GB2370621A

GB2370621A - A sensor having constant movement between sensor parts regardless of clutch wear

Info

Publication number: GB2370621A
Application number: GB0031513A
Authority: GB
Inventors: Shaun Mepham
Original assignee: Prodrive 2000 Ltd
Current assignee: Prodrive 2000 Ltd
Priority date: 2000-12-27
Filing date: 2000-12-27
Publication date: 2002-07-03
Anticipated expiration: 2020-12-27
Also published as: GB2370621B; GB0031513D0

Abstract

A sensor comprises a sensor tube 22 fixed relative to a clutch actuation cylinder 10 and a sensor sleeve 30 slidably mounted, via friction pads 32, on shaft 16 connected to piston 14. Movement and position of the shaft 16 is determined by sensing the corresponding movement and position of sleeve 30 relative to the sensor tube 22. As a clutch wears the piston 14 moves further to the back of cylinder 10 and sleeve 30 moves with the shaft 16 until the sleeve 30 abuts stop plate 18, hence the relative movement of the sleeve 30 and tube 22, eg distance X, remains constant. The sensor maybe in the form of potentiometer measurements, displacement transducing, proximity sensing, optical or electronic sensing etc.

Description

SENSOR ASSEMBLY

The present invention relates to a sensor assembly and particularly, but not exclusively, to a self-adjusting sensor assembly for a mechanism such as a clutch actuator mechanism or the like.

Clutch mechanisms, for example those used in automotive vehicles for transmitting drive between an engine and a gearbox, are subject to wear. As the clutch mechanism wears, the operative movement of the clutch between an engaged position and a disengaged position increases. In an automatic or semi-automatic clutch/gearbox arrangement, the position of the clutch or its actuator must be accurately sensed in order to ensure smooth clutch engagement As the clutch wears, the position of its operative movement changes. Thus a sensor assembly for sensing the position of the clutch must be capable of measuring not only the travel of the clutch during operation but also changes in position due to clutch wear.

The present invention aims to provide an improved sensor assembly.

Accordingly, the present invention provides a sensor assembly for a mechanism having a movable member which is movable between first and second operative positions, the sensor assembly comprising sensor means located in a fixed position relative to said movable member, sensor actuation means mounted on said movable member for movement with the member and relative thereto, and stop means disposed in fixed relationship to said sensor means for limiting the movement of said sensor actuation means with said movable member, whereby upon changes in said first and second positions, the movement of said sensor actuation means relative to said sensor means remains substantially constant.

Preferably, the movable member comprises a shaft movable in an axial direction within a cylinder. The shaft may be coupled at one end to a piston, the piston being slidably mounted within the cylinder.

Advantageously, the sensor means may comprise a cylindrical tube surrounding the shaft and the sensor actuation means may comprise a sleeve slidably mounted on the shaft for axial movement relative thereto.

The mechanism may, for example, constitute a clutch actuator mechanism having a piston movable in a cylinder, the extent of movement of the piston in the cylinder being variable depending on the extent of movement of an associated clutch which is actuated by fluid pressure.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a section through a perspective view of a clutch actuator mechanism incorporating a preferred form of sensor arrangement according to the invention; and Figure 2a-2d are sectional views of the actuator of Figure I in various positions and states of wear;

Referring to Figure 1, a preferred form of sensor arrangement according to the invention is 9 1 shown as applied to a clutch actuator mechanism. In this embodiment the clutch actuator mechanism is intended for use with an automatic or semi-automatic clutch assembly such as those used in automotive vehicles having automatic or semi-automatic transmissions. It should be noted, however, that the sensor arrangement is in no way limited to such application.

The clutch arrangement of Figure 1 includes a housing in the form of a cylinder 10. The cylinder 10 has an aperture or port 12 at one end 13 through which pressure fluid may be supplied from a pump and valve system (not shown) A piston 14 is disposed within the cylinder 10 for sliding movement therealong forming a chamber 11 in the cylinder.

The cylinder 10 is closed at its end 15 remote from the port 12 by means of a circular stop

plate 18. The stop plate 18 has a central aperture 20, the purpose of which is described below.

A sensor in the form of a cylindrical tube 22 is rigidly connected to the stop plate 18 in axial alignment with the cylinder 10.

An actuator shaft 16 extends from the cylinder 10 in an axial direction, through the aperture 20 in the stop plate 18 and through the cylindrical tube 22, projecting a distance from the end thereof. The shaft 16 is connected at one end 24 to the piston 14 within the cylinder 10 and at its free end 26 to a conventional clutch link (not shown). A gaiter 28 extends from the free end of the tubular sensor 22 to a point on the shaft 16 adjacent to the free end 26 to prevent the ingress of foreign substances into the sensor.

A sensor actuator unit in the fomi-of an elongate collar or sleeve 30 is slidably mounted on the shaft 16. The sleeve 30 is free to move along the shaft relative thereto but any such movement is partially resisted by means of friction pads 32 incorporated into the sleeve. The frictional force generated between the friction pads 32 and the actuator shaft 16 is sufficient to cause the sleeve 30 to move as one with the shaft 16 in the absence of any greater external force being applied thereto. Movement of the sensor sleeve towards the cylinder 10 is limited by the stop plate 18 since the diameter of the sleeve is greater than that of the aperture 20 in the plate.

