Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
1999-02-08
2001-01-09
Walton, George L. (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S015060, C137S238000, C251S129050, C251S129080, C318S632000, C318S701000, C361S146000
Reexamination Certificate
active
06170506
ABSTRACT:
TECHNICAL FIELD
A control valve capable of providing a regulated pressure in a valve system wherein provision is made for purging the valve of oil-borne contaminants.
BACKGROUND OF THE INVENTION
Electrohydraulic valve systems typically include a pressure regulator that responds to electromagnetic forces to position a valve element against a valve spring force. In the case of a pressure regulator valve, the output pressure is determined by a transfer function for the electrical parameter (e.g., magnetizing current) and the mechanical force applied to the valve. Valve systems of this kind typically are characterized by a hysteresis due to the effect of friction caused by oil-borne contaminants and the magnetic hysteresis of the electromagnetic actuator. A major factor in determining the frictional hysteresis is the presence of oil-borne contaminants in the hydraulic fluid.
Hysteresis in the transfer function results in a variable output pressure for any given actuating current. For an electrohydraulic valve with a proportional transfer function, the output pressure obtained when the actuating current increases is less than the output pressure obtained for the same current when the current decreases. The output value for the pressure thus is not precisely proportional to a given input parameter or magnetizing current. The opposite is true for an inversely proportional electrohydraulic valve.
U.S. Pat. No. 4,577,143 describes an attempt to establish a more precise control of the position of a regulator valve for a given value of an input parameter so that a predictable characteristic transfer curve at any value for the input parameter can be determined. This is accomplished in the system described in the '143 patent by changing the current in a direction that is opposite to the direction of the transfer function curve. This effects a reversal of the magnetization to overcome the hysteresis gap between the magnetization curves. The reversal of the magnetization occurs only when a change in command is requested.
Electrical energy is applied only long enough to effect re-magnetization. The transduced value, which is in the same direction as the selected characteristic, will follow the selected magnetization curve. The excess current value is not applied long enough to cause a change in the mechanical output of the valve.
DISCLOSURE OF INVENTION
The invention is a method and a circuit for purging oil-borne contaminants from a hydraulic regulator valve to reduce or to eliminate the effect of friction caused by the contaminants. Current supplied to the electromagnetic actuator for the valve varies in accordance with a transfer function to develop a regulated output pressure. The transfer function characteristics of the electrohydraulic valve, when the effect of contamination in the hydraulic fluid is eliminated, is relatively uniform when the magnetizing current at the solenoid actuator progressively increases. When the magnetizing current progressively decreases, the mechanical friction element of hysteresis that generally characterizes electrohydraulic valve mechanisms of known construction is eliminated. A given magnetizing current applied to the electromagnetic actuator will develop a predictable and calibratable mechanical response of the valve.
The effect of hysteresis and inaccuracies due to contamination can further be reduced by utilizing a dither frequency on the applied current.
Precise proportionality between the magnetizing current and the output pressure throughout the entire extent of the characteristic transfer function can be achieved. This predictable mechanical response of the valve to changes in the magnetizing current is obtained by applying command pulses of short duration at a predetermined points in the operating cycle. The pulse width, the amplitude of the pulse, the direction of the pulse, and the spacing between successive pulses, if more than one pulse is required, are empirically determined from transfer function results that indicate robust performance in the presence of the expected level of contamination.
Provision is made for reducing to a minimum the amplitude of the pulses in order to avoid an undesirable loss of output pressure for the regulator valve, which could lead to a loss of torque capacity in instances in which the regulated pressure is used to engage a clutch or a brake. Unlike the valve system of the '143 patent, where the re-magnetization occurs only when a change in command is requested, the cleaning pulses of the present invention occur during steady-state conditions.
The invention includes a driver circuit that is flexible for purposes of calibration and is programmable for various solenoid valve systems. Bidirectional pulses or unidirectional pulses can be used, depending on output pressure commands relative to a threshold value. The pulses, when the electrohydraulic valve is calibrated, will provide a precise mechanical movement without excessive pressure change in the controlled element such as a transmission clutch or brake.
REFERENCES:
patent: 4017056 (1977-04-01), Schwalenstocker et al.
patent: 4103695 (1978-08-01), Aono
patent: 4313465 (1982-02-01), Holzem
patent: 4345737 (1982-08-01), Kawai et al.
patent: 4373697 (1983-02-01), Phelps
patent: 4386626 (1983-06-01), Hehl
patent: 4577143 (1986-03-01), Eschrich et al.
patent: 4766921 (1988-08-01), Williams
patent: 4796661 (1989-01-01), Hishinuma et al.
patent: 4974622 (1990-12-01), Rader
patent: 5202813 (1993-04-01), Uota et al.
patent: 5422556 (1995-06-01), Graf et al.
patent: 0055518 (1982-07-01), None
Butwin John
Cicala Stephen Michael
Haase Robert Cary
Monaghan Michael J.
Protopapas Maria Eugenia
Ford Global Technologies Inc.
McKenzie Frank G.
Walton George L.
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