IES81042B2 - Clutch control system - Google Patents

Description

CLUTCH CONTROL SYSTEM Field of the Invention This invention relates to automatic control of the clutch in a geared motor vehicle. The invention is particularly directed to an electronic control unit for automation of a servo clutch system in a motor vehicle having a manually-operated gearbox. The invention is further especially directed to adaptation of a pedaloperated clutch in a motor vehicle having a manually-operated gearbox to provide for automatic clutch operation under at least certain operating conditions.

Background Art It is well known to modify the servo clutch of a standard automobiles for use by disabled drivers who have reduced, or no, use of the left leg. A pneumatic, hydraulic or electric actuator is introduced to pull and release the clutch pedal either automatically, semi-automatically or as demanded by the driver (e.g. via a press-button switch or other on the gear-knob.) In all known cases, an electronic circuit interprets a variety of inputs from the vehicle and /or driver and performs the required operation on the actuator to pull or release the clutch pedal.

The ideal system would operate the clutch in a manner similar to the operation of a manual clutch by a good driver, with smooth ‘take-off from standing start without ‘slippage’, as the driver applies the accelerator and the clutch is released automatically. Subsequent gear changes would be executed by the driver first ‘pulling’ the clutch by means of a press-button switch attached to the gear-knob, selecting the gear (while still holding the press button switch) and then releasing the switch. The clutch would now release automatically, at a rate compatible with the engine speed and road speed of the vehicle, so as to avoid slippage or ‘lurch’.

Under normal conditions, on level ground, when the car engine has been started it idles at about 900 revolutions. In the absence of road speed ( i.e. when the car is stopped) and with the accelerator at rest, the clutch pedal is depressed to the floor. First gear can now be selected. When the accelerator is gently depressed, the engine 5 revolutions increase, meanwhile the clutch is released to what is called a ‘biting’ point or first release. The driver may note this by a slight reduction in engine revolutions and by feeling the clutch bite. At this point the revolutions are increased by pressing further on the accelerator while releasing the clutch in sympathy as the car moves off. With an increase in acceleration and a corresponding increase in revolutions per minute (or delta io rpm), the clutch is further released, by a distance equivalent to a sigma change. When the car is moving at about 10 km/h and the clutch is fully released, the engagement of second gear may be in order.

Many factors influence and affect correct clutch control. (a) Too much ‘bite’ and the engine stalls, while too little ‘bite’ and the revolutions increase rapidly with slight accelerator movement and severe slippage occurs. (b) A fast take-off, where wheel-spin results, requires a different strategy in order to avoid stalling. (cl) A ‘hill start’ will require a different release strategy as the engine revolutions are 20 somewhat higher and slight slippage is tolerated for smooth take off. (c2) Reverse gear, when parking, shunting etc. has a higher ratio than first gear and thus requires a release strategy similar to that invoked for a hill start. (e) Finally, two conditions result in ‘normal’ engine revolutions being elevated before ‘take-off. These are the automatic choke and the catalytic converter. The effect of these on the running of an engine are particularly evident on starting the engine on a cold morning, or after it has cooled. The engine normally runs at an elevated number, approximately 1800 revolutions per minute, for about a minute or more before slowing to normal idling. The good driver compensates for this and again modifies his clutch release/accelerator operation to get a smooth take off.

The present inventors have developed a semi-automatic clutch controller that releases the clutch at increments corresponding with a reduction in number of engine revolutions per minute, which will be described hereinafter with respect to the accompanying drawings. This system, although functional, is tedious to implement as several attempts are necessary before the clutch release timing is accurate. Even when this is achieved the return spring on a normal clutch is not usually sufficiently precise to obtain and guarantee perfect repeatability, and requires approximate six monthly readjustment.

Object There is a need for a semi-automatic retro fitted clutch controller that can simulate and adapt to the varying conditions encountered when initially starting and taking off. It is an object of the present invention to provide such a clutch controller, that can control the engagement of a clutch and can adapt for changing driving conditions. The invention is specifically directed to a system to control the clutch operation from a standing start up to the clutch being fully released with the vehicle moving at about 8 km/h in either direction.

