Abstract:
The invention relates to a piston pump for a high-pressure cleaning appliance, including a plurality of pistons that are movable back and forth and each of which enters a pump chamber and is displaceably held at a piston guiding part. The piston guiding part has a supporting wall on which a plurality of guiding elements, each of which guides a piston, are disposed. In order to be able to produce the piston pump in a more cost-effective manner, it is proposed according to the invention that the supporting wall is curved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of international application No. PCT/EP2012/069867, filed on Oct. 8, 2012, which claims the benefit of German application No. 10 2011 054 442.9, filed on Oct. 12, 2011, the entire specification of both being incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a piston pump for a high-pressure cleaning appliance, comprising a plurality of pistons that are movable back and forth and each of which enters a pump chamber and is displaceably held at a piston guiding part, the piston guiding part having a supporting wall on which a plurality of guiding elements, each of which guides a piston, are disposed. 
         [0003]    Piston pumps of this kind are known, for example, from DE 39 18 022 C2. By means of such a piston pump, a liquid, preferably water, can be drawn in, pressurized and subsequently discharged. For this purpose, the pump chamber is connected via a suction valve to a suction line for sucking in liquid, and is connected via a pressure valve to a pressure line for discharging pressurized liquid. An accessory appliance can be connected to the pressure line, for example, a high-pressure hose that carries at its free end a discharge device such as a spray lance or a spray nozzle. 
         [0004]    For delivering the liquid, the pistons are moved in a reciprocating manner such that the volumes of the pump chambers change periodically for suctioning, pressurizing and discharging the liquid. The pistons are displaceably held at a piston guiding part that has a supporting wall and a plurality of guiding elements. The guiding elements each guide a piston. In many cases, the supporting wall forms a cover that is attached to the housing of a drive mechanism, for example, the housing of a wobble plate against which the pistons rest and which is set in rotation by a motor. 
         [0005]    The piston guiding part is subjected to high mechanical load. It therefore usually has reinforcement ribs and a significant material thickness. This results in increased production costs for the piston pump. 
         [0006]    It is an object of the present invention to improve a piston pump of the aforementioned kind in such a manner that it can be produced in a more cost-effective manner. 
       SUMMARY OF THE INVENTION 
       [0007]    This object is achieved according to the invention with a piston pump of the generic kind, in that the supporting wall is curved. 
         [0008]    In the piston pump according to the invention, a piston guiding part having a curved supporting wall is used. Due to the curvature of the supporting wall, on the one hand the mechanical load capacity of the piston guiding part can be significantly increased without the supporting wall requiring reinforcement ribs or a great material thickness for this purpose. On the other hand, due to the curved shape of the supporting wall, its surface area is increased so that the supporting wall also has improved thermal load capacity since due to the greater surface area, reliable heat dissipation is ensured without necessarily having to provide cooling ribs for the supporting wall. The comparatively low material input required for the supporting wall reduces the weight of the piston guiding part. Moreover, the piston guiding part having the curved supporting wall can be produced in a cost-effective manner so that the production costs of the piston pump can be reduced. 
         [0009]    It is particularly advantageous when the supporting wall is curved in the same direction on its front side facing the pump chambers and on its rear side facing away from the pump chambers. The supporting wall thus forms a cavity or a deepened region that provides the supporting wall with particularly high mechanical stability. 
         [0010]    In a preferred embodiment, the supporting wall is curved in the manner of a spherical cap. For example, the supporting wall can form a spherically cap-shaped cover of a housing that accommodates a drive mechanism for the pistons. 
         [0011]    In a preferred embodiment of the invention, the supporting wall is curved in the direction facing the pump chambers or in the direction facing away from the pump chambers. This has the advantage that the central region of the supporting wall is axially offset with respect to its outer circumference. 
         [0012]    The guiding elements are preferably integrally connected to the supporting wall and protrude from the supporting wall on the side of the supporting wall facing away from the pump chambers. For example, it can be provided that the supporting wall is curved in the direction toward the pump chambers so that the supporting wall, on its side facing away from the pump chambers, forms a deepened region or a cavity into which the guiding elements extend. 
