Fluid-pressure and analogous brake systems – Speed-controlled – Antilock control disabled or altered for acceleration or...
Reexamination Certificate
1997-10-14
2001-06-05
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Antilock control disabled or altered for acceleration or...
Reexamination Certificate
active
06241325
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to brake control systems and, more particularly, to antiskid brake control systems.
BACKGROUND OF THE INVENTION
The brake systems of modem commercial airplanes are hydraulic and include electrically operated brake-metering valves, autobrake shuttle valves, and antiskid valves. The valves are controlled by an antiskid/autobrake control unit that produces and sends control signals to the valves of the brake system in accordance with a software program that responds to inputs from various sensors and control sources. Pilot instructions produced by the operation of brake pedals or an autobrake setting control the operation of the brake metering valves and the antiskid valves in a manner designed to decelerate an airplane in a smooth manner. The brake metering valves control brake pressure and the antiskid valves control the release of brake pressure in a manner designed to minimize wheel skidding.
It has been found that antiskid control software used to control antiskid/antibrake control units designed to interface with unigain antiskid hydraulic valves do not, at low speeds, function as well as desired when interfaced with multigain antiskid hydraulic valves. More specifically, antiskid hydraulic valves are controlled by antiskid pressure bias modulation (PBM) control current. PBM control currents are slow to achieve proper bias brake pressure levels when braking is initiated because PBM control currents are based on an integral control algorithm. The slowness in achieving proper bias brake pressure levels when braking is initiated has resulted in the incorporation of a PBM “high step” in antiskid control software that instantaneously increases the integrator to the proper value when braking is initiated. Such antiskid control software works satisfactorily when paired with a unigain antiskid hydraulic valve because a unigain antiskid hydraulic valve is supplied by a source of constant hydraulic pressure. As a result, brake pressure is a function of the PBM control current applied to the valve. In contrast, a multigain antiskid hydraulic valve is supplied with hydraulic pressure metered by the pilot. As a result, brake pressure depends upon both PBM control current and metered hydraulic pressure. If antiskid control is initiated at a low value of metered hydraulic pressure, which may occur when an airplane is taxiing into an airport gate, releasing too much brake pressure when the high step “fires” may result in a loss of braking. For example, in one aircraft, brake contact pressure is generally around 300 psig. If a pilot is metering 600 psig when a PBM high step fires, brake pressure may suddenly be reduced to 200 psig, a value below brake contact pressure. While this will not occur in a system that uses unigain antiskid hydraulic valves because the PBM high step will not release any brake pressure when metered pressure is low, it can occur in a system that uses multigain antiskid hydraulic valves.
The present invention is directed to providing an antiskid control system that eliminates the foregoing problem when interfaced with a multigain antiskid hydraulic valve.
SUMMARY OF THE INVENTION
In accordance with this invention, a low-speed antiskid control for a multigain hydraulic valve brake system is provided. The antiskid control includes low and high pressure bias modulation (PBM) high step thresholds. At high speeds, the low threshold is used, allowing a PBM high step to “fire” (or trigger) in a conventional manner. At low speeds the high threshold is used to prevent a PBM high step from firing unless a deep skid is occurring. The use of a high threshold at low speed prevents low speed control loss due to high step firing reducing brake pressure below minimum brake contact pressure.
In accordance with other aspects of this invention, the low-speed antiskid control is implemented as a modification to the software that controls the antiskid valves of an airplane brake system.
In accordance with further aspects of this invention, in a conventional manner, the antiskid software compares the measured true wheelspeed of the aircraft with a reference wheelspeed that is based on measured wheelspeed. The true wheelspeed is subtracted from the reference wheelspeed to determine slip velocity. Thereafter, also in a conventional manner, a test is made to determine if the slip velocity is above or below an ideal value. The integrator value is set based on the state of the slip velocity. Then, in accordance with the present invention, a test is made to determine if the wheelspeed is above or below a predetermined threshold. If the wheelspeed is above the threshold, the high PBM threshold is set. If the wheel speed is below the threshold, the low PBM threshold is set. Thereafter, again in a conventional manner, a test is made to determine if the antiskid current is above or below the PBM threshold. If the antiskid current is below the PBM threshold, the antiskid current is applied to the multigain antiskid hydraulic valve. If the antiskid current transitions from below to above the PBM threshold, a high step current is applied to the multigain antiskid hydraulic valve.
As will be readily appreciated from the foregoing description, the use of PBM dual thresholds eliminates the problems associated with combining an antiskid control system designed to interface with a unigain antiskid hydraulic valve when interfaced with a multigain antiskid hydraulic valve. At low speed, a high step will fire only if a deep skid is occurring. At low speed, a deep skid will only occur if the metered pressure is high enough to prevent a complete loss of braking if a high step fires. At higher speed, the high step will still function as normal.
REFERENCES:
patent: 2794609 (1957-06-01), Perry
patent: 3724916 (1973-04-01), Hirzel
patent: 3861759 (1975-01-01), McNamara et al.
patent: 3948569 (1976-04-01), Gentet et al.
patent: 4006941 (1977-02-01), DeVlieg
patent: 4053187 (1977-10-01), Cook
patent: 4076331 (1978-02-01), DeVlieg
patent: 4120540 (1978-10-01), Devlieg
patent: 4125234 (1978-11-01), Tregre
patent: 4130322 (1978-12-01), Cook
patent: 4135769 (1979-01-01), Williams et al.
patent: 4180223 (1979-12-01), Amberg
patent: 4198102 (1980-04-01), DeVlieg
patent: 4205735 (1980-06-01), Murray
patent: 4221350 (1980-09-01), Moser et al.
patent: 4260198 (1981-04-01), Cook
patent: 4269455 (1981-05-01), Beck et al.
patent: 4323969 (1982-04-01), Skarvada
patent: 4327414 (1982-04-01), Klein
patent: 4338667 (1982-07-01), Cook et al.
patent: 4360239 (1982-11-01), Boehringer
patent: 4402478 (1983-09-01), Martin
patent: 4430715 (1984-02-01), Gentet et al.
patent: 4484281 (1984-11-01), Skarvada
patent: 4484282 (1984-11-01), Cook et al.
patent: 4485445 (1984-11-01), Braschel
patent: 4523633 (1985-06-01), Furukawa et al.
patent: 4530058 (1985-07-01), Cook et al.
patent: 4562542 (1985-12-01), Skarvada
patent: 4613190 (1986-09-01), Johnson
patent: 4640475 (1987-02-01), Zoerb
patent: 4773014 (1988-09-01), Hagiya et al.
patent: 4881784 (1989-11-01), Leppek
patent: 4923056 (1990-05-01), Nedelk
patent: 5171070 (1992-12-01), Okazaki et al.
patent: 5209329 (1993-05-01), Sigl et al.
patent: 5333942 (1994-08-01), Peczkowski et al.
patent: 5511863 (1996-04-01), Suh
patent: 5615934 (1997-04-01), Abuelsamid
patent: 555392 (1932-07-01), None
patent: 1 756 129 (1970-02-01), None
Gowan John J.
Griffith Thomas T.
Graham Matthew C.
Johnson Kindness PLLC
O'Connor Christensen
The Boeing Company
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