Antiskid operation during degraded operation

A braking system may include a controller, a first wheel and a second wheel. The first wheel may be laterally displaced from the second wheel by a first distance. A first wheel speed sensor may be coupled to the first wheel and a second wheel sensor may be coupled to the second wheel. The controller may be configured to determine at least one of a slip ratio, a coefficient of friction, or a braking pressure of the second wheel in response to failure of the first wheel speed sensor. The controller may be configured to calculate a consistency value of the at least one of the slip ratio, the coefficient of friction, or the braking pressure. The controller may be configured to adjust a braking pressure of the first wheel speed sensor based upon the consistency value and the first distance.

FIELD

The present disclosure relates to braking systems, and, more specifically, to brake control systems.

BACKGROUND

Aircraft often include one or more landing gear that comprise one or more wheels. Each wheel may have a brake, which is part of an aircraft braking system, that is operatively coupled to the wheel to slow the wheel, and hence the aircraft, during, for example, landing or a rejected takeoff. Aircraft braking systems may utilize wheel speed data received from a wheel speed sensor to control braking. From time to time, a wheel speed sensor could cause an aircraft braking system to be deprived of such wheel speed data for the wheel experiencing the wheel speed sensor failure.

SUMMARY

Systems and methods disclosed herein may be useful for controlling the braking of a wheel that is experiencing wheel speed sensor failure. A braking system is provided. A braking system may comprise a controller, a first wheel and a second wheel. The first wheel may be laterally displaced from the second wheel by a first distance. A first wheel speed sensor may be coupled to the first wheel and a second wheel sensor may be coupled to the second wheel. The controller may be configured to determine at least one of a slip ratio, a coefficient of friction, or a braking pressure of the second wheel in response to failure of the first wheel speed sensor. The controller may be configured to calculate a consistency value of the at least one of the slip ratio, the coefficient of friction, or the braking pressure. The controller may be configured to adjust a braking pressure of the first wheel speed sensor based upon the consistency value and the first distance.

In various embodiments, the controller may be configured to adjust the braking pressure applied to the first wheel as a proportion of a braking pressure applied to the second wheel. The first wheel may be separated from the second wheel by a second distance. The second distance may represent that the first wheel is at least one of forward or aft of the second wheel. The first wheel may be disposed on a different landing gear than the second wheel. The controller may be configured to determine at least one of a slip ratio, a coefficient of friction, or a braking pressure of a third wheel. The third wheel may be laterally displaced from the first wheel. The consistency value may comprise a standard deviation. The consistency value may be determined using a weighting factor with the at least one of the slip ratio, the coefficient of friction, or the braking pressure associated with the third wheel.

A braking system may comprise a controller, a first wheel and a second wheel. The first wheel may be displaced from the second wheel in at least one of a forward direction or an aft direction by a second distance. A first wheel speed sensor may be coupled to the first wheel and a second wheel sensor may be coupled to the second wheel. The controller may be configured to determine at least one of a slip ratio, a coefficient of friction, or a braking pressure of the second wheel in response to failure of the first wheel speed sensor. The controller may be configured to calculate a consistency value of the at least one of the slip ratio, the coefficient of friction, or the braking pressure. The controller may be configured to adjust a braking pressure applied to the first wheel based upon the consistency value and the second distance.

In various embodiments, the controller may be configured to adjust the braking pressure applied to the first wheel as a proportion of a braking pressure applied to the second wheel. The first wheel may be disposed on a different landing gear than the second wheel. The controller may be configured to determine at least one of a slip ratio, a coefficient of friction, or a braking pressure of a third wheel. The third wheel may be laterally displaced from the first wheel. The consistency value may comprise a standard deviation. The consistency value may be determined using a weighting factor with the at least one of the slip ratio, the coefficient of friction, or the braking pressure associated with the third wheel.

A method is also provided. The method may comprise the step of determining, by a controller, at least one of a slip ratio, a coefficient of friction, or a braking pressure of the second wheel in response to failure of the first wheel speed sensor coupled to a first wheel. The first wheel may be laterally displaced from the second wheel by a first distance. The method may comprise the steps of calculating, by the controller, a consistency value of the at least one of the slip ratio, the coefficient of friction, or the braking pressure associated with the second wheel, and adjusting, by the controller, a braking pressure applied to the first wheel based upon the consistency value and the first distance.

