WO2010128276A1

WO2010128276A1 - Vehicle driveline including clutches

Info

Publication number: WO2010128276A1
Application number: PCT/GB2010/000853
Authority: WO
Inventors: Benjamin Chetwood Struve; Richard David Maitland Cooke; Alastair John Young
Original assignee: Raicam Clutch Limited
Priority date: 2009-05-02
Filing date: 2010-04-29
Publication date: 2010-11-11
Also published as: EP2425142A1

Abstract

A torsional vibration damping arrangement for a vehicle driveline (10) having a transmission (13) driven by an engine (12) via a drive clutch (11). The arrangement includes a clutch actuator (15) for engaging/disengaging the clutch and an electronic control unit (16) which receives vehicle and clutch operating parameter signals and issues control signals for the engagement/disengagement of the clutch via the clutch actuator (15) during starting and stopping of the vehicle and during ratio changes in the transmission. The electronic control unit (16) is also arranged to control the level of engagement of the clutch to damp lower engine speed torsional vibrations in the drive line by allowing the clutch to slip, and the clutch includes torsional spring damping means (53) to damp higher engine speed torsional vibrations in the driveline. The electronic control unit (16) allows the clutch to slip in order to avoid exciting one or more natural frequencies of an associated driveline of the vehicle.

Description

VEHICLE DRIVELINE INCLUDING CLUTCHES

This invention relates to vehicle drivelines in which a vehicle transmission is driven by an engine via a drive clutch and to arrangements for damping torsional vibrations in such drivelines.

Typically such drivelines have employed mechanical torsional vibration dampers such as complex and expensive twin-mass flywheels or circumferentially acting damping springs provided in the clutch itself.

As such drivelines suffer from noise, vibration and harshness (NVH) over their entire speed of operation mechanical damping arrangements are compromised in order to deliver acceptable damping both in low engine speed idle conditions and in mid and high speed operating conditions.

It is an object of the present invention to provide damping of torsional vibrations in a vehicle driveline which avoids the above problems.

Thus according to the present invention there is provided a torsional vibration damping arrangement for a vehicle driveline comprising a transmission driven by an engine via a drive clutch, the arrangement including :-

a clutch actuator for engaging/disengaging the clutch,

an electronic control unit which receives vehicle and clutch operating parameter signals and issues control signals for the engagement/disengagement of the clutch via the clutch actuator during starting and stopping of the vehicle and during ratio changes in the transmission, the electronic control unit also being arranged to control the level of engagement of the clutch to damp lower engine speed torsional vibrations in the drive line by allowing the clutch to slip, and the clutch including torsional spring damping means to damp higher engine speed torsional vibrations in the driveline.

Such an arrangement enables the electronic unit to take care of the lower engine speed torsional vibrations (i.e. primarily at speeds below 1800 r.p.m.) and the spring damping in the clutch can be chosen specifically to damp vibrations without being compromised by the need to damp low speed idle rattle etc.

Typically the stiffness of the damping springs on the clutch will be chosen to be as low as possible at say 1.2 times the maximum engine torque at the point of maximum travel of the springs.

It has been found that using an arrangement in accordance with the present invention the use of a twin-mass flywheel is unnecessary and a cheaper solid flywheel can be employed.

The present invention is applicable to drivelines in which the clutch is manually controlled by a driver-operated clutch actuating pedal to engage/disengage the clutch during starting and stopping of the vehicle and during ratio changes in the transmission.

The present invention can also be used in arrangements where the engagement /disengagement of the clutch are controlled by the electronic control unit in so-called fully or semi-automated manual transmissions.

The electronic control unit may receive input signals representative of transmission input shaft speed, clutch pedal position, engine speed and engine torque, the control unit processing these signals to provide an output signal to the clutch actuator to command the required level of clutch engagement level to give the clutch slip to provide torsional vibration damping or the clutch engagement position selected by the pedal when provided or the electronic control unit in a fully or semi-automated manual transmission.

