Patent Description:
It is common to use brakes in an aircraft to brake rotating components. For example, a helicopter may be provided with a brake to rapidly slow the rotor rotation after the engine has been shut down, after landing. The brake may also be used to stop the helicopter rotor from rotating under e.g. gusts of wind, while the helicopter is grounded. Similarly, a brake may be provided on an aircraft propulsion system, such as turbopropellor (turboprop), turbofan, prop fan, open rotor etc. to rapidly slow rotation after the engine has been switched off, after landing. The brake may also be used to stop the rotor from rotating under e.g. gusts of wind, while the aircraft is grounded.

It is possible that the brake may be accidentally applied while the engine or propeller is still running, for example, due to a system failure. This can lead to an abnormally high amount of energy being generated by the brake which can cause excessive heating of the brake, potentially causing a fire or thermally damaging aircraft or engine components.

Such conventional brakes have generally been considered satisfactory for their intended purpose but it is desirable to mitigate the risk of overheating of a brake.

<CIT> discloses a brake for an aircraft according to the preamble of claim <NUM>.

<CIT> discloses an automatic braking engagement device with a rotatable shaft and a thermal fuse.

<CIT> discloses a parking brake for aircraft turbo-propeller propulsion units.

According to a first aspect, there is provided a brake for an aircraft, the brake comprising: a housing; a shaft defining an axis and extending into the housing; a floating brake disk arranged to rotate with the shaft and arranged to be axially movable, along the axis, within the housing; a static brake pad arranged on a first side of the floating brake disk; a movable brake pad arranged on a second, opposite, side of the floating brake disk; biasing means for moving the movable brake pad relative to the housing to press the movable brake pad against the floating brake disk, and thereby to press the floating brake disk against the static brake pad to apply braking force to the floating brake disk; and a thermal fuse in thermal contact with the static brake pad, the thermal fuse having a fusing temperature, T, above which the thermal fuse fuses, wherein the thermal fuse is arranged such that, before it fuses, the static brake pad is axially fixed relative to the housing, and after it fuses, the static brake pad is free to move axially relative to the housing away from the floating brake disk.

The floating brake disk is considered to be "floating" because it is axially movable relative to the housing. This floating behaviour relative to the housing may be achieved in different ways. For example, the floating brake disk may be axially movable relative to the shaft, and the shaft may be axially fixed relative to the housing. In this example, the brake disk may, for example, be connected to the shaft via splines that allow movement of the floating brake disk along the shaft axis ensuring that rotation of the shaft causes rotation of the floating brake disk. Alternatively, the floating brake disk may be axially fixed to the shaft that allow movement of the floating brake disk along the shaft axis ensuring that rotation of the shaft causes rotation of the floating brake disk. Alternatively, the floating brake disk may be axially fixed to the shaft or formed integral with the shaft, and wherein the shaft is axially movable relative to the housing.

The static brake pad may be free to move axially along a first axial length after the thermal fuse has fused; and a hard stop is formed in the housing at a location axially in-between the static brake pad and the movable brake pad. The movable brake pad may comprise a flange having a flange surface arranged axially aligned with and facing the hard stop such the flange cannot move axially past the hard stop. A second axial length may be defined as an axial length between the flange surface and the hard stop at a position where the movable brake pad first makes contact with the floating brake disk; wherein the first length is longer than the second length. As such, the static brake pad may always have room to move back from the floating brake disk, even when the movable brake pad is at its furthest limit of travel (i.e. abutting the hard stop).

The thermal fuse may have an axial length that is equal to or greater than the first axial length.

The thermal fuse may comprise a eutectic material; wherein the fusing temperature, T, is a melting temperature of the eutectic material.

The thermal fuse may comprise a continuous-fibre reinforced composite, CFRC, material that comprises: one or more fibres, and a resin having a glass transition temperature, Tg; wherein the fusing temperature, T, is the glass transition temperature, Tg. The resin may be a thermoplastic resin or a thermoset resin.

The thermal fuse may further comprise a thermally conductive material extending at least partially along a length of the thermal fuse; wherein the thermally conductive material is selected to have a higher thermal conductivity than a thermal conductivity of the CFRC material.

The thermal fuse is in direct physical contact with the static brake pad.

