Patent Description:
A servo valve is used in brake control systems to vary hydraulic power to braking systems (e.g., a brake actuator) to control brake pressures and aircraft deceleration. The servo valve may receive an electric current for varying the hydraulic pressure supplied to the braking systems. Typical braking systems operate in a closed-loop mode and utilize pressure feedback signals for adjusting the electric current supplied to the servo valve to maintain the braking pressure at the commanded pressure. Brake control systems are disclosed in <CIT>.

According to the invention a brake control system is disclosed, comprising a servo valve configured to receive a hydraulic fluid and provide the hydraulic fluid to apply braking force to a wheel via a hydraulic line, and a brake control unit in electronic communication with the servo valve. The brake control unit is configured to calibrate the servo valve, determine whether a calibration of the servo valve was successful, in response to the calibration of the servo valve being successful, operate the servo valve in an open-loop system, and in response to the calibration of the servo valve being unsuccessful, operate the servo valve in a closed-loop system.

In various embodiments, the calibrating comprises sending, by the brake control unit, a first electric current to the servo valve, and determining, by the brake control unit, a first pressure applied to the brake system via the servo valve, in response to the first electric current being sent to the servo valve.

In various embodiments, the calibrating further comprises sending, by the brake control unit, a second electric current to the servo valve, and determining, by the brake control unit, a second pressure applied to the brake system via the servo valve, in response to the second electric current being sent to the servo valve.

In various embodiments, the calibrating further comprises calculating, by the brake control unit, a braking pressure versus servo valve current curve based upon the first electric current, the first pressure, the second electric current, and the second pressure.

In various embodiments, the brake control unit utilizes a pressure feedback signal in response to operating in the closed-loop system.

In various embodiments, the brake control unit utilizes a braking pressure versus servo valve current curve generated during the calibration, in response to operating in the open-loop system.

The accompanying drawings illustrate various embodiments employing the principles described herein and are a part of this specification. The illustrated embodiments are meant for description only, and they do not limit the scope of the claims, and in which:.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this invention and the teachings herein described without departing from the scope of the invention as defined by the claims.

Provided herein, according to various embodiments, are systems, methods, and devices for brake control, such as within a braking system of an aircraft. While numerous details are included herein pertaining to aircraft components, such as brake components, the systems and methods disclosed herein can be applied to other systems with other servo valves and the like.

As used herein, the term "weight-on-wheels (WOW) condition" means that at least a portion of the aircraft is supported on the ground via the landing gear with the associated tire in contact with a ground surface.

A brake control system, as disclosed herein, may calibrate a servo valve to generate a transfer function for calculating a servo valve command current for precise pressure control in an open-loop system. The servo valve may be calibrated often, such as before each flight and/or at the beginning of each brake control unit power up. Brake control systems of the present invention may command braking in an open-loop system and eliminate undesirable pressure oscillations associated with typical closed-loop pressure control feedback systems. Furthermore, brake control systems of the present invention provide methods for operating as an open-loop system utilizing the calculated transfer function, or as a closed-loop system in the event of an unsuccessful servo valve calibration.

Brake control systems of the present invention may comprise a pressure control mixed mode of operation which provides additional capability to pressure control by recalibrating the servo valve characteristics at predetermined intervals, such as at every brake control unit power up. This calibration data may determine a transfer function that is used to apply pressure without pressure feedback interaction from the controls which may keep the pressure response stable, provide consistent pressure response, and/or avoid erroneous fault detection in brake control module line replaceable units (LRUs). In addition, systems of the present invention may relieve manufacturing tolerances and ultimately lead to better manufacturing yield, on time delivery, and a lower cost for the brake control module LRUs.

