Patent Publication Number: US-9897086-B2

Title: Vane pump

Description:
TECHNICAL FIELD 
     The present invention relates to a vane pump that is used as a fluid pressure source. 
     BACKGROUND ART 
     A vane pump is used as a hydraulic source that supplies working oil to a hydraulic apparatus such as a transmission, a power steering apparatus, and so forth mounted on a vehicle. 
     JP2001-248569A discloses a vane pump including a plurality of pump chambers that are partitioned by a plurality of vanes between a cam ring and a rotor, suction ports that guide the working oil to the pump chambers undergoing an expansion stroke, discharge ports to which the working oil discharged from the pump chambers undergoing a compression stroke is guided, and groove-like notches that guide the working oil discharged from the pump chambers commencing an initial stage of the compression stroke to the discharge ports. 
     The above-mentioned groove-like notches extend in the opposite direction from the rotation direction of the rotor from opening edges of the discharge ports. The notches each has a shape in which a groove depth and an opening width gradually increase from its distal-end portion towards proximal-end portion and has a part at which a rate of change of the groove depth gradually increases from the distal-end portion towards the proximal-end portion. 
     SUMMARY OF INVENTION 
     However, with the above-mentioned notches, if lengths of the notches are set to be longer, the groove depths and the opening widths are increased at the proximal-end portions of the notches. Therefore, the proximal-end portions of the notches become larger than the space between the cam ring and the rotor. Thus, with the above-mentioned vane pump, because it is not possible to secure a sufficient notch length, there has been a problem in that, as described later, depending on an operating condition, pulsation of the discharge pressure of the working oil occurs. 
     An object of the present invention is to suppress the occurrence of the pulsation of the discharge pressure of a vane pump. 
     According to one aspect of the present invention, a vane pump used as a fluid pressure source includes: a rotor that is rotationally driven; a plurality of vanes that are inserted into the rotor in a freely slidable manner; a cam ring at which tip-end portions of the vanes slides as the rotor rotates; a pump chamber that is defined between the adjacent vanes; a suction port being configured to guide working fluid to the pump chamber; a discharge port through which the working fluid discharged from the pump chamber is configured to be guided; and a groove-like notch that extends from an opening edge of the discharge port in an opposite direction from rotation direction of the rotor, wherein the notch has a gradient-changing portion at which a rate of change of opening area is decreased in the rotation direction of the rotor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a vane pump according to a first embodiment of the present invention. 
         FIG. 2  is a sectional view taken along a line II-II in  FIG. 1 . 
         FIG. 3  is a rear view of a pump cover. 
         FIG. 4  is a front view of a side plate. 
         FIG. 5A  is a sectional view of a notch of the side plate taken along a line VA-VA in  FIG. 4 . 
         FIG. 5B  is a sectional view taken along a line VB-VB in  FIG. 5A . 
         FIG. 5C  is a sectional view taken along a line VC-VC in  FIG. 5A . 
         FIG. 6A  is a line diagram showing a relationship between the notch length and the opening area. 
         FIG. 6B  is a line diagram showing a relationship between the notch length and the rate of change of the opening area. 
         FIG. 7  is an exploded view of the notch, the discharge port, and so forth. 
         FIG. 8  is an exploded view of the notch, the discharge port, and so forth according to a comparative example. 
         FIG. 9A  is a sectional view of the notch according to a second embodiment of the present invention. 
         FIG. 9B  is a sectional view taken along a line IXB-IXB in  FIG. 9A . 
         FIG. 9C  is a sectional view taken along a line IXC-IXC in  FIG. 9A . 
         FIG. 10A  is a line diagram showing a relationship between the notch length and the opening area. 
         FIG. 10B  is a line diagram showing a relationship between the notch length and the rate of change of the opening area. 
         FIG. 11A  is a sectional view of the notch according to a third embodiment of the present invention. 
