GB2356438A

GB2356438A - Clutch control system

Info

Publication number: GB2356438A
Application number: GB0026854A
Authority: GB
Inventors: Diana Katharine Bowker
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 1999-11-20
Filing date: 2000-11-02
Publication date: 2001-05-23
Anticipated expiration: 2020-11-02
Also published as: DE10055737A1; BR0005499A; GB9927717D0; GB0026854D0; BR0005499B1; DE10055737B4; GB2356438B; IT1319347B1; ITMI20002488A1

Abstract

A clutch control system for automatic control of a motor vehicle clutch, controls reengagement of the clutch depending on the difference between the actual engine sped (V<SB>e</SB>) and a reference speed (V<SB>r</SB>). Below a threshold value of vehicle momentum, the reference speed is a function of the degree of throttle opening, and above the threshold value of vehicle momentum, the reference speed is ramped down to promote rapid engagement of the clutch to a fully clamped condition. The ramping down of the reference value reduces take-up time and hence the amount of clutch slip, avoiding overheating of the clutch and excessive wear.

Description

1 2356438 CLUTCH CONTROL SYSTEM The present invention relates to a clutch

control system or device for the automatic control of a clutch, as for example a motor vehicle clutch, which is positioned in the drive train of a motor vehicle, and which connects an engine with a gearbox, the gearbox having a plurality of fixed ratios, such as gears, and selector means by which neutral position or anyone of the fixed ratios may be selected, a throttle control being provided for controlling speed of the engine, the clutch control system automatically controlling the engagement and disengagement of the clutch, to permit engagement and disengagement of different gear ratios.

In accordance with European Patents 0038113; 0696341; 0735957; and German Patent Application 19911332.7; whose content is expressly incorporated in the disclosure content of the present application, in clutch control systems of the type hereinbefore defined, a reference speed which is dependent upon the degree of throttle opening, is defined and the clutch is controlled, so that the engine speed follows the reference speed. The algorithms disclosed in the above mentioned patents/patent application, are adapted to meet the requirements of varying operating conditions of the vehicle including take-up from rest on the flat or on gradients, take-up at elevated engine speeds and take-up at low speed when low speed manoeuvring is required.

There is however a problem with existing algorithms where the difference between the torque required to make the vehicle climb a steep slope and the maximum torque available from the engine is only small. The use of existing algorithms in such circumstances is likely to lead to excessive take-up times and clutch slip, with the likelihood that the clutch will overheat leading to clutch fade. In such circumstances, if the vehicle is, for example, in a queue of traffic on a hill and requires several starts on the hill in quick succession, it is possible that the vehicle could be stranded on the hill having to wait for the clutch to 5 cool down.

In accordance with one aspect, the present invention provides a clutch control system or device for the automatic control of a clutch, as for example a motor vehicle clutch, the clutch being positioned in the drive io train of a motor vehicle and connecting an engine with a gearbox, the gearbox having a plurality of fixed ratios and selector means by which neutral position or anyone of the fixed ratios may be selected, the motor vehicle being provided with a throttle control for controlling the speed of the engine, the clutch control system automatically controlling engagement and disengagement of the clutch to permit changing of the gear ratio, take up of the clutch being controlled depending upon the difference between the actual engine speed and a reference speed; below a predetermined threshold value of vehicle momentum, the reference speed being a function of the degree of throttle opening; and above the threshold value of vehicle momentum, the reference speed being ramped down to promote rapid engagement of the clutch to a fully clamped condition.

With the clutch control system of the present invention, the ramping down of the reference speed after the vehicle momentum has reached its threshold value, will reduce the take-up time and hence the amount of clutch slip, avoiding overheating of the clutch and excessive wear. The momentum of the vehicle will prevent stalling of the engine, as the clutch is engaged.

According to a preferred embodiment of the invention, the clutch driven plate speed or the vehicle speed is taken as a measure of the vehicle momentum.

