TECHNICAL FIELD The present disclosure relates to an annular coupler for a central tyre inflation system (CTIS) for facilitating delivery of air to a driven wheel of a vehicle. Aspects of the present invention relate to an annular coupler, a central tyre inflation system, a vehicle and a method.

BACKGROUND

The present invention was conceived in the context of a central tyre inflation system (CTIS). CTISs were originally developed for military applications, in particular off-road military wheeled trucks and trailers. However, CTISs are nowadays incorporated into non-military vehicles such as specialist construction, agricultural and commercial vehicles.

A CTIS typically comprises one or more compressed air sources located on-board the vehicle in fluid communication with one or more tyres. Tyre pressure can therefore be adjusted by the CTIS. Typically, the CTIS provides for delivery of compressed air to a tyre through a hose connected to the wheel and, in some cases, this is integrated into a vehicle axle. Accordingly, there are vehicle wheels and vehicle wheel assemblies designed to receive incoming flow of compressed air from the axle, and to deliver it to the tyre.

As indicated above, in a CTIS, air may be delivered through the vehicle axle, but this can be particularly difficult to achieve in a driven wheel assembly having a stub axle, as the stub axle can block the passage of the air and is a rotating part.

It is difficult to adapt a standard stub axle to allow the passage of air, as there is very little metal in the stub axle to be adapted to allow the transport of air that is not already being utilised. The problem of how to transport air between rotating and non-rotating points also arises in this situation.

US 6,425,427 B1 discloses an on-axle tyre inflation system.

It is against this background that the present invention has been devised.

SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an annular coupler for a central tyre inflation system (CTIS) for facilitating delivery of air to a driven wheel of a vehicle and for coupling between a knuckle and an axle of the vehicle; a CTIS for facilitating delivery of air to a driven wheel of a vehicle; a vehicle comprising the annular coupler; and a method of delivering air to a driven wheel of a vehicle using a CTIS, as claimed in the appended claims. In particular embodiments the axle is a stub axle.

Thus, according to one aspect of the invention there is provided an annular coupler for a central tyre inflation system (CTIS) for facilitating delivery of air to a driven wheel of a vehicle and for coupling between a knuckle and an axle of the vehicle, the annular coupler comprising: an inlet aperture for receiving air from a source of air, the inlet aperture in fluid communication with an annular channel defined at least in part by a first radially inner wall portion of the annular coupler for delivering the received air to the driven wheel of the vehicle via the axle. Second and third radially inner wall portions arranged adjacent to and on respective sides of the first radially inner wall portion may define, in use, at least two sealing surfaces to define the annular channel therebetween. Suitably, the at least two sealing surfaces are for receiving annular seals.

The annular coupler may comprising at least two annular seals located so as to seal against the at least two sealing surfaces of the annular coupler so as to define the annular channel therebetween. The at least two annular seals may have different diameters.

In some embodiments the inlet aperture of the annular coupler is defined by an inlet port. The second radially inner wall portion may define a ring either having a different diameter to or the same diameter as a ring defined by the third radially inner wall portion, such that, in some embodiments the annular seals may have the same diameter, and in other embodiments the annular seals may have different diameters. In some embodiments the annular coupler suitably comprises an annular projection extending from an end portion thereof to define a sealing surface for cooperation with an annular dirt seal, in use, to inhibit the ingress of dirt along the radially inner wall of the annular coupler. The annular projection may extend radially inwards from a radially inner wall portion of the annular coupler. In some embodiments the sealing surface for cooperation with the dirt seal comprises a wall portion of the annular projection and also a radially inner wall portion of the annular coupler. In another aspect of the invention there is provided an annular coupler assembly for a central tyre inflation system (CTIS) for facilitating delivery of air to a driven wheel of a vehicle. The annular coupler assembly comprises: an annular coupler having an inlet aperture for receiving air from a source of air, the inlet aperture in fluid communication with an annular channel defined at least in part by a first radially inner wall portion of the annular coupler for delivering the received air to the driven wheel of the vehicle via the axle, and second and third radially inner wall portions arranged adjacent to and on respective sides of the first radially inner wall portion defining at least two sealing surfaces for receiving annular seals; at least two annular seals that seal against the at least two sealing surfaces of the annular coupler, in use, for defining the annular channel therebetween; and an axle, the axle suitably has at least one bore communicating with an aperture, which is arranged, in use, to receive air from the annular channel defined by the annular coupler and deliver air to the driven wheel of the vehicle. The at least two sealing surfaces of the annular coupler and/or the at least two respective annular seals, in use, may cooperate with an outer surface of the axle of the vehicle or a collar.