The electronic control unit is arranged to allow the clutch to slip in order to avoid exciting one or more natural frequencies of an associated driveline of the vehicle so as to avoid torsional vibrations in the driveline.

The control unit may receive engine speed signals and does not allow engagement of the clutch until a minimum engine speed has been reached.

During clutch engagement the electronic control unit may ensure that the minimum engine speed is maintained to avoid stalling.

The electronic control unit preferably limits the heat dissipated in the clutch during a clutch engagement by limiting the engine speed and the time during which the clutch is allowed to slip.

The electronic control unit may monitor the pedal position and may be arranged to fully engage the clutch if the driver rides the clutch pedal for more than a predetermined period of time.

The electronic control unit may be arranged to receive one or more vehicle operating parameter signals indicative of a vehicle crash condition and on receiving such a crash signal or signals to disengage the clutch.

The spring means may act on the clutch pedal to provide a pedal effort characteristic which increases up to a maximum effort at approximately the point of disengagement of the clutch and thereafter reduces.

The electronic control unit preferably ensures that the level of engagement of the clutch is greater than the instantaneous torque provided by the engine. Typically the torque capacity of the clutch may be held at 1.1 times the instantaneous torque being generated by the engine (rather than the normal 1.4 times maximum engine torque at all times). This reduction in torque capacity of the clutch reduces the magnitude of transient torques which can be applied to the driveline components, allowing a reduction in their strength and operating loads consequently giving the opportunity for cost savings.

The torque capacity of the clutch may be measured by measuring the force which the clutch release means is applying to disengage the clutch, which opposes the force applied to engage the clutch by the clamping means, hence giving the net clamping force being applied to the clutch which determines its torque transmitting capacity.

The clutch release force may be measured directly by a load cell.

If the clutch is provided with an hydraulically operated release means, the clutch release force may be measured by measuring the pressure in the hydraulic release means.

If the clutch is provided with an electrically operated release means, the clutch release force may be measured by measuring the current used by the electrical release means.

The clutch clamping means preferably applies an engagement force to the clutch which continuously increases as the clutch is disengaged by the release means. This ensures that for each level of force applied by the clamping means there is a unique clutch engagement position.

The electronic control unit preferably calculates the temperature of various components of the clutch and estimates the current effective coefficient of the clutch lining material and hence adjusts the clamping force applied to the clutch by the clamping means as the clutch lining material temperature rises and falls.

The electronic control unit preferably monitors the level of slip in the clutch and adjusts the clamping force if the clutch is slipping when slippage is not intended or expected.

The invention also provides a clutch monitoring system for predicting the wear of a lining material of a vehicle drive clutch using a numerical model, the system including an electronic control unit which receives signals indicative of clutch input and output speeds, clutch ambient temperature, engine torque, thermal capacity of certain clutch components, heat dissipation rate of these clutch components, and wear rate of the clutch lining material as a function of lining temperature and as a function of the rate of energy dissipation in the lining material; the electronic control unit using combinations of the above parameter signals to predict the level of lining wear which has occurred since the system was last reset and providing an indication to the vehicle driver when predetermined wear conditions have been reached. This numerical model can be used in any vehicle clutch no matter whether it is controlled by a system in accordance with the main claim of this application.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 shows diagrammatically a vehicle driveline torsional vibration damping arrangement in accordance with the present invention;

Figure 2a is a diagrammatic spring-mass representation of the inertia and stiffness of a typical vehicle driveline;

Figure 2b shows the mode shape of the torsional vibrations which occur in the spring-mass system of Figure 2a; Figure 3 shows a diagram of a spring arrangement acting on a clutch actuating pedal in the damping arrangement of the present invention;

Figure 4 shows the spring characteristics of the springs operating in the spring arrangement of Figure 3;

Figure 5 shows a typical continuously rising release bearing force/release bearing position curve of a diaphragm spring used to clamp a clutch in the damping arrangement of the present invention and the net clamping force applied to the driven plate;

Figure 6 shows internal details of a spring device used on the clutch pedal;

Figure 7 shows details of a clutch driven plate used in the damping arrangement of the present invention;

Figure 8 shows the torque v deflection characteristic of the driven plate of Figure 7;

Figure 9 shows the flow diagram of the algorithm for clutch slip control exercised by the electronic control unit of the damping arrangement of the present invention; and

Figures 10 and 11 show respectively the slip v engine speed and slip v engine torque lookup tables used in the algorithm shown in the flow diagram of Figure 9.