The brake may further comprise: a member in abutment with the static brake pad, whereby, in an initial position, the member abuts the static brake pad and prevents axial movement of the static brake pad relative to the housing; a spring may be arranged to bias the member away from the initial position and towards a second position in which the member no longer prevents axial movement of the brake pad relative to the housing; wherein the thermal fuse is arranged to hold the member in the initial position, against the bias of the spring, until the thermal fuse fuses.

The second position may be located radially inwards, towards the shaft axis (X), from the initial position, and the member may have a slanted face such that a radially outward portion of the member, radially outward from the shaft axis (X), is spaced apart from the static brake pad in the initial position. This may assist sliding of the member to the second position, even when axially loaded from the static brake pad.

The member may be a first end of a rod; wherein the rod is arranged to be pivotable, under the bias from the spring around a pivot; wherein the thermal fuse is arranged to hold the rod in the initial position until the thermal fuse fuses; and wherein the spring is arranged to bias the rod to pivot around the pivot point to the second position after the thermal fuse has fused.

The member may be a piston, and the spring may be arranged within the housing to bias the piston radially inwards towards the shaft axis; wherein the thermal fuse is arranged radially inward of, and in abutment with, the piston when the piston is in the initial position.

The brake may comprise a plurality of thermal fuses, located at a plurality of positions around a circumference of the static brake pad.

According to a second aspect, there is provided a method of operating the aircraft brake of the first aspect, the method including mounting the thermal fuse in the housing to fix the static brake pad while the thermal fuse is unfused, and fusing the thermal fuse using heat generated between the static brake pad and the floating brake disk to allow the static brake pad to move axially relative to the housing away from the floating brake disk.

Certain embodiments of the present disclosure will now be described in greater detail by way of example only and with reference to the accompanying drawings in which:.

<FIG> shows a known design of aircraft brake <NUM>. The aircraft brake <NUM> comprises a shaft <NUM> extending into a brake housing <NUM>. Inside the brake housing <NUM>, a floating brake disk <NUM> is mounted on the shaft <NUM>, e.g. by splines or teeth, such that the floating brake disk <NUM> may move axially along a shaft axis Y, and is fixed to rotate with the shaft <NUM>. On one axial side of the floating brake disk <NUM> is a static brake pad <NUM>. The static brake pad <NUM> is connected to the housing and is fixed against axial movement and is fixed against rotation within the housing. On the opposite axial side of the floating brake disk <NUM> is a movable brake pad <NUM>. The movable brake pad <NUM> is fixed against rotation within the housing <NUM> (e.g. by splines), and may move axially within the housing <NUM> under force provided by biasing means <NUM>. The biasing means <NUM> may be an electric actuator or a hydraulic actuator for example. A pair of bearings 114a,b support the shaft <NUM> for rotation within the housing <NUM>. The shaft <NUM> connects to a rotating part of an aircraft, such as to a propeller or rotor (not shown), such that when the brake <NUM> brakes rotation of the shaft <NUM>, this brakes rotation of the propeller or rotor.

To activate the aircraft brake <NUM>, the biasing means <NUM> is activated so as to push the movable brake pad <NUM> axially against the floating brake disk <NUM>. The pressure from the movable brake pad <NUM> pushes the floating brake disk <NUM> along the shaft <NUM> to abut against the static brake pad <NUM>. Once the floating brake disk <NUM> is in contact with the static brake pad <NUM>, further pressure applied by the biasing means <NUM> squeezes the floating brake disk <NUM> between the two brake pads <NUM>,<NUM>. The friction between these parts then acts to slow any rotation of the floating brake disk and thereby slow rotation of the shaft <NUM>. When the shaft <NUM> is already static, application of the brake <NUM> merely acts to prevent rotation from starting (e.g. due to gusts of wind acting on a rotor connected to the shaft <NUM>).

It is common to design such an aircraft brake <NUM> for normal conditions under which it can slow down a freely-rotating rotor (i.e. a rotor that is spinning but is not currently being actively driven by an aircraft engine), and such that it can prevent rotation of a static rotor e.g. under gusts of wind. However, if the rotor (and thereby the shaft <NUM>) is being driven in rotation, e.g. by an aircraft engine, when the brake <NUM> is applied, an excessive amount of heat may be generated in the brake <NUM>. This may be termed abnormal operation of the brake <NUM>. This excessive amount of heat may heat up the overall brake <NUM>, in particular the brake housing <NUM>, to be hot enough to cause a fire or to damage nearby aircraft components. It is desirable to avoid excessive heating in a brake unit, particularly under abnormal operation.

