Patent Publication Number: US-2013243629-A1

Title: Pump having a pump cylinder

Description:
PRIOR ART 
     The invention relates to a pump, in particular a piston pump for a vehicle brake system, having a pump piston, which is guided displaceably in a pump cylinder. The invention further relates to a vehicle brake system having a pump of this type and also to a method for producing such a pump. 
     A pump of this type is known for example from DE 199 28 913 A1. It comprises a pump housing, in which, as an individual pump element or pump unit, a pump piston is mounted displaceably in a pump cylinder. Here, the pump piston draws a brake fluid through an inlet opening into the pump cylinder and conveys it out from the pump cylinder through an outlet opening. 
     The object of the present invention is to create a pump that can be produced and assembled in a cost-effective manner. 
     DISCLOSURE OF THE INVENTION 
     A pump, in particular for a vehicle brake system, which is formed with a pump piston, which is guided displaceably in a pump cylinder, is created in accordance with the invention. Here, the pump cylinder is produced specifically by means of deep drawing. 
     Deep drawing is a production method that is very cost-effective in principle because a high degree of deformation with simultaneously high dimensional accuracy can be provided with this method by means of an individual deep drawing or pressing process carried out on a workpiece. However, deep drawing generally means that only very thin-walled workpieces can be processed and produced. These workpieces then have comparatively low resistance or rigidity accordingly with respect to compressive load and in particular with respect to buckling, which actually makes them seemingly unsuitable for the use as pump cylinders. 
     The invention is based on the finding that a deep-drawn pump cylinder can still be used for a pump. The actual problem of low resistance or rigidity can be counterbalanced and completely compensated for, specifically by a further embodiment of the surrounding environment of the pump cylinder deep-drawn in this way. 
     In order to achieve the necessary rigidity, it is advantageous in particular if the pump cylinder is received in a pump housing in such a way that it is supported in a planar manner against the pump housing via its outer lateral surface. The support is particularly advantageously created by a fit with just a low fitting tolerance between the outer face of the pump cylinder and the inner face of the respective receiving opening in the pump housing. The fitting tolerance should be selected in such a way that the pump cylinder can still be inserted into the pump housing with reasonable pressing force, but in so doing still comes to bear against the pump housing substantially over its entire surface. 
     The pump cylinder is particularly preferably beaker-shaped with an annular wall and a base area. 
     Components of the respective pump unit, such as the pump piston with its respective inlet valve, can advantageously be preassembled in the pump cylinder of this type. The preassembly can be carried out cost-effectively in a workpiece support, in which the pump piston is first inserted, followed by the pump piston. Here, the direction of assembly remains the same, which is advantageous for workpiece-support-based assembly. 
     Furthermore, a valve opening with a valve body closing it selectively is preferably formed on the base area. 
     The valve opening arranged in this way can be produced particularly favorably in combination with the deep drawing process because the material region of the base area surrounding said valve opening does not have to be deformed during the deep drawing process itself or only has to be slightly deformed. The base area itself is generally only slightly deformed during the deep drawing process, whereas the material of the annular wall experiences a considerable deformation during the deep drawing process. With the only slightly deformed material region, it is ensured that the valve opening retains its dimensions, even throughout the service life of the respective valve. 
     With a preferred development of the pump according to the invention, at least one inlet opening to the pump piston is also formed on the annular wall. 
     The inlet opening of this type can be produced in the thin-walled material of the pump piston by a cost-effective punching process. 
     A multiplicity of inlet openings, by means of which a filter screen is formed, is particularly preferably formed on the annular wall. 
     A filter screen can be produced very cost-effectively by means of such a formation of many inlet openings on the pump cylinder since the multiplicity of openings can generally be produced by just one punching process. 
     Furthermore, there is then no longer any need for an additional component for the filter, and therefore the procurement costs and assembly costs can also be further reduced. 
     As already mentioned, the at least one opening of this type is particularly preferably produced by means of punching, since this manufacturing method can be carried out very cost-effectively. The punching process is carried out in particular before the pump cylinder has been produced by deep drawing. The punching process can then be carried out on the raw material of the pump cylinder, which is provided as a single sheet metal in substantially planar form. Alternatively or additionally, the opening can be produced by means of laser cutting or etching. The multiplicity of inlet openings themselves can thus be formed very cost-effectively and, at the same time, in a dimensionally accurate manner. The deformation, occurring during the deep drawing process, of the material region in which the inlet openings are located can be taken into account beforehand by a corresponding adaptation of the shape and dimensions of the openings to be punched. 
     An annular disk is preferably also formed at the end of the annular wall arranged opposite the base area. 
     The annular disk can be produced in a largely cost-neutral manner by means of the deep drawing process itself. It is advantageously used to support a ring seal, which is arranged next to said annular disc and is used to seal the axially moving pump piston with respect to its surrounding environment. The ring seal constitutes a low-pressure seal, which prevents fluid from escaping from the intake region of the pump piston. 
     Furthermore, an annular step, in which in particular a ring seal sealing between the pump piston and the pump cylinder is arranged, is preferably formed at the end of the annular wall arranged opposite the base area. 
     The annular step forms an assembly space for a ring seal, which is advantageously mounted at this point at the same time during the assembly steps and is also protected in this position against damage. The ring seal in particular produces a seal between the pump piston and the pump cylinder. With the solution of this type, a further seal between the pump piston and the pump housing surrounding it outside the pump cylinder can also be omitted since the pump cylinder is sealed with respect to the pump housing. This seal can advantageously be created by means of the pressing of the pump cylinder into the pump housing or by means of a caulking of the pump housing at the open end face of the pump cylinder. 
     The invention further comprises a vehicle brake system having a pump of this type. 
     Lastly, the invention also comprises a method for producing a pump having the following steps: forming at least one opening in a sheet metal, deep drawing the sheet metal to form a pump cylinder, in such a way that a valve opening and/or an inlet opening and/or an outlet opening of the pump cylinder is/are formed by the opening, and assembling a pump piston in the pump cylinder of this type. As explained above, these manufacturing steps are then preferably followed by the assembly of the pump cylinder in a pump housing. 
    
