Aerodynamic System for Reducing Wind Resistance of a Vehicle

TECHNICAL FIELD

The present invention relates to an aerodynamic system for reducing wind resistance of a vehicle, particularly a commercial vehicle, a trailer or a semitrailer. In a further aspect, the invention relates to a spoiler adapted to be comprised by an aerodynamic system and a method for refitting an existing vehicle to such an aerodynamic system.

BACKGROUND OF THE INVENTION

It is known in the art that the energy efficiency of a vehicle is directly related to the aerodynamic drag and turbulence caused by the motion of the vehicle. Especially in commercial vehicles, trailers and semitrailers being coupled at the end section of the vehicle have a direct impact on wind resistance and in consequence fuel consumption of the vehicle when the vehicle is moving at a high speed. The current demand of reducing fuel consumption of a vehicle is one of the most challenging issues of the automotive industry. Research concerning fuel reduction technologies for commercial vehicles such as trucks, trailers and semitrailers have revealed that the aerodynamic improvement is a key technology for saving fuel.

In the state of the art it is well-known that the aerodynamic performance can be reduced by the overall shape, for instance a flat-faced frontal area of the truck cab or an aerodynamic frontal design of a trailer or semitrailer, which is generally a square in vehicles like trucks. A portion of the wind resistance originates from the airflow generated underneath the moving vehicle. Turbulences and air drag at the end section of the vehicle have a significant impact on the aerodynamic properties of the vehicle. The airflow underneath the vehicle causes high turbulences in the end section of the vehicle, especially at a high speed, such that the critical aerodynamic properties of the vehicle's tail play a major role in the case of vehicle speeds exceeding for instance 40-50 km/h.

Attempts aimed at solving this problem are known in the prior art. These attempts consist in mounting vertical covers on the sides of the tractor and trailer to close the voids at the side of the vehicle and to boost air into the drag at the rear section of the vehicle. Additionally, diffusors can be installed underneath the vehicle or at the lower end section of a frame of the vehicle. Such diffusors are shaped sections of a vehicle which improve the aerodynamic properties by enhancing the transition between the high velocity of the airflow underneath the vehicle and the much slower free streaming airflow of the ambient atmosphere. Diffusors are based on providing a space for the underbody airflow to decelerate and expand the air so that it does not cause excessive airflow separation and air drag by providing a degree of "wake infill".

Such diffusors can completely cover the underside of the vehicle with vertical and horizontal walls for guiding the airstream, and the airstream at the end section of the vehicle can be directed in an upward direction into the vehicle's wake. Thus air is lifted into the vehicle's wake and decrease the overall vehicle's drag. Such diffusor constructions are rather complex and need to modify the underbody construction of the tail of the vehicle. Minor vehicle damages can completely destroy the diffusor system. A refitting of existing vehicles to such a diffusor construction is rather expensive and technically complex. SUMMARY OF THE INVENTION

The object of the invention is to improve the vehicle's aerodynamics with a simple modification for reducing the turbulences and drag caused by the wake at the end section of a vehicle. In a further aspect, a method is proposed for refitting existing vehicles such that fuel consumption can be reduced.

The objects are achieved by the features of the independent claims. The other claims, the drawing and the description disclose advantageous embodiments of the invention. According to a first aspect of the invention an aerodynamic system is proposed for reducing wind resistance of a vehicle, particularly a commercial vehicle, a trailer or a semitrailer, wherein a spoiler is arranged below an end section of a frame of said vehicle. A spoiler is an automotive aerodynamic device which spoils, i.e.

