Control system for hydraulic circuit apparatus

A hydraulic circuit system comprising:

• a hydraulic circuit apparatus having at least first and second variable displacement hydraulic pumps, at least first and second hydraulic actuators driven by the first and second pumps, hydraulic connections connecting said first hydraulic actuator with said first and second pumps and said second hydraulic actuator with said second pump, and valve means for controlling the hydraulic connections between the second pump and the first and second actuators;
• and
• control means associated with said first and second pumps and said valve means for controlling the displacement volumes of the first and second pumps and said hydraulic connections to thereby control the operations of said first and second actuators, said control means including;
• means setting order of priority of the hydraulic connections between the first actuator and the first and second hydraulic pumps and an order of priority of the hydraulic connections between the second hydraulic pump and the first and second actuators;
• means for sensing the displacement volume of the first hydraulic pump;
• first means for sensing maximization of the sensed displacement volume of the first hydraulic pump;
• means for sensing the displacement volume of the second hydraulic pump;
• second means for sensing that the second displacement volume of the second hydraulic pump has become substantially zero;
• and
• means for deciding target displacement volumes of the first and second hydraulic pumps based on information supplied at least by said priority order setting means and said first and second sensing means such that when the flow rate of hydraulic fluid supplied to the first actuator is increased, the displacement volume of the second hydraulic pump is increased from substantially zero after the displacement volume of the first hydraulic pump is maximized and, when the flow rate of hydraulic fluid supplied to the first actuator is reduced, the displacement volume of the first hydraulic pump is reduced after the displacement volume of the second hydraulic pump has become substantially zero.