In various embodiments, the step of adjusting may comprise adjusting, by the controller, braking pressure applied to the first wheel as a proportion of a braking pressure applied to the second wheel. The method may further comprise the step of adjusting, by the controller, braking pressure applied to the first wheel based upon a second distance. The second distance may separate the second wheel from the first wheel in at least one of the forward or aft direction. The method may further comprise the step of determining, by the controller, at least one of a slip ratio, a coefficient of friction, or a braking pressure of a third wheel. The third wheel may be laterally displaced from the first wheel. The method may further comprise the step of mapping, by the controller, the consistency value to a preliminary amount of braking pressure. The step of calculating may further comprise calculating, by the controller, a standard deviation to produce the consistency value. The method may further comprise the step of weighting, by the controller, the at least one of the slip ratio, the coefficient of friction, or the braking pressure associated with the third wheel in the calculating the consistency value.

DETAILED DESCRIPTION

All ranges and ratio limits disclosed herein may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural.

Systems and methods disclosed herein may be useful for controlling the braking of a wheel that is experiencing wheel speed sensor failure. Although the embodiments herein are described with reference to braking systems used in connection with aircraft, such embodiments are provided for example only as it is contemplated that the disclosures herein have applicability to other vehicles, such as automobiles and/or vehicles with brakes.

Aircraft may comprise one or more types of aircraft wheel and brake assemblies. For example, an aircraft wheel and brake assembly may comprise a non-rotatable wheel support, a wheel mounted to the wheel support for rotation, and a brake disk stack. The brake stack may also have alternating rotor and stator disks mounted with respect to the wheel support and wheel for relative axial movement. Each rotor disk may be coupled to the wheel for rotation therewith, and each stator disk may be coupled to the wheel support against rotation. A back plate may be located at the rear end of the disk stack and a brake head may be located at the front end. The brake head may house one or more actuator rams that extend to compress the brake disk stack against the back plate, or the brake disk stack may be compressed by other means. Torque is taken out by the stator disks through a static torque tube or the like.

The actuator rams may be electrically operated actuator rams or hydraulically operated actuator rams, although some brakes may use pneumatically operated actuator rams. In brake systems that employ fluid powered (hydraulic or pneumatic power) actuator rams, the actuator ram may be coupled to a power source via a brake servo valve (BSV) and a shutoff valve (SOV). The SOV effectively functions as a shutoff valve, wherein in a first position (e.g., an armed position), fluid pressure is permitted to pass through the valve, while in a second position (e.g., a disarmed position) fluid pressure is restricted or prevented from passing through the valve. During normal braking, the SOV is in the armed position, thereby permitting the flow of fluid pressure. The BSV, based on braking commands from the pilot (often via an electronic controller that may implement, for example, antiskid logic) controls the amount of fluid pressure provided to the actuator ram, and thus, the braking force applied to the wheel. To prevent or minimize unintentional braking (e.g., due to a faulty servo valve) at various times, the SOV is set in the disarmed position, thereby removing or decreasing fluid pressure from the BSV. Since the BSV does not receive sufficient fluid pressure, it cannot provide fluid pressure to the actuator ram, and thus, braking cannot be effected. A brake controller may be configured to control the SOV and BSV, among other aspects of aircraft braking.

In electronic brakes, a brake controller (or controller) is coupled to one or more electromechanical actuator controllers (EMAC) for a brake, which drives one or more electromechanical brake actuators. The brake controller may be in communication with a brake pedal, and thus may control the EMAC in accordance with pilot/copilot braking commands. In various aircraft, other means are used to compress a brake disk stack. A brake controller may comprise a processor and a tangible, non-transitory memory. The brake controller may comprise one or more logic modules that implement brake logic. In various embodiments, the brake controller may comprise other electrical devices to implement brake logic.

A controller as disclosed herein may include one or more processor. Each processor can be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. System program instructions and/or controller instructions may be loaded onto a tangible, non-transitory, computer-readable medium (also referred to herein as a tangible, non-transitory, memory) having instructions stored thereon that, in response to execution by a controller, cause the controller to perform various operations. The term “non-transitory” is to be understood to remove only propagating transitory signals per se from the claim scope and does not relinquish rights to all standard computer-readable media that are not only propagating transitory signals per se. Stated another way, the meaning of the term “non-transitory computer-readable medium” and “non-transitory computer-readable storage medium” should be construed to exclude only those types of transitory computer-readable media which were found in In Re Nuijten to fall outside the scope of patentable subject matter under 35 U.S.C. § 101.

