Patent Application
20110226569
The present invention generally relates to electric braking systems and more particularly pertains to systems for selectively inhibiting electric motor actuators for aircraft electric braking systems.
The use of electrically actuated brakes in aircraft and other vehicles is becoming increasingly common. Braking force is typically generated by the pressurization of piston actuators that are configured to compress a brake disk stack between a pressure plate and a backing plate to thereby cause the friction surfaces of adjacent disks to engage one another. Electrically actuated brakes typically apply such a clamping force to a brake pressure plate with electric motor-actuators (EMAs) instead of hydraulic pistons. This eliminates certain disadvantages associated with hydraulic brakes, such as hydraulic leaks, air entrainment in hydraulic fluid, loss of hydraulic fluid causing loss of multiple brakes, a potential for hydraulic fluid fires, and the like. Many of these electrically actuated brake systems employ multiple electric motor-actuators per brake, especially in larger vehicles, or in vehicles where redundancy is required to ensure that braking is not lost due to an electric motor-actuator failure, such as in aircraft braking systems, for example.
One disadvantage of electrically actuated braking systems is that the electric motor-actuators are relatively expensive compared to the cost of hydraulic braking systems. Particularly with aircraft braking systems that operate in a challenging environment with many wear cycles, such electrically actuated braking systems require periodic maintenance or overhaul to repair or refurbish worn parts, which increases the cost of the electrically actuated braking systems. In the case of aircraft braking systems, in which each brake may employ as many as four electric motor-actuators, and in which there may be as many as 4 to 20 brakes depending upon the size of the aircraft, the accumulated costs of utilizing such electric braking systems can be significant.
Braking systems are known that reduce the number of brake applications and hence the wear rate of carbon brakes by disabling one or more brakes during low energy, taxi brake applications. Another known system increases accuracy of clamping force of electric aircraft carbon brakes by providing a first pair of electric brake actuators with a range of low brake clamping force, to be engaged when a low brake clamping force is required, and a second pair of electric brake actuators with a range of high brake clamping force, to be engaged when a high brake clamping force is required.
However, there remains a need for a system and method for inhibiting selected electric brake actuators for braking system utilizing multiple electric brake actuators for operation of each brake, while retaining the capacity of each brake to achieve full commanded braking at all times. Since inhibiting selected electric brake actuators can change the braking “feel” compared to the braking “feel” of activation of all electric brake actuators when such electric brakes are applied, it would also be desirable to provide a system and method for inhibiting selected electric brake actuators that retains a normal braking “feel” when the selected electric brake actuators are inhibited. It would also be desirable to provide a system and method for inhibiting selected electric brake actuators that can discontinue inhibition of selected brake actuators if full commanded braking is required, or if a fault condition exists. The present invention meets these and other needs.
Briefly, and in general terms, the present invention provides for a system and a method for conditionally inhibiting selected ones of a plurality of electric motor-actuators associated with an aircraft wheel brake, in which the capacity for full commanded braking is retained at all times. Conditionally inhibiting electrically actuated brakes utilizing multiple electric motor-actuators per brake according to the present invention can safely and successfully reduce the wear, and hence the cost, of utilizing electric motor-actuators. Reliability of the electric motor-actuators can be improved because individual electric motor-actuators would be subjected to fewer actuation cycles over a given period of time. In addition, conditionally inhibiting electrically actuated brakes utilizing multiple electric motor-actuators per brake according to the present invention ensures that the pedal “feel” remains unchanged, as compared with activation of all electric motor-actuators during braking. This also ensures that the amount of braking effort done by the electric brakes remains constant so that that the electric brakes continue to apply the same amount of braking force and continue to absorb the same amount of braking energy, as compared with activation of all electric motor-actuators during braking. Advantageously, conditionally inhibiting electrically actuated brakes utilizing multiple electric motor-actuators per brake according to the present invention ensures that all the reduction in wear cycles is equally distributed among all the electric motor-actuators. In addition, the present invention permits operation of all electric motor-actuators on a brake, regardless of clamping force command, if a failure is detected that affects any of the electric motor-actuators on that brake. This ensures that maximum available braking capability is retained following any failure condition. Furthermore, by inhibiting selected ones of multiple electric motor-actuators of electric brakes, anti-skid brake control on slippery surfaces can be improved. On aircraft in which electrically actuated brakes are also used for parking, battery drain during parking can be reduced.
While electric motor-actuators of an electric braking system must have the capacity to apply full emergency brake clamping force, the clamping force required during typical braking operations is far less than that required for full emergency braking. Therefore the present invention provides for an inhibited braking mode in which the use of one or more of the available electric motor-actuators on a brake is inhibited during normal braking operations, and an emergency braking mode and a maximum available braking mode in which more or all of the electric motor-actuators are activated when greater clamping force is needed. The brake control system includes logic to determine when selected electric motor-actuators would be inhibited or not, primarily based upon the braking level commanded. If the command is for a braking level that can be accomplished with selected electric motor-actuators inhibited, then the control system would inhibit those electric motor-actuators. If the brake pedal command signal is for a braking force that is above a threshold predetermined braking force requiring more or all of the electric motor-actuators to be activated, then the control system commands more or all of the electric motor-actuators to be activated. Conditionally inhibiting the brakes as described would safely and successfully reduce the wear, and hence the cost, of the electric motor-actuators. It would also improve the reliability of the electric motor-actuators because they would be subjected to fewer actuation cycles over a given period of time.
