Patent Description:
Currently, shimmy oscillations are addressed through the use of friction dampeners, hydraulic dampeners, or a combination of both. These dampeners are passive systems and can require pre-set friction and damping values.

However, the present inventors have identified that hydraulic dampeners have an increased risk of fluid leakages and high maintenance levels. Moreover, friction type dampeners are often restricted to smaller aircraft and are limited by a high degree of wear and tear leading to the need for regular maintenance. Thus, there is a need for an active system to provide reliable, low-maintenance dampening.

<CIT> describes a system for damping vibration and/or shimmy of a landing gear system. The system is a friction-based damping system that utilizes a friction pad and friction wedge to dampen vibration and/or shimmy.

<CIT> describes an axial engagement-controlled variable damper comprising a rotor assembly coupled to a rotor shaft and disposed about an axis of rotation and a stator, coaxially aligned with the rotor assembly.

<CIT> describes a semi-active shimmy damper of an undercarriage and a control method thereof and belongs to the field of shimmy dampers of aircraft undercarriages.

<CIT> describes an aircraft undercarriage fitted with a shimmy-attenuator device.

According to a first aspect of the present invention there is provided a torque link assembly for an aircraft landing gear comprising: an upper torque link; a lower torque link; a joint pin arranged to pivotally couple the upper torque link and lower torque link; an electric motor assembly; a sensor arranged to detect movement of the upper torque link or lower torque link and in response to detecting the movement providing a control signal to the electric motor assembly, wherein the electric motor assembly is configured to linearly translate the joint pin with respect to one of the upper or lower torque links.

When vibration from the wheel assembly causes a shimmy event, the vibrations can travel through the lower torque link to the upper torque link, passing through a joint pin connecting the lower and upper torque links. The present inventors have found that it is advantageous to use the joint pin to restrict the vibrations from travelling from the lower torque link to the upper torque link. For example, by using a sensor to monitor the movement of the lower or upper torque link, an accurate measure of the magnitude of the vibration in the lower or upper torque link can be obtained. The vibration measurement can then be relayed to an electric motor which can operate to exert a force on the joint pin to dampen the vibrations and restrict vibrations reaching other sections of the aircraft. By actively controlling a shimmy event, the likelihood of damaged parts due to excessive vibration is reduced, leading to less frequent maintenance and longer lifetimes of parts. The use of an electric motor is advantageous over known hydraulic dampeners as electric motors can achieve a higher response rate when compared to hydraulic systems.

The electric motor can be fixed relative to one of the upper or lower torque links. This arrangement can allow the sensor system to be integrated into the electric motor and the fixed torque link. Vibration can then be monitored relative to the fixed portion.

The electric motor can be fixed relative to the lower torque link. When the electric motor is fixed relative to the lower torque link, the sensor can be attached to the motor and monitor a sensor target on the lower torque link. As the shimmy events originate from the wheel assembly, they will travel through the lower torque link before the upper torque link. By monitoring the lower torque link, vibrations can be controlled before they reach further assemblies, including the upper torque link.

The electric motor assembly can comprise one or more solenoid motors. This can allow the joint pin of the torque link assembly to be motorised to produce precise motion in response to a signal. The advantage of a solenoid motor is that the system can be relatively simple to construct whilst having a fast transition speed from an on and off position.

The solenoid motor can be a linear solenoid actuator type. This can allow for an efficient method of producing linear motion of the joint pin.

The joint pin can comprise an outer sleeve which comprises a ferromagnetic material.

As a force will be exerted on ferromagnetic material within the magnetic field produced by the solenoid motor, the moving part is required to comprise a ferromagnetic material. Ferromagnetic material can be considerably dense, for example, it is common to use an iron core, or slug, within a solenoid motor. Therefore, the present inventors have found that a joint pin made of a lightweight material that is non-ferromagnetic can be formed with a ferromagnetic component, such as an outer sleeve. The magnetic field can exert a force on the outer sleeve which will in turn exert a force on the joint pin.

The motor assembly can include one or more belleville washers. This arrangement can allow for smaller vibrations to be dampened that may not be registered by the sensor or of high enough magnitude to require the electric motor to be activated.

The motor can be arranged to maintain the force on the joint pin until the vibrations are below a threshold. This can allow the assembly to dampen the vibrations and maintain the dampened state until the shimmy event has been reduced to acceptable levels.

The torque link assembly can further comprise a health monitoring system arranged to record the duration and magnitude of a shimmy vibration event.

The health monitoring system can be arranged to record the duration and magnitude of the force applied to the joint pin by the electric motor.

This health and monitoring system can provide reliable data about the vibrations present during landing gear use. The data can be stored and/or transmitted to a central database for monitoring the shimmy events. The data can be used to assist in determining the wear of the components and provides a general health monitoring system for evaluating potential damage caused by shimmy events.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which:.