Referring now to <FIG>, an aircraft <NUM> includes multiple landing gear systems, including a first landing gear <NUM>, second landing gear <NUM>, and third landing gear <NUM>. The first landing gear <NUM>, second landing gear <NUM>, and third landing gear <NUM> each include one or more wheel assemblies. For example, the third landing gear <NUM> includes an inner wheel assembly <NUM> and an outer wheel assembly <NUM>. The first landing gear <NUM>, second landing gear <NUM>, and third landing gear <NUM> support the aircraft <NUM> when the aircraft <NUM> is not flying, thereby allowing the aircraft <NUM> to take off, land, and taxi without damaging the aircraft <NUM>. In various embodiments, the second landing gear <NUM> is also a nose landing gear for the aircraft <NUM>, and oftentimes, one or more of the first landing gear <NUM>, second landing gear <NUM>, and third landing gear <NUM> are operationally retractable into the aircraft <NUM> when the aircraft <NUM> is in flight and/or airborne.

In various embodiments, the aircraft <NUM> further includes an avionics unit <NUM>, which includes one or more controllers (e.g., processors) and one or more tangible, non-transitory memories capable of implementing digital or programmatic logic. In various embodiments, for example, the one or more controllers are one or more of a general purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), or other programmable logic device, discrete gate, transistor logic, or discrete hardware components, or any various combinations thereof or the like. In various embodiments, the avionics unit <NUM> controls, at least various parts of, the flight of, and operation of various components of, the aircraft <NUM>. For example, the avionics unit <NUM> controls various parameters of flight, such as an air traffic management systems, auto-pilot systems, auto-thrust systems, crew alerting systems, electrical systems, electronic checklist systems, electronic flight bag systems, engine systems flight control systems, environmental systems, hydraulics systems, lighting systems, pneumatics systems, traffic avoidance systems, trim systems, and the like.

In various embodiments, the aircraft <NUM> further includes a brake control unit (BCU) <NUM>. With brief reference now to <FIG>, the BCU <NUM> includes one or more controllers <NUM> (e.g., processors) and one or more tangible, non-transitory memories <NUM> capable of implementing digital or programmatic logic. In various embodiments, for example, the one or more controllers <NUM> are one or more of a general purpose processor, DSP, ASIC, FPGA, or other programmable logic device, discrete gate, transistor logic, or discrete hardware components, or any various combinations thereof or the like, and the one or more memories <NUM> store instructions that are implemented by the one or more controllers <NUM> for performing various functions, such as monitoring a health status of a servo valve, as will be discussed herein. In various embodiments, the BCU <NUM> controls, at least various parts of, the braking of the aircraft <NUM>. For example, the BCU <NUM> controls various parameters of braking, such as manual brake control, automatic brake control, antiskid braking, locked wheel protection, touchdown protection, park capability, gear retraction braking, and the like. The BCU <NUM> may further include hardware <NUM> capable of performing various logic using discreet power signals received from various aircraft systems.

Referring again more particularly to <FIG>, the aircraft <NUM> further includes one or more brakes coupled to each wheel assembly. For example, a brake <NUM> is coupled to the outer wheel assembly <NUM> of the third landing gear <NUM> of the aircraft <NUM>. In operation, the brake <NUM> applies a braking force to the outer wheel assembly <NUM> upon receiving a brake command, such as from the BCU <NUM>. In various embodiments, the outer wheel assembly <NUM> of the third landing gear <NUM> of the aircraft <NUM> comprises any number of wheels.

Referring now also to <FIG>, including with continued reference to <FIG> and <FIG> as well, a braking system <NUM> is shown in accordance with an embodiment of the inventive arrangements. The braking system <NUM> includes the brake control unit (BCU) <NUM> of <FIG> and <FIG>, which is programmed to control the various braking functions described herein. In various embodiments, the braking system <NUM> enables the aircraft <NUM> to brake, thereby slowing aircraft <NUM> when on the ground. However, it will be appreciated that the braking system <NUM> may also be used in connection with other types of vehicles without departing from the scope of the inventive arrangements.

As described herein, the braking system generally includes, inter alia, a hydraulic power source <NUM> acting through i) a left wheel servo valve <NUM> to apply hydraulic pressure through a left hydraulic line <NUM> and shuttle valve <NUM> to apply a braking force to actuators <NUM> of a left wheel/brake assembly <NUM>; and ii) a right wheel servo valve 42r to apply hydraulic pressure through a right hydraulic line 44r and shuttle valve <NUM> to apply a braking force to actuators <NUM> of a right wheel/brake assembly 22r. First pressure sensors <NUM> may be intermediate, and in fluid communication with, the actuators <NUM> and shuttle valves <NUM> of the left wheel/brake assembly <NUM> and right wheel/brake assembly 22r.

In various embodiments, the shuttle valves <NUM>, first pressure sensors <NUM>, and actuators <NUM> may be common to both a primary braking system and a non-primary braking system of the braking system <NUM> of the aircraft <NUM>.

In various embodiments of the braking system, the BCU <NUM> receives brake command signals from a left pilot brake pedal <NUM> and a right pilot brake pedal 14r and/or a left co-pilot brake pedal <NUM> and a right co-pilot brake pedal 16r. The brake command signals from the left pilot brake pedal <NUM> and the right pilot brake pedal 14r and/or the left co-pilot brake pedal <NUM> and the right co-pilot brake pedal 16r are indicative of a desired amount of braking. In various embodiments, the left pilot brake pedal <NUM> may provide a brake command signal to the BCU <NUM> that is indicative of a degree of travel of the left pilot brake pedal <NUM>, and thus the amount of desired braking by the left wheel/brake assembly <NUM>. Similarly, the remaining right pilot brake pedal 14r, the left co-pilot brake pedal <NUM>, and the right co-pilot brake pedal 16r each provide a brake command signal to the BCU <NUM> that is indicative of a degree of travel of the right pilot brake pedal 14r, the left co-pilot brake pedal <NUM>, and the right co-pilot brake pedal 16r, respectively, and thus the amount of desired braking by the left wheel/brake assembly <NUM> or right wheel/brake assembly 22r. In various embodiments, each brake pedal may have a corresponding transducer respectively serving the BCU <NUM> to provide the brake command signal to the BCU <NUM>. However, any suitable brake pedal configuration is within the scope of the present invention.

In addition, the BCU <NUM> receives control signals from an auto-brake interface <NUM> for performing auto-brake and rejected take-off (RTO) braking functions. The BCU <NUM> also receives a series of discrete control signals associated with the aircraft <NUM>, such as engine parameters, aircraft temperatures, or aircraft pressures for example, generally represented as aircraft discretes <NUM>, for providing braking control thereof.

In various embodiments, the BCU <NUM> controls braking of the left wheel/brake assembly <NUM> and the right wheel/brake assembly 22r, as noted above. The left wheel/brake assembly <NUM> includes one or more wheels <NUM> and brake stacks <NUM>. A plurality of actuators <NUM> may be provided for exerting braking forces on the brake stacks <NUM> in order to brake the wheels <NUM>. The right wheel/brake assembly 22r has a similar, mirrored configuration. Both the left wheel/brake assembly <NUM> and the right wheel/brake assembly 22r also include, in various embodiments, wheel speed sensors <NUM> that provide wheel speed information to the BCU <NUM> for carrying out brake control operations.

In various embodiments of the braking system, a hydraulic power source <NUM> serves as a primary brake power supply within the braking system <NUM>. In various embodiments, a primary hydraulic line <NUM> from the hydraulic power source <NUM> includes a check valve <NUM> and an accumulator <NUM>. In various embodiments, the primary hydraulic line <NUM> is input into a brake control module (BCM) <NUM> included within the braking system <NUM>. The BCM <NUM> includes a shutoff valve <NUM> through which the primary hydraulic line <NUM> supplies hydraulic fluid to the left wheel servo valve <NUM> and the right wheel servo valve 42r. However, separate BCMs may be provided for individually supplying hydraulic fluid to the left wheel servo valve <NUM> and the right wheel servo valve 42r without departing from the scope of the present invention. In various embodiments, hydraulic fluid from the left wheel servo valve <NUM> and the right wheel servo valve 42r is respectively provided through a left hydraulic line <NUM> and a right hydraulic line 44r to apply the braking force to the wheels <NUM> during a braking operation.

