Patent Publication Number: US-2015068852-A1

Title: Wear Adjustment Device of a Disc Brake and Corresponding Disc Brake

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Application No. PCT/EP2013/060382, filed May 21, 2013, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2012 009 900.2, filed May 18, 2012, the entire disclosures of which are herein expressly incorporated by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a wear adjustment device of a disc brake, in particular for a motor vehicle. The invention also relates to a corresponding disc brake. 
     Vehicles and certain technical devices frequently use friction brakes, in order to convert kinetic energy. Here, the disc brake is preferred specifically in the passenger motor vehicle and in the commercial vehicle field. In the case of the typical construction of a disc brake, it consists of a brake caliper including inner mechanism, as a rule two brake pads and the brake disc. The cylinder forces are introduced to the inner mechanism via a pneumatically actuated cylinder, are boosted by way of an eccentric mechanism and are transmitted as brake application force via threaded spindles to the brake pads and the brake disc, the wear of the brake disc and brake pads being compensated for via the threaded spindles. 
     The brake application forces act via both brake pads on the brake disc, which experiences a retardation of the rotational movement depending on the level of the brake application force. This retardation is also significantly determined by the coefficient of friction between the brake disc and the brake pad. Since the pads are designed structurally as wear parts and the coefficients of friction are dependent on the strength, they are generally softer than the brake disc, that is to say the pads experience a change in the pad thickness over their service life, and they are subject to wear. This change in the pad thickness results in the necessity that a wear adjustment means compensates for the change and therefore sets a constant brake clearance. A constant brake clearance is required, in order to keep the response times of the brake low, to ensure the freedom of movement of the brake disc and to keep a stroke reserve for cases of critical loading. 
     DE 10 2004 037 771 A1 describes one example of a wear adjustment device. Here, a rotational drive movement is forwarded, for example, by a torque limiting device, for example having a ball ramp, via a continuously acting clutch (slip clutch) to an adjusting spindle of a pressure plunger. Here, the brake clearance is set continuously. 
     As described, wear is produced on the brake pads as a result of normal use, which wear has to be equalized via the wear adjustment device. In the case of the existing system, the problem lies in the fact that it functions on a frictional basis and therefore only within narrow limits or in a manner which is dependent on temperature and vibration, that is to say additional measures are necessary for brake clearance stabilization under the influence of temperature and vibration. 
     The object of the present invention consists in providing an improved wear adjustment device. It is a further object to provide an improved disc brake. 
     The object is achieved by way of a wear adjustment device according to the invention, and by way of a disc brake according to the invention. 
     A wear adjustment device is provided which has a compact construction in a housing and is, as far as possible, friction-independent and, as far as possible, functions in a positively locking manner. 
     A wear adjustment device is provided according to the invention for adjusting friction face wear on the brake pad and the brake disc of a disc brake, in particular for a motor vehicle, having a brake application device, preferably with a rotary lever. The wear adjustment device is coupleable on the drive side to the brake application device, preferably to the rotary lever, and on the output side to a spindle unit of the disc brake. In each case, one rolling body arrangement is arranged axially on both sides of a drive element, of which rolling body arrangements one is configured as an anti-friction bearing and one is configured as a ball ramp coupling. A central shaft is coupled to the ball ramp coupling and has an output interface for coupling to the spindle unit. A radial freewheel is coupled to the ball ramp coupling via an overload spring unit and to the central shaft. A direction-dependent torque device is provided. A housing houses the drive element, the rolling body arrangements, the overload spring unit, the radial freewheel, the central shaft and the direction-dependent torque device. 
     This results in a compact and space-saving construction which is situated in the housing. Moreover, the housing provides a protective function against moisture and dirt. 
     A disc brake according to the invention, preferably actuated by compressed air, in particular for a motor vehicle, having a brake application device, preferably having a brake rotary lever, at least one spindle unit and at least one wear adjustment device which is coupled to the brake application device, preferably to the brake rotary lever, has the wear adjustment device which is specified above. 
     It is provided in one embodiment that the direction-dependent torque device forms a vibration protection device. In this way, an integrated vibration stabilization device is formed. 
     To this end, it is provided, furthermore, that the wear adjustment device is configured by way of the direction-dependent torque device for discontinuous adjustment. An integrated temperature stabilization is thus also possible. 
     In one embodiment, the direction-dependent torque device comprises a moment ramp section which is connected fixedly to the central shaft, a moment ramp disc which is in engagement with the moment ramp section and an application moment spring which loads the moment ramp section and the moment ramp disc with an axial prestressing force which can be fixed in advance. Since the application operation is dependent on geometric variables, a positively locking function is made possible. 
     In a further embodiment, the application moment spring is arranged between a bottom section of the housing and the moment ramp disc. Small dimensions are possible as a result of this compact construction. 
     In a further embodiment, the direction-dependent torque device is configured with flat application ramps for adjustment and with adjusting ramps which are steep in relation to the flat application ramps for adjustment in the service case, which ramps are at least partially in contact. This results in high functionality in a very small space. The torque device can therefore perform a plurality of functions. 
     In a further embodiment, the axial bearing is formed from the drive element, axial bearing balls and a cover section of the housing. The housing therefore likewise has high functionality and reduces the number of components. 
     Another embodiment provides that the central shaft has a guide section which is fixed axially in the housing. The housing can therefore have a high functional integration. 
