Patent Publication Number: US-9903366-B2

Title: Variable displacement vane pump

Description:
TECHNICAL FIELD 
     The present invention relates to a variable displacement vane pump capable of changing a delivery capacity. 
     BACKGROUND 
     Hitherto, the following variable displacement vane pump is known. Specifically, the variable displacement vane pump includes vanes received in slot grooves of a rotor so as to be projectable therefrom and retractable therein. Pump chambers are defined by an inner circumferential surface of a cam ring, an outer circumferential surface of the rotor, and the vanes. Volumes of the pump chambers are changed by a swing of the cam ring. For example, a vane pump described in Japanese Patent Application Laid-open No. 2012-87777 includes a solenoid for applying a biasing force to a control valve for controlling an eccentricity of the cam ring so that a delivery flow rate becomes equal to a desired value. Through the application of a predetermined biasing force using the solenoid, the delivery flow rate is controlled. 
     In the vane pump described in Japanese Patent Application Laid-open No. 2012-87777, however, in a case where a magnitude relationship between a pressure in a first control chamber and a pressure in a second control chamber frequently changes, there is a fear in that a sealing member undesirably moves horizontally to lower durability of an edge portion of the sealing member. Further, if a volume of the first control chamber or the second control chamber is fluctuated due to the swing of a cam ring  8 , the pressure is further fluctuated. Therefore, the phenomenon of the horizontal movement of the sealing member becomes further noticeable. Further, if a leakage occurs from a sealed portion in a state in which an absolute pressure in the first control chamber or the second control chamber is high, cavitation erosion occurs due to air contained in operating oil. In order to avoid the occurrence of cavitation erosion, it is conceivable to select a material having a high hardness and a high strength as a material of the sealing member. If such a material is used, however, when the sealing member moves due to a fluctuation in differential pressure between the first control chamber and the second control chamber, there is a fear in that an adapter ring on which the sealing member is provided may be struck to lower durability of the adapter ring. 
     SUMMARY 
     In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a variable displacement vane pump, including: a pair of sealing grooves formed on a pump-element housing portion so as to have openings opposed to an outer circumferential surface of a cam ring in a radial direction of a rotation axis of a driving shaft, the pair of sealing grooves including a first sealing groove and a second sealing groove formed on an intake port side with respect to the driving shaft so as to be separated away from each other in a circumferential direction; a pair of sealing members including a first sealing member provided in the first sealing groove and a second sealing member provided in the second sealing groove; a pair of pressure chambers formed between the pump-element housing portion and the cam ring in the radial direction so as to be separated by the first sealing member and the second sealing member, the pair of pressure chambers including: a first fluid-pressure chamber formed on a side on which a volume thereof decreases when the cam ring moves to a side on which an eccentricity of the cam ring increases, the first fluid-pressure chamber being configured such that a delivery pressure delivered through a delivery port is introduced; and a second fluid-pressure chamber formed on a side on which a volume thereof increases when the cam ring moves to a side on which the eccentricity of the cam ring increases, the second fluid-pressure chamber being configured such that the delivery pressure delivered through the delivery port is introduced; and a control valve configured to control a pressure in the first fluid-pressure chamber or the second fluid-pressure chamber. 
     Thus, both circumferential sides of each of the first sealing member and the second sealing member are not adjacent to both of the first fluid-pressure chamber and the second fluid-pressure chamber. Therefore, the movement of the first and second sealing members, which is caused along with a change in pressure in the first fluid-pressure chamber or the second fluid-pressure chamber along with a vibration of the cam ring, is suppressed to prevent the sealing members and the sealing grooves from being damaged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view illustrating interior of a vane pump according to a first embodiment of the present invention, as viewed in a direction of a rotation axis. 
         FIG. 2  is a partial enlarged view illustrating an internal configuration of an adapter ring according to the first embodiment. 
         FIG. 3  is a plan view illustrating a pressure plate according to the first embodiment, as viewed from the positive z-axis direction side. 
         FIG. 4  is a view illustrating the front body according to the first embodiment, as viewed from the negative z-axis direction side. 
         FIG. 5  is a schematic view illustrating a relationship between a control section and control-pressure chambers according to the first embodiment. 
         FIG. 6  is an enlarged view of a fourth plane portion according to the first embodiment. 
         FIG. 7  is a front view illustrating a configuration of a cam ring according to a second embodiment of the present invention. 
         FIG. 8  is an enlarged view of a fourth plane portion according to a third embodiment of the present invention. 
         FIG. 9  is a schematic sectional view illustrating a configuration of a variable displacement vane pump according to a fourth embodiment of the present invention. 
         FIG. 10  is a partial enlarged view illustrating an internal configuration of an adapter ring according to a fifth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     &lt;Overview of Vane Pump&gt; 
     An overview of a vane pump  1  according to a first embodiment of the present invention is described. The vane pump  1  is used as a hydraulic-pressure supply source for a hydraulic actuator for an automobile. Specifically, the vane pump  1  is used as a hydraulic-pressure supply source for a belt-type continuously variable transmission (CVT). The vane pump  1  may also be used as a hydraulic-pressure supply source for other hydraulic actuators such as a power steering system. The vane pump  1  is driven by a crankshaft of an internal combustion engine so as to take in and deliver a working fluid. As the hydraulic fluid, operating oil, more specifically, CVT oil is used. The operating oil has a relatively large elastic modulus and has property of greatly changing its pressure in response to a slight change in volume. The vane pump  1  is a variable displacement vane pump that is capable of varying a delivery capacity (fluid amount delivered for one revolution; hereinafter referred to as “pump capacity”). The vane pump  1  includes a pump section  2  and a control section  3  as an integrated unit. The pump section  2  takes in and delivers the working fluid. The control section  3  controls the delivery capacity. 
     &lt;Configuration of Pump Section&gt; 
       FIG. 1  is a partial sectional view illustrating interior of the vane pump  1  as viewed in a direction of a rotation axis. For convenience of description, a three-dimensional Cartesian coordinate system is provided. An x axis and a y axis are set in a radial direction of the vane pump  1 , whereas a z axis is set in the direction of the rotation axis of the vane pump  1 . Specifically, the z axis is provided on a rotation axis O of the vane pump  1 , the x axis is provided in a direction in which a center axis P of a cam ring  8  swings with respect to the rotation axis O, and the y axis is provided in a direction orthogonal to the x axis and the z axis. An upward direction with respect to the drawing sheet of  FIG. 1  is set as a positive z-axis direction. A direction in which the center axis P is away from the rotation axis O (toward a side on which a first confinement region is provided with respect to a second confinement region; see  FIG. 2 ) is set as a positive x-axis direction. A direction toward a delivery region with respect to an intake region is set as a positive y-axis direction. 
     The pump section  2  includes, as main components, a driving shaft  5 , a rotor  6 , a plurality of vanes  7 , a cam ring  8 , an adapter ring  9 , a pressure plate  41 , a rear body  40 , and a front body  42 . The driving shaft  5  is driven by the crankshaft. The rotor  6  is rotationally driven by the driving shaft  5 . The vanes  7  are respectively received in a plurality of slots  61  formed on an outer circumferential surface of the rotor  6  so as to be projectable therefrom and retractable therein. The cam ring  8  is provided so as to surround the rotor  6 . The adapter ring  9  is provided so as to surround the cam ring  8 . The pressure plate  41  is provided on an axial side surface of the cam ring  8  and that of the rotor  6  so as to form a plurality of pump chambers r in cooperation with the cam ring  8 , the rotor  6 , and the vanes  7 . The rear body  40  includes a housing hole  400 . On a bottom portion of the housing hole  400 , the pressure plate  41  is housed. Inside the housing hole  400 , the adapter ring  9 , the cam ring  8 , the rotor  6 , and the vanes  7  are housed. The front body  42  closes the housing hole  400  of the rear body  40  and forms the plurality of pump chambers r in cooperation with the cam ring  8 , the rotor  6 , and the vanes  7 . The rear body  40  and the front body  42  are collectively referred to as “pump housing”. 
     &lt;Configuration of Adapter Ring&gt; 
       FIG. 2  is a partial enlarged view of an internal configuration of the adapter ring  9  according to the first embodiment. The rear body  40  has the housing hole  400  having an approximately cylindrical shape, which extends in the z-axis direction. In the housing hole  400 , the adapter ring  9  having an annular shape is provided. 
     An inner circumferential surface of the adapter ring  9  forms a housing hole  90  having an approximately cylindrical shape, which extends in the z-axis direction. On the positive x-axis side of the housing hole  90 , a first plane portion  91  that is approximately parallel to a yz plane is formed. On the negative x-axis side of the housing hole  90 , a second plane portion  92  that is approximately parallel to the yz plane is formed. On the negative x-axis side, a level-difference portion  920  is formed in approximately the center of the second plane portion  92  in the z-axis direction. 
     On the positive y-axis side of the housing hole  90  and slightly closer to the positive x-axis side with respect to the rotation axis O, a third plane portion  93  that is approximately parallel to the z axis is formed. On the third plane portion  93 , a groove (concave portion  930 ) having a semi-circular shape as viewed in the z-axis direction is formed. On both sides of the concave portion  930 , communication paths  931  and  932 , each radially passing through the adapter ring  9 , are formed. At a position on the third plane portion  93 , which is located on the positive x-axis side with respect to the concave portion  930 , the first communication path  931  has an opening. At a position on the third plane portion  93 , which is located on the negative x-axis side with respect to the concave portion  930 , the second communication path  932  has an opening. On the negative y-axis side of the housing hole  90 , a fourth plane portion  94  that is approximately parallel to an xz plane is formed. On the fourth plane portion  94 , a pair of a first sealing groove  941  and a second sealing groove  942 , each having a rectangular shape as viewed in the z-axis direction, are formed. 
     &lt;Configuration of Cam Ring&gt; 
     Inside the housing hole  90  of the adapter ring  9 , the cam ring  8  having the annular shape is provided so as to be swingable. In other words, the adapter ring  9  is provided so as to surround the cam ring  8 . An inner circumferential surface  80  and an outer circumferential surface  81  of the cam ring  8  are generally circular as viewed in the z-axis direction. A radial width of the cam ring  8  is approximately constant. At a position on the outer circumferential surface  81  of the cam ring  8 , which is located on the positive y-axis side, a groove (concave portion  810 ) having a semi-circular shape as viewed in the z-axis direction is formed. 
     At a position on the outer circumferential surface  81  of the cam ring  8 , which is located on the negative x-axis side, a concave portion  811  having a generally cylindrical shape, which has an axis in the x-axis direction, is formed by drilling to have a predetermined depth. At a position between the concave portion  930  formed on the inner circumferential surface  95  of the adapter ring  9  and the concave portion  810  formed on the outer circumferential surface  81  of the cam ring  8 , a pin  10  (see  FIG. 1 ) extending in the z-axis direction is provided so as to be held in contact with the concave portions  930  and  810  and interposed between the concave portions  930  and  810 . 
     In the concave portion  440  (the first sealing groove  941  and the second sealing groove  942 ) formed on the inner circumferential surface  95  of the adapter ring  9  described above, sealing members  11  are provided. The sealing members  11  include a first sealing member  11   a  and a second sealing member  11   b . The sealing members  11  are held in contact with a portion of the outer circumferential surface  81  of the cam ring  8 , which is located on the negative y-axis side. 
     In the level-difference portion  920  provided on the inner circumferential surface  95  of the adapter ring  9 , one end of a spring  12  as an elastic member is provided. The spring  12  is a coil spring. Into the concave portion  811  formed on the outer circumferential surface  81  of the cam ring  8 , another end of the spring  12  is inserted. The spring  12  is provided in a compressed state and constantly biases the cam ring  8  in the positive x-axis direction against the adapter ring  9 . 
     A dimension of the housing hole  90  of the adapter ring  9  in the x-axis direction, that is, a distance between the first plane portion  91  and the second plane portion  92  is set so as to be larger than a diameter of the outer circumferential surface  81  of the cam ring  8 . The cam ring  8  is supported on the third plane portion  93  with respect to the adapter ring  9  and is provided so as to be swingable in the xy plane about the third plane portion  93  as a fulcrum. The pin  10  suppresses a positional shift (relative rotation) of the cam ring  8  with respect to the adapter ring  9 . 
     The swing of the cam ring  8  is restricted by the contact of the outer circumferential surface  81  of the cam ring  8  with the first plane portion  91  of the adapter ring  9  on the positive x-axis side and by the contact of the outer circumferential surface  81  of the cam ring  8  with the second plane portion  92  of the adapter ring  9  on the negative x-axis side. An eccentricity of the center axis P of the cam ring  8  with respect to the rotation axis O is assumed as δ. At a position at which the outer circumferential surface  81  of the cam ring  8  comes into contact with the second plane portion  92  (minimum eccentricity position), the eccentricity δ has a minimum value. At a position illustrated in  FIG. 2 , at which the outer circumferential surface  81  of the cam ring  8  comes into contact with the first plane portion  91  (maximum eccentricity position), the eccentricity δ has a maximum value. When the cam ring  8  swings, the third plane portion  93  comes into sliding contact with the outer circumferential surface  81  of the cam ring  8 , while the first sealing member  11   a  provided in the first sealing groove  941  and the second sealing member  11   b  provided in the second sealing groove  942  come into sliding contact with the outer circumferential surface  81  of the cam ring  8 . 
     &lt;Configuration of Control-Pressure Chambers&gt; 
     A space between the inner circumferential surface  95  of the adapter ring  9  and the outer circumferential surface  81  of the cam ring  8  is sealed by the pressure plate  41  on the negative z-axis side and by the front body  42  on the positive z-axis side. At the same time, the above-mentioned space is partitioned into two control-pressure chambers R 1  and R 2  in a liquid-tight fashion by the third plane portion  93 , the first sealing member  11   a , and the second sealing member  11   b.    
     The first control-pressure chamber R 1  is formed on the positive x-axis side, whereas the second control-pressure chamber R 2  is formed on the negative x-axis side. The first communication path  931  has the opening oriented toward the first control-pressure chamber R 1 , whereas the second communication path  932  has the opening oriented toward the second control-pressure chamber R 2 . A predetermined gap is ensured between the outer circumferential surface  81  of the cam ring  8  and the inner circumferential surface  95  of the adapter ring  9  when the outer circumferential surface  81  of the cam ring  8  is in the above-mentioned restriction position. Therefore, a volume of each of the first control-pressure chamber R 1  and the second control-pressure chamber R 2  is a predetermined volume or larger and does not become zero. 
     &lt;Configuration of Rotor&gt; 
     The driving shaft  5  is rotatably supported by a body (the rear body  40 , the pressure plate  41 , and the front body  42 ). The driving shaft  5  is coupled to the crankshaft of the internal combustion engine through an intermediation of a chain so as to rotate in synchronization with the rotation of the crankshaft. The rotor  6  is fixed (spline-coupled) coaxially onto an outer circumferential surface of the driving shaft  5 . The rotor  6  is generally columnar and is provided on the inner circumferential side of the cam ring  8 . In other words, the cam ring  8  is provided so as to surround the rotor  6 . In a space surrounded by an outer circumferential surface  60  of the rotor  6 , the inner circumferential surface  80  of the cam ring  8 , the pressure plate  41 , and the front body  42 , an annular chamber R 3  is formed. The rotor  6  rotates with the driving shaft  5  about the rotation axis O in a clockwise direction in  FIG. 2 . 
