Valves and valve actuation – Electrically actuated valve – Remote or follow-up control system for electrical actuator
Patent
1980-12-29
1983-02-15
Michalsky, Gerald A.
Valves and valve actuation
Electrically actuated valve
Remote or follow-up control system for electrical actuator
1374875, F16K 3102
Patent
active
043736971
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention generally relates to servo controlled hydraulic valves of the type operated by an electrically responsive coil, and deals more particularly with a method and apparatus for consistently controlling valve response irrespective of variations in power supply voltage and coil resistance.
BACKGROUND ART
Control systems often employ servo controlled hydraulic valves to control hydraulic line pressure. For example, one application of a servo controlled hydraulic valve is for controlling differentially driven wheel slip in vehicles. Wheel slip is controlled by selectively activating the vehicle's hydraulically operated brakes in a manner which directs braking power to the slipping wheel or wheels. An electrical control system senses wheel slippage and produces pulse width modulated control signals whose duty factors are proportional to the desired response of a hydraulic proportioning valve. The proportioning valve is in turn connected to a control valve which controls the pressure of hydraulic fluid applied to the brakes.
Servo controlled valves of the type mentioned above include an electrically responsive coil for controlling an output of the valve. These coils are selectively energized with a suitable voltage source for time periods corresponding to the periods of the control signals. As will be discussed more fully hereinafter, substantial variations in valve response are experienced as a result of changes in both power supply voltage and the resistance of the coil due to temperature variations. In some cases, valve response, which may be measured in terms of the magnitude of hydraulic output pressure from the valve, may vary considerably. This pressure variation significantly reduces the accuracy of a control system employing servo valves and may prevent their use in some applications.
The present invention is directed to overcoming the problems associated with the prior art discussed above and provides a significantly improved pulse width modulated servo driver which affords consistently repeatable valve response.
DISCLOSURE OF THE INVENTION
According to one aspect of the invention, an improved apparatus for controlling a coil operated hydraulic valve is responsive to pulse width modulated control signals for producing hydraulic output pressures respectively proportionate to the duty factors of the control signals. A constant current source is employed in order to consistently control valve response irrespective of variations in power supply voltage and coil resistance. A switching circuit controls the delivery of constant current pulses to the coil in accordance with the control signals, and a voltage regulator circuit provides regulated supply voltage to the constant current source in order to reduce variations in the coil current at small pulse widths.
According to another aspect of the invention, a method is provided for operating a servo controlled hydraulic valve having a coil operated output for producing preselected, hydraulic output pressures, which substantially eliminates variance in the output pressures due to changes in the magnitude of voltage supplied to the coil or changes in the resistance of the coil due to the effects of temperature or the like. The method includes the steps of: producing control signals having duty factors respectively proportionate to the preselected hydraulic pressures; generating a plurality of current pulses of substantially constant magnitude using the control signals; and, delivering the current pulses to the coil. The current pulses are delivered to the coil by: sensing the control signals; operating a switching circuit using sensed control signals; and, controlling the operation of a constant current source using the switching circuit. Additionally, the method may include the steps of: generating a supply of electrical power; regulating the voltage of the power supply; and, delivering the voltage regulated power to the constant current source.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a known system for
REFERENCES:
patent: 3455536 (1969-07-01), Barker
Caterpillar Tractor Co.
Michalsky Gerald A.
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