     A further advantage which is formed by the common housing lies in the fact that the axial bearing, the ball ramp coupling, the overload spring unit and the radial freewheel are arranged between the guide section and the cover section of the housing, which results in a considerable space saving. 
     In another embodiment, the radial freewheel is configured as a spring assembly and is in engagement with a freewheel toothing system of the central shaft. The radial freewheel can also have radially stacked spring arms. As a result, mutual support can be achieved in the locking direction, it being possible for a defined freewheel moment to be set in the release direction. 
     In a further embodiment, the housing is configured with at least one caliper anti-twist fixing device and/or one anti-twist fixing element. This results in a wide field of use in different brake configurations. 
     In a further embodiment, the ball ramp coupling has overload ramp balls which are positively guided in a ball cage and are arranged between the drive element and an overload ramp element. This results in a space-saving construction, the synchronization of said balls being made possible under different load cases. 
     A disc brake having two spindle units and a synchronizing unit can be configured in such a way that the wear adjustment device is inserted onto or into one of the two spindle units of the disc brake. This is possible by virtue of the fact that the wear adjustment device is configured both as an external design and as an internal design (in or around a threaded spindle). 
     The wear adjustment device according to the invention has the following advantages:
         Integrated “vibration stabilization” (vibration resistance),   application dependent on geometric variables→positively locking,   as insensitive as possible to temperature,   application is discontinuous,   configuration in an external or internal design (in or around a threaded spindle),   functional moments can be set, and   considerably shorter overall design than the prior art.       

     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic sectional view of one exemplary embodiment of a disc brake according to the invention; 
         FIGS. 2 and 2   a  are diagrammatic, perspective exploded illustrations of one exemplary embodiment of a wear adjustment device according to the invention from different viewing angles, 
         FIGS. 3 and 3   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIGS. 4 and 4   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIG. 5  is a diagrammatic, perspective illustration of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIGS. 6 and 6   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIGS. 7 and 7   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIGS. 8 and 8   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIGS. 9 and 9   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIGS. 10 and 10   a  are diagrammatic, perspective illustrations of a component of the exemplary embodiment according to  FIGS. 2 and 2   a;    
         FIG. 11  is a diagrammatic, perspective illustration of a central shaft having a radial freewheel; 
         FIG. 11   a  is a cross-sectional illustration of a plane of the radial freewheel; 
         FIG. 12  is a diagrammatic sectional view of ramps; 
         FIG. 13  is a diagrammatic sectional illustration of the wear adjustment device according to an embodiment of the invention; 
         FIG. 14  is a diagrammatic perspective view of the wear adjustment device in accordance with  FIG. 13 ; 
         FIG. 15  is a diagrammatic sectional illustration of one variant of the wear adjustment device according to the invention; 
         FIG. 16  is a diagrammatic perspective view of the variant according to  FIG. 15 , 
         FIG. 17  is a diagrammatic part view of a second exemplary embodiment of the disc brake according to the invention; 
         FIG. 18  is an enlarged perspective view of the wear adjustment device in accordance with  FIG. 13  on the disc brake according to  FIG. 17 , and 
         FIG. 19  is an enlarged perspective view of the wear adjustment device in accordance with  FIG. 15  on the disc brake according to  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a diagrammatic sectional view of one exemplary embodiment of a disc brake  1  according to the invention. 
     The disc brake  1  is shown here in an embodiment as a two-plunger brake with two spindle units  5 ,  5 ′ with threaded tubes  6 ,  6 ′. A brake caliper  4 , configured here as a floating caliper, reaches over a brake disc  2 , on which in each case one brake pad  3  with a brake lining carrier  3   a  is arranged on both sides. The application-side brake lining carrier  3   a  is connected to the spindle units  5 ,  5 ′ at ends of the threaded tubes  6 ,  6 ′ via pressure pieces  6   a ,  6 ′ a . The other, reaction-side brake lining carrier  3   a  is fixed in the brake caliper  4  on the other side of the brake disc. The threaded tubes  6 ,  6 ′ are arranged rotatably in each case in a crossmember (bridge)  7 . The crossmember  7  and therefore the threaded tubes  6 ,  6 ′ can be actuated by a brake application device (here, a rotary lever  8  with a pivot axis at a right angle with respect to the rotational axis) of the brake disc  2 . Here, the wear adjustment device  10  is inserted into the spindle unit  5  of the two spindle units  5 ,  5 ′ on an adjuster shaft  5   a . The adjuster shaft  5   a  is coupled via a synchronizing device  23  to a driver shaft  5 ′ a  which is inserted into the other spindle unit  5 ′. Here, the synchronizing device  23  comprises a synchronizing wheel  23   a  (here, a chain sprocket) on the application-side end of the adjuster shaft  5   a  of the wear adjustment device  10 , a synchronizing wheel  23 ′ a  (here, a chain sprocket) on the corresponding end of the driver shaft  5 ′ a , and a synchronizer  23   b  (here, a chain). In this way, a synchronous movement of the spindle units  5  and  5 ′ is ensured during wear adjustment operations. 
     The wear adjustment device  10  interacts with the rotary lever  8  via a drive  9 . The drive  9  comprises an actuator  8   a  which is connected to the rotary lever  8 , and an operating lug  13   a  of a drive element  13  of the wear adjustment device  10 . 
