Abstract:
A disc brake with self-servo effect comprises: a movable ramp plate connected to a brake pad for engagement with a brake disc, a ramp bridge, stationary in relation to the ramp plate, rollers movable in ramps in surfaces facing each other of the ramp plate and the ramp bridge, and means for imparting a control movement on the ramp plate. The arrangement is such that a movement of the ramp plate in the tangential direction of the brake disc will cause it to move towards or away from the brake disc. Slack adjusting means for compensating for the wear of the brake pad are arranged between the ramp plate and the brake pad.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of international patent application PCT/SE2004/001374 filed on Sep. 24, 2004 which designates the United States and claims priority from Swedish patent applications SE 0302554-1 filed on Sep. 25, 2003, SE 0302553-3 filed on Sep. 25, 2003, and SE 0401480-9 filed on Jun. 10, 2004, the content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to disc brakes, and in particular, a disk brake with self-servo effect, comprising: a movable ramp plate connected to a brake pad for engagement with a brake disc, a ramp bridge, stationary in relation to the ramp plate, means for imparting a control movement on the ramp plate, and application members between the ramp plate and the ramp bridge for increasing the mutual distance—in the axial direction of the brake disc—between these two members at a relative movement in the tangential direction of the brake disc, such application members for example being rollers movable in ramps in surfaces facing each other of the ramp plate and the ramp bridge.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is well known in the art that a self-servo effect for a disc brake on a vehicle may be obtained by applying a brake pad against the rotating brake disc, where the brake pad is tangentially movable in relation to the brake disc over inclined ramp means or the like.  
         [0004]     The basic problem with such designs was earlier the relatively poor controllability, but actuation by electric motors with modern electronics and with sensors has generally solved this problem. Actuation by other means, such as electro-hydraulic means, is also possible.  
         [0005]     A disc brake with self-servo effect as defined above is disclosed in WO 03/071150 from the same applicant as in the present case. In the design shown therein (reference being made especially to FIGS. 4 and 5) its ramp bridge is connected—by means of a slack adjusting arrangement—to a fixed portion of the disc brake (its housing) at its side facing from the brake disc. As the ramp bridge thus is movable in the axial direction of the brake disc, whereas essential portions of the means for imparting a control movement on the ramp plate (namely an electric motor and associated elements) are arranged in the fixed portion of the disc brake (namely in its housing), a relatively complicated design for the mechanism for imparting the control movement will result. Further, in the known design there is a direct and short heat transfer distance from the brake pad to the comparatively sensitive roller mechanism via the ramp plate, which can be seen as a drawback.  
         [0006]     The main object of the invention is to remove the above and other shortcomings of the known design.  
       SUMMARY OF THE INVENTION  
       [0007]     This is according to the invention attained in that slack adjusting means for compensating for the wear of the brake pad are arranged between the ramp plate and the brake pad.  
         [0008]     This means that the ramp bridge does not need to be axially movable for slack adjusting with a resulting simplification of the design for transmitting the control movement. Also, an improved journalling of a vital part in the means for imparting a control movement may be obtained.  
         [0009]     Further, the distance between the brake pad, which generates heat, and the possibly heat sensitive portions of the mechanism will be increased, and heat transfer can only occur via the slack adjusting means, not over the entire ramp plate area.  
         [0010]     In practice, the slack adjusting means comprise two first adjustment screws in thread engagement with corresponding bores in the ramp plate and rotatably connected to a front pad holder for the brake pad. Each of the first adjustment screws is rotatably connected to a socket attached to the pad holder.  
         [0011]     Each of the first adjustment screws is controllably connected to the means for imparting a control movement. In practice, rotative movement may be transmitted at will from an electric motor—of the means for imparting a control movement—to the first adjustment screw via an adjustment rod in form engagement with the first adjustment screw for allowing ramp plate movements occurring at brake application.  
         [0012]     In order to control the slack adjusting procedure, an electromagnetic clutch may be arranged in the force transmitting chain from the electric motor to the adjustment rod.  
         [0013]     The environment under a moving vehicle and around its brakes is extremely harsh, and measures must be taken to ensure that moist, dirt and the like is effectively prevented from entering the brake mechanism. In the present case, the sealing of the brake mechanism at the side facing the brake pad and the brake disc, where two slack adjusting means extend between the ramp plate and the pad holder, presents a problem. This problem is according to an important aspect of the invention solved in that a brake mechanism opening, facing the brake disc, is sealed against the intrusion of moist, dirt and the like by means of a lid, which is attached to a sidewall defining the opening and which is provided with a generally circular hole for each slack adjusting means, in which hole a sealing bellows is arranged around the adjusting means. Such a generally ring-shaped bellows will allow lateral and axial movements of the slack adjusting means, which otherwise pose problems.  
