Abstract:
The present invention relates to a spot-type disc brake for automotive vehicles and an associated brake pad with a retaining device for the brake pad ( 1 ) on an actuating means ( 2 ), with the brake pad ( 1 ) being additionally clamped to a pad mounting support. These two functions are assumed by two separate spring means ( 4, 13 ) according to the present invention. A first spring means ( 4 ) clamps the brake pad ( 1 ) axially with respect to the actuating means ( 2 ), especially a brake piston, and a second spring means ( 13 ) ensures the radially rattle-free clamping engagement of the brake pad ( 1 ) with respect to an associated pad mounting support. Both spring means ( 4, 13 ) are active irrespective of each other so that undesirable transverse forces on the actuating means ( 2 ), i.e., vertically to the axial direction ( 3 ), are avoided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This specification claims priority to German Patent Application No. 100 45 358.9, filed on Sep. 14, 2000, entitled “Spot-Type Disc Brake and Associated Brake Pad With a Retaining Device for the Brake Pad. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a spot-type disc brake for automotive vehicles and an associated brake pad with a retaining device for the brake pad according to the preamble of patent claim  1 . 
     A generic spot-type disc brake with a retaining device for a brake pad is disclosed in DE 43 18 744 C1. The spot-type disc brake for automotive vehicles described in this patent comprises a floating caliper with two brake pads which are each slidably guided and supported on a brake carrier that is integrated in the steering knuckle of the automotive vehicle. The floating caliper includes a hydraulic actuating unit with a brake piston for the direct application of the first brake pad, while the second brake pad, upon brake actuation, is moved in a known fashion by axial displacement of the floating caliper indirectly into abutment with a brake disc that rotates inbetween the brake pads. The brake pads are secured to the brake piston or floating caliper by way of combined spring elements, on the one side, and clamped with respect to the brake carrier, on the other side. The piston-side brake pad is retained axially and pressed radially against the brake carrier by means of the spring element with respect to the brake disc. The radial and tangential clamping engagement of the spring element in the piston causes undesirable transverse forces on the brake piston which tilt the latter and, thus, cause disadvantageous friction forces during piston movement. Further, manufacturing tolerances may result in an offset positioning in a circumferential direction of the brake pad and the actuating unit. This means there result further undesirable transverse forces on the piston. This causes a loss in clearance which is responsible for washouts on the brake disc and, hence, undesirable brake torque variations. The result of such brake torque variations is, for example, the occurrence of undesirable vibrations such as torsional vibrations of the steering wheel which may lead to low-frequent humming noise. 
     Further, it is known from DE 196 17 373 C2 to secure the piston-side brake pad to the brake piston by way of a mounting element which is fixed with a limited clearance to the brake pad vertically to the axial direction. Due to the limitation of this clearance, the brake piston is, however, also in this arrangement loaded with a force vertically relative to the axial direction because the mounting element also applies a radial force component to the brake pad. Resulting therefrom are the undesirable tilting moments that act on the brake piston (as described hereinabove) and impair the piston&#39;s free slidability in the actuating unit. 
     In view of the above, an object of the present invention is to provide a retaining device for a brake pad of a spot-type disc brake which provides for the brake pad both an attachment to an actuating means, e.g. a brake piston, and a clamping engagement with a pad mounting support, without exerting a force to the actuating means vertically relative to the actuating direction. 
     In accordance with this invention, the retaining device for the brake pad which is slidably guided and supported in a pad mounting support of the spot-type disc brake comprises two separate spring means which both together are attached to the brake pad. With respect to an associated brake disc, the brake pad is clamped axially with the actuating means by way of a first spring means, and is clamped with the pad mounting support by way of a second spring means vertically to the axial direction. 
     The double function of the retaining device for the piston-side brake pad is removed by the use of two spring means which operate independent in their effect. The first spring means ensures the axial attachment of the brake pad to the actuating means, especially the brake piston of an actuating device, while the second spring means clamps the brake pad radially relative to the pad mounting support. The actuating means is not influenced by the force of the second spring means. 
     An improvement of the spot-type disc brake with a retaining device is achieved in that the first spring means is secured with a clearance to the brake pad vertically to the axial direction or actuating direction. The result is that the force components of the two spring means are generally uninfluenced by one another, and no undesirable force effect occurs on the actuating means, especially the brake piston, due to the spring means. 
