permit engagement of the clutch during gear shifting only when the input shaft of the gear change box and the engine have the same speed. In order to enable starting up with this arrangement, the lock actuator must in each case be rendered inoperative at those gear speeds at which starting generally takes place.

Consequently, it is impossible with the known arrangement to prevent damage to the engine resulting from excessive speeds which occurs in the event of incorrect gear changing to a lower gear, because it is precisely then that the lock actuator is inoperative, and upon engagement of the clutch the engine is accelerated into an unacceptable speed range as a result of the high kinetic energy of the vehicle.

With a known differently classified safety control device (German Auslegeschrift 18 09 021) for a motor vehicle gear change box which is electrically controlled by a speed sensor depending on the driving speed, the aforementioned engine damage is avoided by designing the arrangement in such a manner that the speed of the driving engine and/or of the change gear input shaft is measured by way of speed sensors cooperating with an emergency control element which, when a speed of the driving engine shaft or change gear input shaft which lies slightly above the normal maximum speed is exceeded, causes the change gear to be changed to the highest speed by means known per se.

The understanding underlying this measure is that, upon disengagement of the positive or nonpositive connection between the driving engine and the vehicle, the latter is not switched to a safe driving state, but is then completely unpowered and uncontrolled. On mountain roads and on gradients this can lead to other dangerous driving situations for both the entire vehicle itself and for other road users.

The problem underlying the invention is to reliably avoid engine damage resulting from excessive speeds which occur in the event of incorrect gear changing to a lower gear.

According to the invention, there is provided an arrangement for blocking the engagement of a clutch which is connected to the torque transmission system between an internal combustion engine and a gear change box of a motor vehicle, comprising a clutch actuator, which can be actuated between a disengage or throwout position for releasing the clutch and an engage position for engaging the clutch, and a lock actuator which can be switched from an inoperative neutral position into a locking position in which it is connected kinematically to the clutch actuator, comprising a control device which controls the auxiliary control power of the lock actuator and which is influenced by a gear speed through a sensor and which, upon the occurrence of critical values, brings the lock actuator into its locking position, characterised in that the control device is connected, on the input side, to the sensor via an inhibiting or locking circuit and the connection on the output side, between the control device and the lock actuator is maintained irrespective of the positions of the gear change box and the inhibiting circuit transmits an input signal for the control device only above a limiting value and the control device is influenced solely by the gear speed and the kinematic connection is disconnected by a freewheel device upon disengagement of the clutch actuator.

The concept which forms the basis of the invention is that the engine damage described is reliably or safely avoided only if the engine is disengaged from the gear change box. Thus multispeed transmissions which can have sixteen gears are often used in commercial vehicles.

When changing to a lower gear - for example, first or second gear - the engine would be accelerated rapidly in to the critical speed range as a result of the high kinetic energy of the heavy vehicle. Also, this cannot be avoided with an automatic gear change box by changing to a high gear in the event of excessive speed because the high kinetic energy of the vehicle acts upon the engine also under these conditions.

Also, a known arrangement for blocking the engagement of a clutch is disclosed in German Offenlegungsschrift (Laid-Open Specification) No.

23 56 745.

The invention also provides an arrangement for blocking the engagement of a clutch which is connected to the torque transmission system between an internal combustion engine and a gear change box of a motor vehicle, comprising a clutch actuator, which can be actuated between a disengage or throw-out position for releasing the clutch and an engage position for engaging the clutch, and a lock actuator which can be switched over from an inoperative neutral position to a locking position in which it is connected kinematically to the clutch actuator, comprising a control device which controls the auxiliary control power of the lock actuator and which is influenced both by a gear speed through a sensor and by a further reference quantity or value for determining torque transmission and which, upon the appearance of critical speed values, brings the lock actuator into its locking position, wherein the control device is connected, on the input side, to the sensor via an inhibiting or locking circuit and the connection, on the output side, between the control device and the lock actuator is maintained irrespective of the positions of the gear change box, and the inhibiting circuit transmits an input signal for the control device only above a limiting value and the actuation of the clutch actuator is used as a further reference quantity or value and an accompanying second input signal is triggered if the clutch actuator is brought into its release position and only upon the appearance of both the input signals the control device brings the lock actuator into the locking position.

Embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a block diagram of a first embodiment of the invention; Fig. 1 a shows a modification of the arrangement in Fig. 1; Fig. 1 b shows a block diagram of another embodiment of the invention, and Fig. 2 shows a graph of the variation of engine output relative to the speed, with the limited value of the gear speed which is used in the case of the arrangements of Fig. 1, Fig. 1 a and Fig. 1 b.

With reference to Fig. 1 b, the arrangements in Figs. 1, 1 a and 1 b are identical in the following features: The crankshaft 26 of an internal combustion engine 3 is connected by a clutch 5 to the transmission input shaft 27 of a gear change box 4, the output shaft 28 of which is connected to the driven wheels of a motor vehicle in the known manner. A clutch release sleeve is used in the conventional manner as a clutch actuator 8 for engaging and disengaging the clutch 5, which sleeve can be actuated between the illustrated engage position 7 - in which the clutch 5 is engaged -- and a release position 6 - in which the clutch 5 is disengaged -- by a clutch release lever 29. The clutch release lever 29 is connected to a clutch pedal 32 through a hydraulic linkage 31.Connected to the hydraulic linkage 31 is a lock or check valve 30 which can be actuated by an electromagnetic lock actuator 9 out of the illustrated inoperative position 1 0 - in which the hydraulic linkage 31 is unblocked -- into a locking position 33 in which the hydraulic linkage 31 and consequently also the clutch release lever 29 are blocked.

The lock actuator 9 is connected through a connection 1 8 to a control device 13 for which known electronic circuits -- in the case of the arrangement of Fig. 1 b, an AND-element or gate 25 - are used. The control device 13 is connected through an input to an inhibiting or locking circuit 1 7 for which a known electronic threshold element 24 is used.

A sensor 12 transmits a signal 35 which is analogous with the speed nG of the transmission input shaft 27 and which is fed to the input of the threshold element 24 - if necessary, through an electronic transducer 37.

The threshold element 24 transmits an input signal 20 for the control device 1 3 if the speed nG of the transmission input shaft 27 exceeds a limit 1 5. As shown in Fig. 2, the limit 1 5 is approximately equal to the critical speed value 22 and, when this value is exceeded, damage may occur to the internal combustion engine as a result of overspeeding.

With the arrangement in Fig. 1 b, the ANDelement 25 transmits an output signal 39, which brings the lock actuator 9 into the locking position 33, if the input signal 20 and a further input signal 19 appear together. The input signal 19 is triggered from a switching contact 11, if necessary through an electronic circuit or control element 36, when the clutch actuator 8 is brought into its release position 6.

In the event of an incorrect gear change to a too low gear, the speed nG of the transmission input shaft 27 exceeds the critical value 1 5 so that the input signal 20 appears. Since, in this situation also, the clutch 5 is disengaged, the input signal 1 9 also appears whereby the engagement of the clutch 5 is blocked because the lock or check valve 30 blocks the hydraulic linkage 31.

However, it is easily possible to change up to a higher gear and overcome this situation, because when a higher gear is engaged the speed nG of the transmission input shaft 27 falls below the critical value, thereby bringing the lock valve 30 into its inoperative position 1 0.

With the arrangement according to Fig. 1 , the lock valve 30 is triggered merely by using the input signal 20, which is derived from the speed nG of the transmission input shaft 27, and, in the hydraulic linkage 31, a one-way valve 42 which operates as a freewheel device 41 for the free disengagement of the clutch 5 at any time and which is arranged in parallel to the lock valve 30.

Three possible control systems for the lock actuator 9 for actuating the lock valve 30 emerge from the block diagram in Fig. 1. In the first case the threshold control 24 can trigger the lock actuator 9 directly, i.e. it can be used itself as the control device.

