Abstract:
A piston pump as a return pump of a slip-controlled, hydraulic vehicle braking system is disclosed. There is a mushroom-shaped shut-off body as a spring-loaded outlet valve, the shaft thereof extending through a center hole of a tubular damper piston. The shut-off body is movable transversely to the opening and closing direction thereof, so that said shut-off body aligns with a valve seat upon closing. Upon opening, the damper piston forces brake fluid out of a damping chamber in which it is housed so that an opening movement of the outlet valve is dampened.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2010/066302, filed on Oct. 28, 2010, which claims the benefit of priority to Serial No. DE 10 2009 055 228.6, filed on Dec. 23, 2009 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a piston pump for a hydraulic vehicle braking system. Piston pumps of this type are known from slip-controlled vehicle braking systems and they are also designated as recirculating pumps. 
     A piston pump of this type is disclosed in the laid-open publication DE 10 2006 035 055 A1. The known piston pump has a pump piston which can be driven in a to-and-fro lifting movement in a pump bore. What serves as the drive is a rotatably drivable eccentric which is arranged on one end face of the pump piston and against the circumference of which the pump piston bears with its end face. 
     To control a brake fluid throughflow direction, the known piston pump has two spring-loaded nonreturn valves, one of which forms an inlet valve and the other of which an outlet valve of the piston pump. Balls are customary as shut-off bodies of the nonreturn valves. In the known piston pump, one of the two nonreturn valves has a disk-shaped shut-off body, to be precise the inlet valve which is arranged on an eccentric-remote end face of the pump piston. 
     SUMMARY 
     The piston pump according to the disclosure has a spring-loaded nonreturn valve, the shut-off body of which has a damper body together with which it is movable. During the opening of the nonreturn valve, the shut-off body is lifted off from a valve seat of the nonreturn valve and the damper body moves in accompaniment with the shut-off body. For closing, a valve closing spring loads the shut-off body, together with the damper body, against the valve seat. The shut-off body is not connected rigidly to the damper body, but instead is movable with respect to the damper body in the opening and the closing direction. The damper body is received in a damper chamber which, for example, may be a blind hole, out of which said damper body displaces fluid during the opening of the nonreturn valve. The fluid is the fluid which is also conveyed by the piston pump, that is to say brake fluid in a hydraulic vehicle braking system. The fluid may be displaced, for example, through one or more ducts or through a gap between the damper body and a wall of the damper chamber. The list is not conclusive. The displacement of fluid out of the damper chamber by the damper body during the opening of the nonreturn valve has the effect that an opening movement of the nonreturn valve is damped. 
     Advantageous refinements and developments of the of features of the disclosure are set forth below. 
     So that the shut-off body is oriented at the valve seat during the closing of the nonreturn valve, said shut-off body is movable transversely to the opening and closing direction. The shut-off body may be movable with respect to the damper body (claim  3 ) and/or the damper body, together with the shut-off body, may be movable transversely to the opening and closing direction (claim  4 ). 
     In particular, the nonreturn valve according to the disclosure is intended as the outlet valve of the piston pump (claim  8 ) and is arranged at an eccentric-remote end of a cylinder of the piston pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is explained in more detail below by means of embodiments illustrated in the drawing in which: 
         FIG. 1  shows an axial section through a piston pump according to the disclosure; and 
         FIG. 2  shows a modified embodiment of the piston pump from  FIG. 1  according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The piston pump  1  according to the disclosure, illustrated in  FIG. 1 , is intended as what is known as a recirculating pump for a slip-controlled hydraulic vehicle braking system. It has a pump piston  2  which is received axially displaceably in a cylinder  3 . An end face, projecting out of the cylinder  3 , of the pump piston  2  bears against a circumference of a rotatably drivable eccentric  4  which drives the pump piston  2  in a to-and-fro lifting movement in the cylinder  3  when the eccentric  4  is driven in rotation. A piston spring  5  which is arranged in the cylinder  3  holds the pump piston  2  in bearing contact against the circumference of the eccentric  4 . 
     The cylinder  3  is introduced into a pump bore  6  in a pump casing  7 , and the pump bore  6  guides the pump piston  2  axially displaceably at a near-eccentric end projecting out of the cylinder  3 . 
     The piston pump  1  may have a separate pump casing  7 . In the illustrated embodiment of the disclosure, the pump casing  7  is formed by a hydraulic block, in which, in addition to the piston pump  1 , further hydraulic structural elements, such as solenoid valves, of a slip control of the hydraulic vehicle braking system are arranged and are connected hydraulically to one another by means of bores. Such hydraulic blocks are known from slip-controlled vehicle brake systems and will not be explained any further here. 
     An inlet  8  of the piston pump  1  takes place through a bore which intersects the pump bore  6  radially outside the cylinder  3 . The inlet  8  leads, further, through mutually intersecting radial bores  9  into an axial blind hole  10  in the pump piston  2 . An inlet valve  11 , illustrated as a symbol in the drawing, is integrated in the pump piston  2  or is arranged on that end face of the latter which is located in the cylinder  3 . The inlet valve  11  is a spring-loaded nonreturn valve. 