During primary braking operations, hydraulic fluid pressure through the left hydraulic line <NUM> and the right hydraulic line 44r respectively passes to the corresponding actuators <NUM> via one or more of the corresponding shuttle valves <NUM>. Thus, if the braking system <NUM> is functioning in the primary braking mode, the shutoff valve <NUM> is open to the left hydraulic line <NUM> and the right hydraulic line 44r, and the BCU <NUM> controls the amount of hydraulic pressure that is delivered to the wheels <NUM> respectively via the left wheel servo valve <NUM> and the right wheel servo valve 42r acting through the corresponding left hydraulic line <NUM> and right hydraulic line 44r.

In various embodiments, the shutoff valve <NUM>, the left wheel servo valve <NUM>, and the right wheel servo valve 42r are coil valves. In various embodiments, the shutoff valve <NUM> receives a shutoff valve control signal on a bus <NUM> from the BCU <NUM>. Similarly, the left wheel servo valve <NUM> may receive a servo valve control signal on a bus <NUM> from the BCU <NUM>. Likewise, the right wheel servo valve 42r may receive a servo valve control signal on a bus <NUM> from the BCU <NUM>. The servo valve control signal may comprise an electric current signal. Stated differently, electric current supplied to left wheel servo valve <NUM> and/or right wheel servo valve 42r may be varied to adjust braking pressure applied at the brake stacks <NUM> via actuators <NUM>.

In various embodiments, the braking system <NUM> includes first pressure sensors <NUM> for monitoring the hydraulic pressure in the left hydraulic line <NUM> and the right hydraulic line 44r and providing such information back to the BCU <NUM>. In addition, power to the BCU <NUM> is provided from an aircraft power source <NUM>, such as a DC power source within the aircraft <NUM>. In various embodiments, power is transmitted from the aircraft power source <NUM> to the BCU <NUM>.

In various embodiments, the braking system <NUM> further includes an output device and/or output display <NUM> coupled to the BCU <NUM>. The output device and/or output display <NUM> is configured to communicate information to the pilot, co-pilot, and/or maintenance crew relating to the braking operations. For example, in various embodiments, the output device and/or output display <NUM> includes a display, a speaker, a network access device, and/or the like that sends a message to a remote terminal, or the like. In various embodiments, the BCU <NUM> controls the output device and/or output display <NUM> to output the health status of the braking system <NUM>, including the various components thereof.

In various embodiments, the braking system <NUM> may be activated by the left pilot brake pedal <NUM>, the right pilot brake pedal 14r, the left co-pilot brake pedal <NUM>, and the right co-pilot brake pedal 16r respectively acting through the shutoff valve <NUM>, the left wheel servo valve <NUM>, the right wheel servo valve 42r, the left hydraulic line <NUM>, and the right hydraulic line 44r.

The braking system <NUM> utilizes the shutoff valve <NUM> in-line with the left wheel servo valve <NUM> and the right wheel servo valve 42r to provide a level of redundancy that ensures a single valve failure cannot cause inadvertent braking. In order for the braking force to be applied by the braking system <NUM> to the left wheel/brake assembly <NUM> and the right wheel/brake assembly 22r, the shutoff valve <NUM> must be open along with at least one of the left wheel servo valve <NUM> and the right wheel servo valve 42r. To provide a redundancy so that the brakes can be operated when commanded, each of the valves (shutoff and servo) may contain dual control coils with one coil for different dedicated channels in the BCU <NUM>, in accordance with various embodiments.

