Abstract:
In a piston pump, in particular for pressure medium delivery in slip-controlled hydraulic brake systems, including a suction valve and a delivery valve, external preassembly and possibilities of external testing of the delivery and suction valves result from providing the suction valve and the delivery valve within a component which can be handled independently. The component preferably includes a delivery valve provided radially to the center line and a valve seat member, with a valve body of the delivery valve being prestressed by a tongue of a clamp, placed onto the valve seat member, against a valve seat formed within the valve seat member.

Description:
TECHNICAL FIELD 
     The present invention generally relates to a piston pump, and more particularly relates to a piston pump used in slip-controlled hydraulic brake systems. 
     BACKGROUND OF THE INVENTION 
     Such a piston pump, e.g., is known from EP 0 631 050 B1. The piston pump according to this prior art includes a delivery valve and a suction valve, both arranged within a pump housing so that they are separate from each other in terms of location and construction. Moreover, the known delivery and suction valves are assembled within the pump housing one after the other in terms of time and, once assembled, it is no longer possible to test them without a major effort. However, before assembly, it is likewise not readily possible to perform an optimum test of these valves since in such a case the assembled conditions would have to be simulated as accurately as possible and since the valves could be tested only separately. 
     A ball-type-design delivery valve is known particularly in the context of the examples of embodiments of a known piston pump as disclosed in FIGS. 11 through 19 of EP 0631 050 B1. There, a valve body having the design of a ball is prestressed, with a ring means being used, against a valve seat designed as radial bore. This known delivery valve has disadvantages in that the assembly of the ring means on the valve seat member of the delivery valve requires a major effort and in that its type of fastening is not particularly stable. In this known arrangement it is moreover possible that the ring means twists or is displaced and, thus, the ball slips out of its valve seat or there is a change in the pre-stressing force. 
     It is an object of the present invention to avoid the disadvantages of prior art and, in particular, to provide a piston pump enabling both the delivery valve and the suction valve to be preassembled and tested before being assembled into a pump housing, i.e., enabling external preassembly and testing. 
     This inventive task is solved in a generic piston pump in that the delivery valve and the suction valve are provided on a component which can be handled independently. 
     An essential advantage of the present invention consists in that the inventive design of the delivery and suction valves provides a valve cartridge unit allowing external preassembly and testing. Moreover, it is possible to reduce the number of parts used as well as the rejects of defective units and, consequently, the cost of manufacture. A further advantage of this invention is the fact that the time needed for assembling the inventive piston pump is considerably reduced which likewise means a drop in costs. The constructional combination of delivery valve and suction valve, moreover, results both in space being saved and in an optimum utilization of the space available for the valves within the pump housing. Finally, the constructional combination of delivery and suction valves permits a simple recessing of the valve seat member as no separate valves have to be accommodated within the pump body. 
     In a preferred embodiment of this invention, the component is fastened within the pump housing by means of caulking or clinching. This type of fastening is beneficial in terms of cost and enables pressure-tight assembly of the component within the pump housing. Further, this restricts the possibilities of inexpert manipulation of the brake system. 
     So as to reduce the number of parts required for assembling the component it is an advantage to provide one spring element for jointly prestressing the delivery valve and the suction valve. This spring element may have the design of a compression spring or of a tension spring. 
     Advantageously, the component includes a valve seat member wherein there is provided a valve seat for the delivery valve and a valve seat for the suction valve. This results in an especially space-and-material-saving design of the component of the inventive piston pump. 
     According to a further embodiment of this invention, the piston pump includes a cup-shaped pump piston, with the component including an axially projecting gudgeon portion wherethrough the cup-shaped piston is guided. An advantage of this embodiment is the fact that the pump housing does not have to undergo hardening or anodizing. 
