GB2223076A

GB2223076A - Clutch monitoring device

Info

Publication number: GB2223076A
Application number: GB8918398A
Authority: GB
Inventors: Rudy Tellert; Lothar Wuestefeld
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1988-08-18
Filing date: 1989-08-11
Publication date: 1990-03-28
Anticipated expiration: 2009-08-11
Also published as: DE3828128C2; FR2635585A1; FR2635585B1; GB2223076B; DE3828128A1; GB8918398D0

Description

2223076 - 1 TITLE:

Arrangement for monitoring a friction clutch The invention relates to an arrangement for monitoring friction clutch, especially of a motor vehicle, comprising torque-ascertaining device which detects the momentary torque to be transmitted by the clutch, a slip-ascertaining device which detects the momentary difference of rotation rate between the input rotation rate and the output rotation rate of the clutch, a computer which, in dependence upon the torque-ascertaining device and the slip-ascertaining device, delivers data corresponding to the momentary friction performance, an integration device which time-dependently integrates the momentary friction performance data for the ascertainment of friction performance mean value data, a monitor device which compares the friction performance mean value data with pre-determined limit value data for the generation of a limit value exceeding signal and a correction device for the timedependent correction of the data compared with one another by the monitor device. - An arrangement of this kind is known from DE-OS'36 01 708. With its aid it is possible to detect and signal the thermal overloading of a friction clutch, without the need to provide a temperature sensor, which can be installed in rotating components of the clutch only with comparatively great constructive expense. In the known arrangement the friction performance per clutch action leading to heating of the clutch is detected and totalled over several clutch actions. In dependence upon the clutch actuation rate, that is the frequency with which the clutch actions follow one another, the total value is varied in order to take account of the cooling of the clutch by thermal radiation.

With the aid of the known arrangement it is in fact possible to detect and monitor an unacceptable heating of the entire clutch, but not a momentary over-heating of the clutch friction linings, which can lead to increased wear or irreversible damage to the linings.

A further arrangement for monitoring a friction clutch known from DE-OS 33 34 725. In this arrangement again the torque to be transmitted by the clutch and the slip occurring on the clutch are ascertained,and from these data there are calculated data corresponding to the momentary friction performance. Limit values for rest times, which must not be exceeded by the actual time in which the clutch is slipping, are taken from a store of tables in dependence upon the calculated friction performance. This known arrangement too only inadequately takes consideration of the heat flow within the clutch, which can lead to a local overheating of clutch components, especially the clutch friction linings, without this being detected by the known arrangement.

It is the problem of the invention so to improve an arrangement for the monitoring of a-friction clutch of the kind according to this classification that even an unacceptable heating of individual components of the clutch, 1 especially the danger of overheating of the clutch friction linings, can be detected.

Starting from the arrangement as explained at the outset, this problem is solved in accordance with the invention in that several sets of stores are provided for the data to be compared by the monitor device and the monitor device produces separate limit value exceeding signals for the data of each storage set and in that the correction device time- dependently corrects the data, stored in the individual storage sets, with different rates of variation.

In the monitor arrangement according to the invention it is taken into consideration that the components of the clutch have different heat storage capacities and can deliver the heat at different rates. This behaviour is simulated with the aid of the storage sets, so that the data content of the storage sets is a measure for the heating, that is the temperature of the associated clutch components. The friction performance data fed to the storage sets here correspond to the thermal energy fed in each case to the associated clutch components, while the correction data take consideration of the outflow of the thermal energy from these components. The correction data and the limit value data can be ascertained empirically. For the correction either the friction performance data or the limit value data can be time-dependently varied. The friction performance data can be calculated as product of the slip rotation rate of the clutch and the torque to be transmitted by the - 4 clutch. as described by way of example in DE-OS 36 01 708. The torque can be ascertained from the clutch position or however from the position of a power-adjusting member, for example a driving pedal or a throttle valve, in combination with a table store.

