Electric drive unit for construction machine
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 variable displacement type which is driven by a motor/generator, a regulator which performs variable control on the displacement volume of the hydraulic pump, a bidirectional converter which performs variable control on the revolution speed of the motor/generator, and an LS control device which controls the regulator and 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.
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.
2. The electric drive unit for a construction machine according to claim 1 , wherein the command control means comprises:
subtraction means which calculates a difference between the load sensing differential pressure detected by the differential pressure detecting means and the preset target value;
first lowpass filter means which performs processing of removing components changing above a preset first frequency on the difference calculated by the subtraction means;
first command calculation means which calculates the command value for the pump control means according to a difference processed by the first lowpass filter means;
second lowpass filter means which performs processing of removing components changing above a second frequency preset to be lower than the preset first frequency on the difference calculated by the subtraction means; and
second command calculation means which calculates the command value for the motor-generator control according to a difference processed by the second lowpass filter means.