Abstract:
A piston pump for a high-pressure cleaning appliance is provided, including a plurality of pump chambers into each of which one piston which is movable back and forth plunges, and which are each in flow connection via a suction valve with a suction inlet and via a pressure valve with a pressure outlet, the pistons each being surrounded by a sealing ring which is supported in the radial direction by a ring wall and in the axial direction by a support ring. In order to develop the piston pump in such a way that it can be manufactured and assembled more cost-effectively, it is proposed that the piston pump includes a one-piece support shield which forms the support rings and surrounds the ring walls in the circumferential direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of international application number PCT/EP2012/050867, filed on Jan. 20, 2012, which is incorporated herein by reference in its entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a piston pump for a high-pressure cleaning appliance, comprising a plurality of pump chambers into each of which one piston which is movable back and forth plunges, and which are each in flow connection via a suction valve with a suction inlet and via a pressure valve with a pressure outlet, the pistons each being surrounded by a sealing ring which is supported in the radial direction by a ring wall and in the axial direction by a support ring. 
         [0003]    A liquid, preferably water, can be pressurized and directed at an article to be cleaned or a surface to be cleaned by means of such piston pumps. For this purpose, the pistons can be reciprocatingly driven, for example, by means of a swash plate, so that the volumes of the pump chambers periodically change and liquid can be drawn from the suction inlet via the suction valves into the pump chambers, pressurized there and discharged via the pressure valves and the pressure outlet. A pressure hose, for example, which carries at its free end a discharge member for the pressurized liquid, for example, a spray nozzle or a spray lance, can be connected to the pressure outlet. 
         [0004]    The pump chambers are each sealed by means of a sealing ring which surrounds the piston plunging into the pump chamber in the circumferential direction. The sealing ring can form a sealing lip, for example, which under the pressure prevailing in the pump chamber is pressed against the lateral surface of the piston. The sealing ring is usually supported by a ring wall in the radial direction, and a support ring is usually used for support in the axial direction. Such piston pumps are known, for example, from DE 44 45 519 C1. 
         [0005]    In many cases, the liquid is pressurized in the pump chambers to a pressure above 100 bar. While in operation, the piston pump is, therefore, subjected to considerable mechanical stresses and must have a high mechanical stability. The piston pumps, therefore, usually have a substantial material thickness. This involves not inconsiderable manufacturing costs. Furthermore, the relatively high material thickness has the consequence that the housing of the piston pump, which is usually manufactured in a casting process, undergoes a lengthy cooling process during the manufacture, which limits the production rate of the housing. This also increases the manufacturing costs of the piston pump. 
         [0006]    The object of the present invention is to develop a piston pump of the kind mentioned at the outset in such a way that it can be manufactured more cost-effectively. 
       SUMMARY OF THE INVENTION 
       [0007]    This object is accomplished, in accordance with the invention, in a piston pump of the generic kind in that it comprises a one-piece support shield which forms the support rings and surrounds the ring walls in the circumferential direction. 
         [0008]    In the piston pump in accordance with the invention, all of the support rings which support in the axial direction the sealing rings surrounding one piston each in the circumferential direction are integrated in a one-piece support shield. This makes simpler assembly of the piston pump possible as all of the support rings can be positioned in a single assembly step. 
         [0009]    The one-piece support shield used in accordance with the invention has, in addition, the function of surrounding the aforementioned ring walls in the circumferential direction and, therefore, supporting the ring walls in the radial direction. This allows the material usage for the ring walls to be reduced as the resulting reduction in the mechanical stability of the ring walls is compensated by the support shield surrounding all of the ring walls in the circumferential direction. 
         [0010]    The one-piece support shield, therefore, makes it possible to reduce the material usage for the pump housing and to simplify the assembly of the piston pump. 