     The plurality of grooves (slots  61 ) are formed radially on the rotor  6 . Each of the slots  61  is formed linearly so as to extend in the radial direction of the rotor  6  (hereinafter referred to as “rotor radial direction”) from the outer circumferential surface  60  of the rotor  6  toward the rotation axis O by a predetermined depth, as viewed in the z-axis direction. The slots  61  are formed over the entire range of the rotor  6  in the z-axis direction. The slots  61  are formed at eleven positions that equally divide the rotor  6  in a circumferential direction. 
     The vanes  7  are plate members (blades), each having a generally rectangular shape. A plurality of (eleven) vanes  7  are provided. Each one of the vanes  7  is provided so as to be projectable from each of the slots  61 . A distal end portion (vane distal end portion  70 ) of each of the vanes  7  on the rotor outer-diameter side (on the side away from the rotation axis O) is formed so as to have a gently curved surface corresponding to the inner circumferential surface  80  of the cam ring  8 . The number of slots  61  and the number of vanes  7  are not limited to eleven. 
     An end portion (slot proximal end portion  610 ) of each of the slots  61  on the rotor inner-diameter side (on the side closer to the rotation axis O) is formed so as to have a generally cylindrical shape. The slot proximal end portion  610  is generally circular with a larger diameter than a width of a slot main body portion  611  in the rotor circumferential direction, as viewed in the z-axis direction. The slot proximal end portion  610  is not particularly required to be formed so as to have the cylindrical shape, and may be formed so as to have, for example, a groove-like shape similar to that of the slot main body portion  611 . At a position between the slot proximal end portions  610  and rotor inner-diameter side end portions (vane proximal end portions  71 ) of the vanes  7  received in the slots  61 , back-pressure chambers br (pressure-receiving portions) of the vanes  7  are formed. 
     At a position on the outer circumferential surface  60  of the rotor  6 , which corresponds to each of the vanes  7 , a projecting portion  62  having a generally trapezoidal shape, as viewed in the z-axis direction is provided. The projecting portions  62  are formed so as to project from the outer circumferential surface  60  of the rotor  6  to a predetermined height over the entire range of the rotor  6  in the z-axis direction. At an approximately central position of the projecting portion  62 , an opening portion of each of the slots  61  is formed. A length of each of the slots  61  in the rotor radial direction (including the projecting portion  62  and the slot proximal end portion  610 ) is approximately the same as a length of each of the vanes  7  in the rotor radial direction. 
     By providing the projecting portions  62 , a predetermined length or larger of the slots  61  in the rotor radial direction is ensured. Therefore, for example, even if one of the vanes  7  projects from the corresponding slot  61  by a maximum amount in the first confinement region described later, the retention of the vane  7  in the slot  61  is ensured. In other words, the retention of the vanes  7  is improved by the projecting portions  62 , while a thickness other than that of the projecting portions  62  is eliminated on the outer circumferential surface  60  of the rotor  6 . Therefore, the volumes of the pump chambers r are increased by the eliminated thickness so as to improve pump efficiency. In addition, the whole rotor  6  is reduced in weight so as to reduce a power loss. 
     The annular chamber R 3  is partitioned into the plurality of (eleven) pump chambers (volume chambers) r by the plurality of vanes  7 . A distance between the adjacent vanes  7  (between side surfaces of the two vanes  7 ) in a rotating direction of the rotor  6  (hereinafter referred to simply as “rotating direction”) is hereinafter referred to as “one pitch”. A width of one of the pump chambers r in the rotating direction is one pitch. A length of one pitch is not required to be uniform. 
     In a state in which the center axis P of the cam ring  8  is eccentrically located (on the positive x-axis side) with respect to the rotation axis O, a distance between the outer circumferential surface  60  of the rotor  6  and the inner circumferential surface  80  of the cam ring  8  in the rotor radial direction (radial dimension of each of the pump chambers r) becomes larger as a position at which the distance is measured moves in the positive x-axis direction. In accordance with the change in distance, the vanes  7  project from the slots  61  so as to form the pump chambers r. At the same time, the volumes of the pump chambers r on the positive x-axis side become larger than those on the negative x-axis side. By a difference between the volumes of the pump chambers r, on the negative y-axis side of the x axis as a boundary, the volume of each of the pump chambers r becomes larger as the position in the pump chamber r becomes closer to the x axis in the positive x-axis direction that is a positive rotating direction of the rotor  6  (clockwise direction in  FIG. 2 ). On the other hand, on the positive y-axis side of the x axis as the boundary, the volume of each of the pump chambers r becomes smaller as the position in the pump chamber r becomes closer to the x axis in the negative x-axis direction that is the positive rotating direction of the rotor  6 . 
     &lt;Configuration of Pressure Plate&gt; 
       FIG. 3  is a plan view illustrating the pressure plate  41  according to the first embodiment as viewed from the positive z-axis direction. An intake port  43 , a delivery port  44 , an intake-side back-pressure port  45 , a delivery-side back-pressure port  46 , a pin fixing hole  47 , and a through hole  48  are formed in the pressure plate  41 . The pin  10  is inserted into the pin fixing hole  47  so as to be fixed therein. The driving shaft  5  is inserted into the through hole  48  so as to be provided rotatably therein. 
     &lt;Configuration of Intake Port&gt; 
     The intake port  43  is a portion serving as an inlet for introducing the operating oil into the pump chambers r located on the intake side from exterior. The intake port  43  is formed in a portion on the negative y-axis side, on which the volumes of the pump chambers r increase in accordance with the rotation of the rotor  6 . The intake port  43  includes an intake-side arc-shaped groove  430  and intake holes  431  and  432 . The intake-side arc-shaped groove  430  is formed on a surface  410  of the pressure plate  41  on the positive z-axis side and is a groove into which a hydraulic pressure on the pump intake side is introduced. The intake-side arc-shaped groove  430  is formed so as to have a generally arc-like shape about the rotation axis O along the arrangement of the pump chambers r on the intake side. 
     In an angular range corresponding to the intake-side arc-shaped groove  430 , specifically, a range of an angle α corresponding to about 4.5 pitches, which is formed between a starting point A of the intake-side arc-shaped groove  430  located on the negative x-axis side with respect to the rotation axis O and an end point B located on the positive x-axis side with respect to the rotation axis O, an intake region of the vane pump  1  is provided. 
     A terminal end portion  436  of the intake-side arc-shaped groove  430  is formed so as to have a generally semi-circular arc-like shape that is convex in the positive rotating direction. A starting end portion  435  of the intake-side arc-shaped groove  430  includes a main-body starting end portion  433  and a notch  434 . The main-body starting end portion  433  is formed so as to have a generally semi-circular arc-like shape that is convex in a negative rotating direction (counterclockwise direction in  FIG. 2 ). The notch  434  is formed continuously with the main-body starting end portion  433 . The notch  434  is formed so as to have a length equal to about 0.5 pitches so as to extend from the main-body starting end portion  433  in the negative rotating direction. A distal end portion of the notch  434  coincides with the starting point A. A width of the intake-side arc-shaped groove  430  in the rotor radial direction is provided so as to be approximately equal over the entire range in the positive rotating direction and is approximately equal to a width of the annular chamber R 3  in the rotor radial direction when the cam ring  8  is located in the minimum eccentricity position (see  FIG. 2 ). 
     An edge  437  of the intake-side arc-shaped groove  430  on the rotor inner-diameter side is located slightly away from the outer circumferential surface  60  of the rotor  6  (except for the projecting portions  62 ) to the rotor outer-diameter side. An edge  438  of the intake-side arc-shaped groove  430  on the rotor outer-diameter side is located slightly away from the inner circumferential surface  80  of the cam ring  8  to the rotor outer-diameter side when the cam ring  8  is located in the minimum eccentricity position. On a terminal end side of the edge  438 , the edge  438  is located slightly away from the inner circumferential surface  80  of the cam ring  8  to the rotor outer-diameter side when the cam ring  8  is located in the maximum eccentricity position. Each of the pump chambers r on the intake side overlaps the intake-side arc-shaped groove  430  as viewed in the z-axis direction and is held in communication to the intake-side arc-shaped groove  430  regardless of the eccentric position of the cam ring  8 . 
     In approximately the center of the intake-side arc-shaped groove  430  in the rotating direction, the intake hole  431  is formed. The intake hole  431  has a generally elliptical shape as viewed in the z-axis direction. The intake hole  431  has a smaller width in the rotor radial direction than that of the intake-side arc-shaped groove  430  and has a length in the rotating direction equal to about one pitch. The intake hole  431  passes through the pressure plate  41  in the z-axis direction and is formed at a position overlapping the y axis. 
     In the intake-side arc-shaped groove  430 , the intake hole  432  is formed adjacent to the intake hole  431  in the negative rotating direction (on the side closer to the starting point A). The intake hole  432  has the same shape as that of the intake hole  431  and passes through the pressure plate  41  in the z-axis direction. The main-body starting end portion  433 , a portion between the intake holes  432  and  431 , and the terminal end portion  436  of the intake-side arc-shaped groove  430  have a depth (in the z-axis direction) slightly smaller than 20% of the thickness of the pressure plate  41  (in the z-axis direction). 
     The notch  434  is formed so as to have a generally acute-angled triangular shape with a width in the rotor radial direction gradually increasing in the positive rotating direction as viewed in the z-axis direction. A maximum value of the width of the notch  434  in the rotor radial direction is set smaller than the width of the intake-side arc-shaped groove  430 . A depth of the notch  434  (in the z-axis direction) gradually increases from 0 to several % of the thickness of the pressure plate  41  as the position in the notch  434  becomes closer to the main-body starting end portion  433  in the positive rotating direction. Specifically, the sectional area of a flow path of the notch  434  is smaller than that of a main body portion of the intake-side arc-shaped groove  430 . The notch  434  forms a narrowed portion having a gradually increasing sectional area of the flow path in the positive rotating direction. A communication path  439  extending in parallel to the y-axis direction is formed in approximately the center of the intake-side arc-shaped groove  430  so as to be located slightly away from the y axis in the positive rotating direction. The communication path  439  is a groove that is open oriented toward the pressure plate  41  side, which is opposed to the cam ring  8 . The communication path  439  is formed so as to communicate a low-pressure chamber R 4  connected to a low-pressure chamber path  943  formed on the inner circumferential surface  95  of the adapter ring  9  to the intake port  43 . The pressure plate  41  is formed of a sintered material by die molding. The communication path  439  is also formed by using a molding die for the pressure plate  41 . In other words, the communication path  439  is formed by using the same molding die as that for the pressure plate  41 . Therefore, a processing step for the communication path  439  can be omitted. 
     &lt;Configuration of Delivery Port&gt; 
     The delivery port  44  is a portion serving as an outlet for delivering the operating oil from the pump chambers r located on the delivery side to the exterior. The delivery port  44  is formed in a portion on the positive y-axis side, in which the volumes of the pump chambers r decrease in accordance with the rotation of the rotor  6 . The delivery port  44  includes a delivery-side arc-shaped groove  440  and delivery holes  441  and  442 . The delivery-side arc-shaped groove  440  is formed on the surface  410  of the pressure plate  41  and is a groove into which the hydraulic pressure on the pump delivery side is introduced. The delivery-side arc-shaped groove  440  is formed so as to have a generally arc-like shape about the rotation shaft O along the arrangement of the pump chambers r on the delivery side. 
     In an angular range corresponding to the delivery-side arc-shaped groove  440 , specifically, a range of an angle formed between a starting point C of the delivery-side arc-shaped groove  440  located on the positive x-axis side with respect to the rotation axis O and an end point D located on the negative x-axis side with respect to the rotation axis O, a delivery region of the vane pump  1  is provided. The starting point C and the end point D of the delivery-side arc-shaped groove  440  is located away from the x-axis by a predetermined angle in the positive y-axis side. 
     A width of the delivery-side arc-shaped groove  440  in the rotor radial direction is set approximately equal over the entire range in the rotating direction and is slightly smaller than the width of the intake-side arc-shaped groove  430  in the rotor radial direction. An edge  446  of the delivery-side arc-shaped groove  440  on the rotor inner-diameter side (except for the projecting portions  62 ) is located slightly away from the outer circumferential surface  60  to the rotor outer-diameter side. An edge  447  of the delivery-side arc-shaped groove  440  on the rotor outer-diameter side approximately overlaps the inner circumferential surface  80  of the cam ring  8  located in the minimum eccentricity position. The pump chambers r located on the delivery side overlap the delivery-side arc-shaped groove  440  as viewed in the z-axis direction and are held in communication to the delivery-side arc-shaped groove  440  regardless of the eccentric position of the cam ring  8 . 
     In a terminal end portion  444  of the delivery-side arc-shaped groove  440 , which is located on the positive rotating direction side, the delivery hole  442  is formed. The delivery hole  442  has a generally elliptical shape as viewed in the z-axis direction. A width of the delivery hole  442  in the rotor radial direction is approximately equal to that of the delivery-side arc-shaped groove  440 , and a length of the delivery hole  442  in the positive rotating direction is slightly longer than about one pitch. The delivery hole  442  is formed so as to pass through the pressure plate  41  in the z-axis direction. An edge of the delivery hole  442 , which is located on the positive rotating direction side, is formed so as to have a generally semi-circular shape that is convex in the positive rotating direction, and coincides with an edge of the terminal end portion  444 , which is located on the positive rotating direction side. 
     At a position in the delivery-side arc-shaped groove  440 , which is closer to the negative rotating direction and is opposed to the intake hole  432  on the intake side through the rotation axis O therebetween, the delivery hole  441  is formed. The delivery hole  441  has the same shape as that of the delivery hole  442 . The delivery hole  441  has a length of about one pitch in the positive rotating direction and is formed so as to pass through the pressure plate  41  in the z-axis direction. A starting end portion  443  of the delivery-side arc-shaped groove  440  is formed so as to extend from the starting point C to an edge  445  of the delivery hole  441 , which is located on the side closer to the negative rotating direction. The edge  445  is formed so as to have a generally semi-circular shape that is convex in the negative rotating direction, as viewed in the z-axis direction. The end point D of the delivery-side arc-shaped groove  440  is located at the position about five pitches away from the starting point C in the positive rotating direction. A distal end of the starting end portion  443 , which is opposed to the end point B of the intake-side arc-shaped groove  430  in the rotating direction, is formed so as to have a generally rectangular shape as viewed in the z-axis direction and has an edge extending in the rotor radial direction. 
     A depth of a main body portion  484  (in the z-axis direction) provided between the delivery holes  441  and  442  formed in the delivery-side arc-shaped groove  440  is about 25% of the thickness of the pressure plate  41  (in the z-axis direction). A groove depth is smaller in the starting end portion  443  than in the main body portion  484 . An inclination is provided from the starting point C to the edge  445 . The groove depth at the starting point C is about 0 and gradually increases toward the edge  445 . The groove depth becomes slightly smaller than 10% of the thickness of the pressure plate  41  at the edge  445 . 
     The starting end portion  443  is provided to have the following shape. Specifically, a sectional area of a flow path of the starting end portion  443  is smaller than that of the main body portion  484 . A depth (in the z-axis direction) of the starting end portion  443  is formed so as to gradually increase in the positive rotating direction. Thus, the starting end portion  443  forms a narrowed portion having the sectional area of the flow path, which gradually increases in the positive rotating direction. No groove is formed on a portion of the surface  410 , which is located between the end point B of the intake-side arc-shaped groove  430  and the starting point C of the delivery-side arc-shaped groove  440 . In an angular range corresponding to the above-mentioned portion, specifically, in a range of an angle β formed between the end point B and the starting point C with respect to the rotation axis O, the first confinement region of the vane pump  1  is provided. The angular range of the first confinement region corresponds to about one pitch. Similarly, no groove is formed in a portion of the surface  410  between the end point D of the delivery-side arc-shaped groove  440  and the starting point A of the intake-side arc-shaped groove  430 . In an angular range corresponding to the above-mentioned portion, specifically, in a range of the angle β formed between the end point D and the starting point A with respect to the rotation axis O, the second confinement region of the vane pump  1  is provided. The angular range of the second confinement region corresponds to about one pitch. 
