Abstract:
The invention relates to a piston pump with a piston, which is guided so that the piston can move axially in a liner that has been inserted into a pump housing and is driven into a reciprocating stroke motion by means of a cam that is driven to rotate. The invention uses a liner that is manufactured as an injection-molded plastic part. The plastic liner has advantages with regard to manufacture, damping behavior when there are pressure changes, and noise generation. Furthermore, the invention proposes affixing a filter integral with the liner when the liner is injection molded.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a piston pump, for use in a hydraulic vehicle brake system. 
     Piston pumps of this kind are known in and of themselves. They have a for example cylindrical piston, which is guided so that it can move axially in a liner. The liner can be of one piece with a liner bottom on its one end face. The liner in known piston pumps is comprised of steel and is produced by machining or also by shaping, for example by cold pressing. The liner is inserted into a pump housing. A cam drive, for example, can be provided for driving the piston into a reciprocating stroke motion. It is also possible to guide the piston so that it can move axially in a pump housing without a liner. In this instance, the pump housing is comprised of steel. When a liner is used, the pump housing is frequently made of die-cast aluminum. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The pump piston according to the invention, has a plastic liner or, if the piston is guided directly in the pump housing, has a plastic pump housing made. If there is a liner, then the pump housing can likewise be made of plastic or for example can also be made of die-cast aluminum or also of steel. A liner made of plastic or a pump housing made of plastic, i.e. making the part of the piston pump that axially guides the piston out of plastic, yields a considerable cost advantage over the manufacture of this part put of steel. Another advantage is the elimination of work cycles that are required when the part that guides the piston is made of steel, for example machining and/or shaping surface work of a running surface that guides the piston and belongs to the part guiding the piston, or the production of undercuts, recesses, or openings. Moreover, favorable sliding properties of the plastic with low friction and low wear are produced, as well as an elastic behavior of the liner that is improved in relation to steel. The improved elastic behavior has the advantage that for example an inlet or outlet valve of the piston pump, which valve is embodied as a check valve, whose valve seat is disposed on a liner bottom, seals better and closes faster. Furthermore, a striking of a valve closing body against the valve seat is damped when a valve of this kind closes, which reduces noise generation and wear. In addition, the plastic liner or plastic pump housing, by virtue of its elastic behavior, damps pressure vibrations, pressure pulsations, and pressure peaks that are caused by the discontinuous manner in which the piston pump feeds. Another advantage of the manufacture of the part guiding the piston out of plastic is the possibility of producing virtually any geometry desired. As a result, points of the part guiding the piston that are acted on by the flowing fluid during the fluid delivery by means of the piston pump, i.e. for example an inflow region and an outflow region, can be embodied using flow technology with a view to low noise generation and low flow resistance. 
     According to the invention, the liner is of one piece with a filter. This has the advantage that no separate filter is required, which saves on both manufacturing costs and assembly expenditures. Another advantage is that with an equal length of the liner, a filter surface can be embodied as larger as a result of the one-piece embodiment than with a liner that has a filter placed onto it. 
     In one embodiment of the invention the liner has a valve seat part so that the valve seat can be simply embodied in a wear resistant manner. The valve seat part can be made of one piece with the liner, for example by means of injection molding it with the plastic that constitutes the liner. 
     In another embodiment of the invention the liner has a reduced diameter in an axially defined region which, together with a pump bore of the pump housing into which the liner is inserted, constitutes an annular conduit encompassing the liner. An inflow or outflow of the piston pump according to the invention takes place by means of this annular conduit. The annular conduit has the advantage that it assures an inflow or outflow of the piston pump independent of an angular position in which the liner is inserted into the pump housing; therefore, the angular alignment does not have to be observed when installing the liner into the pump housing. Embodying the annular conduit by means of a diameter narrowing of the liner has the advantage that a diameter widening of the pump bore in the pump housing does not have to be embodied, for example by means of turning, which would bring about a considerable manufacturing expense. 
