Abstract:
A vane pump is disclosed that includes a plurality of vanes and radial slots configured to provide a gap between the vane and the radial slot such that the vane has a different angular position relative to the direction of rotation in a radially extended position compared to an angular position in a radially-retracted position. The different angular positions provide different orientation of the arcuate surface of the vane tip portion with respect to the cam body inner surface, thus providing different fluid stop points on the vane tip portion arcuate surface.

Description:
BACKGROUND 
       [0001]    This disclosure relates to vane pumps. Vane pumps include different varieties such as single acting or double acting and can be fixed or variable displacement. This disclosure is applicable to all types of vane pumps. 
         [0002]    A typical double-acting vane pump  10  is depicted in  FIG. 1 . The vane pump includes a plurality of vanes  12  supported in slots in a rotor  14 . A shaft  16  supported concentrically within a cam block  18  rotates the rotor in the direction of arrow  20 . The vanes  12  have radial portions  15  and tip portions  17 , and are driven outward from the rotor into contact or engagement with an inner surface  22  of the cam block  18 . During operation, shaft  16  rotates within the cam block  18  to move each of the vanes  12  about the circumference of the inner surface  22  of the cam block  18 . The contour of the cam block inner surface  22  creates radial movement of each of the vanes  12 , with the vanes  12  moving into and out of the slots in the rotor  14  as they follow the contour of the cam block inner surface  22   
         [0003]    As the vanes move through the inlet regions  24 , a quantity of fluid is trapped within a fluid flow chamber defined between the vanes  12  in the direction of rotation and between rotor  14  and the cam block inner surface  22  in the direction the radial direction. The volume of this chamber begins at an initial size that is progressively increased as the vane transitions from inlet region  24  to pump arc  26 . In the pump arc  26  the vane  12  extends a constant amount from the rotor  14 . As the vane  12  transitions from the pump arc  26  to the discharge region  30 , the radial distance between the rotor  14  and the cam block inner surface  22  is gradually decreased. The decrease in volume of the fluid flow chamber coincides with removal of fluid from the flow chamber through the pump discharge. The discharge pressure is dependent upon the resistance of the downstream system 
         [0004]    The vanes rotate through pump arcs  26  where high pressure is exerted on the leading surface of the vane and low pressure is exerted on the trailing surface, and through seal arcs  28  where low pressure is exerted on the leading surface of the vane and high pressure is exerted on the trailing surface of the vane. In the inlet regions  24 , inlet fluid pressure is provided to support the vanes so that the vanes are radially pressure balanced. In the discharge regions  30 , discharge fluid pressure is provided to support the vanes so that the vanes are also radially pressure balanced in the discharge regions. 
         [0005]    In the pump arc and the seal arc, pressure has often been required under the vanes to maintain a seal between the vane tip and the cam block inner surface. Such under-vane pressure can combine with pressure in the fluid flow chamber to result in excess radial pressure load and outward centrifugal force pushing the vane against the cam inner surface. This can result in high adhesive wear stresses between the vane tips and the inner surface of the cam block resulting in damage to the vane and to the cam block. However, prior attempts to remove or reduce under-vane pressurization have often resulted in inadequate outward radial load during low speed operation such as at startup, when centrifugal forces are insufficient to drive the vanes radially outward into engagement with the cam block surface. 
         [0006]    U.S. Pat. No. 7,637,724 discloses a vane pump where a vane tip  31  has a radius centered on a centerline offset relative to a leading surface of the vane. This offset provides an imbalance of the fluid pressure forces acting radially on the vane tip to generate a positive contact force that in the pump arc that can supplement the centrifugal force at low operating speeds to reduce or eliminate the need for under-vane pressurization in the pump arc. This is depicted in  FIG. 2A , where low (inlet) pressure acts on vane surfaces  32 ,  33 , and  34 , and high (discharge) pressure acts on vane surfaces  36 ,  38 , and  40 . An offset  41  between a centerline  42  of the radial tip  17  and a leading vane surface  44  provides a surface area differential between surfaces  36  and  40  subject high pressure, such that fluid pressure acting on the larger surface  40  and the smaller surface  36  results in a net outward radial load urging the vane into engagement with the cam block inner surface  22 . In the seal arcs  26 , however, as depicted in  FIG. 2B , the larger surface area  40  under the vane tip  31  is not subjected to fluid pressure with the vane in the retracted position. Low (inlet) pressure acts on surfaces  46  and  48 , high (discharge) pressure acts on surfaces  33 ,  50 , and  52 , and a gradient of pressure acts on surface  53 . In the seal arcs  26 , the offset  41  now provides a surface area differential of the surfaces subjected to high pressure, between the larger area of surface  50  and the smaller area of under-vane surface  33 , resulting in a net radial load inward when the surfaces are subjected to fluid pressure. This necessitates the provision of additional pressurization under the vane in the seal arc, which adds complexity, cost, and weight, in addition to subjecting the under-vane cavities to pressure pulsations. 
