WO2005028900A1

WO2005028900A1 - Actuator unit with incorporated device to compensate for wear on the clutch

Info

Publication number: WO2005028900A1
Application number: PCT/EP2004/010647
Authority: WO
Inventors: Andreas Geyer; Alessandro De Cristofaro
Original assignee: Aktiebolaget Skf
Priority date: 2003-09-24
Filing date: 2004-09-22
Publication date: 2005-03-31
Also published as: DE112004001780T5; ITTO20030736A1

Abstract

An actuator (10) is associated with a crank mechanism (20) which converts the movement of the drive into a translational movement of an output rod (30) to cause the disengagement of the clutch by means of a lever (L). A compensation device (60) adapts the position of the rod (30). A rigid transmission member (61, 64), which is interposed between the crank mechanism (20) and the rod (30), is articulated to the crank mechanism (20) and has surfaces (65a, 65b) facing opposite sides of the rod (30) with a small clearance. The rigid transmission member can assume two alternative positions with respect to the rod (30), namely: a first position of axial engagement with the rod (30), in which the surfaces (65a, 65b) are inclined and grip two opposite sides of the rod, to couple the rod axially to the crank mechanism, and a second position of axial disengagement from the rod (30), corresponding to a disengaged condition of the clutch. In this second position, the aforesaid surfaces are parallel to the rod, which is therefore free to slide axially to reach a new axial position adapted to a new rest position (L’).

Description

Actuator unit with incorporated device to compensate for wear on the clutch

The present invention relates to an actuator unit for operating a clutch in a motor vehicle. More particularly, the invention relates to an actuator unit with an incorporated device to compensate for wear on the clutch.

The present invention is applicable to vehicles in which the clutch is disengaged by means of an actuator which acts on an operating lever which emerges from the outer casing of the clutch. If the clutch is not of the self-adjusting type, the initial rest position of the operating lever varies over time as a result of the progressive wear on the clutch. It is therefore necessary to provide a device that compensates for wear on the clutch, in order to ensure that the movement imparted by the actuator always causes the complete disengagement of the clutch, regardless of its degree of wear.

US-5,984,072 describes an actuator unit of the type specified in the precharacterizing part of Claim 1. An actuator is provided with a drive system associated with a crank mechanism which converts the movement of the drive into a translational movement of an output rod hinged to the crank mechanism to cause the disengagement of the clutch. The crank mechanism is coupled to a toggle mechanism which assists in the operation of the clutch. An adjustment device is mounted on the rod to compensate for the wear on the clutch. This device operates on the principle of a wedge stressed by a spring and associated with ball-type locking elements. In the initial position (with the clutch engaged) , the wedge is disengaged and allows the components of the device to move relative to each other, to cause a change in the axial length. When the actuator is operated, the wedge locks the relative positions of the components of the device.

The object of the invention is to provide an actuator unit having compact dimensions and consisting of a reduced number of components, while being reliable in operation and economical to manufacture.

This and other objects and advantages, which will be made clearer below, are achieved according to the invention by an incorporated actuator unit having the characteristics stated in the attached claims.

The structural and functional characteristics of some preferred, but not restrictive, embodiments of an actuator unit according to the invention will now be described, with reference to the attached drawings, in which: Figure 1 is a partially sectional schematic view of a first embodiment of an actuator unit according to the invention coupled to an operating lever of the clutch in an engaged condition; Figure 2 is a view of the actuator unit of Figure 1 in the condition in which the clutch is disengaged; Figure 3 is an enlarged view of a detail of Figure 2; Figures 4 and 5 are enlarged views which schematically illustrate the operating principle of a component of the actuator unit; and Figure 6 is a partially sectional schematic view of a second embodiment of an actuator unit according to the invention.

The actuator unit illustrated in Figures 1 and 2 comprises a drive 10 associated with a crank mechanism 20 which converts the movement of the drive into a translational movement of an output rod 30 which is extended to cause the disengagement of the clutch. The crank mechanism 20 is coupled to two toggle mechanisms 40a, 40b which assist in the operation of the clutch. The actuator unit also incorporates, according to the invention, a device 60 to compensate for the wear on the clutch.