Referring to the drawings, Figure 1 shows diagrammatically a torsional vibration damping arrangement for a vehicle driveline 10 in which an engine 12 drives a transmission13 via a drive clutch 11. Transmission 13 in turn drives wheels 14 of the vehicle. The clutch 11 is mounted on a single mass flywheel 11a and has its driven plate (see Figure 7) clamped against flywheel 11a by a diaphragm spring also not shown. The clutch also has a release means 15 whose operation is controlled by an electronic unit 16. In a typical system, release means 15 includes an electric motor whose rotational movement is converted into axial movement of a hydraulic piston in a master cylinder (not shown) by a nut and screw or ball and screw device. This resulting axial movement of the hydraulic piston is used to operate a hydraulic slave cylinder adjacent the clutch which releases the clutch. In a typical van application a conventional brushless DC motor is used which is controlled by ECU 16 which contains the power electronics to commutate the current in its windings. Alternatively a brushed motor could be used, or a linear electric motor which would

generate a translational force instead of a rotational torque.

In an alternative arrangement the release means can be completely electrical with an electric motor operating a ball and screw device which operates directly on the clutch release mechanism without the use of hydraulics.

The control system has a clutch actuating pedal 17 pivoted on a pedal box 18 about an axis 19. Connected with the pedal is a pedal position sensor 20 (e.g. a rotary potentiometer) which provides a signal to an electronic control unit 16 via line 21 indicative of the angle of depression θ of the pedal 17.

Control unit 16 also receives inputs 22 from other sensors on the vehicle indicative of other vehicle operating parameters such as engine speed, transmission input shaft speed, road speed, selected gear, and temperature from, for example, the vehicle CAN bus.

The clutch driven plate, which is clamped against the flywheel 11a by the diaphragm spring, is released by a clutch release bearing (not shown). The diaphragm spring applies an engagement force to the clutch which continuously increases as the clutch is disengaged by the release means 15 and the release bearing giving the continuously rising force/displacement characteristic shown in Figure 5. By using a diaphragm spring with this continuously rising characteristic each level of release bearing force corresponds to a unique release bearing position thus simplifying the control of the clutch by the electronic control unit 16.

The electronic control unit 16 reads the instantaneous torque being generated by the engine. Generally this data would be theoretically calculated, and made available as an output from the standard engine control unit (not shown) which controls the fuelling and timing of the engine and which is broadcast as a message available via the vehicle's CAN bus.

The movement of the clutch pedal 17 is resisted by a two-rate spring device 25 (see Figure 6) which is mounted on the pedal box 18 at 27 and connected with the pedal at 28 by a rod 28a. An over-centre spring 26 also acts on the pedal at 31 and is connected to the pedal box at 29. The spring device 25 has a housing 40 which contains a first spring 41 of low stiffness (e.g. 9 N/mm) with a high pre-load (e.g. 475 N). This spring is held in place by an end cap 42 retained by a circlip 43. A spring cup 44 is fitted into the end of spring 41. Cup 44 has a flange 44a which contacts the end of spring 41 Inside a spring cup 44 sits a second coil spring 45, which has a higher spring rate than spring 41 (for example 75 N/mm). Rod 28a is provided with flat end 28b which can apply a load to spring 45. Spring 45 has a minimal load when rod 28a is at rest sufficient to ensure there is no free play in the push rod 28a (e.g. 5 N).

When pedal 17 is pressed, push rod 28a moves into housing 40 and spring 45 is compressed until it generates a force equal to the preload of spring 41. This gives a force v displacement characteristic for device 25 equal to the stiffness of spring 45 as shown at 25a in Figure 4. Further movement of the pedal compresses both springs 45 and 41 in series and gives a force v stiffness characteristic equal to the series stiffness of the two springs as shown at 25b in Figure 4.

