Electric drive unit for construction machine

摘要

An electric drive unit for a construction machine is capable of increasing the operating time of the construction machine. The electric drive unit has an electricity storage device, a hydraulic pump of the fixed displacement type which is driven by a motor/generator, a plurality of directional control valves which respectively control the flow of hydraulic fluid supplied to a plurality of hydraulic actuators, a bidirectional converter which performs variable control on the revolution speed of the motor/generator, and an LS control device which controls the bidirectional converter so that LS differential pressure Pls equals a target value Pgr. The bidirectional converter performs regeneration control for converting the inertial force of the rotor of the motor/generator into electric power thereby charging the electricity storage device when the revolution speed of the motor/generator is decreased in response to an excess of the LS differential pressure Pls over the target value Pgr.

主权项

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 which is driven by the motor/generator, a plurality of hydraulic actuators, a plurality of operating devices 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 devices, the electric drive unit comprising:
a bidirectional converter which performs variable control of a revolution speed of the motor/generator; and a command control device which calculates a command value for the bidirectional converter to change a delivery flow rate of the hydraulic pump according to a change in a demanded flow rate determined based on operation command levels from the plurality of operating device, wherein the bidirectional converter performs regeneration control for converting inertial force of a rotor of the motor/generator into electric power and thereby charges the electricity storage device when the revolution speed of the motor/generator decreased so that the delivery flow rate of the hydraulic pump is decreased in response to a decrease in the demanded flow rate, the electric drive unit further comprising: a plurality of pressure compensating valves which perform control so that a differential pressure across each of the directional control valves equals a load sensing differential pressure defined as a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure of the hydraulic actuators; and a load sensing differential pressure detecting device which detects the load sensing differential pressure, the command control device being a load sensing control device which calculates the command value for the bidirectional converter according to a difference between the load sensing differential pressure detected by the load sensing differential pressure detecting device and a preset target value so that the load sensing differential pressure equals the target value and the delivery flow rate of the hydraulic pump matches with the demanded flow rate, and the bidirectional converter performs the regeneration control for converting the inertial force of the rotor of the motor/generator into electric power and thereby charges 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 so that the delivery flow rate of the hydraulic pump is decreased.