GB2149923A

GB2149923A - Friction clutch temperature monitoring arrangement

Info

Publication number: GB2149923A
Application number: GB08426776A
Authority: GB
Inventors: Robert Paul Page; Stuart Ian Howarth; John Nicholas Cheel
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-11-09
Filing date: 1984-10-23
Publication date: 1985-06-19
Also published as: GB8426776D0; GB2149923B

Abstract

A friction clutch temperature monitoring arrangement including a pair of speed transducers 27, 28 for providing an indication of the slip speed between the input and output elements of the clutch and a further transducer 29 which provides a signal representing the pressure urging the components of the clutch into frictional engagement. The arrangement further includes a microprocessor 26 which receives said signals and determines the temperature rise of the clutch components from the slip speed, torque and the thermal mass of the components. <IMAGE>

Description

SPECIFICATION Friction clutch monitoring arrangement This invention relates to a monitoring arrangement for a friction clutch.

During the process of engagement of a friction clutch slip takes place between the clutch elements while at the same time torque is being transmitted therebetween. This leads to the generation of heat which inevitably raises the temperature of the friction elements of the clutch.

The rate of heat generation depends upon the torque being transmitted and the slip speed. It is important to ensure that the temperature of the friction material forming the friction elements does not rise above a predetermined value otherwise permanent damage to the friction material can occur.

The obvious way to measure the temperature of the friction elements is to use a thermal sensitive device such for example as a thermo-couple, set into the friction material. The problem however is to connect the device to the sensing apparatus since the temperature responsive device is mounted upon a rotary component. It would be possible to use slip rings but these would be impractical in for example a vehicle clutch where the operating conditions are particularly severe. It would also be possible to use telementry techniques to obtain the signal from the temperature responsive device but again considering the application of the clutch set out above, such techniques would not be very satisfactory.

The object of the present invention is to provide a friction clutch monitoring arrangement which can provide an indication of the temperature of the friction elements of the clutch making use only of readily measurable clutch operating parameters.

According to the invention a friction clutch monitoring arrangement comprises first means for measuring the slip speed between the input and output elements of a friction clutch, second means for providing an indication of the pressure applied to the clutch components to cause frictional engagement thereof and further means responsive to the signals provided by said first and second means for providing an indication of the temperature of the clutch components.

In the accompanying drawings: Figure 1 is a diagrammatic view of a twin dry plate friction clutch with the elements of the clutch shown in a separated state for the purpose of explanation, and Figure 2 is a diagrammatic view of a vehicle transmission system employing the clutch shown in Fig. 1.

The clutch shown in Fig. 1 is a twin dry plate clutch and comprises a pair of clutch plates 10, 11 which are mounted for axial movement upon a splined clutch output shaft 1 2. Each clutch plate is provided with friction elements 1 3 on its outer sides.

Interposed between the plates 10, 11 is an annular intermediate plate 1 4 which is located in a casing 1 5 which is secured to the flywheel 1 6 of the associated engine. The plate 14 is in spline engagement with the inner surface of the casing so that it can move axially within the casing. Also provided is an annular pressure plate 1 7 which is again non-rotatably coupled to the casing 1 5 but which is able to move axially therein. The pressure plate is biased towards the fly wheel by the clutch actuating springs 1 8 and is movable away from the flywheel by a release sleeve 1 9 axially slidable upon the output shaft.When the sleeve 1 9 is allowed to move towards the flywheel the clearances between the various plates and the flywheel is taken up and drive is transmitted to the output shaft 12 from the engine flywheel.

As shown in Fig. 2 the clutch forms part of a vehicle transmission system and is interposed between the engine 20 and a multi ratio gearbox 21, the output shaft 1 2 of the clutch being the input shaft of the gearbox. The clutch is provided with a pivotal release lever 22 which is connected to the piston of a piston cylinder combination 23. The piston is biased by a spring 24 which is of such strength that it in the absence of pressure within the cylinder, overcomes the force of the clutch springs 18 to disengage the clutch.

Fluid under pressure is supplied to the cylinder by a valve mechanism 25 which includes valves which can allow fluid into the cylinder at different rates and also allow fluid to escape from the cylinder at different rates. The valves are controlled by a microprocessor 26 which also controls the selection of the ratios of the gearbox in a manner to provide an automatic transmission system. It is required to inform the driver of the vehicle if the temperature of the clutch exceeds a predetermined value.

The energy which is dissipated in a clutch when it is slipping is the product of the slip speed, the torque transmitted and time and this can be expressed by the equation Energy

where S is the slip speed, Tq is the torque and T is the time interval during which the clutch is slipping. S and Tq both vary with time and if the time interval T is long then a second term must be included to take account of the loss of heat due to cooling. The time interval T in normal circumstances however is comparatively short and the amount of heat lost by cooling during this time interval will be comparatively small compared to the rate at which heat is produced in the clutch.The clutch described is for a road vehicle and as the clutch is engaged, the release mechanism allows the clutch springs 1 8 to impart an axial force to the pressure plate 1 7 and the friction surfaces of the friction plates start to rub on the adjacent driven surfaces so that heat is developed. It will be assumed that the energy dissipated is shared equally between the four surfaces where rubbing occurs.Half the energy will therefore be dissipated in the intermediate plate 14 which has two rubbing surfaces and a quarter of the energy in each of the flywheel 1 6 and the pressure plate 1 7. If it is assumed that the transfer of heat between the various components of the clutch is small compared with the rate at which heat is produced, it is possible to calculate the temperature rise of each component by calculating the energy input and knowing the thermal mass of the component. In a twin plate clutch the mass of the intermediate plate and the pressure plate are roughly equal but are both considerably less than the flywheel.The highest temperature therefore will be in the intermediate plate and the temperature rise in the intermediate plate can be expressed as

where T2 is the final temperature, T1 is the initial temperature, M is the mass of the intermediate plate, H is the specific heat capacity of the material forming the intermediate plate and Tq, S and T are as expressed above.

The microprocessor 26 in order to provide proper control of the clutch is provided with signals representing the engine speed and the speed of the output shaft 1 2. These signals are provided by speed sensors 27, 28 respectively these sensors being disposed exterior of the clutch. It is therefore possible to derive the slip speed of the clutch. The other unknown of the last equation is the torque (Tq) transmitted by the clutch.

The maximum torque which can be transmitted by the clutch will occur when the full force exerted by the clutch springs 1 8 is applied to press the various plates together and the torque value will be quoted by the clutch manufacturer. In the example the full force which can be developed by the clutch springs is applied when the force exerted by the spring 24 is completely overcome by the fluid pressure in the cylinder acting upon the piston. No torque will be transmitted by the clutch when the force exerted by the clutch springs is zero and this occurs when the fluid pressure in the cylinder is zero thereby allowing the spring 24 to be fully effective in overcoming the force exerted by the clutch springs.Assuming that there is a simple relationship between the torque capable of being transmitted and the force acting to urge the plates into engagement, it will be seen that the fluid pressure in the cylinder.will provide a measure of the torque transmitted by the clutch. A pressure sensor 29 is therefore provided to sense the pressure in the cylinder. In practice the force capable of being applied to the release mechanism by the spring 24 is higher than the force capable of being exerted by the clutch springs 1 8 and hence some pressure must be applied to the piston to just balance the excess force of the spring 24. Then the pressure will have to be further raised to allow the various plates to move into engagement.The pressure in the cylinder required to balance the excess force of the spring 24 has to be determined by experiment and is designated P,. The pressure which is required to be applied to the cylinder to just fully overcome the force developed by the spring 24 is also determined this being designated P2 and corresponds to the maximum torque capable of being transmitted by the clutch. The torque transmitted by the clutch at a pressure P3 intermediate P1 and P2 is given by the expression

where Tpq =the peak torque capable of being transmitted by the clutch.

The microprocessor on the basis of a stored program and on the basis of the variable information supplied to it by the speed sensors and the pressure sensor calculates the energy dissipated in the intermediate plate. A cooling constant is derived experimentally and is taken into account to assess the total energy build up and when the temperature exceeds a predetermined value a warning is given to the driver of the vehicle conveniently by means of a warning lamp. If the total energy value continues to increase then at a second higher value, action can be taken to stop the associated engine or otherwise disable the vehicle.

In a single plate clutch it is the temperature of the pressure plate which is determined and the system is also applicable to multi plate oil immersed clutches.

The pressure applied by the clutch springs 1 8 to the pressure plate 1 7 can be determined by measuring the displacement of the pressure plate 1 7. This measurement can be effected by means of a linear transducer which provides an indication of the axial setting of the sleeve 1 9.

More conveniently the measurement is effected at the piston of the piston cylinder combination 23. Alternatively a rotary transducer can be utilized which is responsive to the angular position of the lever 22.

Claims

1. A monitoring arrangement for a friction clutch housing input and output elements, and components which are urged into frictional engagement to effect torque transmission between the input and output elements, the monitoring arrangement comprising first means for measuring the slip speed between the input and output elements, second means for providing an indication of the pressure applied to the components to cause frictional engagement thereof and further means responsive to the signals provided by said first and second means for providing an indication of the temperature of the clutch components.

2. A monitoring arrangement according to Claim 1 in which said first means comprises first and second speed transducers associated with said input and output elements respectively.

3. A monitoring arrangement according to Claim 1 in which the clutch includes resilient means acting on one of said components to urge ssid components into frictional engagement, said second means comprising a displacement transducer for providing a signal representing the displacement of said one component.

4. A monitoring arrangement according to Claim 1 in which the clutch includes an actuator mechanism including a fluid pressure operable piston and valve means for controlling the fluid pressure applied to said piston, said second means comprising a fluid pressure tranducer responsive to the fluid pressure applied to said piston.

5. A monitoring arrangement according to Claim 4 in which the clutch includes resilient means acting on one of said components to urge said components into frictional engagement, lever means coupling said piston to said one component and spring means biasing said piston in opposition to the fluid pressure acting thereon, said spring means in the absence of fluid pressure overcoming the force exerted by said resilient means.

6. A monitoring arrangement according to Claim 1 in which said further means utilizes the signal provided by said second means to determine the value of the torque transmitted by the clutch and uses the slip speed and the torque value to determine the energy dissipated in the clutch in accordance with the formula Energy

where s = slip, Tq the torque and T the time interval during which clutch slip takes place.

7. A monitoring arrangement according to Claim 4 in which said further means includes a microprocessor, said microprocessor being supplied with information relative to the mass, and the specific heat of the clutch component which can be expected to become most heated together with the proportion of the total energy dissipated in the clutch which is dissipated in that component, the microprocessor computing the temperature rise in accordance with the formula

where T1 = the intial clutch component temperature T2 = the final clutch component temperature S = the slip Tq =the torque T = the time M = the Mass of the clutch component H = the Specific Heat capacity of the clutch component and X = the proportion of the total energy dissipated in the clutch component.

8. A monitoring arrangement for a friction clutch substantially as hereinbefore described with reference to the accompanying drawings.