The monitor arrangement according to the invention permits the distinction of at least three temperature ranges which are relevant for the wearing behaviour of the clutch. A first temperature range covers operational situations which lead as a whole only to permissible temperatures of the clutch components, that is temperatures irrelevant to the wear. In a second temperature range increased wear on clutch linings can already occur, without other clutch components being unacceptably heated. In a third temperature range finally the limit of the maximum permissible temperature of the clutch friction linings is exceeded,. so that irreversible damage to the linings occurs.

the scope of the invention distinction is made between a shortterm, a medium-term and a long-term energy absorption capacity of the clutch. The short-term absorption capacity takes account not of the thermal capacity of the clutch but only of the thermal energy which is contained in the surface regions of the Within expediently friction linings or the surface regions of the presser plate resting thereon, and of the fly-wheel. The thermal energy contained in the surface regions can in the short term lead to very high peak temperatures, which can lie above the permissible temperature of the friction linings. The thermal capacity of the presser plate and of the fly-wheel of the clutch is primarily decisive for the medium-term energy absorption of the clutch. The thermal energy generated in the short term on the friction faces is conducted away by way of these components. The heat absorption capacity of these components is however limited and dependent upon the style of construction of the clutch and the mass of its components. The long-term condition takes account of the long-term emission of heat to the ambient air.

Temperature variations in the above-explained temperature ranges take place at different rapidities. While the medium-term energy absorption of the presser plate and the fly-wheel and for the first time really the longterm energy absorption characterised by the heat emission to the ambient air take place comparatively slowly, in the short term overheating of the friction linings can occur very rapidly. For the mediumterm and the long-term energy absorption it can therefore suffice in the individual case if the driver's attention is drawn, on exceeding of the limit values, to the threatening danger of overheating of the clutch by an optical or acoustic warning signal.

reason of the very high peak temperatures reachable in By the short term in the surface zones of the friction linings, it can be expedient automatically to reduce the clutch work if possible immediately, in addition to or in place of a warning to the driver. It has proved expedient in such a case to disengage the clutch automatically, but preferably rapidly to engage it completely, through a motor-driven servo-control of the clutch, in dependent upon the limit value exceeding signal of the monitor device.

In a preferred development of -the invention separate stores are provided for the simulation of the short-term, medium-term and long-term time behaviour of the heating. It is understood that it is also possible for more or even less stores to be present.

The stores can be connected in series with one another and accordingly accept already time-dependently corrected data from the preceding store in each case. They can however also receive the parallel, in which case corrected according to the More especially the stores friction performance data in they are each independently energy economy to be simulated. can be totalling stores of the integration arrangement, which reduces the construction expense or the calculation expense for the elapse of the algorithms necessary for the correction.

An additional documentation store is expediently provided which is advanced with every exceeding of a limit value. In this way the course of operation can be documented for example for the monitoring of a driver or for possible information in a guarantee case. The documentation store can for example be a journey recorder which is present in any case.

The invention will be explained in greater detail hereinafter by reference to a drawing, wherein: - Figure 1 shows a block circuit diagram of an 1 ---- - 7 arrangement for monitoring a friction clutch of a motor vehicle and Figure 2 shows a partial block circuit diagram oE a variant of the arrangement according to'Figure 1.

Figure 1 shows diagrammatically an internal combustion engine 1 of a motor vehicle which drives a gearing 5 through a friction clutch 3. The friction clutch 3 has a motor servo-drive indicated diagrammatically at controlled by a clutch control system 9 for dependence upon the rotation rate of the internal engine 12 engages and disengages the friction Automatically actuated clutches of this kind are 7 which, example in combustion clutch 3. known, and are not to be explained further. The gear 5 is changed manually; it can however also be a matter of automatically changing gears. The output of the internal combustion engine 1 is controlled from a driving pedal 11 which is coupled in a manner not further illustrated with a powersetting member, for example a throttle valve 13.

The frictional performance converted in the clutch 3 into heat is proportional to the product of the slip rotation rate and the torque transmitted by the clutch 3. The slip rotation rate is the difference between the input rotation rate of the clutch and the output rotation rate. The temperature resulting on the individual components of the clutch depends upon the thermal conductivity of the components of the clutch, the heat storage capacity of these components and the capacity of the clutch to deliver heat to the surroundings. The thermal energy is generated on the mutually rubbing surfaces of friction linings 15 of a clutch disc, designated generally by 17 and connected with an input shaft of the gearing SY for the one part, and the surfaces of a fly-wheel 19 connected with the crank-shaft of the internal combustion engine 1, or a presser plate 23 guided on the fly-wheel 19 through the clutch cover 21. The thermal energy generated in the surface zones flows away into the flywheel 19 and the presser plate 23, while the thermal capacity of the flywheel 19 and of the presser plate 13 determines the temperature to which the surface temperature rising in the short term due to the friction action will adjust itself in the medium term. The heat emission of the entire clutch 3 to the surroundings in the long term determines the temperature of equilibrium. The surface temperature of the friction linings 15 can rise very sharply in the short term, especially above the maximum permissible temperature for the friction linings, so that irreversible damage to the friction linings 15 can occur. Furthermore the temperature of the fly-wheel 19 and of the presser plate 23 can rise in the medium term so far that increased wear of the friction linings 15 occurs, even though the temperature of the friction linings 15 still remains below the maximum permissible temperature at which irreversible damage occurs. A long-term temperature rise of the clutch 3 as a whole takes effect in the same manner.

For the monitoring of the operational condition of the clutch 3 a computer device 25 calculates data which are a measure for the momentary friction performance of the clutch - 9 3. The computer device 25 receives from a rotation rate sensor 27 a signal representing the input rotation rate of the clutch 3 and from a rotation rate sensor 29 a signal which is a measure for the output rotation rate of the clutch 3. The position of the driving pedal 11 is indirectly a measure for the torque to be transmitted by the clutch 3. In dependence upon the position of the driving pedal 11 detected by means of a position detector 31 the torque of the internal combustion engine 1 allocated to the momentary driving pedal position is read out from a table store 33, in which the torqueperformance characteristic curve of the internal combustion engine 1 is stored, and fed to the computer 25. The computer 25 calculates momentary values of the momentary friction performance, in the cadence of the timing control system 35, which values it feeds, likewise in the cadence of the timing control system 35, to a totalling store 37. The totalling store 37 by reason of its integration effect forms a mean time value of the mutually successive momentary friction performance values. Thus its content is a measure for the thermal energy generated in the surface regions of the friction linings 15, of the fly-wheel 19 and of the presser plate 23. The totalling store 37 furthermore receives correction data, from a correction device 39, in the cadence of the timing control system 35, which again step by step in sequence reduce the value accumulated in the store 37 and simulate the heat flow out of the surface regions into the fly-wheel 19 and the presser plate 23. The correction value provided by the correction device 39, that is to say to be subtracted, can for example be a pre-determined, constant fraction of the value momentarily contained in the totalling store.

The medium-term temperature behaviour of the clutch 3 represents the content of a further store 41 which takes over the stored content of the store 37 in the cadence of the timing control system 35, the content of the store 41 however being reduced step by step in the cadence of the timing control system by a further correction device 43, in order to take account of the limited storage capacity and heat outflow of the fly-wheel 19 and the presser plate 23. In the case of the correction device 43 too it can be provided that the medium friction performance taken over step by step from the store 37 is reduced in the cadence of the timing control system 35 by a pre-determined fraction of the friction performance. The rate of variation with which the correction device 43 changes the content of the store 41 is however less than the rate of variation determined by the correction device 39, by reason of the greater heat capacity of the fly-wheel 19 and the presser plate 21.