    
     
       An exemplary embodiment of the solution according to the invention will be explained in greater detail hereinafter on the basis of the accompanying schematic drawings, in which: 
         FIG. 1  shows a longitudinal sectional view of a pump according to the prior art, 
         FIG. 2  shows a longitudinal sectional view of a first exemplary embodiment of a pump with a pump cylinder according to the invention, 
         FIG. 3  shows a longitudinal view of the pump according to  FIG. 2 , 
         FIG. 4  shows a perspective view of the pump cylinder according to  FIGS. 2 and 3 , and 
         FIG. 5  shows a longitudinal sectional view of a second exemplary embodiment of a pump with a pump cylinder according to the invention. 
     
    
    
     In  FIG. 1  a pump  10  in the form of a piston pump for a hydraulic vehicle brake system (not illustrated further) is illustrated and is used for generation of a fluid pressure of brake fluid within the vehicle brake system. To this end, the pump  10  has a beaker-shaped pump cylinder  12 , which is produced as a rotary part and in which a pump piston  16  is mounted displaceably against a helical spring  14 . The pump piston  16  conveys the brake fluid through an annular valve opening  17 , formed in the base region of the pump cylinder  12 , of an outlet valve  18  into a subsequent outflow  20 . The outlet valve  18  has a spring-biased closure member  22 . In order to draw brake fluid into the pump cylinder  12 , a ring filter  24  is arranged as a separate component at the periphery of said pump cylinder and is followed in the direction of flow by an inlet valve  26  arranged on the pump piston  16 . The pump piston  16  is sealed on its low-pressure side by means of a ring seal  28  with respect to a pump housing  30 . 
     Pumps  10  according to the invention are illustrated in  FIGS. 2 to 5 , with which a respective pump cylinder  32  is produced specifically by means of deep drawing. The deep drawing process has been carried out starting from a sheet metal as a blank, wherein a beaker-shaped basic form with an annular wall  34  and a base area  36  has been produced in particular. Here, the annular wall is indeed relatively thin and thus susceptible to buckling caused by a high compressive load, but the pump housing  30  surrounding the pump cylinder  32  is formed in such a way that the annular wall  34  can be supported radially outwardly against the pump housing (see  FIGS. 2 and 5 ), such that the pump cylinder  32  can likewise withstand high internal pressures. 
     A valve opening  38  for the outlet valve  18  and, in the region of the annular wall  34 , many relatively small inlet openings  40  have been punched out beforehand from the thin-walled material of the blank in the region of the base area  36 . 
     With the many inlet openings  40  of this type, a filter screen has been produced very cost-effectively at the pump cylinder  32 , which is then deep-drawn and finished, and can filter oncoming brake fluid for the inlet thereof. 
     During the deep drawing process, an annular disk  42  has also been formed at the end of the annular wall  34  arranged opposite the base area  36 . The annular disk  42  supports the ring seal  28  arranged next to it in the axial direction. 
     With the exemplary embodiment according to  FIG. 5 , an annular step  44  is formed at this end of the annular wall  34 , the ring seal  28  also being covered in the radial direction by said annular step and thus protected.