GB2250075A

GB2250075A - A clutch control system

Info

Publication number: GB2250075A
Application number: GB9023916A
Authority: GB
Inventors: Roger Porter Jarvis; John Francis Gilbert
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1990-11-02
Filing date: 1990-11-02
Publication date: 1992-05-27
Anticipated expiration: 2010-11-02
Also published as: GB9023916D0; GB2250075B; WO1992008065A1

Abstract

A system for preventing a vehicle from running away downhill and for ensuring a smooth take-up from rest, in which signals proportional to engine speed (Ve) and driven plate speed (Vdp) are compared and the larger of the two is compared with a reference signal (Vs). If the reference signal is exceeded the clutch (14) is engaged slightly either to keep the engine speed equal to the reference speed in the take-up from rest or to keep the driven plate speed equal to the reference speed to prevent run-away.

Description

A CLUTCH CONTROL SYSTEM The present invention relates to a clutch control system for a vehicle.

Our earlier patent GB 2 o88 007 describes a clutch control system in which the clutch is progressively engaged as the torque demand issued by the driver increases to temporarily limit the engine speed to a set value. This provides a smooth take up from rest.

It is a disadvantage of these systems as described that if the vehicle while in gear should roll down a hill gathering speed which the enging is still at idle, the clutch will not engage to provide a degree of braking, nor can the driver make it engage without speeding up the engine using the speed control means, an action that would appear to him totally unnatural in a circumstance when he wanted to cause the vehicle to be restrained. Furthermore, if the engine cannot be started duc to failure or partial failure of the self-starting system, the engine cannot be started by any of the commonly accepted emergency starting means such as push-starting or two-starting. It is an object of the present invention to overcome these disadvantages.

The present invention provides a clutch control system for' a vehicle having a clutch, a gearbox and an engine, the system comprising a vehicle speed sensor for generating a vehicle speed signal variable with the speed of the vehicle, an enging speed sensor for generating an engine speed signal variable with the speed of the engine, a reference signal generator for generating a reference signal, comparator means for comparing the engine and vehicle speed signals and the reference signal and clutch actuation means for increasing engagement of the clutch if either one of the engine or vehicle speed signals exceeds the reference signal.

Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 is a schematic of a control system according to a first embodiment of the present invention; Fig. 2 is an analogue circuit diagram of the control system of Fig. 1; Fig. 3 is a block diagram showing the steps used in a microprocessor in a second embodiment of the invention.

Referring to Fig 1 a vehicle clutch system comprises an engine 10 and a gearbox 12 coupled through a clutch 14, via a gearbox input shaft 15. Fuel is supplied to the engine by a throttle 16 which includes a throttle valve 18 operated by accelerator pedal 19. The clutch 14 is actuated by a release fork 20 which is operated by a slave cylinder 22. The gearbox is operated by a gear lever 24.

An engine speed signal generator comprises an engine speed sensor 26 which includes a transducer. The state of the throttle valve 18 is monitored by a throttle valve position sensor 30. The state of the gearbox 12 is monitored by a gear position sensor 32.

The position of the slave cylinder 22 is monitored by an actuation sensor 34. The speed of the gearbox input shaft 15, which is equal to that of a driven plate 40 of the clu-tch 14, is monitored by a driven plate speed sensor 42. Since the speed of the vehicle depends on the driven plate speed and the gear engaged, the driven plate speed sensor 42 acts in effect as a vehicle speed sensor. Signals from the sensors are transmitted to a control unit 36 which controls the actuation of the clutch via a hydraulic control 38.

Referring to Fig. 2, the system also includes a choke position sensor 44 and a reference signal generator 46. ' The throttle position sensor 30 produces a throttle.signal Vt which is fed to an inverting input of sa difference amplifier 50 via a limiter 48. The limiter 48 receives an input from a switching circuit 49. A reference signal Vr from the reference signal generator 46 is combined with a choke signal Vc from the choke position sensor 44 and input to the difference amplifier 50. The output Vs of the difference amplifier 50, being the sum of Vt, Vr and Vc, forms a modified reference signal which fed to the input of a comparator 52.

The engine speed sensor 26 produces an engine speed signal Ve which is fed via the resistors R1 and R2 to the comparator 52. The driven plate speed sensor 42 produces a signal V2 which is fed to a circuit containing diodes 54 and 56 and a high impedence buffer 58. The diode 54 has its output connected to the driven plate speed sensor 42 and its input connected via a resistance R3 to a supply of constant voltage V1 which in this case is 5v. The input of the diode 54 is also connected via the high impedence buffer 58 to the input of the diode 56, the output of which is connected between resistors R1 and R2. This circuit functions to make Vdp equal to V2 up to a maximum of V2. The output Vdp from that circuit forms a vehicle speed signal which is fed to the junction between the resistors Rl and R2.

The resistor R2 is much large than R1 for example 50 times larger such that tie signal Vdp will overide the signal VE when Vdp is greater than VE i.e. when the driven plate speed, which is proportional to the vehicle speed exceeds the engine speed. The resistors R1 and R2 and the comparator 52 together form comparator means for comparing the driven plate speed signal Vdp, the engine speed VE and the modified reference signal Vs.

The comparator 52 produces an error signal E which equals the difference between the modified reference signal Vs and a signal Vx equal to the greater of VE and Vdp.

