Patent Description:
Aircraft typically utilize brake systems on wheels to slow or stop the aircraft during landings, taxiing and emergency situations, such as, for example, a rejected take off (RTO). The brake systems generally employ a heat sink comprising a series of friction disks, disposed between a pressure plate and an end plate, that may be forced into sliding contact with one another during a brake application to slow or stop the aircraft.

A typical hydraulic brake system may include, without limitation, a source of pressurized hydraulic fluid, a hydraulic actuator for exerting a force across the heat sink (e.g., across the pressure plate, the series of friction disks and the end plate), a valve for controlling a pressure level provided to the hydraulic actuator and a brake control unit for receiving inputs from a pilot and from various feedback mechanisms and for producing responsive outputs to the valve. Upon activation of the brake system (e.g., by depressing a brake pedal), a pressurized fluid is applied to the hydraulic actuator, which may comprise a piston configured to translate the pressure plate toward the end plate. A typical electric brake system includes various electromechanical counterparts to a hydraulic brake system, such as, for example, an electromechanical brake actuator (EBA) in place of the hydraulic actuator and a source of electric power in place of the source of pressurized hydraulic fluid. Load cells used in EBAs can be prone to drift over time due to various external factors such as vibration for example. <CIT> relates to a braking system.

The invention concerns a braking system for an aircraft comprising: a brake assembly; a hydraulic braking subsystem having a hydraulic brake actuator configured to operate the brake assembly; an electric braking subsystem having an electric brake actuator configured to operate the brake assembly and a load cell configured to measure a force supplied by the electric brake actuator; a hydraulic brake control unit configured to control the hydraulic braking subsystem; and an electric brake control unit configured to control the electric braking subsystem, the electric brake control unit in operable communication with the hydraulic brake control unit, the electric brake control unit configured to calibrate the load cell by a scale factor based on a measured force from the load cell, a measured hydraulic pressure used to exceed the measured force received from the hydraulic brake control unit, and a piston area of the hydraulic brake actuator.

In a preferred embodiment, the electric brake control unit is further configured to store any scale factors that exceed a scale factor threshold as the scale factor threshold. The electric brake control unit may be further configured to count a number of times the scale factor threshold is applied to a force measurement of the load cell. The electric brake control unit may be further configured to generate a notification in response to the number of times exceeding a count threshold.

In a preferred embodiment, the electric brake control unit is further configured to command the electric brake actuator to supply a first force to a brake stack of the brake assembly; and the hydraulic brake control unit is further configured to command the hydraulic braking subsystem to increase a supplied pressure to the brake stack via the hydraulic brake actuator at a predetermined rate to determine the hydraulic pressure used to exceed the measured force.

In a preferred embodiment, the electric brake control unit is further configured to determine the hydraulic pressure from used to exceed the measured force based on the measured force dropping from an initial measured force and pressure data received from the hydraulic brake control unit.

In a preferred embodiment, the electric brake control unit is further configured to determine a set of scale factors including the scale factor, each scale factor in the set of scale factors associated with a commanded force for the electric brake actuator. A scale factor may be interpolated in response to a second commanded force being between a first commanded force having a first scale factor and the second commanded force having a second scale factor. The electric brake control unit may be further configured to monitor a health of the load cell.

In a preferred embodiment, the electric brake control unit is configured to calibrate the load cell at a predetermined time interval.

A further aspect of the invention concerns an article of manufacture comprising the braking system for an aircraft of the previous aspect and including a tangible, non-transitory computer-readable storage medium having instructions stored thereon that, in response to execution by a processor, cause the processor to perform operations comprising: commanding, via the processor, an electric brake actuator of an electric braking subsystem of a braking system to supply a first force to a brake stack in the braking system; receiving, via the processor and from a hydraulic brake control unit, a pressure data corresponding to a supplied pressure to the brake stack via a hydraulic brake actuator at a predetermined rate; determining, via the processor and based on the pressure data, a pressure that causes a force measurement of a load cell of the electric braking subsystem of the braking system to drop; and calibrating, via the processor, the load cell based on the pressure, the force measurement, and a piston contact area of the electric brake actuator.