         FIG. 11B  is a sectional view taken along a line XIB-XIB in FIG.  11 A. 
         FIG. 11C  is a sectional view taken along a line XIC-XIC in  FIG. 11A . 
         FIG. 11D  is a sectional view taken along a line XID-XID in  FIG. 11A . 
         FIG. 12A  is a line diagram showing a relationship between the notch length and the opening area. 
         FIG. 12B  is a line diagram showing a relationship between the notch length and the rate of change of the opening area. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention will be described below with reference to the attached drawings. 
     A vane pump  1  shown in  FIGS. 1 and 2  is used as a fluid pressure source that supplies working fluid to a fluid pressure supply target. The fluid pressure supply target is, for example, a hydraulic apparatus that is of provided on a transmission, a power steering apparatus, or the like mounted on a vehicle. With the vane pump  1 , working oil is used as the working fluid. With the vane pump  1 , other non-compressive fluid may be used as the working fluid instead of the working oil. 
     The vane pump  1  includes a pump body  10  and a pump cover  50  as a casing. In the pump body  10 , a pump accommodating concave portion  11  that is closed with the pump cover  50  is formed. In the pump accommodating concave portion  11 , a rotor  2 , vanes  3 , a cam ring  4 , a side plate  30 , and so forth are accommodated as pumping mechanisms. Rotation of the cam ring  4  and the side plate  30  relative to the pump cover  50  is locked by two pins  19 . The pump cover  50  is fastened to the pump body  10  by four bolts (not shown). 
     The vane pump  1  is not limited to the configuration mentioned above and may have a configuration in which the cam ring  4  and the side plate  30  are integrally formed with the pump body  10 . In addition, a configuration in which a side plate separate from the pump cover  50  is provided in the vane pump  1  may be employed. 
     The rotor  2  is linked to a drive shaft  9 . The drive shaft  9  is freely rotatably supported between the pump body  10  and the pump cover  50 . Motive force from an engine or an electric motor (not shown) is transmitted to an end portion of the drive shaft  9 . The rotor  2  is rotated in the direction indicated by an arrow shown in  FIG. 1 . 
     A plurality of vanes  3  are interposed between the cam ring  4  and the rotor  2 . In the rotor  2 , a plurality of slits  8  are formed in a radiating pattern at predetermined intervals. The vanes  3  are formed to have a rectangular plate shape and are inserted into the slits  8  in a freely slidable manner. 
     At back sides of the slits  8 , vane back pressure chambers  6  are defined by proximal-end portions of the vanes  3 . As described later, pump discharge pressure is guided to the vane back pressure chambers  6 . The vanes  3  are biased in the directions in which the vanes  3  project out from the slits  8  by the pressure in the vane back pressure chambers  6  that pushes the proximal-end portions of the vanes  3  and by the centrifugal force that is caused by rotation of the rotor  2 . Tip-end portions of the vanes  3  are thereby brought into sliding contact with an inner circumference cam face  5  of the cam ring  4 . 
     A plurality of pump chambers  7  are defined in the cam ring  4  by the inner circumference cam face  5 , the outer circumference of the rotor  2 , and the adjacent vanes  3 . As the rotor  2  is rotated, the vanes  3  that slide on the inner circumference cam face  5  are reciprocated to expand/contract the pump chambers  7 . Thereby, as shown by arrows in  FIG. 2 , the working oil supplied from a tank is guided to suction ports  51  and  53  (see  FIG. 3 ) and suction ports  31  and  33  (see  FIG. 4 ) through a suction passage  25  and is sucked into the pump chambers  7 . As shown by arrows in  FIG. 2 , the working oil that has been pressurized in the pump chambers  7  is discharged to high-pressure chambers  20  from discharge ports  32  and  34  and is supplied to a hydraulic apparatus through discharge passages (not shown) from the high-pressure chambers  20 . 
