Abstract:
A piston pump for brake systems employs a pulsation-smoothing device that functions especially well in the region of the outlet valve. As a result, substantially less noise occurs, and the durability of the piston pump is substantially better. The piston pump is used essentially in traction-controlled motor vehicle brake systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/00891 filed on Mar. 13, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a piston pump intended particularly for a hydraulic traction-controlled vehicle brake system. 
   2. Description of the Prior Art 
   German Published, Nonexamined Patent Application DE 42 26 646 A1 shows a hydraulic vehicle brake system with a pump, in which a pressure damper is provided downstream of an outlet check valve. For the pressure damper provided in the pressure line to have an adequate effect, the pressure damper must be made suitably large. Because of the pressure damper, the known vehicle brake system is relatively large as well, and increased production cost is necessary. Upon actuation of the brake pedal, some of the pressure medium positively displaced via the driver&#39;s foot is forced into the pressure damper. Because the pressure damper must be relatively large for an adequate effect, upon actuation of the brake pedal a relatively large quantity of pressure medium has to be positively displaced, which must be taken into account by suitable dimensioning of the components involved in this process. As a result, the known brake system is rather large in size. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   The piston pump of the invention has the advantage that the pulsation-smoothing device quite effectively overcomes the pressure pulsations and pressure waves that otherwise occur in a piston pump. Because of the high effectiveness of the pulsation-smoothing device, this device can be made rather small while an adequate effect is nevertheless attained. Since the pulsation-smoothing device can be made rather small, the advantage is attained that the overall piston pump is fairly small. This has the advantage of a vehicle brake system that is small overall. Because the pulsation-smoothing device is small because of its good effectiveness, and in particular the storage volume can be kept rather small, the advantage is attained that upon an actuation of the brake pedal, at most an insignificant proportion of the pressure medium put under pressure by the driver&#39;s foot is taken up by the pulsation-smoothing device, so that there is practically no negative effect from the pulsation-smoothing device on the mode of operation of the vehicle brake system during an actuation of the brake pedal. 
   Because the pulsation-smoothing device is rather small, and especially because the storage volume for the pulsation-smoothing device can be kept fairly small, it is advantageously also unnecessary to provide a check valve downstream of the pulsation-smoothing device. Because this check valve is not necessary, the advantage is attained that the production cost and structural size of the vehicle brake system of the invention can be kept small; there is also the advantage that the unnecessary additional check valve cannot become defective. 
   Because of the good damping of pressure fluctuations by the pulsation-smoothing device, the advantage is attained that substantially less noise is created, and the durability of the piston pump is substantially better. 

   
     Drawing BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent from the description contained herein below, taken in conjunction with the drawings, in which: 
       FIG. 1  is a fragmentary longitudinal sectional view of a hydraulic block of a traction-controlled vehicle which brake system in the region of the piston pump of the system; and 
       FIGS. 2-10  are views similar to  FIG. 1  of a plurality of different, preferably selected and especially advantageous exemplary embodiments. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The pump assembly of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (for anti-lock brake system), TCS (traction control system), VDC (vehicle dynamics control) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS or VDC or EHB). In a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB), for instance, the pump is needed. With wheel slip control (ABS or TCS), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (TCS) can for instance be prevented. In a brake system serving as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system. 
     FIG. 1  shows a first, especially advantageous, preferably selected exemplary embodiment, in which a piston pump  1  is built into a hydraulic block, shown in part and in section, of the vehicle brake system. A plurality of piston pumps  1  can be built into the hydraulic block. The hydraulic block forms a pump housing  2  of the piston pump  1 . The piston pump  1  includes a bush  4 , inserted into the pump housing  2 , an eccentric element  6 , an inlet connection  8 , and an outflow conduit  10 . The inlet connection  8  and the outflow conduit  10  extend through the hydraulic block or pump housing  2 . From the outflow conduit  10 , branching lines not shown lead via hydraulic valves, not shown, to a master cylinder and wheel brake cylinders, not shown. An installation chamber  12  is located in the pump housing  2 . The bush  4  and a pump piston  14  are inserted into the installation chamber  12 . The pump piston  14  has one end  14   a  toward the eccentric element  6 . and one end  14   b  remote from the eccentric element  6 . Via the eccentric element  6 . the pump piston is successively driven to execute an intake stroke and a compression stroke in alternation. 
