Variable displacement vane pump

Abstract

An object of the present invention is to provide a variable displacement vane pump capable of further reducing a pulse pressure. A vane pump ( 1 ) includes a cam ring ( 33 ). The cam ring ( 33 ) is annularly formed, and defines a plurality of pump chambers ( 38 ) on an inner peripheral side thereof in cooperation with a rotor ( 31 ) and vanes ( 32 ). An inner peripheral surface ( 330 ) of the cam ring ( 33 ) is formed in such a manner that, assuming that a confinement region refers to a region between an end portion of an intake port ( 221 ) and an end portion of a discharge port ( 222 ), at a timing when the pump chamber ( 38 ) communicates with or is disconnected from the discharge port ( 222 ) on one side corresponding to one of confinement regions or a timing close thereto, a change in a volume change amount of the pump chamber ( 38 ) on another side corresponding to the other of the confinement regions has an extreme value in a direction for reducing a change in a discharge amount at the time of the above-described communication/disconnection.

What is claimed is: 
     
         1 . A variable displacement vane pump comprising:
 a pump housing including a pump element containing portion;   a driving shaft supported on the pump housing;   a rotor provided in the pump housing and configured to be rotationally driven by the driving shaft, the rotor also including an odd number of slots in a circumferential direction of the rotor;   an odd number of vanes provided in the slots in a manner projectable therefrom and retractable therein;   a cam ring movably provided in the pump element containing portion and annularly formed, the cam ring forming a plurality of pump chambers on an inner peripheral side of the cam ring in cooperation with the rotor and the vanes;   an intake port formed in the pump housing and opened to a region where a volume of each of the plurality of pump chambers increases according to a rotation of the rotor;   a discharge port formed in the pump housing and opened to a region where the volume of each of the plurality of pump chambers reduces according to the rotation of the rotor; and   a cam ring control mechanism provided in the pump housing and configured to control an amount of eccentricity of the cam ring from the rotor,   wherein the cam ring has an inner peripheral surface formed in such a manner that,   assuming that a distance between the vanes adjacent to each other in a direction around a rotational axis of the driving shaft is one pitch,   in a first confinement region that is a region from a terminating end portion of the intake port to a start end portion of the discharge port,   a vane projection amount, which is a distance from a center of a rotation of the driving shaft to the inner peripheral surface of the cam ring, gradually increases from the terminating end portion of the intake port and then gradually reduces toward the start end portion of the discharge port after passing through a point where the vane projection amount reaches a maximum value,   the point where the vane projection amount reaches the maximum value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, and   an absolute value of a gradient of a cam profile, which is a change rate of the vane projection amount, is larger in a range from a position ½ pitch away from the terminating end portion of the intake port to the start end portion of the discharge port than in a range from the terminating end portion of the intake port to ½ pitch therefrom.   
     
     
         2 . The variable displacement vane pump according to  claim 1 , wherein, assuming that the second confinement region is a region between a terminating end portion of the discharge port and a start end portion of the intake port,
 the pump housing has a pair of surfaces facing the first confinement region and the second confinement region in a direction along the rotational axis of the driving shaft, the pair of surfaces being formed so as to extend in parallel with each other and each shaped as a flat surface.   
     
     
         3 . The variable displacement vane pump according to  claim 1 , wherein the cam ring is formed in such a manner that the point where the vane projection amount reaches the maximum value is located in a range from a position ½ away from the terminating end portion of the intake port to a position ⅔ away from the terminating end portion of the intake port. 
     
     
         4 . The variable displacement vane pump according to  claim 1 , wherein the inner peripheral surface of the cam ring is formed in such a manner that, when the cam ring is moved by ⅓ of an entire eccentricity amount from a position where the eccentricity amount of the cam ring is maximized toward a position side where the eccentricity amount of the cam ring is minimized, in the first confinement region that is the region between the terminating end portion of the intake port to the start end portion of the discharge port,
 the vane projection amount, which is the distance from the center of the rotation of the driving shaft to the inner peripheral surface of the cam ring, gradually increases from the terminating end portion of the intake port and then gradually reduces toward the start end portion of the discharge port after passing through the point where the vane projection amount reaches the maximum value, 
 the point where the vane projection amount reaches the maximum value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, and 
 the absolute value of the gradient of the cam profile, which is the change rate of the vane projection amount, is larger in the range from the position ½ pitch away from the terminating end portion of the intake port to the start end portion of the discharge port than in the range from the terminating end portion of the intake port to ½ pitch therefrom. 
 