     In the pump body  10 , a flow control valve  40  is accommodated. A part of the working oil discharged from the pump chambers  7  to the discharge passage is returned by the flow control valve  40  as excessive oil to the pump chambers  7  through the suction passage  25 . The flow amount of the working oil fed to the hydraulic apparatus is controlled by the operation of the flow control valve  40 . 
     The annular cam ring  4  has the inner circumference cam face  5  having a substantially oval shape. As the rotor  2  completes a full rotation, respective vanes  3  following the inner circumference cam face  5  reciprocate twice. 
     The balanced vane pump  1  has a first suction region and a first discharge region in which the vanes  3  reciprocate for first time along with the rotation of the rotor  2  and a second suction region and a second discharge region in which the vanes  3  reciprocate for second time. In the first suction region, a first suction stroke in which the volumes of the pump chambers  7  are expanded is carried out. Subsequently, in the first discharge region, a first discharge stroke in which the volumes of the pump chambers  7  are contracted is carried out. Subsequently, in the second suction region, a second suction stroke in which the volumes of the pump chambers  7  are expanded is carried out. Subsequently, in the second discharge region, a second discharge stroke in which the volumes of the pump chambers  7  are contracted is carried out. Transition regions are respectively provided between the first suction region, the first discharge region, the second suction region, and the second discharge region. 
     In the inner circumference cam face  5  of the cam ring  4 , a first suction section  5 A in which the working oil is sucked through the first suction port  31  from the pump chambers  7  that are expanded during the first suction stroke, a transition section  5 B provided in the transition region, a first discharge section  5 C in which the working oil is discharged through the first discharge port  32  from the pump chambers  7  that are contracted during the first discharge stroke, a transition section  5 D provided in the transition region, a second suction section  5 E in which the working oil is sucked through the second suction port  33  from the pump chambers  7  that are expanded during the second suction stroke, a transition section  5 F provided in the transition region, a second discharge section  5 G in which the working oil is discharged through the second discharge port  34  from the pump chambers  7  that are contracted during the second discharge stroke, and a transition section  5 H provided in the transition region are formed. 
       FIG. 3  is a rear view showing an end surface  55  of the pump cover  50  with which the rotor  2  comes in sliding contact. The rotor  2  rotates in the direction shown by an arrow in  FIG. 3 . On the end surface  55  of the pump cover  50 , the suction port  51  and a back pressure port  61  open at the first suction region, a discharge port  52  and a back pressure port  62  open at the first discharge region, the suction port  53  and a back pressure port  63  open at the second suction region, and a discharge port  54  and a back pressure port  64  open at the second discharge region. 
       FIG. 4  is a front view showing an end surface  38  of the side plate  30  with which the rotor  2  comes in sliding contact. On the end surface  38 , the suction port  31  and a back pressure port  41  open at the first suction region, the discharge port  32  and a back pressure port  42  open at the first discharge region, the suction port  33  and a back pressure port  43  open at the second suction region, and the discharge port  34  and a back pressure port  44  open at the second discharge region. 
     On the side plate  30 , a discharge-pressure introducing hole  45  through which the high-pressure chambers  20  and the back pressure port  41  are communicated at the first suction region and a discharge-pressure introducing hole  46  through which the high-pressure chambers  20  and the back pressure port  43  are communicated at the second suction region are formed. With such a configuration, during operation of the vane pump  1 , pump discharge pressure generated in the high-pressure chambers  20  is guided to the vane back pressure chambers  6  in the first and second suction regions through the back pressure ports  41  and  43 . 
     In  FIG. 4 , the rotor  2  rotates in the direction shown by an arrow. Groove-like notches  70  open at the end surface  38  of the side plate  30  so as to extend from the opening edges of the discharge ports  32  and  34  in the opposite direction from the rotation direction of the rotor  2 . Tip-end portions  70 A of the notches  70  are arranged in first and second transition regions. The working oil is discharged to the first discharge port  32  through the notches  70  from the pump chambers  7  that contract in an initial stage and an intermediate stage of the first and second discharge strokes. 