         [0013]    For example, the supporting wall can form a cover for a wobble plate housing, the cover being curved outwardly or extending into the housing. 
         [0014]    Particularly high mechanical stability is achieved in an advantageous embodiment in that the guiding elements have a base that is integrally connected to the supporting wall and protrudes at least from one side of the supporting wall. It is advantageous for the base to protrude from the supporting wall on both sides thereof. 
         [0015]    For increasing the mechanical and thermal load capacity of the piston guiding part, radially protruding reinforcement ribs are preferably formed on the outer sides of the guiding elements. 
         [0016]    It is advantageous when the guiding elements have a base which protrudes from the supporting wall on the side of the supporting wall facing the pump chambers, and which carries radially protruding reinforcement ribs on its outer side. Due to the use of reinforcement ribs, the amount of material used for the bases can be kept low without affecting their mechanical or thermal load capacity. It is particularly advantageous for the reinforcement ribs to protrude beyond the bases in the axial direction. With their axially protruding region, the reinforcement ribs define a receiving space for a ring-shaped component of the piston pump, which ring-shaped component surrounds in the circumferential direction the piston which passes through the guiding element. This can be, for example, a guiding ring or a sealing ring. In a configuration of this kind, the reinforcement ribs serve not only the purpose of increasing the mechanical stability of the bases, but, moreover, they also serve for fixing a ring-shaped component that surrounds a piston in the circumferential direction. 
         [0017]    In an advantageous embodiment of the invention, the guiding elements have a base that is integrally connected to the supporting wall and which is adjoined by a guide sleeve in the axial direction, which guide sleeve encloses a piston in a positive-fitting manner in the circumferential direction. The base can have a greater material thickness than the guide sleeve. In particular, it can be provided that the outer side of the base transitions into the outer side of the guide sleeve via an inwardly directed, preferably radially oriented, step. 
         [0018]    Radially protruding reinforcement ribs are advantageously formed on the outer side of the guide sleeves. 
         [0019]    Particularly high mechanical stability is achieved in a preferred embodiment of the invention in that a cylindrical collar is formed on the outer circumference of the supporting wall. In a preferred configuration, the cylindrical collar engages into a cylindrical housing of a wobble plate. 
         [0020]    The following description of preferred embodiments of the invention in connection with the drawing serves for a more detailed explanation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  shows a schematic sectional view of a first embodiment of a piston pump according to the invention; 
           [0022]      FIG. 2  shows a sectional view of a piston guiding part of the piston pump from  FIG. 1 ; 
           [0023]      FIG. 3  shows a perspective illustration of the piston guiding part from  FIG. 2 , viewed diagonally from the front; 
           [0024]      FIG. 4  shows a perspective illustration of the piston guiding part from  FIG. 2 , viewed diagonally from the rear; 
           [0025]      FIG. 5  shows a sectional view of a second embodiment of a piston pump according to the invention; 
           [0026]      FIG. 6  shows a sectional view of a piston guiding part of the piston pump from  FIG. 5 ; 
           [0027]      FIG. 7  shows a perspective illustration of the piston guiding part from  FIG. 6 , viewed diagonally from the front; and 
           [0028]      FIG. 8  shows a perspective illustration of the piston guiding part from  FIG. 6 , viewed diagonally from the rear. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIGS. 1 to 4  schematically illustrate a first embodiment of a piston pump according to the invention, which as a whole is designated by reference number  10 . The piston pump can be attached in a customary manner to a motor, not shown in the drawing, which rotationally drives a wobble plate  12  that is rotatably mounted in a wobble plate housing  14  by means of a ball bearing  16 . The piston pump  10  comprises a plurality of identically configured pistons  18  that rest against the front side of the wobble plate  12  facing away from the ball bearing  16 , and are pressed toward the wobble plate  12  by means of return springs  20 . The pistons  18  are held at a piston guiding part  22  of the piston pump  10  in a linearly displaceable manner. For this purpose, the piston guiding part  22  has guiding elements  24 , each of which guides a piston  18  and is integrally connected to a supporting wall  26  of the piston guiding part  22 . 
