Abstract:
A friction clutch for a motor vehicle is provided. The friction clutch is disengaged when unpowered and engaged by axial movement of an actuating lever operated by an actuating device via a further lever. In the event of overtravel traversed beyond the unpowered state the friction clutch compensates for an incorrect axial gap between the friction surfaces provided in a friction clutch caused by wear. The friction clutch includes a switchable stop provided on the actuating device. The switchable stop releases an overtravel path for the further lever when a detected engagement path of the further lever exceeds a predefined length.

Description:
This claims the benefit of German Patent Application No. 10 2007 028 669.6, filed on Jun. 21, 2007 and hereby incorporated by reference herein. 
     The invention relates to a friction clutch engaged under pressure by an actuating device, having an adjusting device to compensate for an incorrect gap between the friction contact surfaces. 
     BACKGROUND 
     Friction clutches of this sort are known for example from DE 10 2005 003 505 A1. In general, such incorrect gaps are brought about over the operating life of the friction clutch through wear of the friction linings of the clutch plate and procedures setting the lining resiliency. An expedient way to compensate for wear is through compensating for the incorrect gap by setting the ideal axial spacing of the friction surfaces of the clutch relative to each other by twisting ramp/opposing ramp systems that operate on the circumference opposite each other in such a way that the desired spacing relationships are again produced between the actuating lever, which may take the form of a diaphragm spring, and a stop on the clutch cover. 
     When overtravel is used as the means of compensating for the incorrect gap, the friction clutch is operated by actuation beyond the engaged or disengaged state, by pressing or relaxing the actuating lever accordingly by the actuating system beyond such state. As that is done, the actuating lever lifts off of a device that blocks the ramp/opposing ramp system, so that the latter—usually supported by a corresponding power storage device—can compensate for the incorrect gap by turning the ramps contrary to the opposing ramps. The magnitude of the adjustment depends substantially on the position of the actuating lever. For this type of adjustment by producing overtravel, adjusting systems have proven especially advantageous which provide a device between the ramp/opposing ramp system and the actuating lever by means of which an adjustment is accomplished not by covering the entire overtravel but by adjusting in increments. To this end a so-called drive spring-worm gear device can be used, in which the overtravel and the resulting additional axial motion of the engagement bearing in the direction of disengagement, and the tilting of the actuating lever which in turn results, produces tangential travel of a tongue provided on the drive spring, which thereby jumps over a tooth of the worm gear wheel. At the next engagement procedure, the worm gear twists the ramp/opposing ramp system by a predefined amount. If the wear is greater than the amount adjusted by the engagement travel, the adjustment is repeated in the subsequent engagement procedures until the wear has been compensated for. 
     Typical actuating systems fulfill the function of axially displacing the actuating lever, by prescribing a defined engagement travel distance depending on the desired degree of frictional engagement between the clutch friction surfaces and the output-side friction linings for example of a clutch plate. In this connection, DE 10 2004 009 832 A1 reveals an actuation system in the form of a lever system in which a lever acts on the actuating lever through a roller bearing. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to improve a friction clutch of the named species in such a way that the reproducibility of the adjustment can be improved further. It should be possible to make an improvement without high costs, and it should be adaptable to the existing actuating systems. 
     The invention provides a friction clutch for a motor vehicle which is disengaged when in the unpowered state and is engaged by axial movement of an actuating lever operated by an actuating device by means of a lever, and an incorrect axial gap between friction surfaces provided in the friction clutch is compensated for during overtravel beyond the motion in the unpowered state, where a switchable stop provided on the actuating device releases the lever for overtravel when a detected engagement travel distance of the lever exceeds a prescribed value. Through the choice of two conditions, namely a so-called overtravel stop at which the clutch can be adjusted intentionally and a stop for conventional clutch procedures, exact positioning of the lever and thus of the actuating lever on the friction clutch can be prescribed, so that in the event that an incorrect gap requires compensation, reproducible conditions may prevail. Through the exact setting of the stop, the actuating lever may be at the position that allows adjustment to the original state of the clutch. Furthermore, the switchable stop may make it possible to use actuating devices that return automatically to the non-tensioned state, for example through spring force, so that a complicated approach to this non-tensioned state through use of a clutch actuating system may not be needed. Depending on whether an adjusting procedure is to be initiated or the friction clutch is to be disengaged normally, the actuating device returns to the stop of the non-tensioned state or—if an adjustment is to be made—with the switchable stop swiveled; in that way it moves to the housing stop in a way that defines further travel for the lever, which may be necessary to adjust the friction clutch. 