In a preferred embodiment, the operations further comprise calculating a force based on the pressure and the piston contact area prior to calibrating.

In a preferred embodiment, calibrating the load cell comprises determining a scale factor for force measurement of the load cell that correlated with a commanded force of the electric brake actuator. The operations may further comprise determining a set of scale factors, each scale factor in the set of scale factors associated with the commanded force of the electric brake actuator. The set of scale factors may be associated with a ratio of the commanded force to a max rated force within a range of ratios. The range of ratios may be between <NUM>% and <NUM>% of the max rated force for the electric brake actuator.

An article of manufacture is disclosed herein as an example not part of the invention. The article of manufacture may include a tangible, non-transitory computer-readable storage medium having instructions stored thereon that, in response to execution by a processor, cause the processor to perform operations comprising: determining, via the processor, a set of scale factors for a load cell of an electric braking subsystem of a braking system, each scale factor in the set of scale factors associated with a commanded force of an electric brake actuator; storing any scale factors that exceed a scale factor threshold as being the scale factor threshold; counting a number of times the load cell is scaled using the scale factor threshold as the scale factor; and generating a notification in response to the number of times exceeding a count threshold.

In various examples, the operations further comprise recalibrating, via the processor, the load cell of the electric braking subsystem. The operations may further comprise re-setting, via the processor, the counting to zero in response to the scale factor that exceeded the scale factor threshold dropping below the scale factor threshold.

In various examples, determining the set of scale factors comprises calculating a scale factor for a measured force of the load cell at the commanded force of the electric brake actuator to a brake stack based on a supplied hydraulic pressure that forces a hydraulic brake actuator to reduce the measured force on the brake stack.

The subject matter of the present invention pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present invention, however, may best be obtained by referring to the following detailed description and claims in connection with the following drawings.

While these various 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 changes may be made without departing from the scope of the invention.

Referring now to <FIG>, an aircraft <NUM> includes multiple landing gear systems, including a first landing gear <NUM> (or a port-side landing gear), a second landing gear <NUM> (or a nose landing gear) and a third landing gear <NUM> (or a starboard-side landing gear). The first landing gear <NUM>, the second landing gear <NUM> and the 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>, the second landing gear <NUM> and the third landing gear <NUM> support the aircraft <NUM> when the aircraft <NUM> is not flying, thereby enabling the aircraft <NUM> to take off, land and taxi without incurring damage. In various embodiments, one or more of the first landing gear <NUM>, the second landing gear <NUM> and the third landing gear <NUM> is operationally retractable into the aircraft <NUM> while the aircraft <NUM> is in flight.

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 component, or any of various combinations thereof or the like. In various embodiments, the avionics unit <NUM> controls 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, brake systems and the like.

In various embodiments, the aircraft <NUM> further includes brake control units (BCUs) <NUM> (e.g., hydraulic brake control unit <NUM> and electric brake control unit <NUM> as described further herein). With brief reference now to <FIG>, the BCUs <NUM> include one or more controllers <NUM> (e.g., processors) and one or more memories <NUM> (e.g., tangible, non-transitory memories) capable of implementing digital or programable logic. In various embodiments, for example, the one or more controllers <NUM> is one or more of a general purpose processor, DSP, ASIC, FPGA, or other programmable logic device, discrete gate, transistor logic, or discrete hardware component, or any of various combinations thereof or the like, and the one or more memories <NUM> is configured to store instructions that are implemented by the one or more controllers <NUM> for performing various functions, such as adjusting the hydraulic pressure or electric power provided to a brake actuator depending on the degree of braking desired. In various embodiments, the BCUs <NUM> control the braking of the aircraft <NUM>. For example, the BCUs <NUM> control various parameters of braking, such as manual brake control, automatic brake control, antiskid braking, locked wheel protection, touchdown protection, emergency/parking brake monitoring or gear retraction braking. The BCUs <NUM> may further include hardware <NUM> capable of performing various logic using discrete power signals received from various aircraft systems. Referring again to <FIG>, the aircraft <NUM> further includes one or more brake assemblies coupled to each wheel assembly. For example, a brake assembly <NUM> is coupled to the outer wheel assembly <NUM> of the third landing gear <NUM> of the aircraft <NUM>. During operation, the brake assembly <NUM> applies a braking force to the outer wheel assembly <NUM> upon receiving a brake command from the BCUs <NUM>. In various embodiments, the outer wheel assembly <NUM> of the third landing gear <NUM> of the aircraft <NUM> (or of any of the other landing gear described above and herein) comprises any number of wheels or brake assemblies.

