Abstract:
An under travel actuator, particularly intended for an automobile clutch, including an engine ( 12 ) for the translation movement of a mobile gear ( 14 ) acting on a push stem ( 16 ) for the opening and closing of the clutch, the mobile gear including screw-nut means ( 22, 24 ) cooperating with two combined means of unidirectional driving in order to regulate the length of the push stem ( 16 ) according to the wear of the clutch surfaces subject to friction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
     This application relates to International Application No. PCT/FR2007/051311 filed May 22, 2007 and French Patent Application No. 0651935 filed May 29, 2006, of which the disclosures are incorporated herein by reference and to which priority is claimed. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns a travel compensation actuator, in particular for a motor vehicle clutch. 
     2. Description of Related Art 
     An actuator of this type comprises an electrical reduction motor, which operates a driving mechanism, such as for example, a pusher member acting directly or otherwise on the system to be operated, for example, a clutch pressure plate. 
     If the actuator is of the effort compensating type, it will generally comprise a compensating spring, which acts on a cam or an inclined ramp that is connected to the said driving mechanism so as to apply a force to this mechanism in a particular direction representing the opening of the clutch and which approximately compensates the resistance manifested by the return spring of the clutch pressure plate in such a way that effort delivered by the reduction motor for the actuation of the clutch is reduced to a minimum. 
     When the friction linings of the clutch start to show signs of wear, the pressure plate and thereby also the driving mechanism become displaced as a result of the modification to the travel of this element and by changes in the amount of effort needed to operate its respective actions. 
     Numerous systems have already been proposed to compensate wear in such mechanisms and in general these are integrated into the clutch system itself in order to compensate wear of friction linings as it occurs, so that the wear has no immediate effect on the position of the clutch pressure plate or on the travel of the driving mechanism. 
     However, these known solutions are all relatively complex and in practice their precision and their reliability have frequently been found wanting. 
     Another solution consists in adjusting the length of the driving mechanism in relation to the amount of wear shown by the linings of the clutch in such a way that this adjustment of the length has the effect of compensating the travel of the pressure plate as it becomes affected by the wear to the linings. 
     BRIEF SUMMARY OF THE INVENTION 
     The aim of the present invention is, in particular, to respond to this need in a simple, effective and economic manner. 
     It has, as its object, a travel compensation actuator, applicable in particular to the operating mechanism of a motor vehicle clutch system and comprises the means of adjusting the length of the driving mechanism in such a manner as to allow compensation of the wear sustained by the friction linings of the clutch. 
     To this end, it proposes a travel compensation actuator, in particular for a motor vehicle clutch system, comprising a driving mechanism and a motorised means of operating the said driving mechanism over both outward and return travel, characterised in that it also comprises:
         means of travel compensation, connecting the motor to the driving mechanism, which can be moved by the motor along an adjusted course and along a course of travel of the driving mechanism, with such means of compensation comprising an organ for the adjustment of a bearing block of the said drive mechanism;   and two combined means of unidirectional travel, which are carried by the casing of the actuator and which operate in conjunction with the adjustment organ to advance it by one step in one direction or the other, when the compensation means are displaced in one direction or the other respectively from an intermediary position from their adjustment travel.       

     In this way, according to the present invention, the means of travel compensation, especially in cases where worn friction linings of a clutch have to be compensated, are incorporated in the actuator and not in the clutch mechanism itself, and are thus exposed to much lower stress levels, thereby improving their operating reliability and precision. 
     According to a further characteristic of the invention, the means of travel compensation comprise a slide element, the movement of which is guided in the casing of the actuator and operated by the motor along the aforementioned adjustment and drive travel sections, and a screw-nut arrangement carried by the slide element with the screw forming the drive stop of the driving mechanism, 
     being guided in its movement and immobilised while rotating in the slide element, with the nut being screwed onto the screw and guided in rotation and comprising an external toothing working in conjunction with the two combined means of unidirectional travel when the slide element is dispaced along its adjustment path. 
