Vehicle aerodynamics

Abstract

The diffuser element for the undercarriage comprises, in longitudinal section, a first panel, a second panel, and a gap between the first and second panels, which rise smoothly and monotonically from front to rear, and in which the edge of the second panel adjacent the gap comprises a substantially flat planar portion that is offset from and below the plane of the first panel forward of the gap. This type of gap in the diffuser serves to bleed boundary layer from the airflow passing through the diffuser, thus increasing the effectiveness of the diffuser and the resulting downforce. The gap is preferably located in the front half of the diffuser and may form an entrance to a duct leading to an outlet at the rear of the vehicle.

Description

[Technical field]

[0001] The present invention relates to the aerodynamics of a vehicle, particularly in and around the diffuser at the rear of the vehicle. [Background technology]

[0002] Vehicle aerodynamics is concerned with controlling and directing the flow of air over and around a vehicle to contribute to the vehicle's performance and handling. The primary objective is to reduce the air resistance experienced by the vehicle and, in some implementations, to generate downforce. Another consideration is ensuring that drag and downforce characteristics are stable over a range of driving conditions so that vehicle handling is predictable and safe.

[0003] Generally, the aerodynamics of a vehicle are controlled by the shape of the vehicle body through which the air flows, aided and directed by aerodynamic elements attached to or forming part of the vehicle body, such as splitters, spoilers, wings, diffusers, etc. Splitters are located on the lower front of the vehicle and direct the air coming into the vehicle; spoilers and wings are typically located above the rear of the vehicle and control the air exiting the vehicle as it moves, creating downforce and / or regulating vortices that form behind the vehicle.

[0004] A diffuser, as used herein, refers to a shaped portion of the undercarriage rear that improves the aerodynamics of a vehicle by facilitating the transition between the high-speed airflow underneath the vehicle and the much slower free-flowing ambient air behind the vehicle. It does this by providing space for the airflow underneath the vehicle to slow down and expand in volume, without causing excessive flow separation and drag. Air passing under the vehicle accelerates as it funnels into the space between the vehicle and the ground, per Bernoulli's principle; this is beneficial in that the resulting lower pressure creates a downforce effect, but if the high-speed air is simply dumped into the slower air behind the vehicle, this will increase turbulence in that area and increase the drag experienced by the vehicle. A diffuser therefore opens up the undercarriage volume more gradually, allowing the high-speed air space and time to slow down.

[0005] The diffuser may be an integral part of the vehicle, shaped and defined to the shape of the vehicle, or it may be formed by one or more panels attached to the vehicle body, or it may be a combination of the two.

[0006] Several Formula 1 teams developed "double diffusers" for the 2009 season in response to changes to the sporting regulations that aimed to limit the amount of aerodynamic elements that could be fitted to a car. Unlike road cars, Formula 1 cars feature two flat horizontal surfaces beneath them - a "reference surface" at the lowest point of the chassis, and a "step surface" on either side of the reference surface, slightly higher - with a vertical transition surface filling the gap between them. The 2009 regulations required both the reference surface and the step surface to be flat and continuous, but made no mention of the transition surface. Some teams allowed the air that would have flowed under the step surface to escape laterally into the volume above the reference surface, forming an aperture in the transition surface that flows into what is effectively a second diffuser above the main diffuser, hence the term "double diffuser".

[0007] The vast majority of diffusers (including F1's "double diffuser") are passive devices in that their shape is determined and the diffuser panel is fixed or formed to the undercarriage without further intervention. GB2269142 and WO2021 / 028234 propose arrangements to actively control the airflow under the vehicle by means of suction fans that can selectively draw air from the diffuser; in GB2269142 this is to adjust the aerodynamic centre of pressure of the vehicle for balance, and in WO2021 / 028234 this is to adjust the balance between downforce and drag by controlling the boundary layer. Summary of the Invention

[0008] The present invention therefore provides a vehicle with an underlying aerodynamic element (such as a diffuser) comprising, in order from front to rear, a first panel, a second panel, and a gap between the first and second panels that rise smoothly and monotonically, wherein an edge of the second panel adjacent the gap comprises a substantially flat planar portion that is offset from and below the plane occupied by the first panel forward of the gap.