For the simulation of the long-term temperature behaviour of the clutch 3 a third store 45 is provided which takes over the friction performance data of the store 41 in the cadence of the timing control system 35, but corrects the taken-over data in dependence upon a correction device 472 likewise in the cadence of the timing control system 35.

1 The correction device 47, since it is intended in first approximation merely to take consideration of the heat emission of the clutch 3 to the surroundings, can subtract a constant amount from the value supplied for each timing period from the store 41. The variation rate with which the content of the store 45 is reduced, differs from the variation rates of the correction devices 39, 41 and is especially lower than these two variation rates.

The store content of the stores 37, 41 and 45 is compared in each case separately from associated monitor circuits 49, 51 and 53 with limit values which are a measure for the permissible temperatures. The limit value predetermined by the monitor device 49 represents the maximum permissible surface temperature of the friction linings 15 which must not be exceeded, without need to fear irreversible damage to the linings 15. If the content of the store 37 exceeds this limit value. then the monitor circuit 49 generates a limit value exceeding signal which, through the clutch control system 9, completely engages the clutch 3 to reduce the friction performance. The limit value exceeding signal can be displayed to the driver in a warning device 55.

The limit value pre-determined by the monitor circuit 51 represents a temperature of the fly-wheel 19 or of the presser plate 23 which can lead in the medium term to increased wear of the linings 15. A limit value exceeding signal produced on exceeding of the limit value by the monitor circuit 51 is displayed to the driver in a warning device 57 and is further utilised for a variation of the clutch engagement characteristic of the clutch control system 9, for example to the effect that the speed with which the clutch 3 is engaged is increased to reduce the friction performance. The corresponding is valid f or a limit value exceeding signal generated by the monitor circuit 537 which signal displays an over-elevated temperature of the clutch 3 in a warning device 59 and may change the clutch engagement characteristic of the clutch control system 9.

A documentation store 61, which is advanced by the limit value exceeding signals and chronologically documents the manner of operation of the clutch 3, is connected to the monitor circuits 49, 511 53. The content of the documentation store 61 can be utilised for monitoring the driving behaviour and possibly for purposes of diagnosis of the clutch. The documentation store 61 may for example be a journey recorder present in any case in motor freightvehicles, which marks the occurrence of limit value exceeding signals on the journey recorder card.

Figurp. 2 shows a variant of the monitor arrangement hich differs from the arrangement according to Figure 1 merely in the manner in which data are written into the individual stores representing the temperature behaviour of the clutch. 'Parts of like effect are designated with the reference figures of Figure 1, and provided with the letter a for distinction. For more detailed explanation of the construction and manner of action of the arrangement, 1 - 13 reference is made to the description of Figure 1.

While in the arrangement according to Figure 1 the stores 37 are arranged one behind the other and take over the friction performance data each from the preceding store, in the arrangement according to Figure 2 each of the stores 37a, 41a, and 45a is formed as totalling store and separately forms, in the cadence of the timing control system 35a, a mean value of the friction performance from the momentary friction performance values fed to the computer 25a.

The correction data, by which the correction devices 39a, 43a and 47a reduce the data accumulated in the stores 37a, 41a and 45a, are so dimensioned that they likewise simulate the short-term, medium-term and long-term temperature behaviour of the clutch 3. It can here be provided that the correction device 39a reduces the stored content of the store 37a by a pre-determined fraction of the content per cadence period, just as the correction device 43a reduces the content of the store 41a by a pre-determined fraction of the content, which however is smaller than the fraction of the correction in the store 37a. The correction device 47a on the other hand can again reduce the content of the store 45a by a constant value per cadence period. The monitor devices 49a, 51a and 53a correspond to the monitor devices of the arrangement according to Figure 1.