     It can also be of benefit if, after the incorrect gap has been compensated for, the stop again prevents the overtravel. This means that the stop which has been moved out of contact range of the lever may be moved back into the contact range of the lever after an adjustment has been made, so that it can again fulfill its function as a stop until the next adjustment. In an advantageous design, this can be accomplished by having the lever itself switch this stop back again after an adjustment. 
     Viewed from the perspective of its function, an advantageous exemplary embodiment can comprise a friction clutch in which, in the course of an actuation of the friction clutch, the lever of the actuating system may carries with it a controlling component provided with a ramp, against a first return force. This controlling component may then works together with that ramp, acting on a controlled component that is provided with an opposing ramp and has a stop for the lever, in that the ramps slide on each other and the opposing ramp may be forced through the ramp provided on the controlling component and may thereby be moved perpendicular to the axial movement described by the lever against a second return force. With the lever displaced axially during an engagement process, this may results in swiveling of the stop attached to the controlled component, so that the stop may moves away from the contact surface of the lever. 
     With increasing engagement travel, which is a measure of the increasing degree of wear of the friction clutch and thus a measure of the need for an adjustment to compensate for the incorrect gap, at the engagement distance prescribed for a necessary adjustment provision may be made so that the controlling and controlled components may be fixed in their current position. In that position, as the friction clutch is disengaged it becomes ineffectual for the lever as a result of having been swiveled out with the controlled component, and the lever runs back until it reaches an axially set-back housing stop, at which compensation for the incorrect gap may ensues as a result of the great deflection of the actuating lever. 
     It has been found especially advantageous here if the lever has an additional device, for example a ramp, which moves the controlled component beyond the current position against the second return force when the overtravel is taken, so that the two components may be released again from their fixed position. 
     The previously described ramp mechanisms, which are deflected against corresponding return forces during clutch actuation processes, can be realized simply through beneficial design of the components in the form of leaf springs. For example, the controlling component can be formed by a controlling leaf spring clamped in place on one end, whose free end has a ramp that is carried along by the lever during an engagement process against the first return force formed by the leaf spring constant. In this way, the function of the ramp can be combined with the element that brings about the return, in a component that is easily produced. 
     Furthermore, the controlled component can be formed by a controlled leaf spring clamped in place by one end, whose free end has a ramp that corresponds to the ramp of the controlling leaf spring, and which during an engagement process may be moved contrary to the return force from the controlling leaf spring, which is formed by the leaf spring constant and acts perpendicular to the first return force, while a stop attached to the controlled leaf spring swivels out of a contact surface with the lever as the engagement travel distance increases. Here too, the function of the ramp and of the force that resets the latter may be combined in a single component. It is especially advantageous if both leaf springs are produced as single pieces, for example by being stamped out of suitable spring steel and then bent according to their function. Corresponding behavior of the two ramps means that their shapes may be matched with each other in such a way that the controlled leaf spring exerts a force on the ramp while being displaced, so that through appropriate oblique positioning of the ramps, the displacement of the ramp of the controlling component brings about a reversal of direction of the controlled component. To this end, the ramp surfaces may be advantageously oriented parallel to each other. To reduce friction forces of the ramp surfaces on each other, the surfaces can be treated appropriately, for example by coating, polishing and/or greasing. 
     As soon as an engagement path is detected that requires an adjustment of the friction clutch, according to the invention the stop should be swiveled out, so that the lever of the actuating system can execute an overtravel. Advantageously therefore, when the ramps are in such a position relative to each other an opening may be provided in one leaf spring, into which a locating key of the other leaf spring meshes in such a way that the two leaf springs are locationally fixed in relation to each other in this position. For example, the locating key can snap into the opening elastically. Here the locating key can be provided in the controlling or controlled component and the opening correspondingly in the other component. The fixing causes the controlling component to remain in its position, which corresponds to an engagement distance at which an adjustment may be made. It goes without saying that in this situation the lever can nevertheless be moved back past the untensioned position to the housing stop, because while the controlling leaf spring may be carried along in the direction of engagement by a one-sided guidance system, in the disengagement direction it remains in contact with the lever because of the return force. But the fixing on the controlled leaf spring retains the latter in this position against its return force. On the other hand, the controlled leaf spring also, and with it the stop attached to it, which can be riveted, press-fitted, bolted, welded or connected in some other way to the leaf spring, may remain in its swiveled-out position, so that the lever can traverse the excess distance. 