Ramping down of the reference speed when the threshold value has been reached, is achieved by subtracting a value which is a function of the rate of change of momentum of the vehicle, driven plate speed or vehicle speed, from the throttle opening dependent reference speed value, so that the faster the momentum of the vehicle is increasing, 10 the quicker the reference speed is pulled down and the clutch is engaged. The reference speed is ramped down to a drop out value which is typically equal to the engine idle speed plus a predetermined offset of 15 say 200 rpm. This drop out reference value is used, in known manner, as a basis for subsequently disengaging the clutch when the vehicle is coming to rest or for gear changes on the move. An embodiment of the invention is now described by way of example 20 only with reference to the accompanying drawings, in which:- Figure 1 shows, in diagrammatic form the general layout of a clutch control system of the type covered by the present application; Figure 2 shows plots of engine speed, clutch driven plate speed, clutch engagement, throttle position and reference speed, for a conventional clutch control system, for a vehicle starting on a 16 - 20 % gradient; Figure 3 shows plots similar to Fig. 2 for a clutch control system in accordance with the present invention, for a vehicle starting on a similar gradient; Figure 4 shows plots similar to Fig. 2 for a clutch control system in accordance with the present invention, for a vehicle starting on the flat; and Figure 5 shows plots similar to Fig. 2 for a clutch control system in accordance with the present invention, for a vehicle starting on a similar gradient at 75 % throttle opening.

Fig. 1 shows an engine 10 with a starter and associated starter circuit 1 Oa which is coupled through a main drive friction clutch 14 to a multi-speed synchromesh lay shaft-type gearbox 12, via a gearbox input shaft 15. Fuel is supplied to the engine 10 by a throttle 16, which includes a throttle valve 18, operated by accelerator pedal 19. The invention is however equally applicable to electronic or mechanical fuel injection or diesel engines.

The clutch 14 is actuated by a release fork 20 which is operated by hydraulic slave cylinder 22, under the control of a clutch actuator control means 38. However, the clutch may also be actuated by an electric motor.

The gearbox 12 is controlled by a gear ratio selector lever 24 which is connected mechanically to the gearbox 12 via selector linkage 25, in conventional manner. The gear lever 24 has a load sensing switch means 33, the switch means 33 detecting forces and/or a travel applied to the lever 24 by the driver or caused by it, and producing a signal indicative of an intention to change gear. The signal from switch means 33 is fed to an electronic control unit 36. The electronic control unit 36, upon receipt of the signal from switch means 33, indicating an intention to change gear, causes the clutch actuator control means 38 to disengage the clutch 14.

In addition to signals from switch means 33, the control unit 36 also receives signals from:a sensor 1 9a indicative of the degree of depression of the accelerator pedal 19; a sensor 30 indicative of the degree of opening of the throttle control valve 18; a sensor 26 indicative of engine speed; a sensor 42 indicative of the clutch driven plate speed; and a sensor 34 indicative of the clutch slave cylinder position.

Instead of using sensor 42 to provide a signal indicative of the clutch driven plate speed, the clutch driven plate speed may be calculated from the vehicle speed which will be measured by the vehicle speedometer and the gear engaged, which may be indicated by a sensor 32 on the gearbox 12.

The control unit 36 utilises the signals from the sensors to control reengagement of the clutch 14 at take-up from rest during gear changes on the move and when the vehicle is coming to a rest.

A buzzer 50 is connected to the control unit 36 to warn/indicate to the vehicle operator as certain operating conditions occur. In addition or in place of the buzzer 50, a flushing warning light or other indicating means may be used. 30 While the transmission system described above requires the manual selection of the gear ratio, the invention also applies to semi automatic and automatic transmission systems of the type disclosed in Patent Specifications W096/23671 and EP0933564, whose content is expressly incorporated in the disclosure content of the present application.

With the present invention, re-engagement of the clutch 14 following selection of a gear is controlled by comparison of the engine speed R.,g relative to a reference speed Rref, clutch engagement being controlled to match the engine speed Reng to the reference speed Rr.f- Accordingly, if the engine speed Rwg is above the reference speed RrO, the clutch engagement will be increased to that the load on the engine 10 will pull the engine speed Reng down towards the reference speed R,ef; while if the engine speed Reng is below the reference speed Rrf, the clutch engagement will be reduced, reducing the load on the engine 10 and permitting the engine speed Reng to increase towards the reference speed Rmf- In accordance with the present invention, when the clutch driven plate speed is below a predetermined value, for example 1200 rpm, or more preferably 1500 rpm, the reference speed is a function of throttle opening, for example as disclosed in Patent Specifications EP0038113; EP0043660; EP0059035; EP1 01220; W092/13208; or Patent Application DE1 9911332.7; whose content is expressly incorporated in the disclosure content of the present application.

Above the predetermined value of clutch driven plate speed, the reference speed R,ef is ramped down rapidly to a drop out value Rd., which is a predetermined offset of typically 200 rpm, above the idle speed Ridle of the engine 10.

The rate at which the reference speed R,.f is ramped down to the drop out speed Rd. is a function of the rate of change of driven plate speed RdP.