With reference toFIG. 1, aircraft100on runway102is shown. Aircraft100may comprise right landing gear108and left landing gear106. Nose landing gear104is located under the nose of aircraft100and may not include a brake. Aircraft100may comprise a controller110and pilot controls112. Aircraft100may include a plurality of sensors that detect aircraft status information, such as an avionics unit or aircraft data source116. Aircraft status information may mean any information relating to the status of an aircraft, for example, the presence of weight on wheels, aircraft velocity, aircraft acceleration, wheel position, wheel velocity, wheel acceleration, air temperature, the pressure applied to the brake stack during braking, global positioning system coordinates, aircraft location, aircraft position on a runway, or other aircraft data. An aircraft brake system may have access to various aircraft status information at any given time.

With reference toFIG. 2A, a landing gear of aircraft100having a braking system200is shown schematically in a front view, looking forward to aft, in accordance with various embodiments. Braking system200may comprise right landing gear108and left landing gear106. Braking system200illustrates an example of a set of landing gear having four wheels, however, it is further contemplated and understood that the system described herein may apply to various configurations of landing gear and wheels. For example, additional wheel configurations are shown inFIG. 4. Referring still toFIG. 2A, right landing gear108may be laterally displaced from left landing gear106. Right landing gear108may comprise a plurality of wheels, such as a right outboard wheel202and a right inboard wheel204. Right outboard wheel202may be laterally displaced from right inboard wheel204. Right outboard wheel202may comprise a right outboard brake206, and right inboard wheel204may comprise a right inboard brake210. Right outboard brake206and right inboard brake210may be mounted in a conventional manner to right outboard wheel202and right inboard wheel204, respectively, to apply and release braking force or braking pressure on each respective wheel.

Left landing gear106may comprise a plurality of wheels, such as a left outboard wheel220and a left inboard wheel222. Left outboard wheel220may be laterally displaced from left inboard wheel222. Further, left outboard wheel220and left inboard wheel222may be laterally displaced from right outboard wheel202and right inboard wheel204. Left outboard wheel220may comprise a left outboard brake224, and left inboard wheel222may comprise a left inboard brake228. Left outboard brake224and left inboard brake228may be mounted in a conventional manner to left outboard wheel220and left inboard wheel222, respectively, to apply and release braking force on each respective wheel.

Each landing gear106,108may comprise a plurality of sensors. For example, each brake may include a sensor for detecting a braking pressure or a braking force applied to the respective wheel. Right landing gear108may include a right outboard (ROB) wheel sensor208, a right inboard (RIB) wheel sensor212, a ROB brake sensor214and RIB brake sensor216. ROB brake sensor214may detect a pressure or a force applied to right outboard wheel202by right outboard brake206. RIB brake sensor216may detect a pressure or a force applied to right inboard wheel204by right inboard brake210. ROB wheel sensor208and RIB wheel sensor212may be coupled to each respective wheel to measure one or more characteristics of each wheel, such as wheel position, wheel speed, and/or wheel acceleration, measured in terms of linear or angular position, linear or angular velocity, linear or angular acceleration, or other measurement unit.

Left landing gear106may include a left outboard (LOB) wheel sensor226, a left inboard (LIB) wheel sensor230, a LOB brake sensor232and a LIB brake sensor234. LOB brake sensor232may detect a pressure or a force applied to left outboard wheel220by right outboard brake224. LIB brake sensor234may detect a pressure or a force applied to left inboard wheel222by left inboard brake228. In various embodiments, brake sensors214,216,232,234may detect a pressure applied to the respective wheel by a hydraulic or pneumatic actuator ram. In various embodiments, brake sensors214,216,232,234may be force sensors, such as a load cell, which may detect a force applied to the respective wheel by an electromechanical actuator. LOB wheel sensor226and LIB wheel sensor230may be coupled to each respective wheel to measure one or more characteristics of each wheel, such as wheel position or displacement, wheel speed, and/or wheel acceleration, measured in terms of linear or angular position, linear or angular velocity, linear or angular acceleration, or other measurement unit. In various embodiments, wheel sensors226,230,208,212may comprise wheel speed sensors that output signals indicative of angular velocity or angular displacement, for example, a Hall effect sensor, variable resistance sensor, or the like. Wheel sensors226,230,208, or212may detect a change in a rate of deceleration of the wheels. In various embodiments, each of wheel sensors226,230,208,212may comprise a plurality of sensors, for example a wheel speed sensor and an accelerometer or other sensor. The wheel speed data for each wheel may be sent to controller110and used to detect the onset of wheel skidding, to calculate or estimate a slip ratio for each wheel, and/or to calculate or estimate a coefficient of friction of a runway surface.

