Abstract:
An electromechanically actuated disk brake with mechanical self-boosting includes an automatic wear readjusting device, which can for instance have a positive-engagement detent device. An increased air clearance caused by wear of friction brake linings is prevented by the invention, which thus also prevents an increase in the displacement of the friction brake lining in the direction of rotation of the brake disk when the disk brake is actuated in order to attain the self-boosting.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to an improved disk brake with self-boosting.  
           [0003]    2. Description of the Prior Art  
           [0004]    Disk brakes are known that have a friction brake lining, which for braking can be pressed by an actuation unit against a brake disk, and a self-boosting device which converts a frictional force, which the rotating brake disk upon braking exerts on the friction brake lining pressed against it, into a contact-pressure force, that in addition to the actuation unit presses the friction brake lining against the brake disk. As a result, a contact-pressure force to be exerted by the actuation unit is reduced and self-boosting is attained.  
           [0005]    Mechanical self-boosting devices with wedge mechanisms or lever systems are known. The wedge mechanisms are also known as ramp mechanisms. This list is not exhaustive. Wedge mechanisms have a wedge on a back side of the friction brake lining, remote from the brake disk, that is braced on a ramp. If the friction brake lining for braking is pressed by the actuation unit against the rotating brake disk, the frictional force exerted by the rotating brake disk on the friction brake lining pressed against it displaces the friction brake lining in the direction of a narrowing wedge gap between the counterpart wedge and the brake disk. As a force of reaction, the counterpart wedge exerts a force on the wedge that has one component transverse to the brake disk. This force transverse to the brake disk is an additional contact-pressure force, which in addition to the actuation unit presses the friction brake lining against the brake disk and as a result increases the total contact-pressure force, resulting in the self-boosting. In the case of lever mechanisms, the friction brake lining in braking is braced on a lever that is oblique to the brake disk at a support angle. The support angle corresponds to the wedge angle in the wedge mechanism; both mechanisms are mechanically comparable to one another.  
           [0006]    Still other self-boosting systems, for instance hydraulic ones, are also known.  
           [0007]    The problem exists that a displacement travel distance, by which distance the friction brake lining must be displaced in order to actuate the disk brake until it rests on the brake disk, increases with increasing wear of the friction brake lining.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0008]    The disk brake of the invention has a return-travel limiter for the friction brake lining, which limits a travel by which the friction brake lining is lifted from the brake disk upon release of the brake. As a result, upon release of the disk brake, the friction brake lining is not always moved transversely away from the brake disk to its original outset position, with the consequence of an increasing spacing, with increasing wear of the friction brake lining, between the friction brake lining and the brake disk; instead, the spacing (air clearance) between the friction brake lining and the brake disk is limited.  
           [0009]    The disk brake of the invention furthermore has a bracing means for the friction brake lining, on which bracing means, upon braking, the friction brake lining is braced at a support angle obliquely to the brake disk. The bracing means is movable only in the direction of the brake disk and has a return-travel block. For brake actuation, the bracing means is movable only in the direction toward the brake disk, but not away from it. For changing the friction brake lining, the bracing means can be restorable away from the brake disk. The term return-travel block, unlike the return-travel limiter for the friction brake lining, has been selected because in the friction brake lining, a limited return travel should be possible, to enable lifting the friction brake lining from the brake disk when the disk brake is released. This is not necessary in the case of the bracing means for the friction brake lining. Nevertheless, even with the bracing means, a limited return travel away from the brake disk may be possible; that is, in principle, the return-travel limiter of the friction brake lining and the return-travel block of the bracing means may be embodied identically.  
           [0010]    The invention additionally provides a spring element, which urges the bracing means in the direction of the brake disk.  
           [0011]    For braking, the friction brake lining of the disk brake of the invention is, as in known disk brakes that have self-boosting, pressed against the brake disk by the actuation unit. The self-boosting device brings about the desired self-boosting. Upon release of the disk brake, the return travel by which the friction brake lining is lifted from the brake disk is limited by the return-travel limiter. With increasing wear of the friction brake lining, the friction brake lining accordingly no longer returns to its original outset position but instead, depending on its wear, remains closer to the brake disk, so that the air clearance between the brake disk and the friction brake lining remains approximately constant. Because the friction brake lining no longer returns to its original outset position, the bracing means is displaced by the spring element toward the brake disk. The return-travel block prevents the bracing means, upon the next brake actuation, from moving away from the brake disk. Thus with increasing wear of the friction brake lining, the friction brake lining and the bracing means move in the direction of the brake disk, so that the air clearance between the friction brake lining and the brake disk and a displacement travel distance of the friction brake lining parallel to the brake disk upon actuation of the disk brake do not increase, or increase to only a limited extent. The motion of the friction brake lining and of the bracing means in the direction of the brake disk with increasing wear of the friction brake lining can be effected either continuously or intermittently.  