     &lt;Confinement Regions&gt; 
     The first confinement region and the second confinement region are portions for confining the operating oil in the pump chambers r that are present in the first and second confinement regions so as to prevent the delivery-side arc-shaped groove  440  and the intake-side arc-shaped groove  430  from being brought into communication to each other. The first confinement region and the second confinement region are provided over the x axis (see  FIG. 3 ). 
     &lt;Back-Pressure Ports&gt; 
     The back-pressure ports  45  and  46 , which are held in communication to the bases of the vanes  7  (the back-pressure chambers br and the slot proximal end portions  610 ), are formed through the pressure plate  41  so as to be formed separately for the intake side and the delivery side (see  FIG. 3 ). 
     &lt;Intake-Side Back-Pressure Port&gt; (See  FIG. 3 ) 
     The intake-side back-pressure port  45  is a port for allowing communication between the back-pressure chambers br of the plurality of vanes  7 , which are located in the intake region, most of the first confinement region, and a part of the second confinement region, and the delivery port  44 . The vanes  7  “located in the intake region” means that the vane distal end portions  70  of the vanes  7  overlap the intake port  43  (intake-side arc-shaped groove  430 ), as viewed in the z-axis direction. The intake-side back-pressure port  45  includes an intake-side back-pressure arc-shaped groove  450  and communication holes  451   a  and  451   b.    
     The intake-side back-pressure groove  450  is formed on the surface  410  of the pressure plate  41  and is a groove into which the hydraulic pressure on the pump delivery side is introduced. The intake-side back-pressure arc-shaped groove  450  is formed so as to have a generally arc-like shape about the rotation axis O along the arrangement of the back-pressure chambers br of the vanes  7  (the slot proximal end portions  610  of the rotor  6 ). The intake-side back-pressure arc-shaped groove  450  is formed over a larger range in the rotating direction than that of the intake-side arc-shaped groove  430 . 
     A starting point a of the intake-side back-pressure arc-shaped groove  450  is located slightly away from the starting point A of the intake-side arc-shaped groove  430  (notch  434 ) in the negative rotating direction. An end point b of the intake-side back-pressure arc-shaped groove  450  is located away from the end portion B of the intake-side arc-shaped groove  430  in the positive rotating direction. A dimension of the intake-side back-pressure arc-shaped groove  450  in the rotor radial direction (groove width) is set approximately equal over the entire range in the rotating direction and is approximately equal to a dimension of each of the slot proximal end portions  610  in the rotor radial direction. 
     An edge  454  of the intake-side back-pressure arc-shaped groove  450  on the rotor inner-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor inner-diameter side to the rotor inner-diameter side. An edge  455  of the intake-side back-pressure arc-shaped groove  450  on the rotor outer-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor outer-diameter side to the rotor inner-diameter side. The intake-side back-pressure arc-shaped groove  450  is formed at a position in the rotor radial direction at which most of the intake-side back-pressure arc-shaped groove  450  overlaps the slot proximal end portions  610  (back-pressure chambers br) as viewed in the z-axis direction, regardless of the eccentric position of the cam ring  8 . When the intake-side back-pressure arc-shaped groove  450  overlaps the slot proximal end portions  610  (back-pressure chambers br), the intake-side back-pressure arc-shaped groove  450  is brought into communication to the slot proximal end portions  610 . 
     The communication hole  451   a  is formed in a portion of the intake-side back-pressure arc-shaped groove  450 , which portion is located closer to the negative rotating direction side including the starting point a. The communication hole  451   a  has a generally elliptical shape as viewed in the z-axis direction and has a width in the rotor radial direction, which is approximately equal to that of the intake-side back-pressure arc-shaped groove  450 . Similarly, the communication hole  451   b  is formed in a portion of the intake-side back-pressure arc-shaped groove  450 , which portion is located closer the positive rotating direction side including the end point b. The communication holes  451   a  and  451   b  are formed so as to pass through the pressure plate  41  in the z-axis direction. The communication holes  451   a  and  451   b  are held in communication to the delivery holes  441  and  442  formed in the delivery-side arc-shaped groove  440  through a high-pressure chamber of the rear body  40 . 
     &lt;Delivery-Side Back-Pressure Port&gt; (See  FIG. 3 ) 
     The delivery-side back-pressure port  46  is a port for allowing communication between the back-pressure chambers br of the plurality of vanes  7 , which are located in most of the delivery region, and the delivery port  44 . The vanes  7  “located in the delivery region” means that the vane distal end portions  70  of the vanes  7  overlap the delivery port  44  (delivery-side arc-shaped groove  440 ), as viewed in the z-axis direction. The delivery-side back-pressure port  46  includes a delivery-side back-pressure arc-shaped groove  460  and a communication hole  461 . 
     The delivery-side back-pressure arc-shaped groove  460  is formed on the surface  410  of the pressure plate  41  and is a groove to which the hydraulic pressure on the pump delivery side is introduced. The delivery-side back-pressure arc-shaped groove  460  is formed so as to have a generally arc-like shape about the rotation axis O along the arrangement of the back-pressure chambers br of the vanes  7  (slot proximal end portions  610 ). The delivery-side back-pressure arc-shaped groove  460  is formed over an angular range corresponding to about seven pitches (larger range than that of the delivery-side arc-shaped groove  440 ). 
     A starting point c of the delivery-side back-pressure arc-shaped groove  460  is located on the positive rotating direction side with respect to the starting point C of the delivery-side arc-shaped groove  440 . 
     An end point d of the delivery-side back-pressure arc-shaped groove  460  is located on the negative rotation direction side with respect to the end point D of the delivery-side arc-shaped groove  440 . A dimension (groove width) of the delivery-side back-pressure arc-shaped groove  460  in the rotor radial direction is set approximately equal over the entire range in the rotating direction, and is slightly smaller than that of the delivery-side arc-shaped groove  440  and is approximately equal to the dimension of the slot proximal end portions  610  in the rotor radial direction. 
     An edge  464  of the delivery-side back-pressure arc-shaped groove  460  on the rotor inner-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor inner-diameter side to the rotor outer-diameter side. An edge  465  of the delivery-side back-pressure arc-shaped groove  460  on the rotor outer-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor outer-diameter side to the rotor inner-diameter side. The delivery-side back-pressure arc-shaped groove  460  is formed at a position in the rotor radial direction at which most of the delivery-side back-pressure arc-shaped groove  460  overlaps the slot proximal end portions  610  (back-pressure chambers br) as viewed in the z-axis direction, regardless of the eccentric position of the cam ring  8 . When the delivery-side back-pressure arc-shaped groove  460  overlaps the slot proximal end portions  610  (back-pressure chambers br), the delivery-side back-pressure arc-shaped groove  460  is brought into communication to the slot proximal end portions  610 . 
     At a position at which the delivery-side back-pressure arc-shaped groove  460  intersects the y axis, the communication hole  461  is formed. A diameter of the communication hole  461  is approximately equal to the width of the delivery-side back-pressure arc-shaped groove  460  in the rotor radial direction. The communication hole  461  is formed so as to pass through the pressure plate  41  in the z-axis direction into a generally cylindrical shape. The communication hole  461  has an opening on the surface of the pressure plate  41  on the negative z-axis side and is held in communication to the delivery hole  441  of the delivery port  44  (delivery-side arc-shaped groove  440 ) through the high-pressure chamber of the rear body  40  described later. 
     &lt;Details of Front Body&gt; 
       FIG. 4  is a view illustrating the front body  42  as viewed from the negative z-axis direction side. The front body  42  includes a plate surface  50  projecting in the negative z-axis direction. An intake port  51 , a delivery port  52 , an intake-side back-pressure port  53 , a delivery-side back-pressure port  54 , a pin fixing hole  55 , and a through hole  56  are formed through the plate surface  50 . The pin  10  is inserted into the pin fixing hole  55  so as to be fixed therein. The driving shaft  5  is inserted into the through hole  56  so as to be provided rotatably. The intake port  51 , the delivery port  52 , the intake-side back-pressure port  53 , and the delivery-side back-pressure port  54  are formed at positions respectively corresponding to the intake port  43 , the delivery port  44 , the intake-side back-pressure port  45 , and the delivery-side back-pressure port  46  formed through the pressure plate  41 . 
     &lt;Configuration of Intake Port&gt; (See  FIG. 4 ) 
     The intake port  51  is held in communication to the pump chambers r on the intake side. The intake port  51  is formed in a portion on the negative y-axis side, in which the volumes of the pump chambers r increase in accordance with the rotation of the rotor  6 . The intake port  51  includes an intake-side arc-shaped groove  510  and an intake hole  511 . The intake-side arc-shaped groove  510  is formed so as to have a generally arc-like shape about the rotation axis O along the arrangement of the pump chambers r on the intake side. 
     A starting end portion  516  of the intake-side arc-shaped groove  510  is formed so as to have a generally semi-circular arc-like shape that is convex in the negative rotating direction. A terminal end portion  515  of the intake-side arc-shaped groove  510  is formed so as to have a generally semi-circular arc-like shape that is convex in the positive rotating direction. A width of the intake-side arc-shaped groove  510  in the rotor radial direction is set approximately equal over the entire range in the rotating direction and is approximately equal to the width of the annular chamber R 3  in the rotor radial direction when the cam ring  8  is located in the minimum eccentricity position. 
     An edge  517  of the intake-side arc-shaped groove  510  on the rotor inner-diameter side is located slightly away from the outer circumferential surface  60  of the rotor  6  (except for the projecting portions  62 ) to the rotor outer-diameter side. An edge  518  of the intake-side arc-shaped groove  510  on the rotor outer-diameter side is located slightly away from the inner circumferential surface  80  of the cam ring  8  to the rotor outer-diameter side when the cam ring  8  is in the minimum eccentricity position, and on the terminal end side thereof, the edge  518  is located slightly away from the inner circumferential surface  80  of the cam ring  8  to the rotor outer-diameter side when the cam ring  8  is in the maximum eccentricity position. The pump chambers r located on the intake side overlap the intake-side arc-shaped groove  510  as viewed in the z-axis direction and are held in communication to the intake-side arc-shaped groove  510  regardless of the eccentric position of the cam ring  8 . 
     The intake hole  511  is formed in the intake-side arc-shaped groove  510  so as to extend from the starting end portion to a point short of the terminal end portion (the intake hole  511  includes a semi-circle portion). A width of the intake hole  511  in the rotor radial direction is approximately equal to that of the intake-side arc-shaped groove  510 . The intake hole  511  is connected to an intake path  64  formed in the front body  42 . Through the intake path  64 , the operating oil is supplied. 
     &lt;Configuration of Delivery Port&gt; (See  FIG. 4 ) 
     The delivery port  52  is formed in a portion on the positive y-axis side, in which the volumes of the pump chambers r decrease in accordance with the rotation of the rotor  6 . The delivery port  52  includes a delivery-side arc-shaped groove  520  having a notch  521 . The delivery-side arc-shaped groove  520  is formed so as to have a generally arc-like shape about the rotation shaft O along the arrangement of the pump chambers r on the delivery side. 
     A width of the delivery-side arc-shaped groove  520  in the rotor radial direction is set approximately equal over its entire range in the rotating direction and is slightly smaller than that of the intake-side arc-shaped groove  510  in the rotor radial direction. An edge  526  of the delivery-side arc-shaped groove  520  on the rotor inner-diameter side is located slightly away from the outer circumferential surface  60  of the rotor  6  (except for the projecting portions  62 ) to the rotor outer-diameter side. An edge  527  of the delivery-side arc-shaped groove  520  on the rotor outer-diameter side approximately overlaps the inner circumferential surface  80  of the cam ring  8  when the cam ring  8  is in the minimum eccentricity position. The pump chambers r located on the delivery side overlap the delivery-side arc-shaped groove  520  as viewed in the z-axis direction and are held in communication to the delivery-side arc-shaped groove  520  regardless of the eccentric position of the cam ring  8 . 
     The notch  521  is formed in an end portion of the delivery-side arc-shaped groove  520 , which is located closer to the negative rotating direction side. The notch  521  is formed so as to have a smaller depth than that of the delivery-side arc-shaped groove  520 . 
     An end portion of the delivery-side arc-shaped groove  520 , which is closer to the positive rotating direction side, is formed so as to have a generally semi-circular shape that is convex in the positive rotating direction. The boundary portion between the delivery-side arc-shaped groove  520  and the notch  521 , which is closer to the negative rotating direction side, is formed so as to have a generally semi-circular shape that is convex in the negative rotating direction. 
     &lt;Configuration of Intake-Side Back-Pressure Port&gt; (See  FIG. 4 ) 
     The intake-side back-pressure port  53  and the delivery-side back-pressure port  54 , which are held in communication to the bases of the vanes  7  (the back-pressure chambers br and the slot proximal end portions  610 ), are formed through the plate surface  50  separately on the intake side and the delivery side. The intake-side back-pressure port  53  is a port for allowing communication between the back-pressure chambers br of the plurality of vanes  7  located in most of the intake region and the delivery port  52 . The intake-side back-pressure port  53  includes an intake-side back-pressure arc-shaped groove  530 . 
     The intake-side back-pressure arc-shaped groove  530  is formed so as to have a generally arc-like shape about the rotation axis O along the arrangement of the back-pressure chambers br of the vanes  7  (the slot proximal end portions  610  of the rotor  6 ). The intake-side back-pressure arc-shaped groove  530  is formed over a larger range in the rotating direction than that of the intake-side arc-shaped groove  510 . 
     A dimension of the intake-side back-pressure arc-shaped groove  530  in the rotor radial direction (groove width) is set approximately equal over the entire range in the rotating direction and is approximately equal to that of the intake-side arc-shaped groove  510  and the dimension of each of the slot proximal end portions  610  in the rotor radial direction. 
     An edge  534  of the intake-side back-pressure arc-shaped groove  530  on the rotor inner-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor inner-diameter side to the rotor inner-diameter side. An edge  535  of the intake-side back-pressure arc-shaped groove  530  on the rotor outer-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor outer-diameter side to the rotor inner-diameter side. The intake-side back-pressure arc-shaped groove  530  is formed at a position in the rotor radial direction at which most of the intake-side back-pressure arc-shaped groove  530  overlaps the slot proximal end portions  610  (back-pressure chambers br) as viewed in the z-axis direction, regardless of the eccentric position of the cam ring  8 . When the intake-side back-pressure arc-shaped groove  530  overlaps the slot proximal end portions  610  (back-pressure chambers br), the intake-side back-pressure arc-shaped groove  530  is brought into communication to the slot proximal end portions  610 . Orifice grooves  541  are formed at a starting end and a terminal end of the intake-side back-pressure arc-shaped groove  530  so as to be connected to a starting end and a terminal end of a delivery-side back-pressure arc-shaped groove  540  described later. 
     &lt;Configuration of Delivery-Side Back-Pressure Port&gt; (See  FIG. 4 ) 
     The delivery-side back-pressure port  54  includes the delivery-side back-pressure arc-shaped groove  540 . The delivery-side back-pressure arc-shaped groove  540  is formed so as to have a generally arc-like shape about the rotation axis O along the arrangement of the back-pressure chambers br of the vanes  7  (slot proximal end portions  610 ). The delivery-side back-pressure arc-shaped groove  540  is formed in a range smaller than that of a combination of the delivery-side arc-shaped groove  520  and the notch  521  in the rotating direction. A dimension (groove width) of the delivery-side back-pressure arc-shaped groove  540  in the rotor radial direction is set approximately equal over its entire range in the rotating direction, and is slightly smaller than that of the delivery-side arc-shaped groove  520  and slightly smaller than the dimension of each of the slot proximal end portions  610  in the rotor radial direction. 