     Advantageously this component includes a valve seat member with an axial recess formed on one of its front sides for guiding the pump piston of the piston pump therein or rather for having it plunge into this recess. Preferably, the suction valve is arranged on the other, opposite front side of the valve seat member essentially axially to the center line of the valve seat member while the delivery valve is arranged essentially radially to said line. This arrangement is particularly space-saving as the pump piston, together with its resetting spring, can plunge into the recess whereby the length of the bore wherein the pump piston moves is shortened. 
     According to a variant of this invention, the suction valve includes a compression spring secured by means of a bowl-type spring retainer provided with a stop formed thereon for the valve body of the suction valve and further including means for guiding the compression spring and means for guiding a piston return spring serving to reset the piston. The bowl-type spring retainer thus combines a plurality of different functions which means a saving of space and material. Further, the design of the stop for the suction valve body prevents the suction valve body from becoming jammed within the bowl-type spring retainer. 
     Advantageously, the means for guiding the compression spring and the means for guiding the piston return spring form a cup-shaped portion of the bowl-type spring retainer, with the compression spring being guided on the inside of the cup-shaped portion and the piston return spring being guided on the outside of the cup-shaped portion. The stop of the bowl-type spring retainer preferably serves as an internal guideway for the compression spring. This is particularly beneficial since the bowl-type spring retainer, due to its function as a retaining cage for the suction valve body, is anyway concave, i.e., provided with a cup-shaped portion and since, further, the bowl-type spring retainer anyway includes a stop in order to prevent the suction valve closure member from becoming jammed within the bowl-type spring retainer. 
     In accordance with this invention, further provided is a delivery valve with a valve seat member, in particular for a piston pump, with a valve body of the delivery valve being prestressed by a clamping element, mountable to the valve seat member, against a valve seat formed within the valve seat member. Particularly advantageous is the fact that the clamping element includes a tongue which is formed thereon and prestresses the valve body against the valve seat. The use of this inventive tongue instead of, for instance, a helical spring is possible because the opening pressure of the delivery valve does not have to be adjusted as accurately as that of the suction valve. It is thus possible to substitute the helical spring in the delivery valve for a tongue provided on the clamping element. The tongue urges the valve body perpendicularly onto the valve seat while simultaneously fixing the valve body axially and radially. Fixation of the valve body may even be improved by means of a bore which can additionally be provided within the tongue and at least partially is engaged by the valve body. Further, the arrangement of the tongue on the clamping element also offers the advantage of adjustability of the resiliency over the length of the tongue, even with a predetermined construction of the valve body. Finally, the arrangement of the tongue within the clamping element offers sufficient surface contact between the clamping element and the valve seat member, namely by means of the surfaces adjoining the tongue, whereby the clamping element can much better be fastened on the valve seat member. 
     Preferably, the clamping element has a tab, provided perpendicularly to the tongue, for fastening the clamping element on the valve seat member. Thus it is possible to a great extent to prevent the clamping element from twisting and getting loose. 
     In a preferred embodiment of this invention, the clamping element includes at least one tab, provided parallel to the tongue, for fastening the clamping element in a valve seat member recess serving to receive the valve body. This does not require a separate bore in the valve seat member for fastening the tab. 
     If the clamping element is dimensioned considerably wider than the valve body, the larger contact surface between clamping element and valve seat member results in an improved fastening of the clamping element on the valve seat member because of only the tension of the clamping element. 
     So as to facilitate the radial slipping-on of the clamping element onto the valve seat member the cross sides of the clamping element preferably include end portions arched outwards. Slipping-on, however, may also be done axially, starting from an end portion of the valve seat member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of a longitudinal section of a first example of an embodiment of the present invention. 
     FIG. 2 is a view of a longitudinal section of a second example of an embodiment of the present invention. 
     FIG. 3 is a view of a longitudinal section of a third example of an embodiment of the present invention. 
     FIG. 4 is a view of a longitudinal section of a fourth example of an embodiment of the present invention. 
     FIG. 5 is a view of a longitudinal section of a fifth example of an embodiment of the present invention. 
