Patent ID: 7287375
Filing Date: 2007-10-30
Classification: B66F,F15B

Abstract:
1. A hydraulic control device for controlling supply of hydraulic fluid from a high pressure circuit to a downstream circuit, wherein the downstream circuit includes a plurality of hydraulic actuators and a plurality of switching valves for operating the hydraulic actuators, the hydraulic actuators including at least a first hydraulic actuator and a second hydraulic actuator, wherein the high pressure circuit is connected to a hydraulic fluid return circuit through a bypass line, the hydraulic control device comprising: a flow rate compensation mechanism, which adjusts the opening degree of the bypass line according to the load pressure of the downstream circuit, thereby adjusting the flow rate of hydraulic fluid flowing from the high pressure circuit to the return circuit such that the flow rate of hydraulic fluid supplied from the high pressure circuit to the downstream circuit is compensated for, wherein the flow rate compensation mechanism includes: an actuation valve member, which is movable in an axial direction to adjust the opening degree of the bypass line, wherein the actuation valve member includes a first end and a second end opposite from the first end; a first pressure chamber corresponding to the first end of the actuation valve member, wherein hydraulic fluid from the high pressure circuit is drawn into the first pressure chamber; a second pressure chamber corresponding to the second end of the actuation valve member, wherein hydraulic fluid from the high pressure circuit is drawn into the second pressure chamber, wherein the pressure of hydraulic fluid in the first pressure chamber presses the actuation valve member toward the second pressure chamber, wherein the pressure of hydraulic fluid in the second pressure chamber presses the actuation valve member toward the first pressure chamber, and wherein the actuation valve member is moved in the axial direction according to the pressure of hydraulic fluid in the first pressure chamber and the pressure of hydraulic fluid in the second pressure chamber; a pressure controller, which controls the pressure of hydraulic fluid in the first pressure chamber according to the load pressure of the downstream circuit; a first relief valve mechanism, which limits the pressure of hydraulic fluid in the first hydraulic actuator to a value that is equal to or lower than a predetermined first permissible value, wherein the first relief valve mechanism includes a first relief pressure controller, wherein the first relief pressure controller opens and closes a relief passage that connects the first pressure chamber to the return circuit, thereby adjusting the pressure of hydraulic fluid in the first pressure chamber; and a second relief valve mechanism, which limits the pressure of hydraulic fluid in the second hydraulic actuator to a value that is equal to or lower than a predetermined second permissible value, wherein the second relief valve mechanism includes a second relief pressure controller, and wherein the second relief pressure controller selectively permits hydraulic fluid receiving the load pressure of the second hydraulic actuator to flow to the return circuit, thereby adjusting the load pressure of the second hydraulic actuator acting on the pressure controller.