Background Art When an elongate object, such as a vehicle roof rack cross bar, passes through a volume of air, the air in the path of the moving object is forced to separate to either side of the object until it has passed. This produces an increase in air pressure in front and to either side of the object and an area of reduced air pressure behind the moving object.

As the object moves along its path, displaced air, at a relatively high pressure, starts to move back into the relatively low pressure area behind the moving object. This effect occurs at all speeds of movement and as the speed of the object increases the effect becomes more violent to the point where the rejoining air streams behind the moving object produce noise and vibration.

This phenomena, called vortex shedding, becomes particularly noticeable and annoying when it occurs on vehicle roof mounted luggage carriers, or roof racks as they are more often called. The extent of the problem can vary depending on the position of the roof rack, particularly the front part or parts, the load, if any, being carried,

the prevailing weather conditions and the speed of the vehicle. This can, however, be a problem for a wide range of vehicle appendages, such as pantographs of electric trains by way of example.

A common form of roof rack consists of a horizontal bar, movably attached to which are two supporting and mounting brackets, one located at, or near, each end of the bar, which provide facility for attachment of the assembly to a vehicle. This configuration can be used singly, or in multiple, depending on the load carrying requirements of the user, and is frequently capable of having affixed to it various additional load carrying attachments such as canoe and bike racks, lockable bins and ski racks. This type of rack is quite popular due to its versatility, however, it is particularly prone to producing a loud and annoying howling or humming noise due to the phenomena previously described.

Most of the noise associated with this type of rack is produced by the horizontal, or cross, bar. The prior art reveals a number of attempts to reduce the noise produced by the roof rack cross bar ranging from a perforated shroud as described in German patent 2614365 to the more commonly appearing tear drop or foil shape such as appears in US patents, 4175682,5282560 and 5474218. US patent 5282560 adds to the tear drop or foil shape an additional airflow disturbing strip. The tear drop or foil shape has the added advantage of minimising drag.

While it is recognised that many of the previously proposed systems do reduce the noise produced, they have the disadvantage of not conforming to any particular standard, thus making it difficult to attach extra load carrying attachments, such as ski and bike racks, without using an attachment manufactured specifically for the particular cross bar being used or using specialised adaptation components designed to. match that cross bar. Some have the added disadvantage of being

complicated to set up and use, further, a tear drop or foil shape can only be optimised for one speed and even these cross bars can produce significant amounts of noise at speeds above their optimised range. To extend this range to encompass higher speeds necessitates a longer tear drop or foil profile and this produces a wider bar which is even less amenable to the attachment of additional load carrying equipment.

At the other extreme is the common use of a more or less standard rectangular cross bar of approximately 30mm wide and 20mm deep.

Several companies make roof racks employing cross bars meeting these dimensions and many specialised load carrying attachments made by one company can be readily attached to another companies cross bar. Such bars are also relatively simple and inexpensive to manufacture. While gaining maximum versatility by this approach the disadvantage is that this rectangular cross bar produces a lot of wind noise.

It is possible to place a removable tear drop or foil shape around a standard 30mm x 20mm rectangular cross bar and indeed this has been done. This solution, however, leaves the user in the position of having to decide whether to remove the tear drop or foil shape to affix specialised load carrying attachments and thus re-introduce the noise problem, or to cut holes in the tear drop or foil for these attachments thus leaving visible holes in the tear drop or foil when the specialised load carrying attachment is removed.

In an effort, it would appear, to solve the problem of non compatibility between the various profiles of tear drop or foil shaped roof rack cross bars available, a design incorporating an inverted T slot, in the top of an otherwise standard tear drop or foil shape is sometimes employed.

This serves as an anchoring point for bolts to be used to affix

specialised load carrying attachments. The success of this system with respect to overall flexibility will depend on its level of uptake by the manufacturers of specialised load carrying attachments.

With the current state of division between the two approaches to roof rack design, namely, flexibility and relatively high noise levels versus quietness and a relative lack of flexibility it was felt that there was a need for a roof rack cross bar combining both the flexibility, to attach the many already available specialised load carrying attachments, inherent with the use of a the commonly used 30mm x 20mm profile, with the low noise properties offered by the tear drop or foil shape.