Referring now to <FIG>, schematic details of the brake assembly <NUM> illustrated in <FIG> are provided. In various embodiments, the brake assembly <NUM> is mounted on an axle <NUM> for use with a wheel <NUM> disposed on and configured to rotate about the axle <NUM> via one or more bearing assemblies <NUM>. A central axis <NUM> extends through the axle <NUM> and defines a center of rotation of the wheel <NUM>. A torque plate barrel <NUM> (sometimes referred to as a torque tube or barrel or a torque plate) is aligned concentrically with the central axis <NUM>, and the wheel <NUM> is rotatable relative to the torque plate barrel <NUM>. The brake assembly <NUM> includes an actuator ram assembly <NUM>, a pressure plate <NUM> disposed adjacent the actuator ram assembly <NUM>, an end plate <NUM> positioned a distal location from the actuator ram assembly <NUM>, and a plurality of rotor disks <NUM> interleaved with a plurality of stator disks <NUM> positioned intermediate the pressure plate <NUM> and the end plate <NUM>. The pressure plate <NUM>, the plurality of rotor disks <NUM>, the plurality of stator disks <NUM> and the end plate <NUM> together form a brake heat sink or brake stack <NUM>. The pressure plate <NUM>, the end plate <NUM> and the plurality of stator disks <NUM> are mounted to the torque plate barrel <NUM> and remain rotationally stationary relative to the axle <NUM>. The plurality of rotor disks <NUM> is mounted to the wheel <NUM> and rotate with respect to each of the pressure plate <NUM>, the end plate <NUM> and the plurality of stator disks <NUM>.

An actuating mechanism for the brake assembly <NUM> includes a plurality of actuator ram assemblies, including the actuator ram assembly <NUM>, circumferentially spaced around a piston housing <NUM> (only one actuator ram assembly is illustrated in <FIG>). Upon actuation, the plurality of actuator ram assemblies affects a braking action by urging the pressure plate <NUM> and the plurality of stator disks <NUM> into frictional engagement with the plurality of rotor disks <NUM> and against the end plate <NUM>. Through compression of the plurality of rotor disks <NUM> and the plurality of stator disks <NUM> between the pressure plate <NUM> and the end plate <NUM>, the resulting frictional contact slows or stops or otherwise prevents rotation of the wheel <NUM>. In various embodiments, the plurality of rotor disks <NUM> and the plurality of stator disks <NUM> are fabricated from various materials, such as, for example, ceramic matrix composite materials, that enable the brake disks to withstand and dissipate the heat generated during and following a braking action. As discussed in further detail below, in various embodiments, the actuator ram assemblies comprise a combination of electrically operated actuator rams (or electric brake actuators) and hydraulically operated (or pneumatically operated) actuator rams (or hydraulic brake actuators or pneumatic brake actuators).

Referring now to <FIG>, a braking system <NUM> (or a redundant braking system or a hybrid braking system) is illustrated, in accordance with various embodiments. Generally, the braking system <NUM> may be separated into a hydraulic braking subsystem <NUM> and an electric braking subsystem <NUM>. Referring first to the hydraulic braking subsystem <NUM>, the braking system <NUM> includes a hydraulic brake control unit <NUM>, which is programmed to control the various braking functions performed by the hydraulic braking subsystem <NUM>. The hydraulic braking subsystem <NUM> includes a hydraulic power source <NUM> configured to provide a hydraulic fluid to a primary brake control module <NUM> via a primary hydraulic line <NUM>. A primary pressure transducer <NUM> senses the pressure of the hydraulic fluid and provides a signal reflective of the pressure to the hydraulic brake control unit <NUM> via a data circuit <NUM>. In various embodiments, the hydraulic braking subsystem <NUM> includes a hydraulic fluid return <NUM> that is configured to return hydraulic fluid from the primary brake control module <NUM> to the hydraulic power source <NUM> via a return hydraulic line <NUM>. In various embodiments, the hydraulic power source <NUM> comprises a valve (e.g., a solenoid valve) configured to control a hydraulic pressure supplied to the hydraulic brake actuator <NUM>, in accordance with various embodiments.