     FIG. 6 is a view of a longitudinal section of a sixth example of an embodiment of the present invention. 
     FIG. 7 is a view of a longitudinal section of a seventh example of an embodiment of the present invention. 
     FIG. 8 is a view of a longitudinal section of an eighth example of an embodiment of the present invention. 
     FIG. 9 is a cross-sectional view of an inventive delivery valve along line IX—IX of FIG.  8 . 
     FIG. 10 is a view of a longitudinal section of a ninth example of an embodiment of the present invention. 
     FIG. 11 is a cross-sectional view of a further embodiment of an inventive delivery valve along line XI—XI of FIG.  10 . 
     FIG. 12 is a view of a longitudinal section of a tenth example of an embodiment of the present invention. 
     FIG. 13 is a cross-sectional view of a further embodiment of an inventive delivery valve along line XIII—XIII of FIG.  12 . 
     FIG. 14 is a view of a longitudinal section of an eleventh example of an embodiment of the present invention. 
     FIG. 15 is a perspective view of a retaining bow for being used on the inventive delivery valve as per FIG.  14 . 
     FIG. 16 is a cross-sectional view along line XVI—XVI of FIG. 14 of a preferred embodiment of an inventive delivery valve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 represents a view of a longitudinal section of a first example of an embodiment of an inventive hydraulic pump or rather piston pump  1  preferably used in an ABS (Anti-lock Braking System), TCS (Traction Control System) or ESP (Electronic Stability Program) system of a controlled vehicle brake apparatus. Within its housing  2 , the hydraulic pump  1  constructed as a piston pump includes an eccentric  4  driven by a drive shaft  3 . In this example of an embodiment, a pump piston  6  is connected with a non-illustrated second pump piston via a coupling ring  5  and is thus in contact with eccentric  4 . During the rotation of the drive shaft  3 , the pump piston  6  is linearly reciprocating within a stepped bore  7  of pump housing  2 . A component  8  such as a cartridge seals the end of stepped bore  7 , lying opposite eccentric  4 , in a pressure-tight manner. Cartridge  8  is fastened within the pump housing  2  by means of, e.g., caulking or clinching. On the outside of the cartridge or rather component  8 , an outwards bulging cap  9  forms a pressure damping chamber  10 . According to this invention, cartridge  8  includes a pressure-controlled delivery valve  11  and a pressure-controlled suction valve  12 . The valve cartridge  8  may be preassembled and tested outside the valve block or rather outside pump housing  2 . Delivery valve  11  includes a valve seat member  13 . Valve seat member  13  includes a central bore  14  the center line M of which coincides with the longitudinal axis of pump piston  6 . As seen from the outside to the inside, central bore  14  of the valve seat member  13  includes three stepped sections  15 ,  16 , and  17 . The diameter of the outsidemost section  15  is larger than the diameter of the mid-section  16  while the latter, on its part, is larger than that of the innermost section  17 . The valve seat member  13  includes an outer end portion  18  and an opposite, sleeve-type, inner end portion  19 . The stepped sections  15 ,  16  and part of stepped section  17  of bore  14  are formed within end portion  18 . The sleeve-type end portion  19  of valve seat member  13  likewise includes part of stepped section  17  of bore  14 . The end portion  18  of valve seat member  13  includes an annular channel  20  formed along its outside periphery and leading to a non-illustrated low-pressure accumulator via a schematically indicated bore  21 . When the suction valve  12  is open a bore  22  extending obliquely to line M connects annular channel  20  with a chamber  23  confined by piston  6 , with end portion  19  of valve seat member  13  projecting into chamber  23 . The end of end portion  19  of the valve seat member  13  which faces piston  6  is bent outwards in order to receive a retaining ring  24  slipped onto end portion  19 . A compression spring  25  supports itself on a step formed on the retaining ring  24 , on the one hand, and on a step formed on a valve element  26  of suction valve  12 , on the other hand. Valve element  26  serves as closure member of suction valve  12 . Compression spring  25  prestresses valve element  26  against its seat, i.e., a front side of the valve seat member  13  facing piston  6  and lying radially outside end portion  19 . In this position of suction valve  12 , chamber  23  does not communicate with the low-pressure accumulator. A step between sections  16  and  17  of bore  14  forms a valve seat for a valve element of delivery valve  11 . Said valve element preferably has the design of a ball  27 . Ball  27  is prestressed by a compression spring  28  against its seat while the end of compression spring  28  which is opposite of ball  27  supports itself on a plug  29  arranged within bore  14 . Plug  29  includes a pin element  30 , projecting inside, for guiding compression spring  28 . The outside diameter of pin element  30  approximately corresponds to the inside diameter of compression spring  28 . 
