Patent Publication Number: US-2023140201-A1

Title: Brake piston and brake caliper

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Priority Application No. 102021128309.4, filed Oct. 29, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The disclosure concerns a brake piston, in particular for a disc brake of a vehicle. 
     BACKGROUND 
     The brake piston is usually received displaceably in a cylindrical orifice which, for a fluidically actuatable brake, usually constitutes a fluid cylinder and a pressure chamber which can be loaded with pressurised fluid. Accordingly, by pressurisation of the pressure chamber, the brake piston can be moved in the direction of a brake pad which is thus pressed against an associated brake disc, and brakes this. The pressurised fluid here is usually a hydraulic fluid, so that in this case, the brake piston can be described as hydraulically actuated. 
     Alternatively or additionally, known brake pistons may also be coupled to an electrically actuatable spindle drive which moves the brake piston in the direction of the brake pad. The brake piston may also thus be electrically actuated. This is normally the case so that the brake caliper in which the brake piston is arranged, together with the associated brake disc, can be used as a parking brake. 
     SUMMARY 
     What is needed is an improved brake piston. 
     Accordingly, a brake piston, for example for a disc brake of a vehicle, which has a first tubular piston body portion and a second tubular piston body portion arranged radially inside the first piston body portion, wherein both portions extend along a piston longitudinal axis. The first piston body portion and the second piston body portion are connected together at a first axial end of the brake piston via an annular end wall, so that an annular cavity is formed between the first piston body portion and the second piston body portion. At a second axial end of the brake piston, the second piston body portion is closed by a floor, so that the second piston body portion forms a receptacle. The first piston body portion has a radially inwardly directed floor region. The end wall is axially stepped towards the outside and has a radially outer portion and a radially inner portion, which each have an end face pointing axially away from the brake piston. In this exemplary arrangement, the end face of the radially inner portion is axially offset relative to the end face of the radially outer portion in the direction towards the second axial end of the brake piston. 
     The radially inner portion forms an axial depression in the end wall, so that a distance between the end wall of the brake piston and components of a brake piston drive is increased when the brake piston is in a position in which it is fully advanced towards the brake disc. This arrangement allows for a contact of a spindle flange of a spindle drive with the brake piston to be securely prevented in all positions of the brake piston. Thus installation of the brake and also a bleeding of the brake can always be guaranteed. 
     For example, the end face of the radially inner portion of the end wall is axially offset along an annular step, in the direction towards the second end of the brake piston. The dimensions of the axially inwardly offset region can easily be adapted during production to the dimensions of a spindle flange. 
     In one exemplary arrangement, the end wall delimits the annular cavity. 
     To improve the load transfer from the second piston body portion to the first piston body portion, and to improve the centring of the entire brake piston, a radially outer face of a region axially adjoining the floor of the second piston body portion may be formed conical and rest on a conical counter-face having a complementary cone angle, which is formed on the radially inwardly directed floor region of the first piston body portion. This gives a large superficial contact of the two piston body portions on the second axial end of the brake piston. With respect to the axial direction of the brake piston, the cone angle may e.g. be 45°. 
     In one exemplary arrangement, the floor region is designed to be annular all round, so that an axial force acting on the second piston body portion is conducted evenly into the first piston body portion. 
     In one exemplary arrangement, the conical counter-face is arranged on a radial end face of the floor region. 
     In one exemplary arrangement, an inside of the receptacle is conical at the region axially adjoining the floor of the second piston body portion and is configured to make contact with a counter-cone face of a spindle nut of a spindle drive in the receptacle of the second piston body portion. The axial force transmitted by the spindle nut may therefore be transmitted, by cone faces lying superficially against one another, initially to the second piston body portion and from there to the first piston body portion. 
     In order to optimise the force flow further, a radial end portion of the floor region of the first piston body portion runs axially obliquely inwardly, i.e. in the direction towards the first axial end of the brake piston, in the direction towards the conically formed outer face of the region axially adjoining the floor of the second piston body portion, (in one exemplary arrangement, at right angles), and rests outwardly on the second piston body portion. In one exemplary arrangement, the end portion meets the outer face at an angle of 90°. 
     In one exemplary arrangement, the floor region of the first piston body portion rests circumferentially all round on the outside of the second piston body portion. In one exemplary arrangement, the first piston body portion is not fixedly attached to the outside of the second piston body portion. However, a form-fit connection is advantageous in which the floor region of the first piston body portion rests with its cone surface on the cone surface of the second piston body portion over the entire circumference, in order to achieve an even force distribution. 
     A pressure face for loading a brake pad is positioned at an axially outwardly directed face of the floor region of the first piston body portion. This is the region via which the brake piston transmits an axial force to the brake pad, thereby actuating the disc brake. 
     The end portion of the floor region transforms radially outwardly into the portion of the floor region carrying the pressure face. 
     The first and second piston body portions may have a substantially constant wall thickness. 
     In one exemplary variant, the first and second piston body portions are two separately produced components which are connected together by form fit and/or material bonding in the region of the end face. This connection takes place in the region of the end face of the radially outer portion of the end wall of the brake piston. The material-bonded connection may be a weld connection. In addition, a form-fit connection may be provided by a corresponding design of the first piston body portion and the second piston body portion. 
