GB2271323A

GB2271323A - Vehicle aerodynamics.

Info

Publication number: GB2271323A
Application number: GB9319879A
Authority: GB
Inventors: Valerian J Dare-Bryan
Original assignee: Ricardo A S & A Ltd
Current assignee: Ricardo A S & A Ltd
Priority date: 1989-11-14
Filing date: 1993-09-27
Publication date: 1994-04-13
Anticipated expiration: 2010-11-13
Also published as: GB2271323B; GB9319879D0

Abstract

Air guidance surfaces 53 are provided in advance of a set of rear wheels 52 and have a curvilinear portion 54 merging into a region which is directed inwardly of the side of the trailer. An air guidance surface 56 to the rear of the wheels may also be provided, also guide vanes 17 located to the rear and sides of the tractor cab 10 which surfaces are convexly shaped and aligned at their rear ends with the trailer sides 30. Further convex guides surfaces 20 are located on the cab roof to guide air towards the upper surface of the body 15 and towards the body side surfaces 30. <IMAGE>

Description

Vehicle Aerodynamics This invention relates to vehicle aerodynamics and in particular to the aerodynamics of tractor/articulated trailer vehicle combinations.

Tractor/articulated trailer combinations are inherently difficult to make aerodynamically efficient partly due to the relatively large gap which is required between the tractor and the articulated trailer and partly due to the relatively large boxlike body which is usually mounted on the trailer and which is of larger cross-section than the tractor.

It is an object of the invention to provide means whereby the aerodynamic qualities of tractor/articulated trailers, in particular the trailers, can be improved.

According to one aspect the invention provides a trailer for a tractor/trailer vehicle combination the trailer being intended for towing behind and pivotable relative to a tractor unit which includes a cab mounted on a chassis, in which the trailer has a chassis with a rearward set of wheels, for attachment to the tractor unit, and the trailer has air guidance surfaces located on the trailer chassis, depending therefrom, and lying generally vertically, said air guidance surfaces including portions situated in advance of the set of wheels and to the sides of the trailer and said surfaces at their leading ends each having a region which is radiused to present a curvilinear leading profile merging into a region which is directed inwardly of the sides of the trailer.

Preferably the inwardly directed region lies transversely to the direction of travel of the trailer and extends to adjacent a parking leg of the trailer.

Conveniently the air guidance surfaces includes portions which lie to the rear of said set of wheels and to the sides of the trailer and said surfaces are each inclined inwardly of the trailer in the rearwards direction.

According to another aspect the invention provides a trailer for a tractor/trailer vehicle combination the trailer being intended for towing behind a tractor unit which includes a cab mounted on a chassis, and the trailer having a chassis with a rearward set of running wheels for attachment to the tractor unit and having air guidance surfaces lying generally vertically, located on the trailer chassis and depending therefrom, said air guidance surfaces including a portion situated to the rear of the set of wheels and to the sides of the trailer and said surfaces each being inclined inwardly of the trailer in the rearward direction.

Further features of the invention will appear from the following description of an embodiment of the invention given by way of example only and with reference to the drawings in which: Fig. 1 is a perspective view of a vehicle according to the invention, Fig. 2 is a view, from the front and above, of the vehicle of Fig. 1, Fig. 3 is a side elevation of the vehicle of Fig. 1, Fig. 4 is a perspective view from the rear and one side of a trailer of the vehicle of Figs. 1-3, and Figs. 5A, 5B and 5C are alternative cross-sections at position 5-5 in Fig. 4.

Referring to the drawings and firstly to Figs. 1-4 a tractor/articulated trailer vehicle combination, generally called an articulated vehicle, is shown which in many respects is of conventional form. The vehicle has a tractor unit with a cab 10 which is mounted on a chassis 11, the chassis extending rearwards and having a mounting (not shown) by which a trailer 12 is connected to he tractor for articulation or pivoting about the mounting in a generally horizontal plane. The trailer 12 is generally demountable from the tractor to be supported on its wheels 13 and on parking legs. During use the trailer is supported at its rear end on wheels 13 and at its forward end on the chassis 11 of the tractor.

In the present case the trailer 12 has a chassis which is fitted with a box-like body 15 generally rectangular in cross-section and extending in the fore and aft direction.

