GB2112101A

GB2112101A - Arrangement for preventing engagement of the clutch of a motor vehicle

Info

Publication number: GB2112101A
Application number: GB08236417A
Authority: GB
Inventors: Gerhard Pabinger
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: FR2518938B1; DE3151417C2; GB2112101B; IT8224862A1; IT1155026B; IT8224862A0; DE3151417A1; FR2518938A1

Abstract

An arrangement for blocking the engagement of a clutch (5) of a motor vehicle is provided with a lock actuator (9) which can be switched over to close a valve 30 to prevent damage to the engine (3) as a result of overspeeding which occurs in the event of an incorrect gear change to a too low gear. A control device (13) is connected to engine and gearbox input speed sensors (11.12) via inhibiting or locking circuits (16.17) 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 circuits (16) on the engine side transmits an input signal for the control device (13) only below a limiting value, and the inhibiting circuits on the gear side (17) transmits an input signal for the control device (13) only above a respective limiting value. The control device (13) moves the lock actuator (9) into the locking position only upon the appearance of both the input signals. <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 out of 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 both the engine speed and a gear speed by way of sensors and which, upon the occurrence of critical speed values, moves 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 as a result of overspeeding 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 1 8 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 uncontroiled. On the 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 this 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 lock actuator which can be switched out of 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 both the engine speed and a gear speed by way of sensors and which, upon the occurrence of the critical speed values, moves the lock actuator into its locking position, wherein the control device is connected, on the input side, to two sensors via inhibiting or locking circuits and the connection on the output side, between the control device and the lock actuator is maintained irrespective of the positions of the gear side transmit input signals for the control device only below and above respective limits, and the control device moves the lock actuator into the locking position only upon the appearance of both the input signals.

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 into the critical speed range as a result of the high kinematic 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 kinematic energy of the vehicle acts upon the engine also under these conditions.

It has been found advantageous to keep the limiting value of the engine speed above the noload speed, but to place the limiting value of the gear input speed approximately in the vicinity of the critical excessive speed of the engine.

With the arrangement according to the invention it has been found advantageous to use, as the control device, an and gate or element connected to two threshold elements. Moreover, with the arrangement according to the invention it is advantageous that a lock or check valve, which can be actuated by the lock actuator, is connected to a hydraulic linkage leading to the clutch actuator. This lock valve, however, releases the clutch if in the event of driving on a gradient and critical engine speeds a higher gear is engaged, because the signal on the engine side does not appear under these conditions.

An embodiment of the invention will now be described by way of an example and with reference to the accompanying drawing, in which: Fig. 1 shows a block diagram of the arrangement according to the invention, and Fig. 2 shows a graph of the variation of engine output relative to the speed, with the limiting values of engine speed and transmission speed which are used in the case of the arrangement illustrated in Fig. 1.

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 1 3 for which a known electronic And-element or gate 25 is used.

The And-element 25 is connected through its two inputs to inhibiting or locking circuits 1 6 and 1 7 for which known electronic threshold elements 23 and 24, respectively, are used.

A sensor 11 transmits a signal 34 which is analogous with the speed nM of the crankshaft 26 and which is fed to the input of the threshold element 23 - if necessary, through an electronic transducer 36.

A further 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 23 transmits an input signal 19 if the speed nM lies below a limit 14. As shown in the graph of Fig. 2 - in which the output N of the internal combustion engine 3 relative to the speed nM is plotted -- the limit 14 is placed between the no-load speed 38 of the internal combustion engine 3 and a higher critical speed value 22 for damage caused to the internal combustion engine as a result of overspeeding.

The threshold element transmits an input signal 20 for the And-element 25 is the speed nG of the transmission input shaft 27 exceeds a limit 1 5. As also shown in Fig. 2, the limit 1 5 lies approximately at the critical speed value 22.

The And-element 25 transmits an output signal 39 which moves the lock actuator 9 into the locking position 33 if the input signals 1 9 and 20 appear together.

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 and slightly above the no-load range 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 both the critical speed values 14 and 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 be disengaged to change up to a higher gear because the signal on the engine side does not appear then and the lock actuator 9 therefore keeps the lock valve 30 in the inoperative position 1 0.

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 engage position for engaging the clutch, and a lock actuator which can be switched out of 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 both the engine speed and a gear speed by way of sensors and which, upon the occurrence of critical speed values, moves the lock actuator into its locking position, wherein the control device is connected, on the input side, to two sensors via inhibiting or locking circuits 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 on the engine side and the inhibiting circuit on the gear side transmit input signals for the control device only below and above respective limits and the control device moves the lock actuator into the locking position upon the appearance of only both the input signals.

2. An arrangement according to Claim 1, wherein the limit of the engine speed lies between the maximum zero load or idling speed and a higher critical value in the case of damage caused to the internal combustion engine as a result of overspeeding.

3. An arrangement according to Claim 1 or 2, wherein the limit of the gear speed is approximately equal to the critical value in respect of damage caused as a result of overspeeding.

4. An arrangement according to any one of Claims 1 to 3, wherein an And-element or gate, which is connected to two threshold elements is used as the control device.

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 the gear speed is the gear input speed.

7. An arrangement for blocking the engagement of a clutch substantially as wherein before described, with reference to the accompanying drawing.