     In a preferred embodiment of the present invention, the combined means of unidirectional driving comprise two rings mounted in a rotating manner in the slide element and displaying an internal toothing arrangement intended to work in conjunction with the external toothing of the nut, with these two rings being associated with elastic means of return, which subject them to a rotational stress in opposing directions so as to bring them up against the stops 
     The internal toothing of the two rings is in the form of a very open V and comprises a first part arranged obliquely in relation to the axis of the ring and a second part, which is parallel to the axis of the ring, with the oblique parts of the teeth of one of the rings being parallel to the oblique parts of the teeth of the other ring and orientated in the opposing direction. 
     The outer teeth of the nut are in the shape of a diamond and have two faces that are parallel with the axis of the nut and two faces that are obliquely arranged in relation to the axis of the nut, with these obliquely arranged faces being parallel with the oblique faces of the internal teeth of the rings. 
     The oblique faces of the teeth in the rings and in the nut are parallel with the thread of the screw and orientated in the same direction. 
     Preferably, in order to increase the length of the driving mechanism, the slide element is displaced in the direction of the return of the clutch. 
     In one embodiment of the invention, the adjustment and drive paths of the means of compensation are arranged end to end. As an alternative, they may partially overlap. 
     In one interesting embodiment, the actuator is of the effort compensating type and comprises at least one compensating spring, which acts through the intermediary of an organ rolling along a cam or an inclined ramp, which is connected to the driving mechanism, in the direction representing the opening of the clutch. 
     In a general fashion, the actuator in accordance with the present invention is applicable not only to the operation of a clutch, but also to the operation of a gearbox or a braking system within a motor vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be better understood and other characteristics, details and advantages of the invention will become apparent on reading the following description, which is given by way of example together with a number of drawings, in which: 
         FIG. 1  is a schematic view in perspective in partial cutaway of an actuator in accordance with the invention; 
         FIG. 2  is a larger scale view of the means of travel compensation of the actuator shown in  FIG. 1 ; 
         FIGS. 3 and 4  are schematic views in perspective and on a larger scale of a nut and a means of unidirectional movement of the means of travel compensation; 
         FIG. 5  is a schematic illustration of the operating stages of the means of travel compensation in accordance with the present invention; 
         FIGS. 6 and 7  are schematic views in perspective illustrating an alternative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The actuator shown in  FIG. 1  is intended to be used for the operation of the clutch of a motor vehicle and comprises essentially a casing  10  on which is mounted an electric motor  12 , the output shaft of which is connected by a reducing system and a rack (not shown) to a mobile element  14  that is guided and moved inside the casing  10  in a manner perpendicular to the axis of the electric motor  12 , with the said mobile element acting through the intermediary of a pusher member  16  on a clutch system E, for example, on a clutch pressure plate. 
     The mobile element  14 , which is better seen in  FIG. 2 , comprises essentially a slide element  18  activated by the electric motor  12  and is connected to the pusher member  16  by travel compensation means, which enables the axial displacement of the pusher member  16  caused by the wear sustained by the friction linings of the clutch to be compensated. 
     For this purpose, the slide element  18  has an axial passage  20  in which a screw  22  is moved and arrested in rotation, for example, by means of a flat piece formed on one side of the screw  22  and guided by a flat surface that corresponds to the passage  20 . 
     The screw  22  is moved along the passage by the action of a nut  24 , which is screwed onto the screw  22  and rotated in an annular housing of the slide element  18 , with the rotation of the nut  24  in this housing being converted by the internal thread of the nut as it comes into contact with the outer thread of the screws  22  into an axial movement of the screw  22  inside the slide element  18 . 
     The screw  22  is tubular in shape and comprises a cylindrical axial passage  26  opening out on the side of the pusher element  16  and closed at its other end by a base piece against a rear wall  23  of which is pressed a raised flat head-shaped section  28  formed at a distal end of the pusher member  16 . In this way, an axial movement of the screw  22  inside the slide element  18  is translated by a variation of the visible length of the pusher member  16 , thus allowing the axial displacement of the pusher element due to the wear sustained by the friction linings of the clutch to be compensated. 
