Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-05-12
2001-07-17
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S798000, C361S140000, C361S161000
Reexamination Certificate
active
06262556
ABSTRACT:
TECHNICAL FIELD
This invention relates to an electronically controlled automatic transmission, and more particularly to a current control for a force motor used for hydraulic pressure control.
BACKGROUND OF THE INVENTION
In automatic transmissions and other fluid pressure control systems, solenoid force motors are sometimes used to develop a variable hydraulic pilot pressure for adjusting the operating point of a pressure regulator valve. In general, the force motor pressure varies in direct proportion to the average current supplied to the solenoid coil, and a system controller modulates the coil energization to achieve a desired coil current corresponding to the desired hydraulic pressure.
Experience has shown that the solenoid coil current cannot be reliably controlled with conventional open-loop and/or closed-loop control strategies, due to circuit variations (such as wire harness length) and the wide temperature variations of the control valve environment. Typically, the control valve is submersed in hydraulic fluid, the temperature of which can vary from −40° C. to +150° C., resulting in corresponding changes in the solenoid coil resistance. One approach, disclosed in the U.S. Pat. No. 4,975,628 to Lemieux, utilizes a closed-loop integral control, with integrator gain terms being scheduled as a function of the solenoid temperature. On one hand, the control valve temperature can be easily determined by simply measuring the hydraulic fluid temperature, but on the other hand, the solenoid resistance varies so greatly that it is difficult to accurately and dynamically schedule the control gains over the entire operating range of the valve. As a result, it is difficult to achieve fast response while avoiding overshoot and steady-state error.
SUMMARY OF THE INVENTION
The present invention is directed to an improved force motor current control wherein feed-forward and feed-back control terms are summed to determine a force motor activation for achieving a current command. The feed-forward control term estimates the force motor activation required to achieve the current command, based on the hydraulic fluid temperature, the system voltage and a model of the force motor circuit. The feed-back control term compares an expected response to the actual response and develops a control term that corrects for modeling errors, providing disturbance rejection and improved command following. Additionally, the closed-loop feedback error is used to enable adaptive correction of the feed-forward control so that the estimated force motor activation more nearly produces the commanded current.
In a preferred embodiment, the feed-back control term is determined by: delaying and filtering the current command to determine the expected force motor current, determining a current error based on the difference between the measured current and the expected current, and computing a feed-back control term based on the current error using proportional-plus-integral control. The feed-forward control term is determined by: estimating the force motor circuit resistance based on a reference resistance, a reference temperature and a measure of the force motor temperature, skewing the estimated resistance to achieve an over-damped transient response, and computing a feed-forward control term based on the measured system voltage, the current command, and the skewed resistance estimate. The reference resistance and reference temperature are adaptively adjusted based on operating parameters observed at two different operating points of the force motor when the force motor temperature reaches a steady value and the feedback control term is within a predefined dead-band.
REFERENCES:
patent: 3699989 (1972-10-01), O'Connor et al.
patent: 4070927 (1978-01-01), Polak
patent: 4764711 (1988-08-01), Deller
patent: 4975628 (1990-12-01), Lemieux
patent: 5601506 (1997-02-01), Long et al.
patent: 6013994 (2000-01-01), Endo et al.
Hubbard Gregory A
Runde Jeffrey Kurt
Dang Khanh
General Motors Corporation
Hargitt Laura C.
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