Although discussion has focussed upon roof racks for vehicles it will be appreciated that similar noise issues apply to other vehicle appendages, such as pantographs for electric trains.

Disclosure of the Invention The primary object of the invention is to provide an elongate object, in particular a vehicle roof rack cross bar, which, in use, generates low levels of audible noise over a wide range of operating speeds.

It is a further object of the invention to provide a vehicle roof rack cross bar that is compatible with existing roof rack systems.

It is a further object of the invention to provide a roof rack that is easy to use and manufacture. It would also be desirable to provide a roof rack that produces low drag in use.

Each of the above objects is to be read disjunctively with the object of at least providing the public with a useful choice.

Accordingly, there is provided an elongate vehicle appendage including air flow guiding means defining air flow diverting channels along a leading edge which, in use, direct the flow of air around the vehicle appendage in such a manner as to reduce audible noise associated with vortex shedding.

The fluid flow guiding means may be integrally formed with the vehicle appendage or be in the form of one or more discrete elements attachable to the vehicle appendage.

The channels may be in the form of groves or conduits which direct portions of the fluid flow in a desired manner. In one preferred embodiment the flow diverting channels are angled groves provided at intervals along the vehicle appendage. The groves along the length of the vehicle appendage are preferably parallel to each other. The vehicle appendage may be of rectangular, tear drop or foil cross- section.

Brief Description of the Drawings Preferred embodiments of the current invention will now be described, using a roof rack cross bar as an example, with reference to the accompanying drawings, in which: Figure 1: shows a roof rack according to a first embodiment of the invention in place on a vehicle roof; Figure 2: shows a front view of a portion of a cross bar of the roof rack shown in figure 1; Figure 3: shows a perspective view of a portion of a cross bar of a roof rack shown in figure 1 with lines indicating experimentally observed directions of fluid flow.

Figures 4a & 4b: show cross sectional views of a cross bar of a roof rack shown in figure 1 with lines indicating experimentally observed directions of fluid flow with the cross bar in two different aspects with respect to direction of fluid movement.

Figures 5a & 5b: show perspective views of a tear drop or foil type cross bar incorporating the air flow diverting channels of the invention.

Figure 6: shows a perspective view of a rectangular cross bar incorporating flow diverting conduits according to an alternative embodiment of the invention.

Figure 7: shows a perspective view of a rectangular cross bar incorporating flow diverting channels according to a further alternative embodiment of the invention.

Figure 8: shows a perspective view of a rectangular cross bar incorporating flow diverting channels according to a further alternative embodiment of the invention.

Figure 9: shows a perspective view of a roof rack cross bar having a plurality of air flow guiding means provided along a leading edge thereof.

Figure 10: shows a perspective view of a roof rack cross bar according to another embodiment having a plurality of air flow guiding means provided along a leading edge thereof.

Figure 11 : shows a perspective view of a roof rack cross bar according to a another embodiment having a plurality of air flow guiding means provided along a leading edge thereof.

Figure 12: shows a perspective view of a roof rack cross bar according to a further embodiment having a continuous air flow guiding means provided along a leading edge thereof.

Figure 13: shows a perspective view of a pantograph of an electric train.

Best mode for carrying out the invention Referring to figures 1 to 3 a roof rack incorporating fluid flow diverting channels according to the invention is shown. The preferred cross bar 1 consists of a rectangular section of a length suitable for the vehicle on which its use is intended. The cross bar 1 is preferably of approximate dimensions 30mm wide and 20mm deep and has rounded corners between adjacent faces. On one side of the cross bar 1, in the preferred embodiment this side being a narrow side, there are formed a plurality of air flow diverting channels 2 spaced at intervals across the cross bar 1, such intervals preferably ensuring that the point where an air flow diverting channel 2 exits the upper edge of the cross bar 1 is horizontally displaced on the plane 30 (see figure 3) of the cross bar from any flow diverting channel 2 exiting the lower edge of the cross bar 1 such that an air flow 10 exiting an upper opening of an air flow diverting channel 2 and passing toward the rear of the cross bar 1 does not arrive at the leeward edge of the cross bar 1 above an air flow 9 having exited a lower opening of a air flow diverting channel 2.

