Drive system for construction machinery and method of controlling hydraulic circuit means thereof

A drive system for construction machinery comprising hydraulic circuit means including a plurality of variable-displacement hydraulic pumps and a plurality of hydraulic actuators, each of said pumps being connected in closed circuit to one or a plurality of said actuators through a solenoid-operated valve or valves to drive a movable member or members connected to the actuator or respective actuators when pressurized fluid is supplied to the actuator or actuators from the pump, characterized in that at least one of the selected hydraulic actuators is further connected in closed circuit through a solenoid operated valve to at least one of the hydraulic pumps other than the hydraulic pump which is connected in closed circuit to the selected hydraulic actuator, operator controlled means are provided for generating command signals, and in that preprogrammed control means are provided for controlling said pumps and valves setting a priority order of hydraulic commuication between each hydraulic pump and the hydraulic actuators to which said hydraulic pump is connected in closed circuit through the respective solenoid-operated valves, for closing all of said solenoid-operated valves when no command signals for driving said actuators are produced, for, when a command signal for driving at least one actuator is produced, opening the solenoid-operated valve associated with said one actuator or the actuator higher in the priority order to hydraulic communication with said hydraulic pump while controlling the delivery of the pump by the command signal for driving the actuator with which said opened valve is associated, for, when at least one of command signals which have been produced to drive at least one actuator is removed, closing the solenoid-operated valve associated with the actuator which have been driven by the removed command signal and/or opening or keeping open the solenoid-operated valve associated with the other actuator or actuator higher in the priority order of hydraulic communication with said hydraulic pump among the other actuators while controlling the delivery of the pump by the command signal for driving the actuator with which said opening or opening-kept valve is associated, and for conducting any switching of each solenoid-operatee valve only when the delivery of said pump is zero or has been reduced substantially to zero.

A method of controlling hydraulic circuit means of a drive system for construction machinery in which said hydraulic circuit means includes a plurality of variable-displacement hydraulic pumps and a plurality of hydraulic actuators, each said pump being connected in closed circuit to one or a plurality of said actuators through a solenoid-operated valve or valves to drive a movable member or members connected to the actuator or respective actuators when pressurized fluid is supplied to the actuator or actuators from the pump, at least one of the selected hydraulic actuators being further connected in closed circuit through a solenoid-operated valve to at least one of the hydraulic pumps other than the hydraulic pump which is connected in closed circuit to the selected hydraulic actuator, characterized in that said method comprises the steps of:

• setting a preprogrammed priority order of hydraulic communication between each hydraulic pump and the hydraulic actuators to which said hydraulic pump is connected in closed circuit through the respective solenoid-operated valves generating command signals by an operator;
• closing all of said solenoid-operated valves when no command signals for driving said actuators are produced;
• when a command signal for driving at least one actuator is produced, opening the solenoid-operated valve associated with said one actuator or the actuator higher in the priority order of hydraulic communication with said hydraulic pump while controlling the delivery of the pump by the command signal for driving the actuator with which said opened valve is associated;
• when at least one of command signals which have been produced to drive at least one actuator is removed, closing the solenoid-operated valve associated with the actuator which have been driven by the removed command signal and/or opening or keeping open the solenoid-operated valve associated with the other actuator or actuator higher in the priority order of hydraulic communication with said hydraulic pump among the other actuators while controlling the delivery of the pump by the command signal for driving the actuator with which said opened or opening-kept valve is associated;
• and conducting any switching of each said solenoid-operated valve only when the delivery of said pump is zero or has been reduced substantially to zero.

A drive system for construction machinery comprising:

• hydraulic circuit means including a plurality of reversible variable-displacement hydraulic pumps, a plurality of hydraulic actuator units driven independently and separately from each other by said pumps, said plurality of pumps being less in number than said plurality of actuator units, at least one of said plurality of pumps being connected to at least two of said plurality of actuator units to respectively form closed-circuits, at least one of said plurality of actuator units being connected to at least two of said plurality of pumps to respectively form closed circuits, and a plurality of solenoid-operated valves each incorporated in each of said closed circuits and operative such that each pump is brought into hydraulic communication with only one actuator unit at a time;
• a plurality of manually operated means corresponding to said plurality of actuator units for generating command signals for driving the respective actuator units;
• and
• control means responsive to said command signals for controlling said pumps and valves such that each actuator unit is driven based on only a command signal generated by the corresponding manually operated means, said control means including preprogrammed priority order judging means determining a priority order of said at least two actuator units with respect to a hydraulic communication between said actuator units and said pump connected thereto forming the respective closed circuits, means for controlling said solenoid-operated valves such that a solenoid operated valve associated with the actuator unit selected by said priority order judging means is switched based on a command signal generated by the manually operated means corresponding to the selected actuator unit, and means for controlling said pumps such that a pump connected to said selected actuator unit forming the closed circuit is regulated based on said command signal generated by the manually operated means corresponding to the selected actuator unit to provide a delivery of hydraulic fluid in proportion to said command signal.