           [0012]    The invention has the advantage that the displacement travel distance of the friction brake lining for actuating the disk brake does not increase, or increases only to a limited extent. This has the advantage that a tightening time upon actuation of the disk brake is not lengthened by wear to the friction brake lining.  
           [0013]    Moreover, the disk brake of the invention can be made smaller, because the displacement travel distance of the friction brake lining required for braking is not lengthened parallel to the brake disk by wear to the friction brake lining.  
           [0014]    A further, considerable advantage is also attained in disk brakes with self-boosting that varies over the displacement travel distance of the friction brake lining. The self-boosting devices that vary with the displacement of the friction brake lining have been proposed, for instance to move the friction brake lining transversely to the brake disk quickly for overcoming the air clearance between the brake disk and the friction brake lining, and to attain greater self-boosting in the presence of major braking forces. In a wedge or ramp mechanism, the varying self-boosting is attained by means of a wedge angle that varies in the longitudinal direction of the wedge. If in this kind of self-boosting the displacement travel distance of the friction brake lining, for overcoming the air clearance resulting from wear to the friction brake lining, changes, then the self-boosting that is operative at a certain contact-pressure force also changes, since the friction brake lining is located at a different point on the ramp from that which is structurally provided, and thus is braced at a different support angle from what was intended. In the disk brake of the invention, the situation is different, since the friction brake lining, because of the bracing means that approaches the brake disk in accordance with the wear to the friction brake lining, at a certain contact-pressure force, is always braced at least approximately at the same point of the bracing means and thus at the intended support angle.  
           [0015]    The disk brake of the invention is intended in particular for electromechanical actuation in which the pressing of the friction brake lining against the brake disk is effected in particular by means of an electric motor via a rotation/translation conversion gear, for instance in the form of a helical gear; a step-down gear may be provided between the electric motor and the helical gear. The self-boosting is provided mechanically in particular.  
           [0016]    One embodiment provides a restoring device with which the bracing means and/or the return-travel limiter can be restored to its outset position for changing the friction brake linings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments, taken in conjunction with the drawings, in which:  
         [0018]    [0018]FIG. 1 schematically shows a disk brake of the invention, looking radially inward, that is, from the direction of an imaginary axis of rotation of a brake disk; and  
         [0019]    [0019]FIG. 2 shows a modified exemplary embodiment of the disk brake of FIG. 1 of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    The disk brake  10  of the invention shown in FIG. 1 has a brake caliper  12 , in which two friction brake linings  14 , 16  are located. Between the two friction brake linings  14 , 16 , there is one brake disk  18 . One of the two friction brake linings  14  is disposed fixedly in the caliper  12 , or is braced parallel to the brake disk  18  via a stator (brake retainer) not shown in the drawing. For braking, the other friction brake lining  16  can be pressed by an actuation unit  20  against the brake disk  18 . The caliper  12  is embodied as a so-called floating caliper; it is displaceable transversely to the brake disk  18 , so that contact pressure against the movable friction brake lining  16  displaces the caliper  12  transversely to the brake disk  18 , so that it presses the fixed friction brake lining  14  against the other side of the brake disk  18 .  
         [0021]    An electromechanical actuation unit  20  it includes an electric motor  22  with a step-down gear  24  flanged to it and with a spindle drive which forms a rotation/translation conversion gear, for converting the rotary driving motion of the electric motor  22  or of the step-down gear  24  into a translational motion, pressing the friction brake lining  16  against the brake disk  18 . All that can be seen of the spindle drive in the drawing is a spindle  26 . For the rest, the spindle drive is located in a housing of the step-down gear and is therefore not visible in the drawing. Likewise, all that can be seen of the electric motor  22  and the step-down gear  24  is their housings. The spindle  26  presses with its face end against a wedge plate  28 , on whose side toward the brake disk  18  the movable friction brake lining  16  is secured.  
         [0022]    The disk brake  10  has a mechanical self-boosting device  30 . The self-boosting device  30  includes, besides the wedge plate  28 , a bracing means  32  and roller bodies  34  that are disposed between the wedge plate  28  and the bracing means  32 . The bracing means  32  includes a base plate  36  and a ramp plate  38 , which is secured to the base plate  36  on a side of the base plate  36  toward the wedge plate  28  and the brake disk  18 . The spindle  26  of the spindle drive of the actuation unit  20  penetrates the bracing means  32 , through a hole. Spring elements  40  embodied as tension springs connected the wedge plate  28  and the ramp plate  38  spring-elastically to one another and act upon the bracing means  32  with a spring force acting in the direction of the brake disk  18 .  