In the event of an incorrect gear change to a too low gear, the critical speed value 1 5 is exceeded whereby the threshold AND-element 24 responds and actuates the lock valve 30 to move into the locking position 33 so that engagement of the clutch 5 is prevented. This mode of operation also occurs with the other two possible control systems in which an electronic control device 13 is used, which consists either of a delay circuit 48 or of a delay circuit 49. Each circuit 48, 49 transmits during use the output signal 39 for bringing the lock valve 30 into the locking position 33 upon the appearance of the input signal 20.The function of the two circuits 48 and 49 is to prevent a sudden engagement of the clutch 5 after release of the clutch actuator 8 by means of the lock valve 30 and, for this purpose, to control throttling at the valve opening when the lock valve 30 in the hydraulic linkage 31 is switched over to the inoperative position. With the delay circuit 48 this throttling action is achieved because the decay of the output signal 39 corresponding to the curve path 43 is delayed by the time t, whereby the hydraulic line crosssection in the valve opening of the lock valve 30 is opened gradually. With the delay circuit 49 the signal 39 is timed over a limited time span 44 so that the lock valve 30 is switched between the inoperative position 10 and locking position 33 at short intervals so that engagement of the clutch 5 is damped.

With the arrangement according to Fig. 1 a - which is otherwise identical to the arrangement according to Fig. 1 - precautions are also taken to prevent the engagement of the clutch taking place suddenly after the engagement lock is disconnected. For this purpose an electronic control device 1 3 containing a time function element is first used, the time function element delaying the decay of the output signal 39 for the lock actuator 9 by a time span 45. The control device 13 contains a further time function element which, upon the decay of the input signal 20 during a shorter time span 50, produces an output signal 51 for an electromagnetic clutch-engaging brake valve 52.In a by-pass 47 of the hydraulic linkage 31 which by-passes the lock valve 30, the valve 52 operates between an inoperative position 53 for blocking the by-pass 47 and a brake position 54 for opening the by-pass 47.

Upon the decay of the input signal 20 which is derived from the transmission input speed - i.e.

when the blocking of the disengaged clutch 5 is to be cancelled -- the lock valve 30 remains at first in its locking position 33 whilst the clutchengaging brake valve 52 is brought without delay into its brake position 54 in which the hydraulic medium which is displaced during the engagement operation flows through the brake throttle 46. After expiry of the time span 50 the output signal 51 decays and, after expiry of the time span 45, the output signal 39 also decays.

Thus the by-pass 47 is blocked and the hydraulic linkage 31 is unblocked by way of the lock valve 30.

The delay circuits 48 and 49 according to Fig.

1, as well as the brake control system for engaging the clutch as shown in Fig. 1 a, can be used in like manner also in the arrangement according to Fig. 1 b.

The electromagnetic actuator of the clutchengaging brake valve 52 could also work upon the one-way valve 42 in such a manner that, upon the appearance of the output signal 51, the one-way valve 42 is brought into a brake position for unblocking a throttled valve opening for the hydraulic medium of the linkage 31 which is displaced upon clutch engagement. As a result, the by-pass 47 together with the valve 52 and the throttle 46 could be omitted.

With the arrangement according to Fig. 1 b, the switching contact 11 can also be arranged in a different place in the clutch actuating system between the clutch actuator 8 and the clutch pedal 32.

What is achieved therefore with the arrangement according to the invention is that, on the one hand, the internal combustion engine 3 can be operated both within the entire full-load range 21 (fig. 2) and slightly above the no-load range 38 without the clutch engagement lock becoming operative, but that, on the other hand, the internal combustion engine 3 remains disengaged or disconnected from the gear change box 4 upon the occurrence of critical speed values 1 5 during an incorrect gear change. A further advantage of the arrangement according to the invention is that, in the event of brake failure on a gradient and the running of the internal combustion engine 3 at full speed which is associated with such a failure, the clutch 5 can always be disengaged to change up to a higher gear because, with the arrangements of Figs. 1 and 1 a, the kinematic connection between the lock value 30 and the hydraulic linkage 31 is cancelled by the freewheel device 41 for the disengagement operation and, with the arrangement according to Fig. 1 b, the second input signal 1 9 which is necessary to block the engagement, only appears when the clutch has been disengaged.