<FIG> is a diagram of an aircraft <NUM>. The aircraft <NUM> includes subassemblies such as a nose landing gear <NUM>, main landing gear <NUM> and engines <NUM>. Other aircraft subassemblies will be apparent to the skilled person. A subassembly can be a group of interconnected parts which are arranged to be fitted to the aircraft as a unit.

Referring now to <FIG>, an aircraft subassembly, namely a torque link of an aircraft landing gear assembly <NUM>, <NUM>, is shown generally at <NUM>. The torque link includes an upper torque link <NUM> and a lower torque link <NUM>, connected by a pivoting joint. The lower torque link <NUM> can connect to the sliding tube of the landing gear shock absorber (not shown) and the upper torque link <NUM> can connect to the outer housing, or cylinder, of the landing gear shock absorber. The pivoting joint can be formed by a joint pin <NUM> arranged to pass through a lug on each of the upper <NUM> and lower <NUM> torque links, arranged about a longitudinal axis of the joint pin <NUM>. As shown, the upper <NUM> and lower <NUM> torque links can each extend away from the joint pin <NUM>. The joint pin <NUM> is also connected to a shimmy dampener system <NUM>. The shimmy dampener system <NUM> defines an annulus surrounding a region of the joint pin <NUM>. The torque link assembly <NUM> can be secured by a nut <NUM> at the free end of the pin <NUM>. The upper <NUM> and lower <NUM> torque links can be connected to the joint pin via bushings.

Referring additionally to <FIG>, a cross section of the shimmy dampener system <NUM> is shown. The shimmy dampener system <NUM> comprises a casing <NUM> which houses an electric motor <NUM>, such as a solenoid motor. The casing <NUM> may also house a series of Belleville washers <NUM>. The casing <NUM> and electric motor <NUM> define an annulus arranged to surround a region of the joint pin <NUM>. The casing <NUM> is arranged coaxially and adjacent to the lower torque link <NUM>, about the longitudinal axis of the joint pin <NUM>. The casing <NUM> may be spaced from the lower torque link <NUM> via a washer <NUM> and secured to the lower torque link <NUM> via a bolt or any other suitable means. The upper torque link <NUM> is arranged coaxially and adjacent to the lower torque link <NUM>, about the longitudinal axis of the joint pin <NUM>. The upper torque link <NUM> is arranged to move freely in a lateral motion with respect to the lower torque link <NUM>. In this arrangement, the upper torque link <NUM> may be fixed relative to the joint pin <NUM>.

The casing <NUM> can further comprise a sensor <NUM>, arranged to detect movement of the lower torque link <NUM> via a sensor target <NUM> arranged on the lower torque link <NUM>. The sensor arrangement can be any suitable means of detecting vibration or varying distances, such as an accelerometer or a laser assembly.

The shimmy event assembly <NUM> may further comprise a health monitoring system <NUM> arranged to record the vibration data.

The joint pin <NUM> is arranged to pass through at least the casing <NUM>, the lower torque link <NUM>, and the upper torque link <NUM>. The joint pin <NUM> thus arranges these components about the longitudinal axis of the pin. The joint pin may comprise an outer sleeve <NUM> which is fixed with respect to the pin. The outer sleeve <NUM> is illustrated in segments as the sleeve <NUM> can be formed of connecting parts which enables an efficient means for the pin <NUM> and sleeve <NUM> construction.

Referring additionally to <FIG>, a partial cross section of the shimmy dampener system <NUM> is shown. Features equivalent to those shown in <FIG> have equivalent reference numerals to that of <FIG>. Vibrations, such as those originating at the wheel assembly can travel to the lower torque link <NUM> and cause a shimmy event. If left undamped, these oscillations can propagate to further parts of the aircraft <NUM>. The sensor <NUM> detects the magnitude of vibrations in the lower torque link <NUM>. Once the vibrations have reached a predetermined level, such as a maximum acceptable vibration level, the electric motor <NUM> initiates and applies a force to the joint pin <NUM>. The sensor <NUM> can provide feedback to the electric motor <NUM> to initiate the force or the electric motor <NUM> can comprise an algorithm to determine, based on the sensor data gathered, whether the frequency and/or magnitude of the vibrations is above the threshold limit.

As the joint pin <NUM> can be fixed with respect to the upper torque link <NUM> but free to move with respect to the casing <NUM> and lower torque link <NUM>, the force on the joint pin <NUM> will result in the upper torque link <NUM> moving coaxially closer to or further away from the lower torque link <NUM>. By adjusting the position of the upper torque link <NUM> with respect to the lower torque link <NUM>, the shimmy event can be dampened. Specifically, by closing any gap between the upper <NUM> and lower <NUM> torque links, the vibrations can be reduced until they are within the predetermined threshold. This dampens the vibrations to reduce how far the shimmy event can travel to other assemblies of the aircraft <NUM>.