     During the operation of the inventive hydraulic pump  1 , the pressure of brake fluid is increased in chamber  23  in a delivery stroke phase wherein pump piston  6  moves to the right according to the view of FIG.  1 . To this end, a seal  31  is provided around the periphery of pump piston  6 . The pressurized brake fluid in chamber  23  now presses the ball  27 , against the prestress of compression spring  28 , away from its seat whereby pressurized brake fluid is transferred to a pressure medium consumer such as the wheel brakes. In a suction phase, while pump piston  6  moves to the left according to the view of FIG. 1, delivery valve  11  remains closed, i.e., under the action of compression spring  28  ball  27  is pressed against its valve seat formed on the bordering surface of sections  16  and  17 . During this suction stroke phase, the relative pressure reduction of the brake fluid in pressure chamber  23  opens suction valve  12 . Then, pressure medium is sucked into pressure chamber  23  via the low-pressure accumulator, bore  21 , annular channel  20  and bore  22 . 
     FIG. 2 represents a view of a longitudinal section of a second example of an embodiment of the present invention. As distinguished from the first example of an embodiment of the present invention already described in the context of FIG. 1, the example of an embodiment according to FIG. 2 features a different design of cartridge  8 . According to the second example of an embodiment of the present invention represented in FIG. 2, suction valve  12  of cartridge  8  is designed as a ball-type valve just as delivery valve  11 , with the arrangement of suction valve  12  within cartridge  8  approximately being perpendicular to that of delivery valve  11 . Cartridge  8  therefore includes a stepped radial bore  32  besides axial bore  14  provided for delivery valve  11 . A ball  33  serving as valve body and prestressed by a compression spring  34  against a step formed within radial bore  32  is the closure member of suction valve  12 . 
     FIG. 3 represents a view of a longitudinal section of a third example of an embodiment of the present invention. In general, the design of the hydraulic pump  1  represented in FIG. 3 is similar to the design of hydraulic pump  1  already described in the context of FIGS. 1 and 2. However, the main differences between the example of an embodiment of this invention, represented in FIG. 3, and those two first examples of embodiments of this invention lie in the design of cartridge  8 . Within cartridge  8 , a delivery valve  41  and a suction valve  42  are constructionally combined. Instead of a ball  27  (cf. FIGS.  1  and  2 ), delivery valve  41  includes as valve body a conical valve tappet  43  preferably made of steel or plastic and prestressed by a tension spring  44  against its valve seat, namely a central bore  45 , within valve seat member  46  of delivery valve  41 . One end of tension spring  44  is fastened to a fastening eyelet or the like of valve tappet  43 . Via a retaining element  47 , the opposite end of tension spring  44  is connected with an essentially conical (lower half of drawing) or plane (upper half of drawing) closure member  48  of suction valve  42 . Closure member  48  is a ring made of plastic. In the third example of an embodiment of the present invention represented in FIG. 3, thus, only one sole spring means, namely tension spring  44 , is provided for prestressing the valve tappet  43  of delivery valve  41  and the closure member  48  of suction valve  42 . 