     The piston pump according to the invention is provided in particular as a pump in a brake system of a vehicle and is used in the control of the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR, or EHB are used for brake systems of this kind. In the brake system, the pump is used, for example, to return brake fluid from a wheel brake cylinder or from a number of wheel brake cylinders into a master cylinder (ABS) and/or to feed brake fluid from a reservoir into a wheel brake cylinder or a number of wheel brake cylinders (ASR, FDR, or EHB). The pump is required, for example, in a brake system with a wheel slip regulation (ABS or ASR) and/or in a brake system used as a steering aid (FDR), and/or in an electrohydraulic brake system (EHB). With the wheel slip regulation (ABS or ASR), for example a locking of the wheels of the vehicle can be prevented during a braking operation when there is a powerful pressure on the brake pedal (ABS) and/or an excess rotation of the driven wheels of the vehicle can be prevented when there is a powerful pressure on the gas pedal (ASR). In a brake system used as a steering aid (FDR) a brake pressure is built up in one or more wheel brake cylinders independent of an actuation of the brake pedal or gas pedal in order, for example, to prevent the vehicle from swerving off the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump feeds the brake fluid into the wheel brake cylinder or cylinders when an electrical 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. 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an axial section through a piston pump according to the invention; and 
     FIG. 2 shows an axial section through a subassembly of the piston pump from FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The piston pump according to the invention, which is depicted in FIG. 1, is inserted into a hydraulic block  10 , of which only a fragment encompassing the piston pump is shown in the drawing for the sake of clarity. The hydraulic block  10  is part of an otherwise not shown hydraulic, slip-regulated vehicle brake system. Other hydraulic components of the vehicle brake system, such as solenoid valves, are inserted into the hydraulic block  10  and are hydraulically connected to one another and to the piston pump. The hydraulic block  10  is hydraulically connected to a master cylinder, not shown; wheel brake cylinders, not shown, are hydraulically connected to the hydraulic block  10 . The hydraulic block  10  constitutes a pump housing of the piston pump and is indicated as such below. 
     The pump housing  10  is comprised of metal, preferably of die-cast aluminum. A continuous stepped pump bore  12  is let into the pump housing  10  and a liner  14  is inserted into this bore. The liner  14  is a hollow, cylindrical plastic injection-molded part with a liner bottom  16  on its one end that is of one piece with it. The addition of TEFLON produces favorable sliding properties of the liner  14  and improves the sliding properties of the plastic which the liner  14  is made of. The plastic comprising the liner  14  has carbon fibers which increase the stability of the liner  14  and improve a wear behavior of the liner  14 . An essentially cylindrical piston  18  is guided so that it can move axially in the liner  14 . The piston  18  is pressed out of the liner  14 , away from the liner bottom  16 , by a piston restoring spring  20  that is inserted into the liner  14  and is supported on the liner bottom  16 . A cam  22  that can be driven to rotate by an electric motor is disposed on a side of the piston  18  remote from the liner bottom  16  and the piston restoring spring  20  presses the piston  18  against the circumference of this cam. The rotating drive of the cam  22  drives the piston  18  into a reciprocating stroke motion in the liner  14 . 
     An end of the piston  18  oriented toward the cam  22  is guided with a guide ring  24  so that it can move axially in the pump housing  10 ; a sealing ring  26  disposed axially adjacent to the guide ring  24  creates a seal between the piston  18  and the pump housing  10 . The guide ring  24  and the sealing ring  26  are inserted into the extension of the liner  14  into the pump bore  12 . 
     An end of the piston  18  that is disposed remote from the cam  22  in the liner  14  is guided with a guide ring  28  so that it can move axially in the liner  14 ; a sealing ring  30  produces a seal between the piston  18  and the liner  14 . The piston  18  narrows at an annular step  32  in the direction of the liner bottom  16 . The annular step  32  is used for the axial contact of the guide ring  28  and the sealing ring  30 , which are slid onto the narrowed end of the piston  18 . 
