Abstract:
A multi-part piston for a brake saddle of a hydraulically and/or mechanically and/or electromechanically actuated disk brake is described herein. The piston is a pot open on one side and including a base and a wall attached thereto in one piece. The base can be impinged by brake pressure coming from the inside of the pot so that an outward-facing abutting surface of the base can be pressed against a brake lining. The inside of the pot receives at least one pressure piece associated with a parking brake mechanism. For simplified manufacture in the form of a modular piston system for use in various applications, it is proposed that the pressure piece and the base comprise conical surfaces facing one another for transferring braking pressure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Patent Application No. PCT/EP2009/057175, filed Jun. 10, 2009, which claims priority to German Patent Application No. 10 2008 028 412.2, filed Jun. 17, 2008, German Patent Application No. 10 2009 001 712.7, filed Mar. 20, 2009, and German Patent Application No. 10 2009 017 167.3, filed Apr. 9, 2009, the contents of such applications being incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/739,808, filed Apr. 26, 2010, which is a U.S. National Phase Patent Application of PCT/EP2008/064348, filed Oct. 23, 2008 that claims priority to German Patent Application No. 10 2007 051 456.7, filed Oct. 27, 2007, the contents of such applications being incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a multi-part piston construction for a hydraulically and/or mechanically and/or electromechanically actuatable brake caliper of a disk brake, which piston is substantially in the form of a pot-like hollow cylinder which is open at one end and includes a base and a wall formed integrally thereon, wherein the base can be subjected to brake pressure coming from the interior of the pot, so that an outwardly oriented abutment face of the base can be pressed against a brake pad, and wherein the interior of the pot receives a pressure piece. 
     BACKGROUND OF THE INVENTION 
     A brake caliper which is actuatable hydraulically and mechanically in combination and includes a piston is known from EP 0 396 231 A1, which is incorporated by reference. In this case the wall has a conical surface which cooperates with a separate cone and with a separately provided threaded nut which is driven by a threaded spindle. Through its basic principle, the known arrangement makes possible a compensation of brake pad wear for use in a disk brake having a parking brake device. Indications of an especially cost-effective construction of a disk brake are not to be found in this document. 
     Furthermore, known arrangements lack an adaptation to electromechanically actuatable brake actuator systems wherein a parking brake device acts on the brake piston by means of a transmission, the transmission converting a rotary motion of an actuator system into a translational motion, causing an actuation of the brake piston in order to execute parking brake operations and holding the brake piston in the actuated position, and wherein the transmission comprises a threaded spindle and a threaded nut. 
     Independently of the above it is necessary, of course, to specify a solution for the structure of a motor vehicle disk brake which is entirely without a parking brake function. 
     Accordingly, differently configured motor vehicle brakes and their actuator systems require in principle differently configured components, which requirement incurs increased complexity and cost both in the production of the vehicle brakes and in subsequent logistics, such as the supply of replacement parts. The same applies in principle to motor vehicle brakes with or without compensation for brake pad wear. 
     It is an object of the invention to make possible a supply of identical parts as comprehensive as possible in the manufacture and subsequent logistics of all vehicle brakes, and to reduce the manufacturing complexity and cost. This goes hand-in-hand with the question of making available an advantageous modular system. 
     SUMMARY OF THE INVENTION 
     The foregoing object of the invention is achieved by a multi-part piston for a brake caliper of a hydraulically and/or mechanically and/or electromechanically actuatable disk brake, which piston is substantially in the form of a pot-like hollow cylinder which is open at one end and includes a base and a wall formed integrally thereon, wherein the base can be subjected to brake pressure coming from the interior of the pot, so that an outwardly oriented abutment face of the base can be pressed against a brake pad, and wherein the interior of the pot receives at least one pressure piece which is incorporated, in particular, in a power flow of a parking brake mechanism, wherein the pressure piece and the base have conical surfaces oriented towards one another for transmitting power. 
     According to aspects of the invention, it is provided that a pressure piece—integrated in the power flow—and a base have conical surfaces oriented towards one another for transmitting brake pressure. The fact that the pressure is applied directly to the base by means of the pressure piece via an inwardly reverse-drawn bead of the base, in conjunction with the adapted pressure piece which acts in a sense as an adapter, makes possible cost-effective manufacture of the piston from sheet metal material, in particular by forming techniques, within a modular piston system. In applications of the piston to disk brakes without parking brake devices or pad wear compensation, the pressure piece can simply be omitted. The need to produce specially adapted pistons is eliminated. 