     A spacing between the brake pads  3  and the brake disc  2  is called a brake clearance. Said brake clearance becomes greater as a consequence of pad and disc wear. If this is not compensated for, the disc brake  1  cannot reach its peak performance, since an actuating stroke of the actuating mechanism (that is to say, the actuating stroke or a pivoting angle of the rotary lever  8  here) is no longer sufficient. 
     The disc brake  1  can have different power drives. Here, the rotary lever  8  is actuated, for example, pneumatically. Reference is made to the corresponding description of DE 197 29 024 C1 with respect to the construction and function of a pneumatic disc brake  1 . 
     The wear adjustment device  10  according to the invention, which will be described in detail further below, is configured for wear adjustment of a previously fixed brake clearance which is called the nominal brake clearance. The expression “adjustment” is to be understood to mean a reduction in the brake clearance. The previously fixed brake clearance is defined by the geometry of the disc brake  1  and has what is known as a structural brake clearance. In other words, the wear adjustment device  10  reduces an existing brake clearance when the latter is too large in relation to the previously fixed brake clearance. 
       FIGS. 2 and 2   a  show diagrammatic, perspective exploded illustrations of one exemplary embodiment of the wear adjustment device  10  according to the invention from different viewing angles. 
     The wear adjustment device  10  comprises a housing  11 , axial bearing balls  12 , the drive element  13  with the operating lug  13   a , overload ramp balls  14  with a ball cage  15 , an overload ramp element  16 , an overload spring unit  17 , a radial freewheel  18 , freewheel balls  19 , a central shaft  20 , a moment ramp disc  21  and an application moment spring  22 . 
     The functional components of the wear adjustment device  10  of the exemplary embodiment according to  FIGS. 2 and 2   a  will now be described in conjunction with diagrammatic, perspective illustrations of the components of  FIGS. 3 to 10 . 
     The expression upper side is to be understood to mean that side of the respective component which points toward the brake application side in the installed state in the disc brake  1 . The underside of the respective component then points toward the brake disc  2 . 
       FIGS. 3 and 3   a  show the housing  11 . It has a substantially hollow-cylindrical body with a circumferential wall  11   a  which is interrupted on approximately one quarter of the circumference of a wall opening  11   f  and is covered at the top by way of a cover section  11   d  with a circular opening  11   b . A bottom section  11   e  which lies parallel to the cover section  11   d  and likewise has a circular opening  11   c  is arranged on the underside of the housing  11 . The housing  11  is flattened on one side adjacently with respect to the wall opening  11   f , a caliper rotational fixing structure  11   g  being formed, by way of which the wear adjustment device  10  can be fixed such that it cannot rotate via the housing  11  in the brake caliper  4 . 
     Here, the wall opening  11   f  is closed partially on its right-hand side (here, in the upper right quarter) by way of a stop  11   h  for the operating lug  13   a  (see also  FIG. 14 ). 
     A guide groove  11   i , which serves to receive a guide section  20   e  ( FIGS. 9 ;  13 ) of the central shaft  20 , is formed on the inner side of the wall  11   a  within the housing  11 . Anti-twist securing elements  11   j  in the form of elongate projections which extend in the circumferential direction are formed below the guide groove  11   i  on the inner side of the wall  11   a . In interaction with securing groove  21   c , the anti-twist securing elements  11   j  serve for the anti-twist fixing of the moment ramp disc  21  (see  FIG. 10 ) in the housing  11 . 
     An axial bearing raceway (not denoted in greater detail) for the axial bearing balls  12  is formed on the inner underside of the cover section  11   d  (see also  FIG. 13 ). 
     Finally, a radially outwardly extending anti-twist fixing element  11   k  in tongue form is formed on the lower bottom section  11   e  below the wall opening  11   f . It serves for the anti-twist securing of the housing  11  in a corresponding receptacle of the crossmember  7  (see  FIGS. 13 ;  17 ;  18 ). 
     The drive element  13  is shown in  FIG. 4  and  FIG. 4   a . It has an annular body, through which the operating lug  13   a  is attached in pin form. The operating lug  13   a  extends radially to the outside from the outer circumference of the annular body. An axial bearing raceway  13   b  for the axial bearing balls  12  is formed into the upper side of the annular body of the drive element  13  ( FIG. 4 ). In addition, an overload ramp raceway  13   c  for the overload ramp balls  14  is formed into the underside of the drive element  13 , which underside is shown in  FIG. 4   a.    
       FIG. 5  shows the ball cage  15  which is provided here for eight overload ramp balls  14 . It can of course be configured to have more or fewer overload ramp balls  14 . 
       FIGS. 6 and 6   a  show the overload ramp element  16 . It is of annular configuration and has an overload ramp raceway  16   a  (corresponding to the overload ramp raceway  13   c ) for the overload ramp balls  14  on its upper side ( FIG. 6 ). Here, four spring fixing grooves  16   b  which serve to fix the overload spring unit  17  ( FIGS. 7-7   a ) are formed on the border circumference of the underside (shown in  FIG. 6   a ) of the overload ramp element  16 . 