The over-centre spring 26 resists depression of the clutch pedal initially in section 26a and when pedal moves over-centre (i.e. when spring attachment point 31 crosses line 32 which joins pedal pivot axis 19 and point 29) the spring 26 assists further movement of pedal 17 in section 26b of the characteristic. The combined effect of spring device 25 and over-centre spring 26 is shown by characteristic 30. This characteristic is essentially the same as that experienced by a driver who presses a normal clutch pedal which directly operates a diaphragm spring type clutch (i.e. pedal load increases up to a maximum at approximately the point of disengagement of the clutch and thereafter reduces). The pedal therefore feels "normal" to the vehicle driver despite the fact that there is no direct connection between the pedal 17 and the actuator 15. If desired the pedal position sensor can be a linear sensor built into the spring unit 25.

Clutch 11 has a driven plate 50 (see Figure 7) which incorporates torsional flexibility between the facings 51 and the splined hub 52 by employing tangentially arranged coils springs 53 in the conventional manner. The torsional stiffness characteristic employed in driven plate 50 is a single torsional spring rate at the lowest possible stiffness which may be practically designed, whilst achieving a torque value of typically 1.2 x maximum engine torque at the point of maximum circumferential rotation of the facing 51 relative to hub 52 where the driven plate articulation is limited by end-stops 54. For a typical van type vehicle this torsional stiffness would be in the range 20 - 24Nm/⁰. The driven plate is also designed to achieve the minimum internal friction within the device whilst the torsional spring system is articulated. A typical torque vs deflection characteristic for the drive plate assembly is shown in Figure 8.

Thus the mechanical damping provided by springs 53 is designed to damp the torsional vibrations which occur in the driveline at higher engine speeds (i.e. above 1800 r.p.m.) and does not need to be compromised by needing to damp the torsional vibrations which occur at lower engine speeds such as the idle rattle range which are damped by the ECU controlled clutch slip control system.

Clutch 11 is of the "normally closed" type cover assembly, without self adjustment. The clutch has the greatest pressure plate mass which could be practically designed in order to maximise its ability to absorb and store heat generated by clutch slip, and thereby minimise temperature reached at the slipping surface. The mass of the pressure plate in a typical van type application is of the order of 3.66kg.

In a typical van application the ECU 16 has the following data inputs:

• Clutch Pedal Position (from the sensor 20 fitted to the clutch pedal described above)

• Engine Speed (this data is broadcast by the Engine Control Module, and may be received by connecting to the vehicle's data network)

• Transmission Input Shaft Speed (this is measured directly from the input shaft in the transmission, preferably by using the known toothed gear type sensor 55 which measures the passage of the teeth of a gear 56 fixed to the input shaft 57 past the sensor. From this signal, the time period between each individual tooth passing the sensor is measured, and based on the number of teeth on the gearwheel 56 the rotational speed of the shaft is instantaneously calculated)

• Engine Torque (This data is calculated within the Engine Control Module and then broadcast via the vehicle's data network.

The data output from the system is the target for clutch position, which is supplied to the control system for the motor which responds by moving the motor to the relevant position. There is no measurement of clutch position itself, it being assumed that the position of the motor and hence the ball screw always has a fixed relationship to the clutch.