     In order to save overall axial length, the pressure piece may be provided with a central through-bore. 
     Receptacles between piston, pressure piece and threaded nut are configured in such a manner that relative rotation is prevented. 
     All the conical surfaces preferably have matching cone angles, so that in principle one tool is sufficient. 
     A recess in the pressure piece may receive a shoulder. For improved venting of the recess at least one passage is advantageous. 
     In general, the pressure piece may be fixed in the piston (through press-forming) both axially and non-rotatably, or it is positioned in the piston in a non-rotatable but axially displaceable manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings. Included in the drawings is the following figures: 
         FIG. 1  shows a first embodiment of a piston together with a drive nut and a drive spindle, 
         FIG. 2  shows an enlarged detail of the piston in  FIG. 1 , 
         FIG. 3  shows a perspective view of the open end of the piston in  FIG. 1 , 
         FIG. 4  shows a second embodiment of a piston, 
         FIG. 5  shows a perspective view of the insert shown in  FIG. 4 , 
         FIG. 6  is an exploded drawing of another alternative embodiment of a piston, 
         FIG. 7  shows a section through the piston arrangement of  FIG. 6 , 
         FIG. 8  shows further details of the piston arrangement according to  FIG. 7  on an enlarged scale, 
         FIG. 9  shows a variant with recess and passage in perspective, and 
         FIG. 10  is a perspective view of a pressure piece with a portion corresponding to  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the figures, parts of a disk brake for a motor vehicle are shown, in some cases schematically and enlarged. 
       FIG. 1  shows a piston  1  with a drive spindle  23  and a drive nut  24  in longitudinal section. The piston  1 , which is embodied in such a way as to be rotationally symmetrical about a longitudinal axis  2 , is configured as a pot which is open at one end, having a wall  3  and a piston head  11 , it being possible for the piston head  11  to be placed against a brake pad (not shown) at the closed end of the piston  1  by means of an axial contact surface  12 . The contact surface  12  is larger than a cross-sectional area  9  at the weakest point of the wall  3 . Moreover, a circumferential groove  6  is rolled into an outer side  4  of the wall  3  in the vicinity of the contact surface  12 , the said groove serving to receive a piston protection cap (not shown) when the piston is installed in the brake caliper. The contour of the rolled-in groove  6  is continued throughout the entire cross section of the wall  3  and thus gives rise to a shoulder  7  on an inner side  5  of the wall  3  of the piston  1 . 
     Arranged on an inner surface  13  of the piston head  11  is a projection  18  with a conical surface  15 , against which the drive nut  24  can be placed. In this arrangement, the conical surface  15  preferably encloses an angle α of about 60° with the longitudinal axis  2  in the axial direction, thereby ensuring centred and defined contact with the drive nut  24 . The piston  1  and the drive nut  24  are connected to one another in a rotationally fixed manner relative to the longitudinal axis  2  and are held in such a way that they can be moved relative to one another in the axial direction. The piston  1  or the drive nut  24  are secured against twisting in the brake caliper housing in a manner which is not shown. As shown in  FIG. 3 , the anti-twist safeguard  27  between the piston  1  and the drive nut  24  is achieved by providing the open end of the piston  1  with an integral end surface  28  that has a contour  29  which forms the positive-locking anti-twist safeguard  27  together with a complementary contour on the drive nut  24 . 
     In the case of mechanical actuation of the disc brake, the drive spindle  23  arranged in the drive nut  24  is turned, for example by means of an electric motor with a gear mechanism arranged on the output side. Since the drive spindle  23  and the drive nut  24  are provided with a ball screw thread  25 , the rotary motion of the drive spindle  23  is converted by the ball screw thread  25  into an axial movement of the drive nut  24 . The said nut comes to rest against the piston  1  by means of a conical surface  26  complementary to the conical surface  15  and moves the said piston. 
     The geometrical configuration of the transitional region  10  between the wall  3  and the piston head  11  is illustrated on an enlarged scale in  FIG. 2 . In its outer surface  14 , the piston head  11  has a recess  19  and, on its inner surface  13 , has the projection  18 , which is formed in a rotationally symmetrical manner, in a ring around the longitudinal axis  2 . The recess  19  is formed in the piston head  11  from the outside by forming, resulting in the emergence of the projection  18  in parallel on the inner surface  13  of the piston head  11 . The recess  19  is substantially at the same distance A from the longitudinal axis  2  of the piston  1  as the projection  18 . 
