Aeronautics and astronautics – Aircraft control – Automatic
Reexamination Certificate
1999-12-09
2001-12-04
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Aircraft control
Automatic
C244S221000, C244S220000, C244S224000
Reexamination Certificate
active
06325331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to control actuators, and in particular, to trim actuators for use in aircraft flight control systems, such as helicopter flight control systems.
2. Background of the Prior Art
Automated steering mechanisms and flight control systems for aircraft have been around for many years. An early automatic pilot for helicopters is disclosed in U.S. Pat. No. 2,479,549 issued Aug. 23, 1949 to Ayres et al. The Ayres electrical control system can be overridden so that the aircraft can be operated manually. In Ayres, an aneroid bellows controls an electric motor for adjusting and maintaining altitude, a directional gyro controls an electric motor for adjusting and maintaining heading, and an attitude gyro controls two electric motors for adjusting and maintaining attitude.
A steering mechanism utilizing a servo motor is disclosed U.S. Pat. No. 4,004,537 issued Jan. 25, 1977 to Nilsson. The Nilsson steering mechanism is designed primarily for boats. In Nilsson, rotation of a wheel is passed through a cable to a ball screw cylinder, where the rotation is transformed into linear movement of bar. The rotatable element in the ball screw cylinder is connected to a servo motor, via gears and a transmission. When the cable rotates faster than the servo motor, the transmission decouples the motor and allows the wheel and cable to override the servo motor. The transmission in Nilsson may be a double-acting free-wheeling clutch.
A motor for use in an aircraft flight control system is disclosed in U.S. Pat. No. 5,233,252 issued Aug. 3, 1993 to Denk. Denk contemplates using a two-pole permanent-magnet rotor and a toothless stator motor. A pair of these motors are incorporated into a flight control system replacing hydraulic or electric motors and potentially eliminating the need for an additional friction brake. The motors have a detent, or holding, mode, wherein they act as brakes, resisting back-driving forces acting on the flaps. In Denk, flux gates are inserted by a solenoid and its plunger into a space between the stator core elements. When the motor is not in use, the plunger is retracted by springs, and the flux gates are removed from the spaces. The permanent-magnet rotor simultaneously rotates to align its magnetic axis with the spaces. Once in this preferred orientation, the permanent-magnet rotor resists imposed torque loads. This is the preferred mode, i.e. holding, for the application to which the Denk patent is directed. The need for a solenoid, spring or other mechanism to activate/de-activate the function is an undesirable complication.
With respect to helicopter flight control systems, the prior art trim actuator devices typically include an electrically-actuable motor, a gear assembly, a brake device for locking the position of the rotor of the electrically-actuable motor, a clutch for mechanically controlling the interaction of the electrically-actuable motor and the gear assembly. Additionally, in the prior art devices, an eddy-current damping system is sometimes provided with a permanent magnet member carried by the rotor of the electrically-actuable motor. When a stepper motor is utilized for the electrically-actuable motor, the brake component can be eliminated; however, prior art devices all require some type of clutch to interface mechanically the electrically actuable motor and the gear assembly.
SUMMARY OF THE INVENTION
The present invention is an improved trim actuator for use in flight control systems, with the preferred embodiment being utilized in flight control systems for helicopters. In accordance with the present invention, the trim actuator interfaces with an automatic flight control system to partially or completely control the mechanical flight controls of air craft. When the aircraft is operating in an entirely automated flight control mode of operation, the automatic flight control system utilizes a controller to execute program instructions to operate the mechanical flight controls by applying electrical current to the electrically-actuable motor which is a part of the trim actuator. In accordance with the present invention, an electrically actuable stepper motor is utilized as part of the trim actuator. The stepper motor includes stator components and a rotor. The automatic flight control system supplies electrical currents to the plurality of windings which make up the stepper motor, controlling the movement of the rotor of the stepper motor. In accordance with the preferred embodiment of the present invention, the use of an electrically-actuable stepper motor eliminates the need for providing a mechanical brake to lock the rotor into a particular position. In accordance with the present invention, supplying currents to the plurality of windings of the stepper motor can lock the rotor into any particular position. Therefore, the brake assembly which is necessary in the prior art devices is eliminated entirely in the present invention. This eliminates a mechanical component which is subject to failure possibly, which requires servicing certainly, and which adds undesirable weight to the aircraft. Therefore, one objective and advantage of the present invention is to eliminate entirely from the trim actuator any mechanical braking device.
Sometimes it is desirable to operate the aircraft in a partially automated mode of operation. In this mode of operation, the controller of the automatic flight control system executes program instructions in response to operator commands and sensor date to control some components of the flight control system, while the pilot manually controls other components of the flight control system. This is a more complex mode of operation, which is conventional in all helicopter craft, which requires that the automatic flight control system operate through the electrically-actuable stepper motor of the trim actuator of the present invention to partially control some components of the mechanical flight controls. For example, a plurality of trim actuators may be utilized in the pitch, roll, and yaw axis for forced trim reference functions. One of more of these force axes may be under computer control, while others are under manual control. Alternatively, the craft may be under a combination of automated and manual control. In still other situations, it may be desirable for the pilot to suspend or terminate all automated flight control, and fly the craft entirely manually utilizing the mechanical flight controls. In these situations, the present invention allows the electrically-actuable stepper motor to free-wheel completely, without any mechanical or electrical interference with the complete manual control of the craft by the pilot. However, in accordance with the present invention, an electrically-actuable, non-contact damping system is provided which facilitates the transition between an automated flight control mode of operation to a completely manual control mode of operation. In accordance with the preferred embodiment of the present invention, an eddy current braking system is provided which does not physically contact the rotor of the electrically-actuable stepper motor, but which dampens the rotor utilizing magnetic fields and eddy currents. The present invention departs from the prior art in the preferred embodiment insofar as it does not provide permanent magnet components in the damping system, thus providing damping of vibration and instabilities during the transition between modes of operation, without any impact whatsoever on the rotor of the electrically-actuable stepper motor when it is free-wheeling during a entirely manually mode of operation. In other words, the preferred embodiment of the present invention provides a non-contact damping system for very brief intervals associated with the transition in control, but otherwise does not impact the mechanical flight controls during manual flight operations. In alternative embodiments, the electrically-actuable damping system may be utilized to provide a predetermined amount of damping to the
Bell Helicopter Textron Inc.
Best Christian M.
Hill & Hunn LLP
Hunn Melvin A.
Jordan Charles T.
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