     The nut  24  comprises a series of diamond shaped teeth  30  distributed around its surface ( FIG. 3 ) and which is intended to work in conjunction with inner toothing  32  of two unidirectional drive rings  34   a ,  34   b  ( FIG. 4 ), which are mounted in a limitedly rotational manner ( FIG. 4 ) inside the slide element  18  are immobilised against any axial movement in relation to the casing  10 . 
     These two rings are intended to be axially crossed by the nut  24  when the slide element  18  is displaced axially in one direction or the other by the electric motor  12  starting from an intermediary position P 1  of its travel being defined between the positions P 0  and P 2 , at which the bottom of the screw  22  is not pressing against the head-shaped section  28  of the pusher member  16  ( FIG. 1 ). 
     The other path of travel of the slide element is defined by the positions P 3  and P 4  and corresponds to the displacement of the pusher member  16  for the opening and closing actions of the clutch. 
     The two unidirectional drive rings  34   a  and  34   b  mounted on the slide element  18  are associated with axial and angular supports  36  mounted on the casing  10 , which limit the axial and the angular movements of these rings during the travel of the slide member  18 , due to the stops or the teeth  38  projecting from the outer peripheries of the rings, coming to rest against the stops  38 . 
     An annular return spring  40  is mounted between the two rings  34   a  and  34   b  and its ends come to rest against the outer stops  38  of these rings providing an angular separation between them. The outer toothing  30  of the nut  24  and the internal toothing  32  of the rings  34   a ,  34   b  are designed in such a way that they have the effect of turning the nut  24  one pitch through its axis when the nut is moved in one direction across a ring  34   a  or  34   b  and of not doing so when it is moved in the opposite direction across this ring  34   a  or  34   b , as will be described below in greater details with the help of  FIG. 5 . 
     The diamond-shaped external teeth  30  of the nut  24  comprise two faces  42  that are parallel to the axis of the nut and two oblique faces  44  that are effectively parallel to each other and connect the two faces  42 . The two faces  42  can be approximately flat. Ideally, the two surfaces  42  form helicoidal surfaces. 
     The internal teeth  32  of the rings  34   a  and  34   b  each comprise a first part  46  situated at the side of the nut, which is oblique in relation to the axis of the ring and a second part  48  on the other side of the nut, which is parallel to the axis of the ring. Similarly for the faces  42 , the part  46  can be approximately flat. Ideally, this part is helicoidal in shape. 
     The first oblique parts  46  of the teeth  32  are parallel to the oblique faces  44  of the external teeth  30  of the nut  24 . 
     Furthermore, the oblique parts  46  of the teeth of the ring  34   a  are orientated in the opposite direction of the oblique parts  46  of the teeth of the other ring  34   b , as can be seen clearly in  FIG. 5 . 
     In this Figure, the different stages of the movement of the nut  24  in both directions in relation to the rings  34   a  and  34   b  from the intermediary position P 1  are represented by the  FIGS. 1 to 10 . 
     In  FIG. 5-1 , the nut  24  is in the position P 1  and its external teeth are in a mid-position between the rings  34   a  and  34   b.    
     In  FIG. 5-2 , the nut  24  has been moved in the direction of the ring  34   b , that is to say in the direction of the position P 2 , and its external teeth  30  come to rest against the ends of the oblique parts  46  of the teeth of the ring  34   b . In this position, the ring  34   b  rests against a fixed stop  36  and cannot rotate around its axis in the direction marked by a downward pointing arrow in  FIG. 5-2 . 
     In  FIG. 5-3 , the nut  24  has again been moved in the direction of position P 2  and its teeth  30 , by sliding along the oblique parts  46  of the teeth of the ring  34   b , have had the effect of turning the nut by one turn in the direction marked by an upward pointing arrow. 