     Starting from the longitudinal axis  2  of the piston  1 , the piston head  11  is described by a flat outer and a flat inner head surface  16 ,  17 , both of which extend substantially perpendicularly to the longitudinal axis  2 . The outer head surface  16  is designed with a slight axial offset V in relation to the axial maximum dimension of the piston  1 , making it impossible for this region of the piston  1  to be placed against a brake pad (not shown). The flat outer head surface  16  merges into the annular recess  19 , which has a rounded triangular contour in longitudinal section. The inner flat head surface  17  opens out into the annular projection  18 , which rises substantially parallel to the recess  19  from the piston head  11  and bears the conical surface  15 . The projection  18  is formed closer to the longitudinal axis  2  than the recess  19  by an amount which allows a substantially constant wall thickness S in the piston head  11 . Like the recess  19 , the projection  18  has a rounded triangular contour. 
     Likewise starting from the longitudinal axis  2 , both the recess  19  and the projection  18  are formed backwards in the axial direction, the recess  19  merging directly into the contact surface  12 . Together with the shoulder  7  on the inner side  5  of the wall  3 , the projection  18  on the inner surface  13  of the piston head  11  forms a gap  20  brought about by folding, making it possible to form the conical surface  15  for contact with a drive nut  24  without a thickened portion in the transitional region  10 . Depending on the size of the piston diameter, the gap  20  will tend to be a more or less zero-volume fold at small diameters or a volume in the form of a gap at large diameters. The inner shoulder surface  8  facing the piston head  11  can furthermore be designed as a bevel. 
       FIG. 4  shows an embodiment corresponding to an equivalent means of achieving the object of the invention. Here, the piston head  11 ′ of the piston  1 ′ does not have a projection but forms the conical surface  15 ′ for the application of a drive spindle on a cup  21 , which forms part of a two-piece arrangement, as a separate component, in the piston  1 ′ and is produced from a flat metal sheet by forming. This cup  21  is supported axially against the piston head  11 ′ and is connected in a sealing manner to the wall  3 ′ of the piston  1 ′. This has the effect that the dead volume of the piston  1 ′ is reduced, the leaktight connection between the cup  21  and the wall  3 ′ being achieved by means of laser or friction welding. In this arrangement, the conical surface  15 ′ of the cup  21  preferably encloses an angle α of about 60° with the longitudinal axis  2  in the axial direction. 
     This illustrative embodiment of the equivalent solution will also be used to show a further way of embodying an anti-twist safeguard  27 ′ between the drive nut and the piston  1 ′, although there is no intention to restrict this safeguard to the illustrative embodiment under consideration. Here, an insert  22  is provided, this insert being connected in a rotationally fixed manner to the wall  3 ′, by crimping for example. This insert  33  bears the contour  29 , which forms the positive-locking anti-twist safeguard  27 ′ with a complementary contour on the drive nut. The contour  29  can be in the form of a rounded hexagon. 
     Another illustrative embodiment of the invention is shown in  FIGS. 6-10 . The figures show a piston  101  and, at least partially integrated therein, a threaded spindle  102  with a threaded nut  103  of a parking brake device, which threaded spindle  102  and threaded nut  103  act as a transmission for converting a rotary drive motion into a translational piston displacement in a so-called electromechanically actuatable, combined motor vehicle brake (EPB). With regard to the operation and marginal conditions of an electromechanically actuatable, combined motor vehicle brake, reference is made to the disclosure of WO2007/051809A1, which is incorporated by reference. 
     The piston is in principle in the form of a hollow cylinder which is rotationally symmetrical about a longitudinal axis  104  and is open at one end, and which has a wall  105  with a base  106  arranged integrally thereon, said piston being guided in an axially displaceable manner in a housing  107 . In most cases a so-called protective cap is sufficient to prevent relative rotation between housing  107  and piston  101 . A sealing element (not shown) which bears elastically against the wall  105  from radially outside may also serve to prevent rotation between housing  107  and piston  101 . The base  106  can in principle be impinged upon by pressure medium coming from the interior  108  of the pot. In consequence, an outwardly oriented, substantially circular abutment face  109  of the base  106  is pressed against a brake pad  110 . The brake pad  110  comprises a backplate  111  and a friction lining  112  which is applied to a brake disk (not drawn). Although it is not apparent in detail from the schematic figure, the abutment face  109  against the backplate  111  may preferably have a mean diameter which is configured to be smaller in comparison to a mean diameter of the wall  105 . From considerations of stress, the abutment face  109  may be dimensioned such that it is larger than a smallest cross section of the wall  105  at its weakest point. For reasons of strength, and for a defined and reproducible application of force over the abutment face  109 , the remainder of the base  106  is set back with respect to the backplate  111  in such a manner that, in principle, there is no further direct contact with the backplate  111 . This is achieved by the provision adjacent to the abutment face  109  of an annular continuous bead  113  and of a circular face  114  adjacent thereto, the circular face  114  being, for example, set back at least slightly—for example, by a few tenths of a millimeter—with respect to the abutment face  109 . As is apparent in  FIG. 7 , the bead  113  has an obtuse aperture angle β with two sides, the radially inner side of which is provided for the transmission of force through a conical surface  118 . 
