Abstract:
The radial piston pump possesses a pump body with a plurality of cylinder borings for the reception of pump pistons which can be driven by a cam. The cylinder borings are closed by valve plugs in which pressure passages are provided. In the pressure passages, outlet valves are inserted which respectively possess a valve stem ( 7 ) an end of which, proximate to the pump piston ( 1 ), is provided with an impact plate.

Description:
FIELD OF THE INVENTION 
     The present invention concerns a radial piston pump with a pump body, in which a plurality of cylinder borings are provided to receive pump pistons, which are driven by an eccentric cam. 
     BACKGROUND OF THE INVENTION 
     A radial piston pump, as a component of an automatic transmission, has been made known by DE A 41 39 611 and serves for the supply of oil for lubrication as well as for control and activation of equipment. The driving part of the radial piston pump, in this service, is connected with a startup apparatus placed ahead of the transmission, wherein the eccentric cam driving the individual pump pistons, for instance, can be connected with the impeller of a hydrodynamic converter. 
     The cylinder borings of the radial piston pump are customarily closed, in a radially outward direction, by a valve plug which possesses a centrally located through boring thus forming a pressure passage, wherein all the valve plugs of the radial piston pump are covered by a circumferential band spring. In order to attain a better loading of this band spring by the delivered pump pressure, the plugs, on their upper sides, are provided with parallel striations which terminate within the machined sealing area of the exposed surfaces and the striations are aligned in the circumferential direction of the radial piston pump. In this arrangement, the band spring seals the said centrally located pressure passages as well as the said striations by spring pressure against a collection channel radially located outside of the valve plug. When a radial piston is in the delivery stroke, the band spring is forced free of the sealing surface by means of the pressure in that boring and in the striations which lie in the pressure zone of the radial piston pump. 
     In the area of the radially, outward directed sides of the pistons, an intake suction port is placed coaxially to the pump axis. This suction port intersects the cylinder boring. Suction intake openings are made by means of this intersection. An annular flow resistance is interposed between the side of the piston and the individual suction port, on each respective piston. 
     The disadvantage of radial piston pumps of this design is the generation of noise which can extend to an excessive point. These noises arise from the ejection of the oil from the necessary lifting of the band spring. The band spring, when lifted, must push against the pressurized oil standing in the annular collection channel. This burdens the ejection of the oil by the delivering piston and is hence a party to pressure peaks in the cylinder boring which, in the first place, make lifting of the band spring possible. 
     The purpose of the present invention is to create a radial piston pump with a substantially reduced generation of noise. 
     SUMMARY OF THE INVENTION 
     The invention also provides, that in each case, an outlet valve is placed in the pressure passages which penetrate the valve plugs, which valve, on its end proximal to the pump piston, is provided with an impact plate. 
     Advantageously, both ends of the pressure passage are tapered in a conical manner. 
     The outlet valve further possesses a valve stem, the end of which, proximate to the annular collection channel, is shaped as a cone or a sphere. 
     A spring embracing the valve stem is between the impact plate and the valve plug and the spring loads the valve stem toward the closed direction. 
     Because of the fact that the invented radial piston pump has an outlet valve in each valve plug, instead of having a valve band, the advantage is achieved that only a minimal amount of oil is forced into the collection space, by the controlled expulsion of oil from the cylinder borings, so that pressure peaks at the pump pistons in the cylinder borings are substantially reduced. Upon a forward piston thrust in the pumping of oil, a dynamic pressure, which enables an eased opening of the outlet valve, arises on the impact plate. The expelled oil, on this account, is pumped in all directions in the annular collection channel in contrast to the situation in the case of the conventional band spring, wherein the oil could only exit from the sides of the spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a longitudinal cross section through a conventional radial piston pump, 
     FIG. 2 is a longitudinal cross section through an invented radial piston pump during the delivery stroke, and 
     FIG. 3 is a longitudinal cross section through an invented radial piston pump during the suction intake stroke. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Radial piston pumps are well known to the pump expert so that, in the following description as well as in the figures, only those components necessary for an understanding of the invention are described and illustrated, whereby the same parts in the figures are provided with the same reference numbers. 