         [0014]     Practically, the adjustment rod is in form engagement with an adjustment sleeve, rotatable by means of a drive belt, which is in driving engagement with a drive sprocket, driven via the electromagnetic clutch by a gear transmission from the electric motor.  
         [0015]     So far reference has only been made to a disc brake design at one side of the brake disc, but normally disc brake actuation is performed at both sides of the brake disc. In the present case a brake yoke, force-transmittingly connected to the ramp bridge, extends to the opposite or rear side of the brake disc and is there provided with a rear pad holder with a rear brake pad for braking engagement with the brake disc.  
         [0016]     In a first embodiment the ramp bridge is attached to a fixed part of a vehicle chassis in which the disc brake is arranged, and the brake disc is axially movably arranged on its shaft.  
         [0017]     In a second embodiment the ramp bridge is floatingly arranged in relation to a vehicle chassis in which the disc brake is arranged and axially guided in relation to the brake disc, and the brake disc may be axially fixed to its shaft.  
         [0018]     Means may herewith be provided for adjusting the position of the brake yoke in relation to the ramp bridge for accomplishing a slack adjustment in relation to the wear of the rear brake pad.  
         [0019]     Practically, this may be obtained in that the drive belt also extends over adjustment nuts rotatably arranged in the ramp bridge and threadingly engaging second adjustment screws at the respective ends of the brake yoke.  
         [0020]     For different reasons, among other things that an improved control over the distribution of the pad wear may be obtained, it may be of advantage to arrange slack adjusting means at both sides of the brake disc. In a disc brake as described above, rear slack adjusting means for the rear brake pad may be arranged in the rear part of the brake yoke and may be driven by the same arrangement that is driving the slack adjusting means for the front brake pad.  
         [0021]     A rotatable transmission bar for the rear slack adjusting means may extend through the brake yoke from its front part to its rear part, and a rotatable adjustment bar or drive belt may extend drivingly from the transmission bar in the rear part of the brake yoke for driving the slack adjusting means.  
         [0022]     In a first practical embodiment, wedge-shaped adjustment members in engagement with corresponding, slanted internal surfaces in the rear part of the brake yoke can be transferred by the adjustment bar for advancing the rear brake pad.  
         [0023]     In a second practical embodiment, third adjustment nuts, rotatably drivable by the adjustment rod or drive belt, can be in thread engagement with non-rotatable adjustment screws connected to the rear brake pad.  
         [0024]     Axial force sensing means may be arranged in the brake force transmitting chain between the ramp bridge and the rear pad holder.  
         [0025]     Alternatively or additionally, tangential force sensing means are arranged at suitable locations in the disc brake. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The invention will be described in further detail below under reference to the accompanying drawings, in which  
         [0027]      FIGS. 1-10  are schematical top views, partly in section, of ten embodiments of a disc brake according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     In a vehicle chassis, a disc brake shown in a first embodiment in  FIG. 1  is placed astraddle of a rotatable brake disc  1 , which is to be brakingly engaged by a front brake pad  2  and a rear brake pad  3 . These brake pads  2  and  3  are attached to a front and a rear brake pad holder  4  and  5 , respectively. The rear brake pad holder  5  is attached to a brake yoke  15  to be described. The brake pads may alternatively lack separate pad holders.  
         [0029]     It will appear that in this first embodiment the disc brake is fixedly attached in the vehicle chassis, which means that the brake disc  1  must have a certain (although limited) axial movability in relation to the disc brake (namely in the practical case in relation to its shaft).  
         [0030]     By adjustable distance means  6  to be described below the front brake pad holder  4  is attached to a ramp plate  7 . The ramp plate  7  is in turn connected to a ramp bridge  8  by means of application members, namely in the shown case rollers  9  between ramps  7 ′ and  8 ′ on the ramp plate  7  and the ramp bridge  8 , respectively. The rollers  9  are preferably arranged in a common roller cage (not shown) for obtaining full control and a completely synchronous movement of the rollers  9  (irrespective of their actual number). The need for a roller cage is especially relevant, if the ramps  7 ′ and  8 ′ are curved for obtaining certain brake characteristics.  
         [0031]     The ramps  7 ′ and  8 ′ are exposed to high forces and much wear and can therefore be constructed as inserts of harder and higher quality material.  
         [0032]     Other application members than the rollers  9  are feasible, such as tiltable parallelepipedical members in correspondingly shaped recesses in the ramp plate and the ramp bridge.  
