POLYMERIC TRANSMISSION SYSTEM COMPONENTS

SUMMARY OF THE INVENTION

The present invention relates to polymeric transmission system components and methods for their manufacture.

BACKGROUND TO THE INVENTION

Vehicle transmission systems comprising input and output shafts, parallel axis gear sets, gear selectors, synchronisers, plates, discs, clutches and the likes are well known in the art.

Transmission systems may be controlled manually by the driver or by automatic or semi-automatic operation by an electro-hydraulic or electro-mechanical actuation system.

One such transmission system is the conventional automotive gearbox that employs a synchroniser to allow a change of gear ratio within the transmission by synchronising the speed of the input side of the gearbox to that of the new gear set while the drive from the engine is disconnected via the main vehicle clutch.

A synchroniser is actuated via the linear axial movement of a gear change fork, connected either by a mechanical linkage to a gear lever in a manual transmission, or to an electrically controlled actuator in an automated or dual clutch transmission (DCT).

Synchronisers use a low capacity wet cone clutch system to perform the speed synchronisation, before engaging a robust dog clutch to allow transmission of drive in the new gear once the vehicle's clutch is re-engaged. The wet cone clutch that performs the speed synchronisation is defined by the conical surface of the interior of a synchroniser (or "blocking") ring and a conical counter surface provided on the gear that is to be engaged.

Movement of the synchroniser ring brings its conical internal surface into frictional contact with the matched counter surface of the gear that is to be engaged, while it rotates with a speed difference proportional to the step in gear ratio. The internal or external surface of the synchroniser ring is optimised for operation as a lubricated (wet) friction clutch, both in terms of material selection and surface structure. Synchroniser or "blocking" rings are typically be manufactured from brass or steel, and in the case of the latter may have a supplementary friction lining surface applied such as molybdenum, sintered brass, or carbon fibre.

More recently, synchroniser rings formed from polymeric materials have become know in the art. US 2015/0211585 A1 discloses a transmission gear synchroniser ring moulded from a thermoplastic material.

A drawback of known polymeric synchroniser rings is the negative effect of oil lubrication on the frictional performance of the wet friction clutch during the clutch phase of the synchronisation process.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a transmission component comprising a friction surface formed from a composition comprising a polymeric material, wherein the friction surface is provided with a roughened surface texture.

Optionally, the transmission component and the friction surface are of unitary construction formed from the composition comprising a polymeric material. Optionally, the friction surface is a separate part or parts that is/are affixed to the transmission component.

Optionally, the transmission component is a synchroniser system, wherein the friction surface is an inner surface of said synchroniser system. Preferably, the friction surface is a conical inner surface of said synchroniser ring. Said component may be an intermediate ring in, for example, a dual or triple cone synchroniser system. Said component may be an inner cone or ring, in for example, a dual or triple cone synchroniser system. Said component may be a blocking ring, in for example, a single, a dual or triple cone synchroniser system. Optionally, the blocking ring further comprises an outer surface having a plurality of clutch teeth disposed circumferentially about a circumference thereof. Optionally, the transmission component is a friction plate of a wet clutch. Preferably, the roughened surface texture is a random surface texture, preferably with substantially no line of symmetry. Most preferably, the roughened surface texture is a grit-blasted surface texture. The grit blasting process removes material from the surface of the component. Such a process is in contrast to a coating process in which new material is added to the existing surface. Optionally, the roughened surface texture is formed by one or more of a shot-peening, laser etching, chemical etching, acid etching. It will be appreciated that the term "grit blasted surface texture" describes a roughened surface texture formed through blasting an abrasive media onto the friction surface.

Optionally, the roughened surface texture is formed directly on the friction surface.

Optionally, the roughened surface texture is formed indirectly on the friction surface, for example via a corresponding roughened surface impression formed on a cavity of a mould within which the friction surface and/or transmission component comprising said friction surface is formed.

Optionally, the roughened surface texture has a minimum arithmetical mean height (Sa) less than 100 μηι. Preferably, said surface texture has a minimum arithmetical mean height (Sa) less than 50 μηι. More preferably, the roughened surface texture has a minimum arithmetical mean height (Sa) less than 20 μηι. Optionally, the roughened surface texture has a minimum arithmetical mean height (Sa) greater than 1 μηι. Optionally, the roughened surface texture has a maximum arithmetical mean height (Sa) in the range 4 to 12 μηι. Optionally, the roughened surface texture has a maximum arithmetical mean height (Sa) in the range 6 to 30 μηι.