       FIG. 5A  is a sectional view of the notch  70  taken along a line VA-VA in  FIG. 4 . As shown in this sectional view, the notch  70  has the distal-end portion  70 A located at a distal position from the discharge port  32  and a proximal-end portion  70 B that opens at an inner wall  32 A of the discharge port  32 . The notch  70  has an upstream groove portion  71  that extends from the distal-end portion  70 A in the rotation direction of the rotor  2 , a gradient-changing portion  72  that is provided at a downstream end of the upstream groove portion  71 , and a downstream groove portion  73  that extends from the gradient-changing portion  72  in the rotation direction of the rotor  2 . The gradient-changing portion  72  is a step which is formed between the upstream groove portion  71  and the downstream groove portion  73 . 
       FIG. 5B  is a sectional view taken along a line VB-VB in  FIG. 5A . As shown in this sectional view, the upstream groove portion  71  of the notch  70  has a triangular cross-sectional shape. The upstream groove portion  71  is formed to have a tapered shape in which the opening area of the notch  70  is gradually increased from the distal-end portions  70 A in the rotation direction of the rotor  2  (in the direction approaching the gradient-changing portion  72 ). Note that the opening area of the notch  70  is the cross-sectional area of the notch  70  perpendicular to the center line N of the notch  70  (see  FIG. 4 ). 
       FIG. 5C  is a sectional view taken along a line VC-VC in  FIG. 5A . As shown in this sectional view, the downstream groove portion  73  of the notch  70  has a rectangular cross-sectional shape. The downstream groove portion  73  is formed such that the opening area of the notch  70  remains unchanged and is kept constant from the upstream groove portion  71  in the rotation direction of the rotor  2  (in the direction approaching the discharge port  32 ). 
       FIG. 6A  is a line diagram showing a relationship between the length of the notch  70  in the circumferential direction of the rotor  2  and the opening area of the notch  70 . As shown in  FIG. 6A , the opening area of the notch  70  is gradually increased from the distal-end portions  70 A towards the gradient-changing portion  72  in the upstream groove portion  71 , is increased in one step at the gradient-changing portion  72 , and becomes a constant value at the downstream groove portion  73 . 
       FIG. 6B  is a line diagram showing a relationship between the length of the notch  70  in the circumferential direction of the rotor  2  and the rate of change of the opening area of the notch  70 . Note that the rate of change of the opening area of the notch  70  is a rate of change in the opening area of the notch  70  in the rotation direction of the rotor  2  relative to the length of the center line N of the notch  70  (see  FIG. 4 ). As shown in  FIG. 6B , the rate of change of the opening area of the notch  70  is gradually increased from the distal-end portions  70 A towards the gradient-changing portion  72  in the upstream groove portion  71 , is increased/decreased in one step at the gradient-changing portion  72 , and becomes zero at the downstream groove portion  73 . The gradient-changing portion  72  is a part at which the rate of change of the opening area of the notch  70  is discontinuously changed and decreased from the upstream groove portion  71  towards the downstream groove portion  73 . 
     The gradient-changing portion  72  is not limited to the configuration mentioned above, and may be configured by curved surfaces with which the rate of change of the opening area of the notch  70  is continuously changed and decreased from the upstream groove portion  71  towards the downstream groove portion  73 . 
     Next, an operation of the vane pump  1  will be described. 
     When the rotor  2  is rotated at low speed, the working oil that is discharged to the discharge port  32  through the notches  70  from the pump chambers  7  commencing the initial stage to the intermediate stage of a compression stroke and the working oil that is discharged to the discharge port  32  from the pump chambers  7  commencing a latter stage of the compression stroke are joined and discharged to the high-pressure chambers  20 . With such a configuration, in the vane pump  1 , the change in the working oil pressure from the pump chambers  7  to the discharge port  32  is made moderate through the notches  70 , and it is possible to suppress the occurrence of vibration and noise. 
