CONSTRUCTION MACHINE HYDRAULIC DRIVE SYSTEM HAVING EXHAUST GAS PURIFYING DEVICE

摘要

A construction machine hydraulic drive system that performs load sensing control is capable of efficiently burning and removing deposits on a filter in an exhaust gas purifying device through pump output increasing control and to be free from faults in the pump output increasing control even when an actuator is operated during the pump output increasing control. A solenoid switching valve is switched so that output pressure of an engine speed detecting valve is guided to a pressure receiving portion of an LS control valve and a pressure receiving portion of an unloading valve when a start of regeneration is not directed, and delivery pressure of a pilot pump is guided to the pressure receiving portion and the pressure receiving portion when the start of the regeneration is directed, to thereby disable load sensing control to increase capacity of a main pump and increase set pressure of the unloading valve.

主权项

1. A construction machine hydraulic drive system including:
an engine (1); a variable displacement hydraulic pump (2) driven by the engine; a plurality of actuators (3a, 3b, 3c . . . ) driven by hydraulic fluid delivered from the hydraulic pump; a plurality of flow and directional control valves (6a, 6b, 6c . . . ) that control a flow rate of the hydraulic fluid supplied from the hydraulic pump to the actuators; a pump control device (17) including: a torque control section (17-1) that performs absorption torque maintaining control that prevents absorption torque of the hydraulic pump from exceeding predetermined maximum torque (Tmax) by reducing capacity of the hydraulic pump as delivery pressure of the hydraulic pump increases; and a load sensing control section (17-2) that performs load sensing control that ensures that the delivery pressure of the hydraulic pump is higher than maximum load pressure of the actuators by target differential pressure; an unloading valve (15) connected to a line (4a) to which a delivery fluid from the hydraulic pump is guided, the unloading valve opening when the delivery pressure of the hydraulic pump is higher than the sum of the maximum load pressure and an unloading set pressure, to thereby return the delivery fluid of the hydraulic pump to a tank (T), thus restricting an increase in the delivery pressure of the hydraulic pump; and a pilot pump (30) driven by the engine, the hydraulic drive system comprising: an exhaust gas purifying device (42) that purifies exhaust gases from the engine; an instruction device (43, 44, S100) that directs a start of regeneration of the exhaust gas purifying device; and a changeover control device (17d, 15d, 35, 70, S110) that selects to enable or disable the load sensing control performed by the load sensing control section by enabling the load sensing control of the load sensing control section when the instruction device does not direct the start of the regeneration of the exhaust gas purifying device and disabling the load sensing control of the load sensing control section when the instruction device directs the start of the regeneration of the exhaust gas purifying device to thereby increase the capacity of the hydraulic pump; when disabling the load sensing control, by guiding predetermined pressure generated based on the delivery fluid of the pilot pump to the unloading valve to thereby increase the unloading set pressure.