TECHNICAL FIELD

The application relates to a vehicle cross bar. More specifically, the application relates to a vehicle cross bar with an aerodynamic profile that reduces noise generated from the bar when fitted to a moving vehicle.

BACKGROUND ART

Vehicle roof racks are well known in the art typically comprising a leg or legs that retain the rack to the vehicle via direct attachment to the roof or to side rails. The leg or legs then attach to a cross bar on which various accessories or items may be mounted. As should be appreciated, since the cross bar faces directly in to the direction of travel of the vehicle, the cross bar has the propensity to produce considerable noise and drag as the vehicle is driven.

Various cross bars exist to attempt to minimise roof rack noise and drag. Some examples include the Thule Aero™ cross bar, the Whispbar™ cross bar and others.

These types of bar are sometimes very effective at reducing wind noise and drag but they tend to be more expensive to produce due to their greater complexity and shape.

Some cross bars make no attempt to address wind noise whatsoever, an example being a very simple extruded rectangular bar. The industry standard is that this bar has a height of 22mm and a width of 32mm. This type of bar is noisy and has considerable drag but one advantage is that it is very simple and inexpensive to manufacture as it is a very simple metal extrusion shape.

It should be appreciated that it would be useful to produce a simple low cost rectangular cross bar that also reduces wind noise and even drag.

One attempt to address this is taught in WO 01/98109. In this specification a metal extruded rectangular bar includes channels recessed into the cross bar leading face with a view to reducing wind noise. While this technique does reduce wind noise, it is more expensive to manufacture as it requires an operator to press or cut the channels into the metal extrusion thereby taking considerable time and labour to manufacture. The design also leaves sharp edges that can be a hazard when fitting items to the cross bar.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinence of the cited documents. For the purpose of this specification, and unless otherwise noted, the term 'comprise' and grammatical variations thereof shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements.

SUMMARY

The application broadly relates to a vehicle cross bar used as part of a roof rack system for attaching objects to the roof of a vehicle. The cross bar has improved aerodynamic characteristics compared to many existing cross bars on the market and is easy to

manufacture and produce.

In a first aspect there is provided a roof rack cross bar with an approximately rectangular cross section wherein:

a. the leading face of the cross bar as it is fitted to a vehicle is shaped to have an upper and lower forward facing projection;

b. the projections have a plurality of notches that direct air flow around the bar thereby reducing audible noise produced by the cross bar;

c. the region intermediate the two projections is slightly recessed so as to form a groove intermediate the two projections; and

d. the transition between the groove and projections is smooth and the groove

presents a concave surface to the airflow.

(n a second aspect there is provided a roof rack cross bar including an approximately rectangular cross section cross bar extrusion along with a casing that fits over at least the leading face of the cross bar extrusion, wherein the leading face of the casing when fitted to the cross bar and fitted to a vehicle is shaped to have an upper and lower forward facing projection and wherein the projections have a plurality of notches therein.

Advantages of the cross bar include reduced wind noise. By reducing the noise, the drag effect may also be reduced resulting in improved vehicle fuel economy as well.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present application will become apparent from the following description that is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 illustrates a perspective view from above of one aspect of the leading edge of the cross bar;

Figure 2 illustrates a detail perspective view of the leading face of the cross bar;

Figure 3 illustrates a detail perspective view of one end of the cross bar;

Figure 4 illustrates a front elevation view of a section of the cross bar leading face; Figure 5 illustrates a plan view of one side of the cross bar view from above;

Figure 6 illustrates a bottom view of one side of the cross bar when viewed form underneath;

and

Figure 7 illustrates a comparative study of the sound pressure levels emitted by the

improved cross bar described compared to other types of cross bar on the market.

DETAILED DESCRIPTION

As noted above, the application broadly relates to a vehicle cross bar used as part of a roof rack system for attaching objects to the roof of a vehicle. The cross bar has improved aerodynamic characteristics compared to many existing cross bars on the market and is easy to manufacture and produce.