Referring now to <FIG>, and also to <FIG>, an autobrake initialization system <NUM> for BCU <NUM> for controlling shutoff valve <NUM> is illustrated, in accordance with various embodiments. Autobrake initialization system <NUM> may include an AND gate <NUM> configured to receive a plurality of signals for indicating that an aircraft is in a desirable condition for braking. AND gate <NUM> may output a shutoff valve signal <NUM> in response to all of the signals being true (e.g., in response to receiving power from all of the signals) for opening shutoff valve <NUM>. AND gate <NUM> may receive a first autobrake signal <NUM>. First autobrake signal <NUM> may be sent in response to a signal from an operator of the aircraft (e.g., a pilot may actuate a switch in the cockpit) which indicates that autobraking is desired. AND gate <NUM> may receive a second autobrake signal <NUM>. Second autobrake signal <NUM> may be sent in response to a signal from an operator of the aircraft (e.g., a pilot may actuate a switch in the cockpit) which indicates that autobraking is desired. AND gate <NUM> may receive a left hand (LH) throttle signal <NUM>. LH throttle signal <NUM> may be sent in response to a throttle position of a left hand engine being set below a predetermined position (e.g., at idle). For example, AND gate <NUM> may receive LH throttle signal <NUM> from an avionics unit or other on-board controller which monitors the throttle position of the aircraft engines. AND gate <NUM> may receive a right hand (RH) throttle signal <NUM>. RH throttle signal <NUM> may be sent in response to a throttle position of a right hand engine being set below a predetermined position (e.g., at idle). AND gate <NUM> may receive a main landing gear (MLG) weight-on-wheel (WOW) signal <NUM>. MLG WOW signal <NUM> may be sent in response to an aircraft's main landing gear touching down onto a ground surface. In various embodiments, the MLG WOW signal <NUM> is sent in response to an aircraft's main landing gear touching down onto a ground surface for a predetermined amount of time, to ensure that the main landing gear is not bouncing on the ground surface during braking for example. AND gate <NUM> may receive MLG WOW signal <NUM> from an avionics unit or other on-board controller which monitors the landing gear position (e.g., whether the shock strut is compressed) and/or which monitors the rotational velocity of the aircraft wheels. For example, a compressed shock strut may indicate that the main landing gear has touched the ground surface and is partially supporting the aircraft. Furthermore, a rotational velocity of a wheel may indicate that the wheel is rotating against the ground surface. However, any system and/or method of determining that a main landing gear is under a WOW condition is within the scope of the present invention.

AND gate <NUM> may output shutoff valve signal <NUM> in response to all of the signals being true (e.g., in response to the autobrake signal <NUM> indicating that the autobrake system is powered on, in response to LH throttle signal <NUM> indicating that the LH engine is at or below a predetermined throttle position, in response to RH throttle signal <NUM> indicating that the RH engine is at or below a predetermined throttle position, and in response to the MLG WOW signal <NUM> indicating that the main landing gear is under a WOW condition for opening shutoff valve <NUM>. In this manner, the aircraft brake system may be operated only under conditions where the landing gear has contacted the ground surface, the aircraft is not moving, and braking has been commanded. Although illustrated as operating through an autobrake enable logic, servo valve calibration systems and methods may be operated through other logics to determine whether the aircraft is under a WOW condition and not moving relative to a ground surface (i.e., the wheels are not spinning), without departing from the scope of the present invention.

In various embodiments, autobrake initialization system <NUM> may further include an OR gate <NUM> configured to receive SOV control signals from various systems. For example, OR gate <NUM> may receive a control signal from the autobrake system (e.g., shutoff valve signal <NUM>), a gear retract braking control signal (e.g., to apply braking during gear retracting), and a manual braking control signal (e.g., for a pilot to manually apply braking from the cockpit). The OR gate <NUM> may supply a shutoff valve control signal, e.g., via bus <NUM>, in response to receiving a control signal from any one of the autobrake, gear retract, or manual braking systems. In this manner, hydraulic pressure may be supplied to the braking system in response to any of these various braking systems being operated.

In various embodiments, AND gate <NUM> may comprise a hardware component. AND gate <NUM> may comprise one or more field-effect transistors (FETs) electronically coupled together in a known manner. AND gate <NUM> may provide a HIGH output (<NUM>) only if all the inputs to the AND gate <NUM> are HIGH (<NUM>). If none or not all inputs to the AND gate are HIGH, a LOW (<NUM>) output may result. In this regard, each signal <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be received by the AND gate via a plurality of electrical wires or other conductive material. Stated differently, a conductive material may be used to electronically couple AND gate <NUM> to the respective electronic components whereby the signals <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are received. However, AND gate <NUM> may be implemented in software without departing from the scope of the present invention.

