Hydraulic drive system for construction machine
First Claim
1. A hydraulic drive system for a construction machine, comprising:
- a variable displacement type hydraulic pump;
a plurality of actuators which are driven by hydraulic fluid delivered from the hydraulic pump;
a plurality of flow control valves which respectively control flow rates of the hydraulic fluid supplied from the hydraulic pump to the actuators;
a plurality of operating devices corresponding respectively to the actuators, each of the operating devices includes a remote control valve for generating operation pilot pressures for driving the corresponding flow control valve;
a plurality of pressure compensating valves which are connected to a supply line of the hydraulic pump and which respectively control differential pressures across the flow control valves;
a pilot primary pressure circuit which supplies, as pilot primary pressure, a pressure of a pilot hydraulic pressure source to the remote control valves of the operating devices; and
a pump control system which performs load sensing control of a displacement of the hydraulic pump,wherein the plurality of actuators include a travel motor for moving a track structure, a swing motor for driving a swing structure, and a boom cylinder, an arm cylinder and a bucket cylinder for driving a front work implement;
wherein the plurality of operating devices include travel motor operating device for the travel motor, and operating devices other than the travel motor operating device, which include a swing motor operating device for the swing motor, a boom cylinder operating device for the boom cylinder, an arm cylinder operating device for the arm cylinder and a bucket cylinder operating device for the bucket cylinder;
wherein the pressure compensating valves are of the type in which full closing of the valves is not attained at a stroke end in a direction of decreasing an opening area;
wherein the travel motor is such an actuator that during a combined operation with the other actuators, the load pressure of the travel motor can be increased to such an extent that the pressure compensating valves for the other actuators reach a stroke end;
wherein the pilot primary pressure circuit includes;
a first circuit which supplies the pilot primary pressure to the remote control valve of the travel motor operating device, anda second circuit which supplies the pilot primary pressure to the plural remote control valves of the swing motor operating device, the boom cylinder operating device, the arm cylinder operating device and the bucket cylinder operating device, andwherein the second circuit includes a selector valve which is switched in accordance with an operation of the travel motor operating device to control the pilot primary pressure supplied to the plural remote control valves of the second circuit,the selector valve being configured such that when the travel motor operating device is not operated, the selector valve is switched in a position in which the pilot primary pressure is supplied directly to the plural remote control valves of the second circuit and when the travel motor operating device is operated, the selector valve is switched in a position in which the pilot primary pressure is reduced and the reduced pilot primary pressure is supplied to the plural remote control valves of the second circuit.
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Accused Products
Abstract
Pressure compensating valves not fully closing at the stroke end are employed, and upon the operator'"'"'s operation for the traveling, pilot primary pressure is reduced and supplied to remote control valves 34c-34h of non-travel operating devices. Thus, the inflow of the hydraulic fluid into non-travel actuators is suppressed and a necessary amount of hydraulic fluid for travel motors is secured in travel combined operation. Accordingly, when saturation occurs in a construction machine'"'"'s hydraulic drive system performing the load sensing control due to combined operation with a great load pressure difference between two actuators, deceleration/stoppage of an actuator on the low load pressure side is prevented by preventing full closure of the pressure compensating valve on the low load pressure side, while also preventing deceleration/stoppage of a high load pressure actuator by securing a necessary amount of hydraulic fluid for the high load pressure actuator.
22 Citations
7 Claims
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1. A hydraulic drive system for a construction machine, comprising:
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a variable displacement type hydraulic pump; a plurality of actuators which are driven by hydraulic fluid delivered from the hydraulic pump; a plurality of flow control valves which respectively control flow rates of the hydraulic fluid supplied from the hydraulic pump to the actuators; a plurality of operating devices corresponding respectively to the actuators, each of the operating devices includes a remote control valve for generating operation pilot pressures for driving the corresponding flow control valve; a plurality of pressure compensating valves which are connected to a supply line of the hydraulic pump and which respectively control differential pressures across the flow control valves; a pilot primary pressure circuit which supplies, as pilot primary pressure, a pressure of a pilot hydraulic pressure source to the remote control valves of the operating devices; and a pump control system which performs load sensing control of a displacement of the hydraulic pump, wherein the plurality of actuators include a travel motor for moving a track structure, a swing motor for driving a swing structure, and a boom cylinder, an arm cylinder and a bucket cylinder for driving a front work implement; wherein the plurality of operating devices include travel motor operating device for the travel motor, and operating devices other than the travel motor operating device, which include a swing motor operating device for the swing motor, a boom cylinder operating device for the boom cylinder, an arm cylinder operating device for the arm cylinder and a bucket cylinder operating device for the bucket cylinder; wherein the pressure compensating valves are of the type in which full closing of the valves is not attained at a stroke end in a direction of decreasing an opening area; wherein the travel motor is such an actuator that during a combined operation with the other actuators, the load pressure of the travel motor can be increased to such an extent that the pressure compensating valves for the other actuators reach a stroke end; wherein the pilot primary pressure circuit includes; a first circuit which supplies the pilot primary pressure to the remote control valve of the travel motor operating device, and a second circuit which supplies the pilot primary pressure to the plural remote control valves of the swing motor operating device, the boom cylinder operating device, the arm cylinder operating device and the bucket cylinder operating device, and wherein the second circuit includes a selector valve which is switched in accordance with an operation of the travel motor operating device to control the pilot primary pressure supplied to the plural remote control valves of the second circuit, the selector valve being configured such that when the travel motor operating device is not operated, the selector valve is switched in a position in which the pilot primary pressure is supplied directly to the plural remote control valves of the second circuit and when the travel motor operating device is operated, the selector valve is switched in a position in which the pilot primary pressure is reduced and the reduced pilot primary pressure is supplied to the plural remote control valves of the second circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification