This application claims priority to, and the benefit of, EP Patent Application No. 21461618.7, filed Nov. 11, 2022 and titled “CRUSHABLE BODY FOR POSITION ADJUSTMENT,” which is incorporated by reference herein in its entirety for all purposes
The following description relates to a crushable body used in a position adjustment assembly for example in a piston assembly with an adjuster assembly. The following description also relates to a piston assembly, an adjuster assembly, a cartridge for an adjuster assembly, a brake system, and a method of assembling a piston assembly.
Assemblies are known in various fields where a position of a moveable member needs to be adjusted due to changes in operation conditions or requirements and where the position adjustment is provided using a crushable body that, in certain operating conditions, is crushed to a shorter axial length which determines the position of the moveable member. One example of the use of such adjustment assemblies is in a brake system. Brake systems typically include friction elements that are brought into engagement with each other when a braking action is required to cause braking. The friction elements, which are typically friction discs, are selectively engaged and disengaged by use of one or more pistons. Such braking systems are known in many applications e.g. in machinery and also in vehicles and aircraft. Such multi-disc braking systems include a plurality of friction discs, also known as a heat sink, which are collectively operated to brake a rotating body such as a wheel e.g. a wheel on the landing gear of an aircraft.
During a braking action, wear of the surfaces of friction elements may occur over time. Such wear of the friction discs or other elements causes an increased clearance between friction surfaces of the friction elements when the brake system is disengaged. This increased clearance results in a longer stroke length of a piston or pistons required to engage the brake system, and therefore a longer engagement time.
To compensate for the increased clearance periodic manual adjustment of the brake system may be undertaken. Automatic adjusters are also known. One such mechanical automatic adjuster utilizes a tube on the piston and a tube expander element on a rod extending from the housing and through a head of the piston to be received in the tube. As the stroke length of the piston increases, the tube expander element attached to the housing is drawn axially along the bore of the tube and radially outwardly expands the tube to establish a new retracted position for the piston. Such adjuster assemblies may also be found in other applications. Another solution is to use a crushable tube to adjust the stroke length as the brake components wear. The tube is made of a material that crushes under force, but does not return to its original length when the force is removed. Such tubes, however, have been found to have an irregular radial inner and outer diameter when crushed. This irregular shape can result in the crushed tube interfering with other parts of the overall system where the assembly is used e.g., in a brake system, the spring guide and the piston. The forces generated by the crushed tube when in such an irregular crushed shape may also be irregular.
According to an aspect of the disclosure, there is provided a crushable body for use in a position adjustment assembly, the crushable body comprising a thin-walled tube comprising a corrugated crushable body portion between two flat end portions, the corrugated crushable body portion configured to form a crushed body of reduced axial length compared to the axial length of the tube when a predetermined force is applied to the tube. In a particular aspect, there is provided a piston assembly comprising a housing defining a piston cylinder; a piston axially moveable within the cylinder responsive to a force applied to an end of the piston; and an adjuster assembly including a piston stroke limiter configured to limit the length of a return stroke of the piston from an extended stroke position, with respect to the cylinder, and a retracted stroke position, with respect to the cylinder; and a crushable body acting between the piston and the piston stroke limiter, the crushable body comprising a corrugated thin walled sleeve extending coaxially with the piston and being arranged to reduce in axial length when a length of an extension stroke exceeds a length of a retraction stroke to set the axial position of the piston stroke limiter to maintain the length of the return stroke.
The crushable body may be between the piston and the piston stroke limiter.
The crushable body may be a sleeve surrounding at least part of the piston.
The crushable body may be in the piston cylinder.
Expansion of the crushable body in a radial direction may be constrained by the piston. Expansion of the crushable body in a radial direction may be constrained by the housing.
The crushable body may be arranged to progressively deform over a plurality of stroke cycles of the piston.
The piston assembly may comprise an extension stroke stop and a retraction stroke stop, wherein the piston stroke limiter comprises a limiting member movable in an axial direction between the extension stroke stop and the retraction stroke stop.
The extension stroke stop and the retraction stroke stop may be formed by the housing.
