Abstract:
The invention relates to a clutch assembly which is designed to be self-adjusting. The invention relates to a multi-plate clutch assembly as well as to a method for operating a multi-plate clutch which can be produced cost-effectively in a structurally simple manner and which has an improved release characteristic. In particular the clutch has a more constant release characteristic with a high operating accuracy over the entire service life.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a self-adjusting clutch assembly, in particular for commercial vehicles or tractors, as well as to a method for operating a clutch assembly. 
     2. Description of Related Art 
     Clutch assemblies having a multi-plate clutch are already known. 
     These known clutch assemblies which are used in the case of commercial vehicles or tractors, have a driving clutch as well as a clutch for additional implements. These clutches are operable separately through a clutch pedal or through a hand lever. 
     These known clutch assemblies are suitable for use in vehicles where a separate clutch is to be provided for driving and a separate clutch is to be provided for the implements. 
     These known clutches all have the drawback that when the clutch discs wear out the operating point of the clutch is shifted so that the release force required to operate the clutches varies accordingly. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to provide a clutch assembly for a multi-plate clutch as well as a method for operating a multi-plate clutch which can be produced cost-effectively in a structurally simple manner and which has an improved release characteristic, more particularly a more constant release characteristic with a high operating accuracy over the entire service life. 
     Thus according to the invention it is proposed to design a clutch assembly, more particularly a clutch assembly for a motor vehicle, such as a commercial vehicle or a tractor, with at least a self-adjusting clutch device with at least one clutch disc and at least two contact pressure plates. 
     The clutch assembly preferably has a clutch disc which can be coupled, more particularly with keyed engagement, to two contact pressure plates. 
     It is also preferable if the clutch assembly has a number of clutch discs, such as for example two clutch discs which can each be coupled, more particularly with keyed engagement, to one or more contact pressure plates. 
     The invention is particularly advantageous because the operating force of the clutch assembly can be kept within a predetermined tolerance band as a result of the self-adjusting device of the clutch assembly or of the clutches. The width of this tolerance band is preferably aimed at zero. 
     According to a particularly preferred embodiment of the invention a device is provided which keeps the installation position of a plate spring substantially unchanged throughout the entire wear on the lining and thus keeps the release force of the clutches, more particularly of two clutches, unchanged and guaranteed throughout the service life. The plate spring thereby preferably loads pressure plates which act on the linings or the discs. 
     This device which keeps the installation position of the plate springs substantially constant preferably has at least one cast ring and at least two sheet metal tapered rings wherein one of these sheet metal tapered rings is connected rotationally secured to a pressure plate, more particularly to the pressure plate on the transmission side. This device also preferably has two circumferentially mounted compression springs which in the event of wear at least partially or under predetermined conditions turns one of the tapered rings relative to the other tapered ring until the wear in the axial direction is compensated. This device is preferably coupled to a driving clutch or to a clutch on the transmission side. 
     In a particularly preferred embodiment during activation of the clutch through an operating mechanism, for example through a lever, the cast ring is displaced in the axial direction, with a stepped bolt or friction device causing a pressure plate to lift off from the friction lining or disc. More particularly the friction force applied to the stepped bolt is greater than the operating axial compression spring force—according to the geometry of the taper. 
     It is preferable if, in the event of wear on the clutch disc on the engine side or on the transmission side, as a result of force applied by a plate spring a contact pressure plate, more particularly a pressure plate on the engine side, draws the stepped bolt through the bolt head of this stepped bolt out from the friction device and thus release a gap at a shoulder or ledge of the stepped bolt. 
     Then preferably when operating a clutch, more particularly a clutch on the transmission side, through a lever the cast ring is moved up to the shoulder or to the ledge of the stepped bolt so that the tapered rings can be turned relative to each other under the action of a compression spring force acting on at least one of these tapered rings, preferably on both tapered rings, so that the wear in the axial direction is compensated and the plate spring swings back again in its original installation position. The level of the release force of the clutch device thus corresponds again to the level in the new state or in the substantially unworn state. 
     Thus according to the invention an assembly of several clutches is provided wherein the release characteristic of at least two of these clutches is constant or unchanged over the entire service life of the clutches or at least an element of these clutches. An element of this kind over the service life of which the release characteristic of the clutch or the release characteristics of the clutches is constant is in particular at least a disc or at least a clutch lining of the clutch assembly. 
     The element over the service life of which the release characteristic of the clutch or clutches is constant is preferably an element which has the fundamental property of influencing the release characteristic of the clutch assembly. 
     It is proposed for example that an element, such as for example a friction lining or a disc is provided which when changed or shifted in position would or does basically influence the release characteristic of the clutch or one of the clutches. Despite the presence of such an element the release characteristic is preferably kept substantially constant. This is achieved for example in that the influence which the thickness of the friction lining or the thickness of the discs has on the release characteristic is substantially compensated by a self-adjusting device. 
     According to the invention it is thus proposed that a clutch assembly having at least one clutch disc and at least two contact pressure plates is provided with an adjustment device for compensating at least in part changing or changed operating conditions of the clutch device. 
     By operating conditions of the clutch assembly are meant here in particular the characteristic values of the clutch assembly or characteristic values which characterise the operating process of the clutch assembly. By way of example the operating time for releasing the clutch or the operating force or the time path of the operating force or the like can be considered as an operating condition. 
     It is also preferable if predetermined operating conditions or predetermined operating characteristic values are set whereby when these are changed or at the start of a change the adjustment device triggers, more particularly independently or automatically, measures for compensating this change. According to the invention it is preferable if the adjustment device controls or regulates predetermined positions or relative positions of structural elements. 
     This problem is further solved by a clutch assembly having at least one clutch disc and at least two pressure plates. 