         [0011]    In an advantageous embodiment, the support shield comprises a plurality of support sleeves into each of which a ring wall extends. As explained above, the pump chambers are sealed by means of the sealing rings which surround one piston each and, in turn, are surrounded by a ring wall and are supported on a support ring in the axial direction. In the advantageous embodiment of the invention, the ring wall extends into a support sleeve which is defined by the one-piece support shield. 
         [0012]    It may, for example, be provided that the piston pump in accordance with the invention comprises three pistons which plunge into one pump chamber each, each pump chamber having a ring wall associated therewith, which supports a sealing ring in the radial direction and extends into a support sleeve of the support shield. In such a configuration, the ring wall can be of particularly thin-walled construction and yet the liquid to be pumped can be pressurized in the pump chambers to a high pressure. 
         [0013]    In a particularly preferred configuration of the invention, the piston pump comprises a pump block which includes the pump chambers and is connected to the support shield by substance-to-substance bonding. This allows the manufacturing costs to be additionally reduced and the assembly of the piston pump to also be simplified. 
         [0014]    An adhesive connection, for example, can be used as substance-to-substance bonded connection. A layer of adhesive can, for example, be provided between the ring walls surrounding one sealing ring each in the circumferential direction and the support shield surrounding the ring wall in the circumferential direction. This makes a connection between the pump block and the support shield possible, which is able to withstand mechanical stress. The layer of adhesive can additionally serve as sealing element for the liquid to be pumped. A uniform distribution of tension and transfer of force can also be achieved by the adhesive connection. Tension peaks, as may often occur with a screw connection, can be reduced. 
         [0015]    In a particularly preferred embodiment of the invention, the pump block is welded to the support shield. This makes a connection possible, which has a particularly high resistance to stress and also reliably withstands very high pressures. 
         [0016]    It is expedient for the ring walls surrounding one sealing ring each in the circumferential direction to each be welded to a surrounding support sleeve. 
         [0017]    The pump block and the support shield are preferably made of a plastic material. This allows the pump block to be connected to the support shield by, for example, ultrasonic welding. If the support shield comprises support sleeves, as explained hereinabove, the support sleeves can be fitted on one ring wall each and welded to it in a constructionally simple way. The welded connection makes it possible for the two parts to be permanently fixed to each other so that they are subsequently unable to execute any relative movement. As optimum sealing can also be achieved with the welded connection, additional seals between the two parts can be dispensed with. 
         [0018]    It is advantageous for the support shield to be fitted on a guide shield comprising guide members for guiding the pistons in the axial direction. The pistons can be guided in the axial direction by means of the guide members of the guide shield. The guide shield simultaneously has the function of supporting the support shield in the axial direction. 
         [0019]    It may, for example, be provided that the support shield comprises support collars preferably aligned coaxially with the support sleeves. The support collars are fitted on the guide shield and surround one piston each in the circumferential direction. The support shield can be supported on the guide shield in a constructionally simple way by means of the support collars. In addition, the use of the support collars has the advantage that the mechanical stability of the support shield is increased, with the material thickness of the support shield being able to be kept relatively low. 
         [0020]    The support collars preferably comprise one drainage opening each, for example, a drainage slot. Liquid leaking inadvertently from the pump chambers via the sealing ring surrounding one piston each can be discharged to the environment via the drainage opening. 
         [0021]    In a particularly preferred embodiment of the invention, a particularly high mechanical stability with relatively low material usage can be achieved by the support shield being supported by a guide shield of convex shape, which forms a cover for a swash plate housing. In such a configuration, the guide shield supporting the support shield in the axial direction is of convex construction. This imparts a particularly high mechanical stability to it and allows the material thickness of the guide shield to be reduced. In addition to its function of guiding the pistons in the axial direction and supporting the support shield in the axial direction, in such a configuration, the guide shield assumes the function of a cover for the swash plate housing in which a swash plate is arranged, with which the pistons interact in order to bring about a reciprocating movement. The swash plate can be rotated about the longitudinal axis of the piston pump, and the pistons can be driven by the rotational movement of the swash plate so as to move back and forth, under the action of which the volumes of the pump chambers are periodically changed. 
