WO1991007305A1

WO1991007305A1 - Vehicle aerodynamics

Info

Publication number: WO1991007305A1
Application number: PCT/GB1990/001738
Authority: WO
Inventors: Valerian John Dare-Bryan
Original assignee: Ricardo A.S. & A. Limited
Priority date: 1989-11-14
Filing date: 1990-11-12
Publication date: 1991-05-30
Also published as: GB9024679D0; GB8925725D0; AU6646490A; GB2238762B; GB2238762A

Abstract

A tractor/trailer vehicle combination is made aerodynamically efficient by providing a series of air guidance surfaces for the vehicle when travelling. The surfaces include 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). Guide surfaces (53, 56) may also be provided on the trailer (12) including side surfaces below the trailer body to each side of the rear wheels (52).

Description

Vehicle Aerodynamics

This invention relates to vehicle aerodynamics and in particular to the aerodynamics of tractorfarticulated 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 box¬ like* 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 can be improved.

According to one aspect the invention provides a tractor/trailer vehicle combination comprising a tractor unit having a cab mounted on a chassis, the cab having to each of its sides air guidance surfaces extending to the rear of the cab; an articulated trailer pivotable relative to the tractor unit and spaced from the cab, the trailer having a body of a width greater than that of the cab_f the air guidance surfaces being convexly shaped in horizontal cross-section and being generally aligned with the side surfaces of the body towards their trailing edges.

Preferably the air guidance surfaces extend from the upper end of the cab to the level of the vehicle wheels.

Conveniently the air guidance surfaces each have a curvilinear outer profile in horizontal cross-section which towards the forward end is of smaller radius adjacent the side wall of the cab_f said radius increasing in the rearwards direction.

Moreover each of the air guidance surfaces may have along its rearmost edge a generally vertically directed projection. Preferably the air guidance surfaces at each side of the cab are in two sections, an upper section mounted on the cab and a lower section mounted on the cab chassis, the sections overlapping to permit relative movement between the cab and the chassis.

The forward ends of the side surfaces of the trailer body where the ends meet the front surface of the body are conveniently radiused.

According to another aspect the invention provides a tractor/trailer combination comprising a tractor unit including a cab mounted on a chassis; and an articulated trailer pivotable relative to the tractor unit and spaced from the cab, the trailer having a body of a width and height greater than that of the cab, the cab roof having air guidance surfaces whereby the air is guided during travel to pass along roof and side surfaces of the trailer body, the cab roof surfaces including an upwardly facing surface and side surfaces to each side of the upwardly facing surface and the upwardly facing surface and the side surfaces each having a convexly-shaped profile in cross section with the rear portion of the upwardly facing surface being generally aligned with or directed towards the upper leading edge of the trailer body.

Preferably the upper leading edge of the trailer body has a forwardly projecting curvilinear portion to which the rear of the upwardly facing surface is directed.

Towards their rearward ends the side surfaces are conveniently aligned with air guidance surfaces located to the rear and sides of the cab.

According to another aspect the invention provides a tractor/trailer vehicle combination comprising a tractor unit including a cab mounted on a chassis; and an articulated trailer having a width and height greater than that of the tractor unit, the trailer having a chassis with a rearward set of wheels and, located on the trailer chassis and depending therefrom, air guidance surfaces including generally vertical guidance surfaces in advance of said set of wheels and to the sides of the trailer, the leading ends of said vertical guidance surfaces being shaped to present a curvilinear leading profile.

Preferably the air guidance surfaces on the trailer include generally vertical surfaces to each side of the trailer behind the set of wheels which surfaces are each inclined inwardly in the rearwards direction.

It will be seen that the surfaces provided to guide the air flow in the transition between the cab and body are contoured to enable the flow of air to pass smoothly from the cab and its associated surfaces towards and along the sides and roof of the trailer body. In this way the air does not suffer from excessive eddying and the creation of induced negative air pressures is minimised. In particular air passing towards the transition region between the cab and trailer body is not directed out sideways or upwards away from the body sides and roof.

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. 2 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/articulatedtrailervehicle combination, generallycalled 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 the tractor for articulation or pivoting about the mounting in a generally horizontal plane. The trailer 12 is generally demountable from the tractor and supported at its rear end on wheels 13 and at its forward end on the chassis 11 of the tractor.

In this 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 cab 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 larger 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 rearwards 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 there 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 surfaces 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 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 relatively large radius surface as at 54. Air flow which becomes detached from the vehicle after passing over the lower parts 17B of the 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 surf ces to each side taper inwardly towards one another in the rearwards direction.

Claims

1. A tractor/trailer vehicle combination comprising a tractor unit having a cab mounted on a chassis, the cab having to each of its sides air guidance surfaces extending to the rear of the cab; an articulated trailer pivotable relative to the tractor unit and spaced from the cab, the trailer having a body of a width greater than that of the cab, the air guidance surfaces being convexly shaped in horizontal cross-section and being generally aligned with the side surfaces of the body towards their trailing edges.

2. A combination according to claim 1 wherein the air guidance surfaces extend from the upper end of the cab to the level of the vehicle wheels.

3. A combination according to claim 1 or 2 wherein the air guidance surfaces each have a curvilinear outer profile in horizontal cross-section which towards the forward end is of smaller radius adjacent the side wall of the cab, said radius increasing in the rearwards direction.

4. A combination according to claim 1, 2 or 3 wherein each of the air guidance surfaces has along its rearmost edge a generally vertically directed projection.

5. A combination according to any one of the preceding claims wherein the air guidance surfaces at each side of the cab are in two sections, an upper section mounted on the cab and a lower section mounted on the cab chassis, the sections overlapping to permit relative movement between the cab and the chassis.

6. A tractor/trailer vehicle combination comprising a tractor unit including a cab mounted on a chassis; and an articulated trailer pivotable relative to the tractor unit and spaced from the cab, the trailer having a body of a width and height greater than that of the cab, the cab roof having air guidance surfaces whereby the air is guided during travel to pass along roof and side surfaces of the trailer body, the cab roof surfaces including an upwardly facing surface and side surfaces to each side of the upwardly facing surface and the upwardly facing surface and the side surfaces each having a convexly-shaped profile in cross-section with the rear portion of the upwardly facing surface being generally aligned with or directed towards the upper leading edge of the trailer body.

7. A combination according to claim 6 wherein the upper leading edge of the trailer body has a forwardly projecting curvilinear portion to which the rear of the upwardly facing surface is directed.

8. A combination according to claim 6 or 7 wherein the vertical leading edges of the trailer body are arcuately profiled.

9. A combination according to claim 6, 7 or 8 wherein the side surfaces of the cab roof are generally aligned with or directed along the sides of the trailer body.

10. A tractor/trailer vehicle combination comprising a tractor unit including a cab mounted on a chassis, and an articulated trailer having a width and height greater than that of the tractor unit, the trailer having a chassis with a rearward set of wheels and, located on the trailer chassis and depending therefrom, air guidance surfaces including generally vertical guidance surfaces in advance of said set of wheels and to the sides of the trailer, the leading ends of said vertical guidance surfaces being shaped to present a curvilinear leading profile.

11. A tractor/trailer combination according to claim 10 wherein the air guidance surfaces on the trailer include generally vertical surfaces to each side of the trailer behind the set of wheels which surfaces are each inclined inwardly in the rearwards direction.

12. A combination according to claim 10 or 11 wherein the trailer carries a box like body on its chassis and the upper surface of the body has a downwardly inclined portion at its rearward end flanked by ridges at the side edges.

13. A tractor/trailer vehicle combination substantially as described with reference to the drawings.