Patent ID: 6029689
Filing Date: 2000-02-29
Classification: F15B,Y10T

Abstract:
A counter balance valve, comprising:a spool, which is moved to a neutral position to shut off a first pump port from a first motor port and to shut off a second pump port from a second motor port, a first position to shut off the first pump port from the first motor port and to communicate the second pump port with the second motor port, and a second position to communicate the first pump port with the first motor port and to shut off the second pump port from the second motor port;springs, which maintain the spool in the neutral position;a left chamber, where the spool is moved from the neutral position toward the first position;a right chamber, where the spool is moved from the neutral position toward the second position;a first communication area switching section, which changes a communication area of the left chamber with the first pump port; anda second communication area switching section, which changes a communication area of the right chamber with the second pump port; wherein:the communication area of the first communication area switching section is large at a start of a stroke when the spool is moved from the first position toward the neutral position, small at a middle of the stroke, medium at an end of the stroke, and intermediate between small and medium when the spool is moved from the neutral position to the second position; andthe communication area of the second communication area switching section is large at the start of a stroke when the spool is moved from the second position toward the neutral position, small at the middle of the stroke, medium at the end of the stroke, and intermediate between small and medium when the spool is moved from the neutral position to the first position.