     Thus according to the invention it is proposed to provide a clutch assembly with at least one spring device, more particularly a plate spring device, wherein the position of the plate spring device can be controlled or regulated by a control or regulating device. The plate spring device thereby preferably acts on the contact pressure plate. The plate spring device thereby preferably acts on the contact pressure plates so that the pressure plates when the operating device for operating the clutch is not activated are pressed against the friction linings or the discs of the clutch assembly so that the clutches are substantially in a closed state. 
     It is however also preferred if when the operating device of the clutch assembly is not activated the spring device or the plate spring device holds one or more of the pressure plates in an opened state so that the relevant clutch is substantially opened. 
     Two contact pressure plates are thereby preferably provided to form when the clutch is closed a positive, more particularly a keyed, connection with the clutch discs or friction linings. The plate spring device thereby preferably tensions the contact pressure plates between the clutch discs. 
     It is thereby preferred if a predetermined operating characteristic is maintained within a predetermined interval with a predetermined interval length by the regulating device or control device. More particularly it is preferred if the operating characteristic is maintained within an interval so that a maximum permissible upper deviation and a maximum permissible lower deviation is defined for each operating point. It is also preferable if the maximum upper deviation and the maximum lower deviation agree with each other and is substantially the same for all operating points of the operating characteristic. 
     It is preferred if the interval length of the interval aims at being zero so that the operating characteristic is actually maintained substantially constant. 
     According to a particularly preferred further development of the invention the clutch assembly is provided with at least one adjustment device by which at least one clutch characteristic value can be regulated in dependence on the wear on the clutch, more particularly the wear on the clutch discs or linings. 
     An adjustment device is preferably provided by which in dependence on at least one operating characteristic value, such as for example the spring force existing in a predetermined state of the plate spring device, at least a further characteristic value of the plate spring device can be adjusted so that the spring force of the plate spring device is regulated substantially to a predetermined value under predetermined conditions. 
     Thus according to the invention it is proposed for example that the position of the plate spring device under predetermined conditions is displaced in dependence on the spring force of the plate spring device so that the spring force of the plate spring device again assumes its original value. It should be noted that predetermined conditions hereby preferably exist. By way of example a predetermined position is set of the pressure plates (e.g. extreme position) or a predetermined position of the operating lever of the operating device of the clutches (e.g. extreme position). 
     According to a particularly preferred embodiment of the invention the adjusting device or the self-adjusting device for adjusting the clutch device or the clutches is designed to be path-controlled. 
     According to a particularly preferred embodiment of the invention the clutch device has at least one operating device, such as for example an operating lever, for operating the clutch. It is preferable if separate operating devices are provided for the different clutches, i.e. more particularly for different spots at which the force flow can be selectively interrupted or closed. It is also preferable if a single operating device, such as for example a single operating lever or the like is provided for operating several clutches. 
     According to a particularly preferred embodiment of the invention during the course of the self-adjusting process of the clutch assembly, or clutch devices, a force equilibrium is set, more particularly increasing. It is also preferred if with a path-controlled adjustment device during the self-adjusting process a force equilibrium is increasingly set. By way of example the position of a plate spring device is hereby regulated or controlled whereby the force applied by the plate spring device interacts with other forces so that a force equilibrium is set. 
     A particularly preferred clutch assembly according to the invention has n clutch discs and/or m clutches and/or p pressure plates wherein n, mεN and pεN≧2. 
     A clutch assembly according to the invention preferably has two clutches which in a particularly preferred embodiment are both self-adjustable. 
     It is particularly preferred if the clutches, more particularly the two clutches, are self-adjusting by an identical adjustment device. It is thereby particularly preferred if the self-adjusting process is substantially in part identical substantially independently of the identity of the worn clutch discs. 
     By way of example in the event of wear on any one clutch disc or any one friction lining a plate spring device adopts a position which it would likewise adopt if wear of a similar amount were to appear on any other clutch disc or any other friction lining or if the sum of the wear on several clutch devices would correspond to this wear. In the adjusting process the original position or installation position of this plate spring device for example is produced again so that independently of where the wear has occurred, during the adjustment process a substantially identical first position of the plate spring device is changed each time into a likewise substantially identical second position of the plate spring device. 
     According to a particularly preferred embodiment of the invention the clutch assembly or the clutches has/have n clutch discs and p pressure plates wherein an adjustment device is related to the p pressure plates. By this is meant that the adjustment device takes into account the potential wear occurring on each friction face of a clutch disc which forms a friction-locking connection at least at times with one of the p pressure plates so that the relevant clutch is closed. 
     According to a particularly preferred embodiment of the invention the adjustment or self-adjustment of the clutch assembly is carried out under predetermined conditions. By way of example the adjustment or self-adjustment is always carried out when the clutch is released. 
     It is also preferred if the self-adjustment is undertaken during engagement of the clutch. 
     According to a particularly preferred embodiment of the invention a device is provided for preventing uncontrolled adjustment of the adjustment device. A device of this kind has for example a pin, such as a bolt or a stepped bolt. A device of this kind for preventing an uncontrolled adjustment of the adjustment device is preferably designed as a friction device and/or as a clamping device. It is thereby ensured by a friction and/or clamping device of this kind that an adjustment is only possible under predetermined conditions, such as for example in the presence of predetermined force conditions. 
     These predetermined forces can be determined for example by geometric conditions, such as in particular the geometric conditions of the clutch discs, thus e.g. the question of the presence or absence of wear. 
     According to a particularly preferred embodiment of the invention adjustment is carried out (automatically) so that with the clutch closed the pressure plates apply each time substantially a constant force on the clutch discs throughout the service life. 
     A motor vehicle with clutches according to the invention preferably has at least one driving clutch and/or at least one clutch for assemblies. 
