Abstract:
The invention relates to a self-boosting electromechanical disk brake with a frame caliper equipped with a wear readjustment device which for instance is automatic and which upon tensing of the disk brake stores energy by prestressing a torsion shaft, which upon release of the disk brake converts this energy into a wear readjustment motion. In the process, a spacing between two brake lining holders of the frame caliper in the disk brake is decreased.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an improved self-boosting electromechanical disk brake which is intended in particular for use as a wheel brake in motor vehicles.  
         [0003]     2. Description of the Prior Art  
         [0004]     One self boosting electromechanical disk brake known from German Patent Disclosure DE 101 51 950 A1 has a floating caliper of U-shaped cross section as its brake caliper, which fits over a brake disk on the circumference and in which two friction brake linings are located, one on either side of a brake disk. The brake caliper is supported displaceably transversely to the brake disk and is accordingly what is known as a floating caliper. However, the use of a fixed caliper is equally possible.  
         [0005]     For actuation, the known disk brake has an electromechanical actuating device, with which a friction brake lining can be pressed against one side of the brake disk. As a result of the one friction brake lining being pressed against one side of the brake disk, the caliper is displaced transversely to the brake disk and presses the other friction brake lining against the other side of the brake disk, as a result of which the brake disk is braked. The electromechanical actuating device has an electric motor, an optional step-down gear, and a rotation-to-translation conversion gear. The most various kinds of gears may be used; besides gear drives, a rotatable cam as a rotation-to-translation conversion gear can for instance also be considered. Instead of an electric motor, an electromagnet can be used, for instance. In the generic terminology here, the adjective “electromechanical” accordingly refers to the type of actuation of the disk brake.  
         [0006]     As its self-boosting device, the known disk brake has a wedge mechanism, with a wedge disposed on a back side, remote from the brake disk, of one friction brake lining; this wedge is braced on an oblique face in the caliper. The oblique face extends obliquely to the brake disk; there is a wedge-shaped gap between the oblique face and the brake disk that becomes narrower in a circumferential direction to the brake disk, specifically in the intended direction of rotation of the brake disk. If the friction brake lining is pressed against the rotating brake disk for actuation of the disk brake, then the rotating brake disk exerts a frictional force on the friction brake lining in the circumferential direction, and thus in the direction of the increasingly narrow wedge-shaped gap between the oblique face and the brake disk. Because of the principle of a wedge, the oblique face exerts a force on the friction brake lining, which includes a force component transverse to the brake disk. This force component transverse to the brake disk is a contact pressure, which presses the friction brake lining against the brake disk in addition to a contact pressure exerted by the actuating device. In this way, the contact pressure exerted by the actuating device is increased, and self boosting occurs. The wedge mechanism converts a frictional force, exerted by the rotating brake disk on the friction brake lining pressed against it, into a contact pressure of the friction brake lining against the brake disk. The wedge and the oblique face need not have a constant wedge angle over their entire length; the wedge angle may vary as a function of a displacement distance of the friction brake lining along the oblique face. In that case, the term ramp mechanism may be used. Preferably at the onset of tensing the disk brake, a large wedge angle or ramp angle is selected, for the sake of rapidly overcoming an air play between the friction brake linings and the brake disk. At the end of the tensing, when the braking force and contact pressure are high, a small wedge angle or ramp angle and consequently high self boosting are preferably selected.  
         [0007]     To attain self boosting even for the reversed direction of rotation of the brake disk (travel in reverse), it is known to use a second wedge mechanism with an oppositely disclosed wedge and an oppositely extending oblique face. The wedge angle can differ for travelling forward and travelling in reverse, in order to attain self boosting actions of different strengths.  
         [0008]     Other self-boosting devices are also known, for instance with one or more support levers that brace the friction brake lining, pressed against the brake disk, obliquely at a support angle to the brake disk. The support angle is equivalent to the wedge angle of the wedge mechanism.  