Each air flow diverting channel 2 is formed at an angle 6 across the narrow face of the cross bar 1, such angle being sufficient to ensure the upper opening of the flow diverting channel 2 is displaced, in a direction along the cross bar 1, by a distance preferably not less than approximately 1.5 times the width of the air flow diverting channel 2.

The dimension of each air flow diverting channel 2 is preferably between 2mm and 20mm wide and more preferably approximately 10mm wide and between 2mm and 10mm deep and more preferably approximately 6mm deep. In the preferred embodiment all edges and corners of the flow diverting channels 2 are rounded and smoothed.

The distance between air diverting channels is preferably between 20 to 80mm, and more preferably about 50mm. These dimensions may be applied to the other embodiments described herein (except for the groove dimensions for the embodiment utilising fluid flow conduits).

In the preferred embodiment, the air flow diverting channels 2 are preferably arranged such that all air flow diverting channels 2 on one side of the lengthways centre of the cross bar 1 are arranged parallel to each other and all air flow diverting channels 2 on the remaining side of the lengthways centre of the cross bar 1 are arranged parallel to each other and more preferably all air flow diverting channels 2 across the full length of the cross bar 1 are arranged parallel to each other.

When mounted above a vehicle roof 4, by way of a set of roof rack bar supports 5, the cross bar 1 is aligned such that the side of the cross bar 1 containing the air flow diverting channels 2 is facing the vehicles direction of travel 3. When the vehicle is in motion, air striking the cross bar 1 is split, by passage of the cross bar 1 through it, into air 7 passing under the cross bar 1 and air 8 passing over the cross bar 1 (see figure 3). Due to the angle of the air flow diverting channels 2, the air passing under 9 the cross bar 1 that comes into contact with on one of the air flow diverting channels 2, exits the air flow diverting channel 2 at a position displaced, across the plane 30 of the cross bar, from the air passing over 10 the cross bar 1 that exits from the other end of the air flow diverting channel 2.

Additionally, the airflow diverting channels 2 tend to concentrate the air flows 9,10 that come under their influence such that the air flows 9,10 exit the air flow diverting channels 2 in a jet like manner and briefly separate from the cross bar 1 before rejoining near the leeward edge. From the experimentally observed flow patterns it can be seen

that the flows 9,10, influenced by the air flow diverting channels 2, while displaced from each other across the plane 30 of the cross bar and thus being prevented from intersecting, actually tend to pass each other in a plane 31 normal to the cross bar. This effect, combining altered airflows 9,10 with horizontal displacement of said flows serves to suppress noise generation by reducing the occurrence of vortex shedding.

When mounted on the roof 4 of a vehicle the air flow striking a roof rack cross bar 1, particularly one mounted toward the front of the vehicle roof 4 is often influenced by the near presence of the vehicle wind screen such that the air coming up the wind screen, frequently referred to as screen wash, causes the air striking the front of such a cross bar 1 to strike said cross bar 1 from an angle 15 below the horizontal (see figure 4). From experimentally observed flow patterns generated by a cross bar tilted at an angle 15, in this case being an angle of approximately 16°, to simulate windscreen wash, it can be seen that the flows passing under 11 and over 12 the cross bar 1 without coming under the influence of the air flow diverting channels 2 follow its outer surface profile to the leeward edge as does the flow 13 passing under the cross bar having been influenced by the air flow diverting channel 2. The flow 14 passing over the top of the cross bar 1 having been influenced by the air flow diverting channel 2 lifts away from the cross bar 1 and does not contact it again.

In practice the phenomena of vortex shedding manifests itself in two ways with respect to vehicle roof rack cross bars. When the air flow strikes the cross bar on the horizontal plane 30, i. e. without any vertical component, the overall noise level produced is not the key source of annoyance, rather it is the single note produced by the vortex shedding at a level that is continuously audible that causes the problem. When there is a vertical vectorial component introduced, as

would be produced by screen wash, this single note is replaced by a multi frequency howling sound that produces an overall noise level well in excess of the situation when screen wash is not a factor.