   The installation chamber  12  provided in the pump housing  2  is sealed off from the outside by a closure piece  16 . The closure piece  16  has a bottom  17  on its face end, oriented outward. The bush  4  has a bottom  18  on its end, toward the closure piece  16 . A restoring spring  19  braced on the bush bottom  18  and on the pump piston  14  keeps the end  14   a  of the pump piston  14  in contact with the eccentric element  6 . Between the bush bottom  18  and the end  14   b , remote from the eccentric element  6 , of the pump piston  14 , there is a compression chamber  20  that increases in size during an intake stroke and decreases in size during a compression stroke. 
   The piston pump  1  has an inlet valve  22 . The inlet valve  22  has a valve seat  22   a , a closing body  22   b , and a closing spring  22   c . The closing spring  22   c  urges the closing body  22   b  against the valve seat  22   a  provided on the pump piston  14 . 
   The piston pump  1  has an outlet valve  24 . The outlet valve  24  has a valve seat  24   a , a closing body  24   b , a closing spring  24   c , and a retaining element  24   d . The closing spring  24   c  urges the closing body  24   b  against the valve seat  24   a , which is structurally connected to the housing and for instance is provided on the bush bottom  18 . One end of the closing spring  24   c  is braced on the closing body  24   b , and one end of the closing spring  24   c  is braced on the retaining element  24   d  structurally connected to the housing. The retaining element  24   d  is secured to the bottom  18  of the bush  4 . The retaining element  24   b  serves not only to brace the closing spring  24   c  but also to guide the closing body  24   b . The retaining element  24   d  has at least one passage of adequate size, through which the pressure medium can flow. 
   An inlet passage  26  leads from the inlet connection  8  to the inlet valve  22 . A passage  28  leads from the compression chamber  20  through the bush bottom  18  to the outlet valve  24 . The valve seat  24   a  surrounds the passage  28 . 
   On the side of the closing body  24   b  remote from the passage  28 , there is an outflow chamber  30 . In other words, the outflow chamber  30  is the chamber that adjoins the valve seat  24   a  downstream. In the exemplary embodiment selected, the outflow chamber  30  is located between the bush bottom  18  and the bottom  17  of the closure piece  16 . The closing spring  24   c  and the retaining element  24   d  are located in the outflow chamber  30 . 
   An elastically resilient wall  32  is built in, inside the installation chamber  12 . The elastically resilient wall  32  is located downstream of the valve seat  24   a , in the immediate vicinity of the outlet valve  24 . The outer circumference of the elastically resilient wall  32  is built in tightly and firmly inside the closure piece  16 . The resilient wall  32  is acted upon by the pressure prevailing in the outflow chamber  30 . On the side of the resilient wall  32  remote from the outflow chamber  30 , there is a counterpart chamber  36 . Inside the counterpart chamber  36 , a gas is for instance tightly trapped. However, it is also possible for the counterpart chamber  36  to communicate with the atmosphere via an opening  38 . 
   A compressible body  34  is built into the outflow chamber  30 , in the immediate vicinity of the outlet valve  24 . The compressible body  34  is acted upon on one side by the pressure prevailing in the outflow chamber  30 , and on the other side, the compressible body  34  is predominantly braced against the resilient wall  32 . The compressible body  34  covers the entire surface of the resilient wall  32 . On its outer circumference, the compressible body  34  additionally serves to provide sealing between the outflow chamber  30  and the counterpart chamber  36 . The volume of the compressible body  34  is dimensioned to be great enough that at low-frequency pressure fluctuations in the outflow chamber  30 , the volume of the compressible body  34  varies in accordance with the pressure pulsations, so that the pressure pulsations are intercepted by the compressible body  34  and thus smoothed out. The compressible body  34  is preferably made of rubber or an elastomer material. The compressible body  34  preferably has intrinsically minimally small gas-filled voids, so that upon pressure changes, a change in volume of the compressible body  34  can take place. 
