The invention relates to a drag reducing apparatus for a vehicle and a method for reducing drag of a vehicle.

Drag, in particular aerodynamic drag, is created whenever a vehicle travels at speed. Aerodynamic drag is comprised of two principle components - skin friction drag and form drag. The effects of flow separation, in particular of the boundary layer, accounts for 45% of the total vehicle resistance.

A drag reducing apparatus for a vehicle is known by US 9,193.399 B2, which provides an active and passive boundary layer control system to keep the boundary layer flow attached to the surface of a component of a vehicle.

An Object of an embodiment of the invention is to provide a drag reducing apparatus for vehicle and a method for reducing drag of a vehicle, with wich the drag can be further reduced. The task is solved by a drag reducing apparatus for a vehicle, in particular a land vehicle, a water craft or aircraft, comprising at least one fluid guide channel with an fluid inlet, by which fluid can stream in a compression section of the fluid guide channel, with an exhaust section, having a fluid outlet, which has in particular a nozzle-like structure and by which the fluid can stream to the rear end of the vehicle, and with a pressure build-up section, which is located between the compression section and the exhaust section, and comprising at least one pressure build-up device, which is arranged in the pressure build-up section and by which the total pressure of the fluid from the compression section can be increased and the fluid can be guided to the exhaust section, wherein the fluid guide channel is arranged or locatable in or on a vehicle component.

By having at least one fluid guide channel to lead fluid from the fluid inlet to the fluid outlet, the total pressure in the rear end of a vehicle can be increased. By increasing such pressure at the rear end of a vehicle, the drag of the vehicle is decreased.

By using a pressure build-up device, the pressure of the fluid passing the fluid guide channel can be further increased, which also increases the effect of reducing the drag of the vehicle.

By arranging the fluid guide channel in or on a vehicle component, the drag reducing apparatus can be integrated to a component of the vehicle that exists anyway. Therefore, components of the vehicle are effectively used.

Total pressure comprises a static pressure component and a dynamic pressure component. Outside the fluid guide channel the total pressure is constant. Only the amount of the static pressure component and dynamic pressure component are varying.

Inside the fluid guide channel the total pressure can be increased by the pressure build-up device.

It proofs to be advantaged, that the proposed drag reducing apparatus accelerates the fluid flow by introducing energy by using the pressure build-up device. Doing so, it is possible to introduce energy to specific areas of the rear end of the vehicle reduce turbulence and stagnation pressure, smoothen the airflow around the vehicle and to improve the airflow separation at rear.

In one embodiment of the apparatus the compression section and/or the exhaust section has/have a funnel like cross-section, each having its smallest width at its side facing the pressure build-up section. Because the compression section has a funnel like cross-section, having its smallest width at its side facing the pressure build-up section, the velocity of the fluid flowing in direction to the build-up device increases. It is the other way around for the exhaust section, in which the velocity of the fluid decreases from build-up device in direction to the fluid outlet.

The decrease of velocity in the exhaust section from the pressure build-up device in direction to the fluid outlet can be reduced, if the thickness of the exhaust section becomes smaller in direction from the pressure build-up device to the fluid outlet.

The at least one pressure build-up device can be realized by any device, having the technical function to increase the pressure of fluid. The pressure build-up device can be realized easily, if the least one pressure build-up device comprises a compressor, a turbocharger, a supercharger and/or a designated blower.

Further it proofs to be advantaged, if the fluid inlet, the compression section, the exhaust section and/or the fluid outlet has/have a fixed or adjustable cross-section.

If the fluid inlet, the compression section, the exhaust section and/or the fluid outlet has a fixed cross-section, the apparatus can be realized easy and inexpensive. In case the fluid inlet, the compression section, the exhaust section and/or the fluid outlet have an adjustable cross-section, the fluid velocity and the total pressure components can be adjusted easily.