     In  FIG. 5-4 , a rotation of one turn of the nut  24  has been effected, the teeth  30  of the nut have come to rest against the rectilinear parts  48  of the teeth the ring  34   b  and the displacement of the nut in the direction of the position P 2  does not provoke any additional displacement of the nut. 
     When subsequently, as shown in  FIG. 5-6 , the nut  24  is displaced in the opposite direction and returned to the position P 1 , the displacement of its teeth  30  along the rectilinear parts  48  of the teeth of the ring  34   b  does not have the effect of provoking any rotation of the nut or the ring up to the position shown in  FIG. 5-7 . 
     As the displacement of the nut in the direction of the position P 1  takes place, the teeth  30  of the nut come to rest against the oblique parts  46  of the ring  34   b  as shown in  FIGS. 5-8  and induce this to turn in the direction marked by an upwards pointing arrow until the teeth  30  of the nut are released from the teeth of the ring  34   b  as shown in  FIGS. 5-9  are reach the position shown in  FIGS. 5-10 , which corresponds to the position P 1  of the nut. 
     When the teeth  30  of the nut  24  are released from the teeth  32  of the ring  34   b , this latter is returned to its initial position by the return spring and then turns in the direction shown by the downward pointing arrow in  FIGS. 5-10 . 
     It can be seen that this outward and return movement of the nut  24  between the positions P 1  and P 2  has the effect of rotating the nut by one turn around its axis in a direction that is determined by the angle of inclination of the oblique parts  46  of the teeth of the ring  34   b.    
     When the nut  24  is displaced in the other direction, that is to say between its positions P 1  and P 0 , the other ring  34   a  makes it rotate by one turn in the other direction with each outward and return movement. 
     Each rotation of the nut  34  by one turn in one or the other direction is translated by an axial turn of the screw  22 , in one direction or the other, in relation to the slide element  18  and thereby by a visible elongation or shortening of the pusher member  16 . 
     By appropriately adjusting the fixed stops  36  which limit the axial and the angular travel of the rings  34   a  and  34   b , the axial positions P 0  and P 2 , which demarcate the adjustment path, can be defined in relation to the positions P 3  and P 4 , which demarcate the drive path. 
     In the example shown schematically in  FIG. 1 , it can be seen that the slide member  18  can be displaced between its positions P 0  and P 2  without the position of the pusher member  16  being modified and that this adjustment path is separated from the path of the slide member along which it propels the pusher member  16 . 
     The length L of the screw  22 , which can be adjusted by screwing inside the nut, represents the path that can be compensated. 
     Preferably, in order to increase the visible length of the pusher member  16 , the mobile element  14  is displaced in the direction of the return of the clutch. This enables the effort required for the adjustment to be reduced and standardised. 
     For this, it is also advantageous for the helicoidal surfaces of the thread of the screw  22  and the oblique parts of the rings  34   a  and  34   b  to be orientated in the same direction. 
       FIGS. 6 and 7  represent schematically an alternative embodiment, in which each ring  34   a ,  34   b  is an integral part of two longitudinal parallel legs enabling the device to be positioned correctly in relation to the slide member in the actuator casing. 
     The legs  50  of the ring  34   a  situated on the side opposite to the clutch extend from the side opposite the clutch, whereas the legs  50  of the ring  34   b  situated on the side of the clutch extend in the direction of the clutch. 
     The legs  50  are portions of a cylinder, as is clearly shown in  FIG. 7 , and can limit the amount of rotation and axial diplacement of each ring  34   a ,  34   b  by means of stops on the actuator casing  10 . 
     Furthermore, the actuator in accordance with the present invention is advantageously of the effort compensating type and comprises, as shown in 
       FIG. 1 , a compression spring  52  arranged in the casing  10  in a manner parallel to the motor and acting, through the intermediary of a rolling element  54 , on an inclined ramp or on a cam  56  carried by the mobile element  14 . The force exerted by the spring  52  on the mobile element forces the latter in the direction of the opening of the clutch, which has the effect of reducing the torque to be provided by the motor to operate the clutch.