   The compressible body  34  comprises a material of such a kind that it has a volume that is variable as a function of pressure. A material is selected that upon varying its volume dissipates some of the energy of the pulsations by means of internal friction. 
   The resilient wall  32  is preferably a relatively thin, platelike disk of a springy material, preferably spring steel. The elasticity and resilience of the springy, resilient wall  32  is dimensioned such that at high-frequency pressure pulsations in the outflow chamber  30 , upon a sudden pressure increase, the resilient wall  32  yields in the direction of the counterpart chamber  36 , while upon a high-frequency, sudden pressure drop in the outflow chamber  30 , the resilient wall  32  springs back in the direction of the outflow chamber  30 . It is thus attained that high-frequency pressure pulsations are smoothed out in the immediate vicinity, just downstream of the valve seat  24   a.    
   The outflow chamber  30  communicates with the outflow conduit  10  via a throttle  39 . The throttle  39  is disposed in the vicinity of the outlet valve  24 , close to the outlet valve  24 . With the aid of the throttle  39 , it is attained that the pressure pulsations occurring in the region of the outlet valve  24  inside the outflow chamber  30  act in concentrated form on the resilient wall  32  and on the compressible body  34 . By means of the resilient wall  32  and the compressible body  34 , pressure pulsations are prevented from occurring in the immediate location where the pulsations would otherwise occur, so that the pulsations cannot spread past the throttle  39  into the outflow conduit  10 . 
   In the exemplary embodiment shown in  FIG. 1 , the shape of the outflow chamber  30  in cooperation with the elastically resilient wall  32 , the compressible body  34 , the counterpart chamber  36 , and the throttle  39 , forms a highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed in the immediate vicinity of the outlet valve  24 . As a result, the hydraulic resilience of the pulsation-smoothing device  40  can be kept relatively slight. This has the advantage that despite very good pulsation smoothing, the hydraulic system in the outflow conduit  10  can be kept fairly rigid, even without using an additional check valve downstream of the pulsation-smoothing device  40 . 
   By building the wall  32 , the body  34 , and the counterpart chamber  36  into the closure piece  16 , the advantage is attained that a small total number of components is needed, and that the assembly of the piston pump  1  can be accomplished without additional expense. The closure piece  16  is built into the installation chamber in pressure-tight fashion, by way of a crimped connection known per se. The closure piece  16  seals off the high-pressure region of the piston pump  1  from the outside. 
     FIG. 2  shows a further, especially advantageous, preferably selected exemplary embodiment. 
   In all the drawings, elements that are the same or function the same are identified by the same reference numerals. Unless anything is said to the contrary or shown to the contrary in the drawing, what is said for and shown in one of the drawings applies to the others as well. Unless otherwise stated in the explanations, the details of the individual exemplary embodiments and the various drawings can be combined with one another. 
   In the exemplary embodiment shown in  FIG. 2 , a retaining element  42  is press-fitted into the closure piece  16 . The retaining element  42  keeps the resilient wall  32  in contact with a shoulder  44  provided on the closure piece  16 . Between an annular end face  46  of the retaining element  42  and the resilient wall  32 , a compressible annular body  48  is installed. The compressible annular body  48  provides sealing between the outflow chamber  30  and the counterpart chamber  36 . For the annular body  48 , the same material as for the compressible body  34  can be used. 
   At low-frequency pressure pulsations in the outflow chamber  30 , the compressible annular body  48  is compressed radially outward upon a pressure increase, while at low-frequency pressure drops, the annular body  48  springs back radially inward. As a result, low-frequency pressure pulsations are eliminated, or at least damped considerably, directly in the outflow chamber  30 . 
