Abstract: A lift attached to a truck has a tail gate supported by at least one hydraulic lift and at least one tilt cylinder for respectively lifting the tail gate as a whole and rotating it for opening and closing. A control system for moving such a tail gate up and down as a whole and rotating it to open and close it is provided with a power unit including a hydraulic pump, an electric motor for the hydraulic pump, and a plurality of valves for selectably allowing or not allowing transport of a hydraulic liquid by the hydraulic pump into the hydraulic cylinders, a sensor for measuring the pressure inside the hydraulic pump, external switches, and a controller which includes a CPU, a timer and a semiconductor switch and serves to calculate on real time the speed of the tail gate from signals from the sensor and the timer. The position of the tail gate is accurately determined therefrom and the tail gate is gradually started, accelerated and decelerated to prevent damage to its cargo.

Abstract: A lift attached to a truck has a tail gate supported by at least one hydraulic lift and at least one tilt cylinder for respectively lifting the tail gate as a whole and rotating it for opening and closing. A control system for moving such a tail gate up and down as a whole and rotating it to open and close it is provided with a power unit including a hydraulic pump, an electric motor for the hydraulic pump, and a plurality of valves for selectably allowing or not allowing transport of a hydraulic liquid by the hydraulic pump into the hydraulic cylinders, a sensor for measuring the slope angle of the tail gate, external switches, and a controller which serves to transmit output signals to the motor and to the valves in response to input signals from the sensor and the external switches and is capable of stopping rotary motion of the tail gate at a horizontal position irrespective of the slope of the vehicle and starting and stopping the rotary motion of the tail gate gradually.

Abstract: A lift having a freight-receiving table which is rotatably supported by one or more each of hydraulic lift and tilt cylinders for respectively lifting and tilting the table is controlled such that an overloaded condition of the table is detected by measuring the internal pressure of the tilt cylinder or both the tilt and lift cylinders. If the measured pressure exceeds a pre-determined critical value, the operation of the lift is automatically and immediately stopped.

Abstract: A hydraulic oil power unit includes a motor for driving a hydraulic pump, a piston driven by the hydraulic pump, a driving power supply for the motor and a switch for providing the driving power supply for the motor. A switching device includes a semiconductor for switching on and off a conductive path for the motor, a detecting circuit for detecting the completion of the motion of the piston from a motor current fed with the motor and a holding circuit for holding the switching device in a non-conductive state while the switch is closed based on a detection signal from the detecting circuit indicating a detection of the completion of the motion of the piston.