Limited-slip brake control system
First Claim
1. A limited-slip brake control system for controlling the brake force to be developed by a braking means for a wheel of a vehicle, said limited-slip brake control system comprising:
- first means for comparing measured deceleration of the wheel with a selected reference deceleration representing a level of brake force generally lying in a nonslip portion of a characteristic Mu/slip curve for the vehicle, and operative to provide a fixed-level, first output signal generally having a first polarity representing a decrease in brake force when said measured wheel deceleration exceeds said selected reference deceleration and generally having a second polarity representing an increase in brake force when said selected reference deceleration exceeds said measured wheel deceleration, said first output signal switching between said first and said second polarities only when the difference between said measured wheel deceleration and said selected reference deceleration exceed a predetermined amount representing an incremental deceleration less than said selected reference deceleration;
second means for comparing said measured wheel deceleration with a second reference deceleration representing a level of brake force generally lying in a slip portion of said characteristic Mu/slip curve and operative to provide a second output signal when said measured wheel deceleration exceeds said second reference deceleration, said second output signal having said first polarity representing a decrease in brake force and having a level proportional to the amount by which said measured wheel deceleration exceeds said second reference deceleration;
third means for additively combining said first and second output signals to obtain a summed output signal;
fourth means for integrating said summed output signal to obtain a brake control signal representing a desired level of brake force, said brake control signal increasing and decreasing at a rate dependent on the level of said summed output signal; and
fifth means for controlling brake force in inverse proportion to the level of said brake control signal.
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Accused Products
Abstract
A limited-slip brake control system includes a basic deceleration control circuit responsive to a wheel deceleration signal and to a selected reference deceleration signal to provide a first brake control signal which is used to modulate brake pressure applied to a braked wheel of a vehicle in order to maintain the vehicle deceleration at a selected reference deceleration representing a level of brake force generally lying in the nonslip portion of a characteristic Mu/slip curve for the vehicle. A large deviation control circuit is also responsive to the wheel deceleration signal and functions to modify the first brake control signal to cause brake pressure to be reduced when the wheel deceleration exceeds a second reference deceleration representing a level of brake force generally lying in a slip portion of the characteristic Mu/slip curve, or, corresponding to a situation where the braked wheel encounters a sudden decrease in the available coefficient of friction and is forced into a skid by the basic deceleration control circuit. A second brake control signal is also provided by the large deviation control circuit when the actual wheel deceleration exceeds a third reference deceleration, higher than the second reference deceleration, signifying that the braked wheel has gone into a deep skid, which second brake control signal is used to immediately reduce brake pressure. An initial skid circuit functions to modify the first brake control signal to minimize or eliminate the tendency of the basic deceleration control circuit to place the braked wheel into a skid upon the initial application of brake pressure, and a dynamic compensation circuit is responsive to the wheel deceleration signal to provide a compensating brake control signal which is combined with the first brake control signal in order to compensate the brake pressure command represented by the first brake control signal for apparent changes in wheel deceleration occasioned by landing gear strut assembly oscillation.