Optionally, the roughened surface texture has a minimum height (Sz) less than 200 μηι. Optionally, the roughened surface texture has a minimum height (Sz) greater than 2 μηι. Optionally, the roughened surface texture has a minimum height (Sz) in the range 39 to 150 μηι. In a most preferred embodiment, the roughened surface texture has a minimum height (Sz) in the range 80 to 150 μηι.

Optionally, the roughened surface texture has a minimum core roughness depth (Sk) less than 60 μηι. Preferably, the roughened surface texture has a minimum core roughness depth (Sk) greater than 1 μηι. Preferably, the roughened surface texture has a minimum core roughness depth (Sk) in the range 1 to 55 μηι. More preferably, the roughened surface texture has a minimum core roughness depth (Sk) in the range 10 to 55 μηι.Ιη a most preferred embodiment, the roughened surface texture has a maximum core roughness depth (Sk) in the range 36 to 55 μηι.

In a preferred embodiment, the roughened surface texture has an arithmetical mean height (Sa) in the range 10 to 25 μηι. In a most preferred embodiment, said mean height (Sa) is in the range 12 to 20 μηι. Advantageously, the roughened surface texture increases the frictional coefficient of an otherwise smooth friction surface.

Optionally, the coefficient of friction of the friction surface comprising the roughened surface texture is less than 0.15. Optionally, the coefficient of friction of the friction surface comprising the roughened surface texture is in the range 0.09 to 0.15. In a most preferred arrangement, the coefficient of friction of the friction surface comprising the roughened surface texture is approximately 0.1.

Optionally, the friction surface comprises a plurality of raised formations formed thereon, the roughened surface texture being formed upon said raised formations. Optionally, the raised formations are defined by a plurality of recesses or recessed regions formed in the friction surface. Forming of the raised formations may be during moulding of the friction surface, or post moulding. Optionally, the raised formations are arranged in a regularly repeating pattern. The pattern may have at least one line of symmetry. Optionally, the raised formations have a height less than 3 mm. Optionally, the raised formations have a height in the range of 0.05 to 0.2 mm. Optionally, the raised formations have a width less than 3 mm. Optionally, the raised formations have a width in the range of 0.05 to 3 mm. Optionally, the raised formations are spaced apart at a distance of 0.05 to 3 mm.

Optionally, the raised formations define at least one groove, most preferably a plurality of grooves, preferably extending substantially across the width of the friction surface. Said grooves may be operable to enable fluid flow to promote cooling of the friction surface during operation. Optionally, the raised formations may be cubic, cuboid, parallelepiped, or cylindrical in shape.

Conveniently, the raised formations and the corresponding recesses of the friction surface augment the breaking of the oil film layer formed at the interface of the friction surface and the conical counter surface provided on a gear that is to be engaged in use.

Advantageously, in combination with the roughened surface texture, the raised formations may augment the increased frictional coefficient of the friction surface.

Optionally, the polymeric material is a polyaryletherketone (PAEK) polymer having a repeat unit of formula (I)

Formula (I) where t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2. Said polyaryletherketone suitably includes at least 90, 95 or 99 mol % of repeat unit of formula I.

Said polyaryletherketone preferably consists essentially of a repeat unit of formula I . Preferred polymeric materials comprise (especially consist essentially of) a said repeat unit wherein t1=1 , v1 =0 and w1 =0; t1 =0, v1 =0 and w1 =0; t1 =0, w1 =1 , v1=2; or t1=0, v1 =1 and w1=0. More preferred comprise (especially consist essentially of) a said repeat unit wherein t1 =1 , v1 =0 and w1 =0; or t1 =0, v1 =0 and w1 =0. The most preferred comprises (especially consists essentially of) a said repeat unit wherein t1=1 , v1 =0 and w1 =0.

In preferred embodiments, said polymeric material is selected from polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone and polyetherketoneketone. In a more preferred embodiment, said polymeric material is polyetherketone or PEEK.

Said polyaryletherketone suitably has a melt viscosity (MV) of at least 0.06 kNsm ^"2 , preferably has a MV of at least 0.09 kNsm ^"2 , more preferably at least 0.12 kNsm ^"2 . Said polyaryletherketone may have a MV of less than 1.00 kNsm ^"2 , preferably less than 0.5 kNsm ^"2 . Said polyaryletherketone may have a MV in the range 0.09 to 0.5 kNsm ^"2 , preferably in the range 0.1 to 0.45 kNsm ^"2 . An MV of 0.45 kNsm ^"2 has been found to be particularly advantageous. MV is suitably measured using capillary rheometry operating at 400°C at a shear rate of 1000s ^"1 using a tungsten carbide die, 0.5mmx3.175mm.