unfavourably influences, the air movement along a vehicle's body in motion. A spoiler disrupts the airflow passing underneath the vehicle's under-surface and spoils the laminar flow of the air. It is well-known that a spoiler dome is arranged on top of a cab such that drag caused by air resistance from the trailer, which may be taller than the cab, can be reduced. The inventive spoiler is arranged below an end section of the vehicle's basis frame and is designed to lift air into the wake behind the vehicle's rear end. The wake comprises a large volume of low atmospheric pressure and provides a "suction force" on the rear part of the trailer which increases the total aerodynamic force on the drag. By decreasing the volume's size of the wake, the aerodynamic drag properties are positively influenced. The spoiler arranged beneath the rear end part of the truck "scoops" the air which is flowing under the truck into the wake behind the vehicle's tail. In consequence, the size of the "wake bubble" is decreased and the aerodynamic drag is improved. A simple spoiler construction can be arranged at the rear lower end section of the frame of a vehicle such that the aforementioned positive properties can be attained. In contrast to complex diffusor constructions with vertical and horizontal walls guiding the airstream and decreasing the drag, such a simple spoiler configuration increases the overall drag of the vehicle in a first place because the spoiler spoils the airflow instead of guiding it. So a spoiler firstly works against a favourable aerodynamic design by bringing a blockage in the flow path underneath the vehicle. By lifting the air up into the wake, a positive effect is reached in a second place surpassing the negative effect of an increased wind resistance caused by the spoiler.

The spoiler may have a wedge-like cross section. For instance the lower side of the spoiler can be even or can be curved. The curvature of the lower and upper side of the spoiler can be optimized for an optimized air flow. It is also possible to arrange two or more spoiler-like curved sheets in parallel providing multiple air guiding surfaces.

The position of the spoiler can favourably be as low as possible, for instance providing a clearance of a few cm from the floor, i.e. the road surface level. The upper part may be connected to the beam, for instance close to the rear lights. This arrangement allows for retrofitting the spoiler to existing vehicles. It can be added to almost all kind of trailers, busses, vans, trains etc. According to a favourable embodiment of the invention, said spoiler can be attached to a rear underrun protection device. A rear underrun protection device is designed for protecting other vehicles in case of a crash to underrun the vehicle's frame and enhances crash safety of surrounding vehicles. An optimized lifting of the airstream can be achieved by arranging the spoiler at a height near the surface of the road, which is normally also the height of a lower crossbar of a typical rear underrun protection device. Therefore, said spoiler can advantageously be arranged on a crossbar or fixing bars of the underrun protection device to provide an inventive aerodynamic system. The spoiler can be made of any material, e.g. metallic panels. Favourably, the spoiler is made of plastics, which is lightweight and easy to install. The spoiler can also be made of a flexible canvas material, and can be arranged in a slightly inclined position underneath the vehicle's rear end.

According to a favourable embodiment of the system, the spoiler has a width in accordance with the frame width of the end section or with the width of said rear underrun protection device, preferably a crossbar of the rear underrun protection device. Thus, the total width of the frame can be used for lifting up the airstream into the wake at the vehicle's end section, which optimizes air insertion into the wake. According to a favourable embodiment, the spoiler is arranged between a rear wheel axle and said underrun protection device. The spoiler can be

advantageously arranged at the underrun protection device or between the underrun protection device and the rear wheel axle of the vehicle such that the overall length is maintained and the free space between the rear wheel axle and the normally unused space at the end section of the vehicle can be favourably occupied by the spoiler.

According to a favourable embodiment, the spoiler can have a wedge-like cross- section. A wedge-like shape of the spoiler has a minimized drag against the airflow and can direct air efficiently in the wake of the vehicle's end section. Furthermore, it can be advantageous if the underside of the spoiler is substantially flat and the upper side of the spoiler is curved in order to deflect the airflow upwardly. A flat underside of said spoiler does not spoil the airflow between the road surface and the spoiler underside and does not provoke further turbulences, and a curved upper side can optimally deflect the airflow upwardly into the wake of the trailer's end section such that the "suction" effect of the trailer's wake can be minimized.

According to a favourable embodiment, a drive unit can be operatively coupled between the spoiler and an under-surface of the vehicle's frame for moving said spoiler between a passive retraced upper position close to said under-surface of the vehicle's frame and an active exposed lowered position close to a road surface level or to a rear underrun protection device level. A drive unit can move the spoiler from a retracted position such that the spoiler does not influence the airflow to an exposed position such that the airflow is positively deflected upwardly towards the vehicle's wake. The drive unit can be an electrically driven motor, a hydraulic or pneumatic actuator or a passively driven mechanism which can move the spoiler between an active and a passive position due to the influence of a driving velocity or force of the airstream underneath the vehicle's frame. By moving the spoiler from an active to a passive position, preferably in a parking position of the vehicle, while driving rearwardly or at a low speed, the additional drag caused by the spoiler can be eliminated, the spoiler does not hinder driving in a loading/unloading position towards a loading platform, the spoiler can be protected from accidentally damage and manoeuvring can be simplified.