     According to a particularly preferred embodiment of the invention the adjustment device has at least a first and a second device wherein the first device releases an area in the event of wear on at least one of the clutch discs. By way of example a lash or play is produced in the event of wear. This area or this play is eliminated or compensated again by the second device for removing the wear-conditioned influence on predetermined operating characteristic values of the clutch or clutch adjustment process under predetermined conditions, thus in particular at predetermined time points or under predetermined conditions. By way of example an element, such as a stepped bolt, is mounted with friction engagement in a contact pressure plate. The friction engagement existing between this bolt or this element and the pressure plate can thereby be overcome under predetermined conditions whereby a relative displacement of the element opposite the pressure plate is produced in particular by a first (part) device. This relative displacement preferably corresponds to the wear which has appeared on at least one of the clutch discs. 
     As a result of this relative displacement of the bolt opposite the pressure plate the bolt also changes its position relative to a further element, such as for example a further plate aligned parallel with the pressure plate. 
     In order to compensate the wear-conditioned influences on the clutch process the relative displacement which the bolt has undergone relative to the additional plate, such as intermediate plate, is then compensated under predetermined conditions by a second device. The relative position of the further plate (intermediate plate) opposite the aforementioned pressure plate is hereby preferably changed. 
     The relative displacement between the further plate (intermediate plate) and the pressure plate thus preferably also corresponds to the wear which has appeared. 
     If now for example the distance has changed between at least one of two friction linings and at least one of two clutch discs, since at least one of these clutch discs has worn, then for example the path change between these clutch discs is compensated through a change in the spacing between an intermediate disc and a pressure plate whereby the interspace between the friction linings is filled out more particularly by a series connection of the pressure plate, the intermediate plate and a spring device, such as plate spring device, and where applicable further substantially rigid elements. 
     According to a particularly preferred embodiment of the invention the clutch assembly according to the invention has at least one sensor device for detecting a relative movement between different pressure plates. This sensor device detects more particularly a changed relative position of the pressure plate under predetermined conditions, By way of example this sensor device detects a changed maximum spacing between the pressure plates. This maximum spacing is for example determined by the spacing of two friction linings or discs. The spacing changes as a result of the wear on these friction linings. 
     According to a preferred embodiment of the invention this sensor device has at least one bolt. It is also preferred if the sensor device or adjustment device is coupled to at least one operating element for operating at least one of the clutches so that the adjustment or detection of a relative movement is automatically undertaken during operation of this operating element. 
     According to a particularly preferred embodiment of the invention the sensor device is coupled to at least one component part which is moved during an operating process of one of the clutches in dependence on the operating movement. 
     A component part of this kind is for example an intermediate lever. 
     According to a particularly preferred embodiment of the invention the adjustment device and/or the sensor device has at least one clamping or friction device. A clamping or friction force is preferably applied by a friction or clamping device of this kind. This clamping or friction action is provided in particular to connect elements which are or are to be coupled together under first conditions and which are to be mounted movable relative to each other under second predetermined conditions. 
     By way of example a clamping or friction connection of this kind is provided between a bolt, more particularly a stepped bolt, and one of the pressure plates. 
     It is preferable if a predetermined clamping or friction force can be applied by the friction or clamping device and which is produced for example by a fitting with oversize, such as a close tolerance or transition fit, or by means of a spring device or the like. 
     By way of example the friction or clamping device has a clamping screw which, screwed in axially or circumferentially, applies in the radial direction a clamping force on a bolt device. A screw of this kind is screwed into the pressure plate for example and contains in its inner space a bolt device or stepped bolt device. It is also preferred if a clamping screw of this kind is formed as a type of clamping sleeve. 
     It is preferred if a substantially adjustable clamping force or friction force can be applied by the clamping screw or sleeve or friction or clamping device. 
     By way of example a substantially constant clamping force can be applied throughout the service life by the clamping or friction device or the clamping screw or sleeve whereby this clamping force is exerted preferably on a bolt device, such as a stepped bolt device and thus holds this stepped bolt device always fixed opposite the pressure plate when the relative force between the pressure plate and stepped bolt is less than a relative force, which is predetermined in terms of direction and size, between the stepped bolt and this pressure plate. 
     According to a particularly preferred embodiment of the invention the clamping screw and/or the clamping sleeve is a component part which is slit substantially lengthwise at least in part or is slit with a longitudinal component. This component part is slit in screw fashion for example. A slit of this kind makes it possible for example for the walls of the clamping screw or clamping sleeve to move radially inwards when biased by radial force and thus to apply a clamping force. 
     It is preferable if the clamping force is overcome under predetermined conditions when wear appears on at least one of the clutch devices. By way of example the clamping force is overcome immediately if wear has occurred, so that a relative displacement takes place between the bolt and pressure plate. It is also preferred if the bolt device slides relative to the pressure plate at another point in time. 
     According to a particularly preferred embodiment of the invention the bolt embraced by the friction or clamping device is a stepped bolt which has different diameter ranges so that an axial stop is formed. 
     According to a preferred embodiment of the invention a second stop can be additionally provided to restrict movement in a second axial direction, and is mounted more particularly on the stepped bolt, for example in the form of a bolt head. 
     According to a particularly preferred embodiment of the invention the bolt device which is embraced by the friction or clamping device is arranged so that it runs substantially axially movable through a first pressure plate and an intermediate plate which is mounted between a first and second pressure plate. 
     It is preferable if the aforementioned stops or ledges serve as a stop for this first pressure plate and this intermediate plate. 
     According to a particularly preferred embodiment of the invention the bolt device is secured against slipping out. More particularly the bolt device is secured against slipping out from the contact pressure plates or the intermediate plate. 
     According to a particularly preferred embodiment of the invention an intermediate device, such as for example an intermediate plate, is mounted spatially between the first and second pressure plate, with the intermediate plate being held through a friction device at a certain distance from the second pressure plate, and this distance being variable in the event of wear. A plate spring device ensures for example force is applied on the pressure plates in the direction of the relevant clutch disc or friction lining, whereby the plate spring device is mounted between the first pressure plate and the intermediate plate. 