With reference toFIG. 2B, a schematic block diagram of braking system200is shown in accordance with various embodiments. Braking system200includes a controller110in communication with pilot controls112and an antiskid control unit114. Controller110may comprise additional control modules (such as autobraking control, brake control executive, brake pressure control unit, etc.) for controlling brakes206,210,228,224. Controller110may receive input from pilot controls112, antiskid control unit114, and/or aircraft data source116and may determine an amount of braking pressure or braking force to be applied to the brake disk stack of each brake206,210,228,224. Controller110may receive input from wheel sensors226,230,208, or212and from brake sensors214,216,232,234. Controller110may use data from the inputs to determine a reference wheel characteristic for one or more of the wheels of the braking system200. A reference wheel characteristic may be a slip ratio of a wheel, a coefficient of friction experienced by a wheel, a braking pressure applied at the time of wheel skid, or other value correlating to the environment or performance associated with the wheel.

Controller110and/or antiskid control unit114may be in communication with wheel sensors226,230,208, and212. During normal operation, wheel sensors226,230,208,212may transmit the wheel speed data250(i.e., the angular velocity and/or acceleration of the wheel) of each wheel to controller110and/or antiskid control unit114. Antiskid control unit114and controller110may further be in communication with an aircraft data source116. Antiskid control unit114may receive aircraft data from aircraft data source116, and for example, may receive the aircraft velocity252. Antiskid control unit114may also receive wheel speed data from wheel sensors226,230,208,212. Antiskid control unit114may determine if a wheel is skidding based on the aircraft velocity252, the wheel speed data250, and/or other inputs from aircraft data source116. A wheel skid may occur in response to the braking force or braking pressure applied to a wheel exceeding the traction available to that wheel. In response to a wheel experiencing wheel skid, antiskid control unit114and controller110may adjust the braking force or braking pressure of the corresponding brake.

Wheel sensors226,230,208, or212may, from time to time, fail. Without wheel speed data250, antiskid control unit114and controller110may encounter difficulty controlling the brake associated with the failed wheel sensor, shown inFIG. 2Bas RIB wheel sensor212. For example, antiskid functionality may be degraded, autobrake functionality may be degraded, and/or overall braking force may be degraded. In various embodiments, autobrake functionality refers to a braking control scheme where a desired deceleration is input to controller110and controller110adjusts braking pressure to achieve the desired deceleration. Due to the loss of wheel speed data250, a controller may cease commanding braking pressure to the wheel associated with the failed sensor. Such ceasing of braking pressure, however, decreases the aircraft braking system's ability to slow the aircraft. This may be problematic on runways with contaminants such as ice, slush, snow, oil, and other materials that reduce the coefficient of friction of the runway surface.

In various embodiments, braking system200is configured to control the braking of the wheels202,204,220,222of aircraft100, including the wheel associated with the failed sensor. For illustration purposes, RIB wheel sensor212of right inboard wheel204is shown inFIG. 2Bas a failed wheel sensor. Braking system200may use information about one or more reference wheels, such as wheels202,220,222, to determine a braking pressure or braking force to apply to right inboard wheel204associated with the failed RIB wheel sensor212. The term reference wheel or wheels may be used to indicate the wheels used to determine a braking pressure to be applied to a wheel having a failed wheel speed sensor. Antiskid control unit114may receive wheel speed data250from wheel sensors226,230,208and may determine when wheels202,222,220experience skidding. Antiskid control unit114may not receive wheel speed data250from the failed RIB wheel sensor212, and thus, may not determine when right inboard wheel204experiences skidding. Braking system200may use the available wheel speed data250as well as braking feedback data254to control right inboard brake210while reducing the risk of skidding by right inboard wheel204. Thus, controller110determines a reference wheel characteristic of one or more reference wheels to control, in substantially real-time, the braking of the wheel having a failed wheel speed sensor. The reference wheel characteristic may include a braking pressure applied to the reference wheel at the time of wheel skid.

Controller110may receive wheel skid information256from antiskid control unit114as well as braking feedback data254from brake sensors214,216,232,234. Wheel skid information256may include the time at which a wheel skid event occurred. Wheel skid information256may include wheel speed data250and/or data from aircraft data source116. Braking feedback data254may include the pressure or force applied to a brake206,210,228,224. Controller110may determine the braking pressure or braking force at which a wheel experiencing skidding based on the braking feedback data254and the wheel skid information256. Controller110may gather data for the skid events of wheels202,222,220into a sample.

