Abstract:
Disclosed is a radial piston pump having a longitudinally movable pump piston in a cylinder chamber which communicates with a suction valve. A closing body of the suction valve is loaded by a valve closing spring in the direction of its valve seat affixed to the housing. The valve closing spring is supported on the pump piston. The radial piston pump is especially useful in fuel injection systems of internal combustion engines, particularly in common rail injection systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/01815 filed on Jun. 22, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is radial piston engines; 
     2. Description of the Prior Art 
     A radial piston pump of this kind has been disclosed in DE 23 38 489 B2. In this known pump the suction valve has a shaft which leads from its closing body equaxially to the pump piston and supports the valve closing spring outside the cylinder chamber. This valve closing spring engages the shaft at one end and indirectly engages the pump housing at the other end. When the suction valve opens, the closing force of the spring therefore increases along with the stroke. 
     Radial piston pumps of this kind, which have a number of pump pistons (pump elements), must meet strict requirements with regard to uniform delivery: with a low supply quantity, all of the pump elements should be feeding and variation between the supply quantities of the individual pump elements should remain within strict limits. At a low pressure of the fuel supplied to the radial piston pump, difficulties in meeting these requirements arise, even with low opening pressure differences between the suction valves of the pump elements. 
     In the crown piston pump mentioned, the opening process of the suction valve should be assisted by virtue of the fact that the closing body of the valve disposed in the cylinder chamber, at the top dead center of the pump piston is largely encompassed by the pump piston and as a result, the piston exerts an aspirating action on the closing body during the intake stroke. 
     SUMMARY OF THE INVENTION 
     The radial piston pump according to the invention, has the advantage over the prior art that the opening of the suction valve is assisted at a low pressure of the supplied fuel by virtue of the fact that the closing force of the valve closing spring decreases as the intake stroke of the pump piston increases. In a multi-piston pump, an opening of all of the suction valves is thus reliably achieved and a relatively high degree of delivery uniformity is produced. As a result, an opening pressure adjustment of the suction valves can be eliminated or can be carried out with reduced precision. 
     DE 44 06 803 A1 has in fact disclosed a radial piston pump with a pump piston that is flowed through axially, in which a suction valve is disposed, whose valve closing spring engages the closing body of the suction valve at one end and engages the pump piston at the other end. When the suction valve opens, however, the closing force of the spring, increases along with the stroke. 
     Another feature of the invention permits the size of the radial piston pump to be reduced since the valve closing spring is disposed essentially inside the structural volume of the pump piston. This disposition simultaneously achieves a guidance of the valve closing spring. 
     Another feature enables sufficient guidance of the closing body shaft to be likewise achieved while simultaneously reducing the dead volume of the pump. 
     In a modification of the invention, direct introduction of the spring force into the components is used to control the valve. As a result, only the dimensional deviations of a few components affect the adjustment of the suction valve. 
     Other features and advantages of the invention will be apparent from the detailed description contained below, taken with the drawings, in which: 
     FIG. 1 is a sectional view of a radial piston pump and 
     FIG. 2 shows an enlarged detail II from FIG. 1 of a suction valve of the pump. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A non-adjustable radial piston pump  10  shown in FIG. 1 is provided for generating high fuel pressure in fuel injection systems of internal combustion engines, in particular in a common rail injection system. The radial piston pump  10  has a housing  11  in which a drive shaft  12  with a cam section  13  is supported. A stroke ring  14  is guided on the cam section  13 . In FIG. 1 of the drawings, the stroke ring  14  supports a piston base  15  of a pump piston  16  that is guided so that it can move longitudinally in the pump housing  11 , radial to the drive shaft  12 . Due to the action of a piston spring  17  disposed coaxial to the pump piston  16 , which spring engages the piston base  15  at one end and the pump housing  11  at the other, the piston base  15  is kept in constant contact with the stroke ring  14 . The pump piston  16  is also associated with a suction valve  18  and a pressure control valve  19 . The suction valve  18  can be supplied with low-pressure fuel, for example diesel oil, by means of a conduit  20  of the pump housing  11 . A conduit  21  of the pump housing  11  leads from the pressure control valve  19  and diverts high-pressure fuel delivered by the pump piston  16 . The pump piston  16  with the piston base  15 , piston spring  17 , suction valve  18 , and pressure control valve  19  constitutes a pump element  22  of the radial piston pump  10 . This pump is equipped with additional pump elements  22 , for example a total of three of them, which are disposed offset from one another by 120° (not visible in the drawing) in a plane radial to the axis of the drive shaft  12  in the pump housing  11 . The additional pump elements  22  likewise communicate with the conduits  20  and  21 . The subsequent description of the pump element  22  in conjunction with FIG. 2 consequently applies equally to the rest of the pump elements. 