The axle may in some embodiments comprise two apertures for receiving air from the annular channel, each aperture communicating with a respective bore for facilitating delivery of air to the driven wheel of the vehicle. The one or more bores having apertures in communication with the annular channel of the annular coupler may suitable be arranged generally radially through a wall of the axle so as to communicate with a common axial bore through a central portion of the axle.

An outer surface portion of the axle may define at least one annular sealing surface for receiving an annular seal. Suitably, there are two annular sealing surfaces; the two annular sealing surfaces typically having different diameters in use to receive annular seals of different diameters.

In some embodiments the annular coupler assembly includes a collar adapted, in use, to be arranged between the annular coupler and the axle of the annular coupler assembly. The collar has a radially outer wall and a radially inner wall. At least an axial portion of the radially outer wall in use opposes the second and third radially inner wall portions of the annular coupler, and at least an axial portion of the radially inner wall in use opposes an outer wall of the axle. In some such embodiments the radially outer wall advantageously has a constant diameter in the axial portion opposing the second and third radially inner wall portions of the annular coupler. In this way, the annular seals for sealing between the annular coupler and the collar may suitable have essentially the same diameter. In other embodiments, however, the annular seals may have different diameters, for example, for sealing between an annular coupler of the invention and the axle.

The radially inner wall of the collar may suitably dimensioned to have a diameter matching the outer wall diameter of the axle in the axial portion opposing the collar, in use.

In some embodiments at least the radially outer wall surface of the collar may be coated with a corrosion resistant material, for example a ceramic coating, more specifically a ceramic coating such as Nitrotec® which is commercially available from Nitrotec, or Apticote Ceramic 2000 which is commercially available from Poeton..

The radially inner wall of the collar may, in some embodiments, be provided with at least one annular groove for receiving a seal; the seal for cooperating with an outer wall portion of an axle.

One or more of the annular seals may be formed of polytetrafluoroethylene (PTFE) and/or rubber.

In some embodiments the annular coupler comprises an annular projection extending from an end portion of the annular coupler. The annular projection suitable defines a sealing surface for cooperating with an annular dirt seal. Thus, the CTIS may include an annular (dirt) seal for cooperation with a wall of the annular projection. In use, the annular projection of the annular coupler, together with the dirt seal, defines a labyrinth path to inhibit the ingress of dirt between the annular coupler and the axle or collar. The sealing surface for cooperation with the dirt seal may comprise a wall portion of the annular projection and a radially inner wall portion of the annual coupler. In some embodiments the annular projection extends radially inwards from a radially inner wall portion of the annular coupler.

In another aspect the invention provides a central tyre inflation system (CTIS) for facilitating delivery of air to a driven wheel of a vehicle comprising an annular coupler assembly as described hereinabove. In another aspect the invention provides a vehicle comprising an annular coupler of any aspect or embodiment of the invention; an annular coupler assembly as described hereinabove; or a CTIS according to any aspect or embodiment of the invention. In yet another aspect the invention provides a method of delivering air to a driven wheel of a vehicle using a central tyre inflation system (CTIS). The CTIS comprises:

an annular coupler for coupling between a knuckle and an axle of the vehicle, the annular coupler comprising: an inlet aperture for receiving air from a source of air, the inlet aperture in fluid communication with an annular channel defined at least in part by a first radially inner wall portion of the annular coupler for delivering the received air to the driven wheel of the vehicle via the axle; and second and third radially inner wall portions defining at least two sealing surfaces, the second and third radially inner wall portions arranged adjacent to and on respective sides of the first radially inner wall portion, in use, to define the annular channel therebetween; and

at least two annular seals that seal against the at least two sealing surfaces of the annular coupler, in use, for defining the annular channel. The CTIS also comprise an axle, the axle having at least one bore having at least one aperture arranged, in use, for receiving air from the annular channel and for facilitating delivery of air to the driven wheel of the vehicle.

