A method for controlling of the pivotable upper carriage of a construction machine, and a hydraulic control system for performing the method.

摘要

A method of controlling the slewing operation of a slewing mechanism for slewing the revolving superstructure of a hydraulic backhoe or the like. The method comprises setting a swing mode selector valve (2) in a driving position to supply a working fluid discharged from a hydraulic pump (1) through a supply-and-discharge line to a hydraulic motor (3) to drive the hydraulic motor for a driving operation, setting one of a pair of relief valves (4a, 4b) provided between the swing mode selector valve and the hydraulic motor, associated with the supply side of the hydraulic motor for a set relief pressure higher than the set relief pressure of a main relief valve (12) for limiting the pressure in supply-and-dis­charge lines to the set relief pressure of the main relief valve while the hydraulic motor is operating in a driving mode, and setting the other relief valve associated with the discharge side of the hydraulic motor for a set relief pressure lower than the set relief pressure of the main relief valve to limit the pressure in the supply-and-dis­charge line associated with the discharge side of the hydraulic motor to the set relief pressure of the other relief valve while the hydraulic motor is operating in a braking mode. The method brakes the slewing mechanism smoothly to prevent the rapid abrasion of the braking surfaces of the components of the slewing mechanism.