     Referring to FIG. 4, a fourth example of an embodiment of the present invention is described. The fourth example of an embodiment of the present invention, represented by a view of a longitudinal section, in general is similar to the third example of an embodiment of this invention represented in FIG.  3 . However, the design of the valves, namely of delivery valve  41  and suction valve  42 , combined within valve cartridge  8  is different from the above-described variants of this invention. Delivery valve  41  includes a valve seat member  46  with a central bore  45  serving on its outside as a seat for a valve tappet  53 . Valve tappet  53 , preferably made of steel or plastic, includes a pin portion  54  and two end portions  55 ,  56  conically flaring outwards. End portion  55  serves as valve body for delivery valve  41  (cf. valve tappet  43  as per FIG.  3 ), while end portion  56  serves to support the valve tappet  53  within a central bore  57  of a retaining plate  58 . An especially inwards- bent outside-periphery portion  59  of retaining plate  58  is provided for the support of a compression spring  60  designed as a helical spring. Suction valve  42  has an annular closure member  61  made of plastic. Closure member  61  comprises a central bore  62  wherein valve tappet  53  moves. On its front side facing pump piston  6 , closure member  61  of suction valve  42  includes an annular step  63  serving to support and guide compression spring  60 . On its front side averted from pump piston  6 , closure member  61  is conical or plane and abuts on a mating valve seat, formed within the valve seat member  46 , when suction valve  42  is closed. Compression spring  60  presses closure member  61  of suction valve  42  against its seat in order to prestress suction valve  42  into the closed condition and further presses end portion  55  of valve tappet  53  against its seat in order to prestress delivery valve  41  into its closed condition. The pump piston  6  moving to the right according to the view of FIG. 4 during a delivery stroke, the pressurized brake fluid opens delivery valve  41 . In doing so, the hydraulic pressure of the brake fluid acts against the prestressing force of the compression spring  60 . The pump piston  6  moving to the left according to the view of FIG. 4 during a suction stroke phase, the relative vacuum forming within chamber  64  ensures the opening of the suction valve  42  against the prestressing force of compression spring  60 . 
     Please note that the respectively third and fourth examples of embodiments of the present invention represented in FIGS. 3 and 4 are advantageous in that only one spring element is required for both the delivery valve  41  and the suction valve  42 . As compared with the examples of embodiments as per FIGS. 1 and 2, this saves one spring so that the (valve) cartridge  8  in accordance with the third and fourth examples of embodiments includes only  5  elements, namely valve seat member  46 , closure member  48  or  61 , respectively, retaining element  47  or retaining plate  58 , respectively, tension spring  44  or compression spring  60 , respectively, and valve tappet  43  or  53 , respectively. 
     FIG. 5 represents a view of a longitudinal section of a fifth example of an embodiment of the present invention. The design of valve cartridge  8  in accordance with FIG. 5 in general is similar to the design of valve cartridge  8  as per the second example of an embodiment described in the context of FIG.  2 . This is particularly true in so far as cartridge  8  includes an axial delivery valve  11  on one end portion and a suction valve  12  provided radially thereto. What is different from the example of an embodiment of FIG. 2 is that cartridge  8  includes a valve seat member  70  provided with a gudgeon  71  preferably made of steel and formed inwards or rather towards eccentric  4 . A peripheral groove  72  is provided on gudgeon  71  and serves to receive a gasket  73 . Designed on the front side of gudgeon  71 , in FIG. 5, is a stepped bore  74  serving to receive a compression spring or rather a piston return spring  75  and forming a chamber  76 . The pump piston driven by the eccentric  4  is designed as cup-shaped piston  77 . The cup-shaped piston  77  includes a bore  78  the inside diameter of which approximately corresponds to the outside diameter of gudgeon  71 . Designed on a bottom section of bore  78  is an axial projection  79  the outside diameter of which essentially corresponds to the inside diameter of compression spring  75 . The outside diameter of projection  79  slightly tapers outwards so as to facilitate the assembly of compression spring  75 . The cup-shaped piston  77  is preferably made of steel and, e.g., may be an extruded part. This allows the play between the cup-shaped piston  77  and gudgeon  71  to be kept very small because of almost the same coefficients of expansion. Besides, there is no further need for the housing  2  to be anodized or hardened. This prevents any pollution caused by clinching in or rather by caulking the valves and caps. It is noticed from FIG. 5 that compression spring  75  is arranged within the cup-shaped piston  77  and, more precisely, within a chamber  76  formed by the cup-shaped piston  77  and gudgeon  71 . 