Consequently, on the basis of the algorithm disclosed in EP0038113; below a driven plate speed of 1500 rpm Rref Ri,t + K, + K2 OC where Rj, engine speed at initiation of take-up; and cc % throttle opening.

and above a driven plate speed of 1500 rpm Rref =Rit + K, = K2 oc K3dRdP/dt [down to R,,f = RdJ Fig. 2 shows a typical plot of reference speed Rr.,; engine speed Re"g; driven plate speed RdpI clutch engagement and throttle opening for a vehicle with an 800cc, 70Nrn engine, starting from rest on a gradient of 16 to 20 %.

As illustrated in Fig. 2, with zero percent throttle no gear engaged and the clutch engaged, the reference signal Rrf is an offset value, typically 400 rpm above the engine idle speed Rid, le. R,ef = Ridle +400.

At time to when the gear [ever 24 is moved to engage a take-up gear, for example first or reverse gear, the signal from switch means 33 causes the clutch 14 to disengage. In order to avoid unnecessary delays in clutch re-engagement, the clutch plates may then be moved together from the fully disengaged position towards the touch point at which torque begins to be transmitted by the clutch 14. However, as long as the throttle 18 remains closed, and the reference speed Rref i s above the engine speed Reng the clutch 14 will remain disengaged.

At time tj, when the throttle 18 is fully opened, the engine speed Rng and reference speed R,e, both increase. Filters in the control unit 36 control the rate of increase of the reference speed Rref SO that is approximates the rate of increase of engine speed Reng when the engine 10 is unloaded.

When at time t2, the engine speed Rng increases above the reference speed Rmfl the clutch 14 begins to be re-engaged, loading the engine 10 and causing the engine speed Reng to be drawn down towards the reference speed R,ef. This continues, the degree of clutch engagement increasing and decreasing to match the engine speed Rng to the reference speed R,ef, until the engine speed Reng approaches the clutch driven plate speed Rdp, at time t3- At time t3 when the engine speed approaches the driven plate speed within predefined limits, the reference speed R,,f is reduced rapidly to a drop out reference R,,,,, following a predetermined profile. This rapid drop in reference speed Rr.f causes the clutch 14 to be fully clamped after which the driven plate speed Rdp Will follow the engine speed R,,,,, .

With the clutch re-engagement controlled in this manner, the take-up time from tj to t4 was 4.4 seconds and the clutch slip time, during which the clutch driven plate and the clutch plates are in frictional engagement but are slipping relative to one another, t2 to t, was 3.7 seconds.

Fig. 3 shows plots similar to Fig. 2 for the same vehicle starting on the same gradient, clutch 14 being controlled in accordance with the present invention.

The clutch control from tO to t2 follows the conventional clutch control system described by reference to Fig. 2. However, at t3.1 when the driven plate speed RdP reaches 1500 rpm, the reference speed Rr.f is ramped down as a function of the rate of change of driven plate speed 5 dRdP/dt, to a limit value Rd.. This ramping down of the reference speed R,,f causes rapid clamping of the clutch plates so that the driven plate speed Rdp quickly matches the engine speed Reng the engine speed initially being pulled down by the increased load on the engine. In this example, the take-up time tj to t4 was reduced to 2.9 seconds and the slip time t2 to t, was reduced to 2.2 seconds.

The early clamping of the clutch 14 in this manner does result in a perceptible drop in engine speed, but this is only equivalent to that expected with manual clutch control and is acceptable to the driver.

The drop in engine speed is also beneficial in terms of torque transfer from the engine to the vehicle/road wheels.

As shown in the plots illustrated in Fig. 4, when the clutch control system of the present invention is used for starting on the flat the driven plate speed Rdp increases to the threshold value more quickly. Moreover, the threshold value of the clutch driven plate speed may be reduced to 1200 rpm. As a consequence, the time t3. is brought forward with consequent further reductions in take-up time tj to t4 tO 1.9 seconds and slip time t2 to t4 to 1.6 seconds.

Moreover, as illustrated in Fig. 5, when starting on the same gradient as illustrated in Fig. 2, even when starting at 75 % throttle, the takeup time tj to t4 is reduced to 3 seconds and the slip time t2 to t4 is reduced to 2.4 seconds.

As illustrated above, the clutch control system of the present invention provides significant improvements in take-up time and slip time, without any significant detriment to the ride quality. While this clutch control system is particularly advantageous for vehicles with small, low powered engines, it may be used to advantage on higher powered vehicles.