Experimentally, a roof rack cross bar constructed in accordance with the preferred embodiment has been compared, in a wind tunnel, with a plain rectangular cross bar similar to the preferred embodiment but lacking air diverting channels, and with a foil shaped cross bar designed, engineered and purported to be at least as quiet as any other similarly shaped bar. The results are as follows : Cross Noise with Noise with airflow Noise increase Bar horizontal air from 16° going from 0° Type flow below horizontal to 16° below (from 0° below horizontal horizontal) Plain-1. 2 * +3. 4 +5. 2 Foil +0. 7 + 1. 4 + 1. 3 Preferre 0.0 0.0 + 0. 6 d * While the overall noise level was lower for this measurement it included a very audible single note which stood out from the base wind noise.

Noise levels in this table are expressed in dB. The base noise level of the wind tunnel has been subtracted and the overall noise levels of the plain and foil cross bars are given relative to the preferred embodiment.

It can be seen from the table that the preferred embodiment has met its primary objective of producing a rectangular cross bar at least as quiet as a tear drop or foil shaped bar. It has also demonstrated itself

to be considerably less susceptible to the effects of screen wash than either the plain bar or the foil shaped bar tested.

When applied to a tear drop or foil shape cross bar 16 (see figure 5) the air flow diverting channels may be formed 17 so as to wrap around the leading edge of the cross bar 16, in a manner so as to preserve the reduced wind resistance characteristics of such a profile cross bar, or they may be formed 30 to pass through the cross bar without attempt to internally match the cross bars 16 profile. This would produce a similar effect to the rectangular section cross bar 1 and thus extend the optimised operating speed range for the tear drop or foil shape cross bar 16 by preventing the return of the vortex shedding phenomena that would otherwise be exhibited at higher speeds by a tear drop or foil shape bar.

In figure 6 is shown a rectangular profile cross bar 18 where the angled air deflecting slots 2 of the preferred embodiment have been replaced by notches 19,20 formed in the upper and lower windward corners of the cross bar 18. Such notches are considered to be provided along leading edges of the cross bar 18. Each upper notch 19 is adjacent paired with lower notch 20 such that the air flows passing through an upper notch 19 do not intersect with the air flows passing through a lower notch 20. This embodiment has been tested in practical use, and has been found to work well.

In figure 7 is shown an embodiment combining a rectangular profile cross bar 21, a flow amplifying channel 22 and air flow diverting channels 23. In this embodiment the flow amplifying channel 22 serves to increase the air flows passing through the air flow diverting channels 23 and over or under the cross bar 21 by diverting air striking across the full width of the cross bar 21 along the flow amplifying channel 22 to where these flows can find vent through the air flow

diverting channels 23, thus adding to the air flows already passing through the air flow diverting channels 23. This embodiment has been tested in practical use and in a wind tunnel and has been found to work well to prevent vortex shedding but not to be quite as quiet, with respect to general wind noise, as the preferred embodiment.

In Figure 8 is shown an alternative embodiment where the air flow diverting channels are in the form of conduits 26 & 27 passing from the windward side, being the side facing the direction of travel 3, of a rectangular section cross bar 24 toward the top 29 and bottom 28 leeward corners of the cross bar 24. The upper conduits 27, passing from the windward side of the cross bar 24 toward the upper leeward corner 29 of the cross bar 24 are angled toward one side of the vehicle while the lower conduits 26, passing from the windward side of the cross bar 24 toward the lower leeward corner 28 of the cross bar 24 are angled toward the opposite side of the vehicle. The conduits are so spaced as to ensure the upper conduits 27 exit in a position horizontally displaced from the exit point of the lower conduits 26. To maximise the amount of air passing through the conduits 26, 27 there is preferably incorporated in the windward side of the cross bar 24 a flow amplifying channel 25 passing along the length of the cross bar 24. The purpose of the flow amplifying channel 25 is to trap air striking the full width of the front of the cross bar 24 within the confines of the flow amplifying channel 25 and thus create an area of higher pressure that is forced to find vent through the conduits 26,27 thus maximising flow passing through these conduits. This embodiment has been tested in practical use and in the wind tunnel and has been found to work well, being only slightly noisier than the preferred embodiment.

In operation, the above embodiments are used in exactly the same manner as any other similarly dimensioned rectangular cross bar would

be used and can have affixed to it all of the many specialised load carrying attachments designed to work with the 30mm x 20mm rectangular profile and, provided it is mounted with the air flow diverting channels facing in the direction of travel the preferred embodiment will produce substantially less noise than a similarly dimensioned cross bar without air flow diverting channels and no more noise than a tear drop or foil shaped cross bar.