[0009] This type of gap in the diffuser serves to bleed the boundary layer from the airflow passing through the diffuser, thus increasing the effectiveness of the diffuser and the resulting downforce generated.

[0010] The gap can form an entrance to a duct that ideally leads smoothly to an exit formed at the rear of the vehicle without impeding the airflow within the duct. In this way, the low pressure wake or "base suction" formed behind the vehicle as it passes through the air provides a suction effect that draws air through the duct, aiding in boundary layer removal. In this case, the cross-sectional area of ​​the duct preferably increases monotonically along its length to the exit.

[0011] However, the duct is not strictly necessary and depending on the particular characteristics of the vehicle in question, it may be advantageous to omit the duct and its associated weight. Our research has shown that venting the air bled through the gap to the rear of the vehicle through a duct not only further increases the effectiveness of the diffuser but also benefits weight reduction. The choice will therefore be one of the designer's choice, considering their relative merits.

[0012] The portion of the second panel adjacent the rear of the substantially flat planar portion adjacent the gap ideally appears smoothly and monotonically raised when viewed from the side.

[0013] The gap is preferably located in the front half of the diffuser, typically forward of the center of the rear wheels, and more specifically, the horizontal distance between the leading edge of the first panel and the leading edge of the second panel is preferably between 1 / 10 and 1 / 2 the horizontal distance between the leading edge of the first panel and the trailing edge of the vehicle.

[0014] A suitable width for the gap is between 10 and 50 mm, measured perpendicular to the first panel.

[0015] To provide additional height to accommodate the diffuser, the underside of the vehicle may be shaped to define first and second such aerodynamic elements on either side of a central spine that projects below the first and second panels. The central spine may then accommodate the vehicle's driveline. Two drive shafts may each extend outwardly to a respective rear wheel. In such a configuration, the duct may conveniently pass above the drive shafts and the second panel may be located below the drive shafts. Furthermore, at least two of the rear suspension arms may extend outwardly from either side of the central spine to support a respective rear wheel, with each second panel being an aerodynamic element located above those suspension arms.

[0016] In that case, the first and second aerodynamic elements are each bounded, ideally on their respective outer sides, by upstanding walls projecting below the first and second panels, thus defining a channel in the undercarriage for air to flow. This means that the first and second panels are bounded on at least one side by upstanding walls projecting below the first and second panels. If the vehicle is designed with a central spine, it can help define the channel.

[0017] The present invention also relates to an undercarriage diffuser element comprising a first panel, a second panel, and a gap between the first and second panels, which in longitudinal section rise smoothly and monotonically from front to rear, wherein an edge of the second panel adjacent the gap comprises a substantially flat planar portion that is offset from and below the plane of the first panel forward of the gap.

[0018] Alternatively, the diffuser may be defined as comprising, from front to rear, a first panel extending from a point of minimum clearance of the aerodynamic element from the ground and rising smoothly and monotonically, an exhaust outlet, and a second panel extending toward the rear of the vehicle adjacent the exhaust outlet and having a substantially flat portion, wherein the exhaust outlet is defined between an upper surface that meets smoothly with the first panel and a lower surface that meets the second panel at an acute angle.

[0019] Other aspects of a diffuser according to either definition are as described above, for example, the horizontal distance between the point of minimum clearance from the ground to the junction of the lower inner surface and the second panel is between 1 / 10 and 1 / 2 the horizontal distance between the point of minimum clearance from the ground and the rear of the vehicle. [Brief description of the drawings]

[0020] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows a vehicle underside according to the invention. [Diagram 2]FIG. 2 shows a vertical section (on II-II in FIG. 1) through the relevant parts of a vehicle in a first embodiment of the invention. [Diagram 3] FIG. 3 shows the airflow pattern under and through the vehicle in the first embodiment. [Figure 4] FIG. 4 shows the airflow patterns under and through a vehicle in a second embodiment of the invention. [Diagram 5] FIG. 5 shows a vertical section through the relevant part of a vehicle in a third embodiment of the invention. [Figure 6] FIG. 6 shows the opening of FIG. 5 in more detail. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 1 shows the underside of a vehicle in accordance with the present invention, in this example a performance car 10. An underbody panel 12 has recesses towards each corner to accommodate front and rear wheels 14, 16 supported on suspension arms 18 connected to the vehicle chassis.