Such vehicle combinations have proved difficult to improve in terms of their aerodynamic efficiency which is generally low.

In order to improve the passage of air over the vehicle and hence its aerodynamic efficiency a standard cab and a standard trailer body has been fitted with various air guidance means with the object of smoothing the flow of air as it passes from the cab to the body but these have offered inadequate benefits.

It will be seen that the body 15 cross-section is of relatively larger dimensions than the cab 10 and that the nature of articulated vehicles is such that there is a relatively large gap between the cab 10 and the body 15.

The cab 10 is fitted at its sides and projecting beyond the cab rear towards the body 15 with vanes 17 which extend the full height of the cab and down to the level of the wheels 18 of the vehicle cab. The upper sections 17A of the vanes are attached to the cab structure, usually at the junction of the side wall and the rear wall of the cab in an adjustable manner. The lower sections 17B of the vanes are attached to the cab chassis 11 and the upper and lower sections 17A and 17B are overlapped to provide a generally continuous air guidance outer surface and for relative movement between the chassis and the cab.

At their upper ends the upper vane sections 17A extend upwards beyond the top of the cab 10 to define the rearward end of a roof air guidance structure 20. The shape of the vanes 17 will be described more fully with reference to Figs. 5A, 5B and 5C.

The air guidance structure 20 is fitted onto the roof of the can 10 and the structure 20 defines an upwardly facing surface 21 with side surfaces 22 to each side of the surface 21. The upwardly facing surface 21 is of generally convex profile in section in the fore and aft direction with a leading portion 21A adjacent the roof of the cab which is curved at a relatively small radius (see especially Fig. 3), the radius progressively increasing in the rearwards direction so that the curvature of the surface at portion 21A is of a large radius. Moreover the profile of the surface 21 is such that an imaginary line 21C taken from the rear of the surface 21 is generally directed towards the forward end of the roof 25 of the box-like body 15.

At the forward end of the roof 25 at the junction between the roof 25 and the front end wall 26 of the body there is provided a radiused protrusion 27 which in this case (Figs. 1-3) is formed on a forwardly extending portion of the body.

The side surfaces 22 of the structure 20 are contoured to merge with the surface 21 along their upper ends and are of convex profile in cross-section, the verticality of the surfaces 22 increasing in the rearwards direction so that towards their rearward ends the surfaces 22 are generally upright and directed towards the side surfaces 30 of the body 15. To accommodate the increasing verticality of the side surfaces 22 the upwardly facing surface 21 increases in width in its rearward direction so that towards its rearmost end the width of the surface 21 approaches the width of the body 15.

In the Figs. 1-4 arrangement the portions of the surfaces to the sides of the structure 20 are contiguous with the vanes 17.

In Figs. 5A, 5B and 5C are shown different cross-sectional profiles on the line 5-5 of Fig. 3 which may be adopted for the vanes 17. The outer air guidance surfaces 42 of the profiles differ primarily depending on the relative widths of the cab 10 and the body 15, the profile 42 of Fig. 5A being applicable when the relative widths have a small difference, the profile 42 of Fig. 5C when the difference is large and the profile 42 of Fig.

5B when the difference is intermediate those of Figs. 5A and 5C.

In each case it will be seen that at the leading edge 42A of the vane 17 the curvilinear shape is of relatively small radius and the radius increases in the rearwards direction until, towards the rearward edge, the radius is large or non-existent as at 42B.

Towards the rearwards edge the outer surface of each vane is generally aligned with the side surface 30 of the body 15 but their is provided a continuous vertical projecting ridge 44 extending along the rearmost edge and directed outwards of surface 42B. At the forward end of the trailer side surface 30 the junction between the surface 30 and the end wall 26 of the body is radiused as at 43.

The width of the vanes 17 in the fore and aft direction is selected to be as large as is compatible with obtaining access between the cab 10 and the body 15 and with the need for the trailer to articulate relative to the cab during manoeuvring of the vehicle. In this way the gap between the cab and body is minimised.

The function of the vanes 27 and the shape of the air guidance surfaces is to guide the air flow from the sides of the cab so that it passes over the surfaces 42 of the vanes and then passes to the sides 30 of the body in a smooth continuous flow. In practice the flow of air is speeded up as it passes over the surface 42 and the function of the projecting ridge 44 is to ensure a clean cut-off of the air flow as it passes from the vanes.

