Abstract:
A piston pump for delivering fluids includes a cylinder, a piston that is movably mounted in the cylinder, and a pressure chamber that is arranged between an inlet valve and an outlet valve and that is closed off by a cover. The piston pump further includes a throttle element that is disposed in the fluid flow downstream of the outlet valve and that is configured to throttle the fluid flow. The throttle element is in the form of a resiliently elastic disk that is inserted into the cover. The cover further includes a mechanism configured to pre-center the throttle element.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/060043, filed on May 29, 2012, which claims the benefit of priority to Serial No. DE 10 2011 079 876.5, filed on Jul. 27, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure starts from a piston pump for delivering fluids. In addition, the present disclosure relates to an assembly process for such a piston pump. 
     Piston pumps are known from the prior art in various embodiments. For example, radial piston pumps having a plurality of pump elements for delivering pressure media, wherein at least one piston is movable reciprocatingly by means of an eccentric, are frequently used in vehicle brake systems. These so-called pump elements typically consist of a piston, a piston running surface often in the form of a cylinder, inlet and outlet valves and sealing elements. The valves serve to control the fluid during the pumping movement of the piston. In this case the inlet valve serves to prevent the fluid from flowing back into the suction chamber during the compression phase. The outlet valve prevents the fluid from flowing back from the pressure side into the pump interior and is typically housed in the cover of the pump. In order to optimize noise and pulsation, at least one throttle arrangement for throttling the fluid flow is provided downstream of the outlet valve. 
     The patent application DE 10 2008 002 740 A1 describes, for example, a piston pump for regulating brake pressure in a hydraulic vehicle brake system. The piston pump described comprises a pump housing, a receiving bore for the piston pump arranged in the pump housing and a valve cover closing the receiving pump to the outside, in which cover an outlet valve and first and second channel sections of a discharge channel are accommodated. The discharge geometry influences the noise behavior of the piston pump and is therefore usually implemented with a suitable narrowing of the discharge channel, which then provides a throttling effect. 
     The patent application DE 10 2006 027 555 A1 describes, for example, a piston pump with reduced noise generation. The piston pump for delivering fluids which is described comprises a piston, a cylinder element, and a pressure chamber which is arranged between an inlet valve and an outlet valve and is closed by a cover; the outlet valve comprises a closing body in the form of a ball, a pretensioning device in the form of a helical spring acting on the closing body; the pump further comprises a base element for supporting the pretensioning device and a disk element, a sealing seat of the outlet valve being arranged in the disk element. The use of the disk element is intended to ensure that component tolerances of various components of the piston pump do not negatively affect the outlet valve. 
     SUMMARY 
     The sensor unit according to the disclosure for a vehicle has, in contrast, the advantage that it makes possible a cost-neutral pre-centering of a throttle element configured as a resilient disk in a cover without impeding the oscillating movement of the throttle element in operation. 
     The core of the disclosure is a cost-neutral centering of the throttle element configured as a resilient disk. The throttle element is inserted in the cover of the piston pump during assembly. The pump cylinder is then pressed onto the cover. Although centering of the throttle element is provided in the pump cylinder, deformation of an insufficiently pre-centered throttle element can occur as a result of rapid assembly. It is therefore appropriate to pre-center the throttle element in the cover prior to assembly of the pump cylinder. However, this pre-centering must not restrict the movement of the throttle element since a blocked throttle element impedes the operation of the piston pump and can lead to system failure through overloading of a drive. 
     Embodiments of the present disclosure make available a piston pump for delivering fluids comprising a cylinder, a piston mounted movably in the cylinder and a pressure chamber which is arranged between an inlet valve and an outlet valve and is closed by a cover, a throttle element for throttling the fluid flow being provided in the fluid flow downstream of the outlet valve. According to the disclosure the throttle element is configured as a resilient disk which is inserted in the cover, means for pre-centering the throttle element being present in the cover. 
     In a process according to the disclosure for assembling a piston pump comprising a cylinder, a piston mounted movably in the cylinder and a pressure chamber which is arranged between an inlet valve and an outlet valve and is closed by a cover, a throttle element for throttling the fluid flow being provided in the fluid flow downstream of the outlet valve, the throttle element is configured as a resilient disk and is inserted in the cover. In this case centering means arranged in the cover effect a pre-centering of the throttle element in the cover, and the cylinder element is pressed into the cover after the throttle element has been inserted and pre-centered. 
     Advantageous improvements of the piston pump specified in the disclosure are made possible by the measures and developments enumerated in the dependent claims. 
     It is especially advantageous that at least two pressing lugs against which the cylinder is pressed together with the cover are formed on the cover, at least one recess formed between two pressing lugs acting as a discharge channel for the fluid flow. The centering means include, for example, at least one chamfer which is arranged on such a pressing lug rearwardly in the pressing-in direction. In this region obstructions resulting from the pressing-in of the cylinder advantageously cannot occur. In addition, the chamfers can be implemented in a cost-neutral manner in the cover which is produced, for example, as a cold-formed part. 