A flow diagram describing how the input data is used to control clutch position is shown in Figure 9. ^"The control algorithm monitors engine speed (which corresponds to clutch input speed) and clutch output speed (which corresponds to transmission shaft input shaft speed) and controls the level of engagement of the clutch to maintain controlled clutch slip speed, in accordance with a fixed calibration map which depends on engine speed and torque output. Also, when the driver depresses the pedal, it allows the clutch pedal demand to override the control system, so that the clutch may be opened manually. The values of speed are measured in rpm, values of torque are measured in Nm, and the clutch position is measured 0 to 1 (0 fully closed, 1 fully open). The transmission input shaft speed value 60 from sensor 55 is inverted in block 61 and added to the engine speed value 62 in block 63 to give the difference between the two speeds. The absolute value of this difference is taken in block 64, so that a positive numerical value for speed difference (clutch slip) is calculated whether the vehicle is accelerating (with the engine running faster than the transmission input) or decelerating (with the transmission input turning faster than the engine). This absolute measured value is fed into the PID closed control loop 65 as the measured input. The engine speed 62 is also fed into the 'Slip v Engine Speed' lookup table 66 an example of which for a typical van application is shown in Figure 10. Additionally the engine torque signal is fed into the 'Slip v Engine Torque' table 68 an example of which for a typical van application is shown in Figure 11.

The output from both of these tables is multiplied together in block 69, the product being the required value of clutch slip. This value is fed into the PID Control Loop 65 as the Set Point. The Control Loop generates an output value based on the difference between the Set Point and the measured value. This value may be used to control the clutch directly.

As indicated previously, it is necessary for the driver to be able to override the control system manually when desired in order to open the clutch, for example when starting stopping or changing gear. This override is achieved by blocks 70 and 71. Block 70 compares the value of the clutch pedal position signal, with the output value of the control block. When the driver depresses the pedal, the clutch pedal position value may become higher than the control output value (i.e. the driver demands that the clutch be opened further). In this instance block 70 sends a Boolean value of 'true' to the 'switch' switch block 71 and the switch selects that the signal 72 from the clutch pedal position value to be sent to the clutch position output 73 from the control system. However, if the clutch pedal is insufficiently pressed to give a clutch pedal position value higher than the control system output, the Boolean value is false, and the output from the control system is sent to the clutch position output.

Figure 2a shows a representation of the inertia and stiffness of a typical vehicle driveline. The mode shape of the torsional vibrations which occur in the spring-mass system of Figure 2a are shown in Figure 2b. A typical vehicle under investigation was found to have three natural frequencies of 5Hz, 40 Hz and 60 Hz respectively. It was found that with a typical 4 cylinder 4 stroke combustion engine running at 1800 rpm the 60 Hz natural frequency was excited.

In accordance with the present invention the control unit 16 is programmed to take over control of the level of clutch engagement from pedal 17 when the clutch pedal is fully raised to reduce the clamp pressure of the clutch actuator 15 when the driveline is rotating in the ranges 1100 to 1300 r.p.m. (40Hz) and 1700 to 1900 r.p.m (60Hz) as shown in Figure 10. This allows the clutch to slip thus dissipating the increased torsional vibration which would otherwise occur at these speeds of rotation, as each natural frequency within the driveline becomes excited. This control of clutch slippage is automatic and invisible to the vehicle driver.

In addition to the above control algorithm the electronic control unit may continually adjust the level of clutch release force applied to the clutch by the release means 15 (which opposes the clamping force applied by the diaphragm spring) until the net clamping force applied to the clutch provides a clutch torque capacity which is slightly greater than the torque instantaneously being generated by the engine. Typically the torque capacity of the clutch is maintained by the control unit 16 at 10% higher than the torque issuing from the engine.

One of the main advantages of controlling the torque capacity of the clutch in the above manner is that if there is a sudden change in the operating conditions of the vehicle (such as the torque transmitting capability of the wheels of the vehicle changing if the wheels suddenly move from a low to a higher μ surface) shock loads in the driveline are avoided as the clutch will temporarily slip until clutch input and output speeds have re-synchronised.

The torque capacity of the clutch is calculated by the control unit 16 from the net clamping force and the current value of the coefficient of friction of the clutch lining material. The current value of the coefficient of friction of the clutch lining material is calculated using data received by the control unit 16 relating to engine speed, transmission input shaft speed (real or calculated), ambient temperature, engine torque (real or calculated, thermal capacity of clutch components,(such as the clutch driven plate/flywheel), heat dissipation rate of clutch components, and coefficient of friction of clutch lining material vs. temperature. The calculation iteratively calculates the temperature of the clutch components according the heat input due to the slipping clutch vs. the heat lost through cooling, and consequently estimates the coefficient of friction of the lining material. Hence the clamping force of the clutch required for any given torque capacity may be adjusted by the control unit as the clutch temperature changes by adjusting the release force applied by the release means 15.