   In the exemplary embodiment shown in  FIG. 2 , the shape of the outflow chamber  30 , in cooperation with the wall  32  that is elastically resilient as a function of pressure, the compressible annular body  48 , the counterpart chamber  36 , and the throttle  39 , forms the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed in the immediate vicinity of the outlet valve  24 . 
     FIG. 3  shows a further, especially advantageous, preferably selected exemplary embodiment. 
   The resilient wall  32  can for instance, as shown in  FIG. 2 , comprise a single spring-elastic plate. However, as shown in  FIG. 3 , the resilient wall  32  can also be assembled from a first spring-elastic plate  32   a  and a second spring-elastic plate  32   b . It is also possible, however, to modify the exemplary embodiment in such a way that the resilient wall  32  is put together from three plates resting flatly against one another and preferably compressed somewhat, or even four or more such plates. What in this case are at least two spring-elastic plates  32   a ,  32   b  are put together in such a way that between them, a friction device  49  is created. 
   Upon high-frequency pressure pulsations in the outflow chamber  30 , the resilient wall  32  yields in the direction of the counterpart chamber  36 , or back in the direction of the outflow chamber  30 . The result is flexing of the resilient wall  32 . Because of this flexing, the spring-elastic plates  32   a  and  32   b  shift relative to one another. This creates a relative motion between the plates  32   a ,  32   b , and because of the friction, damping occurs. The result is especially effective damping of the high-frequency pressure pulsations in the outflow chamber  30 . 
   In the exemplary embodiment shown in  FIG. 3 , the shape of the outflow chamber  30 , in cooperation with the elastically resilient wall  32 , the throttle  39 , the annular body  48 , the counterpart chamber  36 , and the friction device  49 , forms the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed in the immediate vicinity of the outlet valve  24 . 
   It is noted that the friction device  49  can be installed in the exemplary embodiments shown in the other drawings as well. Particularly in  FIGS. 1 ,  2 ,  4 ,  6  and  7 , the elastically resilient wall  32  provided for the sake of forming the friction device  49  can also be put together from a plurality of plates contacting one another and rubbing against one another. 
     FIG. 4  shows a longitudinal section through a further, especially advantageous, selected exemplary embodiment. 
   In the exemplary embodiment shown in  FIG. 4 , the elastically resilient wall  32  is approximately in the form of a top hat. The outer rim of the elastically resilient wall  32  is press-fitted into the closure piece  16 . The counterpart chamber  36  communicates with the outflow conduit  10  via a connection  51 . The cross section of the connection  51  is dimensioned such that the flow of pressure medium is throttled somewhat in this connection  51 . The connection  51  has a connecting throttle  51   a.  However, the throttling action of the throttle  39  is preferably substantially stronger than the throttling action of the connecting throttle  51   a.    
   Upon pressure pulsations in the outflow chamber  30 , an elastic deformation of the wall  32  occurs. In the elastic deformation of the wall  32 , some of the energy upon pressure pulsations is intercepted by the resilient wall  32 . As a result, the pressure pulsations are attenuated substantially and cannot spread, or can spread only with substantial attenuation, via the throttle  39  into the outflow conduit  10 . The substantially attenuated pressure pulsations reaching the outflow conduit  10  are operative through the connection  51  as far as the counterpart chamber  36 . Because of the travel distance and because of the throttle  39  as well as the connecting throttle  51   a  that may be provided in the connection  51 , the pressure pulsations reach the counterpart chamber  36  with a phase offset relative to the pressure pulsations in the outflow chamber  30 . This reinforces the elastic flexing of the resilient wall  32 , so that because of the pressure pulsations in phase opposition in the counterpart chamber  36 , an especially effective breakdown of pressure pulsations in the outflow chamber  30  results. As a result, very uniform flow of pressure medium is obtained in the outflow conduit  10 . 
   In the exemplary embodiment shown in  FIG. 4 , the shape of the outflow chamber  30 , along with the elastically resilient wall  32 , the counterpart chamber  36 , the throttle  39 , and the connection  51  connecting the counterpart chamber  36  with the outflow conduit  10 , form the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed in the immediate vicinity of the outlet valve  24 . 