The stream of the fluid can be easily adjusted, if the fluid inlet and/or the fluid outlet provide an adjustment body to at least adjust the streaming direction of the fluid and/or if the fluid inlet and/or the fluid outlet provide a drive element to move the adjustment body from a first position, in which the fluid streams in a first direction, to a second position, in which the fluid streams in a second direction.

Further it is preferred, if the fluid inlet and/or the fluid outlet comprises at least one opening, which is aligned in, transversely or obliquely to the direction of travel. ln case the fluid inlet comprises at least one opening, that is aligned in direction of travel, the velocity of the fluid stream inside the compression section

correspondence to the driving velocity of the vehicle. Doing so, the kinetic energy of the vehicle can be used at least partly to drive the apparatus.

In a further embodiment of the apparatus, the apparatus provides a boundary layer suction device, which is arranged at or in the surface of the vehicle component and which is built by the fluid inlet, comprising a plurality of openings, which are aligned transversely or obliquely to the direction of travel.

If the plurality of openings of the fluid inlet build a boundary layer suction device the apparatus can be built component reduced. With the boundary layer suction device, the boundary layer surrounding the surface of the component can partly be controlled to prevent boundary layer separation to further reduce the drag of the vehicle.

To easy control the stream of the fluid, it had turned out to be advantaged, if the fluid inlet and/or the fluid outlet provide at least one closure device, which can be driven from an open position, in which fluid is approved to stream inside the fluid inlet and/or outside the fluid outlet, to an close position, in which fluid is prevented to stream inside the fluid inlet and/or outside the fluid outlet, an/or to a plurality of intermediate positions, in which the cross-section of the fluid inlet and/or fluid outlet is reduced compared to the open position.

Providing a closure device, it is possible to stop the fluid stream of the apparatus by closing the closure device. Further, by arranging the closer device in intermediate positions, the mass flow of the fluid can be controlled easily.

To attach the apparatus easily to the vehicle, it is preferred, if at least one of the at least one fluid guide channel is unsolvable attached to the vehicle component, in particular being a one-piece structure of the component or being glued, welded, soldered and / or riveted to the component, and/or at least one of the at least one fluid guide channel is releasably attached to the vehicle component, in particular form-fitted, force-fitted, clipsed and/or screwed attached. The apparatus and the vehicle component can be one part, in which the different sections of the fluid guide channel are formed by a structure of the vehicle component. If the vehicle component is built by molding or injection molding, said structure can be provided by injection molding process.

In case the apparatus, in particular the fluid guide channel, is unsolvable attached to the vehicle component, a compact structure can be reached. In case the fluid guide channel is releasably attached the vehicle component, it easily can be changed or removed.

To easily drive the apparatus, it has found to be advantaged, if at least one control unit to control at least the drive element, closure device and/or the pressure build-up device.

Therefore, the pressure build-up device can easily be controlled by the control unit.

Further, also the closure device and/or the drive element can be easily adjusted by the control unit.

In a further development of the latter embodiment, it is preferred that the apparatus comprises at least one sensor arranged at the rear end of the vehicle, by which at least the total pressure, the static pressure component and/or the dynamic pressure component can be detected and which is functionally assigned to the control unit.

By detecting the total pressure, the static pressure component and/or the dynamic pressure component at the rear end of the vehicle an information about the drag of the vehicle is given to the control unit easily.

In a further embodiment the control unit comprises a storing device in which predetermine or predefinable all total pressure, static pressure component and/or dynamic pressure component can be saved and compared by the control unit, when the apparatus is driven. Therefore, the power of the pressure build-up device can be increased if the detected pressure is to low or decreased, if the detected pressure is too high. Further, the closure device and/or the adjustment body can be adjusted to control for mas flow and/or the direction of streaming.

In a further embodiment of the apparatus, the apparatus provides at least two fluid guide channels, which are being arranged or locatable in or at the same or in or at different vehicle components.

Said at least two fluid guide channels can be attached in the same vehicle component or in different vehicle components. In an embodiment of the apparatus one fluid guide channel is attached to roof top of the vehicle and one fluid guide channel is attached to a vehicle floor. In a further embodiment at least two fluid guide channels are attached to the same vehicle component, in particular parallel to each other.

