GB2023519A

GB2023519A - An Air Flow Diverter for Reducing the Aerodynamic Drag of a Vehicle

Info

Publication number: GB2023519A
Application number: GB7918770A
Authority: GB
Original assignee: Centro Ricerche Fiat SCpA
Current assignee: Centro Ricerche Fiat SCpA
Priority date: 1978-06-07
Filing date: 1979-05-30
Publication date: 1980-01-03
Also published as: FR2427939A1; BE876813A; DK234479A; IT1108592B; DE2921355A1; LU81360A1; CH634515A5; SE7904881L; GB2023519B; FR2427939B1; NL7904439A; IT7868316A0; DE7915232U1; CA1105527A; JPS558988A

Abstract

An air flow diverter for a vehicle having a front roof portion (3) and a rear roof portion (9) at a higher level than the front roof portion has superimposed laminar elements (5, 6), the lowermost of which is adjacent the front roof portion (3) of the vehicle. The or each other laminar element has its front edge disposed in proximity to the laminar element below it, defining therewith a transverse entrance slit (7). Each pair of adjacent laminar elements furthermore define a divergent duct downstream of the respective entrance slit. In operation of the vehicle a part of the air flow passes through the divergent duct, increasing in pressure, to establish a high pressure region downstream of the diverter, substantially fixed relative to the vehicle, which encourages the deflection of the principal part of the air flow over the roof and sides of the vehicle when the vehicle is in motion. <IMAGE>

Description

SPECIFICATION Airflow Diverter for Reducing the Aerodynamic Drag of a Vehicle The present invention relates to air flow diverters for vehicles having a front roof portion and a rear roof portion disposed at a higher level than the said front roof portion. Such diverters are mounted above the front roof portion for the reduction of the aerodynamic drag of the vehicle.

in such vehicles the air flow diverter mounted above the front portion of the roof has the function of diverting the flow of air which impinges on the roof when the vehicle is moving, over the rear portion of the roof. For this purpose deflectors mountable on such vehicles are usually in the form of a foil which extends substantially linearly transversely across the vehicle and is inclined upwardly from a leading edge to a trailing edge (see for example British Patent No.

1,404,038 and U.S. Patent No. 3,972,556).

Sometimes such diverters further include two vertical side walls positioned at each lateral end of the foil, in such a way as to divert the said flow of air not only over the rear portion of the roof but also around the sides of the vehicle (see for example U.S. Patent No. 3,972,556). The use of such vertical side walls gives rise, however, to the disadvantage that the vehicle has reduced lateral instability when taking bends.

According to one aspect of the present invention an air flow diverter for the reduction of the aerodynamic drag of a vehicle having a front roof portion and a rear roof portion disposed at a higher level than the front roof portion, comprises a plurality of superimposed laminar elements and mounting means for mounting the diverter on the said front roof portion of the vehicle in such a way that the laminar elements extend from side to side of the vehicle with a trailing edge higher than a leading edge, and with the leading edge of the lowermost laminar element disposed closely adjacent the front roof portion of the vehicle, the leading edge of each other laminar element being situated close to the underlying element in such a way as to define with it a transverse slit, and any two adjacent laminar elements of the said diverter defining between them rearwardly of the respective slit, a duct having an area increasing towards the rear part of the diverter.

The rearwardly increasing area of the duct causes an increase of pressure in that portion of the air flow which, when the vehicle is moving, passes through the said slit, thus encouraging the formation, downstream of the diverter itself, of a zone of high -pressure which is substantially stationary with respect to the vehicle, and which therefore causes the diversion of the flow of air both over the rear portion of the roof and around the sides of the rear part of the vehicle.Because of this use of the deflector of the present invention allows a reduction of the aerodynamic drag of the vehicle to be obtained which is greater than, or at least comparable to, that obtainable with known deflectors of the type provided with vertical side walls, and at the same time avoids the disadvantage of instability of the vehicle which is characteristic of the use of deflectors having vertical side walls.

The type of vehicle to which the deflector of the present invention can be fitted may be, for example, a motor lorry, in which the case the front roof portion is constituted by the cabin of the lorry, whilst the rear roof portion is constituted by the roof of the body of the lorry, or possibly by the upper horizontal surfaces of the load being transported by the lorry. Alternatively the vehicle may be a composite vehicle, including a towing vehicle and a trailer, or an articulated vehicle comprising a tractor and semi-trailer. A particular example of the use of the air flow diverter of the present invention is a composite towing vehicle and trailer unit, in which the towing vehicle is constituted by a motor car and the trailer by a caravan.