         [0030]    The supporting wall  26  is configured in the manner of a spherical cap, and in the embodiment illustrated in  FIGS. 1 to 4 , it is curved in the direction facing away from the wobble plate  12 . The supporting wall forms a cover that is mounted onto a cylindrical casing  28  of the wobble plate housing  14 . A cylindrical collar  30  is foamed on the outer circumference of the supporting wall  26 , and engages into the casing  28  of the wobble plate housing  14  with a sealing element  32  being situated in between. 
         [0031]    The guiding elements  24  have an identical design, and in each case comprise a cylindrical base  34  that is integrally connected to the supporting wall  26  and protrudes from the supporting wall on the front side  36  of the supporting wall  26  facing away from the wobble plate  12 , and also on the rear side  38  of the supporting wall  26  facing the wobble plate  12 . In the direction toward the wobble plate  12 , a guide sleeve  40  is integrally connected to the base  34  and encloses the respective piston  18  in a positive manner. The material thickness of the base  34  is selected to be greater than the material thickness of the guide sleeve  40 . 
         [0032]    As is apparent in particular from  FIG. 4 , the outer sides of the bases  34  transition into the outer sides of the guide sleeves  40  via radially inwardly oriented steps  42 . Reinforcement ribs  44  are integrally formed onto the outer sides of the bases  34 , and protrude radially on both sides of the supporting wall  26  and are disposed uniformly distributed over the peripheries of the bases  34 . The reinforcement ribs  44  disposed on the front side  36  of the supporting wall  26  protrude beyond the cylindrical bases  34  in the axial direction. This is apparent in particular from  FIG. 3 . 
         [0033]    In contrast to the bases  34 , the guide sleeves  40  formed on the bases  34  on the rear side  38  of the supporting wall  26  have no reinforcement ribs on the outside. 
         [0034]    A pump block  46  of the piston pump  10  is attached to the piston guiding part  22 , and a pump head  48  of the piston pump  10  is attached to the pump block  46 . The pump block  46  and the piston guiding part  22  are clamped between the pump head  48  and the wobble plate housing  14  by means of tensioning screws  50 . 
         [0035]    The pump block  46  has pump chambers  52  each of which a piston  18  enters and which are in flow communication with a suction line  56  via an inlet opening  54 , and are in flow communication with a pressure line  60  via an outlet opening  58 . A suction valve known per se, which is not illustrated in the drawing, is disposed in each case between the pump chambers  52  and the suction line  56 , and a pressure valve known per se, which is not illustrated in the drawing, is disposed in each case between the pump chambers  52  and the pressure line  60 . 
         [0036]    The suction line  56  connects the pump chambers  52  to a suction inlet  62  of the piston pump  10 , to which a suction hose, for example, can be connected. The pressure line  60  connects the pump chambers  52  to a pressure outlet  64  of the piston pump  10 , to which a pressure hose, for example, can be connected. 
         [0037]    When the wobble plate  12  is set in rotation about its axis of rotation  66 , the pistons  18  perform a reciprocating movement parallel to the axis of rotation  66 , the pistons thereby periodically changing the volume of the respective pump chamber  52  which they enter so that liquid can be drawn into the pump chamber  52  via the suction inlet  62  and the suction line  56 , subsequently pressurized and then discharged via the pressure line  60  and the pressure outlet  64 . The pistons  18  are guided in the axial direction, i.e., parallel to the axis of rotation  66 , by means of the piston guiding part  22 . For this purpose, the pistons  18  in each case slide along a guide sleeve  40  that is integrally connected to the supporting wall  26  via a base  34 . Due to its spherical cap-shaped configuration, the supporting wall has high mechanical stability that is increased by the cylindrical collar  30  which is aligned concentrically with respect to the axis of rotation  66  and is integrally connected to the supporting wall  26 . Moreover, the supporting wall  26  is characterized by high thermal stability since it has a comparatively large surface via which heat can be dissipated. 
