Clark Equipment Compnay

George J Trusock

James J Bauer

Willard L Chichester

Bhupen Gandhi

An hydraulic control system is disclosed for energizing a load, such as the lift cylinder of an electric lift truck, with a minimum of power loss during the transition from zero to full energization, i.e. during the feathering range. An electric motor drives a positive displacement pump which supplies the flow requirements of different load circuits, one having a greater flow requirement than the other and requiring higher pump speed. A proportioning valve of the open center type provides full flow to the tank when the valve is closed and full flow to the load circuit having the greater flow requirement when the valve is open. A manually actuable lever actuates the valve through the feathering range with the pump motor in a low speed range and actuates a speed control switch to operate the motor in the high speed range when the valve is fully open.

Hydraulic system with proportional control

A traction drive system for a vehicle is disclosed which comprises a pair of series wound motors (32,34) which are connected in series with each other and which drive independent traction wheels (22,24), respectively, of the vehicle. The no-load torque of each traction wheel is correlated with the transient torque characteristic of the motors so that each motor produces a transient driving torque greater than the threshold-load torque of the wheels. Further, the no-load torque of each wheel is great enough so that the transient driving torque will not fall below the threshold-load torque during a predetermined time interval. This arrangement permits one traction wheel to move the vehicle at low speed while the other traction wheel spins on ice or otherwise fails to exhibit tractive effort.

Series connected series motors for independent loads

An electric work vehicle with a battery powered traction motor and pump motor is provided with an auxiliary power supply for a load circuit requiring voltage lower than that of the battery. The pump motor is provided with an auxiliary brush at a location between a pair of motor brushes and the auxiliary load circuit is connected between the auxiliary brush and one of the motor brushes. The auxiliary brush is positioned relative to the motor brush so that it supplies the voltage required by the auxiliary load circuit.

Auxiliary electric power supply for electric work vehicles

A lift truck is disclosed with a changeable speed electric motor for driving a single positive displacement pump to supply the power steering and various work handling hydraulic load circuits. Manually actuable selector means are operatively connected with the load circuits and a speed range control means is operatively connected with the selector means for energizing the electric motor in different speed ranges according to the actuation of the selector means. A priority demand valve is connected between the pump and the respective load circuits and supplies fluid to the load circuits, giving priority to the power steering circuit. The speed range control means includes speed regulating means for the electric motor. The motor is energized from the battery and the regulating means includes a pulsing circuit with a motor current feedback to vary the mark/space ratio of the pulses produced by the pulsing circuit.

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Battle Creek, MI, United States of America

George J Trusock