     On the other hand, when the rotor  2  is rotated at high speed, in a case where air is mixed into the working oil or a cavitation occurs, there is a delay in the pressure increase in the working oil pressurized in the pump chambers  7  commencing the initial stage of the compression stroke. Therefore, there is a possibility of the occurrence of a reverse-flow phenomenon in which the working oil that is discharged from the pump chambers  7  commencing the intermediate stage to the latter stage of the compression stroke abruptly flows through the notches  70  into the pump chambers  7  commencing the initial stage of the compression stroke. 
       FIG. 7  is an exploded view showing by arrows a state in which the working oil flows into and flows out from the pump chambers  7  commencing the compression stroke, when the above-mentioned rotor  2  is rotated at high speed. In this exploded view, respective pump chambers  7  move in the direction shown by an arrow E. In the pump chambers  7  commencing the initial stage of the compression stroke, the air or vacuum portion contained in the working oil is compressed, and thereby, the pressure increase in the working oil is delayed. Therefore, as shown by arrows K and J, the working oil discharged from the pump chambers  7  commencing the intermediate stage of the compression stroke flows through the notches  70  into the pump chambers  7  commencing the initial stage of the compression stroke. By allowing the pressure of the working oil to propagate to each other between the pump chambers  7  facing against the notches  70  through the notches  70  in this way, the pressure increase in the pump chambers  7  commencing the initial stage of the compression stroke is facilitated. On the other hand, as shown by arrows F, G, and H, the working oil compressed in the pump chambers  7  commencing the latter stage of the compression stroke is discharged to the discharge port  32 . By facilitating the pressure increase in the pump chambers  7  commencing the initial stage of the compression stroke through the notches  70 , as shown by an arrow I, flow of the working oil that has been discharged to the discharge port  32  into the notches  70  is suppressed. By suppressing reverse flow of the working oil between the discharge port  32  and the notches  70  in this way, the occurrence of pulsation of discharge pressure at the discharge port  32  is suppressed. 
       FIG. 8  is an exploded view of a vane pump of a comparative example. With a notch  170  in this vane pump, the opening area is gradually increased from a distal end  170 A to a proximal end  170 B, and the rate of change of the opening area becomes a constant value or is gradually increased from the distal end  170 A to the proximal end  170 B. In this case, because the length of the notch  170  cannot be secured in the circumferential direction of the rotor  2 , as shown by an arrow i, the reverse-flow phenomenon in which the working oil in the discharge port  32  abruptly flows into the pump chambers  7  commencing the initial stage of the compression stroke through the notch  170  occurs, thereby causing the pulsation of the discharge pressure at the discharge port  32 . 
     According to the above-mentioned first embodiment, operational advantages shown below can be afforded. 
     [1] The vane pump  1  including the groove-like the notches  70  that extend from the opening edges of the discharge ports  32  and  34  in the opposite direction from the rotation direction of the rotor  2  is configured so as to have parts (the gradient-changing portions  72 ) at which the rate of change of the opening area of the notches  70  is decreased in the rotation direction of the rotor  2 . 
     With the vane pump  1 , because the gradient-changing portions  72  at which the rate of change of the opening area of the notches  70  is decreased towards the discharge ports  32  and  34  are provided, it is possible to set the lengths of the notches  70  to be longer while suppressing the increase in the opening width of the notches  70  with the increase in the lengths of the notches  70 . 
     By sufficiently securing the lengths of the notches  70  in the circumferential direction of the rotor  2 , it is possible to set the lengths of the notches  70  such that the plurality of pump chambers  7  commencing the compression stroke communicate with the notches  70 . With such a configuration, the pressure of the working oil is propagated to each other between the plurality of pump chambers  7  arranged along the circumferential direction of the rotor  2  through the notches  70 , the reverse-flow phenomenon in which the working oil that has been discharged from the pump chambers  7  to the discharge ports  32  and  34  abruptly flows through the notches  70  into the pump chambers  7  commencing the initial stage of the compression stroke is suppressed, and the occurrence of the pulsation the discharge pressure at the discharge ports  32  and  34  is suppressed. 