     
     
         5 . The variable displacement vane pump according to  claim 4 , wherein the cam ring is formed in such a manner that the vane projection amount constantly reduces according to the rotation of the rotor in the first confinement region when the cam ring is located at the position where the eccentricity amount of the cam ring is maximized. 
     
     
         6 . The variable displacement vane pump according to  claim 1 , wherein the cam ring is formed in such a manner that the absolute value of the gradient of the cam profile satisfies 1.1<=(the range from the position ½ pitch away from the terminating end portion of the intake port to the position of the start end portion of the discharge port)/(the range from the position of the terminating end portion of the intake port to the position ½ pitch therefrom). 
     
     
         7 . The variable displacement vane pump according to  claim 6 , wherein the cam ring is formed in such a manner that the absolute value of the gradient of the cam profile satisfies 1.15<=(the range from the position ½ pitch away from the terminating end portion of the intake port to the position of the start end portion of the discharge port)/(the range from the position of the terminating end portion of the intake port to the position ½ pitch therefrom). 
     
     
         8 . The variable displacement vane pump according to  claim 1 , wherein the cam ring is formed so as to have a region where the gradient of the cam profile has a negative value in a second confinement region, which is a region from a terminating end portion of the discharge port to a start end portion of the intake port, when the cam ring is located at a position where an eccentricity amount of the cam ring is minimized. 
     
     
         9 . The variable displacement vane pump according to  claim 1 , wherein the discharge port includes a notch portion only on a start end portion side of the discharge port. 
     
     
         10 . A variable displacement vane pump comprising:
 a pump housing including a pump element containing portion;   a driving shaft supported on the pump housing;   a rotor provided in the pump housing and configured to be rotationally driven by the driving shaft, the rotor also including an odd number of slots in a circumferential direction of the rotor;   an odd number of vanes provided in the slots in a manner projectable therefrom and retractable therein;   a cam ring movably provided in the pump element containing portion and annularly formed, the cam ring forming a plurality of pump chambers on an inner peripheral side of the cam ring in cooperation with the rotor and the vanes;   an intake port formed in the pump housing and opened to a region where a volume of each of the plurality of pump chambers increases according to a rotation of the rotor;   a discharge port formed in the pump housing and opened to a region where the volume of each of the plurality of pump chambers reduces according to the rotation of the rotor; and   a cam ring control mechanism provided in the pump housing and configured to control an amount of eccentricity of the cam ring from the rotor,   wherein the cam ring has an inner peripheral surface formed in such a manner that, assuming that a distance between the vanes adjacent to each other in a direction around a rotational axis of the driving shaft is one pitch, when the cam ring is moved by ⅓ of an entire eccentricity amount from a position where the eccentricity amount of the cam ring is maximized toward a position side where the eccentricity amount of the cam ring is minimized, in a first confinement region that is a region from a terminating end portion of the intake port to a start end portion of the discharge port,   a vane projection amount, which is a distance from a center of a rotation of the driving shaft to the inner peripheral surface of the cam ring, gradually increases from the terminating end portion of the intake port and then gradually reduces toward the start end portion of the discharge port after passing through a point where the vane projection amount reaches a maximum value,   the point where the vane projection amount reaches the maximum value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, and   an absolute value of a gradient of a cam profile, which is a change rate of the vane projection amount, is larger in a range from a position ½ pitch away from the terminating end portion of the intake port to the start end portion of the discharge port than in a range from the terminating end portion of the intake port to ½ pitch therefrom.   
     
     
         11 . The variable displacement vane pump according to  claim 10 , wherein the cam ring is formed in such a manner that the vane projection amount constantly reduces according to the rotation of the rotor in the first confinement region when the cam ring is located at the position where the eccentricity amount of the cam ring is maximized. 
     
     
         12 . The variable displacement vane pump according to  claim 10 , wherein the cam ring is formed so as to have a region where the gradient of the cam profile has a negative value in a second confinement region, which is a region from a terminating end portion of the discharge port to a start end portion of the intake port, when the cam ring is located at a position where an eccentricity amount of the cam ring is minimized.