Control apparatus for use in a power transmission system of construction vehicles

A control apparatus for use in a power transmission system of construction vehicles, comprising at least one work implement adapted to be actuated by a hydraulically driven actuator means, a transmission gear adapted to be actuated by a speed-change clutch means, and a torque converter interposed between an engine and said transmission gear so as to transmit the power for rotation generated by the engine to the transmission and having a stator clutch, characterized in that the control apparatus comprises a hydraulic fluid supply source;

• a first and a second solenoid actuated clutch pressure change-over valves connected with two hydraulic circuits which connect the hydraulic fluid supply source with the speed-change clutch means and said stator clutch, respectively, said first and second clutch pressure change-over valves being adapted to change the fluid pressure in said hydraulic circuits over to a high value and a low value;
• an engine rotation sensor connected on the output side thereof with respective solenoids of the first and second clutch pressure change-over valves, respectively, and adapted to detect the rotational speed of the engine;
• a pressure sensor adapted to detect the fluid pressure in the hydraulically driven actuator means;
• a speed-change lever position sensor adapted to detect the shift of the speed-change lever to its first speed position;
• and a controller connected on the input side thereof with said engine rotation sensor, said pressure sensor and said speed-change lever position sensor, wherein said first and second clutch pressure change-over valves are controlled in response to the input signal from their respective sensors.