Hydraulic apparatus for construction machinery.

摘要

Hydraulic apparatus for construction machinery has an actuator (1), such as a piston and cylinder for operating the machinery and a control device (16) with a manual lever (7) usable by an operator to cause fluid to flow to and from the actuator (1) via a switching unit (3) installed between a pump (2) and a storage tank (13). An inflow variable restriction valve (4) is located between the pump (2) and the switching unit (3).The restriction action of the valve (4) is controlled in accordance with the operation of the lever (7). An outflow variable restrictor valve (26) is installed between the tank (13) and the actuator (1) and Pressure difference control means controls the difference in pressure between the inlet and exit ports of said inflow variable restriction valve (4). The restriction areas of said inflow and outflow variable restriction valves (4,26) are controlled independently and said outflow variable restriction valve (26) is controlled in accordance with fluctuations in the pressure of an inlet chamber of the actuator (1) thereby preventing the occurrence of cavitation whilst still ensuring the desirable control characteristic that the actuator drive speed corresponds to the operation of the lever (7).