     An edge  544  of the delivery-side back-pressure arc-shaped groove  540  on the rotor inner-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor inner-diameter side to the rotor outer-diameter side. An edge  545  of the delivery-side back-pressure arc-shaped groove  540  on the rotor outer-diameter side is located slightly away from the edges of the slot proximal end portions  610  on the rotor outer-diameter side to the rotor inner-diameter side. The delivery-side back-pressure arc-shaped groove  540  is formed at a position in the rotor radial direction at which most of the delivery-side back-pressure arc-shaped groove  540  overlaps the slot proximal end portions  610  (back-pressure chambers br) as viewed in the z-axis direction, regardless of the eccentric position of the cam ring  8 . When the delivery-side back-pressure arc-shaped groove  540  overlaps the slot proximal end portions  610  (back-pressure chambers br), the delivery-side back-pressure arc-shaped groove  540  is brought into communication to the slot proximal end portions  610 . 
     End portions of the delivery-side back-pressure arc-shaped groove  540 , which are respectively closer to the positive rotating direction side and the negative rotating direction side, are formed so as to have generally semi-circular shapes that are convex in the positive rotating direction and the negative rotating direction, respectively. 
     &lt;Lubricating-Oil Grooves&gt; (See  FIG. 4 ) 
     A lubricating-oil groove  57  held in communication to a portion in the second confinement region, which portion is on the outer circumferential side with respect to the intake port  51  and the delivery port  52 , is formed at an end of the delivery-side arc-shaped groove  520  of the delivery port  52  closer to the negative rotating direction side. Further, a lubricating-oil groove  58  held in communication to a portion in the first confinement region, which portion is on the outer circumferential side with respect to the intake port  51  and the delivery port  52 , is formed at a portion of the delivery-side arc-shaped groove  52  closer to the positive rotating direction. Through the lubricating-oil grooves  57  and  58 , the operating oil is supplied as lubricating oil to a portion between the swinging cam ring  8  and the plate surface  50 . 
     On the outer circumferential side of the intake port  51 , a lubricating-oil groove  59  is formed. Through the lubricating-oil groove  59 , the operating oil in the first control-pressure chamber R 1  is supplied as lubricating oil from a lubricating-oil intake hole  591  to the portion between the swinging cam ring  8  and the plate surface  50 . 
     &lt;Details of Control Section&gt; 
     Returning to  FIG. 1 , the control section  3  is provided to the rear body  40 . The control section  3  includes a control valve  30 , a first passage  31 , a second passage  32 , and the control-pressure chambers R 1  and R 2 . The control valve  30  is a spool valve for controlling inflow and outflow of the hydraulic fluid into/from the first control-pressure chamber R 1  and the second control-pressure chamber R 2 . The control valve  30  includes a spool  302 , a spring  303 , an adjustment mechanism  304 , and a solenoid  301  with a plunger  301   a . The spool  302  is housed in a housing hole  401  of the rear body  40 . The spring  303  biases the spool  302  toward the solenoid  301 . The adjustment mechanism  304  adjusts a retaining position (set spring load) for the spring  303 . The plunger  301   a  applies a biasing force for the spool  302  in a direction opposite to a load direction of the spring  303 , as requested. In an end portion of the housing hole  401  on the positive x-axis side, an upstream-side port  401   a  to which a delivery pressure on the upstream side of a metering orifice  700  described later is supplied. The first passage  31  is formed so as to be adjacent to the upstream-side port  401   a  in the negative x-axis direction. A first land portion  302   a  of the spool  302  is provided so as to allow communication between the upstream-side port  401   a  and the first passage  31  or interrupt the communication therebetween. On the other hand, in an end portion of the housing hole  401  on the negative x-axis side, a downstream-side port  401   b  to which a delivery pressure on the downstream side of the metering orifice  700  described later is supplied is formed. The second passage  32  is formed so as to be adjacent to the downstream-side port  401   b  in the positive x-axis direction. A second land portion  302   b  of the spool  302  is provided so as to allow communication between the downstream-side port  401   b  and the second passage  32  or interrupt the communication therebetween.  FIG. 5  is a schematic view illustrating a relationship between the control section and the control-pressure chambers according to the first embodiment. On a passage connecting a delivery chamber  493  for the pump chambers r and a delivery passage  65 , an upstream-side oil path  65   a  and a downstream-side oil path  65   b  are provided. The upstream-side oil path  65   a  branches on the upstream side of the metering orifice  700  and is connected to the upstream-side port  401   a . The downstream-side oil path  65   b  branches on the downstream side of the metering orifice  700  and is connected to the downstream-side port  401   b . Through the intake port  51  of the variable displacement vane pump, the operating oil, which is taken in through a strainer  101  immersed into the operating oil contained in an oil pan  100  through a filter for removing an impurity such as contamination or the like, is supplied to the pump so as to supply the delivery pressure to various types of hydraulic-pressure control units. The oil pan  100  is provided in a lower part of a transmission unit in which the CVT is mounted. 
     &lt;Functions&gt; 
     Functions of the vane pump  1  according to the first embodiment are described (see  FIG. 2 ). 
     &lt;Pump Functions&gt; 
     By rotating the rotor  6  in a state in which the cam ring  8  is located eccentrically in the positive x-axis direction with respect to the rotation axis O, the pump chambers r periodically expand and contract while rotating about the rotation axis O. On the negative y-axis side, on which the pump chambers r become larger in the positive rotating direction, the operating oil is taken in through the intake port  43  into the pump chambers r. On the positive y-axis side, on which the pump chambers r become smaller in the positive rotating direction, the taken in operating oil is delivered from the pump chambers r to the delivery port  44 . 
     Specifically, the description is now given focusing on one of the pump chambers r. In the intake region, until one of the vanes  7  of the pump chamber r on the negative side in the rotating direction (hereinafter referred to as “rear-side vane  7 ”) passes through the end point B of the intake-side arc-shaped groove  430 , in other words, until the other of the vanes  7  on the positive side in the rotating direction (hereinafter referred to as “front-side vane  7 ”) passes through the starting point C of the delivery-side arc-shaped groove  440 , the volume of the pump chamber r increases. Meanwhile, the pump chamber r is held in communication to the intake-side arc-shaped groove  430 . Therefore, the operating oil is taken in through the intake port  43 . At a rotational position at which the rear-side vane  7  (surface thereof oriented in the positive rotating direction) of the pump chamber r coincides with the end point B of the intake-side arc-shaped groove  430  and the front-side vane  7  (surface thereof oriented in the negative rotating direction) coincides with the starting point C of the delivery-side arc-shaped groove  440  in the first confinement region, the pump chamber r is brought into communication neither to the intake-side arc-shaped groove  430  nor to the delivery-side arc-shaped groove  440  and is held in a fluid-tight state. 
     After the rear-side vane  7  of the pump chamber r passes through the end point B of the intake-side arc-shaped groove  430  (after the front-side vane  7  passes through the starting point C of the delivery-side arc-shaped groove  440 ), the volume of the pump chamber r decreases in the delivery region in accordance with the rotation and the pump chamber r is brought into communication to the delivery-side arc-shaped groove  440 . Therefore, the operating oil is delivered from the pump chamber r to the delivery port  44 . 
     At a position at which the rear-side vane  7  of the pump chamber r (surface thereof oriented in the positive rotating direction) coincides with the end point D of the delivery-side arc-shaped groove  440  and the front-side vane  7  (surface thereof oriented in the negative rotating direction) coincides with the starting point A of the intake-side arc-shaped groove  430  in the second confinement region, the pump chamber r is brought into communication neither to the delivery-side arc-shaped groove  440  nor to the intake-side arc-shaped groove  430  and is held in a fluid-tight state. 
     In the first embodiment, the range of each of the first confinement region and the second confinement region corresponds to one pitch (corresponding to one pump chamber r). Therefore, while the intake region and the delivery region are prevented from being brought into communication to each other, pump efficiency can be improved. Each of the first and second confinement regions (distance between the intake port  43  and the delivery port  44 ) may be provided over a range larger than one pitch. In other words, the angular range of each of the confinement regions can be set arbitrarily as long as the delivery region and the intake region are not brought into communication to each other. 
     When the front-side vane  7  (surface thereof oriented in the negative rotating direction) moves from the first confinement region to the delivery region, the pump chamber r and the delivery-side arc-shaped groove  440  are not suddenly brought into communication to each other due to the narrowing function of the starting end portion  443 . Therefore, the pressures at the delivery port  44  and in the pump chamber r are prevented from fluctuating. Specifically, the operating oil is prevented from suddenly flowing from the delivery port  44  at a high pressure to the pump chamber r at a low pressure. Thus, a flow rate of the operating oil to be supplied from the delivery port  44  to an external pipe connected through the delivery hole  442  is prevented from suddenly decreasing. Thus, the pressure fluctuation (oil hammer) in the pipe can be suppressed. Further, the flow rate of the operating oil to be supplied to the pump chamber r can be prevented from suddenly increasing. Therefore, the pressure fluctuation in the pump chamber r can also be suppressed. The starting end portion  443  may be omitted as needed. 
     When the front-side vane  7  (surface thereof oriented in the negative rotating direction) moves from the second confinement region to the intake region, the pump chamber r and the intake-side arc-shaped groove  430  are not suddenly brought into communication to each other due to the narrowing function of the notch  434 . Therefore, the pressures at the intake port  43  and in the pump chamber r are prevented from fluctuating. Specifically, the volume of the pump chamber r is prevented from increasing at a time. Thus, the operating oil is prevented from suddenly flowing out from the pump chamber r at the high pressure into the intake port  43  at the low pressure. Further, the notch  434  may be omitted as needed. 
     &lt;Capacity Varying Functions&gt; 
     A state in which the solenoid  301  is unactuated is first described. An initially set load is applied to the spool  302  by the spring  303  in the positive x-axis direction. In an early stage of actuation of the pump, in which the flow rate is relatively low, a differential pressure between a pressure before the passage through the metering orifice  700  and a pressure after the passage therethrough is not so large. The spool  302  is biased in the positive x-axis direction by a load of the spring  303 . Thus, the first land portion  302   a  interrupts the communication between the upstream-side port  401   a  and the first passage  31 , whereas the second land portion  302   b  allows communication between the downstream-side port  401   b  and the second passage  32 . As a result, the delivery pressure is not supplied to the first control-pressure chamber R 1 , whereas the delivery pressure is supplied to the second control-pressure chamber R 2 . Therefore, the cam ring  8  is placed in an eccentric state so as to increase a pump delivery flow rate in accordance with an rpm. When the pump delivery flow rate increases, the differential pressure between the pressure on the upstream side and the pressure on the downstream side of the metering orifice  700  becomes larger. At this time, a large force acting in the negative x-axis direction is exerted on the first land portion  302   a  of the spool  302  so as to start exerting a force larger than the initially set load of the spring  303 . Then, the first land portion  302   a  allows communication between the upstream-side port  401   a  and the first passage  31 , whereas the second land portion  302   b  interrupts the communication between the downstream-side port  401   b  and the second passage  32 . As a result, the high delivery pressure on the upstream side of the metering orifice  700  is supplied to the first control-pressure chamber R 1 , whereas the supply of the delivery pressure to the second control-pressure chamber R 2  is stopped. As a result, the eccentricity of the cam ring  8  becomes smaller. Thus, even when the rpm of the pump increases, the pump delivery flow rate does not increase. If the pump delivery flow rate becomes too small, the differential pressure between the pressure on the upstream side and the pressure on the downstream side of the metering orifice  700  becomes smaller. Thus, the cam ring  8  is located eccentrically again so as to appropriately increase the delivery flow rate again. 
     When the solenoid  301  is in the unactuated state, the hydraulic pressure is the only force against the initially set load of the spring  303 . Thus, if the delivery flow rate does not become large, a sufficiently large differential pressure between the pressure on the upstream side and the pressure on the downstream side of the metering orifice  700  cannot be ensured. Therefore, after a relatively high delivery flow rate is achieved, a constant flow rate is maintained. Next, when the solenoid  301  is energized so as to generate a predetermined biasing force, the same effects as those obtained when the initially set load of the spring  303  is changed smaller are obtained. Thus, at earlier timing than that in the case where the solenoid  301  is unactuated, the state of the spool  32  is switched. Even if the differential pressure between the pressure on the upstream side and the pressure on the downstream side of the metering orifice  700  is not large, the spool  302  is actuated under a slightly small differential pressure. After a relatively low delivery flow rate is achieved, a constant flow rate is maintained. Specifically, the delivery flow rate can be controlled by the biasing force to be generated by the solenoid  301 . A CVT control unit  300  appropriately controls a line pressure of the CVT in accordance with running conditions including an accelerator opening degree, an engine rpm, and a vehicle speed. Therefore, when the high delivery flow rate is requested, a current (electromagnetic force) to flow through the solenoid  301  is turned OFF or is reduced. On the other hand, when the low delivery flow rate is requested, the current (electromagnetic force) to flow through the solenoid  301  is increased. 
     &lt;Configuration of Sealed Portion&gt; 
     Next, a problem relating to the pair of sealing members  11  ( 11   a  and  11   b ) provided to the fourth plane portion  94  is described. In the variable displacement vane pump, a proper delivery amount can be varied by controlling the eccentricity of the cam ring  8 . By changing the delivery flow rate as needed, an unnecessary pump driving torque can be reduced, which contributes to an improvement of fuel efficiency. The eccentricity of the cam ring  8  is controlled by controlling the pressures in the first control-pressure chamber R 1  and the second control-pressure chamber R 2 . Thus, it is necessary that the first control-pressure chamber R 1  and the second control-pressure chamber R 2  are formed separately in the partitioned manner. Hitherto, the first control-pressure chamber R 1  and the second control-pressure chamber R 2  are formed separately in the partitioned manner by providing a single sealing member so as to be received in a concave portion formed on the inner circumferential surface  95  of the adapter ring  9  and pressing the sealing member against the outer circumferential surface  81  of the cam ring  8  so as to bring the sealing member into sliding contact therewith. In this structure, however, in a case where a magnitude relationship between the pressure in the first control-pressure chamber R 1  and that in the second control-pressure chamber R 2  frequently changes, there is a fear in that the sealing member moves horizontally to lower durability of an edge portion of the sealing member. Further, when the volume of the first control-pressure chamber R 1  or the second control-pressure chamber R 2  varies due to the swing of the cam ring  8 , the pressure is further fluctuated. Therefore, the phenomenon of the horizontal movement of the sealing member becomes further noticeable. Further, if a leakage occurs from a sealed portion in a state in which an absolute pressure in the first control-pressure chamber R 1  or the second control-pressure chamber R 2  is high, cavitation erosion occurs due to air contained in operating oil. In order to avoid the occurrence of cavitation erosion, it is conceivable to select a material having a high hardness and a high strength as a material of the sealing member. If such a material is used, however, when the sealing member moves due to a fluctuation in differential pressure between the first control-pressure chamber R 1  and the second control-pressure chamber R 2 , there is a fear in that the adapter ring  9 , to which the sealing member is provided, may be struck to lower durability of the adapter ring  9 . Thus, in order to provide a sealing structure in which the sealing member does not move regardless of a state of the control pressures in the first control-pressure chamber R 1  and the second control-pressure chamber R 2 , the following configuration is adopted. 
       FIG. 6  is an enlarged view of the fourth plane portion  94  according to the first embodiment. The first sealing groove  941  is formed on the fourth plane portion  94  of the adapter ring  9  so as to be located on the right of the y axis in  FIG. 6  and be concave in the y-axis direction. The first sealing groove  941  includes a bottom portion  941   a , a first low-pressure chamber side wall portion  941   c , and a first high-pressure chamber side wall portion  941   b . The bottom portion  941   a  is located on the outermost diameter side in the radial direction. The first low-pressure chamber side wall portion  941   c  rising from the bottom portion  941   a  in the positive y-axis direction is provided on the low-pressure chamber R 4  side. The first high-pressure chamber side wall portion  941   b  rising from the bottom portion  941   a  in the positive y-axis direction is provided on the second control-pressure chamber R 2  side. A first pressure introduction path  941   d  cut in the z-axis direction is formed through the first high-pressure chamber side wall portion  941   b  so that a control pressure in the second control-pressure chamber R 2  can be introduced into the first sealing groove  941 . In the first sealing groove  941 , the first sealing member  11   a  is provided. The first sealing member  11   a  is formed of a fiber reinforced resin material by die molding. The first sealing member  11   a  is formed so as to have a cuboidal shape with a generally rectangular sectional shape and approximately the same length as a thickness of the cam ring  8  and that of the adapter ring  9  in the z-axis direction. A circumferential length of the first sealing member  11   a  is set so as to be smaller than a circumferential length of the bottom portion  941   a  of the first sealing groove  941 . In a state in which the first sealing member  11   a  is held in contact with the first low-pressure chamber side wall portion  941   c , a gap is formed between the first sealing member  11   a  and the first high-pressure chamber side wall portion  941   b . Further, a virtual line L 1  in the radial direction is set in a middle point of the low-pressure chamber R 4  in the circumferential direction. The first low-pressure chamber side wall portion  941   c  is formed so that a distance between the wall surface of the first low-pressure chamber side wall portion  941   c  and the virtual line L 1  becomes smaller as a position at which the above-mentioned distance is measured becomes closer to the driving shaft  5 . Specifically, a length x 2  between the wall surface of the first low-pressure chamber side wall portion  941   c  and the virtual line L 1  on the radially inner side in  FIG. 6  is formed so as to be shorter than a length x 3  on the radially outer side. As a result, when the first sealing member  11   a  is pressed against the outer circumferential surface  81  of the cam ring  8 , a contact surface of the first sealing member  11   a  lies along a tangential direction of the cam ring  8 , thereby improving sealability. 
     Similarly, the second sealing groove  942  is formed on the fourth plane portion  94  of the adapter ring  9  so as to be located on the left of the y axis in  FIG. 6  and be concave in the y-axis direction. The second sealing groove  942  includes a bottom portion  942   a , a second low-pressure chamber side wall portion  942   c , and a second high-pressure chamber side wall portion  942   b . The bottom portion  942   a  is located on the outermost diameter side in the radial direction. The second low-pressure chamber side wall portion  942   c  rising from the bottom portion  942   a  in the negative y-axis direction is provided on the low-pressure chamber R 4  side. The second high-pressure chamber side wall portion  942   b  rising from the bottom portion  942   a  in the negative y-axis direction is provided on the first control-pressure chamber R 1  side. A second pressure introduction path  942   d  cut in the z-axis direction is formed through the second high-pressure chamber side wall portion  942   b  so that a control pressure in the first control-pressure chamber R 1  can be introduced into the second sealing groove  942 . In the second sealing groove  942 , the second sealing member  11   b  is provided. The second sealing member  11   b  is formed of a fiber reinforced resin material by die molding. The second sealing member  11   b  is formed so as to have a cuboidal shape with a generally rectangular sectional shape and approximately the same length as the thickness of the cam ring  8  and that of the adapter ring  9  in the z-axis direction. A circumferential length of the second sealing member  11   b  is set so as to be smaller than a circumferential length of the bottom portion  942   a  of the second sealing groove  942 . In a state in which the second sealing member  11   b  is held in contact with the second low-pressure chamber side wall portion  942   c , a gap is formed between the second sealing member  11   b  and the second high-pressure chamber side wall portion  942   b . Similarly to the case of the wall surface of the first low-pressure chamber side wall portion  941   c , the virtual line L 1 , which connects the middle point of the low-pressure chamber R 4  in the circumferential direction and the rotation axis of the driving shaft  5 , is set. The second low-pressure chamber side wall portion  942   c  is formed so that a distance between the wall surface of the second low-pressure chamber side wall portion  942   c  and the virtual line L 1  becomes smaller as a position at which the above-mentioned distance is measured becomes closer to the driving shaft  5 . As a result, when the second sealing member  11   b  is pressed against the outer circumferential surface  81  of the cam ring  8 , a contact surface of the second sealing member  11   b  lies along the tangential direction of the cam ring  8 , thereby improving the sealability. 
     At a position between the first sealing groove  941  and the second sealing groove  942  on the fourth plane portion  94  of the adapter ring  9 , a low-pressure chamber path  943  is formed so as to be concave in the y-axis direction with a depth smaller than those of the sealing grooves  941  and  942 . The low-pressure chamber path  943  is formed at a position slightly away from the y axis in the positive rotating direction. The communication path  439  extending in parallel to the y-axis direction is formed in approximately the center of the intake-side arc-shaped groove  430  on the surface  410  of the pressure plate  41  so as to be slightly away from the y axis in the positive rotating direction. The communication path  439  is formed so as to allow the communication between the low-pressure chamber path  943  formed on the inner circumferential surface  95  of the adapter ring  9  and the intake port  43 . 
     As illustrated in  FIG. 6 , the low-pressure chamber R 4  is formed in a region defined by the first sealing member  11   a , the second sealing member  11   b , a portion of the inner circumferential surface  95 , which is located between the first sealing groove  941  and the second sealing groove  942 , and the outer circumferential surface  81  of the cam ring  8 . The low-pressure chamber R 4  is constantly connected to the intake port  43 . A pressure in the low-pressure chamber R 4  is always lower than those in the first control-pressure chamber R 1  and the second control-pressure chamber R 2  regardless of control states of the first control-pressure chamber R 1  and the second control-pressure chamber R 2 . Thus, the first sealing member  11   a  and the second sealing member  11   b  are pressed against the outer circumferential surface  81  of the cam ring  8  by control pressures introduced into the sealing grooves  941  and  942  through the first pressure introduction path  941   d  and the second pressure introduction path  942   d , and are also pressed against the first low-pressure chamber side wall portion  941   c  and the second low-pressure chamber side wall portion  942   c . Even if a pressure fluctuation occurs in the first control-pressure chamber R 1  or the second control-pressure chamber R 2 , the first sealing member  11   a  and the second sealing member  11   b  are prevented from moving horizontally in  FIG. 6 . 
     Further, a virtual line connecting the center axis on the inner circumferential surface of the cam ring  8  and the middle point of the low-pressure chamber R 4  in the circumferential direction and moving along with the movement of the cam ring  8  is assumed as a cam-ring virtual center line L 3 . Then, a first intersection P 1  is an intersection between a virtual line L 22  extending along the wall surface of the first low-pressure chamber side wall portion  941   c  toward the driving shaft  5  and a virtual line L 21  extending along the wall surface of the second low-pressure chamber side wall portion  942   c  toward the driving shaft  5 . The first sealing groove  941  and the second sealing groove  942  are formed so that the cam ring  8  is located between the maximum eccentricity position and the minimum eccentricity position when the cam-ring virtual center line L 3  passes through the first intersection P 1 . In other words, the first low-pressure chamber side wall portion  941   c  and the second low-pressure chamber side wall portion  942   c  are formed so that the first intersection P 1  is present in a region dx through which the cam-ring virtual center line L 3  passes. In this manner, when the first sealing member  11   a  and the second sealing member  11   b  come into contact with the outer circumferential surface  81  of the cam ring  8 , the cam ring  8  moves within a range including a position at which a contact angle between each of the first sealing member  11   a  and the second sealing member  11   b  and the outer circumferential surface  81  becomes the smallest. A maximum value of the relative angle at a portion at which each of the sealing members  11   a  and  11   b  and the cam ring  8  comes into contact with can be reduced when the cam ring  8  is located in the maximum eccentricity position or the minimum eccentricity position. As a result, partial contact of each of the sealing members  11   a  and  11   b  is suppressed. 
     &lt;Effects&gt; 
     Now, effects of the vane pump  1 , which are understood in the first embodiment, are listed. 
     (1-(1)) The variable displacement vane pump includes: the pump housing including a pump-element housing portion; the driving shaft  5  rotatably supported by the pump housing; the rotor  6  provided inside the pump housing so as to be rotationally driven by the driving shaft  5 , the rotor  6  including the plurality of slots  61  arranged in the circumferential direction, which is the direction about the rotation axis of the driving shaft  5 ; the plurality of vanes  7  provided in the plurality of slots  61  so as to be projectable therefrom and retractable therein; the cam ring  8  formed so as to have an annular shape, the cam ring  8  being provided so as to be movable inside the pump-element housing portion, the cam ring  8  forming the plurality of pump chambers on the inner circumferential side in cooperation with the rotor  6  and the plurality of vanes  7 ; the intake port  43  formed in the pump housing, the intake port  43  having the opening in the intake region, in which the volumes of the plurality of pump chambers r increase along with the rotation of the rotor  6 ; the delivery port  44  having the opening in the delivery region, in which the volumes of the plurality of pump chambers r decrease along with the rotation of the rotor  6 ; the pair of sealing grooves formed on the pump-element housing portion so as to have the openings oriented toward the outer circumferential surface of the cam ring  8  in the radial direction, which is the radiation direction of the rotation axis of the driving shaft  5 , the pair of sealing grooves being the first sealing groove  941  and the second sealing groove  942  formed on the intake port  43  side with respect to the driving shaft  5  so as to be separated away from each other in the circumferential direction; the pair of sealing members which are the first sealing member  11   a  provided in the first sealing groove  941  and the second sealing member  11   b  provided in the second sealing groove  942 ; the pair of pressure chambers formed between the pump-element housing portion and the cam ring  8  in the radial direction so as to be separated by the first sealing member  11   a  and the second sealing member  11   b , the pair of pressure chambers being: (i) the first fluid-pressure chamber R 1  provided on the side on which the volume thereof decreases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the first fluid-pressure chamber R 1  being configured such that the delivery pressure delivered through the delivery port  44  is introduced so that the pressure in the first fluid-pressure chamber R 1  becomes higher than the pressure in the low-pressure chamber R 4 , which is the pressure chamber formed between the first sealing member  11   a  and the second sealing member  11   b ; and (ii) the second fluid-pressure chamber R 2  provided on the side on which the volume thereof increases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the second fluid-pressure chamber R 2  being configured such that the delivery pressure delivered through the delivery port  44  is introduced so that the pressure in the second fluid-pressure chamber R 2  becomes higher than the pressure in the low-pressure chamber R 4 ; and the control valve  30  configured to control the pressure in the first fluid-pressure chamber R 1  or the second fluid-pressure chamber R 2 . Specifically, the first sealing member  11   a  and the second sealing member  11   b  are biased toward the low-pressure chamber R 4  respectively by the pressures from the first fluid-pressure chamber R 1  and the second fluid-pressure chamber R 2 . As a result, the magnitude relationship between the pressures on both sides of the first sealing member  11   a  and the second sealing member  11   b  in the circumferential direction is prevented from being changed. Thus, the sealing members  11   a  and  11   b  can be prevented from moving inside the sealing grooves  941  and  942  to suppress damage to the sealing members  11   a  and  11   b  and the sealing grooves  941  and  942 . The delivery pressures are only required to be introduced at least temporarily to the first fluid-pressure chamber R 1  and the second fluid-pressure chamber R 2 , and the delivery pressures are not necessarily required to be constantly introduced into the first fluid-pressure chamber R 1  and the second fluid-pressure chamber R 2 . Further, when a high-strength material is used as countermeasures against the cavitation erosion, costs are increased. With the sealing structure described above, however, the cavitation erosion is suppressed. Thus, a low-cost material can be used. Both of the pressure in the first fluid-pressure chamber R 1  and the pressure in the second fluid-pressure chamber R 2  may be controlled, or any one thereof may be controlled. 
     (2-(2)) In the variable displacement vane pump according to Item (1-(1)), the low-pressure chamber R 4  is connected, through the communication path  439 , to the intake region of the pump housing, into which the intake pressure is introduced. Therefore, the pressure in the low-pressure chamber R 4  can be set as the intake pressure. Thus, stability of the first sealing member  11   a  and the second sealing member  11   b  can be improved. 
     (3-(3)) In the variable displacement vane pump according to Item (2-(2)), the pump housing includes the pressure plate  41  provided inside the pump-element housing portion so as to be opposed to the cam ring  8  and the rotor  6  in the axial direction, which is the direction of the rotation axis of the driving shaft  5 . The pressure plate  41  includes: the delivery port  44  through which the delivery pressure delivered opposite to the cam ring  8  with respect to the pressure plate  41  in the axial direction is introduced to bias the pressure plate  41  toward the cam ring  8 ; and the intake port  43  formed through the pressure plate  41  on the side opposed to the cam ring  8  so as to have the opening in the intake region. The communication path  439  is a groove having the opening on the pressure plate  41  side, which is opposed to the cam ring  8 , and is formed so as to connect the low-pressure chamber R 4  and the intake port  43  to each other. Therefore, the communication path  439  can be formed with a simple structure and a small length. 
     (4-(4)) In the variable displacement vane pump according to Item (3-(3)), the pressure plate  41  is made of a sintered material by the die molding, and the communication path  439  is formed by using the same molding die as a molding die for the pressure plate  41 . Thus, a processing step for the communication path  439  can be omitted. 
     (5-(8)) In the variable displacement vane pump according to Item (1-(1)), the first sealing groove  941  is formed on the second fluid-pressure chamber R 2  side with respect to the low-pressure chamber R 4  in the circumferential direction, the second sealing groove  942  is formed on the first fluid-pressure chamber R 1  side with respect to the low-pressure chamber R 4  in the circumferential direction. The first sealing member  11   a  is formed so that the length thereof in the radial direction is smaller than the length of a gap between the first sealing groove  941  and the cam ring  8  in the radial direction, and that the length thereof in the circumferential direction is smaller than the length of the first sealing groove  941  in the circumferential direction. The first sealing member  11   a  is biased toward the cam ring  8  in the radial direction and toward the low-pressure chamber R 4  in the circumferential direction by introduction of the pressure in the second fluid-pressure chamber R 2  into the first sealing groove  941 . The second sealing member  11   b  is formed so that the length thereof in the radial direction is smaller than the length of a gap between the second sealing groove  942  and the cam ring  8  in the radial direction, and that the length thereof in the circumferential direction is smaller than the length of the second sealing groove  942  in the circumferential direction. The second sealing member  11   b  is biased toward the cam ring  8  in the radial direction and toward the low-pressure chamber R 4  in the circumferential direction by introduction of the pressure in the first fluid-pressure chamber R 1  into the second sealing groove  942 . Thus, the biasing force can be obtained without providing a biasing member for biasing the first sealing member  11   a  and the second sealing member  11   b.    
     (6-(9)) The variable displacement vane pump according to Item (5-(8)) further includes: the first pressure introduction path  941   d  configured to allow communication between the first sealing groove  941  and the second fluid-pressure chamber R 2 ; and the second pressure introduction path  942   d  configured to allow communication between the second sealing groove  942  and the first fluid-pressure chamber R 1 . Even in a state in which the first sealing member  11   a  is located closer to the second fluid-pressure chamber R 2  and the second sealing member  11   b  is located closer to the first fluid-pressure chamber R 1 , and thus the pressures are not easily introduced into the first sealing groove  941  and the second sealing groove  942 , the pressures can be reliably introduced. 