       BRIEF DESCRIPTION 
       [0007]    In some aspects of the disclosure, a vane pump comprises a housing including an inlet and an outlet. A cam block is disposed in the housing, and has a continuous inner surface including a pump arc and a seal arc. A rotor is configured to rotate within the cam block, and includes a plurality of radial slots. A plurality of radially-extendable vanes are disposed in the slots and configured to radially extend from the slots as they rotate past the cam block pump arc. The vanes retract as they rotate past the cam block seal arc. Each of the vanes comprises a radial portion in one of the radial slots and a tip portion extending transverse to the radial portion in a direction of rotation of the rotor. The tip portion has an arcuate surface that engages with the cam block inner surface to provide a fluid seal point along the arcuate surface. Each of the plurality of vanes and radial slots are configured to provide a gap between the vane and the radial slot such that the vane has a different angular position relative to the direction of rotation in a radially extended position compared to an angular position in a radially-retracted position. The different angular positions provide different orientation of the arcuate surface of the vane tip portion with respect to the cam body inner surface, thus providing different fluid stop points on the vane tip portion arcuate surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a schematic depiction of a typical balancing vane pump; 
           [0010]      FIGS. 2A and 2B  schematically depict a vane configuration having a tip portion offset to enhance the distribution of radial forces on the vanes; 
           [0011]      FIGS. 3A and 3B  schematically depict a vane configuration; and 
           [0012]      FIG. 4  is a schematic depiction of a vane configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIGS. 3A and 3B , a vane configuration is depicted having a gap between the vane and the radial slot as described herein. The vane in  FIGS. 3A and 3B  differs from that of  FIGS. 2A and 2B  in that it does not require the  FIG. 2  offset  41  to provide outward radial load on the vanes in the pump arcs.  FIG. 2  depicts an offset  41  where a centerline  42  of the radial tip  17  is offset from the leading vane surface  44  toward the direction of rotation to provide the pressure and surface area differential for outward radial load in the pump arcs. It should be noted here that the term “centerline” as used herein refers to an imaginary line extending from the center of the arcuate surface of the radial tip to the arc center point (i.e., the center of an imaginary circle of which the vane tip arcuate surface is a part). The vane in  FIG. 3  has an offset  55  where the offset from the leading vane surface  44  is away from the direction of rotation instead of toward the direction of rotation. The offset  55  (which can be referred to as a negative offset, with the offset  41  of  FIG. 2  referred to as a positive offset) can be configured to provide balanced or biased radial loads during operation in the seal arc as described in more detail below. However, this disclosure can also be used to provide variable seal point configurations for vane designs having different zero offsets, or even with positive offsets such as offset  41  of  FIG. 2 . The disclosure can also be used to provide variable seal point configurations for straight vanes, as well as for balanced vane configurations such as those depicted in  FIGS. 1-4 . 
         [0014]    As shown in  FIG. 3B , during operation in the seal arc, tangential pressure differences provided by high fluid pressure acting on surface  52  urges the vane against the leading slot edge  56  ( FIG. 3B ). The offset  55  provides a surface area differential between the surfaces  33  and  60  subject to high pressure in the seal arc, where high (discharge) pressure acts on surfaces  33 ,  52 , and  60 , low (inlet) pressure acts on surfaces  40 ,  46  and  62 , and a gradient of pressure acts on surface  53 . During operation in the seal arc, fluid pressure acting on the larger surface  33  and the smaller surface  60  can result in a net outward radial load urging the vane into engagement with the cam block inner surface  22 . As mentioned above, however, a negative offset is not required and embodiments are contemplated where a zero offset is utilized to provide balanced radially-acting pressure, or a positive offset similar to or smaller in magnitude than the positive offset depicted in  FIG. 2A . 
