Patent ID: 6058962
Filing Date: 2000-05-09
Classification: B62D,Y10T

Abstract:
A flow control valve for a hydraulic pump, comprising:a variable constriction (3) arranged in the middle of a hydraulic fluid feed passage for feeding hydraulic fluid discharged from a hydraulic pump (VP);a body (10);a spool (7) slidably incorporated in the body (10);a pressure chamber (8a) arranged so as to face one end of the spool (7);a drain port (5) arranged so as to communicate with a tank;a first pilot chamber (101A) arranged so as to face the other end of the spool (7);a spring (9) arranged so as to act initial load on the end of the spool (7) facing the first pilot chamber (101A);the pressure chamber (8a) having a pressure on an upstream side of said variable constriction (3) guided thereto;the first pilot chamber (101A) having a pressure on a downstream side of said variable constriction (3) guided thereto;the pressure chamber (8a) having a pressure therein which overcomes elastic force of the spring (9) and an action of a pressure in the first pilot chamber to move the spool (7) when a pressure difference between both sides of the variable constriction (3) reaches a predetermined level or more;the pressure chamber (8a) being rendered open to the drain port (5) at a degree of opening corresponding to a position of the spool (7);a piston (102) arranged so as to face the first pilot chamber (101A) while being opposite to the other end of the spool (7) and abutted against said spring (9);a second pilot chamber (101B) arranged opposite to the first pilot chamber (101A) with the piston (102) being interposed therebetween; anda change-over spool (106) slidably incorporated in the piston (102) to permit a pressure in the first pilot chamber (101A) to act thereon;the change-over spool (106) draining the second pilot chamber (101B) at a normal position thereof and moving to permit the second pilot chamber (101B) to communicate with the first pilot chamber (101A) when a pressure in the first pilot chamber (101A) reaches a predetermined level or more;the piston (102) being so formed that a first pressure receiving surface thereof facing the first pilot chamber (101A) has an area smaller than that of a second pressure receiving surface thereof facing the second pilot chamber (101B),characterized in that:constrictions (106A) and (106B) are arranged in the middle of a communication passage through which the second pilot chamber (101B) is drained and in the middle of a communication passage which permits said second pilot chamber (101B) to communicate with the first pilot chamber (101A), respectively.