According to a further development of the aforementioned embodiment, a control unit for controlling said drive unit can comprise a speed measuring means of said vehicle for moving said spoiler to said passive/active position depending on whether the actual vehicle speed is below/above a predetermined speed value, respectively. In the case that the drive unit is an actively driven actuator, a control unit can be provided for activating/deactivating the drive unit. For an automatic controlling of the active/passive position of the spoiler, said control unit can comprise a speed measuring means and can activate the spoiler position for instance when a vehicle is running faster than for instance 50 km/h. The control unit can control the drive unit to drive the spoiler in a passive position while driving rearwardly or driving with a speed less than 50 km/h. As such, an automatic active or passive position of the spoiler for optimizing fuel consumption can be provided, an optimized protection of the spoiler and manoeuvrability of the vehicle can also be provided.

In a second aspect of the invention, a spoiler is suggested which is adapted to be comprised by any embodiment of the aforementioned aerodynamic system. The spoiler comprises fixing means for attaching said spoiler to a rear underrun protection device of a vehicle, preferably to a crossbar of the rear underrun protection device. Such a spoiler can be made of metal plates or of plastics or can comprise a flexible canvas designed to deflect the airstream upwardly to the wake of the vehicle's end section. The fixing means can be thread bolts, screws or types of a clipping mechanism to fix or clip the spoiler to the underrun protection construction. Preferably, the spoiler can be screwed to a crossbar of the underrun protection device and can easily be replaced in case of damage.

According to a third aspect of the invention, a method for refitting an existing vehicle to an aerodynamic system is proposed, wherein a spoiler is attached to an under-surface or to a rear underrun protection device of said vehicle. The method enables refitting existing vehicles, which are usually equipped with an underrun protection device, or which have fixing elements at an end section of a frame part, to an aerodynamic system according to the invention. Thus, a cheap, simple and easy to install spoiler can be attached to already existing elements of an end section of a vehicle's frame in order to provide the benefits of the invention. In this way, wind resistance of existing vehicles can be improved and fuel consumption can be reduced. The spoiler can offer an improvement in the drag coefficient Cd of approximately two percent or more when installed to a standard truck-trailer configuration. By optimizing shape and placement of the spoiler, the Cd value can further be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but is not restricted to these embodiments, wherein is shown schematically:

Fig. 1 a cross-section of a first embodiment of a spoiler according to the invention;

Fig. 2 two different views a) and b) of a schematic three-dimensional illustration of a vehicle comprising an embodiment of an aerodynamic system according to the invention;

Fig. 3 an airflow and an effect of the aerodynamic system of Fig. 2; Fig. 4 another embodiment of an aerodynamic system according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.

Fig. 1 depicts schematically a cross-section 32 of a spoiler 14. The spoiler 14 has a flat underside 24 and a curved upper side 26 for deflecting an airflow 28 along the vehicle's under-surface upwardly into a wake of an end section of the vehicle (not shown in the Figure). The cross-section 32 has a wedge-like shape and can also have a flat upper side (instead of a curved upper side 26 as shown in the Figure). The spoiler comprises fixing means 42 in the form of thread bolts for fixing the spoiler 14 to a crossbar of a rear underrun protection device of the vehicle (not shown in the Figure). The fixing means 42 can also be arranged on the thinner side of the spoiler 14 instead on the thicker side of the spoiler 14. The spoiler 14 can be made of plastics, but it can also be made of metal plates or can be fabricated from a thin textile canvas.