     A favorable embodiment of the spot-type disc brake with a retaining device is achieved because the first spring means has at least two spring arms for the abutment on the actuating means. This allows the brake pad with retaining device to safely cling to the actuating means. Starting from the point of attachment of the spring means to the brake pad, the spring arms extend in a substantially radial direction, and they are distributed particularly evenly over a corresponding circumference. The brake pad is thereby clamped uniformly with respect to the actuating means. 
     The second spring means is secured to the brake pad without a clearance according to a preferred design of the retaining device. The spring means is in particular riveted to a projection of the brake pad or fixed on the brake pad in a comparable manner. With another portion the second spring means is supported on the actuating means in order to apply the desired force component to the brake pad vertically relative to the axial direction or actuating direction. To realize a low-cost version of the retaining device with a small number of components, the second spring means additionally serves as an attachment means for the first spring means. In detail, the first spring means is retained vertically to the axial direction on the brake pad by means of the second spring means by maintaining a clearance. This causes no radial forces on the actuating means, especially the brake piston. 
     The two spring means may especially have the configuration as simple wire springs, bow springs or leaf springs, or sheet-metal springs. Of course, still other spring materials which exhibit the above-mentioned construction features are also possible. 
     Retaining devices with two above-described spring means can favorably be used with brake pads which are arranged on respectively one brake piston of an actuating device. The retaining device of this invention with two separate spring means is, however, not limited to a use in connection with brake pistons. The actuating means by which a corresponding retaining device with its spring means moves into abutment may also be configured as a portion of a brake caliper or brake housing. In such a case, the associated brake pad is retained on the brake caliper by means of the retaining device. 
     In addition, protection is sought for a corresponding brake pad with a retaining device of the above type. The retaining device, as has already been described, serves for the detachable connection of the brake pad to an actuating means of the spot-type disc brake, the said retaining device comprising a first and a second spring means. According to the present invention, the first spring means clamps the brake pad axially to the actuating means, i.e., a brake piston, while the second spring means clamps the brake pad with respect to the actuating means vertically relative to the axial direction. The first spring means is secured with a clearance to the brake pad by means of the second spring means vertically relative to the axial direction. This permits a relative displacement between the two spring means, with the result that mutual influencing of the two spring means is prevented. Preferably, the first spring means is secured to the brake pad also with an axial clearance by means of the second spring means. In particular, the first and the second spring means are secured to the brake pad in an unrotatable fashion, with respect to a rotation about the axial direction, in order to accomplish a safe support on the brake pad. Advantageously, the first and the second spring means are unrotatably connected to each other already before they are secured to the brake pad. This simplifies handling of the two spring means in general and their assembly. 
    
    
     Favorable embodiments of the present invention will be illustrated in the accompanying drawings and explained in detail hereinbelow. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows two partial cross-sectional views of a brake pad with a retaining device according to the present invention and a brake piston (shown in dotted lines); 
     FIG. 2 is an enlarged cross-sectional view of the brake pad with a retaining device; 
     FIG. 3 shows a first design of a first spring means with two spring arms in two views; 
     FIG. 4 shows a second design of a first spring means with three spring arms in two views; 
     FIG. 5 shows a design of a second spring means in two views; and 
     FIG. 6 shows another favorable design of the two spring means in three views. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The embodiments of the brake pad with a retaining device as shown in: FIGS. 1 to  6  are appropriate for application in a generic spot-type disc brake, as it is e.g. known from the above-mentioned state of the art of U.S. Pat. No. 5,860,495. The basic mode of operation of a spot-type disc brake of this type is sufficiently known in the art and, therefore, need not be described herein. A spot-type disc brake of this type usually comprises a brake caliper with at least one actuating device for the displacement of at least one brake pad  1  to urge the latter against an associated brake disc (not shown). For this purpose, the actuating device includes an actuating means which is slidably arranged in the brake caliper, which is detachably coupled to the brake pad  1  and is frequently configured as brake piston  2 . Lateral projections  5  of the brake pads  1 , which are arranged on either side of the brake disc, are axially slidably received in a pad mounting support of the spot-type disc brake and supported in the circumferential direction of the brake disc. Such a pad mounting support can either be integrated into the brake caliper, such as in fixed-type calipers, or can be designed on a brake mounting element separated from the brake caliper, such as e.g. in floating calipers. 
