Variable displacement vane pump

Abstract

A variable displacement vane pump includes a drive shaft; a rotor formed with slots; vanes received by the slots; a cam ring which can become eccentric and cooperates with the rotor and vanes to define pump chambers; suction and discharge ports opened to the pump chambers; a sealing member dividing a space on an outer circumferential surface of the cam ring into first and second fluid pressure chambers; a metering orifice formed on a discharge passage connected with the discharge port; and a pressure control section adapted to control a pressure which is introduced into the first or second fluid pressure chamber. The pressure control section includes a high pressure chamber into which an upstream pressure of metering orifice is introduced, a medium pressure chamber into which a downstream pressure of metering orifice is introduced, and a low pressure chamber connected with a reservoir tank. The vane pump further includes a relief valve adapted to drain the downstream pressure of metering orifice to the reservoir tank; and a variable metering mechanism configured to narrow an area of the metering orifice at least when the relief valve is opened.

1 . A variable displacement vane pump comprising:
 a pump body;   a drive shaft supported rotatably by the pump body;   a rotor disposed inside the pump body and adapted to be rotatably driven by the drive shaft, the rotor being formed with a plurality of slots spaced from each other in a circumferential direction of the rotor;   a plurality of vanes received by the slots so as to be movable out from the slots and into the slots;   a cam ring formed in an annular shape and disposed inside the pump body to permit the cam ring to become eccentric relative to the drive shaft, the cam ring cooperating with the rotor and the vanes to define a plurality of pump chambers on an inner circumferential side of the cam ring;   a first plate member and a second plate member disposed on axially both sides of the cam ring;   a suction port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a discharge port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a sealing member provided on an outer circumferential side of the cam ring, the sealing member dividing a space on an outer circumferential surface of the cam ring into a first fluid pressure chamber and a second fluid pressure chamber, wherein a flow rate of working fluid discharged from the discharge port is increased when the cam ring moves to the first fluid pressure chamber, wherein the flow rate of working fluid discharged from the discharge port is decreased when the cam ring moves to the second fluid pressure chamber;   a metering orifice formed on a discharge passage connected with the discharge port;   a pressure control section adapted to control a pressure which is introduced into the first fluid pressure chamber or the second fluid pressure chamber, the pressure control section comprising
 a high pressure chamber into which an upstream pressure of the metering orifice is introduced, 
 a medium pressure chamber into which a downstream pressure of the metering orifice is introduced, and 
 a low pressure chamber connected with a reservoir tank for storing working fluid; 
   a relief valve provided between a downstream side of the metering orifice and the reservoir tank, the relief valve being adapted to be opened by receiving a pressure greater than or equal to a predetermined level and thereby to drain the downstream pressure of the metering orifice to the reservoir tank; and   a variable metering mechanism configured to narrow a cross-sectional area of opening portion of the metering orifice at least when the relief valve is opened.   
   
   
       2 . The variable displacement vane pump as claimed in  claim 1 , wherein
 the cam ring is adapted to swing so as to gradually block the opening portion of the metering orifice, the variable metering mechanism being achieved by the metering orifice and the cam ring; and   the metering orifice comprises the opening portion formed in an axial end surface of the first plate member or the second plate member.   
   
   
       3 . The variable displacement vane pump as claimed in  claim 2 , wherein
 the variable metering mechanism is configured to gradually narrow the opening portion of the metering orifice after the cam ring has swung to its position having a predetermined angle.   
   
   
       4 . The variable displacement vane pump as claimed in  claim 2 , wherein
 a circumferential width of the opening portion of the metering orifice is greater than a radial width thereof.   
   
   
       5 . The variable displacement vane pump as claimed in  claim 4 , wherein
 the opening portion of the metering orifice is formed in an elliptical shape or a slot shape.   
   
   
       6 . The variable displacement vane pump as claimed in  claim 4 , wherein
 the metering orifice comprises a plurality of holes.   
   
   
       7 . The variable displacement vane pump as claimed in  claim 2 , further comprising
 a pilot orifice provided on a passage connecting the discharge port with the high pressure chamber.   
   