[0022] At the front 20 of the vehicle 10, a ground effect inlet 22 directs air under the floor. Towards the rear of the vehicle, a pair of diffuser structures 24, 26 are provided on either side of a central spine 28 which houses the chassis elements necessary to support the rear suspension arms 18. The diffuser structure 24, 26 is defined by the shape of the underbody panel 12; as shown in Figure 1 this is a single panel, but is actually made up of several smaller panel sections which together define the required shape.

[0023] Thus, air passing under the vehicle 10 is directed rearward by the ground effect inlets 22 towards a low point 30 just in front of the diffuser structures 24, 26, creating a low pressure area under the vehicle in accordance with Bernoulli's principle. This creates additional downforce on the vehicle 10 in a conventional manner. This is aided by the diffuser structures 24, 26, which allow the high velocity air passing through this (effectively) venturi structure defined between the vehicle 10 and the ground to be slowed down before mixing with the air behind the vehicle.

[0024] Each diffuser structure 24, 26 includes an upper panel structure 32 that generally rises toward the rear 34 of the vehicle 10, passes horizontally over the lower rear suspension arms 18, and then rises again toward the rear of the car. The airflow path is bounded internally by a substantially vertical wall provided by a central spine 28, and externally by substantially vertical wall portions 36. Apertures (not visible) are provided in the spine 28 and walls 36 to allow the suspension arms 18 to pass therethrough, and are large enough to allow the arms 18 to articulate under load.

[0025] An opening 38 is provided in the top panel structure 32, midway through each diffuser structure 24, 26, just forward of the horizontal section that passes through the suspension arms. It is therefore forward of the centerline of the rear wheels 16, and forward of the rear suspension arms 18, but rearward of the front-most part of the rear wheels 16. It is more generally in the front half of the diffuser structures 24, 26. To create the correct airflow pattern, part of the diffuser should be forward of the opening 38, and therefore it is preferred that at least one-tenth of the diffuser length is forward of the opening 38.

[0026] FIG. 2 shows a cross section along line II-II of FIG. 1, illustrating one shape of the diffuser structure 24. The top panel structure 32 that defines the upper surface of the diffuser 24 comprises a first top panel 40 forward of the opening 32 toward the front of the diffuser 24, and a second top panel 42 that extends from the opening 32 to the rear 34 of the vehicle 10. The opening 32 is designed to bleed a boundary layer from the air flowing over the first top panel 40 into a duct 44. The duct 44 rises gently and smoothly, passing through a drive shaft 46 to the rear wheels 16 (not shown), then to an outlet 48 on the rear 34 of the vehicle 10, which is covered by a grill. The duct 44 has a gently increasing cross section to ease the airflow along it; there is (in this embodiment) no constriction or other flow restriction along its length.

[0027] The outlet 48 opens into the area behind the vehicle 10 where so-called "base suction" occurs - a low pressure area in the space behind the vehicle 10 caused by the movement of the vehicle 10 through the air. A positive suction force is therefore created within the duct 44, which serves to draw boundary layer air into the opening 32.

[0028] The opening 32 itself is shaped to bleed the boundary layer of the airflow over the first upper panel 40 before it reaches the second panel. In such a passive system, the bleed opening 32 should be a reasonable distance aft from the leading edge of the diffuser element, allowing the airflow pattern with the boundary layer to develop and stabilize ahead of the opening 32. We have found that a spacing of 1 / 10 to 1 / 2 the distance along the diffuser (horizontally) provides good performance. Thus, as shown in FIG. 2, after the smoothly rising flat first panel 40, below which the airflow can be established, the opening 32 defines an outlet for only the boundary layer between 10 and 50 mm. The acutely defined nose 50 divides the airflow into a duct 44 for the boundary layer and the remainder of the diffuser below the second panel 42, which continues horizontally through the rear suspension area. By joining the lower surface 52 of the duct 44 to the second panel 42 at an acute angle, a sharp nose 50 is defined, allowing for a clean separation of the two airflows. Similarly, by smoothly joining the upper surface 54 of the duct 44 to the first panel, boundary layer flow into the opening 32 is maintained.

