WO1991009233A1

WO1991009233A1 - Torque control device

Info

Publication number: WO1991009233A1
Application number: PCT/GB1990/001964
Authority: WO
Inventors: Trevor Charles Wells
Original assignee: Dunlop Limited
Priority date: 1989-12-16
Filing date: 1990-12-16
Publication date: 1991-06-27
Also published as: GB8928438D0; AU6976991A

Abstract

A torque control device such as an aircraft brake assembly comprises a plurality of discs of friction material such as a carbon-carbon composite material, some of said discs being stator discs and others being rotor discs with each rotor disc interposed between a pair of stator discs, and pressure means for axially compressing the assembly of substantially co-axially arranged discs for transmission of torque between the rotor and stator discs wherein a radially peripheral edge of a disc opposite a radially peripherally supported edge of that disc is of a non-cylindrical profile over an axially extending thickness which corresponds to at least a substantial part of the wear allowance of the disc.

Description

TORQUE CONTROL DEVICE

This invention relates to a torque control device such as a friction brake for the dissipation of energy or a friction clutch for the selective control and transmission of torque.

The invention relates in particular, although not exclusively, to torque control devices of the multi-disc type and comprising for example a plurality of discs of carbon-carbon composite material such as are well known for use in multi-disc aircraft brakes.

The use of carbon-carbon composite material is desirable for many applications because of the good ability of that material to withstand high operating temperatures and thermal shock. However, the material is expensive to produce and it is therefore important to minimise damage to discs both during initial manufacture and during subsequent usage.

Furthermore because of the cost of manufacture it is desirable to extend overall life by refurbishing fully worn discs by a method such as that described in U K Patent Application 2167821A. If during use discs have become damaged they are generally not suitable for refurbishment.

During manufacture damage often can occur at edges of the disc, where an inwardly or outwardly facing axially-extending and generally cylindrically shaped edge surface meets a radially inner or outer extremity of a disc wear face region, the damage in this area taking the form of edge chipping which reduces the available friction surface area of the disc and can cause other problems. This feature of chipping can be overcome or mitigated in many cases by providing small chamfers at the edge regions and these usually are effective in avoiding accidental chipping during handling of discs prior to and during brake assembly procedures.

During operation it is found that even though the wear (friction) faces of the discs may be planar when new, each disc necessarily embeds into the confronting face of an adjacent disc as wear occurs; shoulders develop at the boundaries between the radially outer drive areas and the friction face on rotors and the radially inner drive areas and the friction face on stators as shown by the cross-sectional views of Figures la and lb. Figure lji shows three stator discs 1 interleaved by two rotor discs 2 for rotation about an axis 3, with all the discs being new. Figure lb shows those discs in a worn condition in which shoulders 4 as described above have developed.

The shoulders would not present a problem if the rotor and stator discs always remained truly co- axially concentric. In practice, however, they run eccentrically because of the dimensional clearances which must be provided to allow movement of discs relative to associated wheel or axle structure, because of the need to allow for thermal movement and because of the structural distortion to which the brake structure is subject as the weight of the aircraft is transmitted to the wheels and as braking forces arise.

Local damage can therefore occur in drive areas at which, in the case of a vehicle or aircraft brake, torque is transmitted from a wheel or associated structure to rotor discs or at which torque is transmitted from stator discs to an associated structure within a brake or clutch. Damage in the drive areas is particularly likely if those areas experience high local forces, and especially high intermittent variations of force.

The conventional design of multi-disc brakes for aircraft is found commonly to result, after initial wear of discs, in the creation of high local forces and intermittent variation of force at the aforementioned drive areas.

Consequently it is desirable to provide a radial clearance between the shoulder on a rotor and the adjacent radially outer cylindrical edge of a stator and similarly to provide a radial clearance between the shoulder on a stator and the adjacent radially inner cylindrical edge of a rotor.

This clearance is commonly provided by using multi-disc brakes of a "grooved" kind in which the radially inner edge of a stator wear face or outer edge of a rotor wear face is bounded by an annular groove. Such grooves also restrict heat transmission or possibly minimise vibration difficulties.

Further during brake operation so-called wear profiles may develop at the radially inner and outer edges of the wear face(s) of each disc where it embeds into the confronting wear face of an adjacent disc. This wear pattern can arise in multi-disc brakes irrespective of whether or not they are of a grooved kind. In relation to brake discs of a grooved type this wear pattern is described and illustrated in more detail in the specification of U S Patent No. 4804071 which also postulates a reason for the formation of the non-planar wear surface.