     The piston  18  with the sealing ring  30  slid onto it encloses a displacement chamber  34  in the liner  14  between its end oriented toward the liner bottom  16  and the liner bottom  16  itself. A reciprocating stroke motion of the piston  18  increases and decreases a volume of the displacement chamber  34  and as a result, feeds fluid in a manner that is intrinsically known from piston pumps. 
     For the entry into the piston pump of fluid to be fed, an inlet bore  36  is let into the pump housing  10  radial to the pump bore  12  and this inlet bore feeds into the pump bore  12 . The inlet bore  36  feeds into an annular conduit which encompasses the liner  14  and is enclosed between an outer circumference of the liner  14  and the pump housing  10  and is part of the pump inlet. The annular conduit  38  extends in the axial direction from the inlet bore  36  into the vicinity of the open end of the liner  14  oriented toward the cam  22 . The annular conduit  38  is formed by means of a diameter narrowing of the liner  14  in the direction from the liner bottom  16  toward the cam  22  and by means of a narrowing of the pump bore  12  in the vicinity of the open end of the liner  14 . In terms of the axial direction, the annular conduit  38  is disposed outside the displacement chamber  34  of the piston pump. In the region of the displacement chamber  34 , the liner  14  rests against the pump housing  10  with its entire surface so that in the region of the displacement chamber  34  in which high pressure can be produced during the operation of the piston pump, the liner  14  is supported over its entire surface by the pump housing  10 . 
     On its open end, the liner  14  is provided with filter windows  40  in the form of openings that pass through its wall and are separated from one another in the circumference direction by means of filter ribs  42  extending in the longitudinal direction of the liner  14  and are defined in the axial direction by an end ring  44 . The filter ribs  42  and the end ring  44  are made to be of one piece with the liner  14  by means of injection molding. In the region of the filter windows  40 , a tubular filter cloth  46  is non-detachably connected to the liner  14  by means of injection molding with the plastic that constitutes the liner  14  during the manufacture of the liner  14 . The filter cloth  46  or a filter that contains the filter cloth  46 , the filter ribs  42 , and the end ring  44  is consequently of one piece with the liner  14 . The filter cloth  46  completely covers the filter windows  40  so that no fluid to be fed can flow unfiltered into the piston pump. The filter windows  40  are disposed in the region of the annular conduit  38  enclosed between the liner  14  and the pump housing  10 . The filter ribs  42  and the end ring  44  are flush with an inner circumference of the liner  14  so that the filter ribs  42  and the end ring  44 , as well as the liner  14  over its remaining length, are in a position to guide the piston  18  so that it can move axially. 
     From the filter windows  40 , the fluid inlet of the piston pump continues on by means of a circumferential groove  48  in the piston  18  into transverse bores  50 , which are let into the piston  18  so that they cross each other in the region of the groove  48 . The transverse bores  50  cross an axial blind bore  52  of the piston  18  at the bottom of the blind bore  52 . The blind bore  52  extends outwardly, forming a conical valve seat  54  at an end face of the piston  18  that defines the displacement chamber  34 . 
     The valve seat  54  embodied on the piston  18  is part of an inlet valve  56  of the piston pump that is embodied as a spring-loaded check valve: a valve ball  58  acting as a valve closing body of the inlet valve  56 , is pressed against the valve seat  54  by a helical compression spring acting as a valve closing spring  60 . The valve closing spring  60  and the valve ball  58  are contained in a bowl-shaped valve retainer  62 , which is produced as a deep-drawn part out of sheet metal. The valve closing spring  60  is supported against a bottom  64  of the valve retainer  62 . Through flow openings  66  are let into the circumference and the bottom  64  of the valve retainer  62 . With an annular step-shaped widening  66  on its open end, the valve retainer  62  is attached to the end of the piston  18  oriented toward the displacement chamber  34 . A free edge of the valve retainer  62  is shaped so that it protrudes radially outward to a spring plate  70 . The piston restoring spring  20  presses against the spring plate  70  and by way of this, presses the piston  18  into contact with the circumference of the cam  22 . At the same time, the piston restoring spring  20  holds the valve retainer  62  against the piston  18  by way of its spring plate  70 . The piston restoring spring  20  is embodied as considerably stronger than the valve closing spring  60  of the inlet valve  56  so that the piston restoring spring  20  holds the valve retainer  62  securely against the end of the piston  18  oriented toward the displacement chamber  34  counter to the force of the valve closing spring  60  at all loads that occur during the operation of the piston pump. 