A secondary hydraulic line <NUM> fluidly couples the primary brake control module <NUM> to a brake assembly <NUM>, similar to the brake assembly <NUM> described above with reference to <FIG>. More particularly, the secondary hydraulic line <NUM> is fluidly coupled to a hydraulic brake actuator <NUM> (or a plurality of hydraulic brake actuators) housed within the brake assembly <NUM>. In various embodiments, a fuse <NUM> is fluidly coupled to the secondary hydraulic line <NUM> downstream of the primary brake control module <NUM>. The fuse <NUM> acts as a shut-off valve or switch in the event the secondary hydraulic line <NUM> experiences a loss of pressure - e.g., in the event of a leak in the secondary hydraulic line <NUM> or the brake assembly <NUM> - thereby preventing hydraulic fluid from continuing to flow to the secondary hydraulic line <NUM> and leaking out of the hydraulic system. A secondary pressure transducer <NUM> is fluidly coupled to the secondary hydraulic line <NUM> and electrically coupled to the hydraulic brake control unit <NUM> via the data circuit <NUM>. In the event the secondary pressure transducer <NUM> senses a loss of pressure within the secondary hydraulic line <NUM>, the hydraulic brake control unit <NUM> may, in redundant fashion, pass control of the braking system <NUM> to the electric braking subsystem <NUM>. As illustrated, the secondary hydraulic line <NUM>, the fuse <NUM>, the secondary pressure transducer <NUM> and the brake assembly <NUM> are replicated for each of a plurality of outer wheel assemblies <NUM> and for each of a plurality of inner wheel assemblies <NUM> comprised within the braking system <NUM>. Without loss of generality, in various embodiments, the hydraulic braking subsystem <NUM> also includes wheel speed transducers and brake temperature sensors, such as, for example, an inboard wheel speed transducer <NUM> and an outboard wheel speed transducer <NUM>, and an inboard brake temperature sensor <NUM> and an outboard brake temperature sensor <NUM>.

Referring now to the electric braking subsystem <NUM>, the braking system <NUM> includes an electric brake control unit <NUM>, which is programmed to control the various braking functions performed by the electric braking subsystem <NUM>. The electric braking subsystem <NUM> includes an electric power source <NUM> configured to provide electric power to an electric brake actuator controller <NUM>, which, for example, may be an inboard electric brake actuator controller or an outboard electric brake actuator controller. The electric power is provided to the electric brake actuator controller <NUM> via an electric power circuit <NUM>. The electric brake actuator controller <NUM> is electrically coupled to an electric brake actuator <NUM> (or a plurality of electric brake actuators) that is housed within the brake assembly <NUM>. In various embodiments, the electric brake control unit <NUM> provides force commands to the electric brake actuator controller <NUM>, which in turn provides a current command to the electric brake actuator <NUM> to apply force, directing the electric brake actuator <NUM> to cause the brake assembly <NUM> to mechanically operate, thereby driving the brake assembly <NUM> to provide braking power. In various embodiments, the electric brake actuator controller <NUM> monitors the load cell <NUM> (e.g., via the control circuitry <NUM>) to apply more or less current to achieve a desired force. In various embodiments, the electric brake actuator controller <NUM> is coupled to the electric brake control unit <NUM> via a communication link <NUM>. The communication link <NUM> may comprise, for example, a controller area network bus <NUM>. Similar to the hydraulic braking subsystem <NUM>, and without loss of generality, the electric braking subsystem <NUM> also includes wheel speed transducers, such as, for example, an inboard wheel speed transducer <NUM> and an outboard wheel speed transducer <NUM>, or brake temperature sensors.