Various modifications may be made without departing from the invention. For example, while as described above, the driven plate speed RdP is taken as a basis for the vehicle momentum, for triggering a rapid decrease in reference speed and also controlling the rate of decrease, other suitable criteria may be used, for example the vehicle speed itself. Alternatively, a momentum algorithm which quantifies the momentum possessed by the vehicle and the momentum transfer required to optimise performance, with regard to drive feel and driver perception, may be used. Such algorithms may also incorporate: the degree of throttle opening as an indication of how much torque is demanded by the driver; and/or torque information from the engine management system, to refine the control strategy.

While in the above embodiment hydraulic means are used for actuation of the clutch actuator means; hydraulic, pneumatic or electrical actuators, for example electric motors or solenoids, may be used for actuation of the clutch actuator means and in semi-automatic and automatic transmissions, the gear selector mechanism; for example as disclosed in DE1 9504847; W097/10456 or DE1 9734023; whose content is expressly incorporated in the disclosure content of the present application.

The patent claims submitted with the application are proposed formulations without prejudice to the achievement of further patent protection. The applicant reserves the right to submit claims for further combinations of characteristics, previously only disclosed in the description and/or drawings.

References back used in sub-claims refer to the further development of the subject of the main claim by the characteristics of the respective sub-claim; they are not to be understood as a waiver with regard to achieving independent item protection for the combination of io characteristics in the related sub-claims.

Since the subject of the sub-claims can form separate and independent inventions with reference to the prior art on the priority date, the applicant reserves the right to make them the subject of independent claims or of division declarations. Furthermore, they may also contain independent inventions which demonstrate a design which is independent of one of the objects of the preceding sub-claims.

The embodiments are not to be considered a restriction of the invention. Rather, a wide range of amendments and modifications is possible within the scope of the current disclosure, especially those variations, elements and combinations and/or materials which, for example, the expert can learn by combining individual ones together with those in the general description and embodiments in addition to characteristics and/or elements or process stages described in the claims and contained in the drawings with the aim of solving a task thus leading to a new object or new process stages or sequences of process stages via combinable characteristics, even where they concern manufacturing, testing and work processes.

Claims

1. A clutch control system for the automatic control of a motor vehicle clutch, said clutch connecting an engine with a gearbox, the gearbox having a plurality of fixed ratios and selector means by which neutral position or any one of the fixed ratios may be selected, the motor vehicle being provided with a throttle control for controlling the speed of the engine, the clutch control system automatically controlling engagement and disengagement of the clutch to permit changing of the gear ratio, take up of the clutch being controlled depending upon the difference between the actual engine speed and a reference speed; below a predetermined threshold value of vehicle momentum, the reference speed being a function of the degree of throttle opening; and above the threshold value of vehicle momentum, the reference speed being ramped down to promote rapid engagement of the clutch to a fully clamped condition.

2. The clutch control system according to claim 1 in which the predetermined threshold value is a predetermined value of speed of a driven plate of the clutch.

3. The clutch control system according to claim 2 in which the predetermined value of clutch driven plate speed is at least 1200 rpm.

4. The clutch control system according to claim 2 or 3 in which the predetermined value of clutch driven plate speed is about 1500 rpm.

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5. The clutch control system according to claim 1 in which the predetermined threshold value is a predetermined value of vehicle speed.

6. The clutch control system according to claim 1 in which the predetermined threshold value is based on a momentum algorithm which takes into account the momentum possessed by the vehicle and the momentum transfer required to optimise performance.

7. The clutch control system according to claim 6 in which the algorithm includes a function dependant on the degree of throttle opening and/or a function dependant on torque information from the engine management system.

8. The clutch control system according to any one of claims 1 to 7 in which above the predetermined threshold value, the reference speed is ramped down as a function of rate of change of vehicle momentum.

9. The clutch control system according to claim 8 in which above the predetermined threshold value, the reference speed is ramped down as a function of rate of change of speed of a driven plate of the clutch.

10. The clutch control system according to claim 9 in which:below the predetermined value of driven plate speed; Rref "'-- Rint + K, + K2a; and above the predetermined value of driven plate speed; Rref Rint + K, + K2 OC- K3dRdp/dt; where:- Rr.f Reference Speed; Rin, Engine Speed at initiation of take-up; - 14 cc % Throttle opening; and Rdp = Driven Plate Speed.

11. The clutch control system according to any one of the preceding claims in which above the predetermined value, the reference speed is ramped down to a predetermined drop out value.

12. The clutch control system substantially as described herein, with reference to and as shown in figures 1 and 3 to 5 of the accompanying drawings.