   
       8 . The variable displacement vane pump as claimed in  claim 2 , further comprising
 a damper orifice provided on a passage connecting the metering orifice with the medium pressure chamber.   
   
   
       9 . The variable displacement vane pump as claimed in  claim 1 , wherein
 the variable displacement vane pump further comprises a piston adapted to move in response to a swing of the cam ring; and   the metering orifice is formed in the piston.   
   
   
       10 . The variable displacement vane pump as claimed in  claim 1 , wherein
 the variable metering mechanism is configured to vary the area of opening portion of the metering orifice on the basis of a downstream pressure of the relief valve.   
   
   
       11 . The variable displacement vane pump as claimed in  claim 10 , wherein
 the variable metering mechanism is achieved by a spool adapted to controllably vary the area of opening portion of the metering orifice by moving relative to the metering orifice.   
   
   
       12 . A variable displacement vane pump comprising:
 a pump body;   a drive shaft supported rotatably by the pump body;   a rotor disposed inside the pump body and adapted to be rotatably driven by the drive shaft, the rotor being formed with a plurality of slots spaced from each other in a circumferential direction of the rotor;   a plurality of vanes received by the slots so as to be movable out from the slots and into the slots;   a cam ring formed in an annular shape and disposed inside the pump body to permit the cam ring to become eccentric relative to the drive shaft, the cam ring cooperating with the rotor and the vanes to define a plurality of pump chambers on an inner circumferential side of the cam ring;   a first plate member and a second plate member disposed on axially both sides of the cam ring;   a suction port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a discharge port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a sealing member provided on an outer circumferential side of the cam ring, the sealing member dividing a space on an outer circumferential surface of the cam ring into a first fluid pressure chamber and a second fluid pressure chamber, wherein a flow rate of working fluid discharged from the discharge port is increased when the cam ring moves to the first fluid pressure chamber, wherein the flow rate of working fluid discharged from the discharge port is decreased when the cam ring moves to the second fluid pressure chamber;   a metering orifice formed on a discharge passage connected with the discharge port;   a pressure control section adapted to control a pressure which is introduced into the first fluid pressure chamber or the second fluid pressure chamber, the pressure control section comprising
 a high pressure chamber into which an upstream pressure of the metering orifice is introduced, 
 a medium pressure chamber into which a downstream pressure of the metering orifice is introduced, and 
 a low pressure chamber connected with a reservoir tank for storing working fluid; 
   a relief valve provided between a downstream side of the metering orifice and the reservoir tank, the relief valve being adapted to be opened by receiving a pressure greater than or equal to a predetermined level and thereby to drain the downstream pressure of the metering orifice into the reservoir tank; and   a variable metering mechanism configured to narrow a cross-sectional area of opening portion of the metering orifice when a discharge pressure on a downstream side of the discharge port is higher than or equal to a predetermined pressure.   
   
   
       13 . The variable displacement vane pump as claimed in  claim 12 , wherein
 the variable metering mechanism is achieved by a fluid-pressure sensor adapted to sense the pressure discharged from the discharge port and an electromagnetic valve adapted to be opened based on a sensed signal of the fluid-pressure sensor.   
   
   
       14 . The variable displacement vane pump as claimed in  claim 12 , wherein
 the variable metering mechanism is achieved by a spool adapted to controllably vary the area of opening portion of the metering orifice by moving relative to the metering orifice.   
   