     To block this overtravel for the other actuation process until the next adjustment may be due, it is advantageous if the fixing of the two components is released again automatically immediately after the adjustment is completed. To this end, after a compensation for the incorrect gap the position fixing can be suspended by means of an unblocking profile provided on the lever, such as an unblocking lug, where the latter moves the controlled leaf spring against the controlling leaf spring against the second return force far enough so that the opening and the locating key are separated from each other again. This unblocking profile can also be formed by a ramp, which meshes with an opposing profile of the controlled leaf spring and shifts it accordingly. 
     The forms of all profiles may be matched advantageously to the motion sequences. Corresponding designs not only with a linear surface, but also as curved, epicyclic and otherwise-shaped surfaces may be components of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in greater detail on the basis of  FIGS. 1  through  7 . The figures show the following: 
         FIG. 1 : a schematic depiction of a friction clutch with an adjusting device, 
         FIGS. 2   a - 2   d : a schematic depiction of various functional states of a switchable stop, 
         FIG. 3 : a lever engager with a switched stop, 
         FIG. 4 : an exemplary embodiment of a switched stop made of leaf springs, 
         FIG. 5 : a section along cutting line A-A through the exemplary embodiment of  FIG. 4 , and 
         FIG. 6 : a side view of an exemplary embodiment of a switched stop. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic depiction of a clutch system  1  with a friction clutch  2 . Friction clutch  2  consists essentially of an opposing pressure plate  6 , a clutch plate  5 , a pressure plate  3 , a clutch cover  4  and an actuating lever  10 , which is constructed here as a diaphragm spring. The friction clutch  2  depicted in  FIG. 1  as an example is what is known as a pressure engaged clutch, which is disengaged when in the force-free state, and is caused to engage when actuating lever  10  is subjected to a force specified by the disengager through an axial movement of actuating lever  10 , by bringing the frictional surfaces of the clutch plate  5  on the one hand and the friction surfaces of pressure plate  3  and of opposing pressure plate  6  into frictional engagement. Accordingly, in the depicted exemplary embodiment the clutch actuating device is what is known as a lever engager  11 , and the bearing on actuating lever  10  is an engagement bearing  12 . It goes without saying that in so-called pressure disengaged clutches a corresponding use of the clutch actuating device as a lever disengager can be similarly advantageous, and is therefore also included in the disclosure. 
     The lever engager for friction clutch  2  consists substantially of a lever system which is situated on a support  13  and firmly connected to the housing. The lever engager acts by means of a lever  7  of length L on engagement bearing  12 , which is situated around a transmission input shaft and which as an axial bearing evens out the differences in speed of rotation between the friction clutch  2  turning at engine speed and the lever  7  fixed to the housing. 
     In  FIG. 1  the spring device, here in the form of a compression spring  9 , the radially outer end of lever  7  with the contact point A, a roller unit  8  that is movable between the two ends of lever  7 , with the contact point B, and the contact point C on the radially inner lever end resting on engagement bearing  12 , are essentially in a single line of action. Friction clutch  2  is operated by shifting roller unit  8 , which causes lever  7  to be moved at contact point C against the force of compression spring  9 . In the exemplary embodiment shown, friction clutch  2  is disengaged; in consequence the contact points A and B coalesce when the roller unit is at its radially outermost position. To engage friction clutch  2 , movable roller unit  8  runs directly inward on an essentially radial partial surface of lever  7 , with support on a base plate or on the wall of the transmission housing. Lever  7  is not shown flat in  FIG. 1 . Rather it is to a certain extent concave-shaped, from the perspective of roller unit  8 , which enables the development of force on the actuating lever  10  and thus on the friction surfaces of the friction clutch to be adapted. Roller unit  8  comprises a plurality of rollers  31 , which roll in one case on the surface of lever  7  and in the other case on the base plate, depending on the direction of running. 
     At the position of roller unit  8  or of contact point B shown in  FIG. 1 , the tensioning force of energy storage element  9  acts on a lever arm with a length of zero. For that reason, no torque from lever  7  is able to act on engagement bearing  12 . If roller unit  8  is now moved radially toward engagement bearing  12 , the lever length between energy storage element  9  and fulcrum  8  continues to increase. At the same time, the lever length of the contact B to contact point C on engagement bearing  12 , carried along with roller unit  8 , becomes shorter. Shifting contact point B brings about a change in the force on engagement bearing  12 , causing the engagement force to become greater the closer contact point B approaches engagement bearing  12 . Conversely, because of the force relationships, absence of a force on roller unit  8  causes it to be moved radially outward away from engagement bearing  12 , so that friction clutch  2  is disengaged again. That makes it possible to achieve a self-disengaging effect of friction clutch  2  in a simple manner. This effect is especially advantageous, in particular when used in a double clutch. 
