Flow rate control device for a pump

A flow rate control device for a pump, comprising:

• a housing;
• a pump pressure chamber provided in said housing, into which a pump discharge pressure is led;
• a choke tubular passageway communicating with said pump pressure chamber;
• an output chamber communicating through said choke tubular passageway with said pump pressure chamber, a pressure obtained by reducing the pump discharge pressure being led to said output chamber;
• a pressure reducing chamber which is provided in said housing and communicates with said output chamber;
• a by-pass port which is provided in said housing and communicates with a pump suction side;
• a spool valve which is slidably provided in said housing, which has both ends exposed in said pump pressure chamber and said pressure reducing chamber, respectively, said spool valve causing a pressure medium from said pump pressure chamber to flow into said by-pass port as much as said spool valve slides in an axial direction thereof;
• a central shaft member arranged in said housing, on which said choke tubular passageway is formed;
• and
• a sleeve member provided around said central shaft member;
• wherein said sleeve member is moved from said pump pressure chamber towards said pressure reducing chamber with respect to said central shaft member in such a manner as to change an opening area of said choke tubular passageway.