     (7-(12)) In the variable displacement vane pump according to Item (1-(1)), each of the first sealing member  11   a  and the second sealing member  11   b  is formed so as to have a generally rectangular sectional shape in the direction orthogonal to an axial direction. The first sealing groove  941  is formed so that the distance between the first low-pressure chamber side wall surface  941   c  on the low-pressure chamber R 4  side, which is one of the pair of wall surfaces opposed to each other in the circumferential direction, and the virtual line L 1  connecting the middle point of the low-pressure chamber R 4  in the circumferential direction and the rotation axis of the driving shaft  5  becomes smaller as a position at which the distance is measured becomes closer to the driving shaft  5 . The second sealing groove  942  is formed so that the distance between the second low-pressure chamber side wall surface  942   c  on the low-pressure chamber R 4  side, which is one of the pair of wall surfaces opposed to each other in the circumferential direction, and the virtual line L 1  connecting the middle point of the low-pressure chamber R 4  in the circumferential direction and the rotation axis of the driving shaft  5  becomes smaller as a position at which the distance is measured becomes closer to the driving shaft  5 . Therefore, a direction of the contact surfaces of the sealing members  11   a  and  11   b  with the cam ring  8  is located closer to the tangential direction of the cam ring  8 . Thus, the sealability of the first sealing member  11   a  and the second sealing member  11   b  can be improved. 
     (8-(13)) In the variable displacement vane pump according to Item (7-(12)), when the virtual line connecting a center point on the inner circumferential surface of the cam ring  8  and the middle point of the low-pressure chamber R 4  in the circumferential direction and moving along with movement of the cam ring  8  is defined as the cam-ring virtual center line L 3 , the first sealing groove  941  and the second sealing groove  942  are formed so that the cam ring  8  is located between the maximum eccentricity position and the minimum eccentricity position when the cam-ring virtual center line L 3  passes through the first intersection P 1 , which is an intersection between the virtual line L 21  extending along the first low-pressure chamber side wall surface  941   c  toward the driving shaft  5  and the virtual line L 22  extending along the second low-pressure chamber side wall surface  942   c  toward the driving shaft  5 . In other words, the first low-pressure chamber side wall surface  941   c  and the second low-pressure chamber side wall surface  942   c  are formed so that the first intersection P 1  is present within the region dx through which the cam-ring virtual center line L 3  passes. Thus, the maximum value of the relative angle at the position at which each of the first sealing member  11   a  and the second sealing member  11   b  and the cam ring  8  come into contact with each other can be reduced when the cam ring  8  is located in the minimum eccentricity position or the maximum eccentricity position. Thus, the partial contact of the first sealing member  11   a  and the second sealing member  11   b  can be suppressed. 
     (9-(14)) The variable displacement vane pump includes: the pump housing including the pump-element housing portion; the driving shaft  5  rotatably supported by the pump housing; the rotor  6  provided inside the pump housing so as to be rotationally driven by the driving shaft  5 , the rotor  6  including the plurality of slots  61  arranged in the circumferential direction, which is the direction about the rotation axis of the driving shaft  5 ; the plurality of vanes  7  provided in the plurality of slots  61  so as to be projectable therefrom and retractable therein; the cam ring  8  formed so as to have an annular shape, the cam ring  8  being provided so as to be movable inside the pump-element housing portion, the cam ring  8  forming the plurality of pump chambers on the inner circumferential side in cooperation with the rotor  6  and the plurality of vanes  7 ; the intake port  43  formed in the pump housing, the intake port  43  having the opening in the intake region, in which the volumes of the plurality of pump chambers r increase along with the rotation of the rotor  6 ; the delivery port  44  having the opening in the delivery region, in which the volumes of the plurality of pump chambers r decrease along with the rotation of the rotor  6 ; the pair of sealing grooves formed on the pump-element housing portion so as to have the openings oriented toward the outer circumferential surface of the cam ring  8  in the radial direction, which is the radiation direction of the rotation axis of the driving shaft  5 , the pair of sealing grooves being the first sealing groove  941  and the second sealing groove  942  formed on the intake port  43  side with respect to the driving shaft  5  so as to be separated away from each other in the circumferential direction; the pair of sealing members which are the first sealing member  11   a  provided in the first sealing groove  941  and the second sealing member  11   b  provided in the second sealing groove  942 ; the pair of pressure chambers formed between the pump-element housing portion and the cam ring  8  in the radial direction so as to be separated by the first sealing member  11   a  and the second sealing member  11   b , the pair of pressure chambers being: (i) the first fluid-pressure chamber R 1  formed on the side on which the volume thereof decreases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the first fluid-pressure chamber R 1  being configured such that the delivery pressure delivered through the delivery port  44  is introduced; and (ii) the second fluid-pressure chamber R 2  provided on the side on which the volume thereof increases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the second fluid-pressure chamber R 2  being configured such that the delivery pressure delivered through the delivery port  44  is introduced; the control valve  30  configured to control the pressure in the first fluid-pressure chamber R 1  or the second fluid-pressure chamber R 2 ; and the low-pressure chamber R 4 , which is the pressure chamber formed between the first sealing member  11   a  and the second sealing member  11   b  in the circumferential direction, the low-pressure chamber R 4  being configured such that the working fluid at the intake pressure is introduced. Specifically, the first sealing member  11   a  and the second sealing member  11   b  are biased toward the low-pressure chamber R 4  respectively by the pressures from the first fluid-pressure chamber R 1  and the second fluid-pressure chamber R 2 . As a result, the magnitude relationship between the pressures on both sides of the first sealing member  11   a  and the second sealing member  11   b  in the circumferential direction is prevented from being changed. Thus, the sealing members  11   a  and  11   b  can be prevented from moving inside the sealing grooves  941  and  942  to suppress damage to the sealing members  11   a  and  11   b  and the sealing grooves  941  and  942 . 
     (10-(15)) In the variable displacement vane pump according to Item (9-(14)), the low-pressure chamber R 4  is connected, through the communication path  439 , to the intake region of the pump housing, into which the intake pressure is introduced. Therefore, the pressure in the low-pressure chamber R 4  can be set as the intake pressure. Thus, stability of the first sealing member  11   a  and the second sealing member  11   b  can be improved. 
     (11-(16)) In the variable displacement vane pump according to Item (10-(15)), the pump housing includes the pressure plate  41  provided inside the pump-element housing portion so as to be opposed to the cam ring  8  and the rotor  6  in the axial direction, which is the direction of the rotation axis of the driving shaft  5  The pressure plate  41  includes: the delivery port  44  through which the delivery pressure delivered opposite to the cam ring  8  with respect to the pressure plate  41  in the axial direction is introduced to bias the pressure plate  41  toward the cam ring  8 ; and the intake port  43  formed through the pressure plate  41  on the side opposed to the cam ring  8  so as to have the opening in the intake region. The communication path  439  is the groove having the opening on the pressure plate  41  side, which is opposed to the cam ring  8 , and is formed so as to connect the low-pressure chamber R 4  and the intake port  43  to each other. Therefore, the communication path  439  can be formed with a simple structure and a small length. 
     (12-(17)) In the variable displacement vane pump according to Item (11-(16)), the pressure plate  41  is made of the sintered material by die molding, and the communication path  439  is formed by using the same molding die as the molding die for the pressure plate  41 . Thus, processing step for the communication path  439  can be omitted. 
     (13-(20)) The variable displacement vane pump includes: the pump housing including the pump-element housing portion; the driving shaft  5  rotatably supported by the pump housing; the rotor  6  provided inside the pump housing so as to be rotationally driven by the driving shaft  5 , the rotor  6  including the plurality of slots  61  arranged in the circumferential direction, which is the direction about the rotation axis of the driving shaft  5 ; the plurality of vanes  7  provided in the plurality of slots  61  so as to be projectable therefrom and retractable therein; the cam ring  8  being formed so as to have an annular shape, the cam ring  8  provided so as be movable inside the pump-element housing portion, the cam ring  8  forming the plurality of pump chambers on the inner circumferential side in cooperation with the rotor  6  and the plurality of vanes  7 ; the intake port  43  formed in the pump housing, the intake port  43  having the opening in the intake region, in which the volumes of the plurality of pump chambers r increase along with the rotation of the rotor  6 ; the delivery port  44  having the opening in the delivery region, in which the volumes of the plurality of pump chambers r decrease along with the rotation of the rotor  6 ; the pair of sealing grooves formed on the pump-element housing portion so as to have the openings oriented toward the outer circumferential surface of the cam ring  8  in the radial direction, which is the radiation direction of the rotation axis of the driving shaft  5 , the pair of sealing grooves being the first sealing groove  941  and the second sealing groove  942  formed on the intake port  43  side with respect to the driving shaft  5  so as to be separated away from each other in the circumferential direction; the pair of sealing members which are the first sealing member  11   a  provided in the first sealing groove  941  and the second sealing member  11   b  provided in the second sealing groove  942 ; the pair of pressure chambers formed between the pump-element housing portion and the cam ring  8  in the radial direction so as to be separated by the first sealing member  11   a  and the second sealing member  11   b , the pair of pressure chambers being: (i) the first fluid-pressure chamber R 1  formed on the side on which the volume thereof decreases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the first fluid-pressure chamber R 1  being configured such that the delivery pressure delivered through the delivery port  44  is introduced; and (ii) the second fluid-pressure chamber R 2  provided on the side on which the volume thereof increases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the second fluid-pressure chamber R 2  being configured such that the delivery pressure delivered through the delivery port  44  is introduced; and the control valve  30  configured to control the pressure in the first fluid-pressure chamber R 1  or the second fluid-pressure chamber R 2 . Specifically, both circumferential sides of each of the first sealing member and the second sealing member are not adjacent to both of the first fluid-pressure chamber R 1  and the second fluid-pressure chamber R 2 . Therefore, the movement of the first and second sealing members, which is caused along with a change in pressure in the first fluid-pressure chamber R 1  or the second fluid-pressure chamber R 2  along with a vibration of the cam ring  8 , is suppressed to prevent the sealing members and the sealing grooves from being damaged. 
     Second Embodiment 
     Next, a second embodiment of the present invention is described. A basic configuration is the same as that in the first embodiment, and therefore only different points are described. In the first embodiment, the communication path  439  is formed on the pressure plate  41 . The second embodiment differs from the first embodiment in that communication paths  8439  are formed on the cam ring  8  side.  FIG. 7  is a front view illustrating a configuration of the cam ring  8  according to the second embodiment. The communication paths  8439  are formed on both axial end surfaces of the cam ring  8  so as to connect the low-pressure chamber R 4  and the intake port  43  to each other. Although the communication paths  8439  are formed on the both axial sides of the cam ring  8  in the second embodiment, the communication path  8439  may be provided only one axial side. The cam ring  8  is formed of a sintered material by die molding. The communication paths  8439  are formed by using a molding die for the cam ring  8 . In other words, the communication paths  8439  can be formed by using the same molding die as that for the cam ring  8 . Thus, a processing step for the communication paths  8439  can be omitted. The cam ring  8  swings, and therefore positions of the communication paths  8439  with respect to the adapter ring  9  move along with the swing of the cam ring  8 . The communication paths  8439  are formed so as to be constantly located in a region sandwiched between the first sealing member  11   a  and the second sealing member  11   b  regardless of the position to which the cam ring  8  moves by swinging. Thus, the intake pressure is constantly introduced into the low-pressure chamber R 4  through the communication paths  8439 . Accordingly, a low-pressure state can be stably maintained. As described above, the following functions and effects are obtained in the second embodiment. (14-(5)) In the variable displacement vane pump according to Item (2-(2)), the cam ring  8  is formed of a sintered material by die molding. The communication path  8439  includes communication paths  8439 , which are formed so as to have a groove shape on both end surfaces of the cam ring  8  in the axial direction, which is the direction of the rotation axis of the driving shaft  5 , so as to connect the low-pressure chamber R 4  and the intake port  43  to each other. The communication paths  8439  are formed by using the same molding die as a molding die for the cam ring  8 . Therefore, the communication paths  8439  through which the low pressure can be introduced from the both axial sides into the low-pressure chamber R 4  can be formed without any processing. 
     Third Embodiment 
     Next, a third embodiment of the present invention is described.  FIG. 8  is an enlarged view of the fourth plane portion  94  according to the third embodiment.  FIG. 8  illustrates a state in which the hydraulic pressure in the second control-pressure chamber R 2  is higher than that in the first control-pressure chamber R 1 . In the first embodiment, the low-pressure chamber R 4  is provided between the first sealing member  11   a  and the second sealing member  11   b . The low-pressure chamber R 4  is formed by pressing the first sealing member  11   a  against the first low-pressure chamber side wall portion  941   c  and pressing the second sealing member  11   b  against the second low-pressure chamber side wall portion  942   c . The third embodiment differs from the first embodiment in that an intermediate-pressure chamber R 5  for introducing an intermediate pressure between the hydraulic pressure in the first control-pressure chamber R 1  and that in the second control-pressure chamber R 2  is provided in place of the low-pressure chamber R 4 . A first sealing groove  941 ′ is formed on the fourth plane portion  94  of the adapter ring  9  so as to be located on the right of the y axis in  FIG. 8  and be concave in the y-axis direction. The first sealing groove  941 ′ includes a bottom portion  941   a ′, a first intermediate-pressure chamber side wall portion  941   c ′, and a first high-pressure chamber side wall portion  941   b ′. The bottom portion  941   a ′ is located on the outermost diameter side in the radial direction. The first intermediate-pressure chamber side wall portion  941   c ′ rising from the bottom portion  941   a ′ in the positive y-axis direction is provided on the intermediate-pressure chamber R 5  side. The first high-pressure chamber side wall portion  941   b ′ rising from the bottom portion  941   a ′ in the positive y-axis direction is provided on the second control-pressure chamber R 2  side. The first sealing member  11   a  is provided in the first sealing groove  941 ′. The first sealing member  11   a  is formed of the fiber reinforced resin material by die molding. The first sealing member  11   a  is formed so as to have the cuboidal shape with the generally rectangular sectional shape and approximately the same length as the thickness of the cam ring  8  and that of the adapter ring  9  in the z-axis direction. The circumferential length of the first sealing member  11   a  is set so as to be smaller than a circumferential length of the bottom portion  941   a ′ of the first sealing groove  941 ′. In a state in which the first sealing member  11   a  is held in contact with the first intermediate-pressure chamber side wall portion  941   c ′, a gap is formed between the first sealing member  11   a  and the first high-pressure chamber side wall portion  941   b′.    
     Similarly, a second sealing groove  942 ′ is formed on the fourth plane portion  94  of the adapter ring  9  so as to be located on the left of the y axis in  FIG. 8  and be concave in the y-axis direction. The second sealing groove  942 ′ includes a bottom portion  942   a ′, a second intermediate-pressure chamber side wall portion  942   c ′, and a second high-pressure chamber side wall portion  942   b ′. The bottom portion  942   a ′ is located on the outermost diameter side in the radial direction. The second intermediate-pressure chamber side wall portion  942   c ′ rising from the bottom portion  942   a ′ in the positive y-axis direction is provided on the intermediate-pressure chamber R 5  side. The second high-pressure chamber side wall portion  942   b ′ rising from the bottom portion  942   a ′ in the positive y-axis direction is provided on the first control-pressure chamber R 1  side. The second sealing member  11   b  is provided in the second sealing groove  942 ′. The second sealing member  11   b  is formed of the fiber reinforced resin material by die molding. The second sealing member  11   b  is formed so as to have the cuboidal shape with the generally rectangular sectional shape and approximately the same length as the thickness of the cam ring  8  and that of the adapter ring  9  in the z-axis direction. The circumferential length of the second sealing member  11   b  is set so as to be smaller than a circumferential length of the bottom portion  942   a ′ of the second sealing groove  942 ′. In a state in which the second sealing member  11   b  is held in contact with the second high-pressure chamber side wall portion  942   b ′, a gap is formed between the second sealing member  11   b  and the second intermediate-pressure chamber side wall portion  942   c′.    