     The overload spring unit  17  is shown in  FIG. 7  and  FIG. 7   a  and, here, comprises two springs  17   a  and  17   b  which are arranged with their inner openings on one another and are configured as disc springs. The overload spring unit  17  is configured as a spring assembly, the two disc springs being connected to one another at their inner openings via assembly connections  17   c . The springs  17   a  and  17   b  are provided in each case with four fixing projections  17   d  on the outer circumferential edges. The fixing projections  17   d  of the upper spring  17   a  are provided for interaction with the spring fixing grooves  16   b  of the overload ramp element  16 . The fixing projections  17   d  of the lower spring  17   b  interact with the radial freewheel  18  which is shown in  FIG. 8  and  FIG. 8   a.    
     The radial freewheel  18  which is shown with its underside in  FIG. 8  and with its upper side in  FIG. 8   a  is likewise of annular design. A freewheel axial bearing raceway  18   a  for the freewheel balls  19  is formed on its underside. Here, eight freewheel springs  18   b , which extend radially obliquely to the inside and have a profiling  18   c  at their free ends, are formed on the edge of the circumference of the inner opening of the radial freewheel  18 . Here, the profiling  18   c  is of toothed configuration and is provided for interaction with a freewheel toothing system  20   h  of the central shaft  20  (see  FIGS. 9 ;  11  and  11   a ). Here, four spring fixing grooves  18   d  for fixing the fixing projections  17   d  of the lower spring  17   b  of the overload spring unit  17  are formed at the outer circumferential edge of the upper side of the radial freewheel  18  ( FIG. 8   a ). 
       FIG. 9  shows the central shaft  20  as viewed from its upper side. A view from the underside of the central shaft  20  is shown in  FIG. 9   a . In this exemplary embodiment, the central shaft  20  is a hollow cylinder with a circular cross section. The hollow cylinder has an upper drive section  20   a  and a lower output section  20   b  with an output interface  20   c  with output elements  20   k  on the inner wall. The drive section  20   a  is closed on its upper side and is provided with a disc-like toothed rim which has a sensor toothing system  20   i . Here, a hexagonal journal is attached centrally on the closed upper side of the drive section  20   a  of the central shaft  20  as adjusting interface  20   d  in the axial direction. The adjusting interface  20   d  serves to attach a tool, for example a hexagon key, for manual adjustment of the wear adjustment device  10 , which will be explained in greater detail below. A sealing ring groove  20   j  for receiving a sealing ring, for example a round section sealing ring (O-ring), is formed at the transition point between the hexagonal journal and the drive section  20   a  in order to seal with respect to the brake caliper  4 . 
     The two sections  20   a  and  20   b  are divided by way of a disc-like guide section  20   e , the external diameter of which in this example is approximately a third greater than the external diameter of the two sections  20   a  and  20   b . Moreover, the external diameter of the guide section  20   e  is greater than the internal diameter of the housing  11  (see  FIG. 13 ), installation taking place through the wall opening  11   f.    
     On its annular upper side, the guide section  20   e  is provided with a freewheel axial bearing raceway  20   f  for the freewheel balls  19 , a moment ramp section  20   g  for interaction with the moment ramp disc  21  according to  FIGS. 10 and 10   a  being formed in and/or on the underside of the guide section  20   e.    
     The output interface  20   c  serves for connection to an upper end of the adjuster shaft  5 , which upper end has axial grooves which correspond with the output elements  20   k . The assembled wear adjustment device  10  can thus be placed onto the adjuster shaft  5   a  in a rotationally fixed manner, which will be described further below. 
       FIG. 10  shows the upper side of the moment ramp disc  21  and  FIG. 10   a  shows its underside. The moment ramp disc  21  is of annular design and is provided on its upper side with moment ramps  21   a  which interact with the moment ramp section  20   g  of the central shaft  20 . Here, four securing grooves  21   c  which are continuous from the underside to the upper side and interact with the anti-twist securing elements  11   j  on the inner side of the wall  11   a  of the housing  11  are formed on the outer circumference of the moment ramp disc  21 . 
       FIG. 11  shows a diagrammatic, perspective illustration of the central shaft  20  with the radial freewheel  18 .  FIG. 11   a  shows a cross-sectional illustration of a plane of the radial freewheel  18 . 
     The freewheel balls  19  are arranged on the freewheel axial bearing raceway  20   g  of the guide section  20   e  and support the radial freewheel  18 . The radial freewheel  18  is placed onto the freewheel balls  19  via the drive section  20   a  of the central shaft  20  in such a way that the profilings  18   c  of the freewheel springs  18   b  are in engagement with the teeth of the freewheel toothing system  20   h  of the central shaft  20 . 
     A plan view of said arrangement on the upper side of the radial freewheel  18  in the installed state in the housing  11  can be seen in the cross-sectional illustration according to  FIG. 11   a . It can be seen here that the wall opening  11   f  is dimensioned to be so large that the central shaft  20  can be inserted with guide section  20   e  through the wall opening  11   f  into the guide groove  11   i  (not visible here), as a result of which the central shaft  20  with the functional components which are arranged on and around it is fixed axially in the housing  11 . 
     Here, the freewheel springs  18   b  are arranged in an angled manner such that a rotational movement of the central shaft  20  (about its longitudinal axis which is not shown but is readily conceivable) is possible here in the plan view in the clockwise direction relative to the radial freewheel  18 . In the counterclockwise direction, the central shaft  20  and the radial freewheel  18  are connected in a positively locking manner and fixedly so as to rotate with one another via the profilings  18   c  of the freewheel springs  18   b , which profilings  18   c  are in engagement with the freewheel toothing system  20   h , with the result that no relative rotational movement is possible between the central shaft  20  and the radial freewheel. The further functions of the radial freewheel  18  in conjunction with the wear adjustment device  10  will be described in detail further below. 