Summary of the Invention Accordingly the invention provides a partially automatic clutch control system for application to a servo clutch system in a motor vehicle having a manually operable gearbox, comprising: sensing means for detecting a power-on mode of the engine of the vehicle, means for incrementally applying the clutch, means for incrementally releasing the clutch, wherein, said sensing means for detecting the power-on mode of the engine is adapted to, on starting the engine of the vehicle, to initiate means to effect a complete application of the clutch and the clutch control system further comprises sensing means for detecting the position of the vehicle's accelerator, means for releasing the clutch to a predetermined position just short of the engagement position, such that said sensing means for detecting the position of the accelerator effects, on application of the accelerator, said means for releasing the clutch to a predetermined position just short of an engagement position.

In a preferred embodiment the clutch control system further comprises; sensing means for detecting the number of revolutions per minute of the vehicle's engine, means for referencing said number of revolutions per minute to a predetermined figure, io such that said sensing means for determining the position of the accelerator determines, on further application of the accelerator and the subsequent increment in said number of revolutions of the engine per minute, the rate of application of the accelerator, wherein said sensing means for detecting the number of revolutions per minute of the vehicle's engine may effect, in situations wherein said rate of application is low, said means for incrementally applying the clutch by one increment when said number of revolutions is greater than said predetermined figure until the clutch is approximately completely engaged, and subsequently increments by one increment when said number of revolutions per minute drops until the clutch is folly engaged, or in situations wherein the accelerator is initially applied folly, said means for effecting release of the clutch, at a higher rate as the number of revolutions increases.

The partially automatic clutch control system preferably further comprises a sensing means for detecting the application of the reverse gear of the vehicle, wherein 25 said means for detection of application of the reverse gear increases, on engagement of reverse gear, the number of revolutions per minute that are required before said means for incrementing release of the clutch to increment the clutch by one unit, increments the clutch by one unit.

In one embodiment the clutch control system further comprises means for detecting the angular pitch of the vehicle, wherein said means for detecting said angular pitch of the vehicle increases, when the vehicle is on an upward slope of greater than an angle in the range 3.5 to 4.5 degrees, the number of revolutions per minute that are required before said means for incrementing release of the clutch increments the clutch by one unit.

If during the period said means for releasing the clutch to a predetermined position just short of the activation position releases the clutch, said means for detecting the number of revolutions per minute detects a number of revolutions greater than said predetermined reference figure, said predetermined reference figure may be replaced by said detected number of revolutions.

The invention also extends to a clutch control system substantially as described herein with reference to and as shown in the accompanying drawings, as well as to a kit for use in providing a motor vehicle with a clutch control system substantially as described herein with reference to and as shown in the accompanying drawings.

Brief Description of the Drawings The invention will now be described with reference to the accompanying drawings, wherein; Figure 1 is a block diagram of an electronic clutch controller according to the invention, and Figure 2 is a circuit diagram of the system of Figure 1.

Detailed description of the Drawings Adverting to Figure 1, this shows the relevant sections of an electronic clutch controller 100, which interfaces with the engine, driver and actuator. It is powered by an ignition switch 1 such that on starting the vehicle, if the controller 100 is switched on, it will automatically operate or pull the clutch. This serves to prevent accidental shunting that may result due to attempting to start in first gear.

The system of the invention has multiple active inputs. The first active input is an engine revolution per minute reference (2) which is derived from either the engine management system, or directly from the distributor contacts or alternator ( not shown). In a similar manner, a road speed reference (3) is input to the controller 100 in a form derived from a sensor on the engine management tachometer or on the drive-shaft. The input signals for revolutions and road speed are preferably electrical pulses whose rate of arrival is proportional to the parameter being measured and in the present design these are converted, using conventional circuitry (8), to a voltage proportional to that parameter. For example a 0 to 5 Volts range represents 0 to 127 km/h or 0 to approx. 6000 Rpm.

A third input 4 monitors the position of the accelerator, and is derived from a linear potentiometer (not shown) which is usually a standard component of most cars, and the output of which is normally within a zero to five volt range proportional to the position of the accelerator. The provision of an electronic threshold sensor 9 signals the controller 100 as to when the accelerator is depressed, even slightly, whereas the proportional voltage from the potentiometer monitors the accelerator position 4.