Said polyaryletherketone may be amorphous or semi-crystalline. It is preferably crystallisable. It is preferably semi-crystalline. The level and extent of crystallinity in a polymer is preferably measured by wide angle X-ray diffraction (also referred to as Wide Angle X-ray Scattering or WAXS), for example as described by Blundell and Osborn (Polymer 24, 953, 1983). Alternatively, crystallinity may be assessed by Differential Scanning Calorimetry (DSC). The level of crystallinity of said polyaryletherketone may be at least 1 %, suitably at least 3%, preferably at least 5% and more preferably at least 10%. In especially preferred embodiments, the crystallinity may be greater than 25%. It may be less than 50% or less than 40%, preferably 30%. The main peak of the melting endotherm (Tm) of said polyaryletherketone (if crystalline) may be at least 300°C.

Optionally, the PEEK is carbon-fibre reinforced PEEK. Optionally, the polymeric material, preferably PEEK, includes up to 60wt%, up to 50wt%, up to 40wt%, up to 30wt% of carbon fibres, up to 20wt% of carbon fibres. In a preferred embodiment said material comprises 40wt%, most preferably 30wt% of carbon fibre. In a preferred embodiment, the polymeric material is PEEK, preferably having an MV of 0.45 kNsm ^"2 comprising 30wt%, carbon fibres.

In an alternative embodiment, the polymeric material may have a repeat unit of formula -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety wherein the repeat units I and II are in the relative molar properties l:ll of from 65:35 to 95:5; and wherein log™ (X%) > 1.50 - 0.26 MV; wherein X% refers to the % crystallinity measured by differential scanning calorimetry as described in Example 31 and MV refers to the melt viscosity measured capillary rheometry operating at 340°C at a shear rate of 1000s ^"1 using a tungsten carbide die, 0.5mm x 3.175mm as described in Example 30 of WO2014/207458 which is herein incorporated by reference.

In an aspect of the invention there is provided a method of manufacture of a friction surface of a transmission component, the friction surface formed from a composition comprising a polymeric material, comprising the steps of:

(a) providing a mould tool having a mould cavity which defines the friction surface of said transmission component;

(b) forming the friction surface by introducing a molten composition polymeric material into the mould tool cavity;

(c) removing the moulded part from the mould tool; and

(d) forming a roughened surface texture on the friction surface. Optionally, the mould cavity provided in step (a) also defines a friction component such that the friction component and the friction surface of said component are formed as a unitary construction from the composition of polymeric material. Optionally, the mould cavity provided in step (a) accommodates a friction component that is inserted into the mould before step (b) such that the friction component and the polymeric friction surface are co-moulded during step (b).

Optionally, the step (d) of forming a roughening surface texture on friction surface comprises blasting the friction surface with an abrasive media.

Optionally, the polymeric material is a polyaryletherketone (PAEK) polymer. Optionally, the polymeric material is a polyetheretherketone (PEEK) polymer as hereinbefore described. Optionally, the PEEK is carbon-fibre reinforced PEEK. In a most preferred embodiment, the polymeric material is PEEK comprising 30wt%, carbon fibres.

In an aspect of the invention there is provided a method of manufacture of a friction surface of a transmission component, the friction surface formed from a composition comprising a polymeric material, comprising the steps of

(a) providing a mould tool having a mould cavity which defines the friction surface of said transmission component;

(b) forming the friction surface by introducing a molten composition polymeric material into the mould tool cavity; and

(c) removing the moulded part from the mould tool; wherein at least a portion of the mould cavity is provided with a roughened surface impression formed thereon such that the roughened surface texture is formed into the friction surface during step (b).

Optionally, the mould cavity provided in step (a) also defines a friction component such that the friction component and the friction surface of said component are formed as a unitary construction from the composition of polymeric material. Optionally, the mould cavity provided in step (a) accommodates a friction component that is inserted into the mould before step (b) such that the friction component and the polymeric friction surface are co-moulded during step (b). Optionally, the polymeric material is a polyaryletherketone (PAEK), preferably a PEEK polymer. In a most preferred embodiment, the polymeric material is PEEK comprising 40wt%, most preferable 30wt% carbon fibres.

