Control system for hydraulic circuit apparatus.

摘要

A hydraulic circuit comprises at least first and second hydraulic pumps (10,12) of the variable displacement type, a first hydraulic actuator (20) arranged for hydraulic connection with the first pump (10) through first valve means (50a) to be driven thereby, and a second hydraulic actuator (21) arranged for selective hydraulic connection with said first and second pumps (10, 12) through second and third valve means (50b, 52b) respectively to be driven thereby. In the control system, the order of priority for hydraulic connection is set beforehand in such a manner that when an operation signal (61) for the second actuator (21) is received while the first pump (10) is inoperative, pump (10) takes priority over the second pump (12) for hydraulic connection with the second actuator (21), and when an operation signal (60) for the first actuator (20) is received while the first pump (10) is in hydraulic connection with the second actuator (21), the first actuator (20) takes priority over the second actuator (21) for hydraulic connection with the first pump (10) and the second actuator (21) is brought into hydraulic connection with the second pump (12), and the displacement volume of the first pump (10) and switching of the second valve means (50b) are controlled in such a manner that when the first pump (10) which is in hydraulic connection with the second actuator (21) is to be brought into hydraulic connection with the first actuator (20) the displacement volume of the first pump (10) is once returned to zero before changing of the hydraulic connection. The control system has first means (76) for judging whether or not the first pump (10) is in hydraulic connection with the second actuator (21) when the operation signal for the first actuator (20) is received, and generating a command for backing up reduction in the inflow of hydraulic fluid into the second actuator (21) simultaneously when the displacement volume of the first pump (10) begins to be returned to zero, when it is judged that the first pump (10) is in hydraulic connection with the second actuator (21), second means (72) for generating a command for switching the third valve means (52b) to an open position in accordance with the backup command from the first means (76) and third means (74) for generating a command for initiating a displacement of the second pump (12) in accordance with the backup command from the first means (76).