     Regarding the sixth example of an embodiment of the present invention represented in FIG. 6, what is different from the example of an embodiment of the present invention represented in FIG. 5 is that compression spring  75  serving to reset the cup-shaped piston  77  is supported on a step formed on the outside of the cup-shaped piston  77 . On its opposite side, compression spring  75  is supported and guided on a step of valve seat member  70 , this step being formed by the bottom of gudgeon  71 . Also serving as chamber or rather as compression chamber  76  in this example of an embodiment according to FIG. 6 is, inter alia, an axial bore  80  within gudgeon  71 . 
     Please note that, as contrasted with the examples of embodiments represented in FIGS. 1 through 4, the examples of embodiments of the present invention represented in FIGS. 5 and 6 are provided with compression spring  75  for resetting the cup-shaped piston  77  instead of with coupling ring  5 . 
     A seventh example of an embodiment of the present invention is schematically represented in FIG.  7 . The cartridge  8  represented in FIG. 7 includes a delivery valve  81  and a suction valve  82 . The suction valve  82  designed in the center of the valve seat member includes a valve body which has the design of a ball  83  and which, in the closed condition of suction valve  82 , abuts on a valve seat formed on a bore  84 . The valve body may be a plate or the like instead of ball  83 . Please note that the design of the cartridge  8  represented in FIG. 7 essentially is characterized by rotation symmetry which simplifies manufacture. Bore  84  is formed on a front side of cartridge  8  and is axially centered. Bore  84  connects the pressure or compression chamber  85  with a channel  86  leading to a (non-illustrated) low-pressure accumulator. Ball  84  is held by a retaining cage  87 . A compression spring  89 , provided between pump piston  6  and a retaining ring  88  and essentially arranged within compression chamber  85 , takes care of the required resetting of the pump piston  6  during operation. Simultaneously, compression spring  89  serves to keep the retaining cage  87 , via retaining ring  88 , on the bottom of recess  90  provided within cartridge  8  and forming compression chamber  85 . Preferably, the retaining ring  88 , however, is also pressed into the cartridge or rather into component  8 . While in the example of an embodiment as per FIG. 7 the suction valve is arranged axially on the end of cartridge  8  which is opposite of pump piston  6  the delivery valve  81  has an annular plate  92  as closure member. This annular plate  92 , e.g., may be a slotted ring of plastic. Plate  92  is prestressed against cartridge  8  by means of a wire circlip  93  so that, in the closed condition, delivery valve  81  ensures a pressure medium tightness between compression chamber  85  and the channel  94  leading to a pressure medium consumer. It is noticed from the representation of FIG. 7 that the valve seat member of cartridge  8  is provided with three clinch-type connections or rather caulkings marked by reference mark C for pressure-tight assembly within a pump housing. Please note that the example of an embodiment of the present invention, represented in FIG. 7, is particularly advantageous in that the inside of the valve seat member of cartridge  8  is designed in a particularly space-and-material-saving manner by providing the compression chamber  85  which, e.g., may axially be recessed. 