     FIG. 5  shows a further selected, especially advantageous exemplary embodiment. 
   The outlet valve  24 , on the side of the closing body  24   b  remote from the passage  28 , has a rear valve chamber  53 . 
   In the exemplary embodiment shown in  FIG. 5 , the ball-shaped closing body  24   b  of the outlet valve  24  is guided in the opening direction along a constriction in the closure piece  16 . The constriction between the closing body  24   b  and the closure piece  16  is so narrow that at most an insignificant, negligibly small fluidic communication exists between the rear valve chamber  53  and the outflow chamber  30 . Because the constriction disconnects the outflow chamber  30  from the rear valve chamber  53 , this constriction will hereinafter be called the disconnection point  52 . 
   A passage  50  connects the outflow conduit  10  with the rear valve chamber  53 . 
   In this exemplary embodiment, the passage  50  is composed of one longitudinal groove  50   a  or a plurality of longitudinal grooves  50   a , one circumferential groove  50   b , and one radial hole  50   c  or a plurality of radial holes  50   c . The circumferential groove  50   b  communicates with the outflow conduit  10  via the at least one longitudinal groove  50   a  and with the rear valve chamber  53  via the at least one radial hole  50   c . If the closing body  24   b  vibrates, which could cause a pressure pulsation in the outflow chamber  30 , pressure medium is exchanged between the rear valve chamber  53  and the outflow conduit  10 . In this process, the pressure medium flows through the passage  50 , which has multiple right angles. These right angles engender an advantageous resistance, which assures that in the rear valve chamber  53 , pressure fluctuations oriented counter to vibration of the closing body  24   b  will build up, which assure effective damping of the vibration of the closing body  24   b . As a result, and especially also in cooperation with the throttle  39  between the outflow conduit  10  and the outflow chamber  30 , it is assured that any pressure pulsations that occur will be effectively reduced, and in particular that any pressure pulsations that occur will not reach the outflow conduit  10 . 
   Between the outflow chamber  30  and the outflow conduit  10 , the throttle  39  is preferably provided, which additionally contributes to smoothing pressure pulsations. The throttle  39  has an especially pulsation-damping effect if it is disposed fairly close to the region of the valve seat  24   a.    
   In the exemplary embodiment shown in  FIG. 5 , the shape of the outflow chamber  30 , in cooperation with the rear valve chamber  53 , the throttle  39 , and the passage  50 , forms the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed in the immediate vicinity of the outlet valve  24 . 
     FIG. 6  shows a further especially advantageous exemplary embodiment. 
   In the exemplary embodiment shown in  FIG. 6 , a barometric cell  54  is inserted into the interior of the closure piece  16  and thus into the installation chamber  12 . The barometric cell  54  preferably shown for instance comprises a first wall  54   a  and a second wall  54   b . The two walls  54   a ,  54   b  are joined in pressure-tight fashion to one another on their circumference, preferably being welded together. As a result, in this exemplary embodiment, the counterpart chamber  36  between the two walls  54   a ,  54   b  is hermetically sealed off from the outside. In the counterpart chamber  36 , there is preferably a readily compressible gas, such as air. The barometric cell  54  is inexpensive to produce and durably assures a sealed enclosure of a gas volume. 
   The first wall  54   a , toward the outflow chamber  30 , forms the elastically resilient wall  32 . Because of the elastically resilient wall  32 , the outflow chamber  30  enlarges somewhat upon pressure pulsations during a pressure increase, so that the pressure increase is substantially less forceful than if the elastically resilient wall  32  were not present. During a pressure drop, the elastically fastened wall  32  springs back in the direction of the outflow chamber  30 , so that the pressure drop in the outflow chamber  30  is not so forceful as if the elastically resilient wall  32  were not present. The throttle  39  assures that the pressure fluctuations are essentially limited to the outflow chamber  30 , where because of the elastically resilient wall  32  an effective smoothing of the pressure fluctuations occurs. As a result, it is attained that a flow with effectively smoothed pressure fluctuations is present in the outflow conduit  10 . 