<FIG> shows a new design of brake for an aircraft, where the brake is not currently applying braking force.

<FIG> shows a brake <NUM> comprising a shaft <NUM>, a static brake pad <NUM>, a floating brake disk <NUM>, a movable brake pad <NUM>, biasing means <NUM>, and a housing <NUM>.

Inside the brake housing <NUM>, the floating brake disk <NUM> is mounted on the shaft <NUM>, e.g. by splines or teeth, such that the floating brake disk <NUM> may move axially along a shaft axis X, and is fixed to rotate with the shaft <NUM>. On a first axial side 16a of the floating brake disk <NUM> is a static brake pad <NUM>. The static brake pad <NUM> is connected to the housing <NUM> and is (initially) fixed against axial movement and is fixed against rotation within the housing <NUM>. On the opposite axial side (i.e. second side 16b) of the floating brake disk <NUM> is a movable brake pad <NUM>. The movable brake pad <NUM> is fixed against rotation within the housing <NUM> (e.g. by splines), and may move axially within the housing <NUM> under force provided by biasing means <NUM>. The biasing means <NUM> may be an electric actuator or a hydraulic actuator for example. Any suitable means for moving the brake pad <NUM> to bias against the floating brake disk may be used. A hard stop <NUM> is formed in the housing <NUM> to limit axial movement of the movable brake pad <NUM>.

In an alternative, the brake disk <NUM> may be secured to the shaft (e.g. via splines) or the shaft <NUM> may be integrally formed with the brake disk <NUM> and, in this case, the shaft <NUM> may be floating within the housing <NUM>, i.e. the shaft <NUM> as a whole may move axially within the housing along axis X. As such, the brake disk <NUM> is considered to be "floating" in this case, as it is axially movable within the housing under pressure from the movable brake pad <NUM>.

A pair of bearings 24a,b support the shaft <NUM> for rotation within the housing <NUM>. The shaft <NUM> may be connected to a rotating part of an aircraft, such as to a propeller or rotor (not shown), such that when the brake <NUM> brakes rotation of the shaft <NUM>, this brakes rotation of the propeller or rotor.

As described in detail later, the static brake pad <NUM> is held axially static only during normal operation of the brake <NUM>. When excessive heating occurs within the brake <NUM>, the static brake pad <NUM> becomes free to move axially away from the movable brake pad <NUM>.

The movable brake pad <NUM> comprises a braking surface 18a that faces towards the floating brake disk <NUM>. The static brake pad comprises a braking surface 14a that faces towards the floating brake disk <NUM>.

To activate the aircraft brake <NUM>, the biasing means <NUM> is activated so as to push the movable brake pad <NUM> axially against the floating brake disk <NUM>. The pressure from the movable brake pad <NUM> pushes the floating brake disk <NUM> axially along the shaft <NUM> to abut against the static brake pad <NUM>. Once the floating brake disk <NUM> is in contact with the static brake pad <NUM>, further pressure applied by the biasing means <NUM> squeezes the floating brake disk <NUM> between the two brake pads <NUM>,<NUM>. This position of the brake <NUM> is shown in <FIG>. The friction between the braking surface 18a of the movable brake pad <NUM> with the floating brake disk <NUM>, and between the braking surface 14a of the static brake pad <NUM>, acts to slow any rotation of the floating brake disk <NUM> and thereby slow rotation of the shaft <NUM>. When the shaft <NUM> is already static, application of the brake <NUM> merely acts to prevent rotation from starting (e.g. due to gusts of wind acting on a rotor connected to the shaft <NUM>). The braking surface 18a of the movable brake pad <NUM> may move axially beyond the hard stop, but the movable brake pad <NUM> may not move axially past the hard stop <NUM>. This may be achieved, e.g. as shown in <FIG>, by having the braking surface 18a extend axially outward from the brake pad <NUM>, and have the braking surface 18a located radially inward from an outer edge of the movable brake pad <NUM>. The brake pad <NUM> may thus be considered to have a flange 18c extending radially outward. The flange 18c may eventually come into contact with the hard stop <NUM> and this may prevent further axial movement of the movable brake pad <NUM>. When the movable brake pad first contacts the floating brake disk <NUM>, the flange 18c is axially spaced from the hard stop <NUM> by a distance <NUM>. When the brake <NUM> is not applying braking force, the movable brake pad <NUM> is held at a distance <NUM> from the floating brake disk <NUM>. This distance <NUM> is defined as the distance between the flange 18c of the movable brake pad <NUM> and the hard stop <NUM>, and this distance <NUM> is larger than the aforesaid distance <NUM> during the braking position.