         [0015]      FIG. 3A  depicts the vane in operation in the pump arc. The vane slot is defined by leading slot edge  56  and trailing slot edge  58 . The extended vane is shown by a dashed line in a forward position in the slot for illustration and comparison. During operation in the pump arc of the vane pump ( FIG. 3B ), high (discharge pressure acts on vane surfaces  40 ,  64 , and  66 , and low (inlet) pressure acts on surfaces  33 ,  34 , and  68 . Tangential pressure differences provided by high fluid pressure acting on surface  64  urges the vane against the trailing slot edge  58  so that the vane moves into the position represented in  FIG. 3A  by the solid line. This tipping movement of the vane re-positions the point of engagement between the arcuate surface of vane tip  17  and cam body inner surface  22  (i.e., fluid stop point  59 ) forward (in the direction of rotation) along the arcuate surface of the vane tip compared to a position of the fluid stop point at or near the centerline  57  when the vane is in a forward position in the slot such as during operation in the seal arc ( FIG. 3B ). This forward repositioning of the fluid stop point on the arcuate surface of the vane tip  17  provides for a relatively smaller surface  66  exposed to high fluid pressure compared to the surface  40 . During operation in the pump arc, fluid pressure acting on the larger surface  40  and the smaller surface  66  can result in a net outward radial load urging the vane into engagement with the cam block inner surface  22 . 
         [0016]    The gap between the radial portion of the vane  15  and the slot in  FIGS. 3A and 3B  is provided by angling the trailing slot edge  58  away from the direction of rotation. Of course, the configuration represented by  FIGS. 3A and 3B  is only one example of a configuration that can provide such a gap, and variations can be made to either or both of the slot shape, dimensions, and configuration, and the vane radial portion shape, dimensions, and configuration. For example,  FIGS. 3A and 3B  depict a trailing slot edge  58  that is at a fixed angle with respect to the leading slot edge  56 . However, the angle can be varied depending on radial distance from the axis of rotation, or the gap can be provided by an angled surface on the leading slot edge  58  or on the leading or trailing surfaces of the vane radial portion  15 . In some embodiments, a fixed angle between the leading slot edge  56  and the trailing slot edge  58  can vary from 0.1° to 2.0°, depending on the cam profile maximum and minimum radius, so called the vane stroke, and vane tip radius. However, a fixed angle is not required, and the gap between the slot and the vane can be provided by irregular shaped configurations such as step recesses. 
         [0017]    The shape and configuration of the arcuate surface of vane tip  17  can be designed based on parameters such as the radius of cam surfaces, length of the radial vane portion  15 , length of extension of the vane out of the slot, and angle of rotation of the van within the slot, to control the location of the fluid stop position along the arcuate surface of the vane tip  17  and to provide desired levels of radial load urging the vane  12  into engagement with the cam block inner surface  22 . The arcuate surface of the vane tip  17  should be configured to have a greater angle of curvature (e.g., smaller radius of curvature) at the point of engagement with the cam block inner surface, and to provide the desired re-positioning of the point of engagement along the arcuate surface of the vane tip  17  in response to tipping of the vane. The vane and slot can be configured to provide an angular rotational range of the vane of 0.1° to 2.0° in the slot in the extended position, more specifically from 0.3° to 1.5°. The vane and slot can be configured to provide an angular rotational range of 0.1° to 2.0° in the extended position, more specifically from 0.0° to 1.5°. 
         [0018]    The capability of angularly re-positioning the vanes of a vane pump at different cycles of the pump&#39;s rotation allows for an offset in the direction of rotation between a fluid stop point where the vane engages the cam block inner surface in the pump arc compared to a leading surface of the vane&#39;s radial portion, while also allowing for a zero or negative offset in the seal arc, so that a desired level of radial load can be maintained on the vanes throughout the pump&#39;s rotational cycle to maintain a desired level of engagement of the vane with the cam block inner surface. This can avoid the need for complex under-vane pressurization schemes to supplement outward centrifugal force that can be insufficient at low pump speeds such as during startup. 
         [0019]    As mentioned above, under-vane pressurization can contribute to under-vane pressure pulsations, which can cause vane tip wear quickly, cavitation, control valve pressure droop, and the avoidance of such under-vane pressurization can help avoid pressure pulsations. Pressure pulsations can be further reduced by a channel to equalize pressure under the vane and the fluid flow chamber area trailing the vane. As shown in  FIG. 4 , an under-vane chamber  68  is connected by channel  70  to a fluid flow chamber  72  bordered by the surface of the rotor  14 , the cam block inner surface  22 , and the vane depicted in  FIG. 4  and an adjacent trailing vane (not shown). The channel  70  can promote steady under-vane pressure as same as the overvane trailing edge pressure regardless of the vane position in the inlet and discharge ports or in pump arc and the seal arc as shown in  FIG. 3A  surfaces  33  and  68  or  FIG. 3B  surfaces  33  and  60 . 
         [0020]    While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.