The release force being applied to the clutch is checked by a sensor 30. This sensor may be a load cell or may be a pressure sensor if a hydraulic release means is used or a current sensor if an electrical release means is used.

Additionally control unit 16, monitors if the currently applied torque capacity of the clutch is appropriate by monitoring the level of slip in the clutch (this is done by comparing clutch input and output speeds). If these speeds are not equal when the control unit expects them to be equal the control unit adjusts the clutch release force to vary the clutch torque capacity. Other checks may be applied. For example, if the control unit reduces the clutch release force to zero (so that the maximum clamping force is applied to the clutch) and the clutch input and output speeds are not equal for a period of time when near maximum.engine torque is applied to the clutch, the control unit will conclude that the clutch lining material is worn out or faulty and will provide an error signal to the vehicle driver. The control unit 16 may also employ a numerical clutch wear model. The control unit receives signals indicative of clutch input and output speeds, clutch ambient temperature, engine torque, thermal capacity of certain clutch components, heat dissipation rate of these clutch components, and wear rate of the clutch lining material as a function of lining temperature and as a function of the rate of energy dissipation in the lining material. The electronic control unit uses combinations of the above parameter signals to predict the level of lining wear which has occurred since the system was last reset and provides an indication to the vehicle driver when predetermined wear conditions have been reached.

Provision is made for the wear model to be reset, for example when a new clutch lining is fitted. The control unit compares the available volume of clutch lining material against the calculated sum of the volume of material consumed, and indicates an error state when all of the available friction material has been used.

This numerical clutch wear model may be used in any vehicle clutch no matter whether it is controlled by a system in accordance with the main claim of this application.

The flywheel, clutch and associated driveline are designed so that their natural frequencies of torsional vibration are as low as possible. For example, the torsional stiffness of the clutch driven plate is low (e.g. 25 Nm/degree of rotation) thus reducing the natural frequency of the driveline.

It has been found that by damping the torsional vibrations of the driveline using limited and controlled clutch slip as described above it is possible to use a solid flywheel (thus obviating the need to use expensive twin mass flywheels) and that it is no longer necessary to include idle and creep rattle dampers in the clutch driven plate. By lowering the natural frequencies of the torsional vibrations of the components of the entire driveline the levels of slippage required to damp these vibrations are also lowered so that excessive levels of clutch slip can be avoided thus reducing the heat generated and the clutch can also be kept fully engaged for most of the time. Typically the clutch is only slipped at or just below the engine speeds at which the natural frequencies are excited.

The control unit 16 can also be programmed to receive signals indicative of the engine speed and, as part of a vehicle launch strategy, not allow the clutch to engage, despite the clutch pedal position, if a minimum engine speed has not been reached in order to avoid stalling and/or vibration of the vehicle. The control system can also slip the clutch if necessary during clutch engagement to ensure that the minimum engine speed is maintained thus further improving the avoidance of stall and/or vibration.

The control unit can also limit the heat generated in the clutch during clutch engagement by limiting engine speed and the time during which the clutch is allowed to slip.

The control unit may also monitor the pedal position signal and if the driver is riding the clutch pedal (i.e. partially depressing the clutch pedal unintentionally) the control unit can be arranged to fully engage the clutch to protect the clutch. This control is implemented by setting a range of angles of depression of the clutch pedal (e.g. 0 to 5 degrees) which is designated as an unintentional depression of the clutch pedal and which is monitored accordingly.

The control unit may also be arranged to receive one or more vehicle operating parameter signals indicative of a vehicle crash condition (e.g. levels of vehicle deceleration, seat belt tensioning and air bag actuating signals or vehicle crash state indications via a data flag carried on the CAN bus) and to disengage the clutch when such crash signals are received. The operation of the pedal 17 to disengage the clutch at any time by the driver is arranged to have priority and always results in immediate disengagement of the clutch for safety reasons.