The drive 10 comprises an electric motor 11 with an output worm 12 which engages with a sector 22 of a worm wheel 21 of the crank mechanism 20. The worm wheel 21 is rotatable about a pivot 23 carried by an outer casing indicated schematically 50. A first end of each of the two toggle mechanisms 40a, 40b is mounted rotatably on a corresponding part 41a, 41b fixed to the casing 50, while the opposite end is hinged to the worm wheel 21 at points 42a, 42b for the application of a pair of auxiliary forces which impart to the worm wheel 21 a rotational impulse in a direction matching the direction of rotation imparted by the electric motor to cause the disengagement of the clutch. The two points of hinging 42a, 42b on the worm wheel 21 are diametrically opposed with respect to the central pivot 23, and the two toggle mechanisms are positioned in an axially symmetrical way with respect to the pivot 23, to apply to the worm wheel 21 two forces of equal intensity, acting in opposite directions along parallel straight lines of operation. These forces are exerted by the corresponding springs 43a and 43b.

The worm wheel 21 consists of two plate elements 21c, 2Id which are parallel, fixed to each other and orientated perpendicularly to the axis of rotation of the central pivot 23. The worm wheel 21 carries a pivot 24 which is in a peripheral position with respect to the central pivot 23 and is orientated parallel to the latter. A bearing with an outer rotatable ring 25 is mounted on the peripheral pivot 24.

The rotary movement of the worm wheel 21 is converted into a translational movement of an output rod 30 which, being translated in the direction indicated by the arrow A along the longitudinal axis x of the rod, causes the disengagement of the clutch by acting with one of its ends 31 on a clutch operating lever L. The rod 30 is guided axially by support and guide elements 51, 52 fixed to the casing 50.

Throughout the present description and in the following claims, terms and expressions indicating positions and orientations such as "radial", "transverse" or "axial" and "longitudinal" are considered to relate to the longitudinal axis x of the rod 30, unless specified otherwise.

According to the invention, the movement of the worm wheel 21 is transmitted to the rod 30 through the device to compensate for the wear on the clutch, indicated overall 60. This device can connect the rod 30 to the crank mechanism 20 to cause the axial translation of the rod during the movements of disengaging and engaging the clutch, and can release the rod axially when the clutch is released, to enable the rod to adapt its position automatically to the progressively further retracted rest positions which the clutch operating lever L assumes as a result of the wear on the clutch.

The compensation device 60 comprises a rigid transmission member 61, 64 interposed between the crank mechanism 20 and the rod 30. The transmission member includes a rigid body 61 mounted slidably on the rod 30. The rigid body 61 has an annular portion 62 in which there is fixed, by means of fixing screws 63, a ring 64 having a radially inner surface of essentially cylindrical shape 65 positioned with a small amount of radial clearance around the rod 30. As shown more clearly in Figure 3, the inner surface 65 preferably has a slightly curved and convex profile which widens at the two opposing axial ends of the ring 64, for reasons which are explained below. The rigid body 61 also has a transverse surface 66, referred to here as the rear surface, for bearing on a stop surface 67 of an abutment element 68, whose longitudinal position can be adjusted by means of a fine adjustment screw 69. The abutment element 68 forms an inner passage 71 for the rod 30.

The rigid body 61 also forms a fork-like portion with a pair of opposing parallel surfaces 61a, 61b defining a transverse guide for the bearing 25. The outer ring of the bearing is housed between the two surfaces 61a, 61b with a predetermined minimum clearance which enables the bearing 25 to . slide in the radial direction with .respect to the axis x when the worm wheel 21 is rotated and moves the rigid body 61 with it along the longitudinal axis x, urging against the surface 61a or the surface 61b, according to the direction of rotation imparted to the worm wheel .