     In addition, a circumferential groove  115  is formed from radially outside, and axially offset from the base  106 , from radially outside in the wall  105  in such a manner that a circumferential shoulder  116  is present radially on the inside. The protective cap (not illustrated further) is in principle fitted into the groove  115 . 
     If the features mentioned are produced without cutting, for example by deep drawing, pressing and/or rolling, in combination with metallic sheet steel materials, an advantageous strain-hardening is achieved, so that workpieces with good load-bearing capacity are produced with a comparatively small outlay of material, and without requiring a hardening process. It is self-evident that this advantageous hardening can even be achieved if cold forming from solid is selected—for example, for producing pistons  101  with comparatively small diameters. 
     As is clearly apparent from the figure, the threaded nut  103  bears indirectly against the conical surface  118  of the base  106  via a pressure piece  117 . In this case the conical surface  118  of the base is obtained at least in principle by the impressing of the bead  113 . The two opposite conical surfaces  118  preferably include with the longitudinal axis AA in the axial direction an angle α of approximately 60°, whereby a centered and defined abutment of the pressure piece  117  is ensured. Conical surfaces of the same basic construction are provided between the threaded nut  103  and the pressure piece  117 , all the conical surfaces especially preferably having matching conicities with matching aperture angles. 
     In order to reduce the axial installation space requirement, it is provided that the pressure piece  117  has a central through-bore  119  for receiving a threaded spindle  102 . This is especially advantageous for space-saving accommodation of the spindle—both in the unactivated state in the case of electromechanical systems and with the use of telescopic brake pad adjustment devices in combination with comparatively new-value brake pads  110 . It is thus made possible for the threaded spindle  102  to pass through large portions of the piston  101  and the pressure piece  117 . For the transmission function, it is also essential that housing  107 , piston  101 , pressure piece  117  and threaded nut  103  are configured to be non-rotatable relative to one another. This is achieved by correspondingly configured receptacles and anti-rotation measures between threaded nut  103  and pressure piece  117 , and between pressure piece  117  and piston  101 . To secure the pressure piece  117  and the threaded nut  103  against relative rotation, there may be provided a holding element  122  having a peg  123  which prevents relative rotation between threaded nut  103  and pressure piece  117  in a form-fitting manner. 
     In another embodiment it is possible to provide the receptacle  120  between pressure piece  117  and threaded nut  103  with a profiling which deviates from the cylindrical shape and prevents relative rotation of the components concerned. This may be effected, for example, by providing a key face or otherwise-designed form-fitting configuration (cam, toothing, flat face, feather key and the like) integrated in the receptacle  120 . 
     For example, a toothing, a flattened key face or the like may be provided between pressure piece  117  and wall  105 . A protective cap (not drawn) may serve to prevent rotation between piston  101  and housing  107 . 
     After the pressure piece  117  has been provided at an end oriented towards the base with a circumferential recess  124  for receiving the shoulder  116 , the shoulder  116  is received therein. In order that such a recess  124  can be vented with acceptable complexity and cost when the system is being filled with pressure medium, said recess  124  is connected to the interior  108  of the pot via at least one passage  125 . The concrete implementation of the passage  125  is preferably such that either the pressure piece  117  is provided with a cut-away portion or the inner wall is provided with a channel-like depression. To achieve an especially large cross section of the passage, the features mentioned may also be provided in combination. 
     Since the pressure piece  117  in the form of an adapter part is made available with a variable overall length and a variable external diameter, and with an identically matching conical surface  118  and receptacle  120 ,  121  for a uniformly configured threaded nut  103  in each case, a modular piston system for different piston diameters making use of a large number of identical parts can be made possible in a simple and low-cost manner, as substantially only piston pots of various diameters with pressure pieces  117  and housings  107  adapted thereto are needed.