Patent Publication Number: US-8113804-B2

Title: Vane pump with rotating cam ring and increased under vane pressure

Description:
BACKGROUND OF THE INVENTION 
     This application relates to a vane pump wherein a cam ring rotates with the vanes, and wherein an under vane pressure is provided with structure to increase the force holding the vane against the cam ring. 
     Vane pumps are known, and typically include a rotor driven to rotate. The rotor carries a plurality of vanes that are biased outwardly of under vane slots, and against an inner periphery of a cam ring. As the rotor rotates, fluid in chambers between the vanes is moved from an inlet toward an outlet. 
     One type of vane pump has a rotating cam ring. The cam ring is caused to rotate with the vanes, typically by a frictional contact between the vane and the cam ring. This type of vane pump raises challenges, in that it is sometimes difficult to ensure the cam ring rotates at a sufficient speed. 
     It is known in vane pumps to provide an under vane pressure to hold the vane outwardly against the inner periphery of the cam ring. However, this has not always proven sufficient to move the cam ring at the desired speed in a rotating cam vane pump. 
     In a balanced vane type of vane pump without the rotating cam ring, but rather a fixed cam ring, it is known to have an under vane pressure wherein a back pressure valve ensures the pressure in the under vane chamber is high. However, this concept has never been applied to a rotating cam vane pump. 
     SUMMARY OF THE INVENTION 
     An example vane pump comprises a shaft driving a rotor. The rotor has a plurality of vane slots, with a vane received in each of the plurality of vane slots, and an under vane chamber for communicating a pressurized fluid into the under vane slots to bias the vanes radially outwardly of the rotor. A cam ring is positioned radially outwardly of the rotor. The cam ring is supported by a bearing and is free to rotate with the rotor through friction from the vanes as the rotor rotates. An inlet delivers a fluid to be pumped into an inlet chamber, and an outlet receives the fluid pumped by the vane pump. An outlet for the fluid biasing the vanes communicates to a main outlet through a passage including a valve to increase the pressure of the fluid in the grooves. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a vane pump. 
         FIG. 2  is a cross-sectional view through the inventive vane pump. 
         FIG. 3  shows porting details. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a vane pump  20  incorporating a rotor  22  driven to rotate by a shaft  19 . The rotor  22  carries a plurality of vanes  24  that are movable within vane slots or grooves  26 . A rotating cam ring  28  is caused to rotate with the vanes, and chambers  30  defined between the vanes carry a fluid from an inlet toward an outlet (not shown in this view). 
     A bearing support housing  32  surrounds a plurality of pivot bearings  40  although other types of fluid film or rolling element bearings may also be used to support the cam ring. 
     A fulcrum  36  receives actuators  34 , and can cause the housing  32  to pivot about a pivot pin  38 . As known, this changes the displacement volume of the vane pump  20  by changing the eccentricity between the cam ring  28  and the rotor  22 . These features are all as known in the prior art. Further, while this invention is shown in a vane pump having the pivot bearings  40  and the pivoting bearing support, or housing  32 , the invention would extend to any vane pump having a rotating cam ring. 
     As shown in  FIG. 2 , grooves  26  receive fluid at discharge pressure. This fluid communicates through passages  38  and  39  to a passage  41 , a passage  42 , into a passage  46 , which communicates with a discharge line  48  for receiving the normal discharge from ports  50  delivered by the pump and the vanes  24   
     A valve  43  is positioned on the under vane return line  41 ,  42 , and includes a spring bias  45 . The under vane pressure will have to overcome the spring bias to move the valve  43  to the right as shown in  FIG. 2  such that fluid can return from the line  41  to the line  42 , and eventually back to the line  46  and the outlet  48 . As is clear from  FIG. 2 , all fluid in the line  41  passes into the line  42  once it has opened the valve  43 . 
     By placing the valve  43  on this line, the under vane pressure is increased relative to the discharge pressure. Thus, the force holding the vanes  24  outwardly against the inner periphery of the cam ring  28  is increased, and the friction and force between the two is increased such that the cam ring  28  is better able to be driven at the same speed as the vanes  24 . 
     Higher under vane pressure is applied to selected vane slots to achieve the highest efficiency and durability. The rotor and vanes rotate about a center which is offset from the center of rotation of the cam ring. This results in relative motion between the vane tip and the cam ring. Only selected vanes at positions of lower sliding motion receive the increased under vane pressure. This approach yields a higher efficiency than other approaches to increase vane tip load such as utilizing heavier vanes. 
     As shown in  FIG. 3 , the higher under vane pressure may be limited to an arc that begins at approximately 180° in the rotation of the cam, and near the end of the inlet arc, passing through the discharge arc. When the housing  32  pivots, the eccentricity of the rotor  22  can change relative to the cam ring  28 . When this occurs, the forces between the vanes and the cam ring change across the circumference of the rotor. Also, the relative velocities between the vane tips and the cam ring vary. In the quadrant wherein the discharge arc is just beginning, the vanes are seeing the highest forces, and the under vane pressure may be most valuable. Thus, the higher under vane pressure may be limited to the slots under only a few vanes. In addition, the under vane pressure may be undesirable at other locations, such as the beginning of the inlet arc. As such, a designer may choose to control the portion of the arc in which the under vane pressure is applied. 
     In  FIG. 3 , the port plate  99  is illustrated. The vanes  24  can be seen further into the plane of the figure. Radially outer inlet ports  100  communicate with the area radially outwardly of the rotor, and define an inlet arc for the pump. In that same area, under vane ports  106  deliver pump fluid to the grooves  26 . A seal arc  104  is positioned between the inlet arc and a discharge arc. In the discharge arc, the chambers outwardly of the rotor communicate with ports  50  to move the pump fluid to discharge. Under vane ports  102  supply under vane pump fluid. As mentioned above, should it be desired to limit the arc that receives the higher pressure, then only one of the ports, port  39  for example, would communicate through the valve  43  to the general discharge. The ports  102  would go through separate paths to the main discharge, and in this way, the higher pressure would only exist for the vanes aligned with the single under vane port  39 . 
     While hydrostatic tilting bearings are shown, other ways of providing support, such as a hydrodynamic or hydrodynamic film bearing in addition to the rolling element bearing may be utilized. 
     Finally, controls may be included such that the increased under vane pressure may be limited to lower pump speeds. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.