Accordingly, the present invention provides for a system for controlling a plurality of electric motor-actuators associated with an aircraft wheel brake. The system includes a plurality of electric motor-actuators operatively connected to an aircraft wheel brake to actuate the aircraft wheel brake. The plurality of electric motor-actuators include first and second portions of the plurality of electric motor-actuators, and an electronic brake actuation controller operatively connected to the plurality of electric motor-actuators and is configured to control the operation of the first and second portions of the plurality of electric motor-actuators. A brake system control unit is connected to the electronic brake actuation controller and is configured to receive a brake pedal command for a commanded braking force, and to control the electronic brake actuation controller, such that one of the first and second portions of the plurality of electric motor-actuators is activated and the other of the first and second portions of the plurality of electric motor-actuators is deactivated during an inhibited braking mode.
In a presently preferred aspect, the brake system control unit is configured to generate a braking force of the activated one of the first and second portions of the plurality of electric motor-actuators greater than the commanded braking force of the brake pedal command to compensate for the other of the first and second portions of the plurality of electric motor-actuators being deactivated during the inhibited braking mode. In another presently preferred aspect, when half of the plurality of electric motor-actuators are deactivated from braking notwithstanding a brake pedal command for a commanded braking force during the inhibited braking mode, the brake system control unit is configured to control the electronic brake actuation controller to cause the activated one of the first and second portions of the plurality of electric motor-actuators to generate twice the commanded braking force of the brake pedal command during the inhibited braking mode. In another presently preferred aspect, the brake system control unit is operative to discontinue the inhibited braking mode and to activate the first and second portions of the plurality of electric motor-actuators during an emergency braking mode in which the commanded braking force is greater than or equal to a predetermined braking force. In another presently preferred aspect, the brake system control unit is operative to detect failure of at least one of the plurality of electric motor-actuators, and the brake system control unit inactivates the inhibited braking mode and activates a maximum available braking mode in which the first and second portions of the plurality of electric motor-actuators are both activated, responsive to detection by the brake system control unit of the failure of the at least one of the plurality of electric motor-actuators.
The present invention also provides for a method for controlling a plurality of electric motor-actuators associated with an aircraft wheel brake, in which a brake pedal command for a commanded braking force is generated for an aircraft wheel brake, the brake pedal command is received, and the electronic brake actuation controller is controlled such that one of the first and second portions of the plurality of electric motor-actuators is activated and the other of the first and second portions of the plurality of electric motor-actuators is deactivated during an inhibited braking mode. In one presently preferred aspect, the braking force generated by the activated one of the first and second portions of the plurality of electric motor-actuators is preferably greater than the commanded braking force of the brake pedal command to compensate for the other of the first and second portions of the plurality of electric motor-actuators being deactivated during the inhibited braking mode.
In another presently preferred aspect, half of the plurality of electric motor-actuators are deactivated from braking notwithstanding a brake pedal command for a commanded braking force during the inhibited braking mode, and the brake system control unit controls the electronic brake actuation controller to cause the activated one of the first and second portions of the plurality of electric motor-actuators to generate twice the commanded braking force of the brake pedal command during the inhibited braking mode. In another presently preferred aspect, the brake system control unit inactivates the inhibited braking mode when the commanded braking force is greater than or equal to a predetermined threshold braking force.
In another presently preferred aspect, the step of controlling the electronic brake actuation controller includes controlling actuation of each of the plurality of electric motor-actuators to generate a commanded braking force according to a first pedal command vs. brake force curve when the inhibited braking mode is inactive, and controlling actuation of the activated one of the first and second portions of the plurality of electric motor-actuators to generate a commanded braking force greater than the brake pedal command during the inhibited braking mode according to a second pedal command vs. brake force curve. In another presently preferred aspect, the first and second portions of the plurality of electric motor-actuators are alternatingly activated during successive actuations of the plurality of electric motor-actuators during the inhibited braking mode.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.
While the use of electrically actuated brakes in aircraft and other vehicles eliminates some disadvantages associated with the use of hydraulic brakes, the accumulated costs of utilizing multiple electric motor-actuators in electrically actuated braking systems, owing to the costs of periodic maintenance, repair and replacement of worn parts hydraulic braking systems, and particularly heavy usage in aircraft braking systems that operate in challenging environments, can be significant.