In various embodiments, OR gate <NUM> may comprise a hardware component. OR gate <NUM> may comprise one or more FETs electronically coupled together in a known manner. In this regard, AND gate <NUM> may be electronically coupled to OR gate <NUM> via one or more wires or other conductive material. However, OR gate <NUM> may be implemented in software without departing from the scope of the present invention.

Referring now to <FIG>, a method of operating a brake control unit including a servo valve calibration process is provided. More specifically, the method begins in a step <NUM>, after which it is determined whether an aircraft is on the ground and not moving (i.e., the wheels are not spinning) at a step <NUM>. If the aircraft is not detected to be both on the ground and not moving at step <NUM>, then the method continues by monitoring whether the aircraft is on the ground and not moving. If the aircraft is detected to be both on the ground and not moving (e.g., at a gate of an airport or other location) at step <NUM>, then the method continues by determining if braking is being applied at step <NUM>. If braking is not presently being applied, then the method proceeds by performing a servo valve calibration at step <NUM>. After the calibration is complete, the method of <FIG> ends at step <NUM>.

Referring now to <FIG>, <FIG>, and <FIG>, step <NUM> may include activating a servo valve calibration process. In various embodiments, the servo valve calibration process may be activated by a pilot, for example by actuating a switch, lever, button, or the like in the cockpit of the aircraft. AND gate <NUM> may receive first autobrake signal <NUM> (e.g., a first electric power signal) and second autobrake signal <NUM> (e.g., a second electric power signal) in response to a pilot activating the autobrake system. In various embodiments, the servo valve calibration process may be activated automatically, for example upon power up of the brake control unit <NUM>. Step <NUM> may include determining, by the brake control unit <NUM>, if the aircraft is on the ground and not moving. Step <NUM> may include determining, by the brake control unit <NUM>, if MLG WOW signal <NUM> is TRUE for a predetermined duration, such as one second for example. The predetermined duration may be any suitable duration for indicating that the landing gear is under a WOW condition and not bouncing. Step <NUM> may include determining, by the brake control unit <NUM>, that the LH throttle signal <NUM> and the RH throttle signal <NUM> are both TRUE (i.e., that the engine throttle is below a predetermined threshold (e.g., at idle).

In response to the brake control unit <NUM> determining that the aircraft is on the ground and not moving, the servo valve calibration process may proceed to step <NUM>. Step <NUM> may include determining, by the brake control unit <NUM>, whether braking is being applied to the brake system of the aircraft. Braking may be detected based upon a pressure feedback signal of the braking system. Any suitable method for detecting whether braking is being applied is within the scope of the present invention.

In response to the brake control unit <NUM> determining that braking is not being applied to the aircraft, the servo valve calibration process may proceed to step <NUM>. Step <NUM> may include performing, by the brake control unit <NUM>, a servo valve calibration process. Said servo valve calibration process includes sending two or more current commands to each servo valve, and measuring the associated braking pressures as a result of these current commands, as described below in further detail, with reference to <FIG>. After the servo valve calibration process is complete, the method ends at step <NUM>.

Over its service life, a servo valves may experience performance degradation in pressure gain characteristics due to wear and tear. Particles in the brake fluid may cause silt inside the sleeve/spool assembly and degrade servo valve performance. This servo valve degradation can cause a change in static and dynamic characteristics of the servo valve which alters the performance of the servo valve, including undesired oscillations as a results of the coupling of the closed-loop controls characteristics and servo valve dynamics.