     Referring to FIGS. 8 and 9, an eighth example of an embodiment of the present invention is explained. The eighth example of an embodiment of the present invention, represented in FIGS. 8 and 9, in general resembles the seventh example of an embodiment of the present invention, represented in FIG. 7, yet differs from the same essentially in that delivery valve  81  features a modified design. Delivery valve  81  as per FIGS. 8 and 9 includes a valve body preferably designed as a ball  95  and provided within a radial bore  96  within a section of cartridge  8 , facing pump piston  6 . This valve body consists of a suitable material, preferably of steel or plastic. Radially outside bore  96 , within cartridge  8 , a peripheral groove  97  is formed which includes a particularly conical section  98  in the location of bore  96 . A retaining bow  99  acting as a leaf spring serves to prestress ball  95  against its valve seat formed by conical section  98 . The use of a leaf spring for delivery valve  81  is possible because of the fact that the opening pressure of delivery valve  81  does not require as accurate an adjustment as that of suction valve  82 . Therefore, no helical spring is needed for delivery valve  81 . Moreover, the opening pressure of the delivery valve is not as decisive as that of the suction valve wherefore the effective sealing seat diameter may be rated smaller. It is noticed from the representation of FIG. 9, in particular, that retaining bow  99 , essentially extending over almost the entire periphery of cartridge  8 , includes a hole  100  in the location of ball  95 . Hole  100  serves to fix ball  95  on the valve seat so that, after assembly having been performed, ball  95  cannot slip out of the cartridge unit. Retaining bow  99  is positively and/or frictionally and operatively fixed on cartridge  8  by, e.g., the caulking C as represented in FIG. 9 in order to prevent bow  99  from twisting. Please note that, in accordance with the representation of FIG. 8, the cross-section of bore  84  is larger than that of bore  96  which is due to the fact that, when sucking brake fluid, little throttling action and hence a larger effective suction cross-section is desirable for the suction valve  82 . As distinguished from the example of an embodiment described in the context of FIG. 7, the eighth example of an embodiment of the present invention, represented in FIG. 8, includes a compression spring  101  between the retaining cage  87  which is preferably made of sheet metal and which also may be referred to as bowl-type spring retainer and ball  83  of suction valve  82 . This enables exact adjustment, i.e., without any great tolerances, of the opening pressure of suction valve  82 . Along its inside periphery, retaining cage  87  likewise serves to guide compression spring  101 . Preferably together with compression spring  101 , frictionally held within retaining cage  87 , retaining cage  87  is pressed into the valve housing so as to abut thereon. Fixation of retaining cage  87  may alternatively also happen by means of one or a plurality of undercuts, provided within the valve housing or rather within cartridge  8 , and by means of catches shaped on retaining cage  87  and (not illustrated) engaging the undercuts. The suction valve  82  assembled, retaining cage  87 , along its outside periphery, likewise serves to guide piston return spring  104 . Piston return spring  104  is provided with a stronger resiliency than compression spring  101  in order to ensure that compression spring  101  cannot push retaining cage  87  out. Please note that in the eighth example of an embodiment of the present invention the various pressure chambers are connected by means of clinching or by means of a “fir-cone-type” connection. Therefore, no separate sealing elements are required. 