The present invention also comprehends a vehicle when fitted with an air flow diverter according to the invention as defined above.

One embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates, in side view, a deflector according to the present invention mounted on a composite vehicle comprising a motor car and a caravan; Figure 2 is a perspective view of the deflector according to the present invention; Figure 3 is a side view of the deflector of Figure 2, and Figures 4 and 5 illustrate two other useful applications of the deflector according to the present invention.

In Figure 1, there is indicated a motor vehicle 1 towing a caravan 2. On the roof 3 of the motor vehicle 1 is mounted, by means of supports 4a, a deflector 4 constituted by two superimposed laminar elements 5, 6. Each of the laminar elements 5, 6 extends in a straight line transversely across the vertical longitudinal plane of the motor vehicle 1. The section in this plane of each of the laminar elements 5, 6 is constituted by a curved line (see Figure 3) sloping rearwardly upwardly, that is sloping up from a leading edge of a higher trailing edge of the element. The lower laminar element 5 has a leading edge 5a disposed closely adjacent the roof 3 of the motor vehicle.

The upper laminar element 6 is provided with a rounded leading edge 6a, disposed adjacent the laminar element 5, in a position set back with respect to the leading edge 5a thereof, in such a way as to define, with the laminar element 5, a transverse slit 7. The laminar elements 5, 6 have a profile such that between them they define, rearwardly of the transverse slit 7, an air guide duct 8 the cross sectional area of which increases rearwardly.

In the embodiment illustrated in Figure 1, the caravan 2 towed by the motor vehicle 1 has a roof 9 the front of which joins a front wall 10 of the caravan 2 by means of a rounded front edge 11.

The plane tangential to the trailing edge 13 of the laminar element 6 is indicated 12; this plane contains the horizontal transverse line 14 defined by the intersection of the projection of the roof 9 of the caravan 2 with the projection of the front wall 10. If the upper front edge 11 of the caravan 2 has a sharp angle, the plane 12 is disposed in such a way as to contain the edge 11.

When the motor vehicle 1 is moving a part of the flow of air resulting from this movement penetrates through the slit 7 and flows out through the divergent duct 8 thereby increasing in pressure. Consequently, this creates, rearwardly of the deflector 4, in the region between the motor vehicle 1 and the caravan 2, a region of high pressure which is relatively fixed with respect to the caravan 2, and which encourages the deflection of the flow of air over the roof 9 of the caravan 2 and around its sides. The deflector of the present invention therefore has no need of vertical lateral walls for diverting the air flow around the sides of the caravan 2 since this function is performed by the region of high pressure generated by the divergent duct 8.The deflector of the invention therefore does not suffer from the disadvantages of instability of the vehicle in conditions when the longitudinal axes of the motor vehicle 1 and the caravan 2 are not aligned, that is when the composite vehicle is taking a bend or corner.

Figure 4 illustrates an application of the deflector of the present invention to an articulated vehicle constituted by a tractor 1 5 and a semitrailer 16. In this case also, the semi-trailer 1 6 has a roof 1 7 which lies at a higher level than the roof 1 8 of the cabin of the tractor 1 5. The air flow diverter 4 allows the diversion of the flow of air which impinges on the tractor, when the vehicle is moving, over the roof 1 7 and to either side of the semi-trailer 1 6.

Figure 5 illustrates the application of the deflector of the present invention to a lorry having a cabin 28 the roof 1 9 of which is at a lower level than the horizontal surface 20 of the rear body 21. The horizontal upper surface 20 could, of course, be defined by the load transported by the lorry.

Tests have been conducted both in wind tunnels and on the road to ascertain the amount of reduction of fuel consumption which can be obtained by the use of the diverter of the invention when used on a composite vehicle constituted by a motor car and a caravan. In these tests the diverter used had the geometry illustrated in Figure 3 in which the inclinations, with respect to the horizontal, of the general planes of the two laminar elements 5, 6 are indicated by a and p respectively. The cross sectional shape of the elements 5 and 6 are defined largely by circular curves the radii of which are indicated R1, R2, R3, and R4 in Figure 3. The lengths which define the main geometry of the profile of the two laminar elements 5, 6 are indicated a, b, c, d, e, as indicated in Figure 3.

The tests were conducted with a deflector having the following geometry: a=13 ; p=26 ; a=b=600 mm; c=140 mm; d=1 70 mm; e=100 mm; R1=70 mm; R2=270 mm; R3=340 mm; R4=250 mm.

