FRICTION DISK

Abstract

A disk having a first major surface and a second major surface, opposite the first, joined by a peripheral edge, at least one of the first and second major surfaces defining a friction surface configured to frictionally contact an opposing friction surface in a rotating system, and wherein a groove formation is provided on the friction surface(s), the groove formation being non-symmetrical with respect to the respective friction surface, preferably in the form of a spiral groove.

Claims

1. A disk having a first major surface and a second major surface, opposite the first, joined by a peripheral edge, at least one of the first and second major surfaces defining a friction surface configured to frictionally contact an opposing friction surface in a rotating system, and wherein a groove formation is provided on the friction surface(s), the groove formation being non-symmetrical with respect to the respective friction surface.

2. A disk as claimed in claim 1, wherein both of the first and the second major surfaces define a respective friction surface.

3. A disk as claimed in claim 1, where the groove formation is a spiral groove extending around and across the friction surface.

4. A disk as claimed in claim 1, wherein the groove formation extends over the entire friction surface.

5. A disk as claimed in claim 1, further comprising radial grooves extending radially across the friction surface and across the non-symmetrical groove formation.

6. A rotating system comprising: a disk having a first major surface and a second major surface, opposite the first, joined by a peripheral edge, at least one of the first and second major surfaces defining a friction surface configured to frictionally contact an opposing friction surface in a rotating system, and wherein a groove formation is provided on the friction surface(s), the groove formation being non-symmetrical with respect to the respective friction surface; and further component having a surface defining a second friction surface, there being relative rotation and frictional engagement between the first and second friction surfaces.

7. The rotating system of claim 6, wherein the at least one disk includes first and second disks in frictional engagement with friction surfaces of other components and wherein the first and second disks form a no-back system

8. The rotating system of claim 7, wherein the other components comprise ratchet wheels or screw shaft flanges.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Preferred embodiments will now be described by way of example only, with reference to the drawings.

[0021] FIG. 1 is a schematic view of a no-back system incorporating a disk according to this disclosure.

[0022] FIG. 2 is a frontal view of a disk according to the disclosure.

[0023] FIG. 3 is a side view of a disk according to the disclosure.

[0024] FIG. 4 is a perspective view of a disk according to the disclosure.

DETAILED DESCRIPTION

[0025] FIG. 1 shows a no-back brake system mounted on the shaft of an actuator screw such as a ball screw 15. This no-back system comprises two friction disks 21 rotationally and coaxially mounted about a collar or flange 20 around the screw shaft 15. The flange is preferable, but not essential. All that is required is a first friction surface with which a (second) friction surface of a friction disk 21 frictionally engages in operation. The disks may be made of carbon or carbon composite.

[0026] Two ratchet wheels 22 are also mounted rotatably and coaxially about the screw shaft, adjacent the friction disks 21. The ratchet wheels 22 cooperate with pawls 23 arranged to permit rotation of the ratchet wheels in one direction but not in an opposite direction.

[0027] In one example, to move a moveable element, a force is applied to the screw shaft 15. The no-back device provides a force resisting rotation of the screw shaft in a direction that would result in movement in one direction (e.g. the direction of aerodynamic force) whilst providing no force resisting rotation in the opposite direction.

[0028] When a force is applied in one direction (e.g. nose up), one surface of the first disk is a first friction surface in frictional engagement with the flange 20 providing a second friction surface and the other surface of the disk is in frictional engagement with the associated ratchet wheel. The other disk is freely rotatable. In another direction (e.g. nose down) the other disk is in frictional engagement with the flange and its associated ratchet wheel. In the following discussion and claims, the first friction surface is the disk friction surface being discussed and the second friction surface is the opposing surface with which it frictionally engages (e.g. ratchet wheel, flange).

[0029] The friction disks 21 comprise opposing major surfaces, providing friction surfaces, joined by a peripheral edge (FIG. 3) and have, on one or both of their friction surfaces, drainage grooves. The disks 21 are immersed in a viscous fluid e.g. oil and the coefficient of friction between the disk and the flange/ratchet wheel will vary during operation depending on various factors e.g. speed.

[0030] At the start of relative movement between the first and second friction surfaces, the coefficient of friction is high to compensate for a tangential force depending on the adhesion of the two surfaces, with little lubricant. As movement continues, sliding velocity increases and the coefficient of friction decreases rapidly with a small amount of lubricant.

[0031] The decrease in the coefficient of friction then accelerates with the sliding velocity to a lowest critical point where the system is in a mixed or heterogenous lubrication regime. Then, the coefficient of friction increases parabolically with respect to the sliding velocity in an established hydrodynamic regime. The change from the mixed to the hydrodynamic regime gives rise to the problem of loss of friction.

[0032] The actual details of the other components of the no-back system will not be described in further detail, as these can be any known system having opposing friction surfaces. One example is described in U.S. Pat. No. 6,109,415. The improvement resides in the form of the friction disks and disks modified according to this disclosure could be used in any known no-back systems of this type.

[0033] As indicated above, the friction disks are immersed in and operate in a bath of fluid such as oil or other viscous fluid, to provide lubrication between the first and second friction surfaces.

[0034] In earlier systems, a wedge or film of oil was formed between the disks, which was found to have an adverse effect on the coefficient of friction.

[0035] This has been resolved by forming, in or on at least one of the major friction surfaces of the disks, drainage grooves. It has been considered preferable for these grooves to be fine and closely spaced and to preferably have their terminal openings outside the friction zone. GB 1,084,958 teaches such drainage grooves.

[0036] It has also been discovered that the fluid deposit can be further reduced by providing a second set of grooves transverse to the first grooves (see, again, GB 1,084,958). An alternative pattern of drainage grooves is described in FR 2989060.

[0037] The inventors of the present disclosure have determined that the symmetric pattern of grooves in the known systems still result in a loss of surface friction and that surface friction is not, therefore, optimised, particularly during the hydrodynamic lubrication regime.

[0038] According to the present disclosure, and with reference to FIGS. 2 to 4, drainage grooves 30 are formed in or on a friction surface of a friction disk 21 in a non-symmetrical pattern, which results in more surface friction in one direction compared to another direction. The grooves 30 are preferably machined into the surface(s), but it is feasible that they could be formed in other ways.

[0039] Most preferably, the non-symmetrical groove pattern is formed as a spiral groove or several spirals around and across the friction surface. Most preferably, the spiral groove(s) covers the whole friction surfacei.e. extends all around and radially right across the disk as shown in FIGS. 2 to 4, starting at an innermost point 50 of the surface of the disk and extending in a spiral form outwards, around the disk, ending at an outermost edge 60 of the disk surface.

[0040] To further optimise surface friction, transverse or radially extending grooves 40 are provided across the friction surface of the disk and across the spiral groove 30 as shown.

[0041] Advantages are provided by a symmetrical groove pattern on either friction surface of the disk or on both friction surfaces of the disk.

[0042] Such drainage grooves have been found to optimise surface friction in systems where two disks have rotational frictional contact with opposing friction surfaces, such as, but not exclusively, in a no-back system.