     [2] The notches  70  are configured so as to have the upstream groove portion  71  at which the opening area is gradually increased from the distal-end portions  70 A in the rotation direction of the rotor  2  and the downstream groove portion  73  at which the opening area of the notches  70  remains the same from the upstream groove portion  71  in the rotation direction of the rotor  2 . 
     According to the above-mentioned configuration, because the downstream groove portions  73  that have the constant opening area are provided, the opening areas of the notches  70  are sufficiently secured, and at the same time, the lengths of the notches  70  in the circumferential direction of the rotor  2  are sufficiently secured. With such a configuration, suppression of the reverse-flow phenomenon in which the working oil abruptly flows into the pump chambers  7  through the notches  70  from the discharge ports  32  and  34  when the rotor  2  is rotated at high speed and smooth introduction of the flow of the working oil from the pump chambers  7  to the discharge ports  32  and  34  through the notches  70  when the rotor  2  is rotated at low speed can both be achieved. 
     [3] The notches  70  are configured such that the opening areas at the discharge ports  32  and  34  sides of the gradient-changing portions  72  are larger than the opening areas at the distal-end portions  70 A sides of the gradient-changing portions  72 . 
     According to the above-mentioned configuration, when the rotor  2  is rotated at high speed, the abrupt flow of the working oil from the discharge ports  32  and  34  through the notches  70  to the pump chambers  7  is restricted at the gradient-changing portions  72 , and so, the reverse-flow phenomenon of the working oil in the notches  70  is effectively suppressed. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIGS. 9A to 9C, 10A, and 10B . In the following, differences from the above-mentioned first embodiment will be mainly described, and components that are the same as those in the above-mentioned first embodiment are assigned the same reference numerals and descriptions thereof will be omitted. 
     The notch  70  according to the above-mentioned first embodiment is configured so as to have the downstream groove portion  73  in which the opening area of the notches  70  is set to be constant. In contrast, a notch  80  according to the second embodiment is configured such that the opening area of the notch  80  is gradually decreased in the rotation direction of the rotor  2 . 
     As shown in  FIG. 9A , the notch  80  has a distal-end portion  80 A located at a distal position from the discharge port  32  and a proximal-end portion  80 B that opens at the inner wall  32 A of the discharge port  32 . The notch  80  has an upstream groove portion  81  that extends from the distal-end portion  80 A in the rotation direction of the rotor  2 , a gradient-changing portion  82  that is provided at a downstream end of the upstream groove portion  81 , and a downstream groove portion  83  that extends from the gradient-changing portion  82  in the rotation direction of the rotor  2 . The gradient-changing portion  82  is a step which is formed between the upstream groove portion  81  and the downstream groove portion  83 . 
       FIG. 9B  is a sectional view taken along a line IXB-IXB in  FIG. 9A . As shown in this sectional view, the upstream groove portion  81  of the notch  80  has a triangular cross-sectional shape. The upstream groove portion  81  is formed such that the opening area of the notch  80  is gradually increased from the distal-end portion  80 A in the rotation direction of the rotor  2  (in the direction approaching the gradient-changing portion  82 ). 
       FIG. 9C  is a sectional view taken along a line IXC-IXC in  FIG. 9A . As shown in this sectional view, the downstream groove portion  83  of the notch  80  has a rectangular cross-sectional shape. The downstream groove portion  83  is formed such that the opening area of the notch  80  is gradually decreased from the upstream groove portion  81  in the rotation direction of the rotor  2  (in the direction approaching the discharge port  32 ). 