A thermal fuse <NUM> is located between the static brake pad <NUM> and the housing <NUM>. In the example brake <NUM> shown in <FIG>, the thermal fuse <NUM> sits directly in abutment with, at one end, the housing <NUM>, and, at the other end, with the static brake pad <NUM>. As described in detail later, the thermal fuse <NUM> may be located at different positions instead.

During normal operation of the brake <NUM>, the thermal fuse <NUM> holds the static brake pad <NUM> at a fixed axial position (i.e. a fixed position along the axis X, defined by the shaft <NUM>) within the housing <NUM>. The thermal fuse <NUM> is located on the side of the static brake pad <NUM> opposite the braking surface 14a.

Specific examples of suitable thermal fuses will be described later. The thermal fuse <NUM> is designed to fuse at a well-defined predetermined temperature, T, at which point it loses structural integrity. For example, the thermal fuse <NUM> may melt, disaggregate, or buckle at the predetermined temperature T.

The brake <NUM> is designed such that, under normal braking operations, the amount of heat dissipated in the brake <NUM> during braking will not cause the thermal fuse <NUM> to exceed the predetermined temperature T. However, if the brake <NUM> experiences abnormal braking conditions, for example, if the brake <NUM> is activated when the shaft <NUM> is still being actively driven by an aircraft engine, then the temperature generated by friction between the floating brake disk <NUM> and the brake pads <NUM>,<NUM> may rise excessively high and may also rise very quickly. When the temperature of the thermal fuse <NUM> rises above the temperature T, the thermal fuse <NUM> fuses (i.e. loses structural integrity) and the static brake pad <NUM> is then free to move axially away from the floating brake pad <NUM>. This disengages the brake <NUM>, i.e. it prevents the brake <NUM> from further resisting rotation of the shaft <NUM>, and this prevents further heating of the brake <NUM>, even if the shaft <NUM> is still being driven in rotation e.g. by an aircraft engine.

The predetermined temperature T may be chosen so as to limit an overall temperature rise of the housing <NUM> under abnormal braking conditions. That is, when the thermal fuse <NUM> fuses at the predetermined temperature T, no further energy is dissipated as heat within the brake <NUM>, and the heat energy that has already been generated in e.g. the brake pads <NUM>,<NUM> may gradually spread out to the housing <NUM>.

As shown in <FIG>, an axial length <NUM> is provided behind the static brake pad <NUM>, the static brake pad <NUM> may move along this axial length <NUM> after the thermal fuse <NUM> has fused. In the embodiment shown in <FIG>, the axial length <NUM> is substantially equal to an axial length of the thermal fuse <NUM>. Alternatively, there may be a recess (not shown) formed in one or both of the housing <NUM> and the movable brake pad <NUM>, for receiving an end of thermal fuse <NUM> (e.g. to securely mount the fuse), in which case the overall length of the thermal fuse <NUM> may be slightly greater than the axial length <NUM>.

When the brake <NUM> is first put into service, the braking surface 18a of the movable brake pad <NUM> has a first thickness. During the operational life of the brake <NUM>, the braking surface 18a will gradually wear down and become thinner. Similarly, during the operational life of the brake <NUM>, the braking surface 14a of the static brake pad will wear down and become thinner.

<FIG> shows the brake <NUM> with worn down braking surfaces 14a,18a. After the braking surfaces 14a, 18a have worn down somewhat, but while the thermal fuse <NUM> is still intact, the movable brake pad <NUM> is still able to squeeze the floating brake disk <NUM> against the static brake pad <NUM>, without the flange 18c of the movable brake pad <NUM> coming into abutment with the hard stop <NUM>. Of course, due to the thinner braking surfaces 14a, 18a, the distance <NUM> between the flange 18c and the hard stop <NUM> during when the brake <NUM> is applied is smaller than when the brake <NUM> was first put into service.

<FIG> shows the brake <NUM> after abnormal braking conditions have led to the thermal fuse <NUM> fusing. This Figure shows one example in which the thermal fuse <NUM> melts. Other thermal fuses <NUM>, such as some of those described below, may not melt but may instead lose structural integrity or disaggregate and, for example, buckle under axial loading. Thus, <FIG> shows merely one example of the brake <NUM> after fusing of the thermal fuse <NUM>.

In <FIG>, the thermal fuse <NUM> has melted due to excessive heat generation in the static brake pad <NUM>. This heat has been generated at the interface where the static brake pad <NUM> meets the floating brake disk <NUM>, and this generated heat heats up the brake pad <NUM>, which, by thermal conduction, heats up the thermal fuse <NUM>. When the temperature in the thermal fuse <NUM> reaches the predetermined temperature, T, the thermal fuse <NUM> melts and, under the action of gravity, falls into a space <NUM> provided in the housing <NUM>. The space <NUM> is positioned within the housing <NUM> so as to receive the molten thermal fuse material when the thermal fuse <NUM> melts. The size of the space <NUM> is also chosen to accommodate the amount of thermal fuse material.

When the thermal fuse <NUM> has fused, as shown in <FIG>, the static brake pad <NUM> is then free to move axially away from the floating brake disk <NUM>. During braking, the movable brake pad <NUM> is pushing against the floating brake disk <NUM> and therefore loading axially against the static brake pad <NUM> as well. However, the range of motion of the movable brake pad <NUM> towards the floating brake disk <NUM> and towards the static brake pad <NUM> is ultimately limited by the hard stop <NUM>. The movable brake pad <NUM> will engage with the hard stop <NUM> before the static brake pad <NUM> has moved the full length <NUM>. That is, when the movable brake pad <NUM> is stopped from further axial movement by the hard stop <NUM>, the static brake pad <NUM> still has space to move back further from the floating brake disk <NUM>. As a result, the floating brake disk <NUM> will no longer be squeezed between the brake pads <NUM>,<NUM>, even if the biasing means <NUM> has pushed the movable brake pad to its furthest possible position (i.e. to the hard stop <NUM>). The floating brake disk <NUM> may move axially along the shaft <NUM>. Once the floating brake pad <NUM> is no longer being squeezed from the first side 16a (i.e. where the static brake pad <NUM> was), the floating brake pad <NUM> will also no longer press strongly against the movable brake pad <NUM> either. As such, there will be very little, if any, frictional-heat generated at interface between the movable brake pad <NUM> and the floating brake disk <NUM> after the thermal fuse <NUM> has fused. In this manner, the brake <NUM> will rapidly disengage after the thermal fuse <NUM> fuses and there will be no further significant heat generation within the brake <NUM>. This action is automatic when the temperature of the thermal fuse <NUM> rises above the predetermined temperature, T, and does not require, for example, any sensor-based monitoring of the brake temperature.

The thermal fuse <NUM> may be a ring-shaped piece that circumscribes the shaft <NUM>. Alternatively, multiple thermal fuses <NUM> may be provided at different circumferential locations around the static brake pad <NUM>, to act as "legs" spacing the static brake pad <NUM> from the housing <NUM>. In the case of multiple thermal fuses, each thermal fuse <NUM> may be a cuboid or cylinder shape.

The thermal fuse <NUM> may be a eutectic material. A eutectic material is a material (typically a metal alloy) formed from two or more components, where both components within the alloy melt at the same temperature. As such, the overall eutectic material may have a well-defined melting point. Eutectic materials may exhibit very low creep under loading and may exhibit high thermal stability up to the melting temperature. This helps ensure the thermal fuse <NUM> holds the static brake pad <NUM> in a fixed position, even under braking loads and even under the heating experienced during normal operation.

In another example, shown in <FIG>, the thermal fuse <NUM> may be formed from a continuous-fiber-reinforced composite (CFRC) material <NUM>. For example, the CFRC material may be formed in a rod-shape or a cylinder. A CFRC material typically comprises a plurality of high-strength fibres, optionally woven together, that have been impregnated with a resin. The resin may be a thermoplastic. Thermoplastics have a glass transition temperature and this temperature may be well-defined for certain thermoplastics. Below the glass transition temperature, the thermoplastic may be essentially solid and have significant structural stiffness. Above the glass transition temperature, the thermoplastic may rapidly lose stiffness and become soft. Alternatively, the resin may be a thermoset resin having a glass transition temperature, Tg. Above the glass transition temperature, Tg, the thermoset resin may rapidly lose stiffness.

The example thermal fuse <NUM> shown in <FIG> is made from a CFRC material having two fibre directions, where the fibres in the first direction extending at <NUM> degrees to fibres in the direction. That is, the fibres in the first direction extend in an axial direction along an axis Z, which is a long axis of the rod-shaped thermal fuse <NUM>. The fibres in the second direction extend circumferentially around the axis Z. When in place within the brake <NUM>, the axis Z of the thermal fuse <NUM> of shown in <FIG> is parallel to the shaft axis X. This means that the loading forces on the thermal fuse <NUM>, from the biasing means <NUM> squeezing the brake pads <NUM>,<NUM>, extends along the axis Z. The fibres at <NUM> degrees are optional. As such, in an alternative, the CFRC material may be a unidirectional CFRC material, where fibres only extend in a single direction within the material. In this example, the fibres may be oriented along the axis Z of the thermal fuse <NUM>.

While the temperature remains below the glass transition temperature, the thermal fuse <NUM> of <FIG> has sufficient stiffness to hold the static brake pad <NUM> in place under loading forces from the biasing means <NUM>. When abnormal braking conditions occur, such that the thermal fuse <NUM> of <FIG> heats up above the glass transition temperature of the resin, the thermal fuse <NUM> loses structural integrity and will buckle under the aforesaid loading forces. At that point, the static brake pad <NUM> may move axially away from the floating brake disk <NUM> and this stops further heat generation in the brake <NUM>.

CFRC materials may have very low creep under loading and may be very stable right up to the glass transition temperature. These properties mean that a thermal fuse <NUM> formed from CFRC material may comfortably withstand the loading and heating under normal conditions of the brake <NUM>, without noticeable degradation unless and until the predetermined temperature is exceeded.

Some CFRC materials have low thermal conductivity. This can lead to the situation where a portion of the thermal fuse <NUM> nearest the static brake pad <NUM> is at a higher temperature (possibly at a temperature above the predetermined temperature), while a portion distal from the static brake pad <NUM> may be at a lower temperature (possibly below the predetermined temperature). In this case, the thermal fuse <NUM> may not fuse all at once, but may only partially fuse or fuse in stages. To help ensure the thermal fuse <NUM> fuses substantially all-at-once, the thermal fuse shown in <FIG> may further comprise a thermally conductive material <NUM>, such as a metal or a liquid, that has a higher thermal conductivity than the CFRC material. The thermally conductive material <NUM> depicted in Figure is a sheath over the outer surface of the CFRC material <NUM>. However, the thermally conductive material may alternatively extend through the middle of the CFRC material <NUM>. The thermally conductive material <NUM> may be a metal sheath. Alternatively, the thermally conductive material may be a liquid stored in a cavity defined by the CFRC material <NUM>. The thermally conductive material <NUM> can transfer heat quickly along a length of the thermal fuse <NUM>. This may ensure that the resin nearest the static brake pad <NUM> is at the same, or approximately the same, temperature as resin distal from the static brake pad <NUM> and, as a consequence, the thermal fuse <NUM> thus formed may be more certain to fuse all at once (e.g. when the temperature rises above the glass transition temperature). It is desirable, but not essential, that the thermally conductive material <NUM> is in direct abutment with the static brake pad <NUM> to ensure rapid and even heating of the thermal fuse <NUM>.

In <FIG>, the thermal fuse <NUM> directly abuts a side of the static brake pad <NUM> opposite the floating brake disk <NUM>. The thermal fuse <NUM> is shown abutting, at one end thereof, the housing <NUM>, and, at the other end thereof, the static brake pad <NUM>.

<FIG>, <FIG> show an alternative design of aircraft brake. The brake <NUM> shown in these Figures is the same as the brake <NUM> described above in relation to <FIG>, except for the region around the thermal fuse <NUM>. As such, the brake <NUM> has the same arrangement of the shaft <NUM>, the static brake pad <NUM>, the floating brake disk <NUM>, the movable brake pad <NUM>, and the biasing means <NUM> as described above in relation to <FIG>.

<FIG> and <FIG> show the brake <NUM> before any abnormal operation (i.e. before any overheating event that fuses the thermal fuse <NUM>). In this initial position, a protrusion 14c of the static brake pad <NUM> abuts against a first end 72a of a rod <NUM>. The first end 72a of the rod (initially) prevents axial movement of the static brake pad <NUM> within the housing <NUM>. The rod <NUM> has a second end 72b and a spring <NUM> is connected to the rod <NUM> near the second end 72b. A pivot point <NUM> is located in between the first end 72a and the second end 72b of the rod <NUM>. The spring <NUM> biases the rod <NUM> to pivot around the pivot point <NUM> but, in the initial position, the thermal fuse <NUM> prevents pivoting of the rod <NUM>.

As such, in the initial position, the rod <NUM> is held such that the first end 72a abuts the protrusion 14c of the static brake pad <NUM>. The thermal fuse <NUM> extends from the housing <NUM> into the rod <NUM> at a location near where the spring <NUM> abuts the rod <NUM>. While the thermal fuse <NUM> has its structural integrity, it acts as a pin extending into the rod <NUM> and the strength of the pin prevents pivoting of the rod <NUM> under the action of the spring <NUM>.

When an abnormal braking operation occurs, such that excessive heat is generated at the brake pads <NUM>,<NUM>, heat generated in the static brake pad <NUM> is thermally conducted to the thermal fuse <NUM>. When the temperature of the thermal fuse <NUM> exceeds the predetermined temperature, T, the thermal fuse <NUM> fuses. After fusing, the thermal fuse <NUM> no longer resists pivoting of the rod <NUM> under the biasing force of the spring <NUM>. As such, the spring <NUM> now causes the rod <NUM> to pivot in a plane normal to the shaft axis X. This pivoting movement moves the first end 72a of the rod <NUM> away from its abutment with the static brake pad <NUM>. This position is shown in <FIG> and <FIG>. The static brake pad <NUM> is thereafter free to move (e.g. under loading forces from the movable brake pad <NUM>, transmitted through the floating brake disk <NUM>) axially away from the floating brake disk <NUM>. In the same manner as described above in relation to <FIG>, when the static brake pad <NUM> is free to move away from the floating brake disk <NUM>, this disengages the brake <NUM> and thereby prevents further heat generation via friction between the brake pads <NUM>,<NUM> and the floating brake disk <NUM>.

To assist the rod <NUM> in sliding relative to the static brake pad <NUM> under the bias of the spring <NUM>, after the thermal fuse <NUM> has fused, a portion of the rod end 72a may have a slightly slanted face in contact with the static brake pad <NUM> such that a radially outward region of the slanted face (radially outward from the shaft axis X) is slightly spaced apart from the static brake pad <NUM>. This slant may allow the rod end 72a to slide more freely radially inwards to a position where it no longer prevents movement of the static brake pad <NUM> away from the floating brake disk <NUM>. This may assist the rod <NUM> in moving without requiring any lubricant between the rod <NUM> and static brake pad <NUM>.

<FIG> show yet a further design of brake <NUM>. The brake <NUM> shown in these Figures is the same as the brake <NUM> described above in relation to <FIG>, and the same as the brake <NUM> described in relation to <FIG>, except for the region around the thermal fuse <NUM>. That is, the brake <NUM> has the same arrangement of the shaft <NUM>, the static brake pad <NUM>, the floating brake disk <NUM>, the movable brake pad <NUM>, and the biasing means <NUM> as described above in relation to <FIG>.

In the example shown in <FIG>, before any abnormal braking operation has occurred, a spring <NUM> is compressed between the housing <NUM> and a piston <NUM>. The compressed spring <NUM> biases the piston <NUM> to move in a generally radially-inward direction, where "radially-inward" means towards the axis X of the shaft <NUM>. The thermal fuse <NUM> rests between the piston <NUM> and a pin <NUM> connected to the housing <NUM>. Before the thermal fuse <NUM> fuses, its structural integrity prevents the piston <NUM> from moving radially inward under the bias of the spring <NUM>. In this example brake <NUM>, the protrusion 14c of the static brake pad <NUM> rests against the piston <NUM>, such that the piston <NUM> prevents axial movement of the static brake pad <NUM> within the housing <NUM>.

When an abnormal braking operation occurs such that excessive heat is generated at the brake pads <NUM>,<NUM>, heat from the static brake pad <NUM> is conducted to the thermal fuse <NUM>. When the temperature of the thermal fuse <NUM> exceeds the predetermined temperature, T, the thermal fuse <NUM> loses structural integrity such that it no longer prevents movement of the piston <NUM> under action of the spring <NUM>. The spring <NUM> therefore pushes the piston <NUM> generally radially inwardly and this moves the piston <NUM> away from its abutment with the static brake pad <NUM>. The piston <NUM> may be pushed, for example, so as to come into abutment with the pin <NUM> that previously supported the thermal fuse <NUM> (i.e. before the thermal fuse <NUM> fused).