In various embodiments, the electric brake actuator controller <NUM> is coupled to the electric brake control unit <NUM> via a communication link <NUM>. The communication link <NUM> may comprise, for example, a controller area network bus <NUM>. Similar to the hydraulic braking subsystem <NUM>, and without loss of generality, the electric braking subsystem <NUM> also includes wheel speed transducers, such as, for example, an inboard wheel speed transducer <NUM> and an outboard wheel speed transducer <NUM>, or brake temperature sensors.

In various embodiments, the load cell <NUM> for each electric brake actuator <NUM> in the electric braking subsystem <NUM> may be prone to drift over time (i.e., when a measured force by the load cell <NUM> fluctuates, leading to inaccurate measurements). In this regard, calibrating the load cell <NUM> may provide a manner of monitoring a load cell health, determining a servicing time for the load cell <NUM>, or the like. In various embodiments, the hydraulic braking subsystem <NUM> may facilitate calibration of the load cell <NUM> as described further herein.

In various embodiments the load cell <NUM> for each electric brake actuator <NUM> in the electric braking subsystem <NUM> measures a force applied to the brake stack <NUM> from <FIG> at the electric brake actuator <NUM> location. In various embodiments, the load cell <NUM> may be calibrated based on comparing the force measured to a hydraulic pressure as described further herein.

Referring now to <FIG>, the brake assembly <NUM> is described with further detail. As illustrated, the brake assembly <NUM> includes a pressure plate <NUM> configured to apply a compressive load against a brake stack or heat sink, which includes a plurality of brake rotors and a plurality of brake stators disposed between the pressure plate and an end plate. As described above, the brake assembly <NUM> includes the hydraulic brake actuator <NUM> (or a plurality of such hydraulic brake actuators) and the electric brake actuator <NUM> (or a plurality of such electric brake actuators). In various embodiments, the brake assembly <NUM> includes four electric brake actuators spaced at ninety degree (<NUM>°) intervals about the pressure plate <NUM> and four hydraulic brake actuators spaced at ninety degree (<NUM>°) intervals about the pressure plate <NUM>, with each electric brake actuator and each hydraulic brake actuator spaced at forty-five degree (<NUM>°) intervals. Fewer or greater numbers of actuators, both electric and hydraulic, are contemplated within the scope of the invention.

Referring back to <FIG>, during operation, a pilot or a co-pilot depresses a pilot brake pedal <NUM> or a co-pilot brake pedal <NUM>, each of which is connected to a hydraulic brake position sensor <NUM> and to an electric brake position sensor <NUM>. The hydraulic brake position sensor <NUM> generates a signal reflective of the pedal position that is transmitted to the hydraulic brake control unit <NUM> via a hydraulic brake sensor bus <NUM>. The hydraulic brake control unit <NUM>, if employed, then activates the hydraulic brake actuator <NUM> based on a current signal that is transmitted to the primary brake control module <NUM> via a primary brake control bus <NUM>. Similarly, the electric brake position sensor <NUM> generates a signal reflective of the pedal position that is transmitted to the electric brake control unit <NUM> via an electric brake sensor bus <NUM>. The electric brake control unit <NUM>, if employed, then activates the electric brake actuator <NUM> based on a force request that is transmitted to the electric brake actuator controller <NUM> via the communication link <NUM>. In various embodiments, an avionics system <NUM> is configured to employ one or both of the hydraulic braking subsystem <NUM> and the electric braking subsystem <NUM> via signals transmitted over a respective data bus <NUM>. In various embodiments, an autobrake selector <NUM> is configured to employ one or both of the hydraulic braking subsystem <NUM> and the electric braking subsystem <NUM> via signals transmitted over an autobrake data bus <NUM>.

