Pump controlling apparatus for construction machine

A hydraulic drive controlling apparatus for a construction machine having a plurality of operation means to be manipulated by the machine operator, comprising:

• at least one variable displacement type hydraulic pump for pumping hydraulic fluid to a delivery pressure;
• a plurality of actuators responsive to respective operation means to be driven with the hydraulic fluid from said hydraulic pump and with respective load pressures;
• directional control valves for controlling said plurality of actuators, said directional control valves being driven in accordance with amounts of manipulation of the operation means;
• means for detecting the delivery pressure of said hydraulic pump;
• means for selecting a maximum load pressure among the load pressures of said plurality of actuators;
• first control means for controlling displacement of said hydraulic pump to bring a differential pressure between the delivery pressure and the maximum load pressure to a specified value in one mode of control;
• second control means for controlling the displacement of said hydraulic pump to bring the delivery pressure thereof to a predetermined set target pressure value in another mode of control;
• first command means for selecting a mode of control of the displacement of said hydraulic pump and outputting a corresponding command signal;
• first selection means for selecting one of said first and said second control means for operation in one of the modes depending upon the command signal from said first command means;
• and
• second command means for outputting a delivery pressure command signal, said second control means including setting means for setting the delivery target pressure value to vary depending upon the command signal from said second command means.

A hydraulic drive controlling apparatus for a construction machine having a plurality of operation means to be manipulated by the machine operator, comprising:

• at least one variable displacement type hydraulic pump for pumping hydraulic fluid to a delivery pressure;
• a plurality of actuators responsive to respective operation means to be driven with the hydraulic fluid from said hydraulic pump and with respective load pressures;
• directional control valves for controlling said plurality of actuators, said directional control valves being driven in accordance with amounts of manipulation of the operation means;
• means for detecting the delivery pressure of said hydraulic pump;
• means for selecting a maximum load pressure among the load pressures of said plurality of actuators;
• first control means for controlling displacement of said hydraulic pump to bring a differential pressure between the delivery pressure and the maximum load pressure to a specified value in one mode of control;
• second control means for controlling the displacement of said hydraulic pump to bring the delivery pressure thereof to a predetermined set target pressure value in another mode of control;
• first command means for selecting a mode of control of the displacement of said hydraulic pump and outputting a corresponding command signal;
• first selection means for selecting one of said first and said second control means for operation in one of the modes depending upon the command signal from said first command means;
• and
• second selection means for judging whether said operation means for a specific one of said actuators is manipulated, for selecting said second control means when said operation means for said specific actuator is manipulated, and for selecting said first control means when said operation means for the other actuators are manipulated.