         [0009]     The self-boosting disk brakes share the feature that the friction brake lining, for attaining the self boosting, is moved in the circumferential direction or the direction of rotation of the brake disk, and this motion, or the frictional force exerted by the brake disk on the friction brake lining pressed against it, is converted into a contact pressure of the friction brake lining against the brake disk. With decreasing thickness of the friction brake lining caused by wear, the displacement distance of the friction brake lining in the circumferential direction or the direction of rotation of the brake disk becomes greater. A displacement distance of the friction brake lining for attaining a defined braking force is lengthened as a result. This has the disadvantage that the time until a desired braking force is attained is lengthened. Another disadvantage is that a sufficiently large installation space for displacing the (worn) friction brake lining must be provided. In electromechanical disk brakes, in which some parts of the actuating device, of the floating caliper, or of a housing are displaced along with the friction brake lining, space problems can arise.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0010]     The disk brake of the invention has a frame caliper with two brake lining holders and with tie rods that connect the brake lining holders outside the brake disk. The brake lining holders are plate-shaped, for instance, and the brake disk is located between them. The friction brake linings are disposed on the side of the brake lining holders oriented toward the brake disk. In comparison to a floating caliper, a frame caliper has the advantage that it can be embodied such that the tie rods that connect the brake lining holders are stressed essentially only by tension as a result of the pressing of the friction brake linings against the brake disk, while conversely a floating caliper is stressed by bending in the yoke region, which is unfavorable for the sake of stability and rigidity of the caliper. The brake lining holders of the frame caliper can be connected on both ends by tie rods, which in terms of the mechanical stress is also more favorable than is the case for the legs of a floating caliper, whose radially inner edges, in terms of the brake disk, are free.  
         [0011]     To compensate for wear, the brake lining holders of the disk brake of the invention are displaceable along the tie rods, so that a spacing of the brake lining holders from one another can be varied. In other words, an inside diameter of the frame caliper in the disk brake of the invention is adjustable. As a result, an air play, that is, a gap between the friction brake linings and the brake disk when the disk brake is not actuated, can be kept constant with increasing wear and decreasing thickness of the friction brake linings. Thus the disk brake of the invention has a wear readjustment. This has the advantage that the displacement distance of the friction brake lining in the circumferential direction or direction of rotation of the brake disk is independent of a thickness of the friction brake lining. Another advantage is that the displacement distance of the friction brake lining is not lengthened with increasing wear and decreasing thickness of the friction brake lining. In a self-boosting device with variable self boosting over a displacement distance of a friction brake lining, the disk brake of the invention has the advantage that the magnitude of the self boosting does not change as a result of a displacement distance that has become longer because of wear of the friction brake lining. Even with a variable step-up, i.e., speed increase, of the electromechanical actuating device, wear to the friction brake lining does not change the step-up.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     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:  
         [0013]      FIG. 1  shows a first exemplary embodiment, partly in section, of a disk brake of the invention, in a view looking radially toward a brake disk; and  
         [0014]      FIG. 2  shows a second embodiment of a disk brake of the invention, in a view corresponding to  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     The self-boosting electromechanical disk brake  10  of the invention, shown in  FIG. 1 , is a so-called partial-lining disk brake; its friction brake linings extend over only a limited angle in the circumferential direction of a brake disk  20 . It has a frame caliper  12  with two brake lining holders  14 ,  16  and two anchor bolts  18 , which as tie rods join the brake lining holders  14 ,  16 . The brake lining holders  14 ,  16  are embodied as plates; they are parallel to one another and parallel to the brake disk  20  that is located between them. The tie rods  18  connect the brake lining holders  14 ,  16  on their ends, outside a circumference of the brake disk  20 . The anchor bolts  18  are disposed transversely to the brake disk  20  and to the brake lining holders  14 ,  16 . The anchor bolts  18  are firmly press-fitted into the brake lining holder  14 . The other brake lining holder  16  has sleeves  22 , in which the anchor bolts  18  rest displaceably. The sleeves  22  protrude from a side, remote from one brake lining holder  14  and the brake disk  20 , of the other brake lining holder  16 . The anchor bolts  18  are provided with screw threads  24  on their ends located in the sleeves  22 . The anchor bolts  18  protrude from the sleeves  22 , and nuts  26  are screwed onto the protruding ends of the anchor bolts  18 ; these nuts are seated on end edges of the sleeves  22  and in this way keep the two brake lining holders  14 ,  16  at the intended spacing from one another.  
         [0016]     On the sides of the brake lining holders  14 ,  16  toward the brake disk  20 , friction brake linings  28 ,  30  are provided. The anchor bolts  18  and the brake lining holders  14 ,  16  are located at approximately the same height as the centers of area of the friction brake linings  28 ,  30 . As a result, when the friction brake linings  28 ,  30  are pressed against the brake disk  20  for braking, the tie rods  18  are stressed only slightly if at all by bending and the brake lining holders  14 ,  16  are stressed only slightly if at all by torsion.  