     According to a particularly preferred embodiment of the invention the intermediate plate, as also preferably the pressure plate, is mounted axially movable wherein it is particularly preferred if under predetermined conditions the movement of the intermediate plate is blocked or prevented in at least one orientation. 
     By way of example the movement is blocked in a first orientation if the second pressure plate adjoins the one disc or a friction lining. 
     According to a particularly preferred embodiment of the invention the adjustment device has an overrunning type device or an overrun which adjusts the clutch assembly under predetermined conditions,. More particularly this adjustment takes place for example at least at times in the event of wear on the friction linings. The overrunning device is mounted for example between the intermediate plate and the second pressure plate. It is preferable if this overrunning-type arrangement in the event of movement in a first direction increases the distance between the intermediate plate and the second pressure plate, whilst the movement is blocked in the counter direction. 
     Under predetermined conditions, more particularly at least at times, the overrun can be moved in its overrunning direction so that the distance between the intermediate plate and the second pressure plate increases. 
     In a corresponding way an adjustment device can also be mounted for example between the plate spring device and one of the pressure plates or between the pressure plates. 
     A corresponding device which is likewise designed for example as a type of overrun, for increasing the distance, which is arranged between the force introduction points of the spring device or plate spring device, is also preferred. 
     According to a particularly preferred embodiment of the invention the adjustment device has at least two elements which contact one another and which in the event of a predetermined movement or with a predetermined introduction of force or force direction execute a movement relative to each other which leads to a change in the spacing, more particularly to an increase in the spacing in a predetermined direction. 
     According to a particularly preferred embodiment of the invention one of these two elements is biased by an energy accumulator device, such as a spring. This spring force is counteracted under first predetermined conditions or circumstances by a counter force so that a relative displacement of the two elements of the adjustment device is substantially avoided. Under second predetermined conditions or circumstances, the counter force decreases at least so that the two elements of the adjustment device move relative to each other under the action of the spring force or a part of the spring force. 
     The two aforementioned elements of the adjustment device are for example the already mentioned tapered rings. By way of example these tapered rings change their axial spacing as a result of their facing inclines during rotation. It is preferable if detents are provided on the slopes of these tapered rings to engage in each other so that a reduction in the spacing of the rings is substantially prevented by the detent formation. 
     It should be noted that other spacers or fixing devices can also be provided in place of or as an addition to the detents. 
     The surface contour, particularly on the slope side, of the tapered rings is preferably formed with a linear rise. It is also preferred if this surface contour is curved or follows an exponential function. Other functional or non-functional surface contours are also preferred. 
     According to a particularly preferred embodiment of the invention the change in the axial spacing of the tapered rings in the event of their rotation corresponds to the play which is to be compensated. More particularly it is preferred if the tapered rings have a linear surface rise wherein a is the pitch angle of this linear rise and tan a corresponds to the play which is to be compensated. 
     It is also preferable if the surface contour on the slope side of the tapered rings which preferably rotate relative to each other is different and follows for example different functions. 
     According to the invention it is preferred if each of the pressure plates when the clutch is closed contacts precisely a clutch disc or precisely a friction lining. It is also preferred if a pressure plate contacts different friction linings when the clutch is closed. By way of example when the clutch is closed a pressure plate contacts two different friction linings simultaneously. It is also preferable if a pressure plate for closing a first clutch contacts a first pressure plate and for closing a second clutch contacts a second pressure plate. It is further preferred if the pressure plate or pressure plates is or are formed with variable thickness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained in further detail with reference to the non-restricting embodiments illustrated by way of example in the drawings in which: 
     FIG. 1 shows an example of an embodiment of the invention in a partial sectional view taken along a first section plane in which the clutch is in a first shift position and the clutch discs are in a first state; 
     FIG. 2 shows the example of an embodiment according to FIG. 1 in a second sectional plane; 
     FIG. 3 shows the example of an embodiment according to FIG. 1 in a second clutch position; 
     FIG. 4 shows the embodiment according to FIG. 3 in a second sectional plane; 
     FIG. 5 shows the example of an embodiment according to FIG. 1 in a second state of the clutch discs; 
     FIG. 6 shows the embodiment according to FIG. 5 in a second sectional plane; 
     FIG. 7 shows the example of an embodiment according to FIG. 1 in a third state of the clutch discs; 
     FIG. 8 shows the example of an embodiment according to FIG. 7 in a second sectional plane; 
     FIG. 9 shows the adjusting device for the clutch used in the example of an embodiment according to the invention in a partial sectional view in a first position; 
     FIG. 10 shows the illustration according to FIG. 9 in a second position; 
     FIG. 11 shows a side view of an example of a clutch device according to the invention in which the operating levers are visible; 
     FIG. 12 shows a sectional view of FIG. 11 along the line  11 — 11   
     FIG. 13 shows a plan view of a pressure plate according to the invention on the transmission side with a friction device. 
     FIG. 14 shows a plan view of a pressure plate on the engine side with a through bore for a stepped bolt, such as is embraced for example by a clutch device according to the invention 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows an example of an embodiment according to the invention in a diagrammatic partially sectional view wherein the clutch discs are located in a first, more particularly unworn, state. The clutch is thereby shifted in a first clutch position. 
     The figure shows two pressure plates  10 ,  12  which with the clutch  14 ,  16  closed adjoin the relevant linings  18  and  20  with friction engagement. The clutch devices  14 ,  16  are each held in a substantially closed clutch position—more particularly by the plate spring device  22 . 
     The contact pressure plates  10 ,  12  are thereby substantially tensioned between the linings  18 ,  20  through the action of the plate spring device  22 . Thus the two clutch devices  14 ,  16  are basically held in a closed position more particularly by a single plate spring device  22 . 