         [0022]    The following description of a preferred embodiment of the invention serves for further explanation in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a schematic longitudinal sectional view of an advantageous embodiment of a piston pump in accordance with the invention; 
           [0024]      FIG. 2  shows a plan view of a pump block, welded to a support shield, of the piston pump from  FIG. 1 ; 
           [0025]      FIG. 3  shows a sectional view of the pump block, welded to the support shield, along line  3 - 3  in  FIG. 2 ; and 
           [0026]      FIG. 4  shows a sectional view of the pump block and the support shield in the manner of an exploded drawing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    An advantageous embodiment of a piston pump in accordance with the invention, generally denoted by reference numeral  10 , is shown schematically in the drawings. The piston pump  10  comprises a pump head  12  with a suction inlet  14 , via which a liquid to be pressurized, preferably water, can be supplied to the piston pump  10 . A supply line, for example, can be connected to the suction inlet  14 . The pump head  12  also comprises a pressure outlet  16  via which the pressurized liquid can be discharged. A pressure hose, for example, carrying at its free end a discharge member for the pressurized liquid, for example, a spray lance or a spray nozzle can be connected to the pressure outlet  16 . 
         [0028]    The pump head  12  is fitted in the axial direction, in relation to a longitudinal pump axis  18 , on a pump block  20  comprising a plurality of pump chambers  22 , into each of which one piston  24  plunges. The piston pump  10  shown in the drawings has a total of three pump chambers. Only one pump chamber  22  is recognizable in the drawings. The pump chambers are arranged so as to be uniformly distributed about the longitudinal pump axis  18  and are each at the same radial distance from the longitudinal pump axis  18 . 
         [0029]    The pump chambers  22  are each in flow connection via a suction valve  26  with the suction inlet  14  and via a pressure valve  28  with a central pressure chamber  30 , which the pump head  12  and the pump block  20  form between them. Adjoining the pressure chamber  30  in the axial direction is a pressure line  32 , aligned coaxially with the longitudinal pump axis  18 , via which the pressure chamber  30  is in flow connection with the pressure outlet  16 . 
         [0030]    A central insert part  34  formed rotationally symmetrically in relation to the longitudinal pump axis  18  is held in the pressure chamber  30 . The insert part  34  is formed in the manner of a piston and is surrounded by two sealing rings arranged between the insert part  34  and the wall of the pressure chamber  30 . The insert part  34  forms a holding element for closing springs  40  of the pressure valves  28 . On its front side that faces away from the closing springs  40 , the insert part  34  has a recess  42  into which a closing member  44  of a central check valve extends, by means of which a central passage of the insert part  34  can be closed. 
         [0031]    The pump chambers  22  are each sealed in the direction facing away from the pump head  12  by means of a sealing ring  46  which has a sealing lip  48  and surrounds a piston  24  in the circumferential direction. The sealing ring  46  is surrounded in the circumferential direction by a collar-like ring wall  50  of the pump block  20 . The ring wall  50  is of cylindrical construction and is aligned coaxially with a longitudinal piston axis  52 . In relation to the longitudinal piston axis  52 , the ring wall  50  supports the sealing ring  46  radially. 
         [0032]    On the side that faces away from the pump head  12 , the pump block  20  is adjoined by a one-piece support shield  54  whose configuration is evident, in particular, from  FIG. 4 . It comprises support rings  56  which support one sealing ring  46  each in the axial direction. Each support ring  56  is adjoined by a cylindrical support sleeve  58  which is aligned coaxially with a longitudinal piston axis  52  and surrounds a ring wall  50  in the circumferential direction. On the rear side that faces away from the support shields  54 , the support shield  54  carries a plurality of cylindrical support collars  60  which are also aligned coaxially with the longitudinal piston axes  52  and have one drainage opening each in the form of a drainage slot  62 . 
