TECHNICAL FIELD

The invention relates to a position sensor for detecting position shifting of a component capable of moving to and fro in an actuator for a vehicle mechanism, comprising a stationary sensor body and a movable sensor body which is connectable to the component and is adapted to moving with the component between positions close to and away from the stationary sensor body, whereby the stationary sensor body is adapted to being relocatable against friction force to new stationary positions in a guide bushing in response to wear of the vehicle mechanism. The invention also relates to a stationary sensor body and a movable sensor body for such a position sensor and to an actuator comprising such a position sensor or such a movable and such a stationary sensor body. In addition, the invention relates to an automatic clutch with such an actuator.

BACKGROUND

When such a position sensor is used for detecting whether a friction clutch for a vehicle is engaged or disengaged, the stationary sensor body gradually relocates in response to wear of the clutch disc. Such a position sensor need therefore not be of increased length to compensate for this wear. The result is better resolution of the signal for detecting the engagement position of the clutch.

In a known position sensor of this kind according to US patent specification 5 758 758, the end of the movable sensor body is used for relocating the stationary sensor body to new stationary positions. If it is desired, for example, to use an anchor pin as a movable sensor body in an inductive sensor, it would be advantageous if the anchor pin might cooperate in a contact-free manner with the stationary sensor body, i.e. without any risk, on the occasion of each clutch engagement, of impinging with relatively great force upon the stationary sensor body, which needs to be held firm by relatively great friction in the guide bushing.

SUMMARY OF THE INVENTION An object of the present invention is therefore to provide a position sensor of the kind indicated in the introduction whereby the movable sensor body need not be subjected to mechanical load and can cooperate in a contact-free manner with the stationary sensor body.

This is achieved by the features indicated in the attached claims.

According to one aspect of the invention, the stationary sensor body is adapted to being shifted by a free end of the component to new stationary positions and the movable sensor body is adapted to moving at a distance from, or with clearance relative to, the stationary sensor body. Thereby, on the one hand, the movable sensor body can be designed almost entirely with respect to optimum sensor function, with insignificant requirements as regards to mechanical strength. On the other hand, the stationary sensor body can be held firm by desired sufficient friction against being shifted to new positions so that it does not risk being unintentionally shifted by, for example, severe vibrations from a large vehicle diesel engine.

According to one embodiment, the free end of the component has a cylindrical recess for accommodating a detection portion of the movable sensor body, so that the free end of a hollow cylinder surrounding the detection portion is adapted to engaging with a shoulder surface of the stationary sensor body in order to shift the latter. In this way, the pressure force from the component can with advantage be distributed concentrically on the stationary sensor body around the sensor's functional portions, e.g. a coil and an anchor pin, which are protected by being accommodated in the cylindrical recess.

Other features and advantages of the invention are indicated by the following detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an oblique view from in front, mainly in longitudinal section, of an actuator with a position sensor according to the invention; FIG. 2 A is a longitudinal sectional view with a pair of regions on a larger scale of an actuator in a first position with a position sensor mainly according to FIG. 1.;

FIG. 2B is a longitudinal sectional view of the actuator in FIG. 2 A in a second position; and

FIG. 2C is a longitudinal sectional view of the actuator in FIG. 2 A in another second position with the position sensor shifted rearwards.

DETAILED DESCRIPTION OF EMBODIMENTS

The actuator 10 depicted in FIG. 1 is intended in a known manner to operate a schematically depicted friction clutch 80 in a vehicle via an operating rod 28. The clutch may serve as an automatic clutch which relieves the driver of operating the clutch. In the example depicted, the actuator 10 comprises a cylinder 11 supplied with compressed air from a compressed air source 74 via a fluid line 76 to an inlet and outlet 12. Higher pressure of the compressed air acts upon a piston 18 which itself pushes the operating rod 28 to a position indicated in FIG. 1 (and FIG. 2A) whereby the clutch is disengaged. Lower pressure of the compressed air allows force from a spring 84 in the clutch 80 to cause the operating rod 28 to push the piston 18 back by a distance s to a position depicted in FIG. 2B whereby the clutch is engaged in order to transmit torque from an engine of the vehicle to the vehicle's powered wheels.

The piston 18 is guided through an endwall 13 of the cylinder 11 via a piston rod 20. A compression spring 26 situated between the endwall 13 and the piston 18 of the cylinder 10 acts together with the compressed air to oppose the pressure force from the clutch 80 upon the operating rod 28 which endeavours to engage the clutch 80.