         [0033]     The ramp bridge  8  is fixedly attached in the vehicle chassis and is provided with means for creating a control force and for maintaining a certain predetermined slack between on one hand the brake disc  1  and on the other hand the brake pads  2  and  3 .  
         [0034]     An electric motor  10  on the ramp bridge  8  can rotate a motor shaft  11  in either direction. (The unit called “electric motor” also preferably contains a gear box for reducing the rotational speed from the motor as well as a parking and safety brake arrangement.)  
         [0035]     A bevel gear  12  arranged on the motor shaft  11  is in driving gear engagement with a bevel gear disc  13  rotationally supported by the ramp bridge  8 . Eccentrically connected to the bevel gear disc  13  is a crank rod  14  pivotally connected to the ramp plate  7 .  
         [0036]     By turning the bevel gear disc  13  in either direction by means of the bevel gear  12  from the motor  10 , the position of the ramp plate  7  in relation to the ramp bridge  8  can be set. When a friction engagement between on one hand the brake pad  2  (and brake pad  3 , as will be described) and on the other hand the brake disc  1  has been established (over the distance means  6  between the ramp plate  7  and the brake pad holder  4 ), an application force amplification will be accomplished by the rollers  9  climbing their ramps  7 ′ and  9 ′ in response to a tangential movement of the ramp plate  7  caused by the friction engagement with the brake disc  1 . The application force may be accurately controlled by rotating the motor  10  in either direction.  
         [0037]     With the exception of a slack adjusting function to be described, the rear brake pad holder  5  with its rear brake pad  3  is fixedly connected to the ramp bridge  8  by means of a brake yoke  15 .  
         [0038]     Axial guiding of the brake yoke  15  and reaction force handling from the braking may either be accomplished by a first guide element  16  as shown to the left in  FIG. 1  or by a second guide element  17  as shown to the right in  FIG. 1 , both fixed in the vehicle chassis. Both guide elements  16  and  17  have axial surfaces for handling reaction forces from the brake pad holder  5 . The first guide element  16  has an axial guide pin  16 ′ cooperating with a hole in the brake yoke  15  for axial guiding of the latter, whereas the second guide element  17  guidingly cooperates with an axial surface of the brake yoke  15 . Throughout this specification, the term “axial” refers to the axial direction of the brake disc  1 .  
         [0039]     The slack adjusting arrangement for the two brake pads  2  and  3  will now be described. The entire arrangement is driven by the electric motor  10  over a drive belt  20 , a drive chain or the like via a gear transmission  21  from the motor shaft  11 , an electromagnetic clutch  22  and a drive sprocket  23  in driving engagement with the drive belt  20 . The electromagnetic clutch  22  is only engaged, when a slack adjustment is desired. The drive belt  20  may be replaced by a gear train.  
         [0040]     The drive belt  20  drives two adjustment sleeves  24 , which are rotatably arranged in the ramp bridge  8  and are intended for the slack adjustment of the front brake pad  2 , and two adjustment nuts  25 , which also are rotatably arranged in the ramp bridge  8  but are intended for the slack adjustment of the rear brake pad  3 .  
         [0041]     An adjustment rod  26  has end means  26 ′ in form engagement with one of the adjustment sleeves  24  and with one of two first adjustment screws  27 , each in thread engagement with a bore in the ramp plate  7 . The connection by the rod  26  means that the adjustment movement may be transmitted in spite of relative movements between the ramp plate  7  and the ramp bridge  8 . The first adjustment screw  27  is rotatably connected to a socket  28  non-rotatably attached to the brake pad holder  4  in such a way that the transmission of tangential forces is secured.  
         [0042]     The first adjustment screw  27  and the socket  28  together form the distance means  6  with a length adjusted after the wear of the front brake pad  2 .  
         [0043]     Each end of the brake yoke  15  is formed as a second adjustment screw  29  in thread engagement with the adjustment nut  25 .  
         [0044]     The thread directions of the adjustment screws  27  and  29  are such that the distance between the two brake block holders  4  and  5  is decreased at a rotation of the electric control motor  10  for compensating for the wear of the brake pads  2  and  3  at braking. Such a slack adjusting rotation may be separate from a rotation for controlling the application of the brake.  
         [0045]     A force sensing means  30  of any suitable kind is arranged between the adjustment nut  25  and the ramp bridge  8  in the bottom of the bore provided therein for the nut  25 . Such a force sensing means  30  can transmit signals indicative of the axial brake force; such signals can be used for feed-back at braking for controlling the electric control motor  10 .  