The method comprises: providing a source of air on the vehicle; providing an air flow path from the source of air to a driven wheel of the vehicle via at least an annular coupler and an axle of the vehicle; delivering a supply of air from the source of air to an inlet of the annular coupler; and regulating the delivery of air from the air flow path into the driven wheel of the vehicle.

In accordance with methods of the invention the annular coupler may be defined according to any of the aspects or embodiments described herein, and/or the central tyre inflation system (CTIS) may be defined according to any of the aspects and embodiments described herein.

In any of the aspects and embodiments of the invention, the axle may be a stub axle of a vehicle.

In any of the aspects and embodiments of the invention, the annular coupler may include one or more fixation-receiving features for receiving fixation members for attaching the annular coupler to a component of a vehicle. In some embodiments the fixation-receiving features are lugs adapted to receive screws or other suitable fixation members. Preferably there are three such fixation-receiving features. More preferably the fixation-receiving features are arranged on the annular coupler in an asymmetric fashion to direct assembly of the annular coupler on a vehicle in a single specific orientation. In some embodiment the CTIS of the invention includes a seal pack arranged to cooperate with the annular seal and to maintain the at least two annular seals in an appropriate configuration so as to stably define the annular channel.

For the avoidance of doubt, references herein to a central tyre inflation system (CTIS) are to an apparatus for controlling the pressure of one or more tyres in a vehicle.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of a central tyre inflation system (CTIS) according to an embodiment of the invention;

Figures 2A and 2B show a schematic representation of an annular coupler according to the invention, which may be incorporated into a CTIS of Figure 1 ; Figure 3 is a schematic representation of a knuckle, seals and stub axle of a CTIS and incorporating the annular coupler in Figures 2A and 2B;

Figure 4 is a schematic perspective representation of the stub axle in Figure 3; Figure 5 is a schematic side representation of the stub axle shown in Figures 3 and 4; Figure 6 is a sectional view of a knuckle, annular coupler, seals and stub axle of an alternative CTIS to that shown in Figure 3;

Figure 7 is schematic perspective representation of a collar for a stub axle of the CTIS of Figure 6;

Figure 8 is an alternative sectional view of a knuckle, annular coupler, seals and stub axle of a CTIS having a different seal arrangement to that shown in Figure 6; Figure 9 is an enlarged view of a part of the CTIS in Figure 8; and

Figure 10 is a sectional view of an arrangement of an annular coupler, seals and stub axle of an alternative CTIS to that shown in Figures 8 and 9. Throughout the description, terms such as 'upper', 'lower', 'left', 'right' and so on relate to the orientation as shown in the accompanying drawings. It will be appreciated, however, that the locator may be used in any suitable orientation.

DETAILED DESCRIPTION

In the following description and in the drawings, reference letters are used to collectively or non-specifically identify equivalent or essentially equivalent components. Where necessary, a specific component in a collection of equivalent or essentially equivalent components is identified by suffixing reference letters in subscript format.