   In this exemplary embodiment as well, a friction device that additionally damps vibration can be provided, as shown in  FIG. 2 , for instance by providing that the first wall  54   a  is composed of two plates resting on one another. 
   In the exemplary embodiment shown in  FIG. 6 , the shape of the outflow chamber  30 , in cooperation with the elastically resilient wall  32 , the counterpart chamber  36 , the throttle  39 , and the barometric cell  54 , forms the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed in the immediate vicinity of the outlet valve  24 . 
     FIG. 7  shows a further especially advantageous exemplary embodiment. 
     FIG. 7  differs from  FIG. 6  in having a compressible body  55  that damps vibration. 
   It has been demonstrated that by incorporating the compressible body  55  into the outflow chamber  30 , pressure pulsations can be smoothed even better. The compressible body  55  is especially effective if, on the downstream side, it is located as close as possible to the outlet valve  24 , in its immediate vicinity. By inserting the compressible body  55  shown in  FIG. 7  into the outflow chamber  30 , an additional compressibility in the outflow chamber  30  is obtained. As a result, despite the insertion of the compressible body  55  into the outflow chamber  30 , the structural size overall can be kept substantially smaller than without the compressible body  55 , and substantially better smoothing of the pressure pulsations is obtained. 
   In the exemplary embodiment shown in  FIG. 7 , the shape of the outflow chamber  30 , in cooperation with the elastically resilient wall  32 , the counterpart chamber  36 , the throttle  39 , the barometric cell  54 , and the compressible body  55 , forms the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed downstream of and in the immediate vicinity of the outlet valve  24 . 
     FIG. 8  shows a further especially advantageous exemplary embodiment. 
   The exemplary embodiment shown in  FIG. 8  corresponds extensively to the exemplary embodiments shown in the other drawings, except for the differences named below. In particular, however, the piston pump shown in  FIG. 8  is largely equivalent to the piston pump shown in  FIG. 5 . 
   In the exemplary embodiment shown in  FIG. 8 , a resilient wall  56  is sealingly inserted into the circumferential groove  50   b  of the passage  50 . Because of the elastic deformation of the resilient wall  56 , resulting from pressure pulsations in the rear valve chamber  53  caused by vibration of the closing body  24   b , damping of the pressure fluctuations arising in the rear valve chamber  53  is obtained. The result is a calming of the vibration of the closing body  24   b . As a result, the flow of pressure medium flowing through the outlet valve  24  and the outflow chamber  30  into the outflow conduit  10  is also calmed, so that overall, substantially weaker pressure fluctuations arise. 
   In the exemplary embodiment shown in  FIG. 8 , the shape of the outflow chamber  30 , in cooperation with the throttle  39 , the passage  50 , the rear valve chamber  53 , and the dampingly resilient wall  56 , forms the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed downstream of and in the immediate vicinity of the outlet valve  24 . 
     FIG. 9  shows a further especially advantageous exemplary embodiment. 
   The piston pump  1  shown as an example in  FIG. 9  is essentially equivalent, except for the differences listed, to the piston pumps  1  shown as examples in the other drawings. 
   In the exemplary embodiment shown in  FIG. 9 , an insert  58  is incorporated into the installation chamber  12 , between the closure piece bottom  17  and the bush bottom  18 . 