       FIG. 12  shows a diagrammatic sectional view of ramps of the ramp section  20   g  of the guide section  20   e  of the central shaft  20  in the assembled state in interaction with the moment ramps  21   a  of the moment ramp disc  21 . The ramp section  20   g  of the central shaft  20  is in engagement with the moment ramps  21   a  of the moment ramp disc  21 , steep ramps and less steep ramps being in contact with one another in such a way that steep adjusting ramps  21   d  of the moment ramp disc  21  bear against steep adjusting ramps  20   g ′ of the central shaft  20 , and that less steep application ramps  21   e  of the moment ramp disc  21  bear against less steep adjusting ramps  20   g ″ of the central shaft  20 . Here, the ramps bear in each case only partially against one another. For example, the adjusting ramps  21   d  and  20   g ′ bear against one another approximately only over half of their ramp lengths in the region of their head sides. In the illustration in  FIG. 12 , the ramps form a type of tooth profile in section. The function of the different gradients of the ramps will be explained further below. 
       FIG. 13  shows a diagrammatic sectional illustration of the wear adjustment device  10  according to the invention, and  FIG. 14  shows a diagrammatic perspective view of the wear adjustment device according to the invention in accordance with  FIG. 13 . 
     The central shaft  20  is inserted in the housing  11  in such a way that the upper side of the drive section  20   a  with the adjusting interface  20   d  protrudes through the opening  11   b  of the cover section  11   d  of the housing  11 , and the cover section  11   d  of the housing  11  is flush with the upper side of the drive section  20   a . The output section  20   b  extends through the opening of the bottom section  11   e  of the housing  11 . The functional components of the wear adjustment device  10  are arranged in the housing  11  in the following order starting from the top. 
     An axial bearing is formed with the axial bearing balls  12  between the underside of the cover section  11   d  of the housing and the upper side of the drive element  13 . The underside of the drive element  13  lies on the overload ramp balls  14  which are held in the ball cage  15  and are guided on the upper side of the overload element  16 . The underside of the overload element  16  lies on the upper spring  17   a  of the spring unit  17  and is coupled fixedly to it so as to rotate together via the fixing projections  17   d  in the spring fixing grooves  16   b . The lower spring  17   b  lies on the upper side of the radial freewheel  18  and is connected fixedly to the latter so as to rotate with it via its fixing projections  17   d  in the spring fixing grooves  18   d  of said radial freewheel  18 . The radial freewheel  18  lies with its underside on the freewheel balls  19  which for their part are guided on the upper side of the guide section  20   e  of the central shaft  20 . The freewheel springs  18   b  (also called spring assemblies here) are in engagement with the freewheel toothing system  20   h  of the central shaft  20 , as has already been described above. 
     The guide section  20   e  is received in the guide groove  11   i  of the housing  11 . The moment ramp disc  21  is arranged below the guide section  20   e  and is in engagement by way of the moment ramps  21   a  of its upper sides with the moment ramp section  20   g  of the guide section  20   e  of the central shaft  20  as a result of spring force of the application moment spring  22 . The application moment spring  22  is arranged between the underside of the moment ramp disc  21  and the inner side of the bottom section  11   e  of the housing and thus exerts an axial prestress against the moment ramp disc  21  as a result of support on the bottom section  11   e . The moment ramp disc  20   g  is secured fixedly in the housing  11  so as to rotate with it, but can be displaced axially, via the engagement of the anti-twist securing elements  11   j  of the inner side of the housing  11  in the securing grooves  21   c , since the securing grooves  21   c  are formed on the circumferential edge of the moment ramp disc  20   g  in an axially continuous manner from the upper side to the underside. 
     In  FIG. 13 , the wear adjustment device  10  is placed with the output interface  20   c  on the upper end of the adjusting shaft  5   a  or a threaded tube  6  and is coupled fixedly to the adjusting shaft  5   a  so as to rotate with it via the output elements  20   k . With respect to the crossmember  7 , the wear adjustment device  10  is fixed against rotation by way of the anti-twist fixing element  11   k  in a receptacle which is not denoted in greater detail. 
       FIG. 14  shows the wear adjustment device  10  as viewed perspectively from below; the stop  11   h  can be seen clearly in the wall opening  11   f . The stop  11   h  lies in the pivoting plane of the operating lug  13   a . The stop  11   h  serves as a stop for the operating lug  13   a , it being possible for said operating lug  13   a  to be pivoted between the left-hand upper edge of the wall opening  11   f  and the stop  11   h  (can be seen clearly in  FIG. 14 ) about a longitudinal axis of the housing  11  and therefore about a longitudinal axis (not shown, but readily conceivable) of the wear adjustment device  10 . The housing  11  accommodates all the functional components of the wear adjustment device  10  in a compact overall design and protects them correspondingly. 
       FIG. 15  shows a diagrammatic sectional illustration of one variant of the wear adjustment device  10  according to the invention, and  FIG. 16  shows a diagrammatic perspective view of the variant according to  FIG. 15 . 