     For example, in consequence of wear in the friction linings of the clutch plate  5  or relaxation of the lining resiliency between the friction linings and the clutch plate, the axial gap between pressure plate  3  and opposing pressure plate  6  is subject to changes over the operating life of friction clutch  2 , which are manifested in part in a lengthening of the engagement travel of actuating lever  10 . Such changes to the engagement path are manifested negatively in the design of the actuation system, since the components and the forces that occur in the friction clutch and in the actuation system should be designed for these changes over the service life. In the friction clutch  2  an adjusting device  14  is therefore provided which sets a compensation between clutch cover  4  and actuating lever  10  that corresponds to the incorrect gap between pressure plate  3  and opposing pressure plate  6 , in that ramps that arise between these parts in the circumferential direction increase an axial interval through twisting. In the non-adjusting state of the clutch, these ramps are impeded for example by friction with regard to twisting in the circumferential direction, and thus in terms of an unwanted adjustment. If actuating lever  10  is moved more than a predetermined amount in the disengagement direction, it lifts off of adjusting device  14 , and the ramps of the adjusting device can be twisted in the circumferential direction—supported for example by a spring device—until they have compensated for the gap that came about through the overtravel of the actuating lever  10 , which ideally corresponds to the error in the gap. It goes without saying that other advantageous adjusting devices—such as for example the adjusting device described earlier with a spring-loaded worm gear, which compensates for only a limited engagement distance at each adjustment, —can also be beneficial, in particular if it is important to prevent the setting of excessively large adjustment paths. 
     It is therefore of critical importance for correct adjustment to set a correct overtravel distance. The lever engager  11  is therefore designed so that when friction clutch  2  is not engaged the lever  7  returns to a neutral position automatically, for example by spring-loading or driven by an actuator, for example an electric motor; the neutral position is formed in the non-actuating state by a stop  15  firmly attached to the housing, on which in addition a switchable stop  16  is situated. The axial positioning of both stops is laid out so that no adjustment occurs. If it is found as a result of an extended axial engagement path that an adjustment is necessary, the switchable stop  6  is removed from the axial path of the lever  7 , so that the latter can traverse a longer overtravel distance beyond the neutral position, which results in an exact adjustment on the adjusting device  14 . More advanced designs for how a switchable stop can be constructed to switch automatically will be described in the subsequent figures. 
       FIGS. 2   a  through  2   d  show a schematic view of a switchable stop  16  in various operating or functional states. The constructional features underlying  FIGS. 2   a - 2   d  will be described first. A controlling component  17  and a controlled component  18  are assigned to lever  7  in order to act on the actuating lever  10  ( FIG. 1 ) of the friction clutch. The controlling component  17  is carried along by lever  7  on one side in the engagement direction E of the friction clutch, against a return force of a spring device  21 , and has a ramp  19  by means of which the controlled component  18  is displaced perpendicular to the direction of motion of engagement direction E against a return force of a spring device  22  through the action of ramp  19  on a corresponding opposing ramp  20  provided on the controlled component  18 . Furthermore, controlled component  18  has a locating key  23  and lever  7  an unblocking profile  24  that enters into interaction with the unblocking edge  25  of controlled component  18 . Controlled component  18  with its pivotable stop  16  gives the possibility of switching an overtravel path that depends on the engagement path E. 
     The function is depicted in four stages in  FIGS. 2   a  through  2   d .  FIG. 2   a  shows the untensioned position of a disengaged friction clutch. Lever  7  rests on stop  16   a  in its maximally retracted position in this stage; both components  17 ,  18  are in a non-tensioned position except for desired pre-tensioning of spring devices  21 ,  22 . 
       FIG. 2   b  shows the state of an engaged friction clutch in which adjustment is not yet necessary. The carrying along of controlling component  17  against the force of spring device  21  effected by a shift of lever  7  in engagement direction E brings about a displacement of controlled component  18  against the force of spring device  22  through opposing ramp  20  sliding off of ramp  19 . While that already swivels out the switchable stop  16  which is integrated into controlled component  18  in proportion to the distance covered by the lever, when the clutch is disengaged in this state controlled component  18  along with stop  16   a  returns to the initial position, since controlled component  18  is moved back again by its spring device. 
     In  FIG. 2   c  the engagement distance has become so great that the edge of the locating key  23  has been passed. The interval of the locating key is chosen so that a necessary adjustment is initiated when the edge is passed. As a result of the application of the force of spring device  22 , controlling component  17  and controlled component  18  are fixed relative to each other. When the friction clutch is disengaged again, lever  7  is moved contrary to the direction of engagement without controlling component  18 . Since controlled component  18  also does not return to its starting position, stop  16   a  is not operative for lever  7 , and an overtravel is set to a stop located further back and fixed on the housing, which results in an adjustment process on the friction clutch with compensation for the incorrect gap. 