For the purposes of this specification, the term 'leading face' or grammatical variations thereof refers to the side of the cross bar facing the into the wind generated by movement of the vehicle on which the cross bar is mounted, generally being a forward direction of travel.

The term 'forward facing projection' or grammatical variations thereof refers to a projection that extends from the leading face surface.

The term 'upper' and 'lower' when used in the context of the cross bar refer to the cross bar orientation when mounted to a vehicle, upper referring to a point on the cross bar furthest from the ground and lower referring to a point on the cross bar closest to the ground.

The term 'audible noise' refers to sound in the frequencies 100-10000Hz and particularly the region 100-400Hz.

The term 'casing' as used herein refers to a cover that at least fits over the leading face of the cross bar. The casing may fit over the leading face and top or bottom or both of the cross bar when mounted to a vehicle. The casing may cover the entire cross bar. The term 'about' refers to a quantity, level, value, number, frequency, percentage, dimension, size, weight, or length that varies by as much as 30, 25, 20, 15, 10,9, 8, 7, 6, 5, 4, 3, 2 or 1 % to a reference quantity, level, value, number, frequency, percentage, dimension, size, weight, or length.

In a first aspect there is provided a roof rack cross bar with an approximately rectangular cross section wherein:

a. the leading face of the cross bar as it is fitted to a vehicle is shaped to have an upper and lower forward facing projection;

b. the projections have a plurality of notches that direct air flow around the bar thereby reducing audible noise produced by the cross bar;

c. the region intermediate the two projections is slightly recessed so as to form a groove intermediate the two projections; and

d. the transition between the groove and projections is smooth and the groove

presents a concave surface to the airflow.

The distance between the two projections and the region intermediate the two projections may range from about for example 1 to 20mm, 1 to 15mm, 1 to 12mm, 1 to 10mm, 2 to 9mm, 3 to 8mm, 4 to 7mm, or 5 to 6mm.

The notches may be transverse grooves located at spaced apart intervals along the length of the cross bar. The notches may be inserted at regular intervals. In one embodiment, the notches may be spaced at asymmetric intervals. Further, the notches in the upper projection may be off set vertically from the notches in the lower projection.

The notch walls may have a rounded profile.

Without being constrained to a set size, the notches may be about for example 0.5 to 30mm, 1 to 20mm, 1 to 15mm, 1 to 10mm, 2 to 8mm, 3 to 7mm, or 4 to 6mm deep

The notches may be spaced approximately about for example 5 to 100 mm, 10 to 80mm, 10 to 60mm, 10 to 40mm, or 15-30mm apart.

Without being bound to any specific theory, the notches on the leading face of the cross bar are understood by the inventors to reduce the amount of noise by reducing the amount of vortex shedding occurring by air as it moves over the cross bar leading face. The notches appear to introduce various small airstreams that disturb or destroy the vortex effect behind the crossbar. The inventors also understand that a region of stagnant air results about the intermediate region on the leading face between the two projections. The stagnant region creates a ram pressure on the air, forcing the air along the respective top and bottom forward facing projections. This is quite different to the art that does not have this stagnant zone of air.

The cross bar may be formed from two parts, the first being an extruded rectangular cross section bar and the second being a casing the fits over the rectangular cross bar and wherein the casing includes features on the forward face of the cross bar.

The casing may be an injection moulding.

The casing extrusion may slide over the cross bar extrusion. In this embodiment, the casing may be sized to have a snug fit over the cross bar extrusion. Alternatively, the casing may be fitted in place by use of a mechanical fastener or fasteners such as a bolt or rivet or instead may be held in place via a chemical fastener such as an adhesive. In a further alternative, the casing may be over-moulded onto the cross bar extrusion.

The use of a casing may be useful as the casing may be made from an inexpensive and easily moulded material such as plastic thereby dramatically reducing the manufacturing time and cost compared to for example the bar taught in WO 01/98109.