With reference toFIG. 3A, a graph is shown having consistency values (i.e., consistency of a sample of braking pressure of wheels202,222,220) on the y axis and the time of each wheel skid event on the x axis. Controller110may gather the braking pressure at the time of wheel skidding for wheels202,222,220and may determine a consistency value based upon the braking pressures in the sample. A consistency value may be any measure to show how different the braking pressures are from one another during the wheel skid events. Stated another way, the consistency value indicates the shape of the distribution of braking pressures during skid events. In various embodiments, the consistency value comprises the standard deviation of the braking pressures in the sample. Higher standard deviations reflect less consistency than smaller standard deviations. The more consistent the braking pressures are among the skid events sampled, the greater confidence there is to command a braking pressure to right inboard wheel204that is similar to the braking pressure applied to the reference wheel(s) without causing right inboard wheel204to skid. Inconsistent braking pressures may indicate a runway surface of varying coefficients of friction, and thus the less confidence there is to command a similar braking pressure to right inboard wheel204having the failed wheel sensor, as skidding becomes a concern.

With reference toFIG. 3B, a graph is shown having consistency values (i.e., consistency of a sample of slips ratios for wheels202,222,220) on the y axis and the time of each sample on the x axis. The reference wheel characteristic may include a slip ratio of the reference wheel(s). Slip ratio as used herein may refer to an expression of the locking status of a wheel, which may be calculated as the difference between the aircraft speed and the wheel speed, divided by the aircraft speed. Controller110may receive aircraft data from aircraft data source116and/or antiskid control unit114, and for example, may receive the aircraft velocity252. Controller110may also receive wheel speed data from wheel sensors226,230,208. Controller110may determine a slip ratio for one or more reference wheels, such as wheels202,222,220. Controller110may determine a consistency value based upon the slip ratios in the sample. A consistency value may be any measure to show how different the slip ratios are from one another, and for example, may be the standard deviation of the slip ratios in the sample. Higher standard deviations reflect less consistency than smaller standard deviations. The more consistent the braking pressures are among the skid events sampled, the greater confidence there is to command a braking pressure to right inboard wheel204that is similar to the braking pressure applied to the reference wheel(s) without causing right inboard wheel204to skid. Inconsistent braking pressures may indicate a runway surface of varying coefficients of friction, and thus the less confidence there is to command a similar braking pressure to right inboard wheel204having the failed wheel sensor, as skidding becomes a concern.

Referring toFIGS. 3A and 3B, controller110may determine a preliminary amount of braking pressure to be applied to right inboard wheel204, based on the consistency value of the reference wheel characteristic, such as a braking pressure at skid or a slip ratio. Controller110may command a braking pressure to right inboard brake210based at least in part on the consistency value. The de-rating line illustrates preliminary amount of braking pressure to be commanded to right inboard brake210. The preliminary amount of braking pressure may be further adjusted as discussed with respect toFIGS. 4 and 5. For a higher consistency value, the preliminary amount of braking pressure is similar to the braking pressure of the reference wheels. For a lower consistency value, the preliminary amount of braking pressure is reduced relative to the braking pressure of the reference wheels. Thus, the difference between the preliminary amount of braking pressure and the braking pressure of the reference wheels is greater at low consistency values than at higher consistency values. In this manner, the antiskid functionality, which controller110performs for wheels having functioning wheel speed sensors, acts as a guide to determine how much to “de-rate” or reduce the braking pressure applied to the wheel having a failed wheel speed sensor.

In various embodiments and with reference toFIG. 5, the reference wheel characteristic may include a coefficient of friction experienced by the reference wheel(s). The coefficient of friction experienced by another wheel (e.g. a reference wheel or wheels) on the aircraft may be calculated or estimated over time to determine the consistency (i.e., produce a consistency value) of the coefficients of friction. The more consistent the coefficients of friction are among the coefficients of friction sampled, the greater confidence there is to command a braking pressure to the wheel having the failed wheel sensor that is similar to the braking pressure applied to the reference wheel(s). Inconsistent coefficients of friction indicate a runway surface of varying coefficients of friction, and thus the less confidence there is to command a similar braking pressure to the wheel having the failed wheel sensor, as skidding becomes a concern.

