Aeronautics and astronautics – Aircraft control
Reexamination Certificate
2000-04-28
2001-05-01
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft control
C244S213000, C188S134000
Reexamination Certificate
active
06224017
ABSTRACT:
The present invention relates to a brake in particular for a flap adjusting mechanism and to a method for condition monitoring of the brake.
Such brakes are used in commercial airplanes to increase passive safe in case of defects in the flap adjusting mechanism or its drive.
In the landing approach the lift of the wings is essentially increased by extendible lift flaps or slats, permitting lower flying speeds. These flaps are normally extended symmetrically on the left and right against the effect of aerodynamic forces. One drive system is provided for each wing.
In case of disturbances in one of the drive systems—for example through shaft failure due to overloading or material fatigue—it could happen that the extended flaps of one wing are moved by the aerodynamic forces back into their stowed position. The lift of the two wings would be asymmetrical so that a critical rolling, motion of the airplane would be initiated.
In order to avoid this state modern commercial airplanes are equipped with a sensor for detecting asymmetry of the two wings and triggering an activation of hydraulically operated brakes. The brakes then prevent further motion of the flaps through aerodynamic forces so that altogether only little asymmetry can arise and the airplane can land safely.
In is known system the monitoring of asymmetry and the hydraulic activation are very elaborate and trouble-prone due to their high complexity. For safety reasons the hydraulic activation is executed redundantly with at least two separate hydraulic systems. The measuring and control signals are all monitored constantly in a central control computer. The great number of signals to be processed by the control computer, which are also produced in other peripheral devices, results in very high complexity of the total control system.
Passively acting brakes are also known for this purpose. They have a housing and a driveshaft motively connected with the flaps which is mounted in the housing so as to be freely rotatable in one direction of rotation and only rotatable in the other direction of rotation by overcoming a certain braking moment. The braking moment is produced by a spring-biased disk assembly. A freewheel is disposed in the torque flow between housing and driveshaft, thereby achieving the free rotatability in one direction.
This brake system exploits the fact that the aerodynamic forces on the flaps at ways act in the “stow” direction. The brake is so installed that the driveshaft motively connected with the brake is freely rotatable for flap adjustment upon extension of the flaps. Upon extension the flap adjustment drive must thus overcome substantially only the aerodynamic forces, When stowing the flaps, which is normally only done after touchdown, the drive must overcome substantially only the braking moment. In case of a defect in the drive of the flap adjusting mechanism, the brake pre vents stowing of the particular flap so as to avoid the critical asymetrical flight condition. The braking moment produced by spring bias on the disk assembly is somewhat greater than the maximum restoring forces from the aerodynamic load on the flap.
The advantages of this system are that it relieves the central control computer of constantly monitoring the system and activating the hydraulic brakes, and omits the hydraulic brakes with their elaborate activation by means of redundantly provided hydraulic lines.
The disadvantage of this system is that it is hardly possible to check operability in the installed state. In particular it is difficult to make statements about whether braking moment is within the permissible range or whether the brake contains the stipulated amount of lubricant. It is desirable to be able to check the operability of the brakes reliably and in a simple way in every flight cycle.
One conceivable way of making a statement about the amount of the braking moment is to measure the current consumption of the drive motor for flap adjustment. However, the result of such a measurement can be considerably falsified by friction in the transmission path between the drive motor and the brake.
Monitoring braking moment by measuring the reaction moment on a spring housing suspension could have an uncontrollable influence on the dynamics of the system.
The problem of the invention is to provide a reliable, passively acting brake in particular for a flap adjusting mechanism whose functional state can be checked in the installed state simply and with a high confidence level. Furthermore, a method is to be provided for condition monitoring of the inventive brake.
This problem is solved by a brake with the features of the main claim. Advantageous developments of the invention are given by the dependent claims.
The temperature sensor or sensors disposed at suitable places on the brake permit monitoring of temperature(s) at the measuring points.
In a normal flight cycle the flaps are extended completely before landing d stowed again completely after touchdown. The full adjusting path corresponds to a certain number of rotations or total rotation angle on the flap adjusting mechanism driveshaft coupled motively with the brake. The amount of desired braking moment which must be overcome for stowing the flaps is likewise known. The amount of frictional work produced when stowing the flaps is equal to the time integral of frictional power during the process. At constant braking moment frictional work is calculated from the product of braking moment and total rotation angle. This friction work leads to a characteristic temperature increase in the brake which can be determined by the temperature sensor or sensors.
If there is a functional disturbance of the brake so that braking moment deviates from desired braking moment, this can be detected with reference to the determined temperature. If braking moment is too small, for example due to a defect of spring elements or wear on friction linings, the temperature increase is smaller than otherwise. If there is too little lubricant in the brake for example, braking moment is greater due to a lack of lubrication on the friction elements and the heat capacity of the brake is also smaller. In this case the temperature increase will be greater.
In order to increase safety further, or obtain data on the temperature distribution in the brake, it is possible to provide a plurality of temperature sensors in the brake. Suitable places are for example in the lubricant area of the brake where a good temperature balance is given, or in the area of friction elements where the influences of heat dissipation to the surroundings are lowest.
Suitable temperature sensors are for example semiconductor thermal elements which have high reliability. However, one can also determine temperature indirectly using expansion sensors fastened to a component exposed to the temperature increase and thereby expanding.
In an advantageous development of the invention, a rotation signal sensor is furthermore provided for measuring the total rotation angle. This sensor permit the brake to be monitored even when the flaps are stowed out of any intermediate position. The lower desired temperature increase results from the accordingly smaller total rotation angle.
The rotation signal sensor can be executed for example as an inductive impulse transmitter. A suitable pitch sequence on the teeth of a transmitter wheel also makes it possible to recognize the direction of rotation, which can be used advantageously for an evaluation algorithm.
If a signal processing unit with an evaluation logic is provided in or on the brake, the central control computer does not need to constantly process the sensor signals otherwise passed thereto and is thereby relieved. The evaluation logic performs the comparison of actual temperature increase during or after stowing of the flaps with a desired temperature increase which is preset or determined from the signal of the rotation signal sensor. An error signal is only conveyed to the central control computer if the temperature increase is outside expected limits.
It is advantageous to di
Fischer Manfred
Hunold Bernard
Zimmermann Karl
Barefoot Galen L.
Jagtiani & Associates
Liebherr-Aerospace Lindenberg GmbH
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