The error signal E is fed to one input of a comparator 60, the other input of which receives a signal from a clutch position sensor 62. The output from the comparator 60 is fed via a phase gain shaping network 64 to a mark to space ratio modulator 66 which also has as input a signal from an oscillator 67. The output signal from the mark to space ratio modulator 66 is fed via an output 68 to a valve 70, which controls the position of the clutch 14 via a hydraulic control 72.

During normal operation, when the vehicle is at rest and the enine is idling neitller Vi nor Vdp is greater than the reference signal so E is positive and the clutch is held in a fully disengaged position by the actuator 72. If the throttle is depressed the engine speed increases until VE is greater than Vs. At that point E goes negative. This causes the clutch to engage slightly which slows the engine, reducing VE and tending to keep E to zero. Provided the throttle is kept depressed the tendency of the engine speed to increase will engage the clutch.

If, again starting from rest, the vehicle begins to roll the driven plate speed signal Vdp will increase with vehicle speed until it is greater than Vs. At that point E will go negative and the clutch will be engaged slightly so that the inertia of the engine brakes movement of the vehicle. Provided the vehicle still tends to roll, the clutch will gradually engage tending to keep E at zero. When the clutch is fully engaged no further braking can br provided by the clutch and E will go negative with increasing magnitude.

If the vehicle is then slowed, for example if the driver brakes, Vdp will decrease unti it is lower than Vs and E starts to go positive. At that point the actuator 72 will start to disengage the clutch in that either Vdp is held at Vs and E is held at zero, or, if the vehicle is slowed by the brakes enough to hold Vdp below Vs, the clutch will be completely disengaged.

In the embodiment described above Vdp will be proportional to the speed at which the vehicle is rolling, but the constant of proportionability will depend on the state of the gearbox, i.e. which gear is engaged. Any parameter directly proportional to driven plate speed could be used to give a similar result. In an alternative Vdp could be obtained by a vehicle speed signal obtained from the speed of an output from the gearbox, or any other parameter directly proportional to vehicle speed. Ilowever in order to facilitate comparison with the engine speed signal and the reference signal, the vehicle speed signal would advantageously be modified, depending on which gear is currently engaged, so as to be directly proportional to the driven plate speed. For this purpose the gear position sensor 32 would be used.

Referring to Fig 3 in a further embodiment of the invention the processing of signals from the sensors and the production of a signal for actuation of the clutch is performed by a microprocessor. At step 1 a basic speed reference is retrieved, the value of the speed reference having been set when the microprocessor was produced. At step 2 the idle speed is examined. The idle speed would have a set value which could be se-t higher, eg for a cold start. If the idle speed is set high, the microprocessor proceeds to step 3 to compute an increased speed reference. If the idle speed is at its normal set value step 3 is by-passed and the speed reference is unaltered. At step 4 a throttle setting signal is generated, and at step 5 the speed reference is increased by an incrementr dependent on the throttle setting signal.At step 6 an engine speed signal is generated and at step 7 a driven plate speed signal is generated. These are compared at step 8. The larger of the two is compared with the speed reference at step 9 to produce a speed error signal representing the difference between the engine speed or driven plate speed and the reference speed. The error signal and the integral with respect to time of the error signal are generated at step 10 and combined to determine at step 11 a required clutch position. When the error is positive the error signal is used to calculate directly the required clutch position.

However when the error is reaches zero or is negative the error signal and its integral are used in combination. An actual clutch position signal is generated at step 12 and composed with the required clutch position signal at step 13 to produce a position error, which generates at step 14 an output signal for the control valve 70 of the clutch hydraulic actuation.

The microprocessor may also be altered so as to operate in an equivalent manner to the analogue circuit described in our carlier patent No. 2079 888, which provides for an improved hill start capacity.

As with the analogue system, the part of the microprocessor which forms a comparator means for performing steps 6 to 9 could be arranged differently and the order of the comparisons of engine speed, driven plate speed and reference could be altered.

For example the engine speed signal and driven plate speed signal could each be compared with the reference signal to produce two error signals, the greater of which could be used to compute a required clutch position.

In order to push start the vehicle a low gear is engaged and the vehicle pushes1. The clutch system will act in the same way as in the downhill rolling situation and engagement of the clutch will occur.

Provided the pushing force is strong enough to turn the engine it will start up.

Claims

1. A clutch control system for a vehicle having a clutch, a gearbox and an engine, the system comprising a vehicle speed sensor for generating a vehicle speed signal variable with the speed of the vehicle, an engine speed sensor for generating an engine speed signal variable with the speed of the engine, a reference signal generator for generating a reference signal, comparator means for comparing the engine and vehicle speed signals and the reference signal and clutch actuation means for increasing engagement of te clutch if cither one of the engine or vehicle speed signals exceeds the reference signal.

2. A system according to Claim 1 wherein the comparator means comprises means for comparing the engine speed signal with the vehicle speed signal and producing a signal variable with the larger of the two.

3. A system according to Claim 1 or Claim 2 wherein the comparator means is adapted to compare only the larger of the engine speed signal and the vehicle speed signal with the reference signal.

4. A system according to any foregoing claim wherein the vehicle speed sensor comprises means for measuring the speed of rotation of a driven plate of the clutch.

5. A system according to any one of Claims 1 to 3 wherein the vehicle speed sensor comprises means for measuring the speed of rotation of an output from the gearbox.

6. A system according to Claim 5 wherein the vehicle speed sensor further comprises means for varying the vehicle speed signal according to the state of the gearbox.

7. A clutch control system according to any foregoing claim wherein the comparator means comprises a microprocessor.

8. A clutch control system substantially as hereinbefore described with reference to the accompanying drawings.