The sensor 22 is arranged to sense the position of the sleeve 30 relative to itself. As the actuator shaft 16 moves relative to the cylinder 10 and sensor 22, the sleeve 30 moves with the shaft and thus the sensor is able to determine the movement and position of the shaft by sensing the corresponding movement and position of the sleeve 30.

Operation of the actuator and sensor arrangement will now be described with reference to Figures to 2a-d. In Figure 2a, the clutch mechanism is in an engaged position with the piston 14 at distance X from the left hand end of the cylinder 10. At this position, the sleeve 30 abuts with the stop plate 18 and is located substantially within the sensor tube 22.

To move the clutch into a disengaged position, pressure fluid is applied to the chamber 11 within the cylinder 10 via port 12. As illustrated in Figure 2b, the pressure fluid forces the piston and shaft 16 to the left (as shown) until the piston abuts against the stop plate 18 and the clutch linkage (not shown) causes the clutch to become disengaged. As the actuator shaft 16 moves to the left, the frictional force between the friction pads 22 in the sleeve 30 and the actuator shaft 16 causes the sleeve to move with the actuator shaft as one. The sleeve thus moves away from the stop plate 18 by a distance X such that the sleeve 30 lies substantially outside the sensor tube.

Movement of the sensor sleeve 30 relative to tube 22 is sensed to detect the exact position of the actuator shaft thereby allowing accurate control of the movement of the shaft in order to achieve smooth clutch engagement and gear changes. The return movement of the clutch mechanism to the engaged position causes the actuator shaft and thus the sleeve 30 to move to the right, back to its original position (Figure 2a) with the piston at a distance X from the stop plate 18.

However, use of the clutch mechanism causes wear. For the actuator of Figure 1, as the clutch mechanism wears, the return movement causes the actuator shaft to return to a different position to its original one. As shown in Figure 2c, the wear of the clutch mechanism causes the actuator shaft 16 and piston 14 to return to a position closer to the end of the cylinder 10 such that the piston 14 lies at a distance X + Y from the stop plate 18.

As the actuator shaft, during its return movement to the right, passes its original engaged position (position X, Figure 2a), the sleeve 30 comes into abutment with the stop plate 18 and is prevented from moving any further to the right. However, the force on the actuator shaft 16 by the return movement of the clutch mechanism overcomes the frictional force generated by the friction pads 32 between the sleeve 30 and the actuator shaft such that the shaft is able to continue further to the right to its final position with the piston 14 at a distance X +Y from the stop plate 18. The sleeve 30 is thus once more substantially within the sensor tube 22.

As illustrated in Figure 2d, the clutch mechanism in its worn condition is disengaged by application of pressure fluid into the chamber of the cylinder 10 via port 12 to move the piston to the left by distance X (as in Figure 2b). The frictional force between the sleeve and the actuator shaft therefore cause the shaft and sleeve to move to the left as one again by distance X. At this position, as in Figure 2b, the sleeve 30 lies substantially outside the sensor tube 22.

It can be seen, therefore, that regardless of the wear on the clutch mechanism and the resulting change in operative movement of the actuator shaft within the cylinder 10 between the engaged and disengaged positions, the relative movement of the sensor sleeve 30 and the sensor tube 22 between the engaged position and the disengaged position remains the same.

Thus, the sensor is able to accurately detect the position of the actuator shaft, and hence the clutch, thereby allowing accurate control of the movement of the shaft in order to achieve smooth clutch engagement and gear changes. In addition, the sensor tube 22 need only be sized to accommodate the engagement/disengagement travel of the shaft (ie distance X) and not any additional travel due to wear. It will be appreciated that this reduces the weight and cost of sensor and also reduces the need for software compensation. Greater accuracy is alsc achieved.

The sensor may utilize any appropriate form of sensing technology to detect the position of the sleeve, for example potentiometer measurements, displacement transducing, proximity sensing, optical or electronic sensing or the like.

A modification to the above described arrangement may be the addition of a measuring scale located on the actuator shaft in order to give an indication of clutch wear. The position of the sleeve relative to the scale on the shaft could be used to estimate the life expectancy of the clutch mechanism.

As indicated above, the sensor arrangement is not limited to application solely with clutch actuators. Clearly, the invention has application in any mechanism having moving parts whose movements varies throughout the operating range of the mechanism or throughout the lifetime of the mechanism, due to wear for example.

Claims

1. A sensor assembly for a mechanism having a moveable member which is moveable between first and second operative positions, the sensor assembly comprising sensor means located in a fixed position relative to said movable member, sensor actuation means mounted on said moveable member for movement with the member and relative thereto, and stop means disposed in fixed relationship to said sensor means for limiting the movement of said sensor actuation means with said moveable member, whereby upon the changes in said first and second positions, the movement of said sensor actuation means relative to said sensor means remains substantially constant.

2. A sensor assembly according to claim 1 wherein the moveable member comprises a shaft moveable in an axial direction within a cylinder.

3. A sensor assembly according to claim 2 wherein the shaft is coupled at one end to a piston, the piston being slidably mounted within the cylinder.

4. A sensor assembly according to claim 2 or 3 wherein the sensor means comprises a cylindrical tube surrounding the shaft and the sensor actuation means may comprise a sleeve slidably mounted on the shaft for axial movement relative thereto.

5. A sensor assembly according to any one of the proceeding claims wherein the assembly defines a clutch actuator mechanism having a piston moveable in a cylinder, the extent of movement of the piston in the cylinder being variable depending on the extent of movement of an associated clutch which is actuated by fluid pressure.