FULLY ELECTRIC SPEED-PROPORTIONAL NOSE WHEEL STEERING SYSTEM FOR AN AIRCRAFT

Abstract

An aircraft drive system having a fully electric speed-proportional control and drive system for the nose wheel of an aircraft in which variable steering authority is accomplished by monitoring of the signal from a tiller and rudder pedals by a nose wheel controller in conjunction with the speed of the aircraft, in order to command and power an electromechanical steering, actuator to achieve speed-proportional variable steering authority. This provides a system with a quicker response time than current hydraulic-based systems which can help reduce nose wheel shimmy, eliminate certain nose wheel steering failure modes associated with hydraulic systems, and reduce weight when used in small-to-medium sized aircraft.

Claims

1. A nose wheel steering system for an aircraft, the nose wheel steering system comprising: at least one nose wheel control input, each at least one nose wheel control input being arranged to produce an electrical output signal proportional to the position of the at least one nose wheel control input; a controller with variable gain at least in part based on speed, arranged to receive the electrical output signal(s) from the at least one nose wheel control input, amplify them individually to compute desired target steering angles, and to output an electrical power output signal; and an electromechanical nose wheel steering drive means arranged to receive the electrical power output signal from the controller.

2. The nose wheel steering system according to claim 1, wherein the at least one nose wheel control input comprises rudder pedals.

3. The nose wheel steering system according to claim 1, wherein the at least one nose wheel control input comprises a hand tiller.

4. The nose wheel steering system according to claim 1, wherein the system further comprises an angle position sensor arranged to relay a current nose wheel angle to the controller.

5. The nose wheel steering system according to claim 1, wherein the system further comprises a ground speed sensor arranged to relay a current ground speed of the aircraft to the controller, the controller being further arranged to base the variable gain at least in part on the current ground speed.

6. The nose wheel steering system according to claim 1, wherein the system further comprises an air speed sensor arranged to relay a current air speed of the aircraft to the controller, the controller being further arranged to base the variable gain at least in part on the current air speed.

7. The nose wheel steering system according to claim 6, wherein the system further comprises a weight-on-wheels microswitch arranged to send an electric signal to the controller when a weight is detected on the wheels of the aircraft.

8. The nose wheel steering system according to claim 1, wherein the electrical output from the controller is of differing polarities depending upon which way the nose wheel is intended to turn.

9. The nose wheel steering system according to claim 1, wherein the system further comprises: a ground speed sensor arranged to relay a current ground speed of the aircraft to the controller; an air speed sensor arranged to relay a current air speed of the aircraft to the controller; and a weight-on-wheels microswitch arranged to send an electric signal to the controller when a weight is detected on the wheels of the aircraft; wherein the controller is further arranged to base the variable gain at least in part on the current ground speed when the weight-on-wheels microswitch sends the electric signal to the controller, and to base the variable gain at least in part on the current air speed when the weight-on-wheels microswitch does not send the electric signal to the controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other advantages and benefits of the present invention will become apparent from a consideration of the following description and accompanying drawings, in which:

[0023] FIG. 1 shows a structural view of the present invention; and

[0024] FIG. 2 shows a graph of the integrated electronic steer authority of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0025] A fully electric speed-proportional nose wheel steering system 100 in accordance with an exemplary embodiment of the present invention is shown in FIGS. 1 and 2.

[0026] The present invention provides an integrated nose wheel control and drive system for an aircraft which provides means to collect the system electronic inputs via a data concentrator function, then a means of detecting, interpreting and computing those inputs with software, and a means of commanding and powering a final electromechanical drive to steer the nose gear.

[0027] FIG. 1 shows a structural diagram of an embodiment of the invention. A nose wheel steering command system 100, comprising inputs from the rudder pedals 102 and a hand tiller(s) 103. The rudder pedals 102 and the hand tiller 103 are located in the cockpit 109 of an aircraft. The rudder pedals 102 and the hand tiller 103, in operation, send electrical command inputs to a nose wheel controller 101 by use of digital rotary variable differential transformers (RVDTs), via an ARINC 429/MIL-STD-1553 databus or equivalent. The electrical command inputs vary depending on the position of the tiller 103 and the pedals 102, which are commanded by the pilot(s). Alternatively, the rudder pedals 102 and hand tiller 103 may send electrical command inputs through an analogue RVDT, a variable potentiometer or a hall effect sensor.

[0028] In accordance with any revision of RTCA DO-254 or equivalent and any revision of RTCA DO-178 or equivalent, the controller is a dual redundant controller comprising two separate boxes i.e. two individual controllers performing the same functions in parallel. However, these two individual controllers will be referred to as a single controller, for the sake of simplicity.