     The variant according to  FIG. 15  differs from the embodiment according to  FIG. 13  in that the housing  11  does not have an anti-twist fixing element  11   k . An anti-twist securing structure consists in that the caliper anti-twist fixing structure  11   g  interacts with associated faces on the brake caliper  4  for anti-twist securing in the installed state of the wear adjustment device  10  (see  FIG. 19 ). 
     A further difference of said variant according to  FIG. 15  with respect to the embodiment according to  FIG. 13  lies in the fact that the output interface  20   c  is configured with axial output tongues  201  with axial output edges  20   m  and with axial recesses which lie between the output tongues  201 . The associated adapted end of the adjusting shaft  5   a  is not shown, but is readily comprehensible. It is provided with axial grooves, into which the output tongues  201  are pushed when the wear adjustment device  10  is placed onto the adjusting shaft  5   a.    
     The construction of the functional components of the variant according to  FIG. 15  of the wear adjustment device  10  in the housing  11  corresponds to the construction which is described in conjunction with  FIG. 13 . 
       FIG. 17  shows a diagrammatic partial view of a second exemplary embodiment of the disc brake  1  according to the invention, and  FIG. 18  shows an enlarged perspective view of the wear adjustment device  10  according to the invention in accordance with  FIG. 13  on the disc brake  1  according to  FIG. 17 . In said second exemplary embodiment, the wear adjustment device  10  is not inserted in the spindle unit  5 , but rather is placed on the end of the adjusting shaft  5   a  of the spindle unit  5 . The wear adjustment device  10  in the embodiment according to  FIG. 13  is placed onto the end of the adjusting shaft  5   a  and the anti-twist fixing element  11   k  is received in the crossmember  7 . The adjusting shaft  5   a  has a chain sprocket as synchronizing wheel  23   a . Furthermore, the end of the driver shaft  5 ′ a  with the synchronizing wheel  23 ′ a  and axial grooves  5 ′ c  for the output elements  20   k  is shown. The wear adjustment device  10  can be placed both onto the adjusting shaft  5   a  and onto the driver shaft  5 ′ a . Instead of chain sprockets as synchronizing wheels  23   a ,  23 ′ a , other gearwheels (spur gears, bevel gears or the like) can of course also be used, for example. 
     Finally,  FIG. 19  shows an enlarged perspective view of the wear adjustment device  10  according to the invention in the variant according to  FIG. 15  attached to the disc brake  1  according to  FIG. 17 . The output tongues  201  of the output interface  20   c  of the wear adjustment device  10  engage into axial grooves of a profile  5   b  of the end of the adjusting shaft  5   a . The caliper anti-twist fixing structure  11   g  forms an anti-twist securing structure of the wear adjustment device  10 . 
     Furthermore,  FIG. 19  shows the drive  9  by way of example. The operating lug  16   a  is in engagement with the actuator  8   a  which is configured here as a groove in a body  8   b  which is connected to the rotary lever  8 . The structural brake clearance can be fixed, for example, by way of the groove of the actuator  8   a.    
     The following functional areas which will be explained in the following text can be realized by way of the described wear adjustment device  10  according to the invention. 
     1. Nominal brake clearance setting
 
2. Brake clearance adjustment
 
3. Overload case
 
4. Service case
 
     5. Miscellaneous 
     1. Nominal Brake Clearance Setting 
     The nominal brake clearance corresponds to the structural brake clearance, and is realized via the operating lug  13   a  on the overload ramp raceway  13   c  and an associated structurally set play with respect to the actuator  8   a  (see also  FIGS. 14 and 19 ), which is not to be described in further detail here. Here, the method of operation is such that the adjusting mechanism of the wear adjustment device  10  is not driven within the structural brake clearance up to a defined actuating angle of the actuator  8   a.    
     2. Brake Clearance Adjustment 
     In the operating case when the existing brake clearance is greater than the nominal brake clearance, an adjusting operation occurs after bridging of the structural brake clearance. Here, the drive element  13  is driven via the operating lug  13   a  by the actuator  8   a  and is rotated in the application direction. Here, the application direction is to be understood to mean the rotational direction which is necessary, in order to adjust the brake pads  3  toward the brake disc  2 . Here, in conjunction with  FIGS. 11 and 11   a , the application direction is the rotational direction in the clockwise direction. 
     There is a positively locking connection via the overload ramp balls  14  to the overload ramp element  16 , there is a positively locking connection from the latter to the overload spring unit  17 , there is a positively locking connection from the latter to the radial freewheel  18 , there is a positively locking connection from the latter to the central shaft  20  by way of blocking of the radial freewheel  18  via the freewheel springs  8   b  which form a positively locking connection with the freewheel toothing system  20   h  of the central shaft  20 , and there is a positively locking connection from said central shaft  20  to the adjusting shaft  5   a  or threaded spindle  6  via the output interface  20   c.    