In accordance with an aspect of the invention there is provided a transmission system comprising a transmission component having a friction surface formed from a composition comprising a polymeric material, wherein the friction surface is provided with a roughened surface texture. Optionally, the polymeric material is a polyaryletherketone (PAEK), preferably a PEEK polymer. In a most preferred embodiment, the polymeric material is PEEK comprising 40wt%, most preferably 30wt% carbon fibres,

In a further aspect of the invention, there is provided the use of polyaryletherketone (PAEK) polymer in the manufacture of the friction surface of a transmission component wherein the friction surface comprises a roughened surface texture. Optionally, the polymeric material is a polyaryletherketone (PAEK), preferably a PEEK polymer. In a most preferred embodiment, the polymeric material is PEEK comprising 40wt%, most preferably 30wt% carbon fibres. The polymeric material may comprise PEEK/PEDEK

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination. Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

Language such as "including", "comprising", "having", "containing", or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word "comprise" or variations thereof such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words "typically" or "optionally" are to be understood as being intended to indicate optional or nonessential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic exploded perspective view of an exemplary transmission gear synchronizer system; Figure 2 is a detailed view of a synchroniser ring in accordance with the invention.

Figures 3a and 3b are a schematic exploded perspective and cross-section views of an exemplary multi-plate wet clutch transmission;

Figure 4 is a schematic diagram showing a friction plate for a wet clutch in accordance with the invention; Figures 5a to 5p are schematic illustrations showing raised formations of a friction surface in accordance with the invention;

Figure 6a is a schematic cross-section of an area of a friction surface comprising raised formations in accordance with the invention;

Figure 6b is a detailed view a portion of a friction surface of a synchroniser ring having raised formations which define a plurality of axially aligned grooves;

Figure 7a is a is a detailed view of a portion of a friction surface of a synchroniser ring formed from a composition comprising a polymeric material and having a coarse roughened surface texture in accordance with the invention;

Figures 7b, 7c and 7d are surface topography images of exemplary coarse, medium and fine roughened surface textures, respectively;

Figure 8a is a table of typical mechanical properties of a range of carbon fibre reinforced polyetheretherketone compounds; Figure 8b is a graph showing the typical final carbon fibre length of the carbon fibre reinforced polyetheretherketone after processing;

Figure 9 is a table showing roughness data in relation to the surface topographies of Figures 7b, 7c and 7d;

Figure 10 is a graph shown the relative increase in coefficient of friction of sample discs of 30% w/w carbon fibre reinforced PEEK having coarse, medium and fine roughened surface textures;

Figure 11 is a table showing velocity over pressure load range derived from test of a synchroniser ring having a carbon fibre reinforced PEEK friction surface in accordance with the invention;

Figures 12 and 13 are graphs showing the comparative results of coefficient of friction tests;

Figure 14 is a graph showing a comparison of the effects of the relative melt viscosity on the coefficient of friction performance of coarse roughened carbon fibre reinforced PEEK surface texture friction surfaces; and

Figure 15 is a graph comparing average overall wear test coefficient of friction performance data of coarse roughened carbon fibre reinforced PEEK friction surfaces formed from a range of PEEK polymer compositions having various weight percentages of carbon fibre reinforcement and with alternative melt viscosities.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figure 1 , there is shown an exemplary transmission synchroniser system 1 of a vehicle gearbox comprising a synchroniser hub or body 2, a synchroniser sleeve 4, a synchroniser ring 6 and a gear 8 which is mounted to a shaft 5 via one or more needle bearing races 7.

Synchroniser ring 6 comprises an outer surface 61 around which a plurality of clutch teeth 63 circumferentially disposed, and a conical inner surface 62. In operation, the synchroniser sleeve 4 is moved axially by a gear change fork (not shown) which engages with an annular grove 41 extending around the synchroniser sleeve 4. Initial movement of the synchroniser sleeve 4 transfers an axial load to the synchroniser (or 'blocking') ring 6 via a plurality of strut detents 20 which are located within detents 21 provided on the synchroniser hub and are biased radially outwardly by means of compression springs 22. The synchroniser ring 6 is moved axially by the synchroniser sleeve 4 so that its conical internal surface 62 is brought into contact with a friction cone 81 provided on the gear 8 to be engaged.

The speed difference, and frictional torque generated at this cone interface of the synchroniser ring 6 and the gear 8 causes the synchroniser ring 6 to be rotated relative to the synchroniser hub 2 within an allowable backlash that is afforded by the specific design of the respective parts. Rotation of the synchroniser ring 6 causes its teeth 63 to become misaligned with internal teeth 42 provided on the synchroniser sleeve 4 with the effect that as the axial load is increased and the strut detents 20 are overcome, the chamfered leading edges of the synchroniser sleeve 4 teeth make contact with similarly chamfered edges 631 of the synchroniser ring teeth 63 (Figure 2). In this position the synchroniser sleeve 4 is prevented (baulked) from further axial movement for as long as a torque is being generated by the rotational friction at the cone clutch interface of the of the synchroniser ring 6 and the gear 8.

