Patent Application
20230082894
This application claims priority to European Patent Application No. 21290056.7 filed Sep. 10, 2021, the entire contents of which is incorporated herein by reference.
The present disclosure relates to a brake for an aircraft and a method of operating the brake.
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.
According to a first aspect, there is provided a brake for an aircraft, the brake. The brake includes: 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 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:
To activate the aircraft brake 100, the biasing means 110 is activated so as to push the movable brake pad 108 axially against the floating brake disk 106. The pressure from the movable brake pad 108 pushes the floating brake disk 106 along the shaft 102 to abut against the static brake pad 104. Once the floating brake disk 106 is in contact with the static brake pad 104, further pressure applied by the biasing means 110 squeezes the floating brake disk 106 between the two brake pads 104,108. The friction between these parts then acts to slow any rotation of the floating brake disk and thereby slow rotation of the shaft 102. When the shaft 102 is already static, application of the brake 100 merely acts to prevent rotation from starting (e.g. due to gusts of wind acting on a rotor connected to the shaft 102).
It is common to design such an aircraft brake 100 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 102) is being driven in rotation, e.g. by an aircraft engine, when the brake 100 is applied, an excessive amount of heat may be generated in the brake 100. This may be termed abnormal operation of the brake 100. This excessive amount of heat may heat up the overall brake 100, in particular the brake housing 112, 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.
Inside the brake housing 22, the floating brake disk 16 is mounted on the shaft 12, e.g. by splines or teeth, such that the floating brake disk 16 may move axially along a shaft axis X, and is fixed to rotate with the shaft 12. On a first axial side 16a of the floating brake disk 16 is a static brake pad 14. The static brake pad 14 is connected to the housing 22 and is (initially) fixed against axial movement and is fixed against rotation within the housing 22. On the opposite axial side (i.e. second side 16b) of the floating brake disk 16 is a movable brake pad 18. The movable brake pad 18 is fixed against rotation within the housing 112 (e.g. by splines), and may move axially within the housing 22 under force provided by biasing means 20. The biasing means 20 may be an electric actuator or a hydraulic actuator for example. Any suitable means for moving the brake pad 18 to bias against the floating brake disk may be used. A hard stop 60 is formed in the housing 22 to limit axial movement of the movable brake pad 18.
In an alternative, the brake disk 16 may be secured to the shaft (e.g. via splines) or the shaft 12 may be integrally formed with the brake disk 16 and, in this case, the shaft 12 may be floating within the housing 22, i.e. the shaft 12 as a whole may move axially within the housing along axis X. As such, the brake disk 16 is considered to be “floating” in this case, as it is axially movable within the housing under pressure from the movable brake pad 18.
A pair of bearings 24a,b support the shaft 12 for rotation within the housing 22. The shaft 12 may be connected to a rotating part of an aircraft, such as to a propeller or rotor (not shown), such that when the brake 10 brakes rotation of the shaft 12, this brakes rotation of the propeller or rotor.
As described in detail later, the static brake pad 14 is held axially static only during normal operation of the brake 10. When excessive heating occurs within the brake 10, the static brake pad 14 becomes free to move axially away from the movable brake pad 16.
The movable brake pad 18 comprises a braking surface 18a that faces towards the floating brake disk 16. The static brake pad comprises a braking surface 14a that faces towards the floating brake disk 16.
To activate the aircraft brake 10, the biasing means 20 is activated so as to push the movable brake pad 18 axially against the floating brake disk 16. The pressure from the movable brake pad 18 pushes the floating brake disk 16 axially along the shaft 12 to abut against the static brake pad 14. Once the floating brake disk 16 is in contact with the static brake pad 14, further pressure applied by the biasing means 20 squeezes the floating brake disk 16 between the two brake pads 14,18. This position of the brake 10 is shown in
A thermal fuse 26 is located between the static brake pad 14 and the housing 22. In the example brake 10 shown in
During normal operation of the brake 10, the thermal fuse 26 holds the static brake pad 14 at a fixed axial position (i.e. a fixed position along the axis X, defined by the shaft 12) within the housing 22. The thermal fuse 26 is located on the side of the static brake pad 14 opposite the braking surface 14a.
Specific examples of suitable thermal fuses will be described later. The thermal fuse 26 is designed to fuse at a well-defined predetermined temperature, T, at which point it loses structural integrity. For example, the thermal fuse 26 may melt, disaggregate, or buckle at the predetermined temperature T.
The brake 10 is designed such that, under normal braking operations, the amount of heat dissipated in the brake 10 during braking will not cause the thermal fuse 26 to exceed the predetermined temperature T. However, if the brake 10 experiences abnormal braking conditions, for example, if the brake 10 is activated when the shaft 12 is still being actively driven by an aircraft engine, then the temperature generated by friction between the floating brake disk 16 and the brake pads 14,18 may rise excessively high and may also rise very quickly. When the temperature of the thermal fuse 26 rises above the temperature T, the thermal fuse 26 fuses (i.e. loses structural integrity) and the static brake pad 14 is then free to move axially away from the floating brake pad 16. This disengages the brake 10, i.e. it prevents the brake 10 from further resisting rotation of the shaft 12, and this prevents further heating of the brake 10, even if the shaft 12 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 22 under abnormal braking conditions. That is, when the thermal fuse 26 fuses at the predetermined temperature T, no further energy is dissipated as heat within the brake 10, and the heat energy that has already been generated in e.g. the brake pads 14,18 may gradually spread out to the housing 22.