The braking system <NUM> may operate in a fully hydraulic mode, employing only the hydraulic braking subsystem <NUM>, or in a fully electric mode, employing only the electric braking subsystem <NUM>. In addition, the invention contemplates, in various embodiments, the hydraulic braking subsystem <NUM> being employed as the principal braking system, while the electric braking subsystem <NUM> is employed as a backup braking system in the event a failure occurs with the hydraulic braking subsystem <NUM>. The invention also contemplates, in various embodiments, the electric braking subsystem <NUM> being employed as a parking brake when the aircraft is at rest. In various embodiments, the hydraulic brake control unit <NUM> and the electric brake control unit <NUM> are configured to communicate with one another via an intercommunication bus <NUM>. Such communication enables, for example, transfer of control from the hydraulic brake control unit <NUM> to the electric brake control unit <NUM> following a failure of the hydraulic braking subsystem <NUM>. For example, in the event the hydraulic brake control unit <NUM> detects a leak of hydraulic fluid within the hydraulic braking subsystem <NUM>, the hydraulic brake control unit <NUM> may communicate with the electric brake control unit <NUM> and transfer control of the braking system <NUM> to the electric brake control unit <NUM>. Similarly, in the event the electric brake control unit <NUM> detects a failure within the electric braking subsystem <NUM>, the electric brake control unit <NUM> may communicate with the hydraulic brake control unit <NUM> and transfer control of the braking system <NUM> to the hydraulic brake control unit <NUM>. In this regard, a primary braking system and a secondary braking system may be determined for each flight cycle as described further herein. Based on a failure to the primary braking system being detected, the BCUs <NUM> are configured to transfer control from the primary braking system to the secondary braking system.

The above invention provides for a hybrid braking architecture. In various embodiments, the architecture employs hydraulic power for normal braking and electric power for an alternate braking system or a parking brake system. The architecture provides a fully redundant braking system for normal pedal operated braking and for emergency braking. In various embodiments, the piston housing (e.g., the piston housing <NUM> referred to in <FIG>) is modified to accept four hydraulic actuators and four electric actuators, spaced equally and alternating between one hydraulic actuator and one electric actuator; though any number of actuators is contemplated by the invention. The equal spacing of forty-five degrees (<NUM>°) between alternating hydraulic and electric brake actuators allows for uniform force application on the brake stack when the hydraulic system is active or the electric system is active.

In various embodiments, the architecture is operated using pedals in the cockpit. This allows seamless activity and minimum pilot effort when, for example, the emergency system is engaged. The architecture is transparent for actuation (e.g., automated), although crew-alerting system (CAS) messages may be employed to inform the pilot that the emergency system (e.g., the electric braking subsystem) has become active. The hydraulic and electric brake control units are in constant communication using, for example, controller area network (CAN) communication links, such that when the primary brake control unit (either the hydraulic or the electric brake control unit) detects a loss of braking or other fault, the alternate brake control unit (either the hydraulic or the electric brake control unit) may take over control and operate the braking. In various embodiments, a switch may also be provided in the cockpit to allow the pilot to manually switch from the one braking subsystem to the other - e.g., the hydraulic subsystem to the electric sub system - depending on the failure and any other issues or faults occurring with the power supplies or other aircraft system degradations.

Referring now to <FIG>, a process <NUM> for calibrating a load cell <NUM> of an electric brake actuator <NUM> of the braking system <NUM> is illustrated, in accordance with various embodiments. The process <NUM> may be performed by the BCUs <NUM> (e.g., the electric brake control unit <NUM> and the hydraulic brake control unit <NUM>), in accordance with various embodiments.

The process <NUM> comprises determining aircraft conditions are acceptable for calibration (step <NUM>). For example, the BCUs <NUM> (e.g., the electric brake control unit <NUM> and the hydraulic brake control unit <NUM>) may determine that a parking brake is enabled, there are weight on wheels, and the BCUs <NUM> have just been powered on. In this regard, the BCUs <NUM> may determine that the aircraft conditions are acceptable for performing the calibration process <NUM>. The calibration process <NUM> may be performed at any predetermined interval (e.g., every <NUM> flight cycles, every <NUM> flight cycles, or the like). The present invention is not limited in this regard.

The process <NUM> further comprises commanding the electric brake actuator <NUM> to supply a first force to a brake stack <NUM> (step <NUM>). In various embodiment, the first force may be based on a percentage of a max rated force for the electric brake actuator (e.g., <NUM>%, <NUM>%, <NUM>%, etc.).