         [0046]     A protective bellows  31  of rubber or the like is arranged between the ramp bridge  8  and the brake yoke  15  around each second adjustment screw  29  for preventing the intrusion of moist, dirt and the like.  
         [0047]     Further, at the side facing the brake pad holder  4  the interior of the disc brake mechanism is protected against the instrusion of moist, dirt and the like in the following way. The ramp bridge  8  has a circumferential wall or sidewall  8 ″ extending towards the brake pad holder  4 . In its opening, which has a considerably larger length (in the plane of the drawing) than width (transversely thereto) a lid  32  is attached. The lid  32  is provided with generally circular openings, in which outer peripheries of bellows  33  of rubber or the like are attached, whereas the inner peripheries thereof are attached to the sockets  28 . These generally circular bellows will without problems allow lateral and axial movements of the first adjustment screws  27  and the sockets  28 .  
         [0048]     A second embodiment of a disc brake according to the invention is shown in  FIG. 2 . This second embodiment has great similarities with the first embodiment according to  FIG. 1 . The description of the second embodiment will in principle be limited to those portions where there are differences in relation to the first embodiment, and for the sake of clarity  FIG. 2  is only provided with a minimum number of reference numerals (which is also true for  FIGS. 3-10 ).  
         [0049]     The main difference of the disc brake according to the second embodiment in relation to the first one is that it is of the floating type, i e its brake disc  1 A is not axially movable on its shaft (not shown). The floating disc brake is instead guided by axial guide pins  35 , which are attached in the vehicle chassis and extend through corresponding holes in the ramp bridge  8 A.  
         [0050]     The brake yoke  15 A extends through holes in the ramp bridge  8 A and is provided with flanges  15 A′ for handling pull forces. Force sensing means  30 A for providing signals indicative of the axial brake forces are arranged between the ramp bridge  8 A and the brake yoke flanges  15 A′.  
         [0051]     The slack adjustment is only performed at one side of the brake disc  1 A (the mechanism side or front side), as the disc brake is floating and the slack will be distributed at both sides. This means that the drive belt  20 A for the slack adjusting arrangement only drives the adjustment sleeves  24 .  
         [0052]     A third embodiment of the invention is shown in  FIG. 3 . This embodiment is closely similar to the second embodiment of  FIG. 2 , and the disc brake accordingly again is of the floating type. The only difference in relation to the second embodiment is the location of the force sensing means for providing signals indicative of the axial brake force. These means  30 B are in this case situated between the rear brake pad holder  5  and the brake yoke  15 B, which here is integrated with the ramp bridge  8 B.  
         [0053]     A fourth embodiment is shown in  FIG. 4 . Again, it is mainly the design of the force sensing means that differs in relation to the second embodiment of  FIG. 2 . The disc brake is also here of the floating type. The axial force sensing means  30 C are arranged between the ramp bridge  8 C, which in this case is a smaller, separate unit than in the other embodiments, and the brake yoke  15 C, that here extends all around the disc brake. The ramp bridge  8 C is axially guided by the brake yoke  15 C for minute movements allowed by the force sensing means  30 C. The electric motor and associated elements are here connected to the brake yoke  15 C but are otherwise of the same design as has been described above. The circumferential wall or sidewall, to which the lid  32  is attached, is in this case integral with the brake yoke  15 C and is accordingly given the reference numeral  15 C′.  
         [0054]     A fifth embodiment is shown in  FIG. 5 . The disc brake shown therein is of the floating type. This means that the brake disc is not axially movable on its shaft, but that the disc brake itself is axially movable in relation to guide pins  35 . Apart from that it has the same design as the first embodiment of  FIG. 1  with slack adjustment at both sides, which means that the distribution of the slack at both sides of the disc is controlled (in contrast to the second embodiment according to  FIG. 2 , with which it otherwise has close similarities).  
         [0055]     A sixth embodiment is shown in  FIG. 6 . The disc brake shown therein is of the fixed type, and slack adjusting is only provided at one side of the brake disc, which means that the disc has to be axially movable on its shaft. Apart from that the sixth embodiment has closest similarities with the one of  FIG. 4 , for example with regard to the position of the axial force sensing means  30 D between the ramp bridge  8 D and the fixed brake yoke  15 D. The lid  32  is attached in the brake yoke  15 D.  
         [0056]     A seventh embodiment is shown in  FIG. 7 . Also this disc brake is of the fixed type, but—as will be further described—slack adjusting is provided at both sides of the brake disc, which means that the latter only needs to have a certain axial movability in relation to its shaft.  