     In the embodiment according to FIG. 1 the plate spring device  22  is supported with one side on the contact pressure plate  10  on the engine side, and with the other side on an intermediate device or intermediate plate  24 . This intermediate plate  24  is substantially in fixed connection with the operating lever  26 . This connection is produced in the example according to FIG. 1 by screwing the intermediate plate  24  onto an intermediate lever  28  which in turn is connected by the articulated joint  30  to the operating lever  26 . 
     The operating lever  26  is in the illustration shown in FIG. 1 a lever through which the clutch device  16  can be opened. 
     By way of example in order to open this clutch device  16  several operating levers  26  are provided, e.g. arranged star-shaped relative to each other. By way of example three operating levers  26  are arranged star-fashion to control the clutch device  16 . 
     Preferably, but not shown in FIG. 1, at least one operating lever is likewise provided for releasing the clutch device  14  on the engine side. By way of example three operating levers are likewise provided for controlling or releasing the clutch device  14 . These operating levers for operating the clutch device  14  are likewise arranged star-fashion relative to each other for example. It is preferable if one operating lever for controlling the clutch device  14  is arranged each time between two operating levers  26  for controlling the clutch device  16 . 
     The operating lever  26  which is attached to the intermediate lever  28  by the articulated joint  30  is attached to the housing at a second articulated point  32 . 
     The intermediate plate  24  is pressed against the pressure plate  12  substantially under the action of the plate spring device  22  so that the pressure plates  10 ,  12  are tensioned against each other. 
     The intermediate plate  24  thereby preferably lies not directly against the pressure plate  12  but against the first tapered ring  34 . This first tapered ring  34  thereby adjoins in the direction of the pressure plate  12  a second tapered ring  36  which in turn is supported against the pressure plate  12 . 
     The first tapered ring  34  and the second tapered ring  36  are biased by the spring device  38 . The spring device  38  which is formed for example as a compression spring or traction spring or as a rotary spring device, biases the first tapered ring  34  so that when there is no or no sufficient counter force the tapered rings  34 ,  36  are moved or turned relative to each other so that the distance between the end of the tapered ring  34  facing the intermediate plate  24  and the end of the second tapered ring  36  facing the pressure plate  12  is increased. Consequently when there is no or no sufficient counter force to the pretensioning force of the spring device  38  the distance between the intermediate plate  24  and pressure plate  12  would increase. This change in the spacing or change in the length is preferably controlled so that it always adapts to the sum of the wear-conditioned erosions on the linings  18 ,  20 . 
     It is hereby possible by way of example according to the invention to keep the plate spring device  22  substantially in a position which is independent of the wear. This in turn means that the spring or pretensioning force of the plate spring device  22  is substantially independent of the wear-conditioned erosion on the linings  18 ,  20 . 
     This in turn makes it possible for the operating force which is to be applied to the operating lever or the operating torque which is to be applied to the operating lever, to be substantially independent of the wear on the linings  18 ,  20 . 
     FIG. 2 shows the embodiment according to the invention of FIG. 1 in a diagrammatic partially sectional view in a second sectional plane. 
     This view likewise shows the first pressure plate  10 , the second pressure  12  and the intermediate plate  24 . 
     FIG. 2 further shows a holding/release device or a friction device or a distance-varying device  50  for varying the maximum permissible spacing between the pressure plates  10  and  12 . 
     This friction device  50  has in the example of the embodiment according to the invention shown in FIG. 2 a bolt which is designed more particularly as a stepped bolt  52  and which extends substantially in or through the pressure plates  10 ,  12  and the intermediate plate  24 . 
     The stepped bolt  52  is thereby preferably mounted substantially freely movable, more particularly freely movable in the axial direction, in the pressure plate  10  and intermediate plate  24 . The stepped bolt is preferably housed in the pressure plate  12  by a friction or clamping device  50  which produces at least at times a substantially fixed connection between the stepped bolt  52  and the pressure plate  12 . 
     The substantially fixed connection between the stepped bolt  52  and the pressure plate  12  is thereby preferably designed so that a clamping screw  54  or the like is screwed into the pressure plate  12  and exerts a normal force on the more particularly sleeve-shaped surface of the stepped bolt  52  so that an axial movement between the stepped bolt and the pressure plate  12  is prevented at least then when the force acting in the axial direction between the pressure plate  12  and the stepped bolt  52  is less than a predetermined force, more particularly one dependent on the clamping force. 
     It is preferable for example if this clamping force is preset or adapted to the pretensioning force of a spring device, more particularly the plate spring device  22 , so that in the event of movement of the stepped bolt  52 , and more particularly an axial movement of the bolt device  52  caused by the spring force of the plate spring device  22 , the pressure plate  12  is also moved along, insofar as substantially only inertia forces, more particularly inertia forces of the stepped bolt  52  and of the pressure plate  12  counteract the spring force of the plate spring device  22 , so that no relative movement takes place between the bolt  52  and the pressure plate  12 . 
     If however the bolt is in a substantially axially fixed position—at least in relation to one orientation—which can be brought about for example by stopping against a stop, more particularly by a bolt head  56  stopping against the pressure plate  10 , then the clamping or holding force is not sufficient to prevent a relative movement between the stepped bolt  52  and pressure plate  12 , if the pressure plate  12  or an object substantially fixedly coupled thereto is not fixed in a similar way to the bolt  52 , so that the relative movement is substantially not or not only achieved by a positive, force or friction locking between the stepped bolt  52  and pressure plate  12 . 
     More particularly if the pressure plate  12  is movable substantially freely, with an axial fixing of the bolt device  52  the intermediate plate  24  is pressed through the plate spring device  22  in a direction away from the bolt head so that this biases the pressure plate  12  through the tapered rings  34 ,  36 . The relative force between this pressure plate  12  and the (held) stepped bolt  52  is thereby greater than the set friction force acting in the axial direction. In this way a relative displacement is possible between the stepped bolt  52  and the pressure plate  12  which will be explained in further detail with reference to the following drawings. 
     It should be pointed out that instead of the clamping screw  54  it is also possible to use corresponding devices such as for example spring-loaded friction devices or the like. 
