Patent ID: 11970838
Assignee: HITACHI CONSTRUCTION MACHINERY CO., LTD.
Field: Civil engineering (Other fields)
Classification: CPC E  F | IPC E  F

Claim 0:
1. A construction machine comprising:
a travel body;
a work device;
a travel hydraulic motor that drives the travel body;
at least one single-rod hydraulic cylinder that drives the work device;
a travel operation lever for issuing an instruction on an operation of the travel hydraulic motor;
a work operation lever for issuing an instruction on an operation of the single-rod hydraulic cylinder;
a closed-circuit pump that is connected through a closed circuit to the single-rod hydraulic cylinder;
a cap-side flow path that connects a delivery port on one side of the closed-circuit pump to a cap-side chamber of the single-rod hydraulic cylinder;
a rod-side flow path that connects a delivery port on another side of the closed-circuit pump to a rod-side chamber of the single-rod hydraulic cylinder;
an open-circuit pump;
a travel flow rate control valve that controls flow rate supplied from the open-circuit pump to the travel hydraulic motor;
a travel switching valve that is capable of opening and closing a travel flow path connecting a delivery port of the open-circuit pump to the travel flow rate control valve;
an assist switching valve that is capable of opening and closing an assist flow path connecting the delivery port of the open-circuit pump to the cap-side flow path;
a controller that controls the delivery direction and delivery flow rate of the closed-circuit pump, opens and closes the travel switching valve and the assist switching valve, and controls the delivery flow rate of the open-circuit pump, according to operations of the travel operation lever and the work operation lever;
a charge pump;
a charge flow path connected to a delivery port of the charge pump;
a charge relief valve provided in the charge flow path;
a check valve provided between the cap-side flow path and the rod-side flow path and the charge flow path; and
a flushing valve provided between the cap-side flow path and the rod-side flow path and the charge flow path,
wherein the controller is configured to:
hold the assist switching valve in a closed position irrespective of whether or not the work operation lever is operated in a case where the travel operation lever is operated, and
correct the delivery flow rate of the closed-circuit pump such that the passing flow rate through the charge relief valve obtained by subtracting the flow rate which the single-rod hydraulic cylinder absorbs from the charge flow path from the sum of the flow rate which the single-rod hydraulic cylinder discharges into the charge flow path and the delivery flow rate of the charge pump becomes equal to or less than a predetermined flow rate.