         [0033]    The support shield  54  is of one-piece construction and is made of a plastic material. A plastic material is also used in each case for the manufacture of the pump head  12  and the pump block  20 . The pump block  20  is welded to the support shield  54  in the area of the ring walls  50  and the support sleeves  58  surrounding these. Therefore, each ring wall  50  is connected by substance-to-substance bonding by way of a circumferential weld seam to a support sleeve  58  into which the ring wall  50  extends. This imparts a high mechanical stability to the ring walls  50  without these having to have a considerable material thickness. 
         [0034]    With the support collars  60 , the support shield  54  is supported in the axial direction on a guide shield  64  comprising a plurality of guide members in the form of guide sleeves  66  aligned coaxially with the longitudinal piston axes  52 . A piston  24  lies slidingly against each guide sleeve  66 . By means of a resetting spring  68  surrounding the guide sleeves  66  in each case, the pistons are pressed against a swash plate  70  which is mounted in a swash plate housing  72  for rotation about the longitudinal pump axis  18 . The guide shield  64  forms a convexly outwardly curved cover for the swash plate housing  72  on which the guide shield  64  is supported in the axial direction. 
         [0035]    The swash plate  70  can be rotated about the longitudinal pump axis  18  in the usual way by a drive motor, known per se and, therefore, not shown in the drawings, in particular, an electric motor, with the rotational movement of the motor shaft being transmitted by a gearing  74  shown schematically in  FIG. 1  to the swash plate  70 . 
         [0036]    A high mechanical stability is achieved by the weld connection to a support sleeve  58 , which surrounds a ring wall  50  in the circumferential direction, in each case, with the material usage being able to be kept relatively low for both the pump block  20  and the support shield  54 . After the welding of the pump block  20  to the support shield  54 , the sealing rings  46  surrounding one piston  24  each in the circumferential direction are reliably secured in both the axial and the radial direction, so that a high degree of tightness can be achieved by means of the sealing rings  46  even under high pressures. Liquid that does, nevertheless, leak from the pump chambers  22  can escape to the outside through the drainage slots  62 . 
         [0037]    To assemble the piston pump  10 , it is possible, after assembly of the swash plate  70 , for the guide shield  64  to be fitted on the swash plate housing  72 , the pistons  24  having been previously inserted in the guide sleeves  66 . The support shield  54  can then be fitted on the guide shield  64  after the suction valves  26  have been previously assembled in the pump block  20  and the pump block  20  has been welded to the support shield  54 . The ring walls  50  surrounding one sealing ring  46  each in the circumferential direction thereby extend into the support sleeves  58 . The ring walls  50  are welded to one support sleeve  58  each. Ultrasonic welding can be used for this purpose as both the pump block  20  and the support shield  54  are made of a plastic material. 
         [0038]    After insertion of the pressure valves  28  and the central insert part  34  including the central closing member  44  into the pump block  20 , in a following assembly step the pump head  12  can be fitted in the axial direction on the pump block  20 , with an elastically deformable sealing ring  76  being positioned between the pump head  12  and the pump block  20 . In a next assembly step, the pump head  12  can then be clamped to the pump block  20 . A clamping element  77 , for example, can be used for this purpose, which is shown only schematically in  FIG. 1  and engages the end face  78  of the pump head  12  that faces away from the pump block  20 . The clamping element  77  can engage over the pump head  12 , the pump block  20  and the support shield  54  and be screwed to radially outwardly facing screw receptacles of the guide shield  64 . 
         [0039]    Manufacture and assembly of the piston pump  10  are, therefore, very simple. Use of the one-piece support shield  54  with the support sleeves  58  surrounding one ring wall  50  each and with the support collars  60  aligned coaxially with the support sleeves  58  makes it possible to keep the material usage of the support shield  54  and also the material usage of the pump block  20  in the area of the ring walls  50  low.