Patent ID: 6068013
Filing Date: 2000-05-30
Classification: E02F,F15B,Y10T

Abstract:
A counter balance valve comprising:a valve body provided with a valve bore having first and second pump-side ports, first and second motor-side ports and an auxiliary port, a spool fitted in the valve bore to be slidable in a longitudinal direction thereof so as to establish communication between said respective ports and to block the communication therebetween, left and right springs maintaining the spool in a neutral position thereof at which said respective ports are closed, a left pressure receiving chamber acting to shift said spool by a pressure oil supplied therein to a first travelling position at which said first pumpside port and said auxiliary port are communicated with each other and said second pump-side port and said second motor-side port are also communicated with each other, and a right pressure receiving chamber acting to shift said spool by a pressure oil supplied therein to a second travelling position at which said second pump-side port and said auxiliary port are communicated with each other and said first pump-side port and said first motor-side port are also communicated with each other;wherein said spool is formed with a first axial bore communicated with said left pressure receiving chamber, a second axial bore communicated with said right pressure receiving chamber, first and second small diameter bores always communicating said first and second axial bores with said first and second pump-side ports, respectively, and first and second large diameter bores communicating said first and second axial bores with an outer peripheral surface of said spool; andwherein said first and second large diameter bores are closed when said spool is positioned in the neutral position and an intermediate position between said first and second travelling positions, and said first and second large diameter bores are communicated with said auxiliary port when said spool is positioned in said first and second travelling positions, respectively.