The wear compensation device 60 also comprises a spring 70 compressed between an annular projection 32, formed on the rod 30, and the ring 64. The spring 70 tends to push the ring 64 and the rigid body 61 in the direction (indicated by the arrow B) opposite to the direction of disengagement of the clutch (indicated by the arrow A) .

The actuator unit according to the invention operates in the following way. Figure 1 shows the actuator unit in a condition in which the clutch is engaged. The two crank mechanisms 40a, 40b are in stable limit positions, aligned along two parallel straight lines which do not coincide, and therefore slightly beyond the dead centre in the direction opposite to the direction of rotation for disengagement of the clutch, indicated by the arrow Al . The springs 43a and 43b are compressed. The axial position of the abutment element 68 has been adjusted manually by means of the adjustment screw 69 in such a way that the transverse surface 66 of the rigid body 61 bears precisely on the end stop surface 67. The rod 30 is pushed into the retracted position (towards the right) by the clutch operating lever L, as shown in solid lines in Figure 1. It is important to note that in this position, shown schematically in Figure 4, the rigid body 61 and the ring 64 are orientated in such a way that the inner cylindrical surface 65 faces the surface of the rod in an essentially coaxial or parallel way, so that the rod is released axially from the drive 10 and from the crank mechanism 20 and is therefore free to slide axially under the action of the clutch operating lever in the direction indicated by the arrow B.

A rotary motion imparted by the electric motor 11 to the worm 12 causes the worm wheel 21 to rotate in the clockwise direction Al to disengage the clutch. When the dead centre is passed, the springs 43a, 43b of the toggle mechanisms 40a, 40b snap into the extended configuration, thus assisting the drive 10 to cause the rapid disengagement of the clutch, even if the electric motor 11 is relatively low- powered.

Owing to the radial clearance provided between the inner cylindrical surface 65 of the ring 64 and the rod 30, the sudden rotation of the worm wheel 21 about the central pivot 23 causes the inclination of the rigid body 61 with the ring 64 with respect to the axis x. Thus the inner surface 65 of the ring 64 moves from the parallel or released condition of Figures 1 and 4 to an inclined locking condition (shown schematically in Figure 5 on an exaggerated scale for greater clarity) . In this inclined position, the inner surface 65 grips the rod 30, engaging two opposite sides of the rod 30 by means of two opposed surface portions 65a, 65b. The rod is thus locked axially to the worm wheel 21. Owing to the engagement between the bearing 25 and the transverse surface 61a of the body 61, the rod 30 is moved axially (towards the left) into the extended position, or clutch disengagement position, shown in Figure 2.

The spring 70 contributes to this locking action by preventing the free sliding of the ring 64 and the block 61 along the rod, to make the gripping of the rod more immediate . As shown more clearly in Figure 2 , the abutment element 68 has, on the side opposite to the stop surface 67 with respect to the rod 30, a surface 67a recessed with respect to the stop surface 67, to enable the rigid body 61 to be inclined with respect to the axis of the rod 30 in the gripping condition.

During the movements of engagement and disengagement of the clutch, and therefore during the movement from Figure 1 to Figure 2 and vice versa, the rod 30 forms a single unit with the ring 64 and the rigid body 61. During these movements, the bearing 25 (which rotates with the worm wheel about the central pivot 23) can slide along the transverse surfaces 61a, 61b of the fork-like portion pf the block 61. With reference to Figure 1 again, the wear on the clutch causes the operating lever L to progressively assume an increasingly retracted engagement (or rest) position, as shown schematically in broken lines and indicated by L' . Since the axial travel imparted by the drive 10 is constant (typically approximately 22 mm) , it is necessary to adapt the initial or rest position of the rod 30 (Figure 1) to the rest position L' reached by the clutch operating lever, in order to ensure that the clutch can be completely disengaged even when it is worn.