         [0057]     A transmission bar  40  is rotatably arranged in the brake yoke  15 E and extends to the rear side of the brake disc  1 . The transmission bar  40  is shown as driven directly by the drive belt  20 , but may alternatively in a more space-consuming way be driven via the inner part of the right adjustment sleeve  24 . The transmission bar  40  is provided at its opposite end with a worm gear or bevel gear  41  transferring the rotative movement to an adjustment bar  42 , which is rotatably arranged in the brake yoke  15 E and is shown as being axially guided by being provided with a guide flange  43  in engagement with corresponding portions of the brake yoke  15 E. (Alternatively, the adjustment bar  42  may be axially guided at its ends.) At either side of the guide flange  43  the adjustment bar  42  is provided with external threads  42 ′ having opposite thread directions. An axially movable, but non-rotatable nut  44  is in engagement with each thread  42 ′.  
         [0058]     A wedge-shaped adjustment member  45  is axially movably arranged at either side of the guide flange  43  in a space confined by the rear pad holder  3 , the nut  44  and a slanted (or wedge-shaped) internal surface  15 E′ of the brake yoke  15 E. The design is such that when the adjustment members  45  are pressed apart by the nuts  44  at adjustment rotation of the adjustment bar  42 , the rear pad holder  5  will be advanced downwards in  FIG. 7  to compensate for the wear of the rear brake pad  3  at that side of the brake disc  1 .  
         [0059]     The brake force sensing means  30 E are arranged at the same positions as in the embodiment according to  FIG. 4 .  
         [0060]     The lid  32  is arranged in the same way as in the embodiment according to  FIG. 6 .  
         [0061]     A bellows  46  of rubber or any other suitable material is arranged to protect the slack adjusting mechanism  42 - 45  at the rear side of the brake disc  1 . The bellows  46  is shown as being attached to flanges of a plate cup  47  at the back side of the rear pad holder  5 .  
         [0062]     An eighth embodiment is shown in  FIG. 8 . Basically, this embodiment is the same as the seventh embodiment but differs therefrom with regard to the design of the slack adjusting means at the rear side of the brake disc.  
         [0063]     A transmission bar  40 A, driven by the drive belt  20 , drives an adjustment bar  42 A over a worm gear or bevel gear  41 A. The adjustment bar  42 A is in drive engagement with the exteriors of third adjustment nuts  50 , which are rotatably arranged in the brake yoke  15 F in the axial direction of the brake disc  1  or in other words perpendicular to the adjustment bar  42 A. Adjustment screws  51  attached to the rear pad holder  5  are in thread engagement in the third adjustment nuts  50 .  
         [0064]     Bellows  52  of rubber or any other suitable material protect the rear slack adjusting mechanism  50 ,  51  against the intrusion of moist, dirt and the like.  
         [0065]     A ninth embodiment is shown in  FIG. 9 . Basically, also this embodiment is the same as the seventh embodiment of  FIG. 7 , but in its practical design it is closely similar to the eighth embodiment of  FIG. 8 . The difference lies in the rotative driving of the third adjustment nuts  50 A, which here is performed by a drive belt  55  in the brake yoke  15 G from the transmission bar  40 B.  
         [0066]     A tenth embodiment is shown in  FIG. 10 . This embodiment has closest similarities with the one according to  FIG. 7 , and reference is made to the description thereof for the general design also of the present embodiment. As in all other embodiments, the bevel gear disc  13  (with its eccentric journalling for the crank rod  14 ) is journalled in the ramp bridge  8 E. In the  FIG. 10  embodiment on the other hand, this journalling occurs in the brake yoke  15 H or housing itself, so that the ramp plate  8 H does not directly partake in the transmission of the control force.  
         [0067]     A few examples have been given of where axial force sensing means may be situated in the design, but other alternatives are of course possible.  
         [0068]     In some cases it may be preferred to alternatively or additionally assess the tangential brake force. Such an assessment may for example be made, at least in the second to fifth embodiments (according to  FIGS. 2-5 ) with floating disc brake designs, at the fixed guide pins  16  and  35  for the disc brake. Alternatively, strain gauges suitably situated on or in the brake yoke  15  may be used for this purpose. Other alternatives are possible, as will be understood by a person skilled in the art.  
         [0069]     It should be observed that reference has above only been made to slack adjusting as a compensation for the wear of the brake pads; in reality also the brake disc is worn calling for a certain compensation by the slack adjusting means.  
         [0070]     Further, reference has above only been made to the existance of one brake disc, with which each disc brake is constructed to cooperate. However, as known in the art, it is possible to have more than one disc, with which each disc brake is constructed to cooperate, and such multi-disc arrangements may also be within the scope of the present invention.  
         [0071]     Other modifications are possible within the scope of the appended claims.