Patent Publication Number: US-2005115792-A1

Title: Device for compensating wear of the clutch in a motor vehicle

Description:
The present invention relates to a device for compensating wear of the clutch in a motor vehicle.  
      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 or on an intermediate hydraulic control device, for example a master cylinder. 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.  
      U.S. Pat. No. 5,984,072 discloses an actuator unit of the type specified in the preamble 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 integrated actuating unit having the features defined in the attached claims. 
    
    
      The structural and functional characteristics of some preferred, but not restrictive, embodiments of a wear compensating device according to the invention will now be described; reference is made to the attached drawings, in which:  
       FIG. 1  is a partially sectional schematic view of a first embodiment of a wear compensating device coupled to a drive device in an engaged condition of the clutch;  
       FIG. 2  is a perspective view of the devices of  FIG. 1  in a condition in which the clutch is disengaged;  
       FIG. 3  is a partially sectional axial view of the wear compensating device of  FIGS. 1 and 2  and a clutch operating lever;  
       FIG. 4  is a partially sectional schematic axial view of a second embodiment of the wear compensation device according to the invention associated with a clutch operating lever; and  
       FIG. 5  is a partially sectional schematic axial view of a third embodiment of the wear compensation device according to the invention associated with a clutch operating lever.  
    
    
      With reference to  FIGS. 1 and 2 , a drive device  10  includes a crank mechanism  20  which converts the movement of the drive into a substantially linear movement of an output device  40  interposed between the drive device  10  and a clutch operating lever L (shown in  FIG. 3 ). The device  40  serves to transmit to the lever L the movements that cause the disengagement of the clutch and to compensate for the wear on the clutch, as described herein after.  
      The drive device  10  comprises an electric motor  11  with an output worm  12  which engages with a toothed sector  22  of a wheel  21  of the crank mechanism  20 , for example a worm wheel. The wheel  21  is rotatable about a pivot  14  carried by an outer casing  15 .  
      The crank mechanism  20  is coupled to two toggle mechanisms  30   a,    30   b  which assist in operating the clutch. A first end  31   a,    31   b  of each of the two toggle mechanisms  30   a,    30   b  is mounted rotatably to the casing  15 , while the opposite end is hinged to the wheel  21  at points  32   a,    32   b  for the application of a pair of auxiliary forces which impart to the 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  32   a,    32   b  on the worm wheel  21  are diametrically opposed with respect to the central pivot  14 , and the two toggle mechanisms are arranged axially symmetrical with respect to the pivot  14 , 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 respective springs  33   a  and  33   b.    
      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 wear compensating device  40 , unless specified otherwise.  
      The wear compensating device  40  comprises a wedge-shaped stem  41  connected to the drive device  10 , a sleeve  42  acting against the clutch operating lever L, an intermediate wedge-shaped member  43  and an elastic element  44  compressed between the intermediate member  43  and the sleeve  42 .  
      In the illustrated example, the sleeve  42  is a cylindrical tubular body with an axial cylindrical cavity  45  open towards the drive device  10  and a closed bottom  46  which constitutes an opposing wall for the elastic element  44 , in the form of a helical compression spring. The sleeve  42  has a rounded outer end surface  47  which cooperates in a thrust relationship with the clutch operating lever L.  
      The stem  41  has a spherical or cylindrical end head  48  articulated to the wheel  21  and an elongated wedge portion  49  partially accommodated within the cylindrical cavity  45 . The wedge portion  49  has an outer side surface  49   a  of semi-cylindrical shape congruent with the shape of the facing cavity  45 , and a substantially flat side surface  49   b  inclined with respect to the central longitudinal axis x of the device  40 .  
      The intermediate member  43  has a main elongated wedge-shape portion  50  partially accommodated within the cylindrical cavity  45 , a transversal end face  51  resting against the compression spring  44 , an outer side surface  50   a  of semi-cylindrical shape congruent with the shape of the facing cavity  45 , and a substantially flat side surface  50   b  inclined obliquely with respect to the central longitudinal axis x. The oblique surfaces  49   b  and  50   b  of the stem  41  and the intermediate member  43  are parallel and facing each other. Further, the intermediate member  43  forms a radial protrusion  52  with an essentially transversal surface  53  intended to rest against a fixed stopping tooth  16  integral with the casing  15  of the drive device.  
      The operation of the compensation device according to the invention is as follows.  
       FIG. 1  shows the actuator unit in a condition in which the clutch is engaged. The two crank mechanisms  30   a,    30   b  are in a stable limit position, aligned along two parallel straight lines, i.e. slightly beyond the dead centre in the direction opposite to the direction of rotation for disengagement of the clutch, indicated by the arrow A. The springs  33   a  and  33   b  are compressed. The clutch operating lever L urges the sleeve  42  towards the drive device  10 . The axial position of the sleeve  42  is determined by the equilibrium of the opposite forces generated by the pressure spring (not shown) of the clutch and the compression spring  44 . The protruding portion  52  of the intermediate member  43  abuts against the stopping tooth  16 . It is important to note that in this position the stem  41  is axially released from the sleeve  42  because it is in a position slightly extracted towards the outside of the cylindrical cavity  45 . In other words, the stem  41  and the intermediate member  43  are accommodated with a slight transversal play within the cavity  45 .  