A fourth input (5) comes from a push-button gear-knob switch, usually mounted on the gear lever, and is the driver’s input to the controller 100. The activation of this normally open switch signals the controller 100 to activate the clutch. In all speed zones above the ‘take-off zone (i.e. km/h > 8), releasing the switch 5 will result in a clutch release at a rate dictated by the various inputs described above. In the ‘take-off zone, pull is automatic unless the driver has activated the accelerator and the engine is running, so activating/releasing this switch 5 has no real effect (except in special circumstances and unusual driving conditions - e.g. racing driver start).

Reverse gear selection 6 is detected by monitoring a reverse switch (10) which is activated to tum on the reversing light. This supplies approximately +12 Volts DC when activated and 0V when not.

A sixth input, a tilt-monitor (7) is activated by a tilt switch 11, which is preferably a commercially available mercury switch, and which may be fitted anywhere in the vehicle and which is activated automatically when the vehicle is parked on an upward slope of more than four degrees. Its function is to indicate to the controller 100 that a ‘hill start’ is being executed when the road speed is less 8 km/h.

The outputs from the controller 100 signal an actuator (not shown) to release or activate the clutch.

“Zone electronics” (13) are a simple voltage level sensing system which output an enable signal 130 to activate the different subsystems of the controller 100 as the vehicle speed changes. Thus, while the vehicle speed is below about 8km/h, “take-off electronics” (14) are enabled and the system will perform pull 120/release 110 according to this take-off logic 14. Above 8km/h, other logic is enabled and the takeoff logic disabled. This other logic, not shown, performs the release operation to cater for conditions encountered such as those during a fourth to third gear change.

First release (15) circuit is another piece of logic which performs a fast partial release of the clutch to a point just short of the ‘bite’ point and is automatic for all releases. This is to reduce the time delay in reaching the ‘bite’ point which, due to momentum, is best controlled while the clutch is being released slowly. This is preferably a timed release which is adjustable to suit different vehicles as each vehicle will have different ‘dead’ zones in their clutches, but may, in some cases use a limit switch.

A release monostable (16) is a pulse width setting device which is triggered by release pulses from the various electronics subsystems such as the take-off electronics 14 or others as dictated by the zone electronics 13. This adjustable pulse width is to cater for variations in different clutches and vehicles.

These improvements are best described with reference to the simplified circuit diagram in Figure 2, and with reference to a standard method referred to, by the present inventors, as “sigma-delta release”.

There are five separate input signals to this section from the main Electronic Clutch Control board 100 as shown in FIG 1. These signals are conditioned by interface circuitry so that revolutions 2 are in the voltage range 0 -5V dc, Reverse 6 and tilt 7 are Vcc, or logic high, when ON and 0V when OFF. First release 15 goes to Logic High for its period of activity while zone 130 is Logic High, as in when the takeoff 14 phase is enabled. In other circumstances they are Logic Low.

The output from this section is a series of Logic high pulses to drive the actuator through a output monostable (16), and thus release 110 the clutch pedal incrementally at a rate dictated by conditions on the inputs.

For simplicity Figure 2 is divided into five sections which will be described in sequence. The first section refers to a system, called a sigma delta release system, which has been developed by the present applicants, whereas the subsequent sections refer and describe improvements to this latter system A) ‘SIGMA DELTA’ or Standard Release The Sigma-delta release system consists of Analog Gate 2, Comparator 2, TS2, NOR 1, INV2 and INV3 plus the associated components. Initially the vehicle engine is running at idling speed (approx. 850 revolutions) and first gear has been selected (The PULL logic 140 ‘knows’ that zone 13 conditions prevail so the clutch is fully pulled.) The driver now presses the accelerator slightly. This immediately signals a first release and a timed pulse is send to the actuator to release the pedal to just before bite point. The duration of this pulse is set for each vehicle and requires periodic adjustment to compensate for wear and tear.

