Abstract:
The invention relates to a master cylinder, in particular for a controlled motor vehicle brake system, including a first and a second piston which is displaceable in a housing and has a captive spring, a first end of the spring bearing at least indirectly against the piston and a second end thereof against a sleeve which is displaceable with respect to the piston and the movement of which with respect to the piston is limited by a pin provided on the piston and by a stop washer, the stop washer being arranged on a free end of the pin. In order to avoid impact noise upon rapid release of the brake, the stop washer of the first piston has a device for the damped abutment of the sleeve.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT/EP2010/059956, filed Jul. 12, 2010, which claims priority to German Patent Application No. 10 2009 035 631.2, filed Jul. 31, 2009, the contents of such applications being incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a master cylinder, in particular for a controlled motor vehicle brake system, comprising a first and a second piston which is displaceable in a housing and has a captive spring, a first end of the spring bearing at least indirectly against the piston, and a second end thereof against a sleeve which is displaceable with respect to the piston and the movement of which with respect to the piston is limited by a pin provided on the piston and by a stop washer, the stop washer being arranged on a free end of the pin. 
       BACKGROUND OF THE INVENTION 
       [0003]    A master cylinder of this type is known, for example, from DE 10 2004 057 137 A1, which is incorporated by reference. It is considered to be a disadvantage of the known master cylinder that upon rapid release of the brake the sleeve of the first piston abruptly strikes the stop washer, since the captive spring urges the first piston back to its starting position against the direction of actuation. In this case undesired impact noise is produced and is transmitted into a passenger compartment of the vehicle via a braking force booster fastened to the master cylinder. 
       SUMMARY OF THE INVENTION 
       [0004]    It is therefore an aim of the present invention to make available a master cylinder which is improved with regard to the disadvantages of the known master cylinder which have been mentioned. 
         [0005]    This is achieved according to aspects of the invention in that the stop washer of the first piston has means for the damped abutment of the sleeve. The troublesome impact noise which occurs especially upon rapid release of the brake can thereby be effectively avoided. 
         [0006]    In order to simplify installation of the stop washer, the means are preferably provided on both sides of the stop washer. It is therefore unnecessary during assembly to pay attention to whether the stop washer is fastened the correct way round on the pin. 
         [0007]    According to an advantageous embodiment of an aspect of the invention, the stop washer has a peripheral groove on both sides and the means are provided as elastic annular elements arranged in the respective peripheral grooves. 
         [0008]    The stop washer preferably has a plurality of axially oriented bores which connect the grooves on both sides of the stop washer. The two annular elements are thereby connected to one another and are fastened to the stop washer in a captive manner. 
         [0009]    Improved anchoring of the material of the annular elements can be achieved if the axially oriented bores have a crowned configuration. 
         [0010]    According to an advantageous configuration of an aspect of the invention, a defined stroke of the first piston can be ensured in that the annular elements are configured in such a way that a collar of the sleeve can rest directly against the stop washer in an unactuated position of the master cylinder. 
         [0011]    To this end the annular elements advantageously each have a peripheral lip and a peripheral recess, the peripheral lip projecting beyond a side face of the stop washer prior to abutment of the collar and being displaceable into the recess upon abutment of the collar. 
         [0012]    The annular elements are preferably vulcanized onto the stop washer. 
         [0013]    Even when the means are provided, the stability of the stop washer can be ensured in that the stop washer is provided as a precision metal stamping. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention is best understood from the following detailed description when read in connection with the accompanying drawing. Included in the drawing are the following figures: 
           [0015]      FIG. 1  shows a known master cylinder in longitudinal section; 
           [0016]      FIG. 2  shows a stop washer with vulcanized-on annular elements of a master cylinder according to the invention in a three-dimensional representation; 
           [0017]      FIG. 3  shows a stop washer according to  FIG. 2  in a partially sectional three-dimensional representation, and 
           [0018]      FIG. 4  shows the stop washer according to  FIG. 2  without annular elements in a partially sectional three-dimensional representation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  shows in longitudinal section a known master cylinder  1  which is used, for example, in a controlled brake system with anti-slip control (ASR) and/or Electronic Stability Program (ESP) and has a plunger-type tandem configuration. 