      When the clutch has to be disengaged, the drive device  10  is activated. A rotary motion imparted by the electric motor  11  to the worm screw  12  causes the worm wheel  21  to rotate in the clockwise direction A 1  to disengage the clutch. Upon passing the dead centre, the springs  33   a,    33   b  of the toggle mechanisms  30   a,    30   b  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.  
      The stem  41  is so pushed in a substantially linear manner towards the clutch and penetrates further into the axial cavity  45  until the oblique surfaces  49   b  and  50   b  come into contact ( FIG. 3 ). Owing to the contact of the oblique surfaces, the axial thrust exerted by the stem  41  creates a radial or transversal thrust component that makes the opposite outer semi-cylindrical surfaces  49   a,    50   a  of the stem  41  and the intermediate member  43  move away from each other. The overall transversal size of the assembly consisting of the stem  41  and the intermediate member  43  therefore increases rapidly until the opposite semi-cylindrical surfaces  49   a,    50   a  get to lock against the cylindrical cavity surrounding them. The spring  44  cooperates in this phase by opposing the sliding movement of the intermediate member  43  in the sleeve  42  to render the tightening action of the wedge-shaped components  41  and  43  in the axial cavity  45  of the sleeve  42  more immediate.  
      By virtue of the reciprocal locking of the sleeve  42 , the intermediate member  43  and the stem  41 , a further motion imparted by the wheel  21  to the stem causes the compensating device  40  to move as a single piece towards the extended or disengaged position of the clutch.  
      When the clutch has to be engaged again, the motor  11  of the drive device  10  is activated inversely. The compensation device  40  as a whole is returned towards the drive device and the pressure spring of the clutch (not shown) cooperates by extending.  
      When the radial protrusion  52  abuts against the stopping tooth  16 , further linear motion of the intermediate member  43  is impeded. This member can no longer follow the linear return motion of the stem  41 , which is now released from the intermediate member  43  and the sleeve  42  and comes partially out of the cylindrical cavity  45 . The spring  44  keeps the sleeve  42  pressed against the clutch lever L.  
      Still referring to  FIG. 3 , the wear on the clutch causes the clutch lever L to progressively assume an increasingly retracted engagement (or rest) position indicated by L′. Since the axial travel imparted by the drive  10  is constant, it is necessary to adapt the initial or rest position of the sleeve  42  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.  
      If, therefore, owing to the wear on the clutch, the operating lever L tends to move to a new rest position L′ which is progressively more advanced towards the actuator, the spring  44  is correspondingly more compressed, as it is weaker than the pressure spring (not shown) of the clutch. In the new equilibrium position of these springs, having regard to the initial non-worn position of the clutch, the sleeve  42  is shifted to a new rest position (not shown) nearer the drive device, whereby the compensating device  40  as a whole is shortened by a length corresponding to the degree of wear on the clutch. In this way the change in the final position L′ of the clutch lever L due to the wear on the clutch is compensated.  
      In order to reduce friction between the inclined surfaces  49   b  and  50   b  and avoid possible jamming of the wedge-shaped components  41  and  43  in the axial cavity  45  of the sleeve  42 , low friction means can be interposed at the interface between the inclined surfaces  49   b  and  50   b,  or either or both of these surfaces can be made of a low-friction material. In the embodiment shown in  FIG. 4 , between the inclined surfaces  49   b  and  50   b  a set of anti-friction elements  60  is interposed, preferably rolling bodies in the form of cylindrical rollers with axes transversal to the longitudinal axis x of the device. In the example of  FIG. 4  the anti-friction rollers  60  are accommodated in a recess  54  formed in the intermediate member  43  and open towards the inclined surface  49   b  of the stem  41 . As an alternative to the rollers, antifriction elements equivalent thereto can for example comprise a sliding block  60  ( FIG. 5 ) of low friction material (e.g. Teflon or PTFE) fitted in the recess  54  or other means for reducing friction while favouring relative longitudinal sliding movement between the stem  41  and the intermediate member  43 . To this end, as a further alternative, at least one of the inclined surfaces  49   b  and/or  50   b  can be covered with a layer of low friction material, or at least one of the wedge-shaped members  41  and/or  43  can be made of a low friction material.  
      As will be appreciated, the wear compensating device of 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 (constant) travel imparted to the stem  41  will always be sufficient to cause the complete disengagement of the clutch.  
      It will also be appreciated that the wear compensating device has a minimum number of components, is easily assembled and that the surfaces ( 45 ,  49   a,    49   b,    50   b,    50   a ) which cooperate in effecting the reciprocal axial locking of the components  41 ,  42  and  43  have an extended contact area involving low contact pressure and therefore an extremely reduced wear of the device itself, which ensures reliable operation with time.  
      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 wear compensating device; 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 transversal cross section of the cavity  45  may have shapes different from the circular one as illustrated, for example square or rectangular, and the outer side surfaces  49   a,    50   a  cooperating with the cavity  45  as a result may be flat instead of semi-cylindrical. Similarly, the interface surfaces of the stopping tooth  16  and the protrusion  52  may for example consist of a cylindrical pin and a flat surface, so as to compensate for changes of orientation undergone by the wear compensating device during its operation.