     In an advantageous configuration of the piston pump according to the disclosure, the individual chamfers are each arranged at an acute angle which preferably is greater than 60°. Because of the acute angle it can advantageously be ensured that the throttle element does not jam against the chamfer or the centering means in operation. 
     In a further advantageous configuration of the piston pump according to the disclosure, an annular channel, which is covered by the throttle element and is filled with fluid when the outlet valve is open, is formed in the cover, which fluid flows out via the throttle element into at least one discharge channel. 
     In a further advantageous configuration of the piston pump according to the disclosure, the throttle element, in the form of a resilient disk, is arranged between the cylinder and the cover and variably adjusts the flow cross section in the at least one discharge channel in dependence on the pressure difference between its upper side and underside. By means of this variable throttle cross section a reduction of pulsation in a fluid system and a robust design can be achieved with simple and low-cost components which can be assembled in a reliable process. The throttle element in the form of a resilient disk may be arranged between the cover and the cylinder with a defined pretension, so that an opening differential pressure is predefined. The pressure difference lifts the throttle element, configured as a resilient disk, from the side with the higher pressure, so that the throttle element configured as a resilient disk performs a deformation movement along the axis of symmetry and enlarges the flow cross section. 
     In a further advantageous configuration of the piston pump according to the disclosure, the deformation movement of the throttle element configured as a resilient disk may be limited by a corresponding shaping of an end face of the cylinder. The service life of the throttle element can thereby advantageously be increased. In the region of the stop, fluidic damping of the end position can further optimize opening and noise behavior. 
     It is especially advantageous that the throttle element configured as a resilient disk has a first opening through which fluid can flow, in which case, in a raised position of the throttle element configured as a resilient disk, fluid flows through the first opening of the throttle element configured as a resilient disk and/or flows around the throttle element configured as a resilient disk. 
     In a further configuration of the piston pump according to the disclosure, a second opening which has a defined constant flow cross section and is opened independently of the differential pressure is present. The second opening may be implemented, for example, as a bore formed in the throttle element configured as a resilient disk, and/or as a depression formed in support surfaces, and/or as an annular gap. The second opening in the throttle element configured as a resilient disk acts as an additional static throttle and makes possible a simple and cost-effective implementation of a dynamic throttle with a static component. The advantage of such a design is that the positive functions of a dynamic throttle can be combined and integrated with a static throttle in a very cost-effective and easily assembled manner. The design involves an additional component which may be implemented, for example, as a stamping or an etched component. If a particular pressure difference is attained, the throttle element configured as a resilient disk bends and the dynamic throttle opens, so that a large additional quantity of fluid can flow out. Below the predefined pressure difference, a smaller quantity of fluid flows out via the static throttle, that is, through the second opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the disclosure is represented in the drawings and is explained more detail in the following description. In the drawings the same reference symbols denote components or elements which perform the same or analogous functions. 
         FIG. 1  shows a perspective sectional representation of a rear portion of an exemplary embodiment of a piston pump for conveying fluids according to the disclosure. 
         FIG. 2  shows a representation of a detail of the piston pump according to the disclosure from  FIG. 1  in a first state. 
         FIG. 3  shows a representation of a detail of the piston pump according to the disclosure from  FIG. 1  in a second state. 
         FIG. 4  shows a perspective representation of a throttle element for the piston pump from  FIG. 1 . 
         FIG. 5  shows a perspective representation of a cylinder for the piston pump from  FIG. 1 . 
         FIG. 6  shows a perspective representation of a cover for the piston pump from  FIG. 1 . 
         FIG. 7  shows a perspective representation of a detail of the cover for a piston pump from  FIG. 6 . 
         FIG. 8  shows a perspective representation of the cover from  FIG. 6 or 7  with the throttle element from  FIG. 4  inserted therein. 
         FIG. 9  shows a detailed perspective representation of a portion of the cover for a piston pump from  FIGS. 6 to 8  with a cylinder pressed therein. 
     
    
    
     DETAILED DESCRIPTION 
     In the integration of a dynamic throttle in a piston pump used, for example, in an antilock system (ABS) and/or for an electronic stability program in the vehicle, the centering of the throttle element may be effected, for example, by means of a small chamfer on the cylinder. Rough centering using the external diameter of the throttle element on the cover is possible to only a limited extent, since deformation of the throttle element can occur as a result of the high pressing-in speeds of the cylinder into the cover, if the throttle element is not correctly centered. Furthermore, it must be prevented that the throttle element abuts on one side, causing possible jamming of the throttle element. A jammed throttle element will prevent the buckling function of the dynamic throttle element and the high through-flow rate. This can lead, inter alia, to a complete system failure since the drive is overloaded. 
     As can be seen from  FIGS. 1 to 9 , the illustrated exemplary embodiment of a piston pump  1  for delivering fluids according to the disclosure in a vehicle brake system comprises a piston (not shown), a cylinder  20  and a pressure chamber  24  arranged between an inlet valve (not shown) and an outlet valve  5 , which pressure chamber  24  is closed by a cover  10 , a throttle element  30  for throttling the fluid flow  3  being provided in a fluid flow  3  downstream of the outlet valve  5 . 