With reference to <FIG>, various braking pressure versus servo valve current curves are illustrated, in accordance with various embodiments. Pressure gain can vary over the life of a servo valve. For example, while a servo valve may be expected or manufactured to operate at an expected or nominal pressure gain, illustrated by curve <NUM>, actual pressure gains may vary, for example between a first actual pressure gain, illustrated by curve <NUM>, and a second actual pressure gain, illustrated by curve <NUM>. Pressure gain, as used herein, may refer to the change in pressure per unit amperage (e.g., psi/mA). Stated differently, the pressure gain may be equal to the slope of the braking pressure versus servo valve current curve. In various embodiments, nominal curve <NUM> may comprise a first pressure gain (e.g., <NUM> psi/mA). In various embodiments, curve <NUM> may comprise a second pressure gain (e.g., <NUM> psi/mA). In various embodiments, curve <NUM> may comprise a third pressure gain (e.g., <NUM> psi/mA). In this regard, actual pressure gain of a servo valve may vary over its life (e.g., between curve <NUM> and curve <NUM>). Furthermore, a servo valve may comprise a dead band. As used herein, dead band may refer to a minimum amount of electric current that the servo valve can receive, before activating. For example, nominal curve <NUM> may comprise a first dead band <NUM> (e.g., <NUM> mA), curve <NUM> may comprise a second dead band <NUM> (e.g., <NUM> mA), and curve <NUM> may comprise a third dead band <NUM> (e.g., <NUM> mA). The dead band of a servo valve may vary due to manufacturing tolerances and may further change over the life of the servo valve.

Having introduced the braking pressure versus servo valve current curve, the servo valve calibration process is now explained in further detail. With combined reference to <FIG> and <FIG>, the brake control unit <NUM> may first apply the autobrake command (e.g., shutoff valve signal <NUM> with momentary reference to <FIG>) to request the shutoff valve <NUM> to open and provide pressure to the servo valves <NUM>, 42r. For a servo valve with a typical current range of 20mA (e.g., 5mA to 25mA), the brake control unit <NUM> will command two or more intermediate current values to the servo valve. For example, 12mA and 24mA. However, these intermediate current values are provided for exemplary purposes only and the intermediate current values may vary depending on the servo valve being calibrated as well as other factors. In response to the current command being reached, the brake control unit <NUM> may detect the associated brake pressure value via pressure sensor <NUM>-e.g., from a brake pressure transducer. The associated brake pressure value may be detected for a predetermined dwell time, such as three seconds for example, in accordance with various embodiments. While acquiring the brake pressure, the signal may be low pass filtered digitally by the brake control unit <NUM> to determine an average pressure reached during the current command. This process may be repeated any desired number of time (e.g., a first time and a second time) for each servo valve to calculate commanded pressure values associated with the commanded currents, respectively. For example, if the nominal dead band is 5mA and the pressure gain is 150psi/mA, then a current of 12mA would lead to a pressure of 1050psi (= (<NUM>-<NUM>)*<NUM>). If on the other hand, the dead band had shifted to <NUM>. 5mA and the gain changed to 140psi/mA, the brake pressure will be: 770psi (= (<NUM>-<NUM>)*<NUM>). After the dwell time, a second current may be commanded, and the filtered pressure read from the brake pressure transducer provides the second calibration point (i<NUM>, P<NUM>). Having the two points (i<NUM>, P<NUM>) and (i<NUM>, P<NUM>), and relying on the servo valve response as being linear, the transfer function sought for servo valve current versus brake pressure can be established: <MAT> where: <MAT>.

In addition to, or in place of, calculating a transfer function, systems of the present invention may include calculating, by the brake control unit <NUM>, a braking pressure versus servo valve current curve and storing said curve in memory, wherein the curve is called upon during braking to determine a current command associated with a desired pressure. In various embodiments, the curve is stored in memory as a lookup table or the like.

With the servo valve calibration complete, the transfer function (see at Eq. <NUM>) for the servo valve is provided such that precise electric currents are calculated for desired braking pressures commanded via the servo valve. In this regard, with the servo valve freshly calibrated, braking may be commanded in an open-loop system which may eliminate pressure oscillations associated with typical closed-loop pressure control feedback systems.

With reference to <FIG>, a brake pressure command architecture <NUM> is illustrated, in accordance with various embodiments. Various logic in brake pressure command architecture <NUM> may be performed by brake control unit <NUM> (see <FIG>). In response to the servo valve calibration being successful, a pressure control <NUM> is bypassed and a current calculated using the calibrated transfer function is used to command the servo valve <NUM> for applying braking during a braking maneuver of the aircraft in an open-loop fashion. In response to the servo valve calibration being unsuccessful, the pressure control <NUM> is utilized and outputs the current to the servo valve <NUM> for applying braking during a braking maneuver of the aircraft in a closed-loop fashion (e.g., utilizing feedback from a pressure transducer).