       
     FIGS. 10 and 11 schematically represent a ninth example of an embodiment of the present invention. As distinguished from the eighth example of an embodiment of the present invention explained in the context of FIGS. 8 and 9, the retaining bow  99  of the ninth example of the invention does no longer have any hole. This is an advantage because this renders any tilted position of the ball  95  impossible. By using the retaining bow  99  of the ninth example of an embodiment ball  95  is pressed always perpendicularly onto the valve seat formed on bore  96 . A bowl-type spring retainer  102  preferably featuring a design characterized by rotation symmetry is arranged in compression chamber  85  and includes an annular, bent-off end portion  103  serving to support one side of the piston return spring  104 . The other side of piston return spring  104  abuts on pump piston  6 . Bowl-type spring retainer  102  includes a central axial bore  105  in order to ensure a flow communication of the pressure medium between compression chamber  85  and suction valve  82 . Preferably, a further means for flow communication of the pressure medium is provided on the periphery of the bowl-type spring retainer  102  in that, on the periphery, webs are provided in a manner not shown wherebetween pressure medium can flow. Further, bowl-type spring retainer  102  includes an annular recess  106  on its side facing suction valve  82 , this recess  106  serving to support one side of compression spring  101  of the suction valve  82 . A portion  107  which projects towards the side of suction valve  82  and wherein bore  105  is formed and the outside of which corresponds to the inside of recess  106  also serves as a stop for the suction valve body, i.e. for the ball  83 . Please note that the bowl-type spring retainer  102  represented in FIG. 10 is made of plastic which renders a considerably simplified manufacture as compared with the sheet-metal retaining cage  87  of the example of an embodiment represented in FIG.  8 . Because of portion  107  of bowl-type spring retainer  102  it is impossible for ball  83  to become jammed in the otherwise conically shaped bowl-type spring retainer  102 . 
     A tenth example of an embodiment of the present invention is represented in FIGS. 12 and 13. The tenth example of an embodiment of the present invention represented in FIGS. 12 and 13 in particular differs from the eighth and ninth examples of embodiments with regard to the design of delivery valve  81 . A sheet-metal strip bent to form a clamp  110  is provided as spring means for pressing ball  95  against the valve seat of delivery valve  81 . About mid-way, an inventive tongue  111  is worked out of clamp  110 . Ball  95  is pressed against its valve seat by means of tongue  111  with a defined force. So as to prevent the clamp  110  from twisting, clamp  110  of this embodiment includes two depressed peripheral portions or tabs  112 ,  113  engaging groove  97 . Thus clamp  110  is fixed on the valve seat member. Further, clamp  110  includes bent ends  114 ,  115  on both of its cross sides. These ends facilitate mounting clamp  110  onto the valve seat member. 
     Referring to FIGS. 14 through 16, an eleventh example of an embodiment of the present invention is described in the following, with FIG. 16 representing a section through FIG. 14 along line XVI—XVI. As distinguished from the tenth example of an embodiment of the present invention represented in FIGS. 12 and 13, clamp  120  has been widened considerably, it thus extends on the outside of cartridge  8  beyond the groove  97  towards the eccentric  4 . Because of the widening of clamp  120  the same is held on cartridge  8  only by its resiliency. Thus no further measures such as welding or caulking are required to fasten clamp  120  on cartridge  8 . According to this invention, ball  95  is pressed against its valve seat by a tongue  121  formed within the clamp  120 . Please note that tongue  121  extends almost over half of the length of clamp  120 . A tab  123  formed within a recess  122  on the front side of clamp  120  serves to fix clamp  120  on cartridge  8 . Please note that, as contrasted with the tenth example of an embodiment, clamp  120  which is embodied in the eleventh example of an embodiment represented in FIGS. 14 through 16 is fixed on cartridge  8  essentially perpendicularly to the resilient action of retaining clamp  120 . Thereby twisting of clamp  120  on cartridge  8  is excluded to a great extent. Further, according to this invention, the prestressing force of tongue  121  towards ball  95  can be determined ore accurately. A bore  124  formed within cartridge  8  is provided for tab  123  so that the latter can be slipped thereinto and in order to avoid any displacement or twisting, respectively, of clamp  120 . It can be noticed particularly from the representation of FIGS. 15 and 16 that clamp  120  extends over half of the periphery of cartridge  8  and, preferably, approximately over two thirds of the periphery of cartridge  8 . Finally, please note that the suction valve body  125  of the eleventh example of an embodiment of this invention is shaped like a hammer and that, on its front side which serves as closure member, it is essentially conical or spherical, with the valve seat then likewise having a conical or spherical shape. On its opposite front side, the hammer-shaped valve body  125  preferably includes an annular groove  126  for receiving and guiding compression spring  101  serving as suction valve spring.