A reference DC voltage, or set-point 50, is permanently supplied to capacitor C4 via a diode D9. Capacitor C4 acts as a memory and is connected to the inverting input of a comparator (COMP 2). This set-point voltage 50 corresponds to about 1050 revolutions and represents the revolutions from which the clutch will start pulsing out. Voltage proportional to the actual revolutions is supplied to the Non-inverting input. Output of COMP 2 is now low as the set-point voltage 50 exceeds the actual revolutions. In normal situations, wherein idling speed < set-point speed, the higher voltage is impressed on C4 and the Analog Gate ANAL GATE 2 serves no purpose.

As the driver presses the accelerator to increase the revolutions, a value above the set-point 50 is reached. The output of COMP 2 goes logic high and this logic high triggers the monostable consisting of NOR1, INV2 and associated components. This sends a short (approximately 2ms) pulse to the actuator monostable and pulses the clutch pedal out one increment to increase ‘bite’. This same pulse also turns on transistor TR2 for 2ms. TS2 and its associated components form a switched constant current source which delivers a fixed charge to C4, thus increasing its voltage to greater than that at the non-inverting input, and switching off COMP2. Revolutions drop slightly as the ‘load’ on the engine increases with a resultant requirement on the driver to press the accelerator still further so as to increase the revolutions to trigger C0MP2 and the monostable, so that a pulse to release the clutch combines with a fixed pulsed increment of voltage on C4. This voltage ‘follows’ the rpm voltage 2. By adjusting the amount of current in the constant current source one can adjust the incremental charge rate of C4 and hence the delta revolution per minute that one requires to pulse out the clutch pedal one increment. The cumulative (sigma) voltage on C4 tracks the clutch position.

This principle of operation, Sigma-delta modulation, is based on a well established technique used in telecommunications but is applied here as an ‘open loop’ control system. This avoids the need for a position monitor on the clutch pedal as the voltage on C4 is constrained to mimic the clutch position.

INV3 and associated components are included here as an inter-pulse delay, in the event of a driver pressing the accelerator excessively, rapid increase of revolutions would produce equally rapid pulses and it has been found that this results in a stall, so a minimum delay between Sigma-Delta pulses is required even for a racing start.

As discussed previously the release system outlined above is tedious to implement as several ‘tries’ may be required to get the timing right. Even when correct timing is achieved engine temperature can cause variations in ‘bite’ point in some cars resulting in excessive/ insufficient bite and subsequent wear and dissatisfaction. The modifications and improvements hereinafter described overcome these problems.

B) Adaptive First Release The invention maintains the performance speed of the old in that a first RELEASE pulse is still used but only for about 90% of the ‘dead’ zone of the clutch pedal. The last 10% is incrementally pulsed out while the engine revolutions are monitored. Pulsing stops when the revolutions are detected to have dropped slightly.

Adverting to section (2) of FIG 2 the invention provides a modification to the arrangement described above with reference to the Sigma Delta system, in that the first release pulse is again used to enable an analog gate, ANAL GATE 1 to charge Cl to a voltage corresponding to the revolutions of the engine at the end of this pulse. It also SETS the S/R Flip-flop. (Q out is logic High ).

Due to small hysteresis (R1,R2) a slightly higher voltage exists on the noninverting input of COMP1 than on the inverting input (Cl). Therefore the output is Logic High. This high now triggers the N0R1/INV2 monostable continuously at a rate dictated by the Minimum inter-pulse delay (INV3 +). The clutch therefore continues to pulse out until a drop in revolutions occurs. This is detected by COMP 1 as the voltage on the non- inverting input drops from that ‘remembered’ by Cl and the output goes to logic Low, This drop of voltage is sensed by C3, inverted by INV1 and after a slight delay, resets the S/R Flop-flop. The Q output now reverts to logic low and disables the output of COMP1 by clamping it to logic low.

