Allis-chalmers Corporation

Arvin Karazija

Michael H Grace

A closed center hydraulic system is provided for a lift truck which includes an accumulator, a motor driven pump for supplying fluid under pressure to the accumulator, a plurality of closed center proportional electrohydraulic control valves for a plurality of hydraulically operated devices on the truck such as the lift jack, the mast tilt jack and the hydraulic powered steering mechanism. The pressure to the steering control valve is reduced by a pressure reducing valve and the pressure fluid supply circuit from the accumulator to the lift and tilt circuits is controlled by a blocking valve which is opened when the manual control member for either the lift or tilt control valve is moved from neutral to an operating position. Initial movement of either manual control member causes the blocking valve to open and further movement meters flow, thus permitting the operator to regulate lift and tilt speeds. A return line interconnects the lift jack and reservoir in bypassing relation to the lift control valve and a pilot operated bypass valve in the return line has its pilot line connected to one of the lift control valve delivery ports. An energy recovery system is disclosed in the return line from the lift jack.

Closed center hydraulic system for lift trucks

A lift truck energized from a battery to supply pressurized fluid to elevate a load-supporting carriage has an energy recovery system for converting kinetic energy of the elevated carriage into battery charging current including a fluid motor through which fluid from the lift ram is exhausted when the carriage is descending, an alternator driven by the fluid motor, a rectifier between alternator and battery, a transistor having its emitter-collector circuit in series with the field winding of the alternator, and a rate-of-descent adjusting potentiometer for selectively varying base drive to the transistor to thereby regulate field excitation of the alternator and the regenerative braking of the fluid motor.

Growing community of inventors

Oak Forest, IL, United States of America

Arvin Karazija