This then allows the static brake pad <NUM> (e.g. under loading forces from the movable brake pad <NUM>, transmitted through the floating brake disk <NUM>) to move axially away from the floating brake disk <NUM>. In the same manner as described above in relation to <FIG>, when the static brake pad <NUM> can move away from the floating brake disk <NUM>, this disengages the brake <NUM> and thereby prevents further heat generation via friction between the brake pads <NUM>,<NUM> and the floating brake disk <NUM>.

To assist the piston <NUM> in sliding relative to the static brake pad <NUM> under the bias of the spring <NUM>, after the thermal fuse <NUM> has fused, the piston <NUM> may have a slightly slanted face in contact with the static brake pad <NUM> such that a radially outward region of the slanted face (radially outward from the shaft axis X) is slightly spaced apart from the static brake pad <NUM>. This slant may allow the piston to slide more freely radially inwards to a position where it no longer prevents movement of the static brake pad <NUM> away from the floating brake disk <NUM>. This may assist the piston <NUM> in moving without requiring any lubricant between the piston <NUM> and static brake pad <NUM>.

The reader will appreciate that in each design described herein above in relation to <FIG>, the thermal fuse <NUM>, in its non-fused state, prevents axial movement of the static brake pad <NUM> away from the floating brake disk <NUM>. Further, in each design, when the thermal fuse <NUM> fuses, the static brake pad <NUM> is thereafter free to move axially away from the floating brake disk <NUM> and this therefore disengages the brake and prevents further heat generation by friction between the brake pads <NUM>,<NUM> and the floating brake disk <NUM>.

In the arrangements shown in <FIG>, the thermal fuse <NUM> is in thermal contact with the static brake pad <NUM>, but is not necessarily in direct physical abutment with the static brake pad <NUM>.

In the example shown in <FIG>, frictional heat generated at the interface between the static brake pad <NUM> and the floating brake disk <NUM> travels through the thickness of the static brake pad <NUM> before heating the thermal fuse <NUM>.

In the example shown in <FIG>, the frictional heat generated at the interface between the static brake pad <NUM> and the floating brake disk <NUM> travels through the thickness of the static brake pad <NUM> before heating the rod <NUM>, and the heat travels through the rod <NUM> to the thermal fuse <NUM>.

In the example shown in <FIG>, frictional heat generated at the interface between the static brake pad <NUM> and the floating brake disk <NUM> travel through the thickness of the static brake pad <NUM> to heat the piston <NUM>, and the heat travels through the piston <NUM> to the thermal fuse <NUM>.

Any of the thermal fuse <NUM> compositions (e.g. a eutectic material, a CFRC material etc.) described hereinabove, may be used with any of the designs of brake <NUM>,<NUM>,<NUM> depicted in <FIG>.

Claim 1:
A brake (<NUM>,<NUM>,<NUM>) for an aircraft, the brake comprising:
a housing (<NUM>);
a shaft (<NUM>) defining an axis (X) and extending into the housing;
a floating brake disk (<NUM>) arranged to rotate with the shaft and arranged to be axially movable, along the axis (X), within the housing (<NUM>);
a static brake pad (<NUM>) arranged on a first side (16a) of the floating brake disk (<NUM>);
a movable brake pad (<NUM>) arranged on a second, opposite, side (16b) of the floating brake disk (<NUM>);
biasing means (<NUM>) for moving the movable brake pad relative to the housing to press the movable brake pad against the floating brake disk, and thereby to press the floating brake disk against the static brake pad (<NUM>) to apply braking force to the floating brake disk;
the brake (<NUM>, <NUM>, <NUM>) for an aircraft characterised by further comprising:
a thermal fuse (<NUM>) in thermal contact with the static brake pad (<NUM>), the thermal fuse having a fusing temperature, T, above which the thermal fuse fuses,
wherein the thermal fuse is arranged such that, before it fuses, the static brake pad is axially fixed relative to the housing, and
after it fuses, the static brake pad is free to move axially relative to the housing away from the floating brake disk.