     In one exemplary arrangement, one or both of the components may be deep-drawn parts, roll-formed parts or extrusions. Also for example, an extrusion may be further processed by roll-forming. 
     In one exemplary arrangement, no axial offset of the two components relative to one another is formed at the material-bonded connection. The annular end wall may be composed of surface portions of both piston body portions. The two piston body portions are connected for example at the end face of the radially outer portion of the end wall, so that the latter comprises portions of the first and second piston body portions. 
     In one exemplary arrangement, the only material-bonded connection between the first piston body portion and second piston body portion lies in this region. For example, only a form-fit contact between the two components is provided at the second axial end of the brake piston. 
     An outer circumferential face of the first piston body portion also comprises a running or slip face of the piston. 
     The brake piston according to the disclosure may be used in a brake which can be actuated both fluidically and via an electric brake piston drive, which e.g. comprises a spindle drive. It is also possible to use the brake piston in a brake which is actuated exclusively fluidically. The brake piston according to the disclosure may also be used in a brake which is actuated exclusively by an electric brake piston drive, i.e. used in a purely electromechanical brake. 
     For the case that the brake piston is displaceably received in the fluid cylinder and delimits the pressure chamber, the brake piston may be actuated fluidically, for example hydraulically. 
     If the brake piston is coupled exclusively to a brake piston drive comprising a spindle drive, this may be actuated purely electrically by the spindle drive. Such a brake caliper may be used for a parking brake. In this context, the brake is also described as an electric parking brake (EPB). Furthermore, such a brake caliper may be used for an electromechanical brake (EMB) which is also used during travel. 
     It is also possible that the brake piston is received in a fluid cylinder and delimits a pressure chamber, and is also coupled to a brake piston drive comprising a spindle drive. Then all above-mentioned functions may be implemented. 
     The disclosure also concerns a brake caliper for a disc brake of a vehicle, with an above-described brake piston which is displaceably received in a cylindrical orifice, and/or which is coupled to a brake piston drive comprising a spindle drive, wherein a spindle nut is accommodated in the receptacle of the second brake piston portion so as to be axially displaceable and not rotatable relative to the brake piston, and receives a drive spindle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure is described in more detail below with reference to an exemplary arrangement shown on the appended figures. In the drawings: 
         FIG.  1    shows a schematic illustration of a brake caliper with a brake piston; 
         FIG.  2    shows a perspective illustration of a brake piston according to the disclosure; and 
         FIG.  3    shows a schematic sectional view of a brake piston drive with a brake piston according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows a brake caliper  10  of a disc brake of a vehicle, which cooperates with a brake disc  12 . 
     The brake caliper  10  comprises a brake caliper body  14  on which a first brake pad  16  is attached. The first brake pad  16  is thus held immovably on the brake caliper body  14 . 
     In addition, a second brake pad  18  is provided which is displaceably mounted on the brake caliper body  14  so that it can be optionally pressed against the brake disc  12  by a brake piston  20 , in order to achieve a braking effect. 
     To this end, the brake piston  20  is displaceably mounted in a cylindrical orifice, here e.g. a fluid cylinder  22 , which is formed on the brake caliper body  14 . 
     A pressure chamber  24 , which can be loaded with pressurised fluid, is delimited by an end of the fluid cylinder  22  facing away from the brake disc  12 , and the brake piston  20 . 
     The pressure chamber  24  is fluidically connected to a pressurised fluid connection  26 , via which a pressurised fluid can be optionally introduced into and discharged from the pressure chamber  24 . 
     For example, the pressurised fluid may be a hydraulic fluid. Thus the fluid cylinder  22  is a hydraulic cylinder. The brake piston  20  can thus be moved hydraulically towards the brake pad  18  and brake disc  12 , so that the brake pad  18  bears on the brake disc  12  and brakes this. 
     In addition, here the brake piston  20  is coupled to a brake piston drive which, in the exemplary arrangement illustrated, is a spindle drive  28 . 
     A spindle nut  30  of the spindle drive  28  is mounted on the brake piston  20  so as to be rotationally fixed but axially displaceable along a piston longitudinal axis A. 
     The spindle nut  30  cooperates with a drive spindle  34  of the spindle drive  28 , which is mounted on the brake caliper body  14  so as to be rotatable about the longitudinal axis A of the brake piston  20  but is otherwise stationary. The drive spindle  34  can optionally be set in rotation by an electric drive motor  36 . 
     Thus the brake piston  20  can also be moved by the spindle drive  28  onto the brake pad  18  and brake disc  12 , so that the brake pad  18  is pressed against the brake disc  12  and brakes this. 
     In one exemplary arrangement, the brake piston  20  may also be used in a purely electromechanical brake. 
       FIGS.  2  and  3    shows the brake piston  20  in detail. 
     The brake piston  20  includes a first tubular piston body portion  38  and a second tubular piston body portion  40 . Both piston body portions  38 ,  40  extend along the piston longitudinal axis A. 