The geometry of both the cone clutch and the respective synchroniser sleeve teeth 42 and synchroniser ring teeth 63 is optimised to ensure that the indexing torque at the teeth contact, generated by the applied axial load on the sleeve and the angle of the chamfers, cannot exceed the cone clutch torque until the cone clutch ceases to generate torque by virtue of the speed difference between the synchroniser ring 6 and the gear 8 decaying to zero.

Once the relative speed of the synchroniser ring 6 and the gear 8 has been reduced to close to zero, by the thermal energy dissipating action of the cone clutch, the applied axial load on the synchroniser sleeve 4 causes re-indexing of the synchroniser hub 2 relative to the synchroniser ring 6 by sliding contact at the chamfered edges of the contacting teeth 63, 42. At this point the synchroniser sleeve 4 is allowed to move axially in past the synchroniser ring 6, and all axial force on the now stationary cone clutch is removed.

The synchroniser sleeve 4 continues to move axially until the leading edges of its teeth 42 make contact with the similarly chamfered edges of the teeth 83 on an engagement body 82 that is permanently attached to the free gear 8. The contact between the chamfered teeth 83 allows the synchroniser sleeve 4 and the gear 8 to rotationally re-index under the applied axial load from the synchronizer sleeve; consequently the teeth begin to overlap and the synchronizer sleeve continues to move axially until reaches its mechanical end stop position.

With the synchroniser sleeve 4 in an end stop position, the respective engaged teeth of the synchroniser sleeve 4 and the those of the engagement body of the gear 8 form a low backlash dog clutch, allowing the vehicle clutch to be closed and the engine torque to be applied to the transmission in the newly engaged gear 8.

With reference to Figures 3a and 3b, there is shown an exemplary wet flat clutch transmission system 100 commonly used in automotive transmissions for either the main vehicle clutch (usually combined to form a dual clutch of dual clutch transmission) or as the ratio change clutch or brake in a planetary automatic gearbox.

A wet flat clutch 100 generally comprises an internal hub 110, a clutch housing 120, and a clutch pack 130 comprising a plurality of transmission components in the form friction plates 131 and clutch discs 132 which are arranged in interspaced relationship. The friction plates 131 are internally splined and are located onto external splines 111 provided on the hub 110. The clutch discs 132 are externally splined and are located internal splines 121 of the clutch housing 120. Upon activation of an hydraulically operated piston the friction plates 131 and clutch discs 132, which are otherwise held open by negative preload spring 140, are brought together to engage transmission of torque forces from the input (i.e. hub 110) side of the assembly to the output (i.e. clutch housing 120) side. The friction plates 131 and clutch discs 132 are usually made from sheet steel, and either of the discs or plates commonly have a dedicated friction lining applied, such as molybdenum, sintered bronze or carbon fibre. Wet clutches are usually sized to allow full torque transfer from the engine into the transmission, and therefore can also be used to perform power shift gear shifts, i.e. when one gear is blended into the next without any loss of drive in between gears, unlike a synchronised gear shift.

With reference to Figure 2, there is shown an embodiment of a transmission component in accordance with the invention in which the component is a synchroniser ring 6. Synchroniser ring 6 has a first face 6a and a second face 6b and comprises an outer surface 61 and an inner surface 62 which extend there between. The relative spacing of the first and second faces 6a, 6b defines the width of the respective inner and outer surfaces 61 , 62. The outer surface 61 comprises a plurality of clutch teeth 63 disposed towards the second face 6b.

The inner surface 62 is a conical friction surface formed from a composition comprising a polymeric material and is adapted for frictional engagement with a complementary conical surface of a gear. In one possible arrangement, the synchroniser ring including the clutch teeth 63 and conical friction surface 62 are of a unitary construction formed from the composition of polymeric material. Such a unitary polymeric synchroniser ring may be formed by injection moulding. In an alternative arrangement, the conical friction surface is formed from a composition comprising a polymeric material whereas the rest of the synchroniser ring is formed from a different polymeric material, or a non-polymeric or a metal material, for example, but not limited to, brass, steel or suitable alloy. Such a two-part synchroniser ring may be formed for example by co-moulding or insert injection moulding whereby the metal part of the synchroniser ring is placed into the injection mould before the polymeric composition is injected into the mould cavity to mould onto said metal part. In either arrangement, the friction surface is provided with a roughened surface texture as described below. In an embodiment of the present invention as shown in Figure 4, the transmission component is a friction plate 9 for a wet clutch, the friction plate comprising a friction surface 92 formed from a composition comprising a polymeric material and comprises a roughened surface texture. In one possible arrangement, the friction surface 92 of the friction plate 9 is integrally formed with the friction plate as a unitary component formed from the composition of polymeric material. In an alternative arrangement, the friction surface 92 is formed from a composition comprising a polymeric material and is bonded to the friction plate 9 which is formed from a different polymeric material, a non-polymeric or a metal material, for example, but not limited to, brass, steel or suitable alloy. Such a two-part friction plate may be formed for example by co-moulding or insert injection moulding whereby the non- polymeric part of the friction plate 9 is placed into the injection mould before the polymeric composition is injected into the mould cavity to mould onto said non- polymeric part. In either arrangement, the friction surface 92 is provided with a roughened surface texture in the manner as described below with reference to the friction surface 62 of a synchroniser ring.

In accordance with the invention, the polymeric material of the friction surface is a PAEK, preferably a PEEK, polymeric material. Preferably, the composition is a carbon fibre reinforced PEEK material. The PEEK material is typically a carbon reinforced compound made from short carbon fibre filler, for example, SIGRAFIL®.

With reference to Figures 7a to 7d, in accordance with the invention, the roughened surface texture is a random texture imparted onto the polymeric friction surface. In embodiments, the roughened surface texture is a pitted texture. Such a roughened texture may be a grit-blasted surface texture as described below, or a texture having the appearance of a grit-blasted surface texture. It will be appreciated that the term "grit blasted surface texture" describes a roughened surface texture formed through blasting an abrasive media onto the friction surface. Alternatively, the roughened surface texture may be one or more of a laser etched, chemically etched, or acid etched surface texture. The roughened surface texture may be created by forming directly onto the friction surface. Alternatively, the roughened surface texture may be formed indirectly on the friction surface, for example via a corresponding roughened surface impression formed on a cavity of a mould within which the friction surface, or a polymeric transmission component comprising such a surface, is formed by moulding. In embodiments, the roughened surface texture may have at least one line of symmetry.

Figures 7b, 7c and 7d show surface topography images of exemplary coarse, medium and fine roughened surface textures provided on the polymeric friction surfaces of synchroniser rings in accordance with the invention, the polymeric friction surfaces being formed from 30% w/w carbon fibre reinforced PEEK (VICTREX® 450CA30). Figure 8a provides a table of typical mechanical properties of a range of carbon fibre reinforced VICTREX® PEEK compounds of differing melt viscosities and percentage fibre contents which may define the material properties of transmission components comprising a friction surface in accordance with the invention. The different PEEK compounds shown in the table of Figure 8a have a grade identifier in the format XX CA YY, wherein the first two digits "XX" represent a relative melt viscosity, the middle letters "CA" indicate that the compound contains carbon fibre reinforcement, and the final two digits "YY" indicate the % w/w of carbon fibre reinforcement. For example, 90CA20 is a very easy flow PEEK compound (MV of 0.09 kNsm ^"2 ) with 30% w/w of carbon fibre reinforcement; 150CA20 is an easy flow PEEK compound (MV of 0.15 kNsm ^"2 ) with 20% w/w of carbon fibre reinforcement; and 450CA40 is a standard flow PEEK compound (MV of 0.45 kNsm ^{" 2} ) with 40% w/w of carbon fibre reinforcement. The typical fibre diameter is approximately 0.007mm, with the typical final fibre length after moulding dependent upon carbon fibre fill percentage and processing steps as illustrated in the graph of Figure 8b.

To provide the roughened surface textures on the carbon fibre reinforced PEEK synchronisation rings, the rings were grit blasted using a Guyson Multiblast RSB cabinet featuring a rotary spindle and fixed nozzle (9.5 mm orifice/4.8 mm nozzle). The synchronisation rings were held in a bespoke fixture and masked to prevent over-spray damage occurring outside of the friction surface. The rings were blasted perpendicular to the inner surface of the ring. The blasting media used to create the coarse, medium and fine roughened surface textures was Saftigrit alumina of 16, 36 and 70 mesh sizes, respectively. In each case, the grit blasting process parameters were as follows: pressure 80 PSI; distance 165mm; rotation Speed 10 RPM; run time 12 seconds (70 and 36 mesh alumina) and 30 seconds (16 mesh alumina).

Roughness data in the format of Sa (arithmetical mean height), Sz (Maximum height) and Sk (Core roughness depth) values in μηι pertaining to the surface topographies of Figures 7b, 7c and 7d are shown in the table of Figure 9. In the table, data for a plain, i.e. unroughened and otherwise smooth, carbon fibre reinforced PEEK friction surface is provided for comparison.

Sa (arithmetical mean height) is the extension of Ra (arithmetical mean height of a line) to a surface. It expresses, as an absolute value, the difference in height of each point compared to the arithmetical mean of the surface. This parameter is used generally to evaluate surface roughness.

Sz (Maximum height) is defined as the sum of the largest peak height value and the largest pit depth value within the defined area.

Sk (Core roughness depth) is calculated as the difference of heights at the areal material ratio values 0% and 100% on the equivalent line; specifically, it is a value obtained by subtracting the minimum height from the maximum height of the core surface.

With reference to Figure 10, initial ring-on-disc wear tests of coarse, medium and fine roughened surface texture sample discs of 30% w/w carbon fibre reinforced PEEK (Victrex ® 450CA30) produced using the grit-blasting process and parameters described above were carried out using a J IS Standard Suzuki Wear Tester (Suzuki wear tester EFM-3-1010-ADX-S). In the ring-on-disc tests, PEEK 450CA30 rings (inside diameter 20mm, outside diameter 25.6 mm) were immersed in a temperature controlled (90 degrees centigrade) bath of Dextron6 ATF lubricating oil and engaged with a steel ring counter surface having a surface roughness ΡθΟ.Οδμηι (i.e. fine) and rotated at constant speed with an axial load applied. As shown in Figure 10, these wear tests found that the coarse roughened surface texture produced the greatest increase in coefficient of friction over plain, i.e. unroughened and otherwise smooth, samples. Thus further wear and application testing was carried out on carbon fibre reinforced PEEK composite samples having a coarse roughened surface texture. To verify the findings of the initial ring-on-disc wear tests obtained using the Suzuki wear tester described above, samples of synchroniser rings formed from 30% w/w carbon fibre reinforced PEEK (Victrex ® 450CA30) compound having a friction surface with a coarse roughened surface texture were tested on a single cone synchroniser system using an industry standard ZF / FZG SSP-180 synchroniser test rig (not shown). In a SSP-180 test rig, the inertia load (i.e. the flywheel of the rig) is accelerated to the maximum delta speed, and the synchroniser ring under test used to brake the flywheel to a stop. The brake torque reaction generated by the synchroniser ring is measured in order to calculate the effective coefficient of friction developed by the friction lining, and this is averaged over each shift cycle.

Synchroniser ring tests were carried out in presence of Pentosin FFL-4 DCT fluid at 90 degrees centigrade and the ring counter surface having a hardness 60HRC and a surface Roughness Ra 0.5 μηι as described below in respect of the modified wear test. To test the roughened synchroniser rings, the transmission application chosen for replication was that of a 2 ^nd gear synchroniser in a typical front wheel drive passenger car gearbox. This represents the highest loaded case of i ^st -2 ^nd gear upshift at a given number of engine revolutions per minute (rpm). The synchroniser rings were mounted on secondary shaft of the test rig, with an upstream inertia load of 0.04 kg.m ² applied. The test loads were chosen to simulate a 1 ^st gear ratio of 4.2, a 2 ^nd gear ratio of 2.3, and a max engine speed of 6500 rpm were used. The resulting velocity over pressure (V/P) load range was 0.2-1.7 m/s.MPa as shown in Figure 1 1. It would be understood by the skilled reader that the data shown is average V/P during each engagement cycle.

To generate representative average loads for a typical synchroniser ring application, the wear tester load profile of the initial ring on disc test was further developed and modified as follows: using a fixed rotation speed rather than decaying speed during an engagement, thus surface speeds are halved from synchroniser test parameters; axial load set to match surface pressure of synchroniser test parameters as set out in Figure 1 1 ; the lubricating oil specification changed to a modern low viscosity oil suitable for use in an OEM DCT transmission, specifically Pentosin FFL-4 DCT fluid; the ring counter surface specification revised to more accurately represent a typical synchroniser counter surface, i.e. having a hardness 60HRC and a surface Roughness Ra 0.5 μηι.

The comparative results of the coefficients of friction obtained via synchroniser ring testing on the SSP-180 test rig and the modified wear tester are shown in the graph of Figure 12. In Figure 12 the wear test data presented is an average of multiple samples of each of 20, 30, 40 and 50% w/w carbon fibre reinforced PEEK including alternative melt viscosities. Synchroniser ring test data is an average of multiple samples of synchroniser rings with friction surfaces formed from formed from 30% carbon fibre reinforced PEEK (Victrex ® 450CA30). In the graph, the coefficient of friction measurements for plain, i.e. unroughened and otherwise smooth samples from both via synchroniser ring testing and sample wear testing are also provided for comparison. It is clear from Figure 12 that a correlation exists between textured specimens tested on both test rig apparatus.