In a second aspect there is provided a roof rack cross bar including an approximately rectangular cross section cross bar extrusion along with a casing that fits over at least the leading face of the cross bar extrusion, wherein the leading face of the casing when fitted to the cross bar and fitted to a vehicle is shaped to have an upper and lower forward facing projection and wherein the projections have a plurality of notches therein the direct air flow around the bar thereby reducing audible noise produced by the cross bar.

As noted above, advantages of the cross bar include reduced wind noise. By reducing the noise, the drag effect may also be reduced resulting in improved vehicle fuel economy as well. The leading face design described dramatically reduces the noise produced by a standard inexpensive rectangular cross section bar. Use of a casing over a standard bar also makes the improved design highly cost effective and simple to manufacture and obtain materials for.

WORKING EXAMPLE

The application is now described with reference to a detailed description of an aspect of the cross bar of the present application.

Referring to Figures 1 to 6 there is illustrated an example of a roof rack cross bar generally indicated by arrow 1. The cross bar 1 shown is made up of a standard rectangular cross section metal extrusion 2 onto which a casing 3 has been fitted.

In the example shown, the casing 3 fully encloses the metal extrusion 2 although it should be appreciated that partial enclosure by the casing 3 may also be completed.

In a further alternative, the bar extrusion 2 may have no casing 3 and instead be one continuous extrusion and/or injection moulded piece of the exterior shape shown in the Figures.

The leading face 4 of the cross bar 1 includes special features designed to reduce wind noise. Note that the term leading face refers to the side of the cross bar facing into the airstream as the cross bar moves forward when attached to a vehicle. The direction of movement forwards is indicated by arrow A. The term leading face is used in a similar manner to the term leading edge used in aeronautical of sailing terminology being the side of the bar 1 that the air stream first hits and tries to move around.

A traditional flat faced rectangular cross section bar presents a sudden flat face to the air and as the air passes over the bar 1 , vortex shedding occurs resulting in considerable noise in the audible spectrum. The faster the vehicle is travelling, the louder the noise.

The front face 4 of the bar 1 includes an upper and lower projection 5,6 that have a series of notches 7 therein. The notches 7 in the top projection 5 are offset from the notches 7 in the lower projection 6. In the example shown, the notches 7 are cut into the projections on an angle and the sides of each notch 7 rounded.

Between the two projections 5,6 the intermediate region 8 presents a smooth concave surface to the airstream 4. Whilst not wanting to be bound to a specific theory, the intermediate region 8 is understood to disperse air through the notches 7.

The notches 7 are understood to reduce or remove the vortex shedding effect thereby eliminating or at least reducing wind noise from the cross bar 1.

To confirm the reduction in wind noise a trial was completed using an independent authority with a test wind tunnel. The cross bar described above was provided to the authority along with a traditional rectangular extrusion cross bar and a cross bar as described in WO 01/98109 with channels cut out of the metal extrusion itself. Three other commercially available cross bars were also tested in comparison including the Whispbar™ manufactured by the applicant and three other key competitor cross bars sold as being aerodynamic.

The trial involved testing each cross bar in a wind tunnel replicating the wind generated by a car moving at 100 km/h. The sound pressure level was measured for a range of frequencies including the range of 100-400 Hz that is normally heard the loudest by the human ear.

The results of the trial are shown in Figure 7.

As shown, the worst or noisiest cross bar was the standard rectangular bar as expected. The application bar performed at a similar level to the bar taught in WO 01/98109 although it should be noted that manufacture of the application cross bar is considerably quicker and less expensive than the channel design of WO 01/98109.

Interestingly a competitor bar sold as being aerodynamic almost performed as badly as the rectangular bar in the 100-400Hz region whilst two other bars also sold as being aerodynamic designs were worse than the application bar but at least better than a rectangular bar.

The Whispbar™ that is sold as having a quiet design was indeed the least noisy bar by a considerable margin.

The above results confirmed that the application design is at least as quiet as existing designs if not quieter than designs currently sold as being aerodynamic.

The aspects described above may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the embodiments relate, such known equivalents are deemed to be incorporated herein as if individually set forth,

Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Aspects of the present application have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the claims herein.