     The second piston body portion  40  is arranged radially inside the first piston body portion  38 , forming an annular cavity  42  between itself and the piston body portion  38 . 
     The first piston body portion  38  and the second piston body portion  40  are connected together at a first axial end  43  of the brake piston  20  via an annular end wall  44 . The annular end wall  44  thus also delimits the cavity  42  in the axial direction. 
     In addition, at its end opposite the end wall  44  along the piston longitudinal axis A, the second piston body portion  40  is axially closed by a floor  46  at a second axial end  45  of the brake piston  20 . The surface of the floor  46  is here flat and stands perpendicular to the piston longitudinal axis A. 
     An outer face  48  of a region  50  axially adjoining the floor  46  is formed conical and widens towards the first axial end  43  of the brake piston  20 , until it transforms into an at least approximately cylindrical portion  52 . 
     Radially in its inside, the second piston body portion  40  forms a receptacle  54  in which the spindle nut  30  is received. 
     The spindle nut  30  is received inside the receptacle  54  rotationally fixedly, i.e. because of the non-round cross-section of the receptacle  54 , but is displaceable along the longitudinal axis A. 
     An end of the spindle nut  30  pointing towards the second axial end  45  of the brake piston  20  is here formed conical, and lies on a conical inside  55  of the receptacle  54  having a complementary angle. 
     The first piston body portion  38  here has a substantially cylindrical outer face  56  which extends from the first axial end  43  to the second axial end  45  of the brake piston  20 . At the second axial end  45 , the outer face  56  transforms integrally into a radially inwardly directed floor region  58 . In its radially end portion  60 , the floor region  58  is bent in the direction towards the first axial end  43  and terminates in a circumferential face which forms a conical counter-face  62  to the conical outer face  48  of the region  50  of the second piston body portion  40 . The floor region  58  thus has a central orifice through which the floor  46  of the second piston body portion  40  protrudes. The inner diameter of the orifice is smaller than the outer diameter of the portion  52  of the second piston body portion  38 . 
     The cone angles of the conical outer face  48  and conical counter-face  62  are complementary. The first piston body portion  38  and second piston body portion  40  in this region lie flat against one another by form fit over the entire periphery, without being fixed to one another. 
     The geometries of the radial end portion  60 , the conical outer face  48  and conical counter-face  62  are here selected such that the end portion  60  meets the conical outer face  48  at an angle α of 90°. 
     At the axially outwardly pointing face of the floor region  58 , a pressure face  64  is formed which serves to be placed against the brake pad  18 , i.e. to load this with a force. 
     The pressure face  64  here extends in substantially annular fashion in the radially outer portion of the floor region  58 . 
     The end wall  44  is axially stepped. A radially outer portion  66  forms a radially outer end face  68 , while a radially inner portion  70  forms a radially inner end face  72 , which is arranged further offset in the axial direction A towards the second axial end  45  than the radially outer end face  68 . The axial step thus formed between the end face  68  and the end face  72  is here formed circumferentially evenly all round. 
     This results in a depression of the end wall  44  radially adjoining the receptacle  54  in the first piston body portion  38 . 
     The region between the end faces  68  and  72  is conical. 
     In its shape and size, this depression is adapted to the shape and clearance of movement of a spindle flange  74  which is arranged outside the receptacle  54  on the drive spindle  34 . 
     The spindle nut  30  always sits between the floor  46  of the receptacle  54  and the spindle flange  74  (see  FIG.  3   ). 
     The brake piston  20  here includes two separately produced components which correspond to the first piston body portion  38  and the second piston body portion  40 . At the end wall  44 , the two components are joined together permanently and fixedly by form fit and material bonding, here by a weld connection sector  76 . The weld connection  76  here lies in the region of the end face  68  of the radially outer portion  66  of the wall  44 , so that this end face  68  is formed both by the first piston body portion  38  and also by the second piston body portion  40 . 
     The radial edges of the two components here run in the longitudinal direction A so that they are connected together in the radial direction r. 
     The two components rest against one another purely by form fit at the second axial end  45  and, in this example, there is no material-bonded connection at this point. 
     The wall thicknesses d of the first and second piston body portions  38 ,  40  are here substantially constant and may be approximately the same. The two components may for example be produced by deep-drawing or in a process which comprises one or more deep-drawing steps. 
     Starting from the position of the brake piston  20  shown in  FIG.  1   , this can be moved to the left by pressurisation of the pressure chamber  24  or by actuation of the spindle drive  28 , so that it bears on the brake pad  18  and presses the latter onto the brake disc  12 . This provokes a braking effect. 
     On use of the spindle drive  28 , the electric drive motor  36  is activated and sets the drive spindle  38  in rotation. This moves the spindle nut  30  to the left. As soon as the spindle nut  30  meets the floor  46  of the brake piston  20 , it carries the brake piston  20  with it in its movement to the left. 
     In this state, the spindle flange  74  does not touch the end wall  44 , since the radially inner end face  72  is offset far enough in the direction towards the second axial end  45  to maintain a sufficient distance from the underside of the spindle flange  74 . This is shown in  FIG.  3   .