Although the present invention has been described above in relation to a clutch system which has a driver operated pedal 17 the present invention is also applicable to so-called automated manual transmissions, that is transmissions in which clutch engagement/disengagement for starting and stopping together with clutch disengagement and re-engagement during ratio changes is controlled by an electronic control unit. In such transmissions the decision to change the operative ratio in the transmission may be made totally by the electronic control unit so that the transmission operates like a completely automatic transmission or the decision to change ratio may be made by the vehicle driver when the transmission is referred to as semi-automated. Some transmissions can be selectively operated as fully automated or semi-automated transmission. In all cases the clutch engagement and disengagement is under the control of the electronic control unit 16 and no driver operated clutch pedal 17 is provided.

The torsional vibration damping arrangement of the present invention can also be used in a vehicle driveline in which more than one clutch is used to couple drive or select the operative ratio in the driveline. For example, the arrangement could be used on both clutches in a so-called twin clutch transmission in which the ratios are divided into two groups with one clutch engaging drive via one group of ratios and another clutch engaging drive via the other group of ratios.

Claims

1. A torsional vibration damping arrangement for a vehicle driveline comprising a transmission driven by an engine via a drive clutch, the arrangement including:

a clutch actuator for engaging/disengaging the clutch,

an electronic control unit which receives vehicle and clutch operating parameter signals and issues control signals for the engagement/disengagement of the clutch via the clutch actuator during starting and stopping of the vehicle and during ratio changes in the transmission,

the electronic control unit also being arranged to control the level of engagement of the clutch to damp lower engine speed torsional vibrations in the drive line by allowing the clutch to slip, and the clutch including torsional spring damping means to damp higher engine speed torsional vibrations in the driveline.

2. A damping arrangement according to claim 1 in which a driver-operated clutch actuating pedal is provided for engaging/disengaging the clutch during starting and stopping of the vehicle and during ratio changes in the transmission.

3. A damping arrangement according to claim 1 in which the transmission is of the fully or semi-automated manual type in which all clutch operations are controlled by the electronic control unit.

4. A damping arrangement according to claim 2 or 3 in which the electronic control unit receives input signals representative of transmission input shaft speed, clutch pedal position, engine speed and engine torque, the control unit processing these signals to provide an output signal to the clutch actuator to command the required level of clutch engagement level to give the clutch slip to provide torsional vibration damping or the clutch engagement position selected by the pedal when provided or the electronic control unit in a fully or semi-automated manual transmission.

5. A damping arrangement according to claim 4 in which engine speed and transmission input shaft speed are compared within the electronic control unit to provide a signal representative of the magnitude of the current clutch slip, this current clutch slip value is compared with a target slip value derived from the product of the values given by predetermined lookup tables of clutch slip v current engine speed and clutch slip v current engine torque which are stored in the electronic control unit, the result of this slip comparison being used as an output signal to the clutch actuator to attempt to attain the current target clutch slip level.

6. A damping arrangement according to any one of claims 1 to 5 in which the electronic control unit allows the clutch to slip in order to avoid exciting one or more natural frequencies of an associated driveline of the vehicle so as to avoid torsional vibrations in the driveline.

7. A damping arrangement according to any one of claims 1 to 6 in which the control unit receives engine speed signals and does not allow engagement of the clutch until a minimum engine speed has been reached.

8. A damping arrangement according to claim 7 in which during clutch engagement the control unit ensures that the minimum engine speed is maintained during engagement.

9. A damping arrangement according to claim 6 or 7 in which the electronic control unit limits the heat dissipated in the clutch during a clutch engagement by limiting engine speed and the time during which the clutch is allowed to slip.

10. A damping arrangement according to claim 2 in which the pedal position is monitored and the clutch is arranged to be fully engaged by the electronic control unit if the driver rides the clutch pedal for more than a predetermined period of time.

