(57) A ram cylinder control system for a wheel type hydraulic comprises a pilot hydraulic
pump 20, pilot-opened check valves 24b for normally prohibiting discharge of working
fluid from the ram cylinders 24 to lock the ram cylinders 24, a ram cylinder control
valve 29 adapted to shift from a home position to an operating position 29a in response
to a valve control signal for allowing the hydraulic oil from the pilot hydraulic
pump 20 to open the check valves so that the hydraulic oil can be discharged from
the ram cylinders 24, brake pressure sensor for detecting hydraulic oil pressure supplied
to the brakes, joystick position detector for detecting position of the joystick to
generate one of a forward position signal, a backward position signal and a neutral
signal, and a controller 19 for applying the valve control signal to the ram cylinder
control valve 29 if the forward position signal or the backward position signal is
received and if the brake pressure is no greater than a set pressure, and for cutting
off the valve control signal applied to the ram cylinder control valve 26 if the neutral
signal is received and if the brake pressure exceeds the set pressure.
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