     A fluid outlet from the displacement chamber  34  of the piston pump takes place by means of a center opening  72  in the liner bottom  16 . On an end remote from the displacement chamber  34 , i.e. on the outside of the liner bottom  16 , a valve seat  74  is embodied that belongs to an outlet valve  78  of the piston pump. The valve seat  74  is embodied on a ring that forms a valve seat part  76 , which is injection molded so that it concentrically encompasses the center opening  72  and is made of the plastic that constitutes the liner bottom  16 . An inner circumferential edge of the valve seat part  76  is rounded and is embodied as a valve seat  74 . 
     An outlet valve  78  is embodied as a spring-loaded check valve. The outlet valve  78  has a valve ball  80  as its valve closing body, which is pressed against the valve seat  74  by a helical compression spring acting as a valve closing spring  82 . The valve closing spring  82  and valve ball  80  are contained in a widened section  84  of the center opening  72 . 
     The widened section  84  of the center opening  72  is disposed in a pin-like extension  86 , which is of one piece with the liner  14  and protrudes from the outside of the liner bottom  16 . The pin-like extension  86  protrudes with a smaller dimension into a countersink  88  of a cylindrical closing part  90 , wherein the valve closing spring  82  of the outlet valve  78  is supported on the bottom of the countersink  88 . The closing part  90  is inserted into an end of the pump bore  12  remote from the cam  22  and is held in the pump bore  12  by means of a circumferential caulking  92  of the pump housing  10 . The caulking  92  produces a pressure tight sealing of the pump bore  12  on its end remote from the cam  22 . A fluid outlet from the widened section  84  of the center opening  72  takes place by means of a radial opening  94  in the pin-like extension  86  and continues on from there by means of a radial groove  96  in the closure part  90  into an annular conduit  98  that encompasses the liner bottom  16  and is enclosed between it and the pump housing  10 . Fluid supplied by the piston pump from the annular conduit  98  flows through a radial outlet bore  100  in the pump housing  10 . 
     For the assembly of the piston pump, first the piston restoring spring  20  is inserted into the liner  14  and then the piston  18 , onto which the guide ring  28  and the sealing ring  30  have been slid and to which the valve retainer  62  with the valve spring  60  and the valve ball  58  has been attached, is inserted into the liner  14 , as shown in FIG.  2 . This produces a subassembly of the piston pump which essentially includes the piston  18  with the guide ring  28  and the sealing ring  30 , the inlet valve  56 , and the piston restoring spring  20 . In the position of the piston  18  in the liner  14  shown in FIG. 2, the piston restoring spring  20  is completely relaxed. When the piston restoring spring  20  is completely relaxed, the piston  18  is guided in the liner  14 , in its filter ribs  42 , and/or in its end ring  44 , i.e. the piston restoring spring  20  does not press the piston  18  out from the liner  14  provided that the subassembly is not yet inserted into the pump housing  10  in which the cam  22  holds the piston  18  in the liner  14  counter to the force of the piston restoring spring  20 . Since the filter ribs  42  and/or the end ring  44  of the filter  42 ,  44 ,  46 , which are of one piece with the liner  14 , thus guide the piston  18  in the liner  14 , the liner  14 , including its filter  42 ,  44 ,  46 , can be embodied as short in the axial direction. A subassembly is obtained that can be favorably manipulated until the insertion into the pump bore  12 . After the assembly of the subassembly, it is inserted into the pump bore  12  of the pump housing  10  and the pump bore  12  is closed with the closing part  90  by affixing the caulking  92 . 
     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.