       FIG. 2   d  depicts the unblocking of the fixing of the two components  18 ,  19  relative to each other. When it overtravels to the stop affixed to the housing, lever  7  acts here by means of its unblocking profile  25  on the unblocking edge  25  provided on controlled component  18 . Through the action of lever  7  on unblocking edge  25 , controlled component  18  is shifted further against the effect of spring device  22 ; the controlled component is released and returns to lever  7 , supported by spring device  21 . At the next engagement process, opposing ramp  20  of controlled component  18  then finally comes into contact again with ramp  19  of the controlling component. 
       FIG. 3  shows an exemplary embodiment of a lever engager  11  with a switchable stop  16 . Lever  7  is moved by a roller unit against the effect of the compression springs  9 ; at the same time a corresponding axial motion occurs at the lever ends  26 , which is transmitted through an engagement bearing to the actuating lever of the friction clutch. See  FIG. 1  for the principle of operation. 
     In the exemplary embodiment shown, the switchable stop  16  is made up of two leaf springs  27 ,  28  joined together in a single piece, which are clamped firmly to the housing by one end and when pivoted return by themselves to the starting position, so that the spring devices depicted in  FIGS. 2   a - 2   d  can be dispensed with or are integrated into the leaf springs. The controlling leaf spring  27  is flexible in the direction of motion of lever  7 , and is carried along by the latter by means of a lug  29  provided on the lever. The controlled leaf spring  28  is flexible perpendicular to the direction of motion of lever  7 , and receives the stop  16   a  at its end. 
     To clarify the function and arrangement of the switchable stop  16  of  FIG. 3 , it is depicted schematically in  FIG. 4  in an isolated view. Advantageously, switchable stop  16  is stamped from spring sheet steel and is appropriately pre-bent. The stop  16   a  is situated at the non-clamped end of controlled leaf spring  28 . For example, an appropriately shaped metal piece is riveted, spot welded or welded on. A profile  30  is formed in the controlling leaf spring  27 , for example by stamping, which interacts with a correspondingly formed opposing profile  31  when in the installed state, so that when controlling leaf spring moves  27  while being carried along by lever  7  ( FIG. 3 ), controlled leaf spring  28  and thus stop  16   a  are moved in the direction of pivoting S. Corresponding to a position in which an adjustment of the friction clutch is to take place, controlled leaf spring  28  has an opening  32  which is engaged by a locating key  33  provided in leaf spring  27 , for example projecting from it, when opening  32  is reached, bringing about a fixing of the two leaf springs relative to each other. The section along cutting line A-A depicted in  FIG. 5  makes the arrangement and design of the opposing profile  31  with the opening  32  clear, which is acted on by profile  30  with locating key  33 . 
       FIG. 6  shows another slightly modified alternative of a switched stop  16  in side view, with a controlling leaf spring  27  and a controlled leaf spring  28  to which the stop  16   a  is attached. Controlling leaf spring  27  itself has a driver lug  34 , which lies on or is hooked into the lever of the actuating system. In this way, an appropriately designed lever can remain unchanged. Profile  30  and opposing profile  31  are designed in accordance with the embodiments shown in  FIG. 4 . Furthermore—contrary to the exemplary embodiments described in relation to  FIGS. 2   a - 2   d —an unblocking lug  35  is provided on the controlling leaf spring  27  which separates the fixing between the opening and the locating key when acted on by the lever. 
     REFERENCE LABELS 
     
         
           1  clutch system 
           2  friction clutch 
           3  pressure plate 
           4  clutch cover 
           5  clutch plate 
           6  opposing pressure plate 
           7  lever 
           8  roller unit 
           9  compression spring 
           10  actuating lever 
           11  lever engager 
           12  engaging bearing 
           13  support 
           14  adjusting device 
           15  fixed stop on the housing 
           16  switchable stop 
           16   a  stop 
           17  controlling component 
           18  controlled component 
           19  ramp 
           20  opposing ramp 
           21  spring device 
           22  spring device 
           23  locating key 
           24  unblocking profile 
           25  unblocking edge 
           26  lever end 
           27  controlling leaf spring 
           28  controlled leaf spring 
           29  lug 
           30  profile 
           31  opposing profile 
           32  opening 
           33  locating key 
           34  driver lug 
           35  unblocking lug 
         E engagement direction 
         S direction of swiveling