     It is necessary in such designs of spot-type disc brakes to detachably fix the brake pad  1  in position on the associated actuating means, in particular, brake piston  2  or a portion of the brake caliper. A first spring  4  which is configured as a sheet-metal spring is provided for the connection between the brake pad  1  and the actuating means, i.e., especially brake piston  2 , in the actuating direction or axial direction  3  with respect to the associated brake disc. The first spring means  4  is only used for clamping the brake pad  1  in an axial or actuating direction  3  on the associated brake piston  2 . To this end, the first spring  4  includes at least two spring arms  6  which extend substantially in a radial direction starting from a base portion  7 . Basically, as is seen in FIG. 4, also the design of three or more spring arms  6  is possible. It is advisable to distribute the spring arms  6  evenly over the circumference around the center of the first spring  4 . The spring arms  6  abut respectively on brake piston  2 . As illustrated in FIG. 1 b , they preferably engage into a circumferential groove  8  or other recess on brake piston  2  in order to clamp the brake pad  1  axially with respect to the actuating means. The spring arms  6  can get hooked especially easily on the actuating means due to the groove  8  or recess. With its base portion  7 , the first spring  4  with clearance “s” is undetachably secured to the brake pad  1  vertically relative to the axial direction  3 . Possible tolerance differences can be compensated thereby, and no undesirable transverse forces are transmitted by way of the brake pad  1  to the brake piston  2 , vertically to the axial direction  3 . For the anti-torsion positioning of the first spring  4  on the brake pad  1 , the first spring  4  has a deflected stop  9  which abuts on matingly shaped projections  10  of the carrier plate  11  of the brake pad  1 . 
     The first spring  4  can be manufactured by corresponding shaping from a spring plate in a particularly easy fashion. However, it is principally also possible to use other materials for the first spring  4 , especially plastics and spring wire. 
     For the radial clamping of the brake pad  1  with respect to the pad mounting support, there is provision of a second spring  13  which maintains the brake pad  1  always in abutment with the pad mounting support and, thus, prevents undesirable pad rattling noises. The second spring  13  is also preferably configured as a sheet-metal spring and can be shaped or bent from a simple sheet-metal blank. More specifically, the second spring  13  is fixed without a clearance to a side of a carrier plate  11  of the brake pad  1  which is opposite to a friction lining  12 . To this end, second spring  13  includes a base portion  14  with a step  15 . Step  15  includes a central through-opening  16  which, during assembly of the retaining device, is penetrated by a projecting pin  17  or projection of the carrier plate  11 . At its free end pin  17  is riveted or deformed after the fitment of the two springs  4  and  13  in order to thicken the free end and, thus, prevent the springs  4  and  13  from sliding off the pin  17  or its projection. Additionally, the second spring  13  is secured to the carrier plate  11  of the brake, pad  1  in a clearance-free and undetachable manner by way of the riveting or deforming operation. To economize the additional operation of riveting, a separate locking washer or a retaining clip may be provided which is hooked on the pin and, thus, fixes the springs  4  and  13  in position on the brake pad  1 . Besides, a separate rivet or notched nail can be used to attach the springs  4  and  13  to the brake pad  1 . Finally, attachment of the second spring  13  to the brake pad  1  by cementing, soldering, or other connecting operations, is also possible. 
     A design according to FIGS. 1 and 2 has proved to be an especially favorable arrangement. The second spring  13  which is secured to the carrier plate  11  in a clearance-free manner is used as an attaching element for the first spring  4 . In the readily assembled condition of the brake pad  1  with a retaining device, the base portion  7  of the first spring  4  extends with a through-opening  18  with a clearance “s” around the step  15  of the second spring  13 . A relative displacement of the first spring  4  with respect to the brake pad  1  vertically relative to the axial direction  3  is thereby allowed, for example, for tolerance compensation. This permits compensation of a possible lack in coaxiality between brake piston  2 , and the brake pad  1  in the mounted condition in the spot-type disc brake. This effect is assisted in that the first spring  4  is secured to the brake pad  1  also with a small axial clearance “S”. Thus, it is ensured that brake piston  2  is not exposed to a force effect vertically to the axial direction  3  due to the attachment of the spring  4  to the brake pad  1 . 