     FIG. 3 shows the example of the embodiment according to the invention shown in FIG. 1 in a released clutch position for the clutch assembly or driving clutch device  16 . 
     Shifting into a released position of the clutch device  16  can be carried out in particular by moving the operating lever  26  in the direction of the arrow  70  or by turning the operating lever  26  about the axis or articulation point  32 . One axis of the articulation point  32  is thereby mounted for example in the housing  72 . 
     The intermediate lever  28  is preferably attached to the operating lever  26  at the bearing point  30 . If—as in the example shown here—the bearing point  30  and the point at which the external force is introduced into the lever  26  are mounted on the same side of the bearing point  32  then the type of force (compression force or tensile force) introduced from outside into the operating lever  26  corresponds substantially to the type of force introduced from the operating lever  26  into the bearing point  30 . This means in particular that in the example shown in FIG. 3, where the bearing point  30  and the point of force introduction are mounted substantially on the same side of the bearing point  32 , when force is applied to the left or in the direction of the arrow  70  the bearing point  30  or the intermediate lever  28  is pressed to the left. According to the invention it is however also preferred if the bearing point  32  is arranged between the point of force introduction into the operating lever  26  and the bearing point  30 . In such a case for example in order to produce a movement of the intermediate lever  28  to the left, a force directed to the right, thus a force directed opposite the arrow  70  would be introduced into the operating lever  26 —for example at the upper end. 
     As a result of the operation of the operating lever  26  the intermediate lever  28  is forced to the left. The intermediate lever  28  runs with—an at least slight—play  74  through the pressure plate  12  and is connected rotationally secured—preferably at its end—to the intermediate plate  24 . By way of example the intermediate lever  28  is screwed to the intermediate plate  24 . Consequently a movement of the intermediate plate  24  in substantially the same direction or to the left corresponds with a lever movement of the lever  26  in this embodiment of the invention. 
     It should be noted that according to an embodiment of the invention (not shown) a spring assembly can be provided for example inside the assembly made up of the lever  26 , intermediate lever  28  and intermediate plate  24 . By way of example a spring assembly of this kind is arranged—for example switched in series—in the transitional area between the intermediate plate  24  and the intermediate lever  28 . Then a movement of the intermediate plate  24  would not automatically correspond with a movement of the lever  26  for example. 
     An assembly having the tapered rings  34  and  36  is preferably mounted between the intermediate plate  24  and the pressure plate  12 . The tapered rings  34 ,  36  are biased by the spring device  38  in the direction of an increasing distance between the intermediate plate  24  and the pressure plate  12 . An uncontrolled adjustment through an unrestricted displacement of the tapered rings  34 ,  36  in the direction of an increasing distance between the intermediate plate  24  and the pressure plate  12  is avoided according to the invention. 
     This is achieved for example in that the force exerted by the spring device  38  on the tapered rings  34  and  36  is varied—substantially controlled. It is hereby proposed for example that the force counteracting the spring force of the spring device  38  and which likewise acts for example on the tapered rings  34 ,  36  is less than the spring force of the spring device  38  when a displacement of the displacement device or assembly of tapered rings is required or desired. 
     In situations where a displacement of the tapered rings is desired or necessary, the counter force to the force of the spring device  38  is preferably set or is such that this is less than the spring force of the spring device  38  so that the tapered rings are displaced opposite one another through the action of a resulting force and thus increase the distance between the pressure plate  12  and intermediate plate  24  or so long until a force equilibrium prevails at the tapered rings  34 ,  36  or until the force directed against the spring device  38  is greater than the force of the spring device  38 . 
     It is hereby particularly preferred that the tapered rings  34 ,  36  are self-holding. It is hereby particularly preferred that the arrangement of tapered rings  34 ,  36  is designed as a freewheel. It is also preferred that at least one of these tapered ramps has a detent locking mechanism. It is also preferred that the ramps have a type of cogged surface wherein the spline is designed so that movement of the ramps relative to each other in a first direction is substantially possible and movement of the ramps in a second orientation opposite the first is substantially prevented. 
     The plate spring device  22  furthermore biases the intermediate plate  24 . This plate spring device  22 , as shown in FIG. 3, is preferably mounted between the first pressure plate  10  and the intermediate plate  24 . So long as the pressure plate is not moved through the operating lever (not shown in FIG. 3) for opening the clutch device  14 ,  16  into a substantially opened clutch position, the pressure plate  10  is pressed substantially against the lining  10  by the plate spring device  22 . 
     In a corresponding way the pressure plate  12  is pressed against the lining  20  by the plate spring device  22  which acts on the intermediate plate  24 , through the coupling between the intermediate device  24  and the pressure plate  12 , which will be described in more detail, provided a force is not introduced into the intermediate plate  24  or pressure plate  12  through the operating lever  26  as a result of which the pressure plate  12  is lifted off from the lining  20 , as shown in FIG.  3 . 
     By way of example the spring force of the spring device  22  is thereby dependent on the spring path or on the elongation. A change in the spring path would consequently condition a change in the force in the spring device  22 . A clutch device  14 ,  16  without any adjustment device according to the invention, as shown for example in the drawings, could have the effect for example that as the wear on the linings increases the pressure plates  10  and  12  are pressed under the action of the spring device  22  against the linings  18 ,  20  whose spacing has increased though the wear, so that the force in the spring device  22  changes. The force in the plate spring device  22  which is therefore changed could have the effect for example that also the operating force which is to be applied onto the operating lever  26  would change. 
     It should be pointed out that the linings  18 ,  10  are preferably resilient. 
     FIG. 4 shows the example of the embodiment of FIG. 3 in a second plane showing in particular one example of the position of the stepped bolt device  52  in a released position. 