[0029] Figure 3 shows the airflow through the diffuser configuration of Figure 2. The vehicle 10 is shown as a negative space and the diagram shows the airflow streamlines around the vehicle's outline. The boundary layer 56 is effectively bled into the duct 44 and the remaining airflow through the diffuser into the area behind the vehicle 10 is smooth and laminar; to further assist in this, the suspension arms 18 can be seen to have an aerodynamic cross section. It is also notable that the wake vortex 58 behind the vehicle 10 is small and controlled.

[0030] Also shown in Figure 3 is an optional active rear spoiler 60 at the upper rear edge of the vehicle 10, which is automatically deployed as needed, but can also be driver activated. The rear spoiler 60 provides a high downforce mode, increasing downforce. Because this added downforce comes at the expense of added drag, the rear spoiler 60 also provides an aero-enhancing braking function. Thus, automatic deployment occurs when the vehicle 10 detects that one or more of the following conditions are present: tight cornering, potential oversteer, or hard braking.

[0031] 4 shows the corresponding airflow patterns with a different design that has less deflection along the path of the duct 44. Such deflection may be necessary to route the duct 44 around other elements within the vehicle 10, such as drive shafts and suspension components, while providing sufficient clearance. This means that the exact shape of the duct 44 is relatively unimportant, with little effect on the airflow in and around the openings and behind the vehicle 10.

[0032] In fact, the duct 44 can be omitted entirely. Figure 5 shows a cross-section of the relevant parts of the vehicle similar to Figure 2, but including the outline (dotted line) of the rear wheel 16 instead of the suspension arm 18, which is not shown. The same diffuser configuration is provided, i.e. a first panel 40 leading to an opening 32 defined by an acute nose 50, and a second panel 42 behind it. However, the duct 44 has been omitted, cut away and leaving only a short channel 62, which simply leads directly into the open space at the rear of the vehicle where the engine is located. In fact, this remaining channel 62 itself can be omitted, leaving only a simple opening 32.

[0033] FIG. 6 shows the opening 32 in more detail, illustrating that the plane 64 occupied by the first panel 40 forward of the opening 32 is located above the acute nose 50 and the second panel 42, thereby defining a depth 66 corresponding to a boundary layer 68 within the airflow 70 entering the channel 62 or duct 44.

[0034] In an example having a boundary layer removal duct actuated by base suction at the rear of the vehicle, it has been discovered that the present invention allows for levels of aerodynamic efficiency as much as 30% more effective than conventional ground effect supercars. When the boundary layer is bled into the engine compartment, i.e. without the benefit of base suction, aerodynamic efficiency is slightly reduced but the weight of the duct is eliminated. Either may be preferable in certain circumstances depending on the overall aerodynamic efficiency of the vehicle, the overall weight of the vehicle, the weight of the ducts involved, and the performance qualities required.

[0035] The ground effect dynamics provided by the present invention contribute significantly to the aerodynamic performance of the vehicle and may reduce or eliminate the need for extraneous wings, skirts, and vents common on modern supercars, which are visually unappealing and impose additional drag loads. The boundary layer control enabled by the design and location of the bleed openings in the diffuser ensures the most effective interaction of the airflow above and below the vehicle, harmonizing drag, downforce, and stability at all speeds, reducing the need for aggressive front-end aerodynamic devices.

[0036] In places in this application we refer to "smooth" or "smoothly" bordering surfaces, meaning that their overall shape is entirely curved, with no sharp transitions, and ideally with a radius of curvature of 100mm or greater. We also refer to particular items as being "substantially flat", meaning that in use, when a vehicle is resting on its suspension and wheels, the particular item will be level within expected tolerances having regard to the inherent resilience of the associated suspension system.

[0037] Of course, it will be understood that many modifications may be made to the above-described embodiments without departing from the scope of the present invention.