In consequence of the eccentric motion of rotor discs relative to stator discs (such as arises when a brake is subject to the weight of an aircraft and the brake torque tube deflects), localised regions of a rotor wear face, adjacent the edges of that wear face when confronting a stator face of the type having an annular groove at a radially inner edge of the stator face, wear intermittently as they are loaded in compression for only part of each revolution of the rotor. This is shown by Figures 2a. and 2b_. Figure 2a_ shows a stator disc 1 aligned with a rotor disc 1 when unloaded (i e in the absence of externally applied forces). Each disc is provided with grooves 5 as described above. When the discs become displaced to lie eccentric relative to one another as shown in Figure 2b_ the region 6 of a rotor face is loaded only intermittently during relative rotation, it being compressed when at the region 6 to the left of the axis 3 and uncompressed at the region 6 to the right of axis 3. (Conversely, stator wear faces will not be subject to uniform wear because certain areas of stator wear faces, including specifically those confronting a grooved rotor face lie outside the continuously swept wear area and wear lips will therefore tend to form) . This is believed to contribute, at least after an initial wear of the discs, to the creation of the aforedescribed potentially damaging high local forces and intermittent variations of force at the rotor drive areas.

In an attempt to mitigate or overcome the problem of damage to the drive areas, and in particular though not exclusively of damage at the drive areas of discs in brake assemblies of the kind incorporating grooved type brake discs such as are referred to in the US patent mentioned above, it is taught by the present invention that the outer edge of a stator disc and/or the inner edge of a rotor disc adjacent a wear face shall be of a non-cylindrical profile, and typically of a chamfered form over an axially-extending thickness which corresponds to the whole or substantially the whole of the wear allowance (i e depth of allowable wear) of that wear face.

In a preferred embodiment of the invention the edge of a disc is chamfered such that the radial extent of the chamfer, between its radial position at zero wear and at the position of maximum allowable wear, is substantially equal to the eccentricity arising between adjacent rotor and stator discs in use of the brake assembly. It is believed that in consequence the usual undesirable tendency for lips of brake material to form in initially unswept areas is mitigated or overcome and that a favourable wear pattern created during the initial wear period perpetuates in the continuing presence of the chamfered surface of an adjacent disc as each disc is worn to its maximum wear allowance; the existence of a favourable wear pattern correspondingly results in avoidance or mitigation of potentially damaging high local forces and intermittent variation of force at the drive areas.

By this means, it is possible to combine the benefits of the chamfer (to reduce damage during manufacture) with the annular groove (to reduce damage to the drive areas arising from relative radial movement of the rotor and stator discs).

The chamfered surface of a disc, or disc of a brake assembly in accordance with the present invention may be rectilinear in cross-section, i e the chamfered surface may be of frusto-conical shape. Alternatively, for example, it may be curved in cross-section, to have either a concave or convex form. In the case of a frusto-conical chamfered surface preferably the included conical angle lies in the range 30° to 80° and more preferably in the range 40° to 70°.

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

Figure 3 is a longitudinal cross-sectional view of part of a conventional aircraft brake assembly;

Figure 4 is a cross-sectional view corresponding to that of Figure 3 of a brake disc for use in the assembly of Figure 3.

Figures 5a_ and 5b_ are cross-sectional views of brake discs in accordance with another embodiment of the invention; Figures 6a. and 6b_ are cross-sectional views of brake discs in accordance with yet another embodiment of the invention, and Figures 7a., 7b_ and 7_c are cross-sectional views of brake discs in accordance with a further embodiment of the invention. In Figure 3 there is shown part of a multi-disc aircraft brake assembly 10 comprising a plurality of carbon-carbon composite rotor discs 11 and double stator discs 12 (only one shown) each having a pair of annular and substantially planar wear faces 13. The discs 11,12 lie sandwiched between end, single stator discs 14,15 one 14 of which is supported axially by a thrust member 16 and the other 15 of which is movable axially by a series of circumferentially disposed hydraulic pistons 17 (one only shown) to compress the stack of discs for braking effect.