The process <NUM> further comprises receiving a force measurement from a load cell <NUM> in response to the first force being supplied to the brake stack <NUM> (step <NUM>). The first force may provide feedback to the electric brake control unit <NUM> that the first force is around the percentage of the max rated force the electric brake actuator <NUM> was commanded to supply.

The process <NUM> further comprises commanding a hydraulic brake actuator <NUM> to increase a supplied pressure to the brake stack at a predetermined rate (step <NUM>). In this regard, the hydraulic brake pressure supplied to the brake stack <NUM> may be steadily increased from zero at the predetermined rate (e.g., <NUM> psi / s (<NUM> kPa / s). Thus, the hydraulic brake actuator <NUM> may be supplying a pressure simultaneously with the electric brake actuator supplying the first force. In various embodiments, the hydraulic brake control unit <NUM> is configured to provide pressure data (e.g., received from primary pressure transducer <NUM>) to the electric brake control unit <NUM> during the process <NUM>.

The process <NUM> further comprises determining a pressure that causes the force measurement to drop (step <NUM>). Once the force measurement being received in step <NUM> begins to drop, the force supplied by the piston due to the hydraulic brake pressure of the hydraulic brake actuator <NUM> will have exceeded the first force supplied by the electric brake actuator <NUM>.

In this regard, based on the pressure determined from step <NUM> and contact area of a piston of the hydraulic brake actuator <NUM>, a force that caused the force measurement provided by the load cell to drop is calculated (step <NUM>). In this regard, the force supplied by the piston due to the hydraulic pressure of the hydraulic brake actuator may be compared to the force measurement from the load cell <NUM>.

Based on the force and the force measurement, the load cell <NUM> may be calibrated (step <NUM>). In various embodiments, steps <NUM> - <NUM> may be repeated for various first forces in step <NUM> (e.g., <NUM>% of max rated force, <NUM>% of max rated force, <NUM>% of max rated force, etc.).

In various embodiments, the calibration step (e.g., step <NUM>) may determine a scaling factor to be applied to force measurements of the load cell <NUM> based on the process <NUM>. For example, if the load cell measurement of the load cell <NUM> is within a predetermined tolerance (e.g., +/- <NUM> lbs (<NUM>)), the electric brake control unit <NUM> may determine that no scaling is to be performed for future force measurements of the load cell <NUM>. In various embodiments, if the load cell measurements of the load cell <NUM> are outside of the predetermined tolerance, the electric brake control unit <NUM> may calculate a scale factor that would scale the force measurement of the load cell <NUM> to the force calculated from step <NUM>. In various embodiments, the scale factor may be associated with a specific force (e.g., <NUM>% of a max rated force has a first scale factor, <NUM>% of max rated force has a second scale factor, etc.). In various embodiments, a single scale factor may be calculated based on averaging a calculated scale factor at various forces between <NUM>% and <NUM>% of a max rated force for the electric brake actuator <NUM>. The present invention is not limited in this regard. In various embodiments, when each rated force has an associated scale factor, the electric brake control unit <NUM> may interpolate a scale factor in response to receiving a force measurement between two force data points from process <NUM>, or use the closest scaling factor associated with the measure value from the load cell <NUM>.

In various embodiments, the electric brake control unit <NUM> may send the scale factor(s) to a database (e.g., memory <NUM>) to be used for all future force measurements by the load cell <NUM> until the process <NUM> is repeated.

Referring now to <FIG>, a process <NUM> for health management of a load cell <NUM> of an electric brake actuator <NUM> is illustrated, in accordance with various embodiments. The process <NUM> may be performed by the electric brake control unit <NUM>. The present invention is not limited in this regard.

The process <NUM> comprises determining a set of scale factors for a load cell <NUM> based on calibrating the load cell <NUM> (step <NUM>). In various embodiments, the set of scale factors may be determined by the process <NUM> from <FIG> as described previously herein.