     As illustrated in  FIG. 8 , the intermediate-pressure chamber R 5  is formed in a region defined by the first sealing member  11   a , the second sealing member  11   b , a portion of the inner circumferential surface  95 , which is located between the first sealing groove  941 ′ and the second sealing groove  942 ′, and the outer circumferential surface  81  of the cam ring  8 . Into the intermediate-pressure chamber R 5 , the intermediate pressure between the control pressure supplied to the first control-pressure chamber R 1  and that supplied to the second control-pressure chamber R 2  is introduced. Therefore, the first sealing member  11   a  and the second sealing member  11   b  are pressed against the outer circumferential surface  81  of the cam ring  8  with the differential pressure between the hydraulic pressure in the first control-pressure chamber R 1  and that in the intermediate-pressure chamber R 5  or the differential pressure between the hydraulic pressure in the second control-pressure chamber R 2  and that in the intermediate-pressure chamber R 5 . At the same time, the first sealing member  11   a  is pressed against the first intermediate-pressure chamber side wall portion  941   c ′, whereas the second sealing member  11   b  is pressed against the second high-pressure chamber side wall portion  942   b ′. Therefore, even if a pressure fluctuation occurs in the first control-pressure chamber R 1  or the second control-pressure chamber R 2 , the differential pressure exerted on the first sealing member  11   a  or the second sealing member  11   b  can be suppressed. 
     As described above, the following functions and effects are obtained in the third embodiment. (15-(19)) The variable displacement vane pump includes: the pump housing including the pump-element housing portion; the driving shaft  5  rotatably supported by the pump housing; the rotor  6  provided inside the pump housing so as to be rotationally driven by the driving shaft  5 , the rotor  6  including the plurality of slots  61  arranged in the circumferential direction, which is the direction about the rotation axis of the driving shaft  5 ; the plurality of vanes  7  provided in the plurality of slots  61  so as to be projectable therefrom and retractable therein; the cam ring  8  formed so as to have an annular shape, the cam ring  8  being provided so as to be movable inside the pump-element housing portion, the cam ring  8  forming the plurality of pump chambers on the inner circumferential side in cooperation with the rotor  6  and the plurality of vanes  7 ; the intake port  43  formed in the pump housing, the intake port  43  having the opening in the intake region, in which the volumes of the plurality of pump chambers r increase along with the rotation of the rotor  6 ; the delivery port  44  having the opening in the delivery region, in which the volumes of the plurality of pump chambers r decrease along with the rotation of the rotor  6 ; the pair of sealing grooves formed on the pump-element housing portion so as to have the openings oriented toward the outer circumferential surface of the cam ring  8  in the radial direction, which is the radiation direction of the rotation axis of the driving shaft  5 , the pair of sealing grooves being the first sealing groove  941 ′ and the second sealing groove  942 ′ formed on the intake port  43  side with respect to the driving shaft  5  so as to be separated away from each other in the circumferential direction; the pair of sealing members which are the first sealing member  11   a  provided in the first sealing groove  941 ′ and the second sealing member  11   b  provided in the second sealing groove  942 ′; the pair of pressure chambers formed between the pump-element housing portion and the cam ring  8  in the radial direction so as to be separated by the first sealing member  11   a  and the second sealing member  11   b , the pair of pressure chambers being: (i) the first fluid-pressure chamber R 1  formed on the side on which the volume thereof decreases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the first fluid-pressure chamber R 1  being configured such that the delivery pressure delivered through the delivery port  44  is introduced; and (ii) the second fluid-pressure chamber R 2  provided on the side on which the volume thereof increases when the cam ring  8  moves to the side on which the eccentricity of the cam ring  8  increases, the second fluid-pressure chamber R 2  being configured such that the delivery pressure delivered through the delivery port  44  is introduced; the control valve  30  configured to control the pressure in the first fluid-pressure chamber R 1  or the second fluid-pressure chamber R 2 ; and the intermediate-pressure chamber, which is the pressure chamber formed between the first sealing member  11   a  and the second sealing member  11   b  in the circumferential direction, the intermediate-pressure chamber being configured such that the working fluid at the intermediate pressure between the pressure in the first fluid-pressure chamber R 1  and the pressure in the second fluid-pressure chamber R 2  is introduced. Specifically, the first sealing member or the second sealing member is biased toward the intermediate-pressure chamber from any one of the first fluid-pressure chamber side and the second fluid-pressure chamber side, in which the pressure is higher, and is biased toward the other fluid-pressure chamber, in which the pressure is lower, from the intermediate-pressure chamber side. As a result, the magnitude relationship between the pressures on both the circumferential sides of the first sealing member and the second sealing member changes. However, the magnitude relationship changes between the high pressure and the intermediate pressure or between the intermediate pressure and the low pressure instead of changing between the high pressure and the low pressure. Thus, the damage to the sealing members and the sealing grooves can be reduced. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention is described.  FIG. 9  is a schematic sectional view illustrating a configuration of a variable displacement vane pump according to the fourth embodiment. In the first embodiment, the communication path  439  held in communication to the intake-side arc-shaped groove  430  is formed so that the intake pressure is introduced into the low-pressure chamber R 4 . The fourth embodiment differs from the first embodiment in that a communication path  9439  passing in the radial direction of the adapter ring  9  is formed between the first sealing groove  941  and the second sealing groove  942  of the adapter ring  9 . In addition, in the fourth embodiment, an exhaust-oil path  201  for allowing communication between a position on an inner circumference of the housing hole  400 , at which the communication path  9439  has an opening, and the exterior of the rear body  40 . In this manner, a low-pressure chamber R 6  onto which an atmosphere releasing pressure constantly acts is formed. Thus, a pressure in the low-pressure chamber R 6  is the atmosphere releasing pressure. Thus, the operating oil leaking from the pump flows into the low-pressure chamber R 6  and is also exhausted through the exhaust-oil path  201 , to thereby flow back to the oil pan  100  that is provided externally. Then, the operating oil is taken into the pump from the intake port  51  through the strainer  101 . As described above, the following functions and effects are obtained in the fourth embodiment. 
     (16-(6)) In the variable displacement vane pump according to Item (1-(1)), the pump housing has the external communication path for allowing communication between the low-pressure chamber R 6  and exterior of the pump housing. Therefore, the pressure in the low-pressure chamber R 6  can be set as an atmospheric pressure. Thus, stability of the first sealing member  11   a  and the second sealing member  11   b  can be improved. 
     (17-(7)) In the variable displacement vane pump according to Item (16-(6)), the external communication path is formed so as to exhaust the hydraulic fluid to the oil pan provided to the exterior of the pump housing, and the hydraulic fluid is taken into the intake port from the oil pan through the strainer. Specifically, when the hydraulic fluid exhausted from the low-pressure chamber is returned to the pump housing, the hydraulic fluid passes through the strainer. Thus, contamination inside the pump housing can be prevented from remaining therein. 
     Fifth Embodiment 
     Next, a fifth embodiment of the present invention is described.  FIG. 10  is a partial enlarged view illustrating an internal configuration of the adapter ring  9  according to the fifth embodiment. In the first embodiment, the first sealing member  11   a  and the second sealing member  11   b  are pressed against the outer circumferential surface  81  of the cam ring  8  by the hydraulic functions of the first control-pressure chamber R 1  and the second control-pressure chamber R 2 . The fifth embodiment differs from the first embodiment in the following. A first biasing member  11   a   1  for biasing the first sealing member  11   a  toward the outer circumferential surface  81  of the cam ring  8  is provided between the first sealing groove  941  and the first sealing member  11   a . Similarly, a second biasing member  11   b   1  for biasing the second sealing member  11   b  toward the outer circumferential surface  81  of the cam ring  8  is provided between the second sealing groove  942  and the second sealing member  11   b . Thus, even in a pump operation start initial stage in which the hydraulic pressure is not generated yet in the first control-pressure chamber R 1  or the second control-pressure chamber R 2 , sea ability can be ensured. As described above, the following functions and effects are obtained in the fifth embodiment. 
     (18-(10)) The variable displacement vane pump according to Item (1-(1)) includes: the first biasing member provided between the first sealing groove  941  and the first sealing member  11   a  in the radial direction, for biasing the first sealing member  11   a  toward the cam ring  8 ; and the second biasing member provided between the second sealing groove and the second sealing member in the radial direction, for biasing the second sealing member toward the cam ring. Thus, the biasing force can be obtained even in the pump operation start initial stage. 
     (19-(11)) In the variable displacement vane pump according to Item (18-(10)), each of the first sealing member and the second sealing member is formed of a fiber reinforced resin material by die molding. Specifically, by using the fiber reinforced resin material, a strength of the sealing members can be improved as compared with a case where the reinforcing fiber is not used. Further, by forming the sealing members of the fiber reinforced resin material by using the die molding, the reinforcing fiber is prevented from being exposed on a surface as compared with a case where the sealing members are formed by cutting or the like. Thus, the damage to the sealing grooves due to the reinforcing fiber can be suppressed. 
     The variable displacement vane pump of the present invention has been described above based on the embodiments. However, the specific configuration of the present invention is not limited to those of the embodiments. A change in design without departing from the scope of the gist of the invention is encompassed in the present invention. For example, the present invention can also be realized as the following embodiment modes. 
     Embodiment Mode (1) 
     A variable displacement vane pump includes: a pump housing including a pump-element housing portion; 
     a driving shaft rotatably supported by the pump housing; a rotor provided inside the pump housing so as to be rotationally driven by the driving shaft, the rotor including a plurality of slots arranged in a circumferential direction, which is a direction about a rotation axis of the driving shaft; a plurality of vanes provided in the plurality of slots so as to be projectable therefrom and retractable therein; a cam ring formed so as to have an annular shape, the cam ring being provided so as to be movable inside the pump-element housing portion, the cam ring forming a plurality of pump chambers on an inner circumferential side in cooperation with the rotor and the plurality of vanes; an intake port formed in the pump housing, the intake port having an opening in an intake region, in which volumes of the plurality of pump chambers increase along with the rotation of the rotor; a delivery port formed in the pump housing, the delivery port having an opening in a delivery region, in which the volumes of the plurality of pump chambers decrease along with the rotation of the rotor; a pair of sealing grooves formed on the pump-element housing portion so as to have openings oriented toward an outer circumferential surface of the cam ring in a radial direction, which is a radiation direction of the rotation axis of the driving shaft, the pair of sealing grooves being a first sealing groove and a second sealing groove formed on the intake port side with respect to the driving shaft so as to be separated away from each other in the circumferential direction; a pair of sealing members which are a first sealing member provided in the first sealing groove and a second sealing member provided in the second sealing groove; a pair of pressure chambers formed between the pump-element housing portion and the cam ring in the radial direction so as to be separated by the first sealing member and the second sealing member, the pair of pressure chambers being: (i) a first fluid-pressure chamber provided on a side on which a volume thereof decreases when the cam ring moves to a side on which an eccentricity of the cam ring increases, the first fluid-pressure chamber being configured such that a delivery pressure delivered through the delivery port is introduced so that a pressure in the first fluid-pressure chamber becomes higher than a pressure in a low-pressure chamber, which is a pressure chamber formed between the first sealing member and the second sealing member; and (ii) a second fluid-pressure chamber provided on a side on which a volume thereof increases when the cam ring moves to a side on which the eccentricity of the cam ring increases, the second fluid-pressure chamber being configured such that the delivery pressure delivered through the delivery port is introduced so that a pressure in the second fluid-pressure chamber becomes higher than the pressure in the low-pressure chamber; and a control valve configured to control the pressure in the first fluid-pressure chamber or the second fluid-pressure chamber. The delivery pressures are only required to be introduced at least temporarily to the first fluid-pressure chamber and the second fluid-pressure chamber, and the delivery pressures are not necessarily required to be constantly introduced into the first fluid-pressure chamber and the second fluid-pressure chamber. Both of the pressure in the first fluid-pressure chamber and the pressure in the second fluid-pressure chamber may be controlled, or any one thereof may be controlled. According to Embodiment Mode (1), the first sealing member and the second sealing member are biased toward the low-pressure chamber respectively by the pressures from the first fluid-pressure chamber and the second fluid-pressure chamber. As a result, the magnitude relationship between the pressures on both sides of the first sealing member and the second sealing member in the circumferential direction is prevented from being changed. Thus, the sealing members can be prevented from moving inside the sealing grooves to suppress damage to the sealing members and the sealing grooves. 
     Embodiment Mode (2) 
     In a variable displacement vane pump according to Embodiment Mode (1), the low-pressure chamber is connected, through a communication path, to the intake region of the pump housing, into which an intake pressure is introduced. According to Embodiment Mode (2), the pressure in the low-pressure chamber can be set as the intake pressure. Thus, stability of the first sealing member and the second sealing member can be improved. 
     Embodiment Mode (3) 
     In a variable displacement vane pump according to Embodiment Mode (2), the pump housing includes a pressure plate provided inside the pump-element housing portion so as to be opposed to the cam ring and the rotor in an axial direction, which is a direction of the rotation axis of the driving shaft. The pressure plate includes: the delivery port through which the delivery pressure delivered opposite to the cam ring with respect to the pressure plate in the axial direction is introduced to bias the pressure plate toward the cam ring; and the intake port formed through the pressure plate on a side opposed to the cam ring so as to have an opening in the intake region. The communication path is a groove having an opening on the pressure plate side, which is opposed to the cam ring, and is formed so as to connect the low-pressure chamber and the intake port to each other. According to Embodiment Mode (3), the communication path can be formed with a simple structure and a small length. 
     Embodiment Mode (4) 
     In a variable displacement vane pump according to Embodiment Mode (3), the pressure plate is made of a sintered material by die molding. The communication path is formed by using the same molding die as a molding die for the pressure plate. According to Embodiment Mode (4), a processing step for the communication path can be omitted. 
     Embodiment Mode (5) 
     In a variable displacement vane pump according to Embodiment Mode (2), the cam ring is formed of a sintered material by die molding. The communication path includes communication paths, which are formed so as to have a groove shape on both end surfaces of the cam ring in an axial direction, which is a direction of the rotation axis of the driving shaft, so as to connect the low-pressure chamber and the intake port to each other. The communication paths are formed by using the same molding die as a molding die for the cam ring. According to Embodiment Mode (5), the communication paths through which the low pressure can be introduced from the both axial sides into the low-pressure chamber can be formed without any processing. 
     Embodiment Mode (6) 
     In a variable displacement vane pump according to Embodiment Mode (1), the pump housing has an external communication path configured to allow communication between the low-pressure chamber and exterior of the pump housing. According to Embodiment Mode (6), the pressure in the low-pressure chamber can be set as an atmospheric pressure. Thus, stability of the first sealing member and the second sealing member can be improved. 
     Embodiment Mode (7) 
     In a variable displacement vane pump according to Embodiment Mode (6), the external communication path is formed so as to exhaust hydraulic fluid to an oil pan provided to the exterior of the pump housing. The hydraulic fluid is taken into the intake port from the oil pan through a strainer. According to Embodiment Mode (7), when the hydraulic fluid exhausted from the low-pressure chamber is returned to the pump housing, the hydraulic fluid passes through the strainer. Thus, contamination inside the pump housing can be prevented from remaining therein. 