     The suction valve  18  is disposed in the pump housing  11 , radially behind the pump piston  16  in relation to the drive shaft  12 . The suction valve has a valve plate  24 , which is held down in a bore  25  of the pump housing  11  by a screw plug. A hollow, conical valve seat  27  is embodied on the valve plate  24 . The valve seat  27  is consequently disposed so that it is fixed in relation to the housing and is connected in a communicating fashion to the conduit  20  that conveys low-pressure fuel. The suction valve  18  has a closing body  28  with a conical valve disk  29 , which cooperates with the valve seat  27  of the valve plate  24 . When the suction valve  18  is closed, the bottom of the valve disk  29  of the closing body  28  is approximately flush with the end face of the valve plate  24  oriented toward the pump piston. 
     The pump piston  16 , which is disposed in a cylinder chamber (displacement chamber)  32  of the pump housing  11 , has a longitudinal bore  33  embodied as a blind hole bore which fiends in a flat bore bottom  34 . The longitudinal bore  33  is disposed coaxial to the pump piston  16  and contains a valve closing spring  35  embodied as a helical compression spring. Since the pump piston  16  when disposed in its top dead center shown in FIG. 2, extends close to the valve plate  24  adjoining the cylinder chamber  22 , the valve closing spring  35  is disposed for the predominant part of its length in the longitudinal bore  33  of the pump piston. The valve closing spring  35  has an outer diameter that is largely adapted to the diameter of the longitudinal bore  33  of the pump piston  16  and engages the bore bottom  34  at one end and engages the valve disk  29  at the other end. The closing body  28  of the suction valve  18  is provided with a pin-shaped shaft  36 , which is guided through the inside of the valve closing spring  35  and in the depicted dead center position of the pump piston  16  and closed position of the suction valve  18 , reaches close to the bore bottom  34 . The shaft  36  of the closing body  28 , whose outer diameter corresponds almost to the inner diameter of the valve closing spring  35 , extends slightly beyond the bottom of valve disk  29  and is guided so that it can move longitudinally in the valve plate  24 . Since the shaft  36  of the closing body  28 , which extends coaxial to the pump piston  16 , together with the valve closing spring  35 , largely fills up the volume of the longitudinal bore  33  of the pump piston  16 , the dead volume of the pump is low, as shown in FIG.  2 . As is also shown in FIG. 2, the cylinder chamber  32  oriented toward the suction valve is slightly enlarged diametrically in relation to the pump piston  16  and communicates with the pressure control valve  19  in this enlarged section. 
     In the depicted position of the pump piston  16 , the valve closing spring  35  exerts a maximal closing force on the valve disk  29  of the suction valve  18  and keeps it closed. During the intake stroke of the pump piston  16 , it is moved out of the depicted position toward the cam section  13  of the drive shaft  12 . As a result, the valve closing spring  35  experiences a reduction in its closing force. The low-pressure fuel supplied to the suction valve  18  by the conduit  20  exerts an opening force on the valve disk  29  counter to the spring force. When the opening force prevails, the suction valve  18  is opened, i.e. the valve disk  29  lifts up from the valve seat  27  and moves into the cylinder chamber  32  by a slight amount. The opening of the suction valve  18  occurs as a function of the pressure of the fuel supplied: at a high pressure, the opening of the suction valve  18  occurs with even a small intake stroke of the pump piston  16 ; at a low pressure, the suction valve is opened when the pump piston  16  has traveled a larger intake stroke. The valve closing spring  35 , however, is designed so that at low pressures of the supplied fuel, the suction valve  18  reliably opens with a large suction stroke of the pump piston  16  and a partial filling of the cylinder chamber  32  takes place. Because of the guaranteed opening of the suction valve  18 , the partial filling of the remaining pump elements  22  of the radial piston pump  10  is also achieved in a corresponding manner. 
     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.