To provide context for the invention, a CTIS is first described with reference to Figure 1 . It should be appreciated that the CTIS described here is merely representative of the type of system that may be used, and many other variations are possible. The CTIS depicted in this embodiment is installed in a vehicle VH that has four wheels, each having a tyre T mounted on a wheel hub (not shown), and supplies air to each of the four tyres. However, it will be appreciated that vehicles may have any number of wheels and that a CTIS according to the invention may supply air to one or more tyres of a vehicle, as desired. The CTIS may therefore comprise one or more of the respective apparatus associated with each wheel of the CTIS as described herein below. The wheels (and the tyres T) of the depicted embodiment are identified herein based on their relative position on the vehicle VH, namely: front left (FL), front right (FR), rear left (RL) and rear right (RR). This nomenclature is employed to identify the components of the CTIS associated with the respective tyres T. The front tyres TFR, TFL are mounted on a front axle and the rear wheels TRR, T _rl are mounted on a rear axle of the vehicle. The CTIS of the depicted embodiment comprises four pneumatic control valves PCV fixedly mounted to the wheel hubs and arranged to control the supply of compressed air to and from a respective tyre cavity. The pneumatic control valves PCV are pneumatically operated in response to changes in the pressure in the associated tyre supply line TSL. Specifically, the pneumatic control valves PCV are operable to cycle sequentially (i.e. to toggle) between an open state and a closed state in response to the application of a pressure exceeding a valve activation pressure. The pneumatic control valves PCV are stable in both the open and closed state via a latching mechanism, i.e. they can each be considered as a pressure actuated bi-stable valve. Herein the application of air at a pressure and time sufficient to switch the valve from one state to its other state, i.e. from open to closed or from closed to open, is referred to as "toggling" the valve, and the application of said air in this manner is referred to as a high pressure (pneumatic) control signal.

A suitable pneumatic control valve PCV for this application is described in UK Patent application GB 2516704 filed on 31 October 2013, the contents of which are incorporated herein by reference in their entirety. It will be appreciated that each pneumatic control valve could have additional operating states which are cycled through sequentially in dependence on said pneumatic control signal.

The CTIS further comprises a valve block 3 for controlling the supply of compressed air to each of the pneumatic control valves PCV. In the depicted embodiment the valve block 3 is fluidly coupled to a first compressed air source 5 and to a second compressed air source 7. However, it will be appreciated that in embodiments of the invention only one, two or more sources of compressed air or other suitable tyre inflation gas may be provided. In the configuration shown in Figure 1 , the first compressed air source 5 provides air at a high flow rate and low pressure (HF/LP); and the second compressed air source 7 is operable to provide air at a higher pressure. As described herein, the first and second compressed air sources 5, 7 are distinct from each other. In the present arrangement, the first compressed air source 5 comprises a first compressor 9; and the second compressed air source 7 comprises a second compressor 1 1 and a reservoir 13. In other embodiments, not depicted, the number of compressors may match the number of air sources, or there may be one compressor for more than one air source. An annular coupler 2 of the invention, which may form part of a CTIS according to the invention is described with reference to Figures 2A and 2B. In use, the annular coupler 2 is coupled between a knuckle of a vehicle (see Fig 3), in particular, but not limited to, a steering knuckle, and an axle of a vehicle (see Fig 3), in particular, but not limited to, a stub axle. The annular coupler 2 is provided to transport air (or other inflation gas) from a source of air in the vehicle (not shown) into a rotating part of the wheel drive assembly.

The annular coupler 2 has an inlet aperture 4 provided in an radially outer surface to receive air from a source of air in the vehicle and subsequently deliver to a tyre of the vehicle (see Fig 1 ). The inlet aperture 4 may be defined by an inlet port 5 provided on a radially outer surface of the annular coupler 2.

In use, in a CTIS according to the invention the inlet aperture 4 is in fluid communication with a source of air, for example, a compressed air supply from a compressor and/or a reservoir provided in the vehicle, as described with relation to Figure 1. In an embodiment, fluid communication between the inlet aperture 4 with the compressed air supply may be established through a supply line (not shown) extending along a central axis of a drive shaft (not shown). The supply line includes a connector for docking with the inlet port 5 of the annular coupler 2.

