TECHNICAL FIELD

This invention relates to a sensor assembly capable of signaling a posi- tion between a first sensor body and a second sensor body in an automotive clutch, said second sensor body, responsive to clutch wear being gradually displaceable to new positions by a reciprocable clutch actuator component including the first sensor body. The invention also relates to a clutch actuator provided with an assembly ac¬ cording to any of the previous claims.

BACKGROUND ART

For gearshift purposes it is known to use proximity sensor signals to de¬ termine the operational state, i.e. a state between and including disengagement and engagement in a servo-assisted automotive friction clutch. As indicated above, by allowing one of the sensor bodies to be gradually pushed forward as the clutch wears, it is also known to compensate for clutch wear. Thereby, accurate sensor sig¬ nals can be repetitively maintained during the operational life of the friction pads in the clutch. A proximity sensor assembly of this kind is disclosed, for example, in ap¬ plicant's Swedish patent application No. 0401859-4. In such an assembly it would be convenient, however, to be capable also of determining the extent of wear, and more precisely when the friction pads are en¬ tering a critical wear state before they are actually worn-out. While clutch wear indica¬ tors are also known in the art (see for example U.S. Patent No. 5,697,472 to Walker et al.), these indicators are not able to signal also the operational state. An object of the present invention is therefore to provide an assembly that is capable also of signaling a critical wear state of the clutch.

DISCLOSURE OF THE INVENTION

In one aspect of the present invention, the assembly comprises means for preventing further displacement of said second sensor body at an end position corresponding to a critical wear state of the clutch, and compliant means to be com¬ pressed between said actuator component and said second sensor body when said second sensor body has reached said end position, for the assembly to be capable

of signaling a position between said sensor bodies that is indicative of said critical wear state.

In this description "critical wear state" is to be understood as a situation when the replaceable wear elements in the clutch have entered a remaining range of possible wear before they are fully worn-out, i.e. when there is no usable friction ma¬ terial left in the wear elements. In this remaining range, the clutch will still be func¬ tional a sufficient period of time for the driver to have enough time for necessary preparations for maintenance of the clutch and replacement of the wear elements. For a large or medium sized truck such range could typically represent a remaining thickness of the friction material amounting to about 5 mm.

By such an assembly an existing clutch sensor assembly can be easily modified to also be capable of sensing clutch wear without compromising the high accuracy of the clutch engagement sensor. The assembly can also be made very lightweight and space saving. The compliant means preferably comprises elastic compliant means and most preferably preloaded spring means. By using a preloaded spring having a pre¬ load that is larger than a friction force opposing displacement of the second sensor body, the signals from the sensor assembly will continue to accurately and repeti¬ tively represent the actual engagement state of the clutch, independently of clutch wear.

Other advantages and features of the invention are apparent from the claims and the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a broken away view, partly in section, showing a clutch wear in¬ dicating assembly according to the invention sensing an engaged normal clutch state;

FIG. 2 is a view corresponding to FIG. 1 showing the assembly depicting excessive clutch wear in a disengaged clutch state; FIG. 3 is a view corresponding to FIG. 2 showing the assembly sensing an engaged clutch state and also sensing the excessive clutch wear;

FIG. 4 is a view in larger scale, partly in section, showing the encircled area 4 of FIG. 2 in more detail; and

FIG. 5 is a view, partly in section, showing a clutch actuator incorporated with a sensor assembly according to the invention.

DETAILED DESCRIPTION With reference to FIG. 1 , there is shown a proximity sensor assembly mounted in a rear end portion of a clutch actuator 70 (fully shown in FIG. 5) for an automotive vehicle. A housing of the clutch actuator has an actuator component comprising a cylindrical sleeve 10. A reciprocable clutch actuator piston rod 20 is slidably guided in the housing to extend axially into the sleeve 10 with radial play to the cylindrical inner surface 12 of the sleeve 10.

A first sensor body 26 in the shape of an axial pin is mounted in a cylin¬ drical recess 26 of the reciprocable piston rod 20 to be movable therewith. The first sensor body 26 projects axially beyond an end face 24 of piston rod 20.

A second sensor body 30 is slidably supported by friction engagement in the cylindrical inner surface 12 of sleeve 10. More precisely, a metal sleeve spring element 32 mounted on the cylindrical outer surface of the sensor body 30 exerts a certain radial force on the cylindrical inner surface 12 such that the second sensor body 30 will not slide by itself in inner surface 12 — for example under influence from normal mechanical vibrations. A projecting portion of second sensor body 30, to be received in recess 22, has a coaxial bore 34 adapted to receive the projecting first sensor body 23 without any mechanical contact that otherwise could damage the first sensor body 26 or adversely affect the resulting signal.

In a manner known in the art and therefore not to be fully described, second sensor body 30 is capable of sensing, e.g. by electric induction in a coil 60 (FIG. 3), the extent of proximity to first sensor body 26 — i.e. advancement of first sensor body 26 into bore 34. The extent of proximity, corresponding to a mutual posi¬ tion between the interengagable wear elements in the clutch, is signaled through a signal line 62 to an electronic signal processing equipment 64 in the vehicle as a rep¬ resentation of the instant state of clutch operation, i.e. a certain degree of disen- gagement or engagement in the clutch. On the basis of the sensor signals, the elec¬ tronic equipment 64 is capable of controlling the operation of the clutch actuator in connection with manual or automatic gearshift in the drive transmission of the vehicle (not shown).

As the clutch wears, the clutch engagement stroke of reciprocable piston rod end 24 will gradually reach further and further into sleeve 10. In order that the amplitude of the successive sensor signals should be independent of clutch wear, i.e. wear of the friction elements in the clutch during their operational life, the second sensor body 30 will compensate for the wear by being gradually displaced by the im¬ pact force of the advancing piston rod end 24 overriding the friction force of spring element 32. For a closer description of a proximity sensor of this type, reference is made to applicant's above mentioned Swedish patent application No. 0401859-4. The proximity sensor assembly described above is also provided with a clutch wear indicating assembly, in combination comprising an end stop 14 for pre¬ venting further displacement of the second sensor body 30 at a position correspond¬ ing to a near worn-out state of the clutch, and a spring assembly 40 positioned be¬ tween the first sensor body 26 and the second sensor body 30.

In the embodiment shown, the end stop 14 comprises an annular retain- ing ring 18 located near the free end of the cylindrical inner surface 12 of sleeve 10 and held in place by a clamping ring 16 inserted in an annual groove of inner surface 12.

With reference to FIG. 4, the spring assembly 40 has an annular com¬ pression spring 42. While other springs may be equally useful, in the embodiment shown the spring 42 is a Smalley® crest-to-crest spiral wave spring. One axial end of compression spring 42 is supported by an external radial flange 36 of second sensor body 30. The opposite axial end of spring 42 rests against a washer 44. The washer 44 is in turn supported by a radial flange of a split clamping ring 46 having an outer L- shaped annular section and received in an annular recess 48 in the second sensor body 30 such that the washer 44 may slide on a cylindrical surface 52 of the second sensor body when the spring 42 is compressed or relieved. To facilitate mounting of clamping ring 46 in recess 48, second sensor body 30 has a frustoconical surface 50 tapering in the direction towards the piston rod 20. On the one hand, the distance between the opposing surfaces of the radial flange 36 and washer 44, and on the other hand, the unloaded length of spring 42, are selected so that the spring 42 is preloaded by a certain force which is so much larger than the above mentioned fric¬ tion force opposing displacement of second sensor body 30 that the spring 42 will not be further compressed during normal unobstructed displacement of sensor body 30.

In operation with a near worn-out clutch, when second sensor body 30 during its gradual displacement reaches retaining ring 18 as indicated in FIG. 2, fur¬ ther wear of the friction clutch results in that the end face 24 of piston rod 20 starts to compress spring 42 at the endpoint of each clutch engagement piston stroke as indi- cated in FIG. 3. This in turn results in the first sensor body pin 26 to extend deeper into second sensor body bore 34 than was previously possible. This closer proximity between the sensor bodies now causes the sensor assembly to transmit a signal of a higher amplitude than previously to the electronic equipment 64. The higher ampli¬ tude of the signal on each engagement stroke is detected by the electronic equip- ment 64 which is then capable also of indicating the above mentioned critical wear state, i.e. the extent of wear close to a fully worn-out state of the clutch, in a suitable manner, for example by communicating a warning message to a display 66 (FIG. 3) in a driver's compartment of the vehicle.

Typically, the sensor assembly 30 has an effective stroke sensing inter- val amounting to about 30 mm, where about 25 mm is used for detection of clutch operational state and about 5 mm for the critical wear state in the clutch. By using a sensor having a sufficient high definition it is also possible to use a first short portion of the critical wear interval for signaling and communicating also an additional early wear warning (not shown) prior to a factual warning.