For this purpose, when the rod 30 returns to the retracted position (Figure 1) the transverse surface 66 of the rigid body 61 abuts against the stop surface 67 of abutment element 68. As a result of this abutment and the inertia of the rigid body 61, the rigid body rotates slightly in a plane of rotation passing through the axis x, and returns to the initial orientation by moving from the locking condition of Figure 5 (where the inner surface 65 is inclined with respect to the axis x of the rod) to the disengaged condition of Figure 4, where the inner surface 65 of the ring 64 is parallel to the surface of the rod. The rod 30 is thus released axially from the transmission device 60.

If, therefore, owing to the wear on the clutch, the operating lever L tends to move to a new rest position L' which is more retracted, the rod 30 is free to be pushed by the lever further towards the right and to slide in the supports 51, 52 until the lever reaches its new rest position.

In the embodiment shown in Figure 6, the rigid block 61 has a hole 61c which rotatably houses the peripheral pivot 24 carried by the worm wheel 21. By contrast with the embodiment of Figures 1 and 2, the variant of Figure 6 does not include axial guide and support elements for the rod of the type indicated by 51 and 52. Consequently, in the variant of Figure 6 the rod 30 does not make a purely translational movement, but is free to make a principal translational movement combined with a limited oscillatory movement, following the rotary movement of the engagement pivot 24 around the central pivot 23 of the toggle mechanism. In other respects, the operation of the actuator unit of Figure 6 is equivalent to that of Figures 1 and 2.

As will be appreciated, the actuator unit according to the present invention enables the clutch operating lever to continually reach new rest positions, determined by the progressive degree of wear on the clutch, and, by adapting itself automatically to these changes of position, ensures that the travel will always be constant and sufficient to cause the complete disengagement of the clutch.

The provision of two toggle mechanisms which are axially opposed with respect to the pivot 23 enables a high disengagement torque to be imparted to the worm wheel without appreciable stress on the pivot 23. This prevents deformation and displacement or fracture of the pivot and reduces the wear on it. It is also advantageous because the two branches of the fork-like portion of the rigid body 61 are guided and retained precisely between the two facing walls 21c and 21d of the worm wheel 21, so that the block 61 is prevented from rotating in an undesired way about the rod 30.

It is to be understood that the invention is not limited to the embodiments described and illustrated herein, which are to be considered as examples of the actuator; in fact, the invention can be modified in respect of the form and arrangements of parts and details of construction, and in respect of its operation. For example, the bearing 25 can be replaced with a transversely slidable block, and the surface 65 for gripping the rod 30 can be made in one piece with the rigid block 61. However, the choice of making a ring 64 separate from the block 61 is advantageous because it enables a single block to be used for rods of different diameters, by selecting a ring 64 having dimensions matched to each rod. Moreover, a gripping surface 65 with a curved profile which is widened at the opposing ends prevents irreversible locking due to jamming of the surface 65 on the rod. Finally, the ring 64 can be replaced by a rigid element having a shape differing from the annular shape illustrated here but mechanically equivalent to it, in order to engage two opposite sides of the rod 30 for the purpose of locking.

Claims

1. An actuator unit for operating a clutch provided with an operating lever (L) , of the type comprising a drive (10) associated with a crank mechanism (20) which converts the movement of the drive into an essentially translational movement of an output rod (30) along the longitudinal axis (x) of the rod to cause the disengagement of the clutch, and a device to compensate for the wear on the clutch, to automatically adapt the position of the rod (30) in accordance with new rest positions (L' ) which the lever (L) tends to assume progressively as a result of the wear on the clutch, characterized in that the compensation device (60) comprises a rigid transmission member (61, 64) interposed between the crank mechanism (20) and the rod (30) , the said transmission member being articulated to the crank mechanism (20) and having surface portions (65a, 65b) facing opposite sides of the rod (30) with a small clearance, in such a way that the rigid transmission member can assume two alternative positions with respect to the rod (30) , namely: a first position of axial engagement with the rod (30) , in which the said surface portions (65a, 65b) are inclined with respect to the axis (x) of the rod (30) as a result of the rotation of the crank mechanism (20) during the movements of engagement and disengagement of the clutch, and the said surface portions grip two opposite sides of the rod, to couple the rod axially to the crank mechanism, and a second position of axial disengagement from the rod (30) , corresponding to a condition of engagement of the clutch, where in the said second position the aforesaid surface portions are essentially parallel to the rod, so that the rod is axially disengaged from the transmission member (61, 64) and from the crank mechanism (20) and is free to slide axially to reach a new axial position adapted to a new rest position (L') which the operating lever (L) tends to assume as a result of the wear on the clutch.

2. An actuator unit according to Claim 1, characterized in that the said surface portions (65a, 65b) are radially opposite portions of an essentially cylindrical surface (65) fixed to the transmission member (61, 64) and positioned around a portion of the rod (30) .

3. An actuator unit according to Claim 1, characterized in that each of the said surface portions (65a, 65b) has a curved and convex profile on at least one of its axial ends.

4. An actuator unit according to Claim 1, characterized in that the said transmission member (61, 64) comprises: a rigid body (61) forming a pair of opposing parallel surfaces (61a, 61b) for engaging in a movable and transverse way an engagement element (24, 25) carried by the crank mechanism (20) , and an annular element (64) mounted rigidly on the rigid body (61) and forming the said essentially cylindrical surface (65) .

5. An actuator unit according to Claim 4, characterized in that the said engagement element (24, 25) carried by the crank mechanism (20) comprises a cylindrical or annular body (25) which is freely rotatable about an axis parallel to and spaced apart from the central axis of rotation (23) of the crank mechanism (20) .

6. An actuator unit according to Claim 4, characterized in that the crank mechanism (20) comprises a wheel (21) consisting of two plate elements (21c, 21d) which are parallel, fixed to each other and orientated perpendicularly to the axis of rotation (23) of the crank mechanism, and in that the said opposing parallel surfaces (61a, 61b) are formed by portions of the rigid body (61) lying between the two parallel plate elements (21c, 2Id) .

7. An actuator unit according to Claim 1, characterized in that the said transmission member (61, 64) comprises: a rigid body (61) having a seat (61c) for rotationally housing an engagement element (24) carried by the crank mechanism (20) , and an annular element (64) mounted rigidly on the rigid body (61) and forming the said essentially cylindrical surface (65) .

8. An actuator unit according to Claim 7, characterized in that the said engagement element (24) carried by the crank mechanism (20) comprises a pivot which is parallel to and spaced apart from the central axis of rotation (23) of the crank mechanism (20) .

9. An actuator unit according to Claim 8, characterized in that the crank mechanism (20) comprises a wheel (21) consisting of two plate elements (21c, 21d) which are parallel, fixed to each other and orientated perpendicularly to the axis of rotation (23) of the crank mechanism, and in that the pivot (24) engages both of the parallel plate elements (21c, 21d) .

10. An actuator unit according to Claim 1, characterized in that the crank mechanism (20) is associated with two toggle mechanisms (40a, 40b) , each provided with a respective elastic means (43a, 43b) and positioned in an axially symmetrical way with respect to the axis of rotation of the crank mechanism, to apply to the crank mechanism two forces of equal intensity in opposite directions, acting along parallel straight lines, to assist in the disengagement of the clutch.

11. An actuator unit according to Claim 1, characterized in that the rigid transmission member (61) has a transverse surface (66) which, in the said second position of the rod (30) , abuts against a stop surface (67) of an abutment element (68) .

12. An actuator unit according to Claim 11, characterized in that the abutment element (68) is provided with fine adjustment means (69) to adjust the longitudinal position of this element .

13. An actuator unit according to Claim 1, characterized in that the compensation device (60) additionally comprises an elastic element (70) acting between the rod (30) and the rigid transmission member (61, 64) to push this member in a direction (B) opposite to the direction (A) followed by the rod (30) in the movement of disengagement of the clutch.