The inlet aperture 4 fluidly communicates with an annular channel 6 defined by a radially inner wall portion of the annular coupler 2 by a bore through the wall of the annular coupler 2. According to the depicted embodiment the annular channel 6 is an open channel which is defined by a first radially inner wall portion 17 flanked by second 8 and third 10 annular radially inner wall portions of the annular coupler 2. The first radially inner wall portion 17 has at least one aperture (not shown) that communicates with the inlet aperture 4 via a bore through the wall of the annular coupler. In use, therefore, air delivered to the inlet aperture 4 is received by the annular channel 6 and can subsequently be delivered to a wheel / tyre, such as a driven wheel of the vehicle (see Fig 1 ) via an axle or stub axle.

The second 8 and third 10 radially inner wall portions of the annular coupler are each defined by a stepped portion of smaller radius than the first radially inner wall portion 17 such that the annular channel 6 has a flattened 'U' shaped profile. However, it will of course be appreciated that any open channel profile may be suitable. Each of the second 8 and third 10 radially inner wall portions defines a (sealing) surface for preventing the escape of air in an axial / lateral direction out of annular channel 6. In the depicted embodiment, the sealing surfaces of the second and third radially inner wall portions 8, 10 receive annular seals (not shown) for the purpose of preventing air loss from the annular channel 6 other than through the route defined by the CTIS. The annular channel 6 may, in use, therefore be regarded as an air-tight region for allowing the passage of air from the inlet aperture 4 of the annular coupler 2 to a axle of a vehicle (not shown).

The second 8 and third 10 radially inner wall portions may either be of different diameters or of the same diameter according to different embodiments, and may thus receive respective annular seals (Fig 3) having corresponding different or same respective diameters such that they are able to cooperate with the sealing surfaces of the annular coupler 2 effectively, in use.

In the depicted embodiment, the annular coupler 2 has an annular projection 12 extending from an end portion thereof. The annular projection 12 defines a sealing surface 12 for cooperating with an annular dirt seal (see Fig 3). When the annular projection 12 is used in combination with an annular dirt seal, the ingress of dirt along the radially inner wall of the annular coupler 2 can be inhibited, as described further below.

The annular projection 12 of this embodiment includes a radially inwardly projecting annular wall 13, such that the dirt seal can be received against a radially inward facing wall portion of the annular projection 12 and a generally perpendicular surface of the wall 13. In use, the annular projection 12 including annular wall 13, and the dirt seal (not shown) together define a labyrinth path to substantially hinder or prevent the ingress of dirt below the annular coupler and into the CTIS.

Three lugs 15 are provided on the radially outer wall of the annular coupler 2 to provide fixation-receiving features in order to allow fixation of the coupler to a component of a vehicle, such as knuckle 14 depicted in Figure 3 described below. In the depicted embodiment the fixation-receiving feature is a through bore to receive a fixation member such as a screw. In other embodiments, not shown, any suitable type or number of fixation- receiving features may be provided on the annular coupler in order that it may be fixed to an appropriate component of a vehicle in use by any appropriate mechanism.

Figure 3 is an exploded schematic representation of how an annular coupler 2 according to the invention may be arranged within a CTIS. Turning to Figure 3, in use, the annular coupler 2 may be coupled to a knuckle 14 of a vehicle. In the embodiment shown the annular coupler 2 is provided with three lugs 15 for receiving appropriate fixation members, such as screws, to provide three points of connection to the knuckle 14. As noted above, however, the connection can be achieved using any suitable mechanism and it will be appreciated that any appropriate number of attachment / fixation mechanisms may be used. In some embodiments the fixation-receiving features are arranged on the annular coupler 2 such that only one orientation of the annular coupler 2 is possible, which aids in achieving the appropriate alignment of annular coupler and thus simplifies and improves the process of assembly the CTIS.

The annular coupler 2 has an inlet aperture 4 that can be connected to an air source of a vehicle (not shown), for example, via an air connector 22. The annular coupler 2 may receive two annular seals 16A, 16B, which, together with the annular coupler 2, define an annular channel 6 for delivering the received air to the driven wheel of the vehicle via the stub axle 18. It will of course be appreciate that the relevant vehicle axle may not be a stub axle and so any appropriate vehicle axle may be used in place of stub axle 18.

In the depicted embodiment the second 8 and third 10 radially inner wall portions of the annular coupler 2 that define sealing surfaces for receiving annular seals 16A, 16B have different diameters in order to match the outer wall surface profile of the sub axle 18 in the portion of the stub axle 18 that opposes the second 8 and third 10 radially inner wall portions of the annular coupler 2 once assembled. Accordingly, annular seals 16A, 16B are of corresponding different diameters in order to effectively cooperate with the respective sealing surfaces of the annular coupler 2 and the stub axle 18.

In the depicted embodiment a seal pack 24 is provided in order to hold the annular seals 16A, 16B in an appropriate arrangement and alignment so as to define a stable configuration of the annular channel 6. The seal pack 24, where provided, cooperates with the annular coupler 2. However, it should be appreciated that in other embodiments of the invention such seal packs 24 are not required and therefore may not be provided in a CTIS of the invention.

It can be advantageous for the annular seals 16A, 16B to have different diameters to each other, as this can make it easier to seal against the outer wall of the stub axle 18, in use, which typically has an outer surface of varying diameter in the portion opposing the annular coupler 2 in use (see also Figures 4 and 5). Accordingly, in such embodiments, the second 8 and third 10 radially inner wall portions of the annular coupler 2 have different diameters to each other and are shaped so as to support the annular seals 16A, 16B. In these embodiments, as described above, the second 8 and third 10 radially inner wall portions of the annular coupler 2 provide clear points of contact for their respective seal, 16A, 16B. In addition, such an arrangement means that it is not necessary to adapt either the annular coupler 2 or the stub axle 18. However, in other embodiments, as described below, it can be advantageous to use identical annular seals 16A, 16B, in which case a collar may be used (see Figure 7).

A stub axle 18 and a dirt seal 20 are also shown in Figure 3 and these components are described in more detail with reference to Figures 4 to 6 below.

Suitably, the annular seals 16A, 16B comprise polytetrafluoroethylene (PTFE) and/or rubber. It is advantageous that the annular seals 16A, 16B comprise PTFE, as this material provides a beneficial seal with the surface of the stub axle 18, which rotates in use, without the need for a lubricant. It can also be advantageous for the annular seals 16A, 16B to additionally comprise rubber, as this can help prevents the ingress of dirt into the CTIS and particularly into the annular channel 6. The dirt seal 20 may be formed from rubber.

As described above, the annular coupler 2 is arranged between a knuckle 14 and stub axle 18 within a CTIS of a vehicle, and the stub axle 18 is arranged between the annular coupler 2 and the axle of a vehicle (not shown). As used herein the term "stub axle" will be understood to also mean the CV joint stem or the CV joint outer cup, both of which may refer to the same component. In the embodiment shown in Figures 4 and 5, the stub axle 18 comprises first and second radially outer wall portions 30, 32, which define sealing surfaces of different diameters to each other. In use, these sealing surfaces support the annular seals 16A, 16B that also cooperate with the second 8 and third 10 radially inner wall portions of the annular coupler 2, thus providing a seal between the annular coupler 2 and the stub axle 18 and aiding to define the annular channel 6 for passage of inflation gas / air to the stub axle 18.

The stub axle 18 has at least one aperture 26 arranged between the first 30 and second 32 radially outer wall portions and arranged (once appropriately assembled) to receive air from the annular channel 6 of the annular coupler 2. The at least one aperture 26 of the stub axle 18 is in fluid communication with at least one bore provided radially through the wall of the stub axle 18. In one embodiment the radial bore connects with an axial bore arranged generally through the central axis of the stub axle 18 (again not shown in Figures 4 and 5 - see Figure 8) such that air can be passed through a passage from the aperture 26 to a wheel of the vehicle. The stub axle 18 is therefore coupled with the annular coupler 2 such that the at least one aperture 26 aligns with and is in fluid communication with the annular channel 6. In the embodiment of the stub axle 18 depicted in Figures 4 and 5, splines 34 are provided in an outer cylindrical portion that cooperate with splines on a complimentary interior cylindrical aperture in a drive flange that is located in a wheel bearing in the knuckle to effect the drive of a vehicle wheel. This part of the arrangement is conventional in the art and will be understood by the person knowledgeable in the art.

