Control system for hydraulic circuit means

A control system for hydraulic circuit means including a variable displacement hydraulic pump and an actuator driven by said pump, the operating speed of said actuator being controlled by the position of a displacement volume varying member of said pump, the control system comprising operating means for generating an operating signal for giving a command with regard to the position of said displacement volume varying member of said pump and thus the operating speed of the actuator, detector means for detecting an actual position of the displacement volume varying member and generating a signal indicative of the actual position, and pump control means for controlling said displacement volume varying member based on said operating signal and said detector signal while restricting the operating speed of the displacement volume varying member to a level below a predetermined maximum speed, wherein said control system comprises:

• maximum speed setting means selectively setting one of a first predetermined maximum speed and a second predetermined maximum speed higher than said first predetermined maximum speed as said predetermined maximum speed for the operating speed of the displacement volume varying member, said first predetermined maximum speed being of the value for allowing the actuator to perform smooth operation upon normal operation thereof and said second predetermined maximum speed being of the value for allowing the actuator to perform swift operation upon emergency halting thereof, rapid reversing of the operation direction thereof, or accurate positioning thereof, said maximum speed setting means including switch means having a first position to select said first predetermined maximum speed and a second position to select said second predetermined maximum speed and connected to said pump control means for providing the selected one of said first and second predetermined maximum speeds as an output to said pump control means, and switch actuating means associated with said operating means and detector means for actuating said switch means so as to take one of said first and second positions, said switch actuating means being operative to actuate said switch means so as to take said first position and thus select the first predetermined maximum speed when said operating means is operated such that the direction of operation of the actuator commanded by the operating signal is the same as the actual direction of operation thereof represented by said detector means signal indicative of the actual position of the displacement volume varying member and to actuate said switch means so as to take said second position and thus select the second position and thus select the second predetermined maximum speed when said operating means is operated such that the operating signal commands returning of the displacement volume varying member into a neutral position or the direction of operation of the actuator commanded by the operating signal is opposite to the actual direction of operation thereof represented by said detector means signal indicative of the actual position of the displacement volume varying member, whereby the pump control means effects speed control of the displacement volume varying member based on the first and second predetermined maximum speed selected by the maximum speed setting means.