The piston rod 20 extends outside the endwall 13 into a guide bushing 14 for a position sensor according to the invention which is denoted generally by ref. 30. In the example depicted, the position sensor 30 is an inductive sensor, but the invention may also be applied with other types of sensor which operate according to other principles, e.g. electrical and/or optical.

The inductive position sensor 30 comprises a stationary sensor body 32 and a movable sensor body 52. The stationary sensor body 32 has a drilled hole or duct 42 which the movable sensor body 52 in the form of a stem or pin can penetrate. The duct 42 is surrounded by a coil 44 (FIG. 2A) in which changes of inductance can be used as a measure of the position of the stationary sensor body 52 when the latter penetrates the duct 42. The prevailing inductance value is signalled via lines 46 to an electronic control unit 70 for the vehicle's clutch. The lines 46 extend from a rear side of the stationary sensor body 32 via a protective sheath 48 to the control unit 70 which, in a conventional manner not depicted in more detail, controls via a signal connection 72 the pressure from the compressed air source 74 in order to engage and disengage the friction clutch 80.

As the engagement surfaces 82 (FIG. 1) of the friction clutch 80 progressively wear, the position of the piston rod 20 of the actuator 10 when the clutch 80 is engaged will relocate rearwards, i.e. to the right in FIG. 2B. According to the invention, the free end of the piston rod 20 then progressively brings the stationary sensor body 32 with it to new stationary positions, with the result that when the engagement surfaces are almost entirely worn down the stationary sensor body 32 will have relocated by a distance w to the position depicted in FIG. 2C.

The piston rod 20 has at its free end a cylindrical recess 22 which accommodates with clearance a tapered cylindrical protrusion or detector portion 34 of the stationary sensor body 32. An annular pressure surface 24 capable of engaging with an annular shoulder 38 of the stationary sensor body 32 radially outside the movable sensor body 52 is thus delineated at the free end of the piston rod 20. Thereby is attained the advantage that the movable sensor body 52 need not participate mechanically in the progressive shifting of the stationary sensor body 32 and can on the occasion of each operation of the clutch penetrate the duct 42 axially in a contact-free manner without risk of causing wear or any other mechanical effect. With regard to choice of material and geometry, the movable sensor body can therefore be designed exclusively for optimum sensor function.

To prevent any risk of the movable sensor body 52 being subjected to harmful radial mechanical action due to unintentional oblique positioning of the duct 42, the sensor body 52 is resiliently fastened in a drilled hole or boring 64 in the bottom of the recess 22 approximately as depicted in the left enlargement in FIG. 2A. More precisely, the fastening end of the movable sensor body 52 has a head 60 made of low- friction plastic moulded on the inner end. The peripheral surface of the head 60 is of spherical shape so that the sensor body 52 can undergo limited rocking or pivoting movements in all directions. The sensor body 52 is inserted, with clearance, through a spring washer 56 which is radially clamped in a peripheral groove 66 in the boring or drilled hole 64. A suitable striplike compression coil spring 62 is clamped between the bottom of the drilled hole 64 and the inside of the head 60 so that the planar outside of the head 60 abuts against the inside of the spring washer 56 and hence by resilient prestress holds the sensor body 52 in the desired axial orientation. An intermediate washer 58 may be placed between the head 60 and the spring washer 56 to compensate for any imperfections of planarity and abutment.

To hold the stationary sensor body 32 in desired factional engagement with the inside 16 of the guide bushing 14, the invention further comprises a spring sleeve 50 made of a resilient thin-walled material and accommodated and axially fastened between flanges in a peripheral recess 40 of a base portion 36 of the stationary sensor body 32. As particularly indicated by the enlargement on the right in FIG. 2 A, the spring sleeve 50 is corrugated in the circumferential direction, resulting in an approximately trapezoidal creased longitudinal section with planar ridges 51 which abut resiliently against the inside 16 of the guide bushing 14. To enable it to be fitted in the recess 40, the spring sleeve is with advantage provided with a longitudinal slit (not depicted) running through it which makes it possible for the spring sleeve 50 to widen when it is fitted on the base portion 36. As the desired spring effect and hence the clamping force of the spring sleeve 50 are determined mainly by the height of the ridges 51, it is relatively easy to dimension the diameter of the recess 40 relative to the inside diameter of the guide bushing 14 in order to achieve desired friction force opposing shifting of the stationary sensor body 32.