Patent ID: 9187880
Filing Date: 2015-11-17
Classification: E02F

Abstract:
1. An electric drive unit for a construction machine equipped with an electricity storage device, a motor-generator which supplies and receives electric power to/from the electricity storage device, a hydraulic pump of the variable displacement type which is driven by the motor-generator, a plurality of hydraulic actuators, a plurality of operating means which command the operation of the hydraulic actuators, and a plurality of directional control valves which respectively control the direction and the flow rate of hydraulic fluid supplied from the hydraulic pump to the hydraulic actuators according to operating directions and operation amounts of the plurality of operating means, comprising: pump control means which performs variable control on a displacement volume of the hydraulic pump; motor-generator control means which performs variable control on the revolution speed of the motor-generator; and command control means which calculates command values for the pump control means and the motor-generator control means according to a change in a demanded flow rate determined based on operation command levels from the plurality of operating means, a plurality of pressure compensating valves which perform control so that differential pressure across each of the directional control valves equals a load sensing differential pressure defined as differential pressure between delivery pressure of the hydraulic pump and a maximum load pressure of the hydraulic actuators; and differential pressure detecting means which detects the load sensing differential pressure, wherein the command control means calculates the command values for the pump control means and the motor-generator control means according to a difference between the load sensing differential pressure detected by the differential pressure detecting means and a preset target value so that the load sensing differential pressure equals the preset target value, and wherein the motor-generator control means performs the regeneration control for converting the inertial force of the rotor of the motor-generator into electric power and thereby charging the electricity storage device when the revolution speed of the motor-generator is decreased in response to an excess of the load sensing differential pressure over the target value.