Fig. 2 depicts two three-dimensional perspective views Fig. 2a and Fig. 2b of a vehicle 12 in the form of a truck/trailer configuration comprising a tractive vehicle 50 and a trailer 52, whereby the tractive vehicle 50 comprises a cab spoiler 54 and air deflectors 56 along both sides of the cap to guide a wind stream around the trailer body 52. At the end section 16 of the trailer 52, a rear underrun protection device 20 is fixed to the frame 18 of the trailer 52. The rear underrun protection device 20 comprises two or more crossbars for preventing following vehicles to crash under the trailer's rear end in case of an accident. A spoiler 14, as depicted in Fig. 1 , extends along the width of the crossbar of the rear underrun protection device 20 and its thinner end is directed towards a rear wheel axle 22 of the trailer 52. An airstream 28 flowing between the road surface and the underside of the frame 18 of the trailer 52 is deflected by the spoiler 14 such that part of the flowing air 28 is guided into the wake at the end section 16 of the trailer 52. Thus, the suction effect decreasing the drag coefficient and increasing fuel consumption is reduced and surpasses a possible worsening in the increased blockage of airstream 28 caused by the spoiler 14. This effect of air being guided into the wake is increasing with increasing speed of the vehicle 12. In conclusion, overall wind resistance is decreased and fuel consumption of the vehicle 12 is reduced. Fig. 3 depicts schematically the flow of air around a vehicle 12 running at a high speed of for instance more than 50 km/h. The ambient air is deflected by the form of the cab 50 and is guided through the cab spoiler 54 over the squared shape of the trailer 52. A large part of air streams between the under-surface of the vehicle's frame 18 and the road surface 36 and causes turbulences at the end section 16 of the trailer 52. Thus, a rear vehicle wake 44 evolves and worsens the wind resistance of the vehicle 12 the higher the speed of the vehicle 12 is. A spoiler 14 is fixed to a rear underrun protection device 20 and is arranged between the end section 16 and a rear wheel axle 22 of the vehicle 12. The spoiler 14 is formed such that the airflow 28 is lifted into the volume of the wake 44 thus increasing the air pressure in the wake 44 behind the trailer's tail 16 (which air pressure within the wake 44 is lower than the air pressure in the areas surrounding the wake 44), i.e. decreasing the difference between the air pressure within the wake 44 behind the trailer's tail 16 and the air pressure in the areas surrounding the wake 44 and thereby improving the drag of the vehicle 12. In conclusion, a large amount of fuel can be saved.

Fig. 4 depicts schematically an embodiment of a vehicle 12 with an aerodynamic system 10, wherein a spoiler 14 can be automatically moved between a passive retracted position depicted in Fig. 4a and an active exposed position, shown in Fig.4b. The vehicle 12 comprises a cab 50 and a trailer section 52 arranged on a common frame 18. At the trailer's end 16, an aerodynamic system 10 is arranged comprising a spoiler 14 attached to a drive unit 30 which can be a hydraulic or electro-mechanically driven actuator designed for lowering a spoiler from a passive retracted upper position to an active exposed lower position. The drive unit 30 is connected to a control unit 38 which comprises a speed measuring means 40. The speed measuring means 40 can be connected to the vehicle's speedometer or can measure velocity of an airflow 28 streaming between road surface 36 and vehicle under-surface 34. In case that the forward speed of the vehicle 12 is lower than a predetermined value (e.g. 40 km/h or 50 km/h) and/or in case the vehicle 12 is backing, the drive unit 30 is instructed by the control unit 38 to move the spoiler 14 to a passive retracted upper position such that

manoeuvring and rearward driving of the vehicle 12, especially for docking onto a loading platform, can be made easily without the risk of damaging the spoiler 14. When driving the vehicle 12 at a high speed, e.g. above the predetermined value (e.g. 40 km/h or 50 km/h), the control unit 38 can instruct the drive unit 30 to move the spoiler 14 automatically to an exposed lowered position such that an airflow 28 is deflected into the wake 44 to increase air pressure within the wake 44 and to decrease the size of the wake 44 such that the wind resistance is lowered. The invention can provide lower wind resistance and a decreased fuel consumption of a vehicle, especially of a commercial truck trailer, by easily installing a spoiler below an end section of a vehicle's tail. Such a spoiler can be refitted to existing vehicles and can be incorporated into the design of new vehicles. A refitting can be made easily in a short time with minimal cost of the spoiler.