The clutch is now at ‘bite’ and severity of the bite may be adjusted (if desired) by varying the hysteresis - but this does not appear to be necessary except perhaps in racing conditions. c)Non-Linear Sigma-Delta (Fast Take-Off) In situations where a fast take off is required, and the accelerator is pressed completely, the aforementioned standard system may result in consistent stalling of the engine for most vehicles. This is due to the fact that if the clutch is released too much before the revolutions had built up the engine torque, which is proportional to revolutions, is insufficient to overcome the inertia of the stationary vehicle. This may be solved by introducing a ‘minimum inter-pulse delay’ -INV3 and associated components. However, this may result in slight slippage, as the clutch pedal release rate ‘followed’ the rpm increase with a slight delay. In a sigma delta standard system, described hereinbefore, stalling is avoided, but at the cost of slippage. Tests show that this slippage persists throughout the release phase and even increases at the higher revolutions before wheel-spin occurs and the vehicle takes-off. This is because the engine torque increases with revolutions and the stationary vehicle inertia opposes motion so revolutions keep increasing with increasing slippage until the clutch is almost fully released - a very undesirable feature leading to severe clutch wear. The circuitry associated with non-linear sigma-delta overcomes this problem.

In the sigma delta standard system the clutch pedal is released, about 0.5mm for each additional change or delta in revolution per minute, above the set-point 50. This results in a smooth take off under normal circumstances, as torque near SET-POINT 50 is low and the extra ‘bite’ of the releasing clutch reduces the revolutions slightly after each incremental pulse as power is transferred in an orderly way to the wheels. If slipping occurs, then the load on the engine is not increased, nor is any power transferred, so engine run-away results until, say twenty to thirty pulses have occurred. Then the wheels spin. The introduction of non-linear sigma-delta 3 reduces this effect as the DELTA revolutions is progressively reduced as revolutions increase -i.e. the clutch releases faster with increasing revolutions. With the increasing torque, a faster clutch release rate can be tolerated and engine revolutions are held by the faster-biting clutch.

Adverting to section (3) of FIG 2 where TS1 and R9 are introduced. This arrangement simply ‘sinks’ a current which is proportional to revolutions, through 5 TSl’s collector. This current is‘stolen’from the constant current source that charges C4. Thus with higher revolutions, this constant current source supplies a smaller voltage step to C4 for each incremental pulse. Consequently the DELTA rpm required to equal that voltage step is reduced, so more pulses are supplied and the clutch pedal is released faster as revolutions increase. io D) HILL START/ REVERSE GEAR START When starting off on a hill, as the Toad’ on the car is increased, a much more gentle release of the clutch is required. The clutch release mechanism for a hill start is similar to that effected when pulling a trailer.

Reverse gear has a higher ratio than first gear and also merits attention as in many cases one is ‘shunting’ to get out of a parking spot and wishes to ‘inch’ forward and backwards carefully. In all these cases the clutch is released more slowly than in a normal take off. Revolutions tend to go up and some slippage is tolerated.

This problem is almost the opposite to the previous one, as a very careful release of the clutch is required with the revolutions well above the set-point. There is a necessity to increase the revolutions before the clutch is pulsed out, or to increase the 25 range of revolutions over which the clutch is being pulsed out. This is done by detecting the condition via either the tilt-switch or reverse gear switch and modifying the DELTA revolutions upwards so that slippage is imminent. Referring to section (4) of FIG 2., two similar circuits are introduced, consisting of a S/R Flip-flop and a switched constant current source (TS3, TS4, R13, R14 and FF2 and FF3.) Considering TS3 and FF2 as a 30 hill take off circuit. If a vehicle is on a upwards slope of greater than 4-5 degrees then the tilt switch is operated. This applies Vcc to the S/R Flip-flop and SETS (FF2) so that the Q output supplies Vcc to R13 . This enabling this CONSTANT CURRENT SOURCE. When a hill start is attempted, additional current is supplied to C4 during each incremental pulse - (approx. 30% extra). This in turn requires a larger DELTA rpm, so more accelerator is required to bring about release of the clutch pedal. A small amount of slippage occurs but take-off is smooth and stall-free. When road speed exceeds about 8kph the zone 1 enable resets the FF2 via the inverter INV4.

TS4 and FF3 operate in a similar manner but the additional current is proportional to the difference in the gear ratio (Approx. 10%).