     The moment ramps of the moment ramp section  20   g  are situated on the central shaft  20 , which moment ramps operate counter to the application moment spring  22  and the moment ramp disc  21  which is secured against rotation with respect to the housing  11  via anti-twist securing elements  11   j  and securing grooves  21   c . The moment ramp disc  21  has two ramps with gradients which are different from one another, as shown in  FIG. 12 . These are the application ramps  21   e  and the adjusting ramp  21   d  which can also be called the service ramp. Said ramps generate a direction-dependent torque as a result of the prestress of the application moment spring  22 . In the case of a rotation in the application direction (in  FIG. 12 , the moment ramp section  20   g  then moves to the left, the moment ramp disc  21  being fixed), the moment ramp disc  21  is displaced axially counter to the application moment spring  22  (downward in  FIG. 12 ) via the flat application ramp  21   e  as a result of the contact of the application ramp  20   g ″ of the moment ramp section  20   g ; the tooth profile has to jump into the next tooth for a permanent reduction in brake clearance, it being necessary for a defined rotary angle and a defined axial displacement to be overcome, and the “application moment” being generated which acts between the adjusting shaft  5   a  (spindle) and the housing  11 . 
     In this way, a direction-dependent torque device is formed which has the moment ramp section  20   g , the moment ramp disc  21  and the application moment spring  22 . 
     The smallest possible application amount is defined by the pitch of the teeth of the moment ramp section  20   g  on the corresponding tooth diameter and the thread pitch which is used, the overall magnitude of the brake clearance reduction is dependent on the pivoting angle of the drive element  13  and/or on the pivoting angle of the actuating mechanism, for example of the rotary lever  8  and the actuator  8   a . As a result, disturbance variables which act on the system from the outside have to overcome the “application moment” for a permanent brake clearance reduction, which “application moment” therefore corresponds to a “vibration securing moment” which can also be called “vibration resistance”. 
     When the disc brake  1  is relieved or the drive element  13  pivots back into the starting position, the brake clearance reduction is maintained as a result of the release of the radial freewheel  18  (see  FIGS. 11 and 11   a ). The starting position is defined unambiguously by way of the stop  11   h  which is integrated into the housing  11 . 
     3. Overload Case 
     When the adjusting operation is ended or the nominal brake clearance is present and the threaded spindles  6 ,  6 ′ bear against the brake pads  3 /brake lining carriers  3   a , further rotation of the drive element  13  in the application direction occurs during the application of the brake application force as a result of elasticities in the brake system, but the threaded spindles are blocked against rotation. The central shaft  20  is likewise blocked as a result of the positively locking connection of the threaded spindles  6 ,  6 ′ (or the adjusting shaft  5   a /driver shaft  5 ′ a  which is coupled thereto) to the central shaft  20 . 
     However, the drive element  13  is rotated further, as a result of which a torque is applied by the overload ramp balls  14 , the overload ramp element  16 , the overload spring unit  17 , and the radial freewheel  18 , but rotation does not occur as a result of the blocked radial freewheel  18 . The overload ramp balls  14  run in the ramp profile of the overload ramp raceway  13   c  of the drive element  13  and the overload ramp element  16  and bring about axial displacement of the overload ramp element  16  counter to the overload spring unit  17  which is compressed. 
     When the disc brake  1  is released and/or the drive element  13  is rotated back, the radial freewheel moment of the radial freewheel  18  has to be so great that the overload ramp balls  14  are pivoted back into the starting position again. The integrated stop  11   h  in the housing  11  ensures that the structural brake clearance is maintained between the operating lug  13   a  and the actuator  8   a.    
     4. Service Case 
     The service case comprises the replacement of the brake pads  3  when they are worn; here, the threaded spindles  6 ,  6 ′ are extended to their maximum and have to be reset into the starting position. Here, a rotation is applied at the adjusting interface  20   d  of the central shaft  20  for adjusting of the adjuster in the opening direction (counter to the application direction). Since the central shaft  20  is connected via the output interface  20   c  in a positively locking manner to the threaded spindle  6 ,  6 ′ (and/or adjuster shaft  5   a  and synchronizing device  11  to the driver shaft  5 ′ a ), the rotational movement is transmitted directly to the threaded spindles  6 ,  6 ′. 
     Here, the moment ramp section  20   g  of the central shaft  20  is rotated with the adjusting ramp  20   g ′ against the adjusting ramp  21   d  (service ramp) of the moment ramp disc  21  (see  FIG. 12 ), and the moment ramp disc  21  is displaced axially counter to the application moment spring  22  because the central shaft  20  is fixed axially in the housing  11  via the guide section  20   e  in the guide groove  11   i . A “ramp restoring moment” is generated. 
     The rotation of the central shaft  20  is transmitted to the overload ramp balls  14  via the blocked radial freewheel  18 , the positively locking connection to the overload spring unit  17  and the positively locking connection to the overload ramp element  16 . The drive element  13  is locked against rotation in the opening direction via the integrated stop  11   h  of the housing  11 , and the overload ramp balls  14  run onto the ramp profile of the overload ramp raceway  13   c  of the drive element  13  and the overload ramp raceway  16   a  of the overload ramp element  16  and displace the overload ramp element  16  axially counter to the overload spring unit  17 , and an “overload restoring moment” is generated. 
     The sum of the two torques “ramp restoring moment” and “overload restoring moment” results in the “service moment” which has to be overcome in order to restore the system (via the adjusting or service interface  20   d ). 
     5. Miscellaneous 
     The overload ramp balls  14  are positively guided by way of the ball cage  15 , in order to ensure synchronization of the overload ramp balls  14  under different load cases. 