       FIG. 10A  is a line diagram showing a relationship between the length of the notch  80  in the circumferential direction of the rotor  2  and the opening area of the notch  80 . As shown in this line diagram, the opening area of the notch  80  is gradually increased from the distal-end portion  80 A towards the gradient-changing portion  82  at the upstream groove portion  81 , is increased in one step at the gradient-changing portion  82 , and is gradually decreased from the gradient-changing portion  82  towards the proximal-end portion  80 B at the downstream groove portion  83 . 
       FIG. 10B  is a line diagram showing a relationship between the length of the notch  80  in the circumferential direction of the rotor  2  and the rate of change of the opening area of the notch  80 . As shown in this line diagram, the rate of change of the opening area of the notch  80  is gradually increased from the distal-end portion  80 A towards the gradient-changing portion  82  at the upstream groove portion  81 , is increased/decreased in one step at the gradient-changing portion  82 , and becomes a negative constant value at the downstream groove portion  83 . The gradient-changing portion  82  is a part at which the rate of change of the opening area of the notch  80  is discontinuously changed and decreased from the upstream groove portion  81  towards the downstream groove portion  83 . 
     The gradient-changing portion  82  is not limited to the configuration mentioned above, and may be configured by curved surfaces with which the rate of change of the opening area of the notch  80  is continuously changed and decreased from the upstream groove portion  81  towards the downstream groove portion  83 . 
     According to the above-mentioned second embodiment, operational advantages shown below can be afforded. 
     [4] The notch  80  has the upstream groove portion  81  at which the opening area of the notch  80  is gradually increased from the distal-end portion  80 A in the rotation direction of the rotor  2  and the downstream groove portion  83  at which the opening area of the notch  80  is gradually decreased from the upstream groove portion  81  in the rotation direction of the rotor  2 . 
     According to the above-mentioned configuration, with the downstream groove portion  83  whose opening area is gradually decreased, the flow of the working oil from the pump chambers  7  commencing the intermediate stage of the compression stroke to the pump chambers  7  commencing the initial stage of the compression stroke is facilitated, and at the same time, the flow of the working oil from the discharge ports  32  and  34  commencing the latter stage of the compression stroke to the notch  80  is suppressed. The propagation of the pressure of the working oil through the notch  80  between the pump chambers  7  facing against the notch  80  is facilitated in this way, and thus, when the rotor  2  is rotated at high speed, the occurrence of the pulsation of the discharge pressure at the discharge ports  32  and  34  is suppressed. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described with reference to  FIGS. 11A to 11D, 12A, and 12B . In the following, differences from the above-mentioned first embodiment will be mainly described, and components that are the same as those in the above-mentioned first embodiment are assigned the same reference numerals and descriptions thereof will be omitted. 
     A notch  90  according to the third embodiment is configured so as to have a restrictor portion  95  provided at the discharge port  32  such that the opening area of the notch  90  is locally decreased. 
     As shown in  FIG. 11A , the notch  90  has a distal-end portion  90 A located at a distal position from the discharge port  32  and a proximal-end portion  90 B that opens at the inner wall  32 A of the discharge port  32 . The notch  90  has an upstream groove portion  91  that extends from the distal-end portion  90 A in the rotation direction of the rotor  2 , a gradient-changing portion  92  that is provided at a downstream end of the upstream groove portion  91 , a downstream groove portion  93  that extends from the gradient-changing portion  92  in the rotation direction of the rotor  2 , a step portion  94  that is provided at a downstream end of the downstream groove portion  93 , and the restrictor portion  95  provided at the discharge port  32  such that the opening area of the notch  90  is locally decreased. The gradient-changing portion  92  is a step which is formed between the upstream groove portion  91  and the downstream groove portion  93 . The step portion  94  is a step which is formed between the downstream groove portion  93  and the restrictor portion  95 . 