   
       15 . A variable displacement vane pump comprising:
 a pump body;   a drive shaft supported rotatably by the pump body;   a rotor disposed inside the pump body and adapted to be rotatably driven by the drive shaft, the rotor being formed with a plurality of slots spaced from each other in a circumferential direction of the rotor;   a plurality of vanes received by the slots so as to be movable out from the slots and into the slots;   a cam ring formed in an annular shape and disposed inside the pump body to permit the cam ring to become eccentric relative to the drive shaft, the cam ring cooperating with the rotor and the vanes to define a plurality of pump chambers on an inner circumferential side of the cam ring;   a first plate member and a second plate member disposed on axially both sides of the cam ring;   a suction port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a discharge port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a sealing member provided on an outer circumferential side of the cam ring, the sealing member dividing a space on an outer circumferential surface of the cam ring into a first fluid pressure chamber and a second fluid pressure chamber, wherein a flow rate of working fluid discharged from the discharge port is increased when the cam ring moves to the first fluid pressure chamber, wherein the flow rate of working fluid discharged from the discharge port is decreased when the cam ring moves to the second fluid pressure chamber;   a metering orifice formed on a discharge passage connected with the discharge port;   a pressure control section adapted to control a pressure which is introduced into the first fluid pressure chamber or the second fluid pressure chamber, the pressure control section comprising
 a high pressure chamber into which an upstream pressure of the metering orifice is introduced, 
 a medium pressure chamber into which a downstream pressure of the metering orifice is introduced, and 
 a low pressure chamber connected with a reservoir tank for storing working fluid; 
   a relief valve provided between a downstream side of the metering orifice and the reservoir tank, the relief valve being adapted to be opened by receiving a pressure greater than or equal to a predetermined level and thereby to drain the downstream pressure of the metering orifice into the reservoir tank; and   a variable metering mechanism configured to narrow a cross-sectional area of opening portion of the metering orifice to a larger extent as the eccentricity of the cam ring becomes smaller when the relief valve is open.   
   
   
       16 . The variable displacement vane pump as claimed in  claim 15 , wherein
 the cam ring is adapted to swing so as to gradually block the opening portion of the metering orifice, the variable metering mechanism being achieved by the metering orifice and the cam ring; and   the metering orifice comprises the opening portion formed in an axial end surface of the first plate member or the second plate member.   
   
   
       17 . The variable displacement vane pump as claimed in  claim 15 , wherein
 the variable metering mechanism is configured to gradually narrow the opening portion of the metering orifice after the cam ring has swung to its position having a predetermined angle.   
   
   
       18 . The variable displacement vane pump as claimed in  claim 15 , further comprising
 a pilot orifice provided on a passage connecting the discharge port with the high pressure chamber.   
   
   
       19 . A variable displacement vane pump comprising:
 a pump body;   a drive shaft supported rotatably by the pump body;   a rotor disposed inside the pump body and adapted to be rotatably driven by the drive shaft, the rotor being formed with a plurality of slots spaced from each other in a circumferential direction of the rotor;   a plurality of vanes received by the slots so as to be movable out from the slots and into the slots;   a cam ring formed in an annular shape and disposed inside the pump body to permit the cam ring to become eccentric relative to the drive shaft, the cam ring cooperating with the rotor and the vanes to define a plurality of pump chambers on an inner circumferential side of the cam ring;   a first plate member and a second plate member disposed on axially both sides of the cam ring;   a suction port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a discharge port provided on a side of at least one of the first plate member and the second plate member and opened to at least one of the plurality of pump chambers;   a sealing member provided on an outer circumferential side of the cam ring, the sealing member dividing a space on an outer circumferential surface of the cam ring into a first fluid pressure chamber and a second fluid pressure chamber, wherein a flow rate of working fluid discharged from the discharge port is increased when the cam ring moves to the first fluid pressure chamber, wherein the flow rate of working fluid discharged from the discharge port is decreased when the cam ring moves to the second fluid pressure chamber;   a metering orifice formed on a discharge passage connected with the discharge port;   a pressure control section adapted to control a pressure which is introduced into the first fluid pressure chamber or the second fluid pressure chamber, the pressure control section comprising
 a high pressure chamber into which an upstream pressure of the metering orifice is introduced, 
 a medium pressure chamber into which a downstream pressure of the metering orifice is introduced, and 
 a low pressure chamber connected with a reservoir tank for storing working fluid; 
   a fluid-pressure sensor adapted to sense a pressure discharged from the discharge port;   a relief valve adapted to drain the downstream pressure of the metering orifice to the reservoir tank, and a pressure-using device adapted to use a pressure supplied from the discharge port; and   a variable metering mechanism configured to narrow a cross-sectional area of flow passage of the metering orifice on the basis of an output signal of the fluid-pressure sensor.   
   
   
       20 . The variable displacement vane pump as claimed in  claim 19 , wherein
 the variable metering mechanism is achieved by an electromagnetic valve adapted to be opened based on the output signal of the fluid-pressure sensor.