65 Citations
26 Claims
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1. A limited-slip brake control system for controlling the brake force to be developed by a braking means for a wheel of a vehicle, said limited-slip brake control system comprising:
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first means for comparing measured deceleration of the wheel with a selected reference deceleration representing a level of brake force generally lying in a nonslip portion of a characteristic Mu/slip curve for the vehicle, and operative to provide a fixed-level, first output signal generally having a first polarity representing a decrease in brake force when said measured wheel deceleration exceeds said selected reference deceleration and generally having a second polarity representing an increase in brake force when said selected reference deceleration exceeds said measured wheel deceleration, said first output signal switching between said first and said second polarities only when the difference between said measured wheel deceleration and said selected reference deceleration exceed a predetermined amount representing an incremental deceleration less than said selected reference deceleration; second means for comparing said measured wheel deceleration with a second reference deceleration representing a level of brake force generally lying in a slip portion of said characteristic Mu/slip curve and operative to provide a second output signal when said measured wheel deceleration exceeds said second reference deceleration, said second output signal having said first polarity representing a decrease in brake force and having a level proportional to the amount by which said measured wheel deceleration exceeds said second reference deceleration; third means for additively combining said first and second output signals to obtain a summed output signal; fourth means for integrating said summed output signal to obtain a brake control signal representing a desired level of brake force, said brake control signal increasing and decreasing at a rate dependent on the level of said summed output signal; and fifth means for controlling brake force in inverse proportion to the level of said brake control signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. In a limited-slip brake control system controlling brake force to be developed by a braking means for a wheel of an aircraft, the wheel being supported by a lightly-damped landing gear strut assembly, the limited-slip brake control system being operative to compare measured deceleration of the wheel with a reference deceleration to obtain a deceleration error signal, and to integrate the deceleration error signal to obtain a brake control signal representing a desired level of brake force, an improvement for compensating the brake control signal for oscillation therein resulting from low-frequency oscillation in the measured wheel deceleration that is produced by the landing gear strut assembly when brake force is developed by the wheel, the improvement comprising a dynamic compensation circuit responsive to measured wheel deceleration for providing a compensating brake control signal having a 90°
- or greater phase lead for a range of frequencies in the measured wheel deceleration surrounding the expected frequency of oscillation produced by the landing gear strut assembly in the measured wheel deceleration, and a lesser phase lead for all other frequencies in the measured wheel deceleration; and
, means for combining said compensating brake control signal with said brake control signal to compensate said brake control signal for said oscillation. - View Dependent Claims (19)
- or greater phase lead for a range of frequencies in the measured wheel deceleration surrounding the expected frequency of oscillation produced by the landing gear strut assembly in the measured wheel deceleration, and a lesser phase lead for all other frequencies in the measured wheel deceleration; and
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20. A method for controlling the brake pressure applied to a brake means for a wheel of a vehicle, comprising the steps of:
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causing said brake pressure to increase and decrease at a predetermined rate to produce a wheel deceleration substantially equal to a selected reference deceleration representing a level of brake force to be developed by the brake means which generally lies in a nonslip portion of a characteristic Mu/slip curve for the vehicle; increasing the rate of brake pressure reduction above said predetermined rate as long as said wheel deceleration exceeds a second reference deceleration representing a level of brake force generally lying in a slip portion of said characteristic Mu/slip curve, said increase in the rate of brake pressure reduction being related to the amount by which said wheel deceleration exceeds said second reference deceleration; and causing brake pressure to be reduced in inverse proportion to the amount by which said wheel deceleration exceeds a third reference deceleration, said third reference deceleration being greater than said second reference deceleration, as long as said wheel deceleration exceeds said third reference deceleration. - View Dependent Claims (21)
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22. An apparatus forming part of a brake control system for an aircraft, the aircraft including a brake means for a wheel of the aircraft, means for applying brake pressure to the brake means, and a brake valve for reducing brake pressure in inverse proportion to the level of a brake control signal supplied thereto, said apparatus comprising:
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means providing a wheel deceleration signal related to the measured deceleration of the wheel; means responsive to said wheel deceleration signal for providing a first output signal generally having either a fixed positive level or a fixed negative level, respectively depending on whether said measured wheel deceleration is greater or lesser than a selected reference deceleration, said first output signal switching between said positive and negative levels only when the difference between said measured wheel deceleration and said selected reference deceleration exceeds a predetermined amount representing an incremental deceleration less than said selected reference deceleration; means responsive to said wheel deceleration signal for providing a second output signal as long as said measured wheel deceleration exceeds a second reference deceleration higher than said selected reference deceleration, said second output signal having a positive level determined by the amount that said measured wheel deceleration exceeds said second reference deceleration; means summing said first and said second output signals to provide a composite output signal; integrating circuit means for integrating only positive levels of said composite output signal to provide said brake control signal which increases and decreases at a rate determined by the level of said composite output signal; and means for applying said brake control signal to the brake valve. - View Dependent Claims (23, 24, 25, 26)
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Specification