The electric motor <NUM> can be a linear solenoid actuator type. In this arrangement, the motor comprises a coil of wire (not shown) which surrounds the joint pin <NUM>. When the vibrations are detected as being at or above the acceptable threshold, the solenoid motor <NUM> provides current to the coil of wire, creating a magnetic field. The strength of the magnetic field is influenced by the current in the wire meaning that the magnetic field strength can be accurately controlled. The magnetic field will exert a force on ferromagnetic material and thus an object comprising ferromagnetic material will be pushed into or pulled out of the coil of wire, depending on the current in the wire. By forming the joint pin or sleeve <NUM>, <NUM> of, at least partially, a ferromagnetic material the joint pin <NUM> can be moved by the motor <NUM> inducing a current through the coil surrounding the pin <NUM>.

Typical ferromagnetic material includes iron, nickel, and cobalt. As iron, for example, is particularly dense, it can be advantageous to form the joint pin <NUM> of a more lightweight material and provide a ferromagnetic outer sleeve <NUM>. The core of the joint pin <NUM> can thus be formed of a material such as titanium alloy, whilst the outer sleeve <NUM> fixed to the core of the pin <NUM> can comprise a ferromagnetic material or an alloy of such material.

In this arrangement, the joint pin <NUM> is moved by the force exerted on it from the outer sleeve <NUM>, which is moving under force provided by the magnetic field. Therefore, the upper torque link <NUM> which is fixed relative to the joint pin <NUM>, will move closer or further from the lower torque link <NUM>, based on the current in the wire.

Alternatively, the electric motor can be a conventional brush motor, brushless motor, or stepper motor providing rotational movement that can be converted to linear motion of the joint pin by convention means such a rack & pinion or worm gear.

<FIG> shows an arrangement in which the joint pin <NUM> is in a central position. This can be achieved when the motor <NUM> is inactive or at a mid-point during a shimmy event. The casing <NUM> can comprise a protrusion <NUM> which extends radially away from the joint pin <NUM>, towards the electric motor <NUM>. The protrusion <NUM> can be surrounded by Belleville washers <NUM> arranged coaxially adjacent to the protrusion <NUM>. When in the central position, the Belleville washers <NUM> are approximately equal in compression either side of the protrusion <NUM>.

<FIG> shows an arrangement in which the joint pin <NUM> is an extreme left position. Here, the joint pin <NUM> has been pushed away from the casing <NUM> until a region on the outer sleeve <NUM> of the joint pin <NUM> formed a mechanical stop <NUM> by abutting the lower torque link <NUM>. The outer sleeve <NUM> can comprise further protrusions to form a mechanical stop with components surrounding the joint pin <NUM>. A mechanical stop can define a maximum displacement of the joint pin <NUM>.

As the protrusion <NUM> on the outer sleeve <NUM> will move with the joint pin <NUM>, the Belleville washers <NUM> on the side of the protrusion <NUM> closest to the torque links <NUM>, <NUM> will compress. The Belleville washers <NUM> on the opposing side of the protrusion <NUM> will relax to at least partially fill the space produced.

<FIG> shows an arrangement in which the joint pin <NUM> is in an extreme right position. Here, the joint pin <NUM> has been pulled towards the casing <NUM> so that the upper <NUM> and lower <NUM> torque links are pulled closer together. The first protrusion <NUM> is thus pulled towards the casing <NUM> closer to the enclosed end of the joint pin <NUM>, compressing the Belleville washers <NUM> on the side of the enclosed end of the joint pin <NUM>. A mechanical stop is provided by the upper <NUM> and lower <NUM> torque link assemblies abutting.

In an alternative embodiment, a combination of electric motors <NUM> can be used. For example, two electric motors concentric to each other or two electric motors in series. By increasing the number of motors and adjusting positions of the motors, the intensity of the dampening force can be adjusted.

The joint pin <NUM> can further comprise a health monitoring system <NUM>. The health monitoring system <NUM> can be arranged at an end of the joint pin <NUM>, such as the end closest to the casing <NUM> along the longitudinal axis, as shown in <FIG> and <FIG>. The health monitoring system <NUM> can be arranged to detect and record the magnitude and duration of joint pin <NUM> movement which can be indicative of the magnitude and duration of a shimmy event. The data gathered can then be stored or relayed to a central database to record shimmy events occurring in the landing gear assembly <NUM>, <NUM>. Reoccurring shimmy events can indicate that parts of the assembly are fatiguing and require maintenance. Alternatively, the health monitoring system <NUM> can be integrated into overall shock strut health monitoring system (not shown).

Claim 1:
A torque link assembly (<NUM>) for an aircraft landing gear comprising:
an upper torque link (<NUM>);
a lower torque link (<NUM>);
a joint pin (<NUM>) arranged to pivotally couple the upper torque link and lower torque link; characterised in that it comprises
an electric motor assembly (<NUM>);
a sensor (<NUM>) arranged to detect movement of the upper torque link or lower torque link and in response to detecting the movement providing a control signal to the electric motor assembly,
wherein the electric motor assembly is configured to linearly translate the joint pin with respect to one of the upper or lower torque links.