Moreover, the displacement of the reference wheel from the wheel having a failed wheel sensor affects the consistency value. For example, if the reference wheel is laterally displaced from the wheel having a failed wheel sensor by a small distance, it is likely that the reference wheel behaves similarly to the wheel having a failed wheel sensor. However, that likelihood decreases as the lateral distance increases. In addition, displacement in a forward/aft direction may indicate that the reference wheel and the wheel having a failed wheel sensor may encounter similar coefficients of friction, or may skid at a similar braking pressure, though offset for the lead or lag time of the reference wheel against the wheel having a failed wheel sensor.

With reference toFIG. 7, aircraft100is illustrated on runway50during landing. Patch56represents ice. Patch54represents a mixture of ice and snow. Patch52represents spilled lubricant, such as oil. Forward direction68is shown 180 degrees opposite aft direction66. Starboard direction62is shown 180 degrees opposite port direction64, though displacement in the starboard direction62and/or port direction64may be referred to herein as lateral displacement. The remainder of runway50may be relatively dry. As aircraft100progresses across runway50, one or more wheels of aircraft100encounters dry runway50along with patches52,54and56. In that regard, each wheel of aircraft100may experience different coefficients of friction (i.e., coefficients of kinetic friction) depending upon the surface encountered.

In various embodiments, controller110may calculate a slip ratio and/or a coefficient of friction experienced by a given reference wheel (e.g., right outboard wheel202, left outboard wheel220, and left inboard wheel222) at regular intervals. For example, controller110may calculate a slip ratio and/or a coefficient of friction for each reference wheel of aircraft100at intervals of from 0.1 Hertz (Hz) to 100 Hz, from 1 Hz to 50 Hz, and from 6 Hz to 15 Hz. Each slip ratio and/or coefficient of friction calculated for each reference wheel may be stored by controller110and accessed at a desired time. In various embodiments, the brake pressure applied to the wheel having a failed wheel speed sensor may be adjusted in substantially real time based on the reference wheel characteristic determined by controller110.

Controller110may gather the coefficients of friction into a sample and determine a consistency value based upon the coefficients of friction in the sample. A consistency value may be any measure to show how different the coefficients of friction are from one another. Stated another way, the consistency value indicates the shape of the distribution of coefficients of friction. In various embodiments, the consistency value comprises the standard deviation of the coefficients of friction in the sample. Higher standard deviations reflect less consistency than smaller standard deviations. Controller110may command braking pressure to one or more wheels of aircraft100. Controller110may command braking pressure from 0% of the brake's potential pressure to 100% of the brake's potential pressure.

With reference toFIG. 4, different aircraft are shown having different numbers of wheels. Aircraft300is shown having wheel301laterally displaced from wheel302by a distance of x. Aircraft310is shown having wheel311and wheel312laterally displaced from wheel314and wheel315. Wheel311is laterally displaced from wheel312by a distance of y. Aircraft320is shown having wheel331and wheel332laterally displaced from wheel335and wheel336. Aircraft320also comprises wheel333and wheel334laterally displaced from wheel337and wheel338. Wheel331is displaced in a forward/aft direction from wheel333by a distance of d and wheel331is laterally displaced from wheel333by a distance z, where z=0. It is noted that distance traveled by wheel331, represented by D, may be derived if the linear velocity and time period is known for wheel331, according to the equation D=vt. Travel distance D and/or forward/aft displacement distance d may be used to determine when wheel333will encounter the runway surface encountered by wheel331. As discussed herein, the term reference wheel or wheels may be used to indicate the wheels used to determine the braking pressure to be applied to a wheel having a failed wheel speed sensor. In this manner, the antiskid functionality, which controller110performs for wheels having functioning wheel speed sensors, acts as a guide to determine how much to “de-rate” or reduce the braking pressure applied to the wheel having a failed wheel speed sensor. The braking pressure may be adjusted based on travel distance D and/or forward/aft displacement distance d between the wheels. For example, controller110may de-rate the braking pressure more where forward/aft displacement d is greater. By de-rating the braking pressure to the wheel having the failed wheel speed sensor, the wheel having the failed wheel speed sensor is less likely to skid.