         [0020]    The master cylinder  1  comprises a first and a second piston  3 ,  4  which are displaceable in a housing  2 , a circular sealing element  5 ,  6  with a dynamically loaded inner sealing lip  26 ,  27  and a statically loaded outer sealing lip  28 ,  29  being provided in an annular groove  23 ,  24  of the housing  2 . The dynamically loaded inner sealing lip  26 ,  27  bears with a first sealing face against the piston  3 ,  4  and the statically loaded outer sealing lip  28 ,  29  bears with a second sealing face against a base of the annular groove  23 ,  24 . An outer face  30 ,  31  of the pistons  3 ,  4  serves as a guide surface. 
         [0021]    In an unactuated state of the master cylinder  1  shown in  FIG. 1 , a first and a second pressure chamber  7 ,  8  are connected via a pressure medium passage  32 ,  33  and a return chamber  11 ,  12  in the housing  2 , and via control apertures  9 ,  10  in a pot-shaped wall  21 ,  22  provided at one end  36 ,  37  of the first and second piston  3 ,  4 , to an unpressurized pressure medium reservoir (not shown). Depending on its configuration, the master cylinder  1  has from four to twenty-four transverse bores  9 ,  10  on the circumference of the piston  3 ,  4 . In this case the pistons  3 ,  4  are preloaded by means of compression springs  34 ,  35 . 
         [0022]    The compression spring  34 ,  35  is arranged at least partially within the pot-shaped wall  21 ,  22 . A central pin  38 ,  39  projects through the middle of the wall  21 ,  22 , ending before its axial exit from the wall  21 ,  22 . This end  40 ,  41  is provided with a stop  42 ,  43  for a sleeve  44 ,  45  which interacts with a collar  46 ,  47  in such a way that the sleeve  44 ,  45  can be retracted telescopically within a limit. In other words, the sleeve  44 ,  45  with the compression spring  34 ,  35  is forced into the interior of the piston upon actuation. As will be seen, the stop  42 ,  43  is preferably an annular stop washer riveted—in particular wobble-riveted—to the pin  38 ,  39 . The opposite end of the sleeve  44 ,  45  carries the plate-like collar  48 ,  49  against which the compression spring  34 ,  35  bears. 
         [0023]    In order to actuate the master cylinder  1 , the first piston  3  is displaced in the actuation direction A. As this happens the movement of the first piston  3  is transmitted to the second piston  4  via the compression spring  34 . As soon as the transverse bores  9 ,  10  are in the region of the sealing elements  5 ,  6 , that is, as soon as the lateral control edge of the bore has been passed, the so-called free travel of the master cylinder  1  has been covered, since pressure medium can no longer reach the pressure chambers  7 ,  8  from the return chambers  11 ,  12  through the transverse bores  9 ,  10 . The connection of the pressure chambers  7 ,  8  to the pressure medium reservoir is interrupted and pressure is built up in the pressure chambers  7 ,  8 . 
         [0024]    The two pistons  3 ,  4 , arranged in tandem, of the master cylinder  1  are practically identical in construction and operation, so that only the first piston  3  will be described further. 
         [0025]    In the event of an ASR or ESP intervention it may be necessary, with the piston  3  unactuated or actuated, to draw pressure medium from the pressure medium reservoir via the pressure chamber  7  in the direction of the wheel brakes, which is preferably effected by means of a pump, the inlet of which is selectively connectable to the pressure chambers  7 ,  8  of the master cylinder  1  or to the wheel brakes in order to pump in the direction of the wheel brakes or of the master cylinder  1  (recirculation principle). For this purpose, in the event of an ASR intervention in the unactuated state of the master cylinder  1 , the pressure medium is drawn from the pressure medium reservoir via the pressure medium passage  32 , the return chamber  11 , the transverse bores  9  and the pressure chamber  7 . In the case of an ESP intervention in the actuated state of the master cylinder  1 , pressure medium is additionally drawn through overflowing of the outer sealing lip  28  of the sealing element  5 , this sealing lip  28  being folded over by the suction pressure in the direction of the inner sealing lip  26 , and the sealing face of the outer sealing lip  28  therefore no longer bearing against the base of the annular groove  23 . In order to make sufficient pressure medium quickly available to the pump in the event of an ASR or ESP intervention, especially in the unactuated position of the master cylinder  1 , it is necessary to keep the throttling resistance of the transverse bores  9  as low as possible, although the free travel of the master cylinder  1  must also be kept as short as possible. 
         [0026]    As is apparent from  FIG. 1 , the transverse bores  9 ,  10  open into respective grooves  15 ,  16  which are provided in inner faces  13 ,  14  of the pistons  3 ,  4  and which reduce the throttling resistance of the transverse bores  9 ,  10 . 