With reference to Figures 6 and 8, the stub axle 18 of this embodiment has two apertures 26 for receiving air from the annular channel 6, each aperture 26 communicating with a respective radial bore (46) for facilitating the delivery of air to the driven wheel of the vehicle (not shown) via a common central axial bore 44.

A radially outer wall portion 28 of the stub axle 18 defines a sealing surface for receiving an annular dirt seal 20, in use to be located between the stub axle 18 and the radially inwardly projecting annular wall 13 upstanding from annular projection 12 of the annular coupler 2. The sealing surfaces in conjunction with the dirt seal 20 define, in this embodiment, a labyrinth path to help prevent the ingress of dirt between the annular coupler 2 and the stub axle 18.

In some embodiments, the annular dirt seal 20 is a centrifugal seal that reduces running friction on the bearing surface as speed increases, thereby maintaining high friction and high seal integrity at low speeds (e.g. during off-road driving) and reduced seal force and reduced drag at higher rotational speed.

In the sections shown in Figures 9 and 10, the interaction between the annular seals 16A, 16B and the annular coupler 2 and stub axle 18 is more clearly visible than in Figure 8. In addition, the annular dirt seal 20, which is located between the stub axle 18 and the radially inwardly projecting annular wall 13 upstanding from the annular projection 12 of the annular coupler 2 in use, is also shown more clearly. In particular, the labyrinth path helps to prevent the ingress of dirt between the annular coupler 2 and the stub axle 18, as can be seen in Figures 9 and 10. The seal arrangements 16A, 16B differ between the two embodiments, although in both cases the seals 16A have a different diameter. The seal arrangements 16A, 16B of the two embodiments shown in Figures 9 and 10 perform the same function as each other, but have different designs, both of which are suitable. As shown in the embodiment of Figure 6, it is beneficial in some circumstances to use annular seals 16A, 16B of the same size. With this in mind, in such embodiments a collar 36 may be provided as part of the CTIS. Referring to Figure 7, the collar 36 may be fitted around the stub axle 18 such that it is arranged between the annular coupler 2 and the stub axle 18 of the CTIS. More specifically, the collar 36 is located, in use, between the stub axle 18 and the opposing second 8 and third 10 radially inner wall portions of the annular coupler 2. The collar 36 has a radially outer (or external) wall 38 and a radially inner (or internal) wall 40 defining an axial aperture through the collar 36. The radially inner wall 40 of the collar 36 has a diameter generally matching the outer wall profile of the stub axle 18 in the axial portions opposing the collar 36, such that it fits snugly around the stub axle 18 in use. The outer wall 38 of the collar 36 of the depicted embodiment has a constant diameter. In the CTIS of this embodiment of the invention, annular seals 16A, 16B are arranged between the annular coupler 2 and the collar 36, rather than between the annular coupler 2 and stub axle 18, such that the seals can have the same diameter. Accordingly, the seals 16A and 16B in these embodiments can be identical. While the entire external wall 38 of collar 36 has a constant diameter in the depicted embodiment, it will of course be appreciated that it is sufficient to achieve the desired effect that only the axial portions of the collar 36 directly opposing the second 8 and third 10 radially inner wall portions of the annular coupler 2 are of the same diameter. In embodiments of the CTIS comprising collar 36 it will be appreciated that the annular channel 6 of the annular coupler 2 is now in defined by the volume between the first 7, second 8 and third 10 radially inner wall portions of the annular coupler 2 and the outer wall 38 of the collar 36. Thus, the collar 36 is arranged directly in the fluid flow path between the source of air and the tyre of the vehicle. Thus the collar 36 is provided with at least one through-bore 42 extending from the outer wall 38 to the inner wall 40 of the collar 36 and arranged, in use, to provide at least one route of fluid communication between the annular channel 6 of the annular coupler 2 and the at least one aperture 42 of the stub axle 18 which is as previously described. In the embodiment shown in Figure 7, the collar 36 has a plurality of apertures 42, but only one aperture 42 is required for the air to be passed from the annular coupler 2 to the stub axle 18 effectively. Whilst the collar 36 has an internal wall 40 profile dimensioned to generally match the external wall profile of the stub axle 18, the profile is shaped so as to create an annular volume 37 (see Figure 6) surrounding an axial outer wall portion 39 comprising apertures 26 (Figure 5) of the stub axle 18 so as to mirror the annular channel 6 of alternative embodiments described herein.