In a further embodiment it is preferred, if the vehicle component comprises a Vehicle roof, vehicle floor and / or side wall and/or wherein the fluid comprises air.

The task could also be solved by a method of reducing drag of a vehicle by using a drag reducing apparatus for a vehicle according with at least one of the described features, comprising the steps: a. Possibly driving the open device from the close position in the open position or an intermediate position; b. Driving the pressure build-up device to provide a predetermined or predefinable total pressure, static pressure component and/or dynamic pressure component at the fluid outlet; c. Detecting the total pressure, static pressure component and/or

dynamic pressure component at the rear end of the vehicle by the sensor; and d. Increasing power of the pressure build-up device by the control unit, if the detected total pressure, static pressure component and/or dynamic pressure component is below the predetermined or predefinable total pressure, static pressure component and/or dynamic pressure component or decreasing power of the pressure build-up device by the control unit, if the detected total pressure, static pressure component and/or dynamic pressure component is over the predetermined or predefinable total pressure, static pressure component and/or dynamic pressure component.

Further features, details and advantages of the invention will become apparent from the appended claims, the drawings and the following description of preferred embodiments of a drag reducing apparatus and a method to reduce drag by using said apparatus and of the method.

In the drawing shows: Figure 1 A schematic symmetric view of a first embodiment of the apparatus;

Figure 2 A sectional view through the line AA of figure 1 ;

Figure 3 A sectional top view of the apparatus according to figure 1 ;

Figure 4 A detailed view of the fluid inlet and compression section of the

apparatus according to figure 1 ;

Figure 5 A detailed view of the fluid outlet and exhaustion section of the

apparatus according to figure 1 ;

Figure 6a A detailed sectional view of the fluid outlet through the line BB with an adjustment body in a first position; Figure 6b A detailed sectional view of the fluid outlet through the line BB with an adjustment body in a second position; Figure 7 A schematic symmetric view of a second embodiment of the apparatus;

Figure 8 A schematic flow chart of a method according to the invention.

The Figures show embodiments and parts of a drag reducing apparatus 2 for a vehicle 4. The vehicle 4, shown in the figures, comprises a land vehicle. The drag reducing apparatus 2 comprises at least von fluid guide channel 6, which has a fluid inlet 8 by which fluid can stream from outside of the vehicle in a compression section 10 of the fluid guide channel 6. The fluid guide channel 6 also comprises an exhaust section 12, having a fluid outlet 14, which has in particular nozzle-like structure by which the fluid can stream to the rear end of the vehicle 6.

Further, the fluid guide channel 6 comprises a pressure build-up area 16, which is located between the compression section 10 and the exhaust section 12.

The apparatus 2 further comprises at least one pressure build-up device 18, which is arranged in the pressure build-up section 16 and by which the total pressure of the fluid from the compression section 10 can be increased and the fluid can be guided to the exhaust section 12.

As can be derived by the embodiments shown in the figures the drag reducing apparatus 2 is arranged in a vehicle component 20. The vehicle component 20 comprises a vehicle roof.

As can be derived from figures 1 , 3 and 7 the compression section 10 and the exhaust section 12 comprise a funnel like cross-section, each having its smallest width at its side facing the pressure build-up section 16.

Figure 2 shows a section view of the apparatus 2 in direction of cut AA according to figure 1. As can be derived from figure 2, the fluid entering the compression section 10 by the fluid inlet 8 increases its velocity, caused by the funnel like cross-section of the compression section 10. The thickness of the compression section 10 is nearly equal over its extension from the fluid inlet 8 to the pressure build-up section 16.

After the fluid passes the pressure build-up device 18, the velocity of the fluid decreases within the exhaust section 12, caused by the funnel like cross-section of the exhaust section 12. The effect is reduced by decreasing the thickness of the exhaust section 12 in its direction from the pressure build-up section 16 to the fluid outlet 14.