     According to the present invention, the described axial attachment of the brake pad  1  to brake piston  2  by the first spring  4  is combined with an elastic clamping engagement of the brake pad  1  with respect to an associated pad mounting support of the spot-type disc brake by the second spring  13  as in FIG.  5 . Principally, the pad mounting support can be integrated either directly into the brake caliper of the spot-type disc brake, as is usual in fixed-type caliper brakes, or it can be configured separately on a separate brake holder. Such a brake holder is frequently employed in floating-caliper spot-type disc brakes and mounted with the vehicle. With two holder arms of a brake caliper, the brake holder straddles the radially outward edge of a brake disc (not shown), the said holder arms including recesses or grooves for the accommodation of the matingly configured lateral projections  5  of the brake pad  1 . 
     The second spring  13  serves for the rattle-free and exact positioning of the brake pad  1  in the pad mounting support. To this end, the brake pad  1  is clamped with the pad mounting support substantially radially, with respect to the associated brake disc. The second spring  13  is preferably shaped or bent from a spring plate and includes at least one portion which is especially configured as spring arm  19 . To ensure a soft spring characteristics, the spring arm  19  must have a design as long as possible in order to be able to compensate occurring tolerances due to the clearance-free attachment of the second spring means  13  on the brake pad  1 . A spring arm  19  which is bent like a V or W is especially advantageous in this respect. However, a design of the spring arm  19  according to the present invention is of course not limited to these design forms. 
     Other design forms for the second spring means are principally also possible, and radial clamping between the brake pad  1  and the pad mounting support is achieved, on the one hand, while the free slidability of the brake pad  1  within the pad mounting support must not be impaired by excessive spring forces, on the other hand. 
     The two springs  4  and  13  are preferably made from a spring plate. Besides, they may generally be likewise fabricated from spring wire or any other appropriate materials, such as plastics. 
     The combination of the two mentioned spring  4  and  13  ensures both an axial fixation of the piston-side brake pad  1  on brake piston  2  and a suspension of the brake pad  1  in relation to the pad mounting support. It is preferred that the brake piston  2  is configured as a brake piston (see FIG. 1) or as a portion of a brake caliper of the spot-type disc brake. The radial clamping engagement between the brake pad  1  and the pad mounting support by the action of the second spring  13  does not act, as is desired, in the way of transverse forces on the actuating means, especially the brake piston  2 , vertically to the axial direction. The free piston movement within the actuating device is hence not influenced disadvantageously. 
     FIG. 6 shows another design of the retaining device with two springs  23  and  24 , the two springs  23  and  24  being interconnected already before their securement to the brake pad. The first spring  24  includes in a known fashion two laterally extending spring arms  6 ′ which start from a base portion  7 ′ and bias the especially brake pad (not shown) in the axial direction  3  against an actuating means, e.g., brake piston or brake caliper. The two springs  23  and  24  can be fixed unrotatably on the brake pad by means of the second spring  23 , as described hereinabove. To this end, the second spring  23  has centrally in its base portion  14 ′ a multi-cornered, e.g. square, opening  25  which is filled by a projection of the brake pad in a form lock after the attachment of the retaining device to the brake pad. After the attachment to the brake pad, the second spring  23  is retained in a form lock on the brake pad, while the first spring  24  can displace relatively thereto within limits. 
     For the unrotatable interconnection of the two springs  23  and  24 , the second spring  23  includes at least one tongue  26  which starts from the base portion  14 ′ and-extends into an associated slot  27  of the first spring  24 . The two springs  23  and  24  are thereby interconnected and form a preassembled construction unit which is easier to handle and mount. Of course, other appropriate measures are also possible for the unrotatable connection of the two springs  23  and  24 , for example, by. designing corresponding projections or stops on the springs  23  and  24 . Further, for additional reinforcement, depressions  28  are shaped especially on the first spring  24  to impart higher rigidity above ail to the base portion  7 ′.