The piston may extend through the crushable body
The piston assembly may comprise a retraction biasing member arranged to bias the piston stroke limiter from an extended position to a retracted position.
The retraction biasing member may be a helical compression spring.
According to an aspect of the disclosure, there is provided an adjuster assembly for maintaining a release clearance between selectively engageable friction parts to compensate for wear in the frictional parts, the assembly comprising a stroke limiter configured to limit the length of a stroke of an extendable member between an extended stroke position and a retracted stroke position; and a crushable body comprising a corrugated thin walled tube arranged to act between the piston and the piston stroke limiter and configured to be at least partially crushed to reduce the axial length of the crushable body in response to an extension stroke movement due to wear of the frictional parts exceeding a retraction stroke movement.
According to an aspect of the disclosure, there is provided a cartridge for an adjuster assembly of a piston assembly comprising a crushable body in the form of a corrugated thin walled tube arranged to reduce in axial length when compressed in an axial direction.
According to an aspect of the disclosure, there is provided a piston assembly comprising a cartridge for an adjuster assembly with a crushable body in the form of a corrugated thin walled tube arranged to reduce in axial length when compressed in an axial direction
According to an aspect of the disclosure, there is provided a brake system for an aircraft comprising at least one of a piston assembly as recited above, an adjuster assembly as recited above, and a cartridge as recited above.
According to an aspect of the disclosure, there is provided a method of assembling a piston assembly comprising: receiving a piston in a piston cylinder of a housing through a first side of the housing in a first direction; receiving an adjuster assembly comprising a crushable body in the form of a corrugated thin walled tube on the piston in the first direction; and enclosing the piston cylinder at the first side.
The subject matter, which is regarded as the disclosure, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings. The description relates to the use of the crushable body of the disclosure in an adjuster of a brake system. The crushable body may, however, have many other applications.
With reference to
The brake system 10 is operable to restrict rotation of a rotating body such as a wheel. In the example shown, the rotating body is an aircraft wheel 11, but the brake system of this disclosure may have other applications. The wheel 11 includes a series of axially extending rotor splines 13 (one shown). Wheel 11 is supported for rotation about an axle 12 by bearings 14. Axle 12 defines an axis A of the brake system 10 and of various components thereof. Reference to the terms axis and axial may include an axis of rotation defined by axle 12 or a dimension parallel to such axis.
The brake assembly 20 includes pressure plate 21, flange 22, torque tube 23, and end plate 24. Torque tube 23 may be an elongated annular structure that includes a reaction plate 25 and a series of axially extending stator splines 26 (one shown). The brake assembly 20 also includes a plurality of friction disks 27. These comprise at least one non-rotatable friction disk (stator) 28, and at least one rotatable friction disk (rotor) 29. The friction disks 27 each include an attachment structure 27a.
The flange 22 is fixedly mounted to the axle 12. The pressure plate 21 is also non-rotatable. The piston assemblies 30 are connected to the flange 22 at circumferentially spaced positions around the flange 22. The piston assemblies 30 face axially toward the wheel 10 and contact a side of pressure plate 21. The piston assemblies 30 are hydraulically powered, however they may be powered mechanically, electrically, or pneumatically. The piston assemblies 30 are configured to exert a force on the friction disks 27 towards reaction plate 25. Actuation of the piston assemblies 30 causes the rotors 29 and stators 28 to be pressed together between the pressure plate 21 and the end plate 24. Although the piston assemblies 20 are shown as part of brake system 10, it is contemplated that the piston assemblies, as disclosed herein, may be employed in a variety of other systems. For example, piston assemblies 30 may be employed in a multi-disk clutch system.
One of the piston assemblies 30 is described in further detail below with reference to
The piston housing 32 includes a main housing body 33 and a locker 34. The locker 34 is secured to an open end of the housing 32 to close the end.
The housing 32 defines a piston cylinder and defines an axis B of the piston assembly 30. The piston 31 is translatable in a longitudinal direction along axis B in the piston cylinder.
The piston 31 has a piston head 36 and a piston rod 37. The piston rod 37 extends from the piston head 36. The piston rod 37 is elongate and extends from the housing 32. A distal end 38 of the piston rod 37 is attached to a disc 39, also known as an insulator, by means of an insulator support 40 on the distal end 38 of the piston rod 37. The disc 39 is secured to the end of the distal end 38 by the insulator support 40 and moves together with the piston rod 37. The insulator is connected to the insulator support by a fastener such as a clip. The disc 39 comprises an engaging surface 39a. The engaging surface 39a is arranged to move into and out of engagement with the friction brake assembly 20. The engaging surface 39a of the disc 39 is arranged to contact and bias pressure plate 21 when moved into engagement in dependence on operation of piston assembly 30.
As is known in the art, movement of the piston relative to the housing is caused by application of a brake or working fluid, for example hydraulic fluid, to the piston head 36. A fluid supply (not shown) is arranged to supply working fluid to the volume.
A seal 41 extends around the piston head 36. The seal 41 is a slidable seal which is configured to slide along and seal with the interior wall of the housing 32. The seal 41 is shown in the example as comprising an o-ring, however alternative sealing arrangements may be provided. The arrangement of the piston 31 and the adjuster assembly 50 with the housing 32 mean that a single sealing arrangement provided by seal 41 is required to fluidly seal between the adjuster assembly 50 and the cavity (not shown) where the pressurized fluid is applied to the piston head. As such, a simple sealing configuration of the piston assembly 30 is provided. Working fluid in the cavity is prevented from flowing to other parts of the assembly by the seal 41.
The piston assembly 30 includes the adjustor assembly 50. The adjustor assembly 50 is received in the housing 32. The adjuster assembly 50 extends in an axial direction. The adjuster assembly 50 includes a spring 52, a spring guide 53, a crushable body 60 and a piston stroke limiter 70 defined at the end of the spring guide. The spring 52 is a biasing member which is arranged to bias the piston 31 into a retracted stroke position, for example as shown in
The spring 52 is a compressive helical spring. The housing 32 defines an annular chamber 54 around the piston that extends in a longitudinal direction about axis B. The annular chamber 54 is accessible at the open end of the housing when the locker 34 is removed. The spring 52 is received in the annular chamber 53 and is retain by the spring guide 53.
The crushable body 60 will now be described in detail with reference to
The crushable body 60 extends in an axial direction in the housing 32. The crushable body 60 has a first end 62 and a second end 63. The thin walled tube 61 is collapsible in an axial direction when the crushable body 60 is compressed in the axial direction between the first and second ends 62, 63. The crushable body 60 defines a tubular arrangement through which the piston rod 37 is extendible.
The term thin walled is used herein to describe elements that have a small thickness in comparison to other dimensions such as length and width. Such elements are deformable in a controlled manner when a compressive force is applied to opposing, distal ends of the element. It will be understood that the thickness of the wall will be dependent on the compressive force required to crush the body 60 as well as the dimensions of the corrugations. In the present arrangement, it is anticipated that the thickness of the walls of the crushable member is in the range of approximately 0.1 mm-0.5 mm (0.004-0.02 inch). The walls may be a sheet material, with a thickness of less than approximately 6 mm (0.24 inch). Other dimensions are also possible provided the crushing performance is such as to maintain a substantially regular shape. It will also be understood that the material of the crushable body 60 may differ, in the present arrangement the crushable body 60 is formed from a ductile metal sheet arrangement, such as stainless steel, for example. Other materials include plastics, composites and foam.
A crushable body is intended to mean a body which is able to reduce in axial length when a compressive force is applied to the crushable body in the axial direction. Upon application of a compressive force in the axial direction above a predetermined value, the body reduces in axial length in a controlled manner, but does not collapse. Such an arrangement is non-resilient, that is, upon release of or reduction of the compressive force on the crushable body, the body 60 does not substantially expand in axial length. The predetermined force that causes crushing is largely independent of the deformed shape of the crushable tube—i.e. its shape at any stage of crushing, and is, therefore as independent of the number of times the axial length has previously been adjusted. It is also desirable that this force value is independent of temperature to avoid loss of adjustment force at high temperatures or to avoid variations in adjustment force due to different temperatures.
The crushable body 60 and the spring guide 53 defining the piston stroke limiter 70 are housed in the housing 32.
The piston stroke limiter 70 transfers the force applied by the piston and the spring 52 between the components.
The limiting member 72 is received in the housing between a retraction stroke stop 76 and an extension stroke stop 77. The retraction and extension stroke stops 76, 77 limit the axial movement of the piston stroke limiter 70. The retraction stroke stop 76 and the extension stroke stop 77 are spaced apart from each other in the axial direction. The spacing, together with the thickness of the spring guide 53 defines the stroke length of the piston stroke limiter 70. It will be understood that the configuration of the stoke stops 76, 77 may differ.
In a neutral condition, as shown in
In use, the piston assembly 30 is assembled with the friction brake assembly 20. The disc 39 is disposed adjacent to but spaced from the pressure plate 21 as shown in
Operation of the piston assembly 30 will now be described briefly. The piston 31 is initially in its neutral position, as shown in
Upon actuation of the piston assembly 30 (
When the actuation of the friction brake assembly 20 is no longer required, the actuating force applied by the working fluid supply on the piston 31 is removed. As such, the biasing force of the spring 52 exceeds the actuating force applied on the piston 31 and the piston 31 is urged to move from its extended stroke position to the retracted stroke position. Such stroke actions may be performed in a plurality of cycles.
As the components of the friction brake assembly wear, such wear is required to be compensated in order to maintain the length of the piston stroke over repeated cycles, and in particular to maintain the release clearance irrespective of the extent of the wear. When such wear occurs, initially the piston 31 will move from its retracted stroke position when pressure is applied and overcomes the biasing force of the spring 52 (2b,
If wear has occurred then the actuating stroke length is greater than the stroke length of the piston stroke limiter 70. When this occurs, the actuating force applied to the piston increases and applies a compressive force on the crushable body 60 above a predetermined crush limit between the piston head and the piston abutting the extension stroke stop 77. When this force exceeds the resistance to crushing of the crushable body 60 (
In the crushed state, the crushable tube 60 transfers the whole load 3 to the locker (load 4).
Upon release of the actuating force on the piston 31, then the biasing force of the spring 52 exceeds the actuating force and urges the piston stroke limiter 70, the crushable body 60 and piston 31 away from the extended stroke position, into the retracted stroke position. As the crushable body 60 is non-resilient, then the reduced axial length of the crushable body 60 is maintained. As such, the release clearance is defined by the movement of the piston from contact with the extension stroke stop 77 to contact with the retraction stroke stop 76. As such, the release clearance in the retracted stroke positon is maintained. The adjustment gap corresponds to the release clearance.
Upon continued operating cycles of the piston assembly 30, and therefore the brake system 10, wear of the discs of the friction brake assembly 20 continues. Upon each cycle, the compression of the crushable body 60 in the axial direction, and therefore the reduction in the axial length of the crushable body 60 corresponds to the wear of the friction brake assembly 20. The prescribed clearance is reestablished upon return of the piston assembly 30 to the retracted stroke position. Such continued wear causes the piston 31 to telescope from the housing 32 relative to adjuster assembly 50 and the piston stroke limiter 70 in which the release clearance is maintained in the retracted stroke position, and the disc 39 engages with the friction brake assembly 20 in the extended stroke position.
The crushable body 60, best seen in different degrees of being crushed in
The behavior of the corrugated crushable tube of this disclosure can be compared to that of a non-corrugated tube by viewing the load vs. axial length plots of
The fully crushed crushable body 60 prevents under adjustment of fully worn brakes. The adjustment force increases in the event of over-adjustment of the system. To replace the fully crushed crushable body 60, the disc 39, locker 34, spring guide 53 and used crushable body 60 are all removed from the same end of the piston assembly 30 without the need to remove the piston 31 from the housing 32. As such, ease of maintenance of the piston assembly 30 is maximized. The number of parts of the system is minimized.
While the disclosure is provided in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the claims. Additionally, while various embodiments of the disclosure have been described, it is to be understood that the exemplary embodiment(s) may include only some of the described exemplary aspects. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
Number | Date | Country | Kind |
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21461618 | Nov 2021 | WO | international |