11. A damping arrangement according to any one of claims 1 to 10 in which the control unit receives one or more vehicle operating parameter signals indicative of a vehicle crash condition and on receiving such crash signal or signals disengages the clutch.

12. A damping arrangement according to any one of claims 1 to 11 in which spring means act on the pedal to generate a pedal effort characteristic which increases up to a maximum effort at approximately the point of disengagement of the clutch and thereafter reduces.

13. A damping arrangement according to any one of claims 1 to 12 in which the clutch has a driven plate with torsional flexibility between outer friction facings and an inner drive hub in the form of tangentially acting coil springs.

14. A damping arrangement according to any one of claims 1 to 13 in which the clutch actuator includes a clamping means for engaging the clutch and a release means for disengaging the clutch, the electronic control unit controlling the level of clutch release force from the release means which opposes the clamping means to provide the necessary level of slip to damp the lower engine speed torsional vibrations.

15. A damping arrangement according to any one of claim 14 in which the electronic control unit receives vehicle operating parameter signals and either receives or calculates the instantaneous torque being generated by the engine and, except when the electronic control unit is slipping the clutch for torsional vibration damping or is engaging/disengaging the clutch during starting and stopping or during ratio changes in the transmission, maintains a level of clutch release force from the release means which opposes the clamping means and ensures a clutch torque transmitting capacity greater than the torque being instantaneously generated by the engine.

16. An arrangement according to claim 15 in which the torque capacity of the clutch is of the order of 1.1 times the instantaneous torque being generated by the engine.

17. An arrangement according to claim 15 or 16 in which the torque capacity of the clutch is measured by measuring the force which the clutch release means is applying to disengage the clutch, which opposes the force applied to engage the clutch by the clamping means hence giving the net clamping force being applied to the clutch which determines its torque transmitting capacity.

18. An arrangement according to claim 17 in which the clutch release force is measured directly by a load cell.

19. A system according to claim 17 in which the clutch is provided with a hydraulically operated release means, the clutch release force being measured by measuring the pressure in the hydraulic release means.

20. An arrangement according to claim 17 in which the clutch is provided with an electronically operated means, the clutch release force being measured by measuring the current used by the electrical release means.

21. An arrangement according to any one of claims 14 to 20 in which the clutch clamping means applies an engagement force to the clutch which continuously increases as the clutch is disengaged by the release means.

22. An arrangement according to any one of claims 14 to 21 in which the electronic control unit calculates the temperature of various components of the clutch and estimates the current effective coefficient of the clutch lining material and hence adjusts the clamping force applied to the clutch by the clamping means as the clutch lining material temperature rises and falls.

23. An arrangement according to any one of claims 1 to 22 in which the electronic control unit monitors the level of slip in the clutch and adjusts the clamping force if the clutch is slipping when slippage is not intended or expected.

24. An arrangement according to any one of claims 1 to 23 which includes a monitoring system for predicting the wear of a lining material of the vehicle drive clutch using a numerical model, the electronic control unit receiving signals indicative of clutch input and output speeds, clutch ambient temperature, engine torque, thermal capacity of certain clutch components, heat dissipation rate of these clutch components, and wear rate of the clutch lining material as a function of lining temperature; the electronic control unit using combinations of the above parameter signals to predict the level of lining wear which has occurred since the system was last reset and providing an indication to the vehicle driver when predetermined wear conditions have been reached.

25. A twin clutch gearbox in which both clutches are provided with a torsional damping arrangement according to any one of claims 1 to 24.

26. A clutch monitoring system for predicting the wear of a lining material of a vehicle drive clutch using a numerical model, the system including an electronic control unit which receives signals indicative of clutch input and output speeds, clutch ambient temperature, engine torque, thermal capacity of certain clutch components, heat dissipation rate of these clutch components, and wear rate of the clutch lining material as a function of lining temperature and as a function of the rate of energy dissipation in the lining material; the electronic control unit using combinations of the above parameter signals to predict the level of lining wear which has occurred since the system was last reset and providing an indication to the vehicle driver when predetermined wear conditions have been reached.