The stator discs are keyed in an arrangement not shown to the splines of the torque tube 18 and the rotor discs are keyed within a wheel support member (not shown) . Each wear face of a rotor or stator disc 11,12,14,15 is provided with an annular groove

20 to restrict thermal conduction away from the wear faces of the discs. The grooves are positioned in the region of the radially outer extremity of the wear face of a stator and the radially inner extremity of the wear face of a rotor.

Each rotor has a chamfered radially inner edge

21 (see Figure 4) and each stator has a chamfered radially outer edge 22 (see Figure 4) adjacent the or each wear face thereof. Each chamfered edge extends from a wear face of the unused discs for a distance at least equal to the wear allowance of that wear face, and each of the two chamfered faces of the double faced rotors 11 and stators 12 has a frusto-conical form the included angle of which is 50°.

It is believed that in the aforedescribed construction the chamfers significantly reduce the tendency for lips of material to develop in unswept areas and thus avoid the potentially damaging effects understood to arise from the origination of such lips. It is further believed that especially useful advantage arises when the invention is applied to discs made of a carbon-carbon composite material of a type which has anisotropic properties, for example discs manufactured from planar arrays of carbon fibres stacked one above another.

In a further embodiment of the invention the chamfered or like, non-cylindrical edge surface at the radially outer edge of a stator varies in cross- sectional profile between two positions angularly spaced about the stator. Thus the stator may have chamfers lying at an included angle of, say, 50° at a pair of diagonally opposite regions and between those regions the chamfer angle may vary progressively or otherwise to a different angle, for example 25° included conical angle. It will be appreciated therefore that the included angle ranges of 30° to 80° and 40° to 70° recited above do not require that angle feature to be present at all circumferential positions, at least in the case of a stator. For a rotor it is envisaged that normally the chamfer or like profile will be constant at all circumferential positions.

It is further envisaged by the present invention that in the case of a grooved type stator a radially outer portion of the groove wall may be chamfered or otherwise profiled in a manner as described herein in relation to the radially inner edge surface of a rotor at least so far as concerns the angle if not the axial extent of that surface. The radially inner wall of a groove in a rotor may be similarly shaped.

In the preceding description there has been described annular groove/chamfer combinations at the edges of wear faces in adjacent rotor and stator discs, and these combinations combine the practical advantages of reducing edge chipping of one disc (containing the chamfer) and drive damage to the other (containing the annular groove) during manufacture and subsequent service.

There is now described a further embodiment which addresses the matter of uneven wear of rotor and stator wear faces resulting from the eccentric positioning of rotor discs relative to the stator discs (as described above in relation to Figure 2).

Referring to Figure 5a. the drives on, and the bore 31 of, a stator disc 30 are positioned eccentrically with respect to the outer diameter of that disc 30, the annular groove 32 and/or any chamfer (not shown) therein. By this means it is possible to compensate for the eccentric rotor motion that occurs in service as apparent from Figure 5b_ which shows the rotor 33 displaced radially under load to an eccentric position relative to the stator 30 thereby to bring the rotor bore 34 concentric and aligned relative to the radially outer edge 35 of a stator groove 32.

During service the rotor is positioned eccentrically relative to the drives on the adjacent stator disc but as the latter are themselves already positioned eccentrically within the stator disc, the stator disc may be positioned so that the radially outer edges of the annular groove in the stator disc and the radially inner edge of the wear face of the adjacent rotor disc are substantially aligned during service. In the same way the radially inner edge of the annular groove in the rotor disc and the radially outer edge of the wear face of the adjacent stator disc are also substantially aligned during service.

In another embodiment (see Figures 6a_ and 6b , a rotor disc 40 having a frusto-conical/cylindrical radially inner edge 41 is positioned against a stator 42 having a frusto-conical/cylindrical radially outer edge 43 in which the bore 44 of the stator and the stator drives are positioned eccentrically in relation to the said outer edge and to annular grooves 45 within the stator faces. The radial width of the chamfers (the frusto-conical portions of the edge) the width of the groove and the eccentricity of the stator bore/drives are all equal and are also equal to the maximum eccentric movement of the rotor relative to the stator. Hence in service, the radially inner edge 46 of the rotot wear face will align with the radially outer edge 47 of the annular groove 45 in the stator.