       FIG. 11B  is a sectional view taken along a line XIB-XIB in  FIG. 11A . As shown in this sectional view, the upstream groove portion  91  of the notch  90  has a triangular cross-sectional shape. The upstream groove portion  91  is formed such that the opening area of the notch  90  is gradually increased from the distal-end portion  90 A in the rotation direction of the rotor  2  (in the direction approaching the gradient-changing portion  92 ). 
       FIG. 11C  is a sectional view taken along a line XIC-XIC in  FIG. 11A . As shown in this sectional view, the downstream groove portion  93  of the notch  90  has a rectangular cross-sectional shape. The downstream groove portion  93  is formed such that the opening area of the notch  90  remains unchanged and is kept constant from the upstream groove portion  91  in the rotation direction of the rotor  2  (in the direction approaching the discharge port  32 ). 
       FIG. 11D  is a sectional view taken along a line XID-XID in  FIG. 11A . As shown in this sectional view, the restrictor portion  95  of the notch  90  has a rectangular cross-sectional shape that is smaller than the downstream groove portion  93 . The restrictor portion  95  is formed such that the opening area of the notch  90  remains unchanged and is kept constant from the downstream groove portion  93  in the rotation direction of the rotor  2  (in the direction approaching the discharge port  32 ). 
       FIG. 12A  is a line diagram showing a relationship between the length in the circumferential direction of the rotor  2  and the opening area in the notch  90 . As shown in this line diagram, the opening area of the notch  90  is gradually increased from the distal-end portion  90 A towards the gradient-changing portion  92  at the upstream groove portion  91 , is increased in one step at the gradient-changing portion  92 , becomes a constant value at the downstream groove portion  93 , is decreased in one step at the step portion  94 , and becomes a constant value at the restrictor portion  95 . 
       FIG. 12B  is a line diagram showing a relationship between the length in the circumferential direction of the rotor  2  and the rate of change of the opening area in the notch  90 . As shown in this line diagram, the rate of change of the opening area of the notch  90  is gradually increased from the distal-end portion  90 A towards the gradient-changing portion  92  at the upstream groove portion  91 , is increased/decreased in one step at the gradient-changing portion  92 , becomes zero at the downstream groove portion  93 , is increased/decreased in one step at the step portion  94 , and becomes zero at the restrictor portion  95 . The gradient-changing portion  92  is a part at which the rate of change of the opening area of the notch  90  is discontinuously changed and decreased. 
     The gradient-changing portion  92  and the step portion  94  are not limited to the configuration mentioned above, and may be configured by curved surfaces with which the rate of change of the opening area of the notch  90  is continuously changed. 
     According to the above-mentioned third embodiment, operational advantages shown below can be afforded. 
     [5] The notch  90  has the restrictor portion  95  provided at the discharge port  32  such that the opening area of the notch  90  is locally decreased. 
     According to the above-mentioned configuration, with the restrictor portion  95  with which the opening area is locally decreased, the flow of the working oil from the discharge ports  32  and  34  commencing the latter stage of the compression stroke to the notch  90  is suppressed. With such a configuration, when the rotor  2  is rotated at high speed, the occurrence of the pulsation of the discharge pressure at the discharge ports  32  and  34  is suppressed. 
     Embodiments of this invention were described above, but the above embodiments are merely examples of applications of this invention, and the technical scope of this invention is not limited to the specific constitutions of the above embodiments. 
     For example, although the notch according to the above-mentioned embodiments has a downstream groove portion at which the opening area is kept constant or decreased, the configuration is not limited thereto, and a configuration in which the notch has a downstream groove portion at which the opening area is gradually increased, and the rate of change of the opening area of this downstream groove portion is smaller than the rate of change of the opening area of the upstream groove portion may be employed. 
     In addition, the present invention may be applied not only to the vane pump in which the discharge capacity (pump displacement) is constant, but to the vane pump in which the discharge capacity can be changed by moving the cam ring. 
     This application claims priority based on Japanese Patent Application No. 2014-12054 filed with the Japan Patent Office on Jan. 27, 2014, the entire contents of which are incorporated into this specification.