With reference toFIG. 5, a graph is shown having consistency values (i.e., consistency of a sample of coefficients of friction μxof wheels) on the y axis and percentage of a brake's potential pressure as applied to the reference wheel(s) on the x axis. As μxbecomes less consistent, the de-rating line illustrates the correction factor to be applied to the braking pressure of the reference wheel to yield a braking pressure to be applied to the wheel having a failed wheel speed sensor. Stated another way, the de-rating line may indicate that at 50% of maximum braking pressure for the reference wheel and moderate consistency values of coefficients of friction, 50% of the braking pressure applied to the reference wheel is to be applied to the wheel having a failed wheel speed sensor. The de-rating line thus creates a preliminary amount of braking pressure to be commanded.

However, as discussed above, because the lateral and/or forward/aft distance between the reference wheel and the wheel having a failed wheel speed sensor influences the confidence level of determining the conditions of the wheel having a failed wheel speed sensor, the de-rating may be adjusted, or offset, by such values. For example, with reference toFIGS. 4 and 5, wheel331may experience a failed wheel speed sensor and wheel338may act as a reference wheel. A controller may calculate coefficients of friction of wheel338and determine a consistency value of such samples.

Controller110may further account for both a lateral displacement distance x and a forward/aft displacement distance d between wheel338and wheel331. To account for forward/aft displacement distance d, the braking pressure to be applied to wheel331may be reduced from the preliminary amount based on the consistency value, as shown inFIG. 5. Thus, if the de-rating line indicates that wheel331should receive 50% of the braking pressure applied to wheel338, adjusting to account for the distance d may yield, for example, that wheel331should receive 45% of the braking pressure applied to wheel338. To account for lateral displacement distance x, the braking pressure to be applied to wheel331may be further reduced, as shown inFIG. 5. Adjusting to account for the distance x may yield, for example, that wheel331should receive 35% of the braking pressure applied to wheel338. With momentary reference toFIGS. 2A, 2B, 3A and 3B, the preliminary amount of braking pressure to be applied by right inboard brake210(shown by de-rating line inFIGS. 3A and 3B) may be similarly adjusted to account for the lateral distance and/or forward/aft distance between right inboard wheel204and the reference wheel(s).

In various embodiments, the forward/aft displacement distance d or a lateral displacement distance x may be zero. For example, with reference toFIGS. 4 and 5, wheel301may experience a failed wheel speed sensor and wheel302may act as a reference wheel. A forward/aft displacement distance d between wheel301and wheel302may be zero. A controller may calculate coefficients of friction of wheel302and determine a consistency value of such samples. To account for lateral displacement distance x, the braking pressure to be applied to wheel301may be reduced. Thus, if the de-rating line indicates that wheel301should receive 50% of the braking pressure applied to wheel302, adjusting to account for the distance x may yield, for example, that wheel301should receive 40% of the braking pressure applied to wheel302.

In various embodiments, wheel331may experience a failed wheel speed sensor and wheel333may act as a reference wheel. A lateral displacement distance z between wheel301and wheel302may be zero. A controller may calculate coefficients of friction of wheel333and determine a consistency value of such samples. To account for forward/aft displacement distance d, the braking pressure to be applied to wheel331may be reduced. Thus, if the de-rating line indicates that wheel331should receive 50% of the braking pressure applied to wheel333, adjusting to account for the distance d may yield, for example, that wheel331should receive 45% of the braking pressure applied to wheel333.

Where multiple wheels are used as reference wheels, a weighting factor may be used to weight the coefficients of friction depending upon the lateral displacement and/or forward/aft displacement of each reference wheel and the wheel experiencing the failed wheel speed sensor. The weighting factor may weight the values produced by a reference wheel closest to the wheel experiencing the failed wheel speed sensor more heavily than reference wheels that are a greater distance from the wheel experiencing the failed wheel speed sensor. Use of a weighting factor allows controller110to better estimate the coefficient of friction actually experienced by the wheel experiencing the failed wheel speed sensor.

With reference toFIG. 6A, a method400of an antiskid operation is illustrated, in accordance with various embodiments. Controller110may determine that a wheel speed sensor has failed in Step402. In Step404, controller110may determine a reference wheel characteristic associated with a second wheel. Controller110may receive inputs from pilot controls112, antiskid control unit114, aircraft data source116, one or more brake sensors, and/or one or more wheels sensors associated with the second wheel, which acts as a reference wheel. Controller110may use data from the inputs to determine a reference wheel characteristic for one or more of reference wheels of the braking system200. For example, a reference wheel characteristic may be a slip ratio of the second wheel, a coefficient of friction experienced by the second wheel, a braking pressure applied to the second wheel at the time of wheel skid, or other value correlating to the environment or performance associated with the second wheel. Where more than one reference wheel is used, one or more weighting factors may be used to weight the reference wheel characteristic.