The process <NUM> further comprises storing (e.g., in the memory <NUM> of the electric brake control unit <NUM>) any scale factors that exceed a scale factor threshold as the scale factor threshold (step <NUM>). For example, a scale factor threshold for each load cell <NUM> may be set, such as <NUM>%, <NUM>%, or the like. In this regard, any scale factor greater than the scale factor threshold (e.g., <NUM> for a <NUM>% threshold) would be reduced to the scale factor threshold (e.g., a measured scale factor of <NUM> would be reduced to <NUM> for storing in the memory <NUM> of the electric brake control unit <NUM> for a <NUM>% threshold), in accordance with various embodiments.

The process <NUM> further comprises counting a number of times the scale factor threshold is applied (step <NUM>). In this regard, every time a measurement of the load cell <NUM> is based on a reduced scaled factor determined from step <NUM>, the electric brake control unit <NUM> may add one to the number of times the scale factor threshold has been applied. In this regard, step <NUM> continues counting each time the reduced scale factor determined from step <NUM> is applied until a count threshold is exceed (e.g., as in step <NUM> as described further herein), or until the load cell <NUM> is recalibrated by process <NUM> and the scale factor no longer exceeds the scale factor threshold. In this regard, in response to the scale factor returning to acceptable ranges (e.g., below the scale factor threshold), the count may be reset, in accordance with various embodiments.

The process <NUM> further comprises generating a notification in response to the number of times the scale factor threshold is applied to the load cell measurement of the load cell <NUM> exceeds a count threshold (step <NUM>). In this regard, the electric brake control unit <NUM> may send a signal to a cockpit of the aircraft indicating the electric brake actuator <NUM> of the respective load cell <NUM> that the electric brake actuator <NUM> should be serviced.

The process <NUM> may further comprise servicing the electric brake actuator (step <NUM>).

In various embodiments, instead of counting a number of times a scale factor threshold is used instead of a calculated scale factor to determining servicing of the electric brake actuator <NUM>, a threshold scale factor rate of change, a threshold standard deviation for the scale factors, or the like may be utilized. In this regard, one skilled in the art may recognize various criteria that may be utilized to determine a load cell <NUM> should be replaced and be within the scope of this invention.

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 limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

In various embodiments, processes <NUM>, <NUM> provide load cell drift compensation and health monitoring for electric brake actuators for braking system <NUM>. In various embodiments, the processes <NUM>, <NUM> provide enhanced performance over time benefits, advanced notice for degraded load cells to be services, and/or provide greater scheduling capabilities for operators to perform maintenance / servicing of electric brake actuators.

After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the invention in alternative embodiments.

Numbers, percentages, or other values stated herein are intended to include that value, and also other values that are about or approximately equal to the stated value, as would be appreciated by one of ordinary skill in the art encompassed by various embodiments of the present invention. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable industrial process, and may include values that are within <NUM>%, within <NUM>%, within <NUM>%, within <NUM>%, or within <NUM>% of a stated value. Additionally, the terms "substantially," "about" or "approximately" as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the term "substantially," "about" or "approximately" may refer to an amount that is within <NUM>% of, within <NUM>% of, within <NUM>% of, within <NUM>% of, and within <NUM>% of a stated amount or value.

Claim 1:
A braking system (<NUM>) for an aircraft, comprising:
a brake assembly (<NUM>);
a hydraulic braking subsystem (<NUM>) having a hydraulic brake actuator (<NUM>) configured to operate the brake assembly;
an electric braking subsystem (<NUM>) having an electric brake actuator (<NUM>) configured to operate the brake assembly and a load cell (<NUM>) configured to measure a force supplied by the electric brake actuator;
a hydraulic brake control unit (<NUM>) configured to control the hydraulic braking subsystem; and characterised by
an electric brake control unit (<NUM>) configured to control the electric braking subsystem, the electric brake control unit being in operable communication with the hydraulic brake control unit, wherein the electric brake control unit is configured to calibrate the load cell by a scale factor based on a measured force from the load cell, a measured hydraulic pressure used to exceed the measured force received from the hydraulic brake control unit, and a piston area of the hydraulic brake actuator.