     As already explained, the intermediate plate  24  for disengaging is displaceable to the left through the operating lever  26  or the intermediate lever  28 . More particularly when there is no wear appearing on the discs  18 ,  20  the stepped bolt  52  substantially follows the movement of the intermediate plate  24  since the intermediate plate  24  is coupled—particularly through the step or through the shoulder  76 —with the stepped bolt  52 —at least in the absence of wear on the discs  18 ,  20  as well as a movement of the intermediate plate to the left, or adjoins the stepped bolt  52 . 
     The stepped bolt  52  is hereby moved to the left. The stepped bolt is thereby pressed in particular through the first pressure plate  10  or the bolt head  56  of the stepped bolt  52  increasingly away from the pressure plate  10 , more particularly to the left. 
     The second pressure plate  12  is in turn fixedly connected to the stepped bolt  52  at least under predetermined conditions—more particularly at least at times and/or at least in part. More particularly the second pressure plate  12  is connected to the stepped bolt  52  through the clamping or friction device  50  under predetermined conditions. More particularly this friction device  50  has a friction or clamping screw  54 . 
     This clamping screw  54  is thereby formed for example as a hollow element. More particularly the clamping screw  54  is formed as a type of sleeve which supports a thread  78  on its outer sleeve face. This thread  78  can be screwed into a thread  80  which is mounted inside the pressure plate  12 . More particularly a radially directed clamping force is exerted on the stepped bolt  52  through this coupling or through screwing the threads  78 ,  80  together. 
     This clamping force is preferably predetermined. It is also particularly preferred if this clamping force is adjustable. According to the invention it is preferably proposed that this clamping force is substantially constant or can be set constant for a predetermined time, more particularly throughout the service life. It is also preferred if the clamping screw  54  is slit at least in part in the longitudinal direction. By an at least partial slit in the longitudinal direction of the clamping screw  54  is meant here in particular that the clamping screw  54  has a slit in its wall along the path of which at least the axial position is also changed. A non-continuous slit is also understood by this for example. 
     According to the invention other clamping devices or friction devices  50 , such as for example a clamping or friction assembly  50  are preferred which have wedges or wedge rings or the like which run towards each other. By way of example a device or element is preferred which allows an at least also radially inwardly aligned force. By way of example an element is preferred, such as a friction lining or the like for example, which acts under spring force on the stepped bolt  52 . The aforementioned wedge rings or wedges can have for example an area in which they are screwed against each other. By way of example the area of one wedge has a through bore whilst an area of the second wedge or wedge ring has an at least radially outwardly aligned oblong hole so that the wedges or wedge rings are able to ‘wander’ radially relative to each other when they are connected to a connecting element, such as for example a screw. 
     The distance between the intermediate plate  24  and the pressure plate  10  is determined in particular by the first tapered ring  34 , the second tapered ring  36  as well as the spring device  38 . More particularly this spacing is substantially not changed or is held constant by the first tapered ring  34 , the second tapered ring  36  and the spring device  38  or is held constant through the interaction of the tapered rings  34 ,  36  as well as the spring device  38  if substantially no wear has appeared on the discs  18 ,  20  which would need compensating. 
     Particularly as the intermediate plate  24  strikes against the shoulder  76  the tapered rings  34  and  36  are not displaced relative to each other as a result of the spring force of the spring device  38  since a corresponding play area does not exist. 
     The bolt device  52  is pressed by the pressure plate  10  which is substantially fixed in its position. The pressure plate  10  adjoins the disc  18  for example. It is also preferable if the pressure plate  10  or the clutch disc  18  is likewise released when the clutch device  16  is released. As can be seen by comparing FIGS. 3 and 4 the distance  77  between the pressure plate  12  and the disc  20  corresponds substantially to the distance  98  between the end face  100  of the bolt head  56  facing the pressure plate  10 , and the end face  102  facing the bolt head  56 , of the pressure plate  10  which serves in particular as a stop for the bolt head  56 . 
     FIG. 5 shows the device according to the invention in a second state. Here the driving disc or the disc  20  is at least partly worn. 
     As can be seen from FIG. 5, the operating lever is substantially unstressed so that the pressure plates  10 ,  12  also substantially adjoin the discs  18 ,  20 . 
     This contact despite the presence of wear is due in particular to the fact that the plate spring device  22  presses the pressure plates  10 ,  12  apart from each other. For this purpose it presses with its one end directly against the pressure plate  10  whilst it presses at its other end against the intermediate plate  24  which through an arrangement which comprises in particular the spring device  38  as well as the tapered rings  34 ,  36 , and/or the friction device  50 , exerts pressure on the pressure plate  12  which is thus pressed against the disc  20 . The plate spring device  22  has hereby relaxed increasingly so that in particular the spring force has changed or reduced. 
     Particularly as a result of this changed plate spring device or its changed position the danger arises that the release force which is required to disengage into a released position is also changed. 
     This is avoided through a device according to the invention, more particularly through an adjustment device according to the invention. 
     FIG. 6 shows a device according to the invention in the state of FIG. 5 in a second plane. 
     It can be seen from FIG. 6 or by comparing FIGS. 2 and 6 that the intermediate plate  24  or the contact pressure plate  12  has moved by the distance  104  relative to the shoulder  76  of the stepped bolt  52 . This distance  104  corresponds substantially to the wear which has appeared on the discs  18 ,  20 , more particularly here on the driving disc or the disc  20 . 
     This distance is due in particular to the fact that the disc  20  which represents for example a type of “stop” has moved to the right so that the pressure plate  12  can move further to the right. The spring device  22  however as already mentioned presses the pressure plates  10 ,  12  apart so that the position of the pressure plate  10  is substantially unchanged, namely adjoining the disc  18 . 