     As is further apparent from  FIG. 1 , the outlet valve  5  comprises a closing body  5 . 1  in the form of a ball, an outlet valve seat  5 . 2  and a return spring  5 . 3 , and establishes the fluid flow  3  between an outlet orifice of the pressure chamber  24  and at least one discharge channel  7  of the piston pump  1 . The throttle element  30  is configured as a resilient disk and is clamped between the cover  10  and the cylinder. In the exemplary embodiment illustrated the throttle element  30  configured as a resilient disk has a first opening  34  which is adapted to the dimension of the closing body  5 . 1 . 
     As is further apparent from  FIGS. 1 to 5 , the throttle element  30  configured as a resilient disk is clamped between a first support surface on the cylinder  20  and a second and third support surface arranged in the cover  10 . In order to set the pretension of the throttle element  30  configured as a resilient disk, an offset dv 1  is present between the second support surface arranged in the cover  10 , against which the outer edge of the throttle element  30  configured as a resilient disk bears, and the third support surface arranged in the cover  10 , against which the inner edge of the throttle element  30  configured as a resilient disk abuts in the region of the first opening  34 , which offset dv 1  leads to a pretension in the throttle element  30  configured as a resilient disk which must be exerted by a prevailing fluid pressure in order to lift the outer edge of the throttle element  30  configured as a resilient disk from the third support surface. As this happens the inner edge of the throttle element  30  configured as a resilient disk abuts both the first support surface arranged on the cylinder element  20  and the second support surface arranged in the cover  10 , independently of the prevailing pressure. 
     As is further apparent from  FIGS. 1 to 5 , a deformation movement ds 1  of the throttle element  30  configured as a resilient disk is limited by a corresponding shaping of an end face  22  of the cylinder  20 . In the exemplary embodiment represented, the end face  22  has a crowned configuration, the dimensions of the crown defining the maximum possible deformation movement of the throttle element  30  configured as a resilient disk.  FIG. 2  shows the piston pump  1  under a differential pressure which is lower than a predefined pressure limit value, so that the throttle element configured as a resilient disk rests against all the support surfaces and only the static throttle is effective, so that an outflowing fluid flow  3 . 1  is determined by a second opening  36  formed as a bore in the throttle element  30  configured as a spring elastic disk.  FIG. 3  shows the piston pump  1  under a differential pressure which is higher than the predefined pressure limit value, so that the outer edge of the throttle element  30  configured as a resilient disk is lifted from the third support surface and only the inner edge of the throttle element configured as a resilient disk abuts the first and second support surfaces. In this state the dynamic throttle is effective, so that a further fluid flow  3 . 2  passes around the throttle element configured as a resilient disk, which fluid flow  3 . 2  forms with the fluid flow  3 . 1  passing through the second opening  36  an outflowing total fluid flow  3 . An annular channel  12  which is covered by the throttle element  30  is formed in the cover  10 . With the outlet valve  5  open, that is, with the closing body  5 . 1  lifted from the outlet valve seat  5 . 2 , the fluid enters the annular channel  58  via a connecting channel  14  and flows out via the throttle element  30  into at least one discharge channel  7 . 
     As is further apparent from  FIGS. 6 to 9 , according to the disclosure centering means  18  which effect a pre-centering of the throttle element  30  in the cover  10  are present in the cover  10 . In the exemplary embodiment illustrated, six pressing lugs  16 , against which the cylinder  20  can be pressed together with the cover  10 , are formed in the cover  10 . Recesses  17 , which act as discharge channels  7  for the fluid flow  3  with the cylinder  20  pressed in, are formed between each two pressing lugs  16 . In the exemplary embodiment represented, the cover  10  of the piston pump  1  has six recesses  18  and the piston pump  1  therefore has six discharge channels  7 . 
     As is further apparent from  FIGS. 6 to 9 , the centering means  18  include at least one chamfer which is arranged on each pressing lug  16  rearwardly in the pressing-in direction. In the exemplary embodiment represented the centering means  18  include six chamfers. As can be seen from  FIG. 9 , the individual chamfers  18  are each at an acute angle α, which is preferably greater than 60°, in order to prevent jamming of the throttle element  30  configured as a resilient disk. 
     According to the process according to the disclosure for assembling a piston pump, the throttle element  30  is configured as a resilient disk and is inserted in the cover  10 . As a result of the centering means  18  arranged in the cover  10 , the throttle element  30  is pre-centered in the cover  10 , and after the throttle element  30  has been inserted and pre-centered the cylinder element  20  can be pressed into the cover  10  without deforming or damaging the throttle element  30  configured as a resilient disk. Two centering means  28 , which are configured as circumferential collars adapted to the first opening  34  in the throttle element  30 , are provided at the outlet orifice  26  of the cylinder  20  and effect final centering of the throttle element  30 . 
     Embodiments of the present disclosure advantageously make possible cost-neutral pre-centering of the throttle element in the cover of the piston pump.