         [0017]     Between the brake lining holders  14 ,  16 , slide sleeves  32  are placed on the anchor bolts  18 . Slide bearing bushes  34  are inserted into the slide sleeves  32 , and the slide sleeves  32  are provided with a grease filling. The slide sleeves  32  are part of a brake holder  36 , which holds the disk brake  10 . The anchor bolts  18  are supported transversely to the brake disk  20  in the slide sleeves  32 . The caliper of the disk brake  10 , embodied as a frame caliper  12 , is accordingly a floating caliper that can be displaced transversely to the brake disk  20 . The slide sleeves  32  are disposed in the same imaginary plane as the brake disk  20  and as a result brace the frame caliper  12  in braking without torque.  
         [0018]     On a side of the other brake lining holder  16  oriented toward the brake disk  20 , there is a ramp plate  38 . The ramp plate  38  and the brake lining holder  16  are provided, on their sides toward one another, with tub or dish-shaped, elongated indentations in which balls  40  as roller bodies are located. The indentations extend for instance straight in a direction of a secant to the brake disk  20  or in a circular arc about an imaginary, common axis that intersects the brake disk  20  at a right angle and preferably coincides with an axis of rotation of the brake disk  20 . In this way, the balls  40  guide the ramp plate  38  displaceably in the secant direction or in a circular arc in the direction of rotation of the brake disk  20 .  
         [0019]     The ramp plate  38 , on its side remote from the other brake lining holder  16  and toward the brake disk  20 , carries the friction brake lining  30 . The friction brake lining  30  is accordingly not disposed directly on the brake lining holder  16 , but instead only indirectly, via the ramp plate  38  guided displaceably on the brake lining holder  16 .  
         [0020]     For actuation of the disk brake  10 , the ramp plate  38  is displaced parallel to the brake disk  20 , in the direction of rotation of the brake disk. The balls  40  roll in the tub-shaped indentations and, since the indentations become shallower toward their ends, the balls press the ramp plate  38  away from the brake lining holder  16 . As a result, the ramp plate  38 , with the friction brake lining  30  disposed on it, moves obliquely toward the brake disk  20 ; the friction brake lining  30  is pressed against the brake disk  20 . Upon further displacement of the ramp plate  38 , the brake lining holder  16 , via the anchor bolts  18 , pulls brake lining holder  14  toward the brake disk  20  and as a result presses the friction brake lining  28  against the other side of the brake disk  20 , which is thereby braked. The rotating brake disk  20  exerts a frictional force on the friction brake linings  28 ,  30  pressed against it, and this force urges the ramp plate  38  in the direction of rotation of the brake disk  20  and thus in the displacement direction of the brake disk. The frictional force exerted by the rotating brake disk  20  on the friction brake lining  30  thus exerts an additional force on the ramp plate  38  in its direction of displacement, which by way of the bracing of the ramp plate  38  with the balls  40  on the brake lining holder  16  exerts an additional contact pressure of the friction brake linings  28 ,  30  against the brake disk  20 . In this way, brake boosting takes place, and the disk brake  10  has a mechanical self boosting. The indentations in the ramp plate  38  and in the brake lining holder  16 , in which the balls  40  are located, form ramps  42 ; the balls  40 , ramps  42 , ramp plate  38 , and the brake lining holder  16  form a wedge or ramp mechanism, which effects the mechanical self boosting upon actuation of the disk brake  10 .  
         [0021]     For actuation of the disk brake  10 , that is, for displacement of the ramp plate  38 , the disk brake  10  has an electromechanical actuating device  44 , with an electric motor  46  and a pivot lever  48 . The pivot lever  48  is supported pivotably on the brake lining holder  16 . In the region of its pivot bearing, the pivot lever  48  is provided with a set of teeth  50 , which meshes with a set of teeth  52  on the ramp plate  38 . The two sets of teeth  50 ,  52  extend such that they remain in engagement with one another upon pivoting of the pivot lever  48  and the attendant displacement of the ramp plate  38 .  
         [0022]     On the end remote from its pivot bearing, the pivot lever  48  is provided with a set of teeth  54 , which extends in a circular arc coaxially about an imaginary pivot axis of the pivot lever  48 . This set of teeth  54  meshes with a pinion  56 , which is fixed against relative rotation to a motor shaft of the electric motor  46 . For actuation of the disk brake  10 , the ramp plate  38  is displaced in the direction of rotation of the brake disk  20  in order to attain the desired self boosting.  