Claims

1. A vehicle with an aerodynamic element underneath, comprising, in order from front to rear: A first panel that rises smoothly and monotonically; and A second panel, and a gap between the first panel and the second panel; wherein an edge of the second panel adjacent the gap has a substantially flat planar portion that is offset from and below a plane occupied by the first panel forward of the gap.

2. The vehicle of claim 1 , wherein the gap forms an entrance to a duct.

3. 3. The vehicle of claim 2, wherein the duct smoothly leads to an outlet formed in the rear of the vehicle.

4. 4. The vehicle of claim 3, wherein the duct leads smoothly to the outlet without impeding airflow.

5. A vehicle as claimed in any one of claims 2 to 4, wherein the cross-sectional area of ​​the duct increases monotonically along its length to the outlet.

6. 10. A vehicle as claimed in any one of the preceding claims, wherein the second panel comprises the substantially flat planar portion adjacent the gap and a smooth and monotonous rising portion rearwardly thereof.

7. 10. A vehicle as claimed in any one of the preceding claims, wherein the horizontal distance between a leading edge of the first panel and a leading edge of the second panel is between 1 / 10 and 1 / 2 of the horizontal distance between a leading edge of the first panel and a trailing edge of the vehicle.

8. 10. A vehicle as claimed in any one of the preceding claims, wherein the width of the gap at the inlet is between 10 and 50mm, measured perpendicular to the first panel.

9. 10. A vehicle as claimed in any one of the preceding claims, wherein the lower portion is shaped to define first and second such aerodynamic elements on either side of a central spine that projects below the first and second panels.

10. 10. The vehicle according to claim 9, depending on any one of claims 2 to 5, further comprising a pair of drive shafts, each extending outwardly and connected to a respective rear wheel, wherein the duct passes above the drive shafts and the second panel is positioned below the drive shafts.

11. 11. The vehicle of claim 9 or claim 10, further comprising a plurality of suspension arms, at least two of which extend outwardly from either side of the central spine and support each rear wheel, and wherein the second panel of each of the aerodynamic elements is located above at least two of the suspension arms.

12. 12. A vehicle as claimed in any one of claims 9 to 11, wherein the first and second aerodynamic elements are bounded on their respective outer sides by upstanding walls projecting below the first and second panels, respectively.

13. 9. A vehicle as claimed in any preceding claim, wherein the first and second panels are bounded on at least one side by an upstanding wall that projects below the first and second panels.

14. 10. A vehicle as claimed in any one of the preceding claims, comprising an exterior body supported by the front and rear wheels.

15. The vehicle of claim 14 , wherein the gap is located forward of the center of the rear wheels.

16. a first panel extending from a point of minimum spacing of the aerodynamic element from the ground and rising smoothly and monotonically; Exhaust vent, a second panel extending toward a rear of the vehicle adjacent the exhaust outlet and having a substantially flat portion; A diffuser element, wherein the exhaust outlet is defined between an upper surface that smoothly meets the first panel and a lower surface that meets the second panel at an acute angle.

17. 17. The diffuser element of claim 16, wherein a horizontal distance between the point of minimum ground clearance and a joint of the lower inner surface and the second panel is between 1 / 10 and 1 / 2 of a horizontal distance between the point of minimum ground clearance and a rear of a vehicle.

18. The diffuser element for the underside of the vehicle is, in longitudinal section, from front to rear: The first panel rises smoothly and monotonously, A second panel, and a gap between the first panel and the second panel; A diffuser element, wherein an edge of the second panel adjacent the gap has a substantially flat planar portion that is offset from and below the plane of the first panel forward of the gap.

19. 20. The diffuser element of claim 18, wherein the horizontal length of the first panel is between 1 / 10 and 1 / 2 of the horizontal length of the entire diffuser element.

20. Diffuser element according to any one of claims 16 to 18, wherein the second panel comprises the substantially flat planar portion adjacent the gap and a smooth and monotonous raised portion thereafter.

21. A diffuser element according to any one of claims 16 to 20, and A duct smoothly leading from an exhaust port of a diffuser element to an outlet formed at a rear part of the vehