Lift, tilt and steering control for a lift truck

Details Lift, tilt and steering control for a lift truck Lift, tilt and steering control for a lift truck

1981-10-15

1984-05-22

Cohen, Irwin C.

Power plants

Pressure fluid source and motor

Having condition responsive control in a system of distinct...

60423, 60428, 180132, B62D 506, F15B 1116, F15B 1306

Patent

active

044493657

ABSTRACT:
A lift truck hydraulic control system designed to conserve energy includes a pair of separately controlled pumps (21, 22). One pump (21) supplies pressure fluid to a valve (12) for a steering cylinder (11) by way of a high priority port (34) of a priority valve (32) with the low priority flow passing to parallel connected lift and tilt valves (19, 18) which control operation of the lift cylinder (15) and tilt cylinders (16, 17), respectively. The capacity of pump (21) is sufficient to provide proper, effective operation of the steering and tilt functions but is not adequate to provide hydraulic fluid flow for high speed expansion of the lift cylinder (15). The other pump (22) is operated to supply additional pressure fluid flow for high speed lift only when the lift valve (19) is shifted to a raise position. In one embodiment, a low speed lift is obtained by using the output of the pump (21) and a high speed lift is obtained by selectively adding the output of the second pump 22. This is achieved by operating the other pump (22) only when the lift valve (19) is placed in an extreme raise position. In another embodiment, the pumps (21, 22) are operated only "on demand," thereby further conserving energy.

REFERENCES:
patent: 3443380 (1969-05-01), Karazija
patent: 3570519 (1971-03-01), Bianchetta
patent: 3991846 (1976-11-01), Chichester et al.
patent: 4002220 (1977-01-01), Wible
patent: 4044786 (1977-08-01), Yip
patent: 4070857 (1978-01-01), Wible

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