Claims

CLAIMS:

l.) Arrangement for monitoring a friction clutch, especially of a motor vehicle, comprising a) a torque- as cer t aining device (31, 33), which detects the momentary torque to be transmitted by the clutch (3), b) a slip-ascertaining device (27, 29) which detects the momentary rotation rate difference between the input rotation rate and the output rotation rate of the clutch (3), c) a computer device (25) which, in dependence upon the torque-ascertaining device (311 33) and the slip ascertaining device (27, 29), supplies data corresponding to the momentary friction performance, d) An integration device (37; 37a, 41a, 45a) which time dependently integrates the momentary friction performance data for the ascertaining of friction performance mean value data.

e) a monitor device (49, 51 53) which compares the friction performance mean value data with pre-determined limit value data for the generation of a limit value exceeding signal, f) a.correction device (39, 431 47) for the time-dependent correction of the data compared with one another by the monitor device (49, 51 53)y characterised in that several sets of stores (37. 41t 45) are provided f or the data to be coinpared by the monitor device (49, 51 53), and the monitor device (49, 51 53) generates separated limit value exceeding signals f or the 6 1 - 15 data of each store set (371 413 45) and in that the correction device (39, 431 47) time-dependently corrects the data stored in the individual store sets (37, 419 45 with different variation rates.
2;) Arrangement according to Claim 1, characterised in that at least two store sets (37, 417 45) are provided the data of which are corrigible with different variation rate, where the correction device (39, 43 47) corrects the data of a first store set (45) for the simulation of the heat emission of the friction clutch (3) to the surroundings with a first variation rate and/or corrects the data of a second store set (41) for the simulation of the heating of clutch presser plate (23) and fly-wheel (19) with a second variation rate, and/or which corrects the data of a third store set (37) for the simulation of the heating of clutch friction linings (15) with a third variation rate.
3.) Arrangement according to Claim 2, characterised in that the limit value exceeding signal generated by the monitor device (51, 53) in dependence upon the data stored in the first (45) and/or second (41) store set triggers a warning signal device (57. 59).
4.) Arrangement accqrding to Claim 2 or 3, characterised in that the friction clutch (3) comprises a motorised servo-drive (7) and in that the limit value exceeding signal generated by the monitor device (51) in dependence upon the data stored in the second store set (41) increases the clutch engagement speed of the servo-drive (7).
1 1 S.) Arrangement according to one of Claims 2 to 4, characterised in that the friction clutch (3) comprises a motorised servo-drive (7) and in that the limit value exceeding signal generated by the monitor device (49) in dependence upon the data stored in the third store set (37) controls the servo-drive (7) in the direction of a reduction of the friction performance, especially engages the clutch (3).
6.) Arrangement according to one of Claims 2 to 5, characterised in that the second variation rate is higher than the first variation rate and/or the third variation rate is higher than the first andlor the second variation rate.
7.) Arrangement according to one of Claims 1 to 6, characterised in that with the monitor device (49, 51 53) there is associated a documentation store (61) which stores limit value exceedings for documentation purposes.
8.) Arrangement according to Claims 1 to 7, characterised in that in the stores (37, 41 45) the data delivered by the integration device (37; 37a, 41a, 45a are storable and the correction device (392 43., 47) chronologically corrects the data of the integration device (37; 37a, 41a. 45a).
Arrangement according to Claim 82 characterised in that the stores (37, 419 45) are connected in series and deliver, data time- dependently corrected by the correction device (391 439 47) to the next store (37, 412 45) in the sequence, the stores (37, 419 45) being so connected with 11 17 one another that the variation rate of the time-dependent correction preferably decreases in the store sequence.
10.) Arrangement according to Claim 8, characterised in that the stores (37a, 41a, 45a) accept the data of the integration device in parallel and in that the correction device (39a, 43a, 47a) separately corrects the data stored in the individual stores (37a,41a, 47a).
ll.) Arrangement according to one of Claims 8 to 10, characterised in that the stores 37; 37a, 41a, 45a) are formed as totalling stores of the integration device.
12.) Arrangement substantially as described with reference to Figure 1 or Figure 2 of the accompanying drawing.

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