   Between the outflow chamber  30  and the outflow conduit  10 , a turbulence-causing throttle  60  is provided. The pressure medium flowing from the outlet valve  24  through the outflow chamber  30  to the outflow conduit  10  must pass through the turbulence-causing throttle  60 . Beginning at the outflow chamber  30 , the turbulence-causing throttle  60  for instance comprises one or more radial grooves  60   a  provided at the insert  58 , a circumferential groove  60   b  made on the insert  58 , one or more oblong slots  60   c  made in the insert  58 , a second circumferential groove  60   d,  one or more radial conduits  60   e , a third circumferential groove  60   f , and one or more longitudinal conduits  60   g . The at least one radial groove  60   a  and the circumferential groove  60   b  are located on the face end of the insert  58  toward the bush bottom  18 . The second circumferential groove  60   d , the at least one radial conduit  60   e , and the third circumferential groove  60   f  are located in the face end of the insert  58  toward the closure piece bottom  17 . The at least one longitudinal conduit  60   g  is preferably machined into an inner circumferential face of the closure piece  16 . The at least one radial groove  60   a  connects the outflow chamber  30  with the circumferential groove  60   b . The at least one oblong slot  60   c  connects the two circumferential grooves  60   b ,  60   d  to one another. The at least one radial conduit  60   e  connects the two circumferential grooves  60   d ,  60   f  to one another. The at least one longitudinal conduit  60   g  connects the third circumferential groove  60   f  with the outflow conduit  10 . 
   Because the flow of pressure medium through the turbulence-causing throttle  60  is deflected many times, and because the turbulence-causing throttle  60  has quite different cross sections in the course of the flow path, and as a result the flow of pressure medium must flow at quite different flow speeds and in quite different directions and with sudden deflections, the overall result is a marked reduction in pulsations within the flow of pressure medium flowing from the outlet valve  24  into the outflow conduit  10 ; that is, it is assured that virtually no pressure pulsations can occur. 
   The essential parts of the turbulence-causing throttle  60  are located on or in the insert  58  that is easy to produce. This has the advantage that despite the turbulence-causing throttle  60 , no complicated machining operations on the other parts of the piston pump  1  are necessary. 
   The rear valve chamber  53  communicates with the outflow chamber  30  only via the disconnection point  52  that allows only very little or practically no pressure medium to pass through it. Upon vibration of the closing body  24   b , pressure fluctuations that are oriented directly counter to a vibration of the closing body  24   b  are engendered in the rear valve chamber  53 . The result is a pronounced calming of the vibration of the closing body  24   b . This result is a substantially more uniform hydraulic flow out of the outflow chamber  30  into the outflow conduit  10 . 
   In the exemplary embodiment shown in  FIG. 9 , the shape of the outflow chamber  30  in cooperation with the rear valve chamber  53 , the disconnection point  52  and the turbulence-causing throttle  60  form the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed downstream of and in the immediate vicinity of the outlet valve  24 . 
     FIG. 10  shows a further especially advantageous exemplary embodiment. 
   Except for the differences shown or described below, the piston pump  1  shown in  FIG. 10  is essentially equivalent to the piston pumps  1  shown in the other drawings. In particular, the piston pump  1  shown in  FIG. 10  is largely equivalent to the piston pump  1  shown in  FIG. 9 . 
   In the exemplary embodiment shown in  FIG. 10 , the circumferential groove  60   d  of the turbulence-causing throttle  60  is widened radially inward so far that the circumferential groove  60   d  changes over into the rear valve chamber  53 . As a result, the pressure medium flowing through the turbulence-causing throttle  60  is calmed, and the partially calmed pressure medium acts on the closing body  24   b  in the rear valve chamber  53 , on the side of the closing body  24   b  remote from the passage  28 . Because the flow of pressure medium is partly calmed by the turbulence-causing throttle  60 , substantial damping of the vibration of the closing body  24   b  results. In the further flow of pressure medium out of the circumferential groove  60   d  in the direction of the outflow conduit  10 , a further calming of the flow of pressure fluid and a further breakdown of pressure peaks then occur. 
   In the exemplary embodiment shown in  FIG. 10 , the shape of the outflow chamber  30 , along with the rear valve chamber  53 , the disconnection point  52 , the turbulence-causing throttle  60 , and the hydraulic communication of the rear valve chamber  53  with the turbulence-causing throttle  60 , form the highly effective pulsation-smoothing device  40 . The components of the pulsation-smoothing device  40  are preferably disposed downstream of and in the immediate vicinity of the outlet valve  24 . 
   The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.