     Since here the bolt head  56  of the stepped bolt stops against the pressure plate  10 , the plate spring device  22  tensions the pressure plate  10  opposite the pressure plate  12  and the pressure plates  10 ,  12  each (ought to) adjoin the discs  18 ,  20 , the clamping force of the clamping device  50  is here overcome at least at some times so that the pressure plate  12  can move, more particularly together with the intermediate plate  24 , along the bolt to the right until the pressure plate  12  stops against the disc  20 . More particularly the spring force of the plate spring  22  is (thereby) then also greater than the clamping force which the clamping device applies or which the clamping screw  54  exerts on the stepped bolt  52  when the plate spring  22  has relaxed in part as a result of the wear. 
     It is thereby preferable if the plate spring  22  is selected and pre-set so that with a predetermined amount of wear and more particularly with the maximum possible amount of wear on one and/or both discs  18 ,  20  the plate spring  22  is greater than the clamping force or friction force which is applied by the clamping or friction device  50 . It is also preferred if under predetermined conditions with a predetermined amount of wear or with the maximum amount of wear the plate spring force of the—in particular partially relaxed—plate spring  22  is greater than the friction force by a predetermined amount. It is further preferred if the ratio of the plate spring force and the friction force or clamping force of the friction device  50  under the aforementioned circumstances is greater by a predetermined amount than one. 
     It should be pointed out that the displacement between the pressure plate  12  and the stepped bolt  52  occurs more particularly when the stepped bolt  52  is fixed in its position—at least in relation to one orientation—more particularly by the bolt head  56  stopping against the pressure plate  10 . So long as this type of fixing does not exist the unit comprising the intermediate plate  24  and pressure plate  12  as well as the stepped bolt  52  is displaced as a whole since in particular the relative force between the stepped bolt  52  and the pressure plate  12  in the axial direction is substantially zero. 
     During the next release process the operating lever  26  illustrated in FIG. 5 is operated anew so that a force is exerted on the intermediate plate  24  through the intermediate lever  28  in the manner substantially explained already above. As a result of this force the intermediate plate  24  which is mounted movable on the stepped bolt  52  is displaced to the left and is thereby removed from the second pressure plate  12  at least so long until the intermediate plate  24  stops against the shoulder  76 . 
     This removal makes it possible for the tapered rings  34 ,  36  to be displaced under the action of the spring device  38  until these tapered rings  34 ,  36  again fill out axially the area released by the displacement of the intermediate plate  24  on the shoulder  76  of the stepped bolt  52 . 
     It is particularly preferred if the component of the force of the spring device  38  which acts in the direction of the holding force of the clamping device  50  is less than the holding force of the clamping device  50 . It is hereby possible in particular that as a result of the spring device  38  as well as the tapered rings  34 ,  36  these rings are only displaced relative to each other until they fill out the aforementioned released area. Then it is basically preferred that no further displacement of the pressure plate  12  takes place in the axial direction. 
     FIGS. 7 and 8 show illustrations corresponding to FIGS. 5 and 6 wherein wear has occurred on the two discs  18  and  20 . 
     FIG. 9 shows the adjustment device in a diagrammatic partial sectional view . An assembly comprising the spring device  38 , a first tapered ring  34  as well as a second tapered ring  36  is provided between the intermediate ring  24  and the pressure plate  12  or the tapered rings  34 ,  36  are enclosed by the relevant plates  24 ,  12 . The tapered ramps each have a pitch which is shown diagrammatically by the pitch triangle  110 . The spring device  38  loads the tapered ring  34  so that it is pressed in the direction of the rising pitch of the ring  36  so that in the event that there is not sufficient counter force opposing this spring force of the spring device  38 , the spacing  112  would increase. As shown for example by the enlarged cut-out section  116  for the area  114 —in order to prevent a reduction in the spacing  112 , holding devices or detent locking devices are provided more particularly acting on one side and arranged in particular along the ramps. 
     FIG. 10 shows the object illustrated in FIG. 9 in a second state in which wear has appeared on the discs  18  and/or  20 . 
     Particularly as a result of the enlarged spacing of the intermediate ring  24  from the pressure plate  12  or through the enlargement of this spacing the spring device  38  presses the tapered ring  34  “high” on the incline  110  so that the spacing  112  is enlarged and the device comprising the tapered rings  34 ,  36  as well as the spring device  38  fills out the interspace between the intermediate plate  24  and the pressure plate  12 . It is also preferred if one or both of the tapered rings  34 ,  36  is coupled to the relevant adjoining plate  24  or  12  so that the spring device  38  displaces a one-piece element  34 ,  24  opposite a one-piece element  36 ,  12  whilst increasing the spacing  112 . It is also preferable if a one-piece coupling of this kind exists only between one of the rings  34 ,  36  and the relevant adjoining plate  24 ,  12 . 
     It should be pointed out that preferably a device (not shown) prevents the rings from escaping in order to avoid an enlargement of the spacing  112 . 
     FIG. 11 shows as an example a plan view of a device as shown by way of example and in partial section in FIGS. 1 to  8 . 
     The illustration according to FIG. 11 shows one example of the arrangement of the operating levers  26 ,  130  wherein the operating levers  26  are provided for coupling or engaging and releasing the clutch device  16  whilst the operating levers  130  are provided for coupling the clutch device  14 . 
     FIG. 12 shows a sectional view along the line  11 — 11  in FIG.  11 . This arrangement shows by way of example the arrangement of the operating lever  26  for operating the clutch device  16  compared with the arrangement of the operating lever  130  for coupling the clutch device  14 . 
     FIG. 13 shows an example of the pressure plate  12  according to the invention on the transmission side. In particular the arrangement of the at least one friction device  50  is shown. 
     FIG. 14 shows an example of the design of the pressure plate  10  on the engine side having through bores  140  for holding the stepped bolts  152 . 
     According to the invention it is thus proposed that the at least one clutch device of a motor vehicle such as for example a tractor or commercial vehicle adjusts automatically and/or independently so that in particular the operating force of the clutch device is moved within a tolerance band substantially throughout the service life, with the width of this tolerance band preferably being moved towards zero.