A comparison of overall average of coefficient of friction performance derived via synchroniser ring testing and sample wear testing is shown in the graph of Figure 13, with the data from each load point being averaged across the whole test (i.e. having equal weighting). Figure 13 shows a close correlation between coefficient of friction data obtained via the alternative test methods and shows the significant increase in coefficient of friction of coarse roughened carbon fibre reinforced PEEK surface texture friction surfaces over plain, i.e. unroughened and otherwise smooth samples, irrespective of test method.

A comparison of the effects of the relative melt viscosity on the coefficient of friction performance of coarse roughened carbon fibre reinforced PEEK surface texture friction surfaces is shown in the graph of Figure 14. Figure 14 shows that there is no large difference in coefficient of friction performance between the various melt viscosities. Data presented in this graph is obtained from sample wear testing.

Figure 15 is a graph comparing average overall wear test coefficient of friction performance data of coarse roughened carbon fibre reinforced PEEK friction surfaces formed from a range of Victrex ® PEEK polymer compositions having various weight percentages of carbon fibre reinforcement and with alternative melt viscosities. For each PEEK grade variant, the average coefficient of friction data for plain, i.e. unroughened and otherwise smooth samples, is also provided. The results of the tests described above demonstrate that a friction surface formed from carbon fibre reinforced PEEK and having a roughened surface texture provides a coefficient of friction in the order of 0.1 and therefore suitable for use in wet clutch applications. Thus the tests conducted indicates that the optimum frictional performance of a friction surface of a transmission component in accordance with embodiments of the invention may be achieved by a 20% to 50% w/w carbon fibre reinforced PEEK having a coarse roughened surface texture.

In summary, the wear tests described above found that the coefficient of friction of injection moulded and roughened surface textured carbon fibre reinforced PEEK friction surfaces of transmission components, acting against machined steel counter surfaces in wet clutch applications, are significantly and consistently increased by applying a random profiled texture to the surface. Furthermore, rough surface textured PEEK friction surfaces of synchroniser rings having 20-50% w/w carbon fibre reinforcement offer similar frictional performance to standard non-polymeric of synchroniser rings within a working load range applicable to mass market synchroniser applications. The ability to tailor the mechanical properties and melt viscosity of carbon-fibre reinforced PEEK compounds conveniently also provides a wide material selection for the construction of polymeric synchroniser rings or friction plates, for example based upon considerations of any one or more of frictional performance required, structural strength required (particularly if the component is to be a single part moulding), manufacturability (lower carbon fibre content permitting better flow during injection moulding), relative cost, material availability, relative wear durability of different compounds.

With reference to Figures 5a to 5p, transmission components in accordance with embodiments of the invention may further comprise raised formations 50 formed in the polymeric friction surface, with the roughened surface texture being provided upon said raised formations. In combination with a roughened surface texture as described in detail above, the raised formations may still further augment the increased frictional coefficient performance of the friction surface.

Raised formations 50 are defined by a plurality of recesses or recessed regions 51 formed in the friction surface. Forming of the raised formations may occur during moulding of the friction surface, or as a post moulding step, for example by the machining of recesses or recess regions 51 into the friction surface. For ease of reference, in Figures 5a to 5p, the raised formations 51 are shown in dark colouring. As shown in Figures 5a to 5p, the raised formations 50 may be arranged in a regularly repeating pattern. The pattern may have at least one line or axis of symmetry. The raised formations 50 may define a plurality of grooves 51 extending substantially across the friction surface. The raised formations may be cubic, cuboid, parallelepiped, cylindrical in shape.

The raised formations may be arranged in a spiral (Figure 5e), or criss-cross pattern (Figure 5i, 5j).

With reference to Figure 6a, which is a schematic cross-section of an area of friction surface, the raised formations 50 may have a height (H 1) of less than 3mm; a width (W1) of less than 3mm; and a spacing (W2) in the range 0.05 to 3 mm.

In embodiments, the height (H1) may be in the range 0.05 to 0.2 mm and/or the width (W1) in the range 0.05 to 3 mm.

With reference to Figure 6b, there is shown in detail a portion of a friction surface of a synchroniser ring in which the raised formations 50 define a plurality of axially aligned grooves. The raised formations and the corresponding recesses of the friction surface assist in breaking the oil film layer at the interface of the friction surface and the conical counter surface provided on the gear that is to be engaged.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.