     The radial freewheel  18  consists of radially stacked spring arms, in order to achieve mutual support in the blocking direction. The corresponding contour on the central shaft  20  is configured as a freewheel toothing system  20   h , in which the spring arms are supported in the blocking direction and a defined freewheel moment is set in the release direction. 
     The sealing ring groove  20   j , into which an O-ring or a diaphragm can be mounted depending on the type of embodiment, is introduced on the central shaft  20  below the adjusting interface  20   d  (hexagonal journal). 
     A toothing system is attached to the central shaft  20  as sensor toothing system  20   i  for wear potentiometer tapping, via which toothing system the wear can be detected, for example, by use of a rotary angle sensor in a manner which is offset axially with respect to the adjuster line of action. The diameter of the sensor toothing system  20   i  is adapted to a wear sensor planetary gear mechanism. 
     The wear adjustment device is designed as a ramp wear adjuster primarily for the wear adjustment for pneumatically applied disc brakes in the commercial vehicle field, but can also be used in all other applications where wear compensation is necessary. 
     The wear adjustment device  10  can be configured both in an external design and in an internal design. An external design is to be understood to mean that the wear adjustment device  10  can be placed around a threaded spindle  6 ,  6 ′ of a spindle unit  5 ,  5 ′ or can be placed onto said threaded spindle  6 ,  6 ′. An internal design means that the wear adjustment device  10  can be inserted into a spindle unit  5 ,  5 ′, for example into a threaded spindle  6 ,  6 ′ as in the first exemplary embodiment of the disc brake  1  according to  FIG. 1 . 
     The above-described exemplary embodiments do not restrict the invention which can be modified within the scope of the appended claims. 
     It is thus conceivable, for example, that compression spring systems, elastomer systems or variations can also be used instead of the described disc spring systems (overload spring unit  17  and application moment spring  22 ). 
     The described ramp systems in the overload ramp raceways  13   c  and  16   a  can be varied freely in terms of the configuration of the ramp raceway and the number of hollows. 
     The gradients and pitches of the described moment ramps  20   g ′,  20   g ″ of the moment ramp section  20   g  of the central shaft  20  and the adjusting ramps  21   d  and application ramps  21   e  of the moment ramps  21   a  can be varied freely. 
     Instead of the described radial freewheel  18 , all freewheel systems which are decoupled from axial forces can be used. 
     The form and embodiment of the configuration of the output interface  20   c  of the central shaft  20  with respect to the threaded spindle  6 ,  6 ′ (and/or adjuster shaft  5   a , driver shaft  5 ′ a ) can be varied freely. 
     The form and embodiment of the fixing means  11   g  and  11   k  of the housing  11  can be varied freely. 
     The form and embodiment of the anti-twist fixing structure (anti-twist securing element  11   j , spring fixing grooves  16   b , assembly connection  17   c , fixing projection  17   d , securing groove  21   c ) can be varied freely. 
     LIST OF DESIGNATIONS 
     
         
           1  Disc brake 
           2  Brake disc 
           3  Brake pad 
           3   a  Brake lining carrier 
           4  Brake caliper 
           5 ,  5 ′ Spindle unit 
           5   a  Adjuster shaft 
           5 ′ a  Driver shaft 
           5   b  Profile 
           5 ′ c  Axial groove 
           6 ,  6 ′ Threaded tube 
           6   a ,  6 ′ a  Pressure piece 
           7  Crossmember 
           8  Rotary lever 
           8   a  Actuator 
           8   b  Body 
           9  Drive 
           10  Adjusting device 
           11  Housing 
           11   a  Wall 
           11   b ,  11   c  Opening 
           11   d  Cover section 
           11   e  Bottom section 
           11   f  Wall opening 
           11   g  Caliper anti-twist fixing structure 
           11   h  Stop
         11   i  Guide groove     11   j  Anti-twist securing element     
           11   k  Anti-twist fixing element 
           12  Axial bearing ball 
           13  Drive element 
           13   a  Operating lug 
           13   b  Axial bearing raceway 
           13   c  Overload ramp raceway 
           14  Overload ramp ball 
           15  Ball cage 
           16  Overload ramp element 
           16   a  Overload ramp raceway 
           16   b  Spring fixing groove 
           17  Overload spring unit 
           17   a ,  17   b  Spring 
           17   c  Assembly connection 
           17   d  Fixing projection 
           18  Radial freewheel 
           18   a  Freewheel axial bearing raceway 
           18   b  Freewheel spring 
           18   c  Profiling 
           18   d  Spring fixing groove 
           19  Freewheel ball 
           20  Central shaft 
           20   a  Drive section 
           20   b  Output section 
           20   c  Output interface 
           20   d  Adjusting interface 
           20   e  Guide section 
           20   f  Freewheel axial bearing raceway 
           20   g  Moment ramp section 
           20   g ′ Adjusting ramp 
           20   g ″ Application ramp 
           20   h  Freewheel toothing system 
           20   i  Sensor toothing system 
           20   j  Sealing ring groove 
           20   k  Output element 
           20   l  Output tongue 
           20   m  Output edge 
           21  Moment ramp disc 
           21   a  Moment ramp 
           21   b  Pressure side 
           21   c  Securing groove 
           21   d  Adjusting ramp 
           21   e  Application ramp 
           22  Application moment spring 
           23  Synchronizing device 
           23   a ,  23 ′ a  Synchronizing wheel 
           23   b  Synchronizer 
       
    
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.