With reference to <FIG>, a brake pressure command architecture <NUM> with antiskid control is illustrated, in accordance with various embodiments. In response to the servo valve calibration being successful, the pressure control <NUM> is bypassed and a current calculated using the calibrated transfer function is sent to a brake control executive <NUM>. The brake control executive <NUM> may further receive an antiskid current command from an antiskid control <NUM>. The brake control executive <NUM> may be configured to send the current command having the lowest value current command (chosen from either the current calculated using the calibrated transfer function or the antiskid current command) to the servo valve <NUM> for applying braking during a braking maneuver of the aircraft. In response to the servo valve calibration being unsuccessful, the pressure control <NUM> is utilized and outputs the current to the brake control executive <NUM>. Again, the brake control executive <NUM> may be configured to send the current command having the lowest value current command (chosen from either the pressure control current command or the antiskid current command) to the servo valve <NUM> for applying braking during a braking maneuver of the aircraft.

With reference to <FIG>, a brake pressure command architecture <NUM> with antiskid control is illustrated, in accordance with various embodiments. Brake pressure command architecture <NUM> may be similar to architecture <NUM>, except that the pressure control <NUM> may be moved behind (downstream) from the brake control executive <NUM>. In response to the servo valve calibration being successful, the pressure control <NUM> is bypassed and a pressure command (e.g., brake pedal command or autobrake command) is sent to a brake control executive <NUM>. The brake control executive <NUM> may further receive an antiskid pressure command from antiskid control <NUM>. The brake control executive <NUM> may be configured to output the lowest of these two pressure commands for calculating a current using the calibrated transfer function, which may be then sent to the servo valve <NUM> for applying braking during a braking maneuver of the aircraft. In response to the servo valve calibration being unsuccessful, the pressure control <NUM> is utilized and a pressure command (e.g., brake pedal command or autobrake command) is sent to the brake control executive <NUM>. The brake control executive <NUM> may further receive an antiskid pressure command from antiskid control <NUM>. The brake control executive <NUM> may be configured to output the lowest of these two pressure commands to the pressure control <NUM>. The pressure control <NUM> then sends a current command to the servo valve for applying braking during a braking maneuver of the aircraft using pressure transducer feedback signals.

With reference to <FIG>, a brake pressure command architecture <NUM> is illustrated, in accordance with various embodiments. Brake pressure command architecture <NUM> may be similar to architecture <NUM>, except that an antiskid control <NUM> and brake control executive <NUM> is added in front (upstream) of the decision block for determining whether the servo valve calibration was successful. Stated differently, the decision block for determining whether the servo valve calibration was successful may receive a pressure command from the brake control executive <NUM>. The brake control executive <NUM> may receive a pressure command (e.g., brake pedal command or autobrake command)-e.g., from a cockpit of an aircraft. The brake control executive <NUM> may further receive an antiskid pressure command from antiskid control <NUM>. The brake control executive <NUM> may be configured to output the lowest of these two pressure commands. In response to the servo valve calibration being successful, the pressure control <NUM> is bypassed and a current calculated using the pressure command and the calibrated transfer function is used to command the servo valve <NUM> for applying braking during a braking maneuver of the aircraft in an open-loop fashion. In response to the servo valve calibration being unsuccessful, the pressure control <NUM> is utilized and outputs the current to the servo valve <NUM> for applying braking during a braking maneuver of the aircraft in a closed-loop fashion.

However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the invention.

The scope of the invention is accordingly to be defined by the claims.

Claim 1:
A brake control system, comprising:
a servo valve (<NUM>, 42r) configured to receive a hydraulic fluid and provide the hydraulic fluid to apply braking force to a wheel via a hydraulic line; and
a brake control unit (<NUM>) in electronic communication with the servo valve;
characterised in that the brake control unit is configured to:
calibrate the servo valve;
determine whether a calibration of the servo valve was successful;
in response to the calibration of the servo valve being successful, operate the servo valve in an open-loop system; and
in response to the calibration of the servo valve being unsuccessful, operate the servo valve in a closed-loop system.