Additionally for shunting if the driver initially selects reverse gear , before selecting first gear, then FF2 is SET and a ‘slippy take-off, e.g. for shunting, follows. Similarly, if one is towing a load - the take-off phase can be improved by momentarily selecting reverse before first gear. Reverse take-off on a hill invokes both constant current sources.

E)Elevated Idling Revolutions Each of the above problems and descriptions assumed that the vehicle engine was idling at normal (circa 850 rpm) and that the set-point 50 exceeded this value (circa 1050 rpm). Thus, after adaptive first release, the driver pressed the accelerator to increase the revolutions to the set-point 50. Automatic chokes and catalytic converters cause engines to idle at almost 2000 revolutions for a short ( If the idling revolutions exceed the set-point 50 value during first release then adjust the set-point 50 to equal the existing revolutions and start Sigma-delta pulses from the new set-point 50. The Analogue Gate ANAL GATE2 (5) deals with this problem. Since the voltage at the input of this gate during first release, exceeds the setpoint 50 voltage via D9, then the higher value dominates and this high idling voltage is impressed on C4, back biasing the diode D9 and giving a new set-point. Any slight increase of the revolutions above the idling value will give an incremental pulse and, because of the non-linear sigma-delta, these pulses will be close together. This is perfectly in order, as the increased engine torque (due to elevated revolutions) readily tolerates this loading and a clean, smooth take-off ensues.

Although the invention is described with reference to an analogue/digital circuit, it will be appreciated by those skilled in the art that the application of the invention can be equally achieved by use of a micro-controller based system.

Claims (4)

Claims

1) A partially automatic clutch control system for application to a clutch system in a motor vehicle having a manually operable gearbox, comprising: a) sensing means for detecting a power-on mode of the engine of the vehicle b) sensing means for detecting vehicle speed c) sensing means for detecting the number of revolutions per minute of the vehicle's engine d) sensing means for detecting the position of the vehicle's accelerator e) means for applying the clutch, f) means for releasing the clutch, g) means for referencing said number of revolutions per minute to a predetermined figure, h) means for releasing the clutch to a predetermined position just short of the engagement position, wherein, said sensing means for detecting the power-on mode of the engine is adapted to, on starting ignition of the engine of the vehicle, initiate means to effect a complete application of the clutch, and said sensing means for detecting the position of the accelerator effects, on application of the accelerator, said means for releasing the clutch to a predetermined position just short of an engagement position, and said sensing means for determining the position of the accelerator determines, on further application of the accelerator and the subsequent increment in said revolutions of the engine per minute, the rate of application of the accelerator, such that said sensing means for detecting the number of revolutions per minute of the vehicle's engine effects, in situations wherein said rate of application is low, said means for incrementally applying the clutch by one increment when said number of revolutions is greater than said predetermined figure until the clutch is substantially equivalent to 90% engaged, and subsequently effects said means for incrementally releasing the clutch increment by increment when said number of revolutions per minute drops, and said sensing means for detecting said number of revolutions of engine per minute effects, in situations wherein the accelerator is initially applied fully, said means for releasing the clutch, at a higher rate as the number of revolutions increases. 5

2. ) The partially automatic clutch control system as claimed in claim 1 further comprising sensing means for detecting the application of the reverse gear of the vehicle, wherein said means for detection of application of the reverse gear increases, on engagement of reverse gear, the number of revolutions per minute that are required before said means for releasing the clutch increments the clutch by one pulse. io

3. ) The partially automatic clutch control system as claimed in claim 1 further comprising means for detecting the angular pitch of the vehicle, wherein said means for detecting said angular pitch of the vehicle increases, when the vehicle is on an upward slope of greater than an angle in the range 3.5 to 4.5 degrees, the number of 15 revolutions per minute that are required before said means for releasing the clutch increments the clutch by one pulse.

4. ) The partially automatic clutch control system as claimed in any of the preceding claims wherein, if during the period said means for releasing the clutch to a 20 predetermined position just short of the activation position releases the clutch, said means for detecting the number of revolutions per minute detects a number of revolutions greater than said predetermined reference figure, said predetermined reference figure is replaced by said detected number of revolutions. 25 5) A partially automatic clutch system substantially as described hereinbefore with reference to and/ or as illustrated in Figures 1 and 2.