Power plants – Pressure fluid source and motor – Having correlated or joint actuation of controller of input...
Reexamination Certificate
1998-12-15
2001-03-20
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having correlated or joint actuation of controller of input...
C091S437000
Reexamination Certificate
active
06202410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic system for a forklift, which supplies hydraulic fluid to a power steering cylinder to steer wheels.
2. Description of the Related Art
A hydraulic system for a forklift is known, in which when a handle is rotatively operated, hydraulic fluid is supplied by a hydraulic pump to a power steering cylinder to steer wheels. Such a conventional hydraulic system has a torque sensor which outputs a signal corresponding to rotational torque when the handle is rotatively operated, a handle angle sensor which outputs a signal corresponding to a handle rotation angle, and a wheel angle sensor which outputs a signal corresponding to a steering angle of the wheels. The hydraulic fluid of a flow rate based on the signal from the torque sensor is discharged from the hydraulic pump to effect the power steering while a solenoid valve is driven based on the signals from the handle angle sensor and the wheel angle sensor to control the steering angle of the wheels in conformity with the handle angle.
The conventional hydraulic system for the forklift suffers from a complicated and expensive sensor mechanism in the handle portion since the torque sensor for outputting the signal corresponding to the rotational torque on the handle and the handle angle sensor for outputting the signal corresponding to the handle rotation angle must be installed on the handle portion.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hydraulic system for a forklift, in which a sensor mechanism on a handle portion is made simple.
In order to solve the problem, a hydraulic system for a forklift according to the present invention is a system in which hydraulic fluid is supplied from a hydraulic pump to a power steering cylinder for steering wheels in accordance with rotational operation of a handle, the system comprising: a handle angle sensor for outputting a rotational angle signal indicative of a rotational angle of a handle; a wheel angle sensor for outputting a wheel angle signal indicative of a steering angle of wheels; and a controller for calculating a rotation angular velocity of the handle based on the rotational angle signal from the handle angle sensor to discharge hydraulic fluid of a flow rate in conformity with the calculated rotation angular velocity from a hydraulic pump, and controlling the flow rate of the hydraulic fluid to be supplied to a power steering cylinder based on the rotational angle signal from the handle angle sensor and the wheel angle signal from the wheel angle sensor to steer the wheels in conformity with the rotational angle of the handle.
When the handle is rotated, the rotation angular velocity of the handle is calculated based on the rotational angle signal output from the handle angle sensor, and the hydraulic fluid of the flow rate corresponding to this rotational angle velocity is discharged from the hydraulic pump. The flow rate of the hydraulic fluid to be supplied to the power steering cylinder is controlled based on the rotational angle signal and the wheel angle signal, so that the wheels are steered in conformity with the rotational angle of the handle.
REFERENCES:
patent: 5201380 (1993-04-01), Callahan
patent: 5275251 (1994-01-01), Thomsen et al.
patent: 5542490 (1996-08-01), Kemshall et al.
patent: 0 283 803 A2 (1987-03-01), None
patent: 0 607 888 A1 (1993-01-01), None
patent: 0 534 332 A1 (1993-03-01), None
patent: 9-263258 (1997-07-01), None
Patent Abstracts of Japan, Publication No. 63219479, Published Sep. 13, 1988.
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Lazo Thomas E.
Look Edward K.
Morgan & Finnegan L.L.P.
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