         [0027]      FIGS. 2 ,  3  and  4  show a stop washer of a master cylinder  1  according to the invention in a partly sectional three-dimensional representation. The master cylinder  1  according to the invention does not differ in principle from the known master cylinder according to  FIG. 1  in operation and construction, so that a repeated description of the operation and construction can be dispensed with and only the differences according to the invention will be discussed below. 
         [0028]    In order effectively to avoid the impact noise upon rapid release of the brake which is considered to be disadvantageous, a stop washer  50  of the first piston  3  of the master cylinder  1  according to the invention has means for the damped abutment of the sleeve  44 . 
         [0029]    It is apparent from  FIG. 3 , in particular, that these means are provided as peripheral annular elements  51 ,  52  which are arranged on both sides  53 ,  54  of the stop washer  50 . In principle it would be sufficient to provide a damping means on only the side against which the collar  46  of the sleeve  44  comes into abutment in the release position shown in  FIG. 1 . However, in order to simplify installation of the stop washer  50 , the annular elements  51 ,  52  are provided on both sides  53 ,  54  of the stop washer  50 . Incorrect fastening of the stop washer  50  to the pin  38  can thereby be excluded. 
         [0030]      FIG. 4  shows the stop washer  50  prior to installation of the annular elements  51 ,  52 . It can be seen that the stop washer  50  has peripheral grooves  55 ,  56  on both sides  53 ,  54 , with a plurality of axially oriented bores  57  connecting the grooves  55 ,  56 . The annular elements  51 ,  52  are molded into the grooves  55 ,  57 , for example by means of vulcanizing. As the rubber material is vulcanized on, the bores  57  are filled, whereby the annular elements  51 ,  52  on both sides  53 ,  54  are connected to one another and fastened captively to the stop washer  50 . 
         [0031]    For improved anchoring of the rubber material, the bores  57  may have a crowned profile, as can be seen from  FIG. 4 . 
         [0032]      FIG. 3  in particular shows that the annular elements  51 ,  52  are configured in such a way that in the unactuated position (release position) of the master cylinder  1  the collar  46  of the sleeve  44  can rest directly against the stop washer in order to ensure a defined stroke of the first piston  3 . For this purpose the annular elements  51 ,  52  each have a peripheral lip  58 ,  59  and a peripheral recess  60 ,  61 , the peripheral lip  58 ,  59  projecting beyond a side face  62 ,  63  of the stop washer  50  prior to abutment of the collar  46  and being displaceable into the recess  60 ,  61  upon abutment of the collar  46 . In this case the recesses  60 ,  61  are dimensioned in such a way that the lips  58 ,  59  can be displaced into them without difficulty. 
         [0033]    If the stop washer  50  is provided as a precision metal stamping, its stability can thereby be ensured even despite the grooves  55 ,  56  and bores  57 . 
         [0034]    Because, as is apparent from  FIG. 1 , the sleeve  45  of the second piston  4  does not come into abutment against the stop washer  43  in the release position, the use of the stop washer  50  described is restricted to the first piston  3 . 
       LIST OF REFERENCES 
       [0000]    
       
           1  Master cylinder 
           2  Housing 
           3  Piston 
           4  Piston 
           5  Sealing element 
           6  Sealing element 
           7  Pressure chamber 
           8  Pressure chamber 
           9  Control aperture 
           10  Control aperture 
           11  Return chamber 
           12  Return chamber 
           13  Inner face 
           14  Inner face 
           15  Internal groove 
           16  Internal groove 
           17  Main body 
           18  Control element 
           19  Outer face 
           21  Wall 
           22  Wall 
           23  Annular groove 
           24  Annular groove 
           26  Inner sealing lip 
           27  Inner sealing lip 
           28  Outer sealing lip 
           29  Outer sealing lip 
           30  Outer face 
           31  Outer face 
           32  Pressure medium passage 
           33  Pressure medium passage 
           34  Compression spring 
           35  Compression spring 
           36  End 
           37  End 
           38  Pin 
           39  Pin 
           40  End 
           41  End 
           42  Stop 
           43  Stop 
           44  Sleeve 
           45  Sleeve 
           46  Collar 
           47  Collar 
           48  Collar 
           49  Collar 
           50  Stop washer 
           51  Annular element 
           52  Annular element 
           53  Side 
           54  Side 
           55  Groove 
           56  Groove 
           57  Bore 
           58  Lip 
           59  Lip 
           60  Recess 
           61  Recess 
           62  Side face 
           63  Side face 
         A Actuation direction