The test were performed at a velocity of or equivalent to 90 km. per hour. The results of the wind tunnel tests indicated a reduction of the coefficient of aerodynamic drag of the vehicle from the value of 2.78 without the diverter of the invention to the value 1.74 with the diverter fitted. The road tests were performed on a motor car having an engine capacity equal to 1800 cc and on a motor car having an engine capacity equal to 2000 cc.

In the first case the utilisation of the deflector of the present invention produced a reduction of the fuel consumption from 21.9 litres per 100 Km to 1 8 litres per 100 Km. This corresponds to a reduction of fuel consumption of 7.8%. This result was obtained using a caravan having a front upper edge with a sharp corner. By using, on the other hand, in the same conditions, a caravan having a rounded front upper edge the fuel consumption was reduced, by fitting the deflector of the invention, from 18.1 litres per 100 Km. to 16.35 litres per 100 Km. This corresponds to a reduction of a fuel consumption of 9.7%.

In the case of a motor car having an engine capacity equal to 2000 cc, the fuel consumption was reduced from 19.7 litres per 100 Km. to 15.75 litres per 100 Km (a reduction of fuel consumption of 20.05%) with a caravan having an upper front edge with a sharp corner, and from 1 5.2 litres per 100 Km. to 14.3 litres per 100 Km (reduction of fuel consumption of 5.9%) with a caravan having a rounded front upper edge.

Claims

1. An air flow diverter for the reduction of the aerodynamic drag of a vehicle having a front roof portion disposed at a higher level than the front roof portion, comprising a plurality of superimposed laminar elements, and mounting means for mounting the diverter on the said front roof portion of the vehicle in such a way that the said laminar elements extend from side.to side of the vehicle each with a trailing edge higher than a leading edge, and with the leading edge of the lowermost laminar element disposed closely adjacent the front roof portion of the vehicle, the leading edge of each other laminar element being situated close to the underlying element in such a way as to define with it a transverse slit, and any two adjacent laminar elements of the said diverter defining between then rearwardly of the respective slit, a duct having an area increasing towards the rear of the diverter.

2. An air flow diverter as claimed in Claim 1, in which the laminar elements extend in a straight line from side to side of the diverter.

3. An air flow diverter as claimed in Claim 1 or Claim 2, in which the laminar elements are curved as viewed in section taken perpendicular to the leading edge thereof.

4. An air flow diverter as claimed in any of Claims 1 to 3, in which there are two laminar elements.

5. An air flow diverter as claimed in Claim 4, in which the upper laminar element has a rounded leading edge.

6. A vehicle having a front roof portion and a rear roof portion disposed at a higher level than the front roof portion, the said vehicle being provided with a diverter mounted above the front roof portion for the reduction of the aerodynamic drag of the vehicle, in which the diverter comprises a plurality of superimposed laminar elements disposed in such a way that they extend from side to side of the vehicle, with a trailing edge higher than a leading edge, and with the leading edge of the lowermost laminar element disposed closely adjacent the front roof portion of the vehicle, the leading edge of each other laminar element being situated close to the underlying element in such a way as to define with it a transverse slit, and any two adjacent laminar elements of the said diverter defining between them, rearwardly of the respective slits, a duct having an area increasing towards the rear of the diverter.

7. A vehicle as claimed in Claim 6, in which the said vehicle is a lorry.

8. A vehicle as claimed in Claim 6, in which the said vehicle is a composite vehicle constituted by a towing vehicle and a trailer.

9. A vehicle as claimed in Claim 8, in which the said towing vehicle is a motor car and the trailer is a caravan.

10. A vehicle as claimed in Claim 6, in which the said vehicle is an articulated vehicle.

11. A vehicle as claimed in any of Claims 6 to 10, in which the diverter has two laminar elements.

12. A vehicle as claimed in Claim 11, in which the upper laminar element has a rounded leading edge.

13. A vehicle as claimed in any of Claims 6 to 12, in which the rear roof portion has a sharp front edge where it joins a front wall, and the plane tangential to the trailing edge of the upper laminar element of the said diverter contains the sharp front edge of the rear roof portion.

14. A vehicle as claimed in any of Claims 6 to 12, in which the rear portion of the roof has a rounded front edge where it joins a front wall, and the plane tangential to the trailing edge of the upper laminar element of the diverter contains the intersection of the projected planes of the rear roof portion and the front wall.

1 5. An air flow diverter substantially as hereinbefore described with reference to the accompanying drawings.

1 6. A vehicle incorporating an air flow diverter, substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 4 or Figure 5 of the accompanying drawings.