As shown in
When the brake 10 is first put into service, the braking surface 18a of the movable brake pad 18 has a first thickness. During the operational life of the brake 10, the braking surface 18a will gradually wear down and become thinner. Similarly, during the operational life of the brake 10, the braking surface 14a of the static brake pad will wear down and become thinner.
In
When the thermal fuse 26 has fused, as shown in
The thermal fuse 26 may be a ring-shaped piece that circumscribes the shaft 12. Alternatively, multiple thermal fuses 26 may be provided at different circumferential locations around the static brake pad 14, to act as “legs” spacing the static brake pad 14 from the housing 12. In the case of multiple thermal fuses, each thermal fuse 26 may be a cuboid or cylinder shape.
The thermal fuse 26 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 26 holds the static brake pad 14 in a fixed position, even under braking loads and even under the heating experienced during normal operation.
In another example, shown in
The example thermal fuse 26 shown in
While the temperature remains below the glass transition temperature, the thermal fuse 26 of
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 26 formed from CFRC material may comfortably withstand the loading and heating under normal conditions of the brake 10, 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 26 nearest the static brake pad 14 is at a higher temperature (possibly at a temperature above the predetermined temperature), while a portion distal from the static brake pad 14 may be at a lower temperature (possibly below the predetermined temperature). In this case, the thermal fuse 26 may not fuse all at once, but may only partially fuse or fuse in stages. To help ensure the thermal fuse 26 fuses substantially all-at-once, the thermal fuse shown in
In
As such, in the initial position, the rod 72 is held such that the first end 72a abuts the protrusion 14c of the static brake pad 14. The thermal fuse 26 extends from the housing 22 into the rod 72 at a location near where the spring 76 abuts the rod 72. While the thermal fuse 26 has its structural integrity, it acts as a pin extending into the rod 72 and the strength of the pin prevents pivoting of the rod 72 under the action of the spring 76.
When an abnormal braking operation occurs, such that excessive heat is generated at the brake pads 14,18, heat generated in the static brake pad 14 is thermally conducted to the thermal fuse 26. When the temperature of the thermal fuse 26 exceeds the predetermined temperature, T, the thermal fuse 26 fuses. After fusing, the thermal fuse 26 no longer resists pivoting of the rod 72 under the biasing force of the spring 76. As such, the spring 76 now causes the rod 72 to pivot in a plane normal to the shaft axis X. This pivoting movement moves the first end 72a of the rod 72 away from its abutment with the static brake pad 14. This position is shown in
To assist the rod 72 in sliding relative to the static brake pad 14 under the bias of the spring 76, after the thermal fuse 26 has fused, a portion of the rod end 72a may have a slightly slanted face in contact with the static brake pad 14 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 14. 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 14 away from the floating brake disk 16. This may assist the rod 72 in moving without requiring any lubricant between the rod 72 and static brake pad 14.
In the example shown in
When an abnormal braking operation occurs such that excessive heat is generated at the brake pads 14,18, heat from the static brake pad 14 is conducted to the thermal fuse 26. When the temperature of the thermal fuse 26 exceeds the predetermined temperature, T, the thermal fuse 26 loses structural integrity such that it no longer prevents movement of the piston 94 under action of the spring 92. The spring 92 therefore pushes the piston 94 generally radially inwardly and this moves the piston 94 away from its abutment with the static brake pad 14. The piston 94 may be pushed, for example, so as to come into abutment with the pin 96 that previously supported the thermal fuse 26 (i.e. before the thermal fuse 26 fused).
This then allows the static brake pad 14 (e.g. under loading forces from the movable brake pad 18, transmitted through the floating brake disk 16) to move axially away from the floating brake disk 16. In the same manner as described above in relation to
To assist the piston 94 in sliding relative to the static brake pad 14 under the bias of the spring 92, after the thermal fuse 26 has fused, the piston 94 may have a slightly slanted face in contact with the static brake pad 14 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 14. 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 14 away from the floating brake disk 16. This may assist the piston 94 in moving without requiring any lubricant between the piston 94 and static brake pad 14.
The reader will appreciate that in each design described herein above in relation to
In the arrangements shown in
In the example shown in
In the example shown in
In the example shown in
Any of the thermal fuse 26 compositions (e.g. a eutectic material, a CFRC material etc.) described hereinabove, may be used with any of the designs of brake 10,70,90 depicted in
While the above has been described in relation to a brake having a single movable brake pad and a single floating brake disk, the present arrangement could equally work with a stacked brake in which, there is the static brake pad and thermal fuse (i.e. as described above) at one end, and then a plurality of floating brake disks interleaved with a plurality of movable brake pads. At the opposite end, there is a final movable brake pad that is driven by biasing means, e.g. an actuator. When the movable brake pad driven by biasing means is driven in a direction towards the static brake pad, the plurality of floating brake disks and plurality of (other) movable brake pads are all squeezed together to brake rotation of the shaft. As above, if the temperature of the thermal fuse exceeds the predetermined temperature, it will fuse and the movable brake pad will be able to move axially away from the stack of movable brake pads/floating brake disks, so as disengage the brake.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21290056.7 | Sep 2021 | EP | regional |