In Step406, a consistency value may be calculated by controller110. The consistency value may be the consistency of the reference wheel characteristic for the second wheel, or for one or more reference wheels. The consistency value, as discussed above, may comprise a standard deviation value. From the consistency value, the controller110may use a map, lookup table, or other data structure to determine a preliminary amount to de-rate the braking pressure commanded at the wheel having the wheel speed sensor failure.

In Step408, controller110may adjust a braking pressure applied to the first wheel based upon the consistency value.

In Step410, controller110may command a brake associated with the wheel having the failed wheel speed sensor. The controller110may command the adjusted braking pressure to the brake associated with the wheel having the failed wheel speed sensor. Thus, the adjusted braking pressure applied to the first wheel may be based on a reference wheel characteristic of the second wheel, and more specifically, based on a consistency value of the reference wheel characteristic of the second wheel.

With reference toFIG. 6B, along withFIGS. 4 and 5, a method500of an antiskid operation is illustrated. Controller110may determine that a wheel speed sensor has failed in Step502. Controller110may receiving at least two coefficients of friction associated with a second wheel in response to failure of a first wheel speed sensor coupled to a first wheel. The first wheel may be laterally displaced from the second wheel by a lateral distance and/or forward/aft distance.

In Step504, controller110may calculate coefficients of friction from one or more reference wheels, such as the second wheel, to form a sample set of coefficients of friction. Where more than one reference wheel is used, one or more weighting factors may be used to weight the coefficients of friction. Also in Step504, a consistency value may be calculated by controller110. The consistency value may be the consistency of the coefficients of friction associated with one or more reference wheels. The consistency value, as discussed above, may comprise a standard deviation value. From the consistency value, the controller110may use a map, lookup table, or other data structure to determine a preliminary amount to de-rate the braking pressure commanded at the wheel having the wheel speed sensor failure. Controller110may adjust a braking pressure applied to the first wheel based upon the consistency value, and may adjust the braking pressure as a proportion of a braking pressure applied to the second wheel.

In Step508, controller110adjusts the preliminary amount to account for lateral distance. In that regard, the larger the lateral distance, the more reduction in braking pressure will be commanded.

In Step510, controller110adjusts the preliminary amount to account for forward/aft distance. In that regard, the larger the forward/aft distance, the more reduction in braking pressure will be commanded.

In Step512, controller commands a brake associated with the wheel having the failed wheel speed sensor. The controller110may command the adjusted braking pressure to the brake associated with the wheel having the failed wheel speed sensor.

With reference toFIG. 6C, along withFIGS. 2B and 3A, a method600of an antiskid operation is illustrated. Controller110may determine that a wheel speed sensor has failed in Step602. In Step604, controller110may receiving a braking pressure for at least two wheel skid events for a second wheel in response to failure of a first wheel speed sensor coupled to a first wheel. The first wheel may be laterally displaced from the second wheel by a lateral distance and/or forward/aft distance.

In Step604, controller110may determine a braking pressure associated with the wheel skid events from one or more brake sensors, such as a brake sensor of the second wheel, to form a sample set of braking pressures. Where more than one reference wheel is used, one or more weighting factors may be used to weight the braking pressures.

In Step606, a consistency value may be calculated by controller110. The consistency value may be the consistency of the braking pressures associated with one or more reference wheels. The consistency value, as discussed above, may comprise a standard deviation value. From the consistency value, the controller110may use a map, lookup table, or other data structure to determine a preliminary amount to de-rate the braking pressure commanded at the wheel having the wheel speed sensor failure.

In Step608, controller110may determine a lateral distance and/or a forward/aft distance between the reference wheel(s) and the wheel having the failed wheel speed sensor.

In Step610, controller110may adjust a braking pressure applied to the first wheel based upon the consistency value, and may adjust the braking pressure as a proportion of a braking pressure applied to the second wheel. In step610, controller110may adjust the preliminary amount to account for lateral distance. In that regard, the larger the lateral distance, the more reduction in braking pressure will be commanded. In Step610, controller110may adjust the preliminary amount to account for forward/aft distance. In that regard, the larger the forward/aft distance, the more reduction in braking pressure will be commanded.

In Step612, controller commands a brake associated with the wheel having the failed wheel speed sensor. The controller110may command the adjusted braking pressure to the brake associated with the wheel having the failed wheel speed sensor.