Claims

1. An arrangement for blocking the engagement of a clutch which is connected to the torque transmission system between an internal combustion engine and a gear change box of a motor vehicle, comprising a clutch actuator, which can be actuated between a disengage or throwout position for releasing the clutch and an engage position for engaging the clutch, and a lock actuator which can be switched from an inoperative neutral position into a locking position in which it is connected kinematically to the clutch actuator, comprising a control device which controls the auxiliary control power of the lock actuator and which is influenced by a gear speed through a sensor and which, upon the occurrence of critical speed values, brings the lock actuator into its locking position, wherein the control device is connected, on the input side, to the sensor via an inhibiting or locking circuit and the connection, on the output side, between the control device and the lock actuator is maintained irrespective of the positions of the gear change box and the inhibiting circuit transmits an input signal for the control device only above a limiting value and the control device is influenced solely by the gear speed and the kinematic connection is disconnected by a freewheel device upon disengagement of the clutch actuator.

2. An arrangement for blocking the engagement of a clutch which is connected to the torque transmission system between an internal combustion engine and a gear change box of a motor vehicle, comprising a clutch actuator, which can be actuated between a disengage or throwout position for releasing the clutch and an engage position for engaging the clutch, and a lock actuator which can be switched over from an inoperative neutral position to a locking position in which it is connected kinematically to the clutch actuator, comprising a control device which controls the auxiliary control power of the lock actuator and which is influenced both by a gear speed through a sensor and by a further reference quantity or value for determining torque transmission and which, upon the appearance of critical speed values, brings the lock actuator into its locking position, wherein the control device is connected, on the input side, to the sensor via an inhibiting or locking circuit and the connection, on the output side, between the control device and the lock actuator is maintained irrespective of the positions of the gear change box and the inhibiting circuit transmits an input signal for the control device only above a limiting value and the actuation of the clutch actuator is used as a further reference quantity or value and an accompanying second input signal is triggered if the clutch actuator is brought into its release position and only upon the appearance of both the input signals the control device brings the lock actuator into the locking position,

3. An arrangement according to Claim 1 or Claim 2 wherein the gear speed is the gear input speed.

4. An arrangement according to any one of Claims 1 to 3, wherein the limiting value of the gear speed is approximately equal to the critical value in respect of damage caused as a result of overspeeding.

5. An arrangement according to any one of Claims 1 to 4 wherein a lock or check valve, which can be actuated by the lock actuator, is connected to a hydraulic linkage leading to the clutch actuator.

6. An arrangement according to any one of Claims 1 to 5, wherein a one-way valve is connected in parallel to the lock valve.

7. An arrangement according to Claim 5 or Claim 6, wherein the lock actuator is switched into the inoperative position during successive opening of the hydraulic line cross-section.

8. An arrangement according to Claim 5 or Claim 6, wherein the switching of the lock actuator into the inoperative position during a limited time span is combined with a switching back movement, which follows for a short time, in the direction of the locking position.

9. An arrangement according to Claim 5 or Claim 6, wherein the switchover of the locking actuator to the inoperative position is delayed by a specific time span and, during this time span, a bypass which contains a throttle and by-passes the lock valve, can be connected to the hydraulic linkage.

10. An arrangement according to Claim 6 or Claim 9, wherein, during the time span for the delayed switchover, the one-way valve can be switched to a throttled opening for the direction of flow which is in principle blocked.

11. An arrangement for blocking the engagement of a clutch substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 1 and 2 modified as shown in Figure 1 a or Figure 1 b of the accompanying drawings.