Other potential embodiments could add to, or replace, the air flow diverting channels on the'front'face of the cross bar with channels on the upper and/or lower faces of the cross bar, such channels being angled in opposing directions. By joining and suitably positioned air flow diverting channels angled across all of the faces of a cross bar, a spiral channel could be produced. While these other embodiments may also be effective at reducing noise, the existence of channels on the upper and lower surfaces of a cross bar would present a number of structural problems with regard to cross bar strength. In practice it has been found that the addition of air flow diverting channels on the upper and lower surfaces of the cross bar adds little to the noise reduction produced by air flow diverting channels on the front only of the cross bar.

In the following examples the fluid flow guiding means is in the form of one or more discrete element which is attachable to the cross bar.

In figure 9 cross bar 35 is provided with holes 33 along its leading edge. A plurality of fluid flow guiding means 36 are affixed via projections 32 which engage in holes 33 to secure the fluid flow guiding means to the leading edge of cross bar 35. The fluid flow guiding means are so spaced as to define fluid flow channels 34 therebetween. When assembled a similar profile to that of the integrally formed cross bar can be achieved.

In use, cross bar 35 may be secured to a roof rack. Once fittings have been secured to the roof rack fluid fiow guiding means 36 may be positioned in the available locations. This construction enables a cross bar 35 of standard dimensions to be produced with the only modification being the drilling of holes 33 along the leading edge.

Fluid flow guiding means 36 may be formed of plastics or the like by injection moulding or other suitable processes.

Referring now to figure 10 an alternative embodiment is shown. In this embodiment cross bar 40 has a T slot 41 formed along the leading edge of cross bar 40. Fluid flow guiding means 42 are provided with T-shaped formations 43 which slideably engage within T slot 41.

In this arrangement at least one side of the roof rack must be detached from cross bar 40 to allow fluid flow guiding means 42 to be fitted (unless they are constructed of sufficiently resilient material that the T shaped portions 43 may be push fitted into T slot 41). Assembly may be slightly less convenient than for the arrangement shown in figure 9 but the fluid flow guiding means 42 will be securely retained in this embodiment.

Referring now to figure 11 a further embodiment is shown in which fluid flow guiding means 51 are provided at intervals along cross bar 50. In this case cross bar 50 is a steel cross bar of standard constructions requiring no modification. Fluid flow guiding elements 51 include a magnetised material enabling fluid flow guiding elements 51 to be magnetically secured to cross bar 50. In this embodiment fluid flow guiding means 51 can be placed at any desired spacing to form channels 52. Fluid flow guiding means 51 may be cut to desired lengths to fit around roof rack fittings. Fluid flow guiding means 51 may alternatively be provided with adhesive on the undersides thereof

to enable them to be secured to a cross bar. Elements 51 may be provided on a support strip at a desired spacing so that an entire assembly can be secured to a cross bar in one action. A suitable backing strip may be provided over the adhesive applied to elements 51 for ease of handling prior to attachment.

Referring now to figure 12 an alternative embodiment is shown in which the fluid flow guiding means 61 is of continuous construction and may be fitted over cross bar 60 of standard dimensions. Channels 62 are formed in fluid flow guiding means 61. Fluid flow guiding means 61 may be formed of plastics or other suitable material.

Referring to figure 13 a pantograph 70 of an electric train is shown.

The techniques of the invention, as applicable to this application, may be applied to cross bars 71 to minimise audible noise.

Although the invention has been principally described in relation to roof racks having rectangular or aerofoil shaped cross sections it is to be appreciated that the invention may be applied to appendages of any cross section, including cylindrical bars.

Although the invention has been described in relation to roof racks it will be appreciated that the invention may be applied to a wide range of vehicle appendages including pantographs of electric trains.

Vehicle appendages constructed according to the invention can significantly reduce audible noise levels whilst being simple to construct, and, in some embodiments, enabling existing components to be modified.

Where in the foregoing description reference has been made to integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example it is appreciated that improvements and/or modification may be made thereto without departing from the scope or the spirit of the present invention.