         [0023]    The wedge plate  28 , and together with it, the movable friction brake lining  16  are displaceable parallel to the brake disk  18  in the caliper  12 .  
         [0024]    The wedge plate  28 , on its side remote from the brake disk  18 , has indentations  42  of V-shaped cross section. Cheek faces of the V-shaped indentations  42  form wedge faces; the V-shaped indentations  42  form double wedges, which can also have different wedge angles. The V-shaped indentations  42  that form the double wedges will hereinafter be called double wedges, that, or simply wedges, and like the indentations themselves will be identified by reference numeral  42 .  
         [0025]    The ramp plate  38  has identical indentations  44  of V-shaped cross section, which are disposed opposite the double wedges  44 . These V-shaped indentations  44  form double ramps and will hereinafter be called that, or simply ramps. The roller bodies  34 , which in the exemplary embodiment of the invention shown and described are embodied as rollers, rest in opposed V-shaped indentations that the double wedges  42  and the double ramps  44  form.  
         [0026]    The self-boosting device  30  functions as follows:  
         [0027]    If the actuation unit  20 , for braking, presses the movable friction brake lining  16  against the rotating brake disk  18 , the latter exerts a frictional force on the friction brake lining  16 , which displaces the friction brake lining  16  in the caliper  12  both parallel to the brake disk  18  and in the direction of rotation thereof. Along with the friction brake lining  16 , the wedge plate  28  is displaced, and consequently the roller bodies  34  roll on the double wedges  42  and the double ramps  44 . The roller bodies  34  each roll on one wedge face of the double wedges  42  and one corresponding, diagonally opposed ramp face of the double ramps  44 . The respective other wedge face and ramp face is intended for displacement of the friction brake lining  16  in the opposite direction, upon a reversed direction of rotation of the brake disk  18 . Via the roller bodies  34 , the friction brake lining  16  is braced on the ramp plate  38  of the bracing means  32 . The displacement of the friction brake lining  16  that in braking is pressed against the brake disk  18  causes, because of the bracing via the roller bodies  34  on the ramp and wedge faces, a force component perpendicular to the brake disk  18 , or in other words an additional contact-pressure force of the friction brake lining  16  against the brake disk  18 . This contact-pressure force is operative in addition to the contact-pressure force exerted by the actuation unit  20 . The disk brake  10  thus has self-boosting, which increases the braking force.  
         [0028]    An elastically bendable plate  48  is inserted into slots  46  in the wedge plate  28 . The plate  48  protrudes laterally out of the wedge plate  28 , and because of the guidance in the slots  46 , the wedge plate  28  is displaceable parallel to the brake disk  18  relative to the elastic plate  48 . The elastic plate  48  is embodied in continuous form, which is represented in the drawing by dashed lines in the middle region of the elastic plate  48 . The outer edges of the elastic plate  48  are embodied obliquely as a result of a chamfer  50 ; with elastic prestressing of the plate  48 , they rest on inside faces  49 , oriented toward one another, of the caliper  12 .  
         [0029]    If for braking the friction brake lining  16  is pressed against the brake disk  18  by the actuation unit  20 , the plate  48  bends elastically. If the disk brake  10  is released again after the braking, the elastic plate  48  returns to its flat, relaxed original shape. In the process, the elastic plate  48  lifts the movable friction brake lining  16  from the brake disk  18 . If the motion of the friction brake lining  16  on being pressed against the brake disk  18  increases because of wear to the friction brake lining  16 , then the outer edges of the elastic plate  48  slide along the inside faces  49  of the caliper, in the direction of the brake disk  18 . As a consequence, when the disk brake  10  is released the friction brake lining  16  is no longer lifted away from the brake disk  18  as far as its outset position but instead less, by the length of a displacement travel distance of the outer edges of the elastic plate  48 . As a result, the wear to the friction brake linings  14 , 16  is compensated for. The elastic plate  48  cooperating with the inside faces  49  of the caliper  12  forms a return-travel limiter for the friction brake lining  16 .  
         [0030]    The base plate  36  of the bracing means  32  has pawls  54  on its sides, which are pressed outward spring-elastically and mesh with sets of teeth  52  of the caliper  12 . The pawls  54  cooperating with the sets of teeth  52  form a return-travel block for the bracing means  32 ; the bracing means  32  can be moved only in the direction toward the brake disk  18 , but not away from it.  