         [0023]     The two nuts  26  screwed onto the anchor bolts  18  are part of a wear readjustment device. By synchronous rotation of the nuts  26  on the anchor bolts  18 , a spacing of the two brake lining holders  14 ,  16  from one another can be adjusted, and as a result, wear to the two friction brake linings  28 ,  30  can be compensated for. For the sake of the synchronous rotation of the nuts  26 , there is a toothed belt  58 , which wraps around the nuts  26  and is in engagement with sets of teeth on the nuts  26 . The toothed belt  58  forms a synchronous drive for the nuts  26 .  
         [0024]     For wear-dependent rotation of the nuts  26 , the disk brake  10  has an automatic readjusting device  60  with a torsion shaft  62  and a return block  64 . The torsion shaft  62  is disposed parallel to the anchor bolts  18 , near one of the two anchor bolts  18 . It has gear wheels  66 ,  68  on both ends, of which one gear wheel  66  meshes with a set of teeth  70  of the ramp plate  38 , and the other gear wheel  68  meshes with the teeth of one of the two nuts  26 . As a result of the displacement of the ramp plate  38  upon actuation of the disk brake  10 , the torsion shaft  62  is rotated, at least on one of its ends, and via its gear wheel  68 , it exerts a torque on the nut  26 .  
         [0025]     The return block  64  is embodied like a ratchet; it has a pawl  72  that cooperates with a ratchet wheel  74  that is seated on the torsion shaft  62  in a manner fixed against relative rotation. The ratchet wheel  74  is a gear wheel with sawtooth-shaped teeth, which is rotatable in one direction of rotation (free-wheeling direction), while conversely the pawl  72  prevents rotation in the opposite direction (blocking direction). In the blocking direction, a rotation of the ratchet wheel  74  as a function of its rotary position relative to the pawl  72  is possible by only one tooth length at maximum.  
         [0026]     The function of the wear readjustment device  60  is as follows: If the ramp plate  38 , for actuation of the disk brake  10 , is displaced in the direction of rotation of the brake disk  20 , then via its teeth  70  it rotates the gear wheel  66  and thus the torsion shaft  62 . This rotation takes place in the free-wheeling direction of the return block  64 . Via its other gear wheel  68 , the torsion shaft  62  rotates the nut  26 . The direction of rotation is selected such that the spacing between the ramp plate  38  and one brake lining holder  14  decreases. When the friction brake linings  28 ,  30  are in contact with the brake disk  20 , a torque for rotating the nuts  26  becomes greater, as a result of which the torsion shaft  62  rotates elastically within itself, or in other words twists. Upon release of the disk brake  10 , the entire procedure takes place in reverse. If because of wear to the friction brake linings  28 ,  30  a rotation of the torsion shaft  62  upon actuation of the brake  10  is so great that the pawl  72  overcomes one tooth of the ratchet wheel  74 , then the reverse rotation of the torsion shaft  62  upon release of the disk brake  10  decreases by one tooth length of the ratchet wheel  74 . If upon release of the disk brake  10  the friction brake linings  28 ,  30  lift away from the brake disk, the nuts  26  become easily rotatable as a result; the elastically twisted torsion shaft  62  relaxes and in the process rotates the nuts  26 , so that a spacing of the brake lining holders  14 ,  16  from one another decreases. As a result, the wear to the friction brake linings  28 ,  30  is compensated for.  
         [0027]     Moving parts of the disk brake  10 , in particular the actuating device  44  and the wear readjustment device  60 , are accommodated in a housing  76 , one wall of which is formed by the ramp plate  38 . Bellows  78 ,  80  provide sealing between the ramp plate  38  and the slide sleeve  32  and between the slide sleeve  32  and one brake lining holder  14 . The moving parts of the disk brake are thus protected from dirt and water.  
         [0028]     In the disk brake  10  shown in  FIG. 2 , instead of the torsion shaft  62 , there is an electric motor  82  for rotating the nuts  26  of the wear readjustment device  60 . The wear readjustment is accordingly accomplished electromechanically and not automatically by the displacement of the ramp plate  38  upon actuation of the disk brake  10 . Otherwise, the disk brakes  10  shown in  FIGS. 1 and 2  are constructed identically and function in the same way. To avoid repetition, see the above description of  FIG. 1 .  
         [0029]     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.