Having a view in figures 4 to 6b, it can be derived, that the fluid inlet 8, the exhaust section 12 and the fluid outlet 14 have an adjustable cross-section. Therefore, an adjustment body 22 is provided to adjust the streaming direction of the fluid. To drive the adjustment body 22, the apparatus 2 provides a drive element 24 to move the adjustment body 22 from a first position, in which the fluid streams in a first direction, to a second position, in which the fluid streams in a second direction.

It can be further derived from the figures, that the fluid inlet 8 and the fluid outlet 14 provide openings 26, which are aligned in direction of travel.

The embodiments shown in the figures provide an apparatus 2, having a fluid guide channel 6, which is unsolvable attached to the vehicle component 20.

Figures 6a and 6b show a section view of the apparatus 2 in direction of cut BB according to figure 5. The fluid outlet 14 is nozzle-like shaped and the opening 26 can be increased or decreased. By increasing the opening 26, the static pressure of the fluid increases while the dynamic pressure decreases.

In Figure 6a the opening 26 is maximal. In Figure 6a the opening is minimal.

Figure 7 shows a second embodiment of the drag reducing apparatus 2. In such embodiment two fluid guide channels 6 are arranged inside the same vehicle component 20 of the vehicle 4 and are extending parallel to each other. Further, the embodiments shown in the figures comprise a sensor 28, which is arranged at the rear end of the vehicle 4 and which can detect total pressure, the static pressure component and/or the dynamic pressure component of the total pressure. The sensor 28 is functionally assigned to a control unit 30, which can control at least the drive element 24 to adjust the adjustment body 22 and the pressure build-up device 18 to adjust the power of the pressure build-up device 18.

Figure 8 shows a schematic flow chart of a method according to the invention. Which reference to figures 1 to 7, the method will be described in the following:

In a possible step 100 an open device (not shown in the figures) can be driven from a closed position in an open position or in an intermediate position, which is located between the closed position and the open position. The step 100 is possible to do and not necessary. Step 100 could be not necessary to do in case the open device is already in the intermediate position or in the open position.

By opening the open device, the fluid inlet 8 is open for the fluid surrounding the vehicle to stream inside the fluid guide channel 6. The fluid first passes the compression section 10 and increases its velocity, caused by the funnel like cross- section of the compression section 10. After passing the compression section 10, the fluid arrives in the pressure build-up area 16. After passing said pressure buildup section 16, the fluid passes the exhaust-section 12 and streams to the fluid outlet 14. Streaming outside the fluid outlet 14, the fluid arrives at the rear end of the vehicle 4 and influences the total pressure in the rear end area of the vehicle 4 to decrease drag of the vehicle 4.

In a step 101 the pressure build-up device 18 is driven to provide a predetermined or predefinable total pressure, static pressure, component and/or dynamic pressure component at the fluid outlet 14. Therefore, the apparatus 2 comprises the sensor 28, which functionally is assigned to the control unit 30.

In a further step 102 the total pressure, static pressure, component and/or dynamic pressure component can be detected at the rear end of a vehicle by the sensor. In another step 103 the control unit 30 increases the power of the pressure build-up device 18, if the detected total pressure, static pressure, component and/or dynamic pressure component is below the predetermined or predefinable total pressure, static pressure, component and/or dynamic pressure component. On the other hand, the control unit decreases the power of the pressure build-up device 18, if the detected total pressure, static pressure component and/or dynamic pressure component is over the predetermined or predefinable total pressure, static pressure, component and/or dynamic pressure component.

The features of the invention disclosed in the foregoing description, in the claims and in the drawing, may be essential both individually and in any combination in the realization of the invention in its various embodiments.

Reference numeral List

2 drag reducing apparatus

4 vehicle

6 fluid guide channel

8 fluid inlet

10 compression section

12 exhaust section

14 fluid outlet

16 pressure build-up area

18 pressure build-up device

20 vehicle component

22 adjustment body

24 drive element

26 opening

28 sensor

30 control unit

100

103 steps of method