In yet anotehr embodiment of the invention (see Figures 7a., 7k> and 7_jc) the stator drives and the stator bore 50 are again positioned eccentrically relative to the stator outer diameter 51, chamfers 52 and annular groove 53. In this embodiment the radial width of the chamfer 52 is equal to the eccentricity of the bore and both are equal to one half the maximum eccentric movement of the adjacent rotor 54. Figure 7ja shows the rotor 54 lying concentric with the bore 50 of the stator 55, Figure 7b_ shows the rotor 54 lying concentric with the annular groove 53 in a stator 55 and Figure 7_c shows the rotor radially displaced to a position of maximum eccentricity. In the condition of Figure lc_ the displacement of the stator bore relative to the rotor equals the radial width of the annular groove 53.

By means of this degree of eccentricity it is possible to restrict the maximum radial width of the unworn lands on the stator disc to be one half the width of the annular groove. This compares with a said radial land width which is one and a half times the width of the annular groove when the rotor and stator discs are manufactured to be wholly concentric. This reduction in said radial land width will in turn reduce local forces and intermittent variations of force at the rotor drive areas.

In addition, impact of the radially outer edge of the stator disc with the radially outer side wall of the annular groove in the adjacent rotor is prevented. Similarly impact of the radially inner edge of the rotor disc with the radially inner edge of the annular groove in the adjacent stator is prevented.

Claims

CLAIMS :

1. A torque control device comprising a plurality of discs of friction material, some of said discs being stator discs and others being rotor discs with each rotor disc interposed between a pair of stator discs, and pressure means for axially compressing the assembly of substantially co-axially arranged discs for transmission of torque between the rotor and stator discs wherein a radially peripheral edge of a disc opposite a radially peripherally supported edge of that disc is of a non-cylindrical profile over an axially extending thickness which corresponds to at least a substantial part of the wear allowance of the disc.

2. A torque control device according to claim 1 wherein the non-cylindrical profile is provided at the radially inner edge of a rotor disc.

3. A torque control device according to claim 1 or claim 2 wherein the non-cylindrical profile is provided at the radially outer edge of a stator disc.

4. A torque control device according to any one of the preceding claims wherein the non-cylindrical profile is provided by a chamfer.

5. A torque control device according to any one of the preceding claims and comprising a plurality of discs of carbon-carbon composite material.

6. A torque control device according to any one of the preceding claims wherein the edge of a disc is of a non-cylindrical profile selected such that the radial extent of that profile, between its radial position at zero wear and at the position of maximum allowable wear, is substantially equal to the maximum eccentricity arising between adjacent rotor and stator discs in use of the torque control device.

7. A torque control device according to any one of the preceding claims wherein the non-cylindrical profile is defined by a chamfer which is rectilinear in cross-section thereby to provide a chamfered edge portion of frusto-conical shape.

8. A torque control device according to claim 7 wherein the chamfered surface has an included conical angle which lies in the range 30° to 80°.

9. A torque control device according to claim 8 wherein said angle lies in the range 40° to 70°.

10. A torque control device according to any one of the preceding claims wherein the wear surface of a disc having a non-cylindrical edge profile adjacent that wear surface confronts a wear surface of a kind provided with an annular groove substantially concentric with that wear surface.

11. A torque control device according to claim 10 wherein that groove is arranged to restrict thermal conduction away from the wear surface.

12. A torque control device according to claim 10 or claim 11 wherein that groove is positioned in the region of a radially peripheral extremity of the confronting wear surface.

13. A torque control device according to any one of claims 10 to 12 wherein the groove has a groove wall of a non-cylindrical profile.

14. A torque control device according to claim 13 wherein the non-cylindrical profile of the groove wall is a profile as recited in any one of claims 1 to 9.

15. A torque control device according to any one of claims 10 to 14 wherein a stator groove lies concentric relative to the outer edge of the stator.

16. A torque control device according to any one of claims 10 to 15 wherein the stator bore lies eccentric relative to the outer edge of the stator.

17. A torque control device according to claim 16 wherein the stator bore is aligned with the bore of a rotor when the device is in an unloaded condition, not subject to externally applied forces.

18. A torque control device according to claim 16 or claim 17 wherein the eccentricity of the stator bore is substantially equal to one half the intended maximum relative eccentric movement of the adjacent rotor.

19. A torque control device according to claim 16, claim 17 or claim 18 wherein the bore of the rotor has a chamfer the radial width of which is equal to one half the intended maximum relative eccentric movement of the adjacent rotor.

20. A torque control device according to claim 19 wherein the radial width of said chamfer is substantially equal to the eccentricity of the stator bore relative to the outer edge of the stator.

21. A torque control device constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.