         [0038]      FIGS. 5 to 8  illustrate a second advantageous embodiment of a piston pump according to the invention, designated as a whole by reference number  70 . The piston pump  70  is configured similarly to the piston pump  10  described above. The piston pump  70  is driven by a wobble plate  72  that is rotatably mounted in a wobble plate housing  74  and is set in rotation by a motor, not illustrated in the drawing. 
         [0039]    Pistons  78 , which are pushed by return springs  80  toward the wobble plate  72 , rest against the wobble plate  72 . The pistons  78  are held at a piston guiding part  82  so as to be displaceable in the axial direction. The piston guiding part  82  comprises guiding elements  84  that are integrally connected to a supporting wall  86  of the piston guiding part  82 . The supporting wall  86  is attached to a casing  88  of the wobble plate housing  74 , and a cylindrical collar  90  is formed on the outer circumference of the supporting wall  86  and encloses an end portion of the casing  88  in the circumferential direction. 
         [0040]    Similar to the supporting wall  26  of the piston pump  10  described above with reference to 
         [0041]      FIGS. 1 to 4 , the supporting wall  86  of the piston pump  70  is also configured in the manner of a spherical cap. However, in contrast to the supporting wall  26 , the supporting wall  86  is curved in the direction facing the wobble plate  72 . Thus, on its front side  96  facing away from the wobble plate  72 , the supporting wall  86  forms a deepened region or cavity, and with its rear side  98  facing the wobble plate  72 , the supporting wall projects into the wobble plate housing  74 . 
         [0042]    The guiding elements  84  of the piston pump  70  each comprise a cylindrical base  94  that is integrally formed onto the supporting wall  86  and protrudes beyond the supporting wall  86  on the front side  96  and also on the rear side  98 . A guide sleeve  100  that faces the wobble plate  72  is integrally connected to the base  94 , the material thickness of the guide sleeve being selected to be less than the material thickness of the cylindrical base  94 . The outer side of the cylindrical base  94  transitions into the outer side of the guide sleeve  100  via a radially inwardly oriented step  102 . This is apparent in particular from  FIG. 8 . 
         [0043]    The cylindrical base  94  has reinforcement ribs  104  only on the outer side of its region protruding beyond the front side  96 , whereas the outer side of the region of the cylindrical base  94  protruding beyond the rear side  98  carries no reinforcement ribs. Instead, further reinforcement ribs  105  are formed on the outer side of the guide sleeves  100 , and allow the material thickness of the guide sleeves  100  to be kept low without affecting the mechanical or thermal stability of the guide sleeves  100 . 
         [0044]    The piston pump  70  comprises a pump block  106  that is attached to the piston guiding part  82 , and a pump head  108  that is attached to the pump block  106 . The pump block  106  and the piston guiding part  82  are clamped between the pump head  108  and the wobble plate housing  74  by means of tensioning screws, not illustrated in the drawing. 
         [0045]    The pump block  106  has pump chambers  112  each of which a piston  78  enters, and which are in flow communication with a suction line  116  via an inlet opening  114 , and are in flow communication with a pressure line  120  via an outlet opening  118 . The pump chambers  112  are connected to a suction inlet  122  via the suction line  116 , and the pump chambers  112  are connected to a pressure outlet  124  via the pressure line  120 . A suction valve, known per se to the person skilled in the art and not illustrated in the drawing, is disposed in each case between the pump chambers  112  and the suction line  116 , and a pressure valve, known per se to the person skilled in the art and not illustrated in the drawing, is disposed in each case between the pump chambers  112  and the pressure line  120 . 
         [0046]    When the wobble plate  72  is set in rotation about its axis of rotation  126 , the pistons  78  are moved in a reciprocating manner so that the volume of the respective pump chamber  112  into which the pistons  78  plunge changes periodically for sucking in, pressurizing and discharging liquid. Each of the pistons is guided in the axial direction, i.e., parallel to the axis of rotation  126 , by a guide sleeve  100  which is integrally connected to the supporting wall  86  via a cylindrical base  94 . Due to its curved configuration, the supporting wall  86  has high mechanical and thermal stability. The mechanical stability is additionally increased by the collar  90  that is formed on the supporting wall  86  and is aligned concentrically with respect to the axis of rotation  126 .