     In FIG. 1, the presented, conventional radial piston pump possesses a pumping piston  1 , which can slidingly move in a cylinder boring. The piston  1  is driven by a slip ring  3  powered by a cam  2 . The reference number  4  designates the customary piston spring and reference number  5  designates the valve plug which closes the upper end of the cylinder boring. The pressure passage provided in the valve plug  5  is closed by a band spring  6  which causes a strong noise to develop during operation of the radial piston pump. 
     In accord with the embodiment presented in FIG. 2, showing an invented radial piston pump, the pumping piston  1  is likewise driven by a cam  2 . Instead of the band spring  6  which closes the pressure passage in the valve plug  5 , an outlet valve is now shown and provided for each valve plug  5  of the radial piston pump. This outlet valve possesses a stem  7  has a lower end, proximate to the pumping piston, which has an impact plate  8  attached thereto. The valve stem  7  is provided to slide in the pressure passage  14  of the valve plug  5  whereby, according to this embodiment, both the under surface of the pressure passage, at location  11 , as well as the upper surface proximate to the annular collection channel  12 , are conically shaped surface. The upper end of the valve stem  7  is correspondingly provided with a section  9 , shaped as a frustum of a cone, for closing the pressure passage during a closure phase of the outlet valve (see intake suction position per FIG.  3 ). In another embodiment, the section  9  of the valve stem  7 , for instance, can be designed as a spherically shaped member (not shown). 
     FIG. 2 shows the pumping piston  1  during its delivery phase in which the conical frustum shaped section  9 , as seen in this embodiment for example, is lifted clear of the conical shaped surface of the pressure passage so that oil, corresponding to the two depicted arrows, can flow into an annular collection channel  12 . 
     During the intake suction stroke of the pump piston  1  (FIG.  3 ), the pump piston  1  uncovers the suction port  16  so that the fluid, i.e., the oil, flows into the cylinder boring because of the lower pressure. Due to the impact plate  8  and because of the necessary space taken by the outlet valve, the oil first predominately flows into the lower half of the cylinder boring (the oil flow is shown by a dotted line). During the course of the subsequent movement of the pump piston  1  (FIG.  2 ), the suction opening  16  is closed and the oil, which has collected under the impact plate  8 , can now flow past this plate  8  toward the pressure passage whereby, a dynamic pressure arises underneath the impact plate  8  which enables the opening of the outlet valve. 
     Subsequently, after exiting exit from the pressure passage, the oil can disperse itself in all directions into a storage or collection space. This is contrary to the conditions with the conventional band spring where the oil could only escape laterally from the band spring. 
     Once the pump piston  1  has terminated the delivery stroke, then the outlet valve closes by means of the valve spring  10  which is positioned between the impact plate  8  and the underside of the valve plug  5 . During this closure, the force of the spring  10  is supported by the still elevated pressure in the storage space. The pump piston  1  can now induce suction to renew the intake of oil. 
     Because of the components of the outlet valve placed in the cylinder boring, only a small quantity of oil is expressed into the annular collection channel  12  upon the opening of the outlet valve. On this account, by the provision of the impact plate  8 , early opening of the outlet valve upon pumping stroke is assured so that the pressure peaks, in the cylinder boring and at the pump piston, can be reduced. 
     It is to advantage if the impact plate  8  lies above the suction opening  16  so that the entering oil flows, as unrestrictedly as possible, into the lower half of the cylinder boring. Employing the annular space between the impact plate and the coil spring  4  of the valve, the through-flow speed of the oil upon thrust movement of the piston, and therewith the generated dynamic pressure underneath the impact plate  8 , can be adjustable. Further, the oil flow into the cylinder boring upon the thrust motion can be changed by means of the shape of the impact plate  8  which relative to the base of the pump piston  1 , for example, can be designed to be concave, convex, or conical. This permits the function of the outlet valve to be adjusted within certain limits. 
     Reference Number and Parts 
       1  pump piston 
       2  cam 
       3  slip ring 
       4  valve piston spring (coil) 
       5  valve plug 
       6  band spring (circumferential) 
       7  Valve stem 
       8  Impact plate 
       9  Section 
       10  Valve spring (around stem) 
       11  Location 
       12  Annular collection channel 
       14  Pressure passage 
       16  Suction port