         [0031]    If because of wear to the friction brake linings  14 , 16  the elastic plate  48  has been displaced along the inside faces  49  of the caliper  12  in the direction of the brake disk  18 , the spring elements  40 , which connect the wedge plate  28  with the ramp plate  38 , pull the ramp plate  38  and with it the bracing means  32  in the direction of the brake disk  18 , so that the pawls  54 , offset by one tooth in the direction of the brake disk  18 , come to mesh with the sets of teeth  52 . As a result of wear to the friction brake linings  14 , 16 , the bracing means  32  thus readjusts in the direction of the brake disk  18  as well. The elastic plate  48  forming the return-travel limiter of the friction brake lining  16  and the locking pawls  54  that form the return-travel block of the bracing means  32  form a readjusting device, which automatically compensates for wear to the friction brake linings  14 , 16 . A displacement travel distance of the friction brake lining  16  parallel to the brake disk  18  upon braking is thus prevented from being longer with increasing wear to the friction brake linings  14 , 16 .  
         [0032]    The elastic plate  48 , which forms the return-travel limiter of the friction brake lining  16  and cooperates with the inside faces  49  of the caliper  12 , acts by frictional engagement. The pawls  54 , which form the return-travel block of the bracing means  32  and cooperate with the sets of teeth  52  of the caliper  12 , operate by positive engagement.  
         [0033]    For changing the friction brake linings  14 , 16 , the disk brake  10  has a restoring device  56 . It includes a first ring  58 , which is disposed fixedly on the spindle  26  and therefore moves along with the spindle  26 , and a second ring  60 , which is axially displaceable on the spindle  26  and is located at the level of the pawls  54 . The first ring  58  is located between the brake disk  18  and the second ring  60 . The pawls  54  are connected to the second ring  60  by tension cables  62 . The second ring  60  is retained axially displaceably but in a manner fixed against relative rotation by a pin  64 , protruding radially outward from it, which engages an oblong slot  66  in the caliper  12 . The oblong slot  66 , which is represented by dashed lines in the drawing, extends axially parallel to the spindle  26  and forms a longitudinal guide for the second ring  60 .  
         [0034]    For restoring the bracing means  32 , the spindle  26  is rotated in reverse; that is, it moves away from the brake disk  18 . With the spindle  26 , the first ring  58  also moves away from the brake disk  18  and strikes the second ring  60  and carries it along with it. With the tension cables  62 , the second ring  60  puts the pawls  54  out of engagement with the sets of teeth  52 , and as a result the base plate  36  of the bracing means  32  becomes movable away from the brake disk  18 . Via the second ring  60 , the first ring  58  carries the base plate  36 , with the reverse-rotating spindle  26 , along with it to its outset position. The wedge plate  28  and the ramp plate  38  can be pressed back into their outset position.  
         [0035]    [0035]FIG. 2 shows a disk brake with a differently embodied device to compensate for wear-caused travel and with a different restoring device  56 . Otherwise, the two disk brakes  10  are embodied identically and function in the same way. To avoid repetition, the above explanation of FIG. 1 is therefore referred to in this respect for explaining FIG. 2. For the same components, the same reference numerals are used in FIGS. 1 and 2.  
         [0036]    For embodying the restoring device  56 , the base plate  36  of the bracing means  32  of the disk brake  10  of FIG. 2 is embodied as a circular-annular disk, with a male thread  68  that meshes with a female thread  70  of the caliper  12 . The threads  68 ,  70  are non-self-locking steep threads. A tubular attachment  72  to the ramp plate  38  reaches through the base plate  36 . The attachment  72  has an outward protruding flange  73 , and compression springs are disposed axially parallel between this flange and the base plate  36  and are braced on the base plate  36  via a common axial bearing  76 . When the base plate  36  is resting on the ramp plate  38 , the compression springs  74  are relaxed and do not rest on the base plate  36 .  
         [0037]    If the ramp plate  38 , upon a brake actuation, moves in the direction of the brake disk  18  because of wear to the friction brake linings  14 , 16 , then the compression springs  74  press the base plate  36  in the direction of the brake disk  18 .  
         [0038]    Since the threads  68 ,  70  are non-self-locking, and since the base plate  36  is freely rotatable because of the axial bearing  76 , the base plate  36  moves in a helical motion in the direction of the brake disk  18 . If the base plate  36  is resting on the ramp plate  38 , friction between the base plate  36  and the ramp plate  38  prevents rotation of the base plate  36 , so that the base plate  36  axially braces the ramp plate  38 .  
         [0039]    For restoration, the spindle  26  is rotated in reverse. A ring  78  fixedly disposed on the spindle  26  strikes an inward-protruding flange  80  of the base plate  36  and moves the base plate away from the brake disk  18  in a helical motion. The compression springs  74  are tightened, and the ramp plate  38  is pulled away from the brake disk  18 . With the ramp plate  38 , via the tension springs  40 , the wedge plate  28  is likewise pulled away from the brake disk  18 .  
         [0040]    The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.