     Embodiment Mode (8) 
     In a variable displacement vane pump according to Embodiment Mode (1), the first sealing groove is formed on the first fluid-pressure chamber side with respect to the low-pressure chamber in the circumferential direction, and the second sealing groove is formed on the second fluid-pressure chamber side with respect to the low-pressure chamber in the circumferential direction. The first sealing member is formed so that a length thereof in the radial direction is smaller than a length of a gap between the first sealing groove and the cam ring in the radial direction, and that a length thereof in the circumferential direction is smaller than a length of the first sealing groove in the circumferential direction. The first sealing member is biased toward the cam ring in the radial direction and toward the low-pressure chamber in the circumferential direction by introduction of the pressure in the first fluid-pressure chamber into the first sealing groove. The second sealing member is formed so that a length thereof in the radial direction is smaller than a length of a gap between the second sealing groove and the cam ring in the radial direction, and that a length thereof in the circumferential direction is smaller than a length of the second sealing groove in the circumferential direction. The second sealing member is biased toward the cam ring in the radial direction and toward the low-pressure chamber in the circumferential direction by introduction of the pressure in the second fluid-pressure chamber into the second sealing groove. According to Embodiment Mode (8), the biasing force can be obtained without providing a biasing member for biasing the first sealing member and the second sealing member. 
     Embodiment Mode (9) 
     A variable displacement vane pump according to Embodiment Mode (8) further includes: a first pressure introduction path configured to allow communication between the first sealing groove and the first fluid-pressure chamber; and a second pressure introduction path configured to allow communication between the second sealing groove and the second fluid-pressure chamber. According to Embodiment Mode (9), even in a state in which the first sealing member is located closer to the first fluid-pressure chamber and the second sealing member is located closer to the second fluid-pressure chamber, and thus the pressures are not easily introduced into the first sealing groove and the second sealing groove, the pressures can be reliably introduced. 
     Embodiment Mode (10) 
     A variable displacement vane pump according to Embodiment Mode (1) further includes: a first biasing member provided between the first sealing groove and the first sealing member in the radial direction, for biasing the first sealing member toward the cam ring; and a second biasing member provided between the second sealing groove and the second sealing member in the radial direction, for biasing the second sealing member toward the cam ring. According to Embodiment Mode (10), the biasing force can be obtained even in a pump operation start initial stage. 
     Embodiment Mode (11) 
     In a variable displacement vane pump according to Embodiment Mode (10), each of the first sealing member and the second sealing member is formed of a fiber reinforced resin material by die molding. According to Embodiment Mode (11), by using the fiber reinforced resin material, a strength of the sealing members can be improved as compared with a case where the reinforcing fiber is not used. Further, by forming the sealing members of the fiber reinforced resin material by using the die molding, the reinforcing fiber is prevented from being exposed on a surface as compared with a case where the sealing members are formed by cutting or the like. Thus, the damage to the sealing grooves due to the reinforcing fiber can be suppressed. 
     Embodiment Mode (12) 
     In a variable displacement vane pump according to Embodiment Mode (1), each of the first sealing member and the second sealing member is formed so as to have a generally rectangular sectional shape in a direction orthogonal to an axial direction. The first sealing groove is formed so that a distance between a first low-pressure chamber side wall surface on the low-pressure chamber side, which is one of a pair of wall surfaces opposed to each other in the circumferential direction, and a virtual line connecting a middle point of the low-pressure chamber in the circumferential direction and the rotation axis of the driving shaft becomes smaller as a position at which the distance is measured becomes closer to the driving shaft. The second sealing groove is formed so that a distance between a second low-pressure chamber side wall surface on the low-pressure chamber side, which is one of a pair of wall surfaces opposed to each other in the circumferential direction, and the virtual line connecting the middle point of the low-pressure chamber in the circumferential direction and the rotation axis of the driving shaft becomes smaller as a position at which the distance is measured becomes closer to the driving shaft. According to Embodiment Mode (12), a direction of the contact surfaces of the sealing members with the cam ring is located closer to the tangential direction of the cam ring. Thus, the sealability of the first sealing member and the second sealing member can be improved. 
     Embodiment Mode (13) 
     In a variable displacement vane pump according to Embodiment Mode (12), when a virtual line connecting a center point on an inner circumferential surface of the cam ring and the middle point of the low-pressure chamber in the circumferential direction and moving along with movement of the cam ring is defined as a cam-ring virtual center line, the first sealing groove and the second sealing groove are formed so that the cam ring is located between a maximum eccentricity position and a minimum eccentricity position when the cam-ring virtual center line passes through an intersection between a virtual line extending along the first low-pressure chamber side wall surface toward the driving shaft and a virtual line extending along the second low-pressure chamber side wall surface toward the driving shaft. According to Embodiment Mode (13), the maximum value of the relative angle at the position at which each of the first sealing member and the second sealing member and the cam ring come into contact with each other can be reduced when the cam ring is located in the minimum eccentricity position or the maximum eccentricity position. Thus, the partial contact of the first sealing member and the second sealing member can be suppressed. 
     Embodiment Mode (14) 
     A variable displacement vane pump includes: a pump housing including a pump-element housing portion; a driving shaft rotatably supported by the pump housing; a rotor provided inside the pump housing so as to be rotationally driven by the driving shaft, the rotor including a plurality of slots arranged in a circumferential direction, which is a direction about a rotation axis of the driving shaft; a plurality of vanes provided in the plurality of slots so as to be projectable therefrom and retractable therein; a cam ring formed so as to have an annular shape, the cam ring being provided so as to be movable inside the pump-element housing portion, the cam ring forming a plurality of pump chambers on an inner circumferential side in cooperation with the rotor and the plurality of vanes; an intake port formed in the pump housing, the intake port having an opening in an intake region, in which volumes of the plurality of pump chambers increase along with the rotation of the rotor; a delivery port formed in the pump housing, the delivery port having an opening in a delivery region, in which the volumes of the plurality of pump chambers decrease along with the rotation of the rotor; a pair of sealing grooves formed on the pump-element housing portion so as to have openings oriented toward an outer circumferential surface of the cam ring in a radial direction, which is a radiation direction of the rotation axis of the driving shaft, the pair of sealing grooves being a first sealing groove and a second sealing groove formed on the intake port side with respect to the driving shaft so as to be separated away from each other in the circumferential direction; a pair of sealing members which are a first sealing member provided in the first sealing groove and a second sealing member provided in the second sealing groove; a pair of pressure chambers formed between the pump-element housing portion and the cam ring in the radial direction so as to be separated by the first sealing member and the second sealing member, the pair of pressure chambers being: (i) a first fluid-pressure chamber provided on a side on which a volume thereof decreases when the cam ring moves to a side on which an eccentricity of the cam ring increases, the first fluid-pressure chamber being configured such that a delivery pressure delivered through the delivery port is introduced; and (ii) a second fluid-pressure chamber provided on a side on which a volume thereof increases when the cam ring moves to a side on which the eccentricity of the cam ring increases, the second fluid-pressure chamber being configured such that the delivery pressure delivered through the delivery port is introduced; a control valve configured to control a pressure in the first fluid-pressure chamber or the second fluid-pressure chamber; and a low-pressure chamber, which is a pressure chamber formed between the first sealing member and the second sealing member in the circumferential direction, the low-pressure chamber being configured such that hydraulic fluid at an intake pressure is introduced. According to Embodiment Mode (14), the first sealing member and the second sealing member are biased toward the low-pressure chamber respectively by the pressures from the first control-pressure chamber and the second control-pressure chamber. As a result, the magnitude relationship between the pressures on both sides of the first sealing member and the second sealing member in the circumferential direction is prevented from being changed. Thus, the sealing members can be prevented from moving inside the sealing grooves to suppress damage to the sealing members and the sealing grooves. 
     Embodiment Mode (15) 
     In a variable displacement vane pump according to Embodiment Mode (14), the low-pressure chamber is connected, through a communication path, to the intake region of the pump housing, into which an intake pressure is introduced. According to Embodiment Mode (15), the pressure in the low-pressure chamber can be set as the intake pressure with a simple structure. Thus, stability of the first sealing member and the second sealing member can be improved. 
     Embodiment Mode (16) 
     In a variable displacement vane pump according to Embodiment Mode (15), the pump housing includes a pressure plate provided inside the pump-element housing portion so as to be opposed to the cam ring and the rotor in an axial direction, which is a direction of the rotation axis of the driving shaft. The pressure plate includes: the delivery port through which the delivery pressure delivered opposite to the cam ring with respect to the pressure plate in the axial direction is introduced to bias the pressure plate toward the cam ring; and the intake port formed through the pressure plate on a side opposed to the cam ring so as to have an opening in the intake region. The communication path is a groove having an opening on the pressure plate side, which is opposed to the cam ring, and is formed so as to connect the low-pressure chamber and the intake port to each other. According to Embodiment Mode (16), the communication path can be formed with a simple structure and a small length. 
     Embodiment Mode (17) 
     In a variable displacement vane pump according to Embodiment Mode (16), the pressure plate is made of a sintered material by die molding. The communication path is formed by using the same molding die as a molding die for the pressure plate. 
     Embodiment Mode (18) 
     In a variable displacement vane pump according to Embodiment Mode (15), the cam ring is formed of a sintered material by die molding. The communication path includes communication paths, which are formed so as to have a groove shape on both end surfaces of the cam ring in an axial direction, which is a direction of the rotation axis of the driving shaft, so as to connect the low-pressure chamber and the intake port to each other. The communication paths are formed by using the same molding die as a molding die for the cam ring. According to Embodiment Mode (18), the communication paths through which the low pressure can be introduced from the both axial sides into the low-pressure chamber can be formed without any processing. 
     Embodiment Mode (19) 
     A variable displacement vane pump includes: a pump housing including a pump-element housing portion; a driving shaft rotatably supported by the pump housing; a rotor provided inside the pump housing so as to be rotationally driven by the driving shaft, the rotor including a plurality of slots arranged in a circumferential direction, which is a direction about a rotation axis of the driving shaft; a plurality of vanes provided in the plurality of slots so as to be projectable therefrom and retractable therein; a cam ring formed so as to have an annular shape, the cam ring being provided so as to be movable inside the pump-element housing portion, the cam ring forming a plurality of pump chambers on an inner circumferential side in cooperation with the rotor and the plurality of vanes; an intake port formed in the pump housing, the intake port having an opening in an intake region, in which volumes of the plurality of pump chambers increase along with the rotation of the rotor; a delivery port formed in the pump housing, the delivery port having an opening in a delivery region, in which the volumes of the plurality of pump chambers decrease along with the rotation of the rotor; a pair of sealing grooves formed on the pump-element housing portion so as to have openings oriented toward an outer circumferential surface of the cam ring in a radial direction, which is a radiation direction of the rotation axis of the driving shaft, the pair of sealing grooves being a first sealing groove and a second sealing groove formed on the intake port side with respect to the driving shaft so as to be separated away from each other in the circumferential direction; a pair of sealing members which are a first sealing member provided in the first sealing groove and a second sealing member provided in the second sealing groove; a pair of pressure chambers formed between the pump-element housing portion and the cam ring in the radial direction so as to be separated by the first sealing member and the second sealing member, the pair of pressure chambers being: (i) a first fluid-pressure chamber provided on a side on which a volume thereof decreases when the cam ring moves to a side on which an eccentricity of the cam ring increases, the first fluid-pressure chamber being configured such that a delivery pressure delivered through the delivery port is introduced; and (ii) a second fluid-pressure chamber provided on a side on which a volume thereof increases when the cam ring moves to a side on which the eccentricity of the cam ring increases, the second fluid-pressure chamber being configured such that the delivery pressure delivered through the delivery port is introduced; a control valve configured to control a pressure in the first fluid-pressure chamber or the second fluid-pressure chamber; and an intermediate-pressure chamber, which is a pressure chamber formed between the first sealing member and the second sealing member in the circumferential direction, the intermediate-pressure chamber being configured such that hydraulic fluid at an intermediate pressure between the pressure in the first fluid-pressure chamber and the pressure in the second fluid-pressure chamber is introduced. According to Embodiment Mode (19), when the pressure between the sealing members becomes the intermediate pressure, the sealing members move toward the intermediate pressure when the pressures are respectively high and intermediate, and move toward the low pressure when the pressures are respectively intermediate and low. If the magnitude relationship between the pressures in the fluid-pressure chambers changes in this state, the high pressure becomes low while the low pressure becomes high. Thus, the sealing members respectively move to the intermediate pressure side and the low pressure side. Although both the high pressure and the low pressure are applied to the single sealing member, the differential pressure between the high pressure and the intermediate pressure or between the intermediate pressure and the low pressure can be set smaller than that between the high pressure and the low pressure. Therefore, the damage to the sealing members and the sealing grooves can be suppressed. 
     Embodiment Mode (20) 
     A variable displacement vane pump includes: a pump housing including a pump-element housing portion; a driving shaft rotatably supported by the pump housing; a rotor provided inside the pump housing so as to be rotationally driven by the driving shaft, the rotor including a plurality of slots arranged in a circumferential direction, which is a direction about a rotation axis of the driving shaft; a plurality of vanes provided in the plurality of slots so as to be projectable therefrom and retractable therein; a cam ring formed so as to have an annular shape, the cam ring being provided so as to be movable inside the pump-element housing portion, the cam ring forming a plurality of pump chambers on an inner circumferential side in cooperation with the rotor and the plurality of vanes; an intake port formed in the pump housing, the intake port having an opening in an intake region, in which volumes of the plurality of pump chambers increase along with the rotation of the rotor; a delivery port formed in the pump housing, the delivery port having an opening in a delivery region, in which the volumes of the plurality of pump chambers decrease along with the rotation of the rotor; a pair of sealing grooves formed on the pump-element housing portion so as to have openings oriented toward an outer circumferential surface of the cam ring in a radial direction, which is a radiation direction of the rotation axis of the driving shaft, the pair of sealing grooves being a first sealing groove and a second sealing groove formed on the intake port side with respect to the driving shaft so as to be separated away from each other in the circumferential direction; a pair of sealing members which are a first sealing member provided in the first sealing groove and a second sealing member provided in the second sealing groove; a pair of pressure chambers formed between the pump-element housing portion and the cam ring in the radial direction so as to be separated by the first sealing member and the second sealing member, the pair of pressure chambers being: (i) a first fluid-pressure chamber provided on a side on which a volume thereof decreases when the cam ring moves to a side on which an eccentricity of the cam ring increases, the first fluid-pressure chamber being configured such that a delivery pressure delivered through the delivery port is introduced; and (ii) a second fluid-pressure chamber provided on a side on which a volume thereof increases when the cam ring moves to a side on which the eccentricity of the cam ring increases, the second fluid-pressure chamber being configured such that the delivery pressure delivered through the delivery port is introduced; and a control valve configured to control a pressure in the first fluid-pressure chamber or the second fluid-pressure chamber. According to Embodiment Mode (20), both circumferential sides of each of the first sealing member and the second sealing member are not adjacent to both of the first fluid-pressure chamber and the second fluid-pressure chamber. Therefore, the movement of the first and second sealing members, which is caused along with a change in pressure in the first fluid-pressure chamber or the second fluid-pressure chamber along with a vibration of the cam ring, is suppressed to prevent the sealing members and the sealing grooves from being damaged. 
     Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teaching and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. 
     The present application claims priority under 35 U.S.C. section 119 to Japanese Patent Applications No. 2014-052436 filed on Mar. 14, 2014. The entire disclosure of Japanese Patent Application No. 2014-052436 filed on Mar. 14, 2014 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.