     The cylinder  3  has a bottom  12  on which the piston spring  5  is supported. The bottom  12  has a middle hole which forms a passage  13  of an outlet valve  14  of the piston pump  1 . The outlet valve  14  is arranged in a blind hole  15  of a cylinder head  16  which is placed onto the bottom  12  of the cylinder  13 . The cylinder head  16  forms a valve casing of the outlet valve  14 . 
     The outlet valve  14  is a spring-loaded nonreturn valve with a mushroom-shaped shut-off body  17 . The shut-off body  17  has a head  18  with a spherical surface which co-operates with a conical valve seat  19  formed at a mouth of the passage  13  in the bottom  12  of the cylinder  3 . The shut-off body  17  has a shank  20  on a flat underside of the head  18 . 
     The shank  20  of the shut-off body  17  passes through a middle hole  21  in an end wall  22  of a tubular damper body  23 . The shank  20  of the shut-off body  17  of the outlet valve  14  has a smaller diameter than the middle hole  21  in the end wall  22  of the damper body  23 . The shut-off body  17  is consequently movable transversely to its opening and closing direction, that is to say radially to the cylinder  3 , and is oriented on the valve seat  19  during the closing of the outlet valve  14 . Any offset of the passage  13  having the valve seat  19  with respect to the cylinder head  16  forming the valve casing is compensated. 
     A valve closing spring  24 , which is designed as a helical compression spring in the illustrated embodiment of the disclosure, loads the damper body  23  and, via this, the shut-off body  17  against the valve seat  19 . The valve closing spring  24  is supported on a base of the blind hole  15  in the cylinder head  16 . 
     When the pump piston  2  displaces brake fluid out of the cylinder  3  during a stroke in the direction of the bottom  12  of the cylinder  3 , the shut-off body  17  is lifted off from the valve seat  19  and the outlet valve  14  is thereby opened. The damper body  23  moves in accompaniment with the shut-off body  17 , the shut-off body  17  being movable with respect to the damper body  23 . During the opening of the outlet valve  14 , the damper body  23  is pressed into the blind hole  15  in the cylinder head  16  and displaces brake fluid out of the blind hole  15  through an annular gap  25  surrounding the damper body  23  in the blind hole  15 . The displacement of brake fluid out of the blind hole  15  has the effect of damping the opening movement of the outlet valve  14 . The blind hole  15 , because of its action damping the opening movement of the outlet valve  14  in co-operation with the damper body  23 , may also be interpreted as a damper chamber  26  and the damper body  23  also as a damper piston  27 . 
     Brake fluid displaced out of the piston pump  1  through the outlet valve  14  flows through radial outlet ducts  28  into a ring line  29  and from there into an outlet  30  which issues radially in the pump casing  7  into the pump bore  6 . The ring duct  29  is enclosed between the cylinder  3  and the pump bore  6  and surrounds the cylinder  3  near the outlet valve-side end of the latter. 
     The mushroom shape of the shut-off body  17  of the outlet valve  14  is not mandatory for the disclosure, and, for example, the shut-off body may also be in the shape of a hemisphere or sphere or a disk.  FIG. 2  shows a further alternative with a cylindrical shut-off body  31  having a spherical end face  32  which co-operates with the conical valve seat  19  at the mouth of the passage  13  in the bottom  12  of the cylinder  3 . With the outlet valve  14  closed, the spherical end face  32  of the shut-off body  31  bears against the valve seat  19 . 
     The shut-off body  31  is received in a tubular damper body  33  which may also be interpreted as a damper piston. The shut-off body  31  is axially displaceable in the damper body  33 , that is to say movable in the opening and the closing direction. In contrast to  FIG. 1 , the shut-off body  31  is not movable in the damper body  33  radially, that is to say transversely to the opening and closing direction. However, in  FIG. 2 , the damper body  33  and, together with it, the shut-off body  31  are movable radially, that is to say transversely to the opening and closing direction, as a result of play in the blind hole  15  in the cylinder head  16 , the blind hole  15  forming a damper chamber  26  here, too. The blind hole  15  has a larger diameter than the damper body  33 , so that there is an annular gap  25  surrounding the damper body  33  between the damper body  33  and a wall of the blind hole  15  in the cylinder head  16 . Orientation of the spherical end face  32  of the shut-off body  31  on the valve seat  19  during the closing of the outlet valve  14  is thereby possible. The shut-off body  33  has an inward radial flange  34  against which the valve closing spring  24  presses. 
     As in  FIG. 1 , in  FIG. 2  too, during the opening of the outlet valve  14  the shut-off body  31 , together with the damper body  33 , is pressed into the blind hole  15  which forms the damper chamber  26 . In this case, the damper body  33  displaces brake fluid out of the damper chamber  26  through the annular gap  25  surrounding said damper body, with the result that the opening movement of the outlet valve  14  is damped in the desired way. 
     With the exception of the differences explained, the piston pump  1  from  FIG. 2  is designed identically to the piston pump  1  from  FIG. 1  and functions in the same way. To avoid repetition, reference is made, to that extent, to the above explanations relating to  FIG. 1  in order to explain  FIG. 2 . Identical components have the same reference numerals in both figures. 
     A conical valve seat  19  is not mandatory for the disclosure. The valve seat may also be formed, for example, by a peripheral edge at the mouth of the passage  13  (not illustrated). The list is not conclusive.