[0029] The system further comprises ground speed and air speed sensing systems 108, 104. The ground speed system 108 is comprised of one or more wheel speed transducers using passive inductive magnetic sensors. The air speed data shall be provided to the nose wheel controller 101 via an ARINC 429/MIL-STD-1553 interface with an on-board air data computer (separate system), which is normally installed on an aircraft to provide airspeed information to the pilots by interpreting pitot pressure. The ground speed and air speed sensing systems 108, 104 send electrical signals to the nose wheel controller 101, which vary depending on the measured speed of the aircraft.

[0030] A weight-on-wheels microswitch 105 detects whether the aircraft is on the ground or in the air, and sends a signal to the nose wheel controller 101 via an ARINC 429/MIL-STD-1553 interface to switch between using ground speed or air speed accordingly.

[0031] A steering angle sensor 107 detects the current steering angle of the nose wheel and relays it to the nose wheel controller 101. The steering angle sensor 107 can be an RVDT, a potentiometer, a hall effect sensor or any other suitable device.

[0032] The nose wheel controller 101 is integrated via an ARINC 429/MIL-STD-1553 databus, or any other suitable device, and receives digital inputs from the rudder pedals 102, hand tiller 103, ground speed and air speed systems 108, 104, weight-on-wheels microswitch 105 and the steering angle sensor 107, in order to determine a target steering angle using an algorithm, and a percentage error or delta comparison value (between the current steering angle and commanded steering angle) which is used to instantaneously determine the correct polarity and magnitude of the power supply to the final electric drive, to achieve the desired angle. The ground speed system 108, air speed system 104, weight-on-wheels microswitch 105 and the steering angle sensor 107 are all associated with the landing gear 110.

[0033] The nose wheel steering actuator 106, also associated with the landing gear 110, is part of a nose wheel steering electromechanical final drive, which may be of multiple configurations. The electromechanical drive comprises an electric motor which drives a recirculating ball jackscrew connected to a rack-and-pinion steering output gear and a steering tube.

[0034] Alternatively, the electromechanical drive means can include an epicyclic gear set driving a nose wheel steering tube via a reduction gearbox. The skilled reader will understand that other arrangements are possible within the scope of the invention. The electric motor may be an AC motor, a DC motor, a brushless DC motor, or any other suitable device. Similarly, other gear systems are readily applicable where necessary in specific systems.

[0035] The electromechanical drive incorporates the steering angle sensor 107, and sends instantaneous actual steering position data to the nose wheel controller 101. A feedback loop is used to compare the instantaneous angle to the commanded steering angle (percentage error, or delta value) in order to make adjustments.

[0036] During a taxiing regime, a pilot will use the tiller 103 and the rudder pedals 102 to adjust the direction of an aircraft. Each of these sends a digital signal to the nose wheel controller 101. The nose wheel controller 101 adjusts the sensitivity of the signal according to the signal received from the ground speed system 108.

[0037] At low speeds, a large turning angle is required for the nose wheel in order to increase maneuverability of the aircraft around an airport or airfield. As such, the sensitivity between the tiller 103 and rudder pedals 102 and the nose wheel is high, allowing the pilot to turn the aircraft through large angles with minimal effort. As the aircraft increases speed, for example, during take-off, only small adjustments are made to the angle of the aircraft. Making large adjustments to the angle at high speeds is extremely dangerous, and so the nose wheel controller 101 restricts the turning angle, reducing the risk of an accident.

[0038] The nose wheel controller 101 uses the signals received from the ground speed system 108 to adjust the steering authority using an algorithm based on an exponential or logarithmic relationship, illustrated by a curve such as the variable gain curve according to the graph shown in FIG. 2.

[0039] FIG. 2 is representative of one or more possible exponents representing gain curves of one or more input controls, e.g. the rudder pedals 102 and tiller 103. Such curves may be expressed in the manner of y=log.sub.b x or y=b.sup.x in terms of exponential gain inversely proportional to speed, or as shown in FIG. 2, an expression such as y=x.2.sup.(t/h) akin to exponential decay, or a half-life where gain is inverse-exponentially proportional to speed. Other formulaic expressions may be used to represent a continuously variable gain curve of steer authority vs speed.

[0040] As will be appreciated by the skilled reader, other variable gain schemes are possible within the scope of the invention. The adjusted signal is then output to the drive actuator part of the electromechanical drive means to adjust the direction of the aircraft.

[0041] The steering angle sensor 107 continuously relays the actual steering angle to the nose wheel controller 101. The nose wheel controller 101 can then make adjustments to the output signal sent to the drive actuator 106.

[0042] As the aircraft leaves the ground, the weight-on-wheels microswitch 105 detects that the aircraft in flight, and may center the nose wheel for retraction. When in flight with the landing gear extended, the nose wheel controller 101 then uses signals sent from the air speed system 104 in order to determine the speed of the aircraft, this provides an alternative means to determine nose wheel steering gain when the wheel may not be turning, such as immediately before landing.

[0043] It is to be appreciated that many of the features described above in the exemplary embodiment are readily replaceable depending on the specific needs of a particular system.