Similarly the air flow over the surfaces 21 and 22 guides the air to the roof and sides of the body in a smooth flow.

In each case the air flow is able to pass over the gap between the cab and the body without any significant amount of air passing into the gap and without the air flow separating appreciably from the vehicle sides which would cause air pressure reductions and eddies.

The trailer 12 is also provided with air guidance surfaces to improve the air flow over the trailer body and adjacent areas.

Thus at the rear of the upper surface or roof 25 of the body 15 there is provided a downwards, rearwardly inclined surface 50 to the sides of which there are side ridges 52 the upper surfaces of which are maintained at the height of the remainder of the roof 25.

Below the level of the box-like body 15 there is considerable gain in maintaining a clean air flow but, due to the presence of the tractor and trailer wheels, a continuous air flow surface is difficult to provide. To improve the air flow in this region there is provided to each side of the trailer and attached to the trailer chassis a downwardly directed vertical member defining a surface 53 in advance of the set of wheels 52 and defined by side walls. The leading ends of the side walls 53 adjacent the front trailer wheels are provided with a region with relatively large radius surface as at 54 which extends inwardly from the radiused region toward and up to the trailer parking leg. Air flow which becomes detached from the vehicle after passing over the lower parts 17B of the vanes 17 becomes reattached to the side surfaces 53.

Behind the rear wheels 52 there is provided further side walls 56 (Fig. 4) which are attached to the chassis and extend vertically downwardly. The side walls 56 in this case define air guidance surfaces which are inclined inwardly relative to the longitudinal direction of the body in the rearwards direction.

Thus the surfaces to each side taper inwardly towards one another in the rearwards direction.

Claims

1. A trailer for a tractor/trailer vehicle combination the trailer being intended for towing behind and pivotable relative to a tractor unit which includes a cab mounted on a chassis, in which the trailer has a chassis with a rearward set of wheels for attachment to the tractor unit, and the trailer has air guidance surfaces located on the trailer chassis, depending therefrom, and lying generally vertically, said air guidance surfaces including portions situated in advance of the set of wheels and to the sides of the trailer and said surfaces at their leading ends each having a region which is radiused to present a curvilinear leading profile merging into a region which is directed inwardly of the sides of the trailer.

2. A trailer according to claim 1 wherein the inwardly directed region lies transversely to the direction of travel of the trailer and extends to adjacent a parking leg of the trailer.

3. A trailer according to claim 1 or 2 wherein the air guidance surfaces includes portions which lie to the rear of said set of wheels and to the sides of the trailer and said surfaces are each inclined inwardly of the trailer in the rearwards direction.

4. A tractor/trailer vehicle having the trailer substantially as described with reference to the drawings.

4. A trailer for a tractor/trailer vehicle combination the trailer being intended for towing behind a tractor unit which includes a cab mounted on a chassis, and the trailer having a chassis with a rearward set of running wheels, for attachment to the tractor unit and having air guidance surfaces lying generally vertically located on the trailer chassis and depending therefrom, said air guidance surfaces including a portion situated to the rear of the set of wheels and to the sides of the trailer and said surfaces each being inclined inwardly of the trailer in the rearward direction.

5. A trailer for a tractor/trailer vehicle substantially as described with reference to the drawings.

Amendments to the claims have been filed as follows 1. A tractor/trailer vehicle combination including a trailer intended for towing behind and pivotable relative to a tractor unit which includes a cab mounted on a chassis, the trailer having a chassis with a rearward set of wheels and the chassis being for attachment to the tractor unit, and the trailer having air guidance surfaces located on the trailer chassis, depending therefrom, and lying generally vertically, said air guidance surfaces including portions situated in advance of the set of wheels and to the sides of the trailer and said surfaces at their leading ends each having a region which is radiused to present a curvilinear leading profile merging into a region which is directed inwardly of the sides of the trailer.

2. A combination according to claim 1 wherein the inwardly directed region lies transversely to the direction of travel of the trailer and extends to adjacent a parking leg of the trailer.

3. A combination according to claim 1 or 2 wherein the air guidance surfaces includes portions which lie to the rear of said set of wheels and to the sides of the trailer and said surfaces are each inclined inwardly of the trailer in the rearwards direction.