In this embodiment the radially outer wall surface 38 of the collar 36 is coated with a corrosion resistant material. The corrosion resistant material may be a ceramic coating, for example it may be Nitrotec® which is commercially available from Nitrotec, or Apticote Ceramic 2000 which is commercially available from Poeton.

The radially inner wall of the collar 36 may be provided with at least one annular groove 41 for receiving an annular seal (not shown), for example an O-ring.

The operation of the CTIS of the invention will now be described in relation to the embodiments of the annular coupler 2 in combination with the other CTIS components as shown in the collective Figures. In this regard, air is transported from an air source of the vehicle (Figure 1 ) to an inlet aperture 4 of the annular coupler 2 via an air supply line (not shown). The inlet aperture 4 is in fluid communication with an annular channel 6 of the annular coupler 2 via a bore through the wall of the annular coupler 2 (see Figures 2A and 2B). The annular channel 6 is defined at least in part by a first radially inner wall portion 17 of the annular coupler 2 and may also be defined by at least two annular seals 16A, 16B and respective second 8 and third 10 radially inner wall portions of the annular coupler 2 with which they cooperate to define at least two sealing surfaces between the annular coupler 2 and either a stub axle 18 or a collar 36 of the CTIS. In the embodiment shown in Figure 6, the stub axle 18 is fitted with a collar 36 and so the annular seals 16A, 16B may have the same diameter.

Air is introduced into the annular channel 6 between the annular seals 16A, 16B. The air is then delivered from the annular channel 6 either directly to the at least one radial bore 46 in the stub axle 18 via the corresponding at least one aperture 26 in the outer wall of the stub axle 18 or via the at least one aperture 42 in the collar 36. In the embodiment shown in Figure 6, which includes collar 36, the air is delivered from the annular channel 6 to the stub axle 18 via a plurality of bores 42 through the wall of collar 36.

From the one or more radial bores 46 in the stub axle 18 air is passaged to a common central axial bore 44 to guide the air through the stub axle 18 towards the wheel(s) of the vehicle such that the tyre can be inflated / deflated. A fluid pathway is thus established between an air supply line / reservoir of the vehicle (not shown) and the interior of the tyre (not shown). Figure 8 shows a cross-section of an alternative embodiment of the annular coupler 2 of the invention in combination with the other CTIS components which does not incorporate a collar 36.

In this embodiment, which is otherwise generally the same as the embodiment depicted in Figure 6, since the CTIS does not include a collar 36, the radially outer wall portions 30, 32 of the stub axle define sealing surfaces (for receiving annular seals 16A, 16B) that are of different diameters. Accordingly, the annular seals 16A, 16B have correspondingly different diameters such that they can achieve an effective seal with the stub axle 18. Two apertures 26 provided in the wall of the stub axle 18 are visible in the embodiment shown in Figure 8, although one or more apertures 26 may be present depending on preferences. Furthermore, while in the embodiment shown in Figure 8, the stub axle 18 has two bores 46 that are arranged generally radially through the wall of the stub axle 18 so as to communicate with a common centrally arranged axial bore 44 through a central portion of the stub axle 18; in alternative embodiments the stub axle 18 may be provided with more than one axial bore 44 to enable the flow of air from the apertures 26 in the stub axle 18 towards the vehicle's wheels via radial bores 46.

It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms without departing from the scope of the appended claims.