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However, during the inhibited braking mode, only one of the selected first or second portions of the plurality of electric motor-actuators contribute to provide the wheel brake's normal braking total or complete brake commanded clamping force curve, while the other of the first and second portions of the plurality of electric motor-actuators that is inhibited do not contribute to the wheel brake's normal braking total or complete brake commanded clamping force curve. This would result in an objectionable change in braking “feel” to the vehicle operator between the times when electric motor-actuators are inhibited vs. not inhibited and during transitions between the two. Accordingly, the brake system control unit is preferably configured to generate a braking force of the activated one of the first and second portions of the plurality of electric motor-actuators greater than the commanded braking force of the brake pedal command to compensate for the other of the first and second portions of the plurality of electric motor-actuators being deactivated during the inhibited braking mode, so that the braking “feel” is the same whether the brakes are inhibited or not.
The brake system control unit preferably controls the electronic brake actuation controller to cause the activated one of the first and second portions of the plurality of electric motor-actuators to generate a braking force of greater than the commanded braking force in direct proportion to the number of electric motor-actuators that are inhibited. Where each of the first and second portions of the plurality of electric motor-actuators constitute half of the plurality of electric motor-actuators, so that half of the plurality of electric motor-actuators are deactivated from braking during the inhibited braking mode notwithstanding a brake pedal command for a commanded braking force, the brake system control unit preferably controls the electronic brake actuation controller to cause the activated one of the first and second portions of the plurality of electric motor-actuators to generate twice the commanded braking force of the brake pedal command during the inhibited braking mode. This ensures that the pedal “feel” experienced by an operator of the electronic wheel braking system remains unchanged. This also ensures that the amount of braking effort produced by the wheel brake applies the same amount of braking force and continues to absorb the same amount of braking energy as when all of the available electric motor-actuators are activated together.
The brake system control unit preferably discontinues the inhibited braking mode and activates the first and second portions of the plurality of electric motor-actuators during an emergency braking mode when the commanded braking force is greater than or equal to a predetermined braking force. Referring to
Another important concern is that the response of the electronic braking system to failure conditions, in aircraft, as well as other vehicles, should include the ability to continue safe operation of the braking system after a failure of one or more of the electric motor-actuators occurs so that repairs can be deferred to a time when those repairs can be made. Accordingly, in the present invention the brake system control unit is operative to detect failure of one or more of the plurality of electric motor-actuators, and the brake system control unit inactivates the inhibited braking mode and activates a maximum available braking mode in which all of the available electric motor-actuators in the first and second portions of the plurality of electric motor-actuators are activated, responsive to detection of failure of one or more of the electric motor-actuators. For example, if the brake system control unit detects that an electric motor-actuator associated with a brake is inoperative, the brake system control unit would then cease to inhibit any of the other electric motor-actuators on that brake until repairs are made. This ensures that maximum available braking capability is retained following any failure condition. Since operation with a failure condition is infrequent, the effect on cost, wear, and reliability would be negligible. In addition, if a failure condition of one or more of the plurality of electric motor-actuators is detected, or one or more of the plurality of electric motor-actuators otherwise become inoperative and the other electric motor-actuators on that brake are commanded to be operative, then the command to the operative electric motor-actuators can be adjusted by the brake system control unit as noted above to ensure no overall change in brake “feel.”
Another important consideration is that if the electric motor-actuator inhibit logic always inhibits the same electric motor-actuators, then the full-time electric motor-actuators would wear out far more rapidly than the inhibited ones, which may be undesirable. The invention also allows for logic that would periodically change which electric motor-actuators are inhibited and which are not. One way to do this for aircraft applications would be to switch every flight cycle as indicated by landing gear extension or some other indication of a flight cycle. A more preferred way would be to switch every time the clamping force command to that brake is removed, in other words every time the brake is released. As is illustrated in
Conditionally inhibiting selected electric motor-actuators when all electric motor-actuators are not needed can also improve brake control on slippery surfaces, and can reduce battery drain during parking. When braking is required on low friction surfaces such as wet pavement or ice, for example, very little clamping force is required to apply an optimum level of braking. When all the electric motor-actuators are operating together, antiskid-controlled braking becomes difficult because only a tiny change in clamping force command causes a large change in actual clamping force. With a portion of available electric motor-actuators inhibited, the same clamping force command causes a proportionately smaller change to the actual clamping force. As a result, the brake control system can more accurately and effectively control braking on slippery surfaces.
Battery drain during parking of aircraft can be reduced. In aircraft, electrically actuated brakes are also used for parking. After the parking brake is set, the brake system control unit continues to operate while the brakes cool. This is necessary because the brake system control unit must periodically re-adjust the electric motor-actuators to account for thermal contractions of the brake, which can take as long as an hour. The brake system control unit must use aircraft battery power during this period of control braking during parking, since that is the only electrical power source available to operate the electric motor-actuators when the aircraft is shut down. This has a significant effect on sizing the battery. It is usually only necessary to apply full clamping force with the parking brake when the engines are running, and at such times electrical power for operating the electric motor-actuators comes from the electrical generators on the engine, not from the battery. The only time when the parking brake must be powered by the battery is when the engines are not operating, and only partial clamping force is necessary at such times. This allows some electric motor-actuators to be inhibited when parking on battery power. By doing so, the power drain on the battery is significantly reduced.
It will be apparent from the foregoing that while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.
