Variable displacement pump

Abstract

A variable displacement pump includes: a rotor mounted in a body; a cam ring mounted radially outside of the rotor, and arranged to move with a change in an eccentricity of the cam ring with respect to the rotor, wherein change of the eccentricity causes a change in a specific discharge rate; and an electromagnetic actuator arranged to actuate the cam ring for regulating the eccentricity. During control of operation of the electromagnetic actuator, a first response is set slower than a second response, wherein the first response is a response of movement of the cam ring to a change of an input signal in a direction to request a decrease in the specific discharge rate, and the second response is a response of movement of the cam ring to a change of the input signal in a direction to request an increase in the specific discharge rate.

What is claimed is: 
     
         1 . A variable displacement pump for supplying working fluid to a hydraulic device mounted on a vehicle, the variable displacement pump comprising:
 a body;   a drive shaft rotatably supported by the body;   a rotor mounted in the body, and arranged to be rotated by the drive shaft;   a cam ring mounted radially outside of the rotor in the body, and arranged to move with a change in an eccentricity of the cam ring with respect to the rotor, wherein change of the eccentricity causes a change in a specific discharge rate as a quantity of discharge of working fluid per one rotation of the rotor;   an electromagnetic actuator arranged to actuate the cam ring for regulating the eccentricity; and   a controller configured to: receive an input signal outputted from a sensor arranged to measure a state of operation of the vehicle; and output a drive signal to the electromagnetic actuator, wherein the controller is programmed to:
 control operation of the electromagnetic actuator with reference to the input signal by outputting the drive signal; and 
 set a first acceleration smaller than a second acceleration, during control of operation of the electromagnetic actuator, wherein the first acceleration is an acceleration of the cam ring when the cam ring is moving in a direction to reduce the specific discharge rate, and the second acceleration is an acceleration of the cam ring when the cam ring is moving in a direction to increase the specific discharge rate. 
   wherein the controller is programmed to prevent the cam ring from overshooting a target position, by reducing the specific discharge rate, immediately before the cam ring reaches the target position, while the cam ring is moving in the direction to increase the specific discharge rate.   
     
     
         2 . A variable displacement pump for supplying working fluid to a hydraulic device mounted on a vehicle, the variable displacement pump comprising:
 a body;   a drive shaft rotatably supported by the body;   a rotor mounted in the body, and arranged to be rotated by the drive shaft;   a cam ring mounted radially outside of the rotor in the body, and arranged to move with a change in an eccentricity of the cam ring with respect to the rotor, wherein change of the eccentricity causes a change in a specific discharge rate as a quantity of discharge of working fluid per one rotation of the rotor;   an electromagnetic actuator arranged to actuate the cam ring for regulating the eccentricity; and   a controller configured to: receive an input signal outputted from a sensor arranged to measure a state of operation of the vehicle; and output a drive signal to the electromagnetic actuator, wherein the controller is programmed to:
 control operation of the electromagnetic actuator with reference to the input signal by outputting the drive signal; and 
 set a first acceleration smaller than a second acceleration, during control of operation of the electromagnetic actuator, wherein the first acceleration is an acceleration of the cam ring when the cam ring is moving in a direction to reduce the specific discharge rate, and the second acceleration is an acceleration of the cam ring when the cam ring is moving in a direction to increase the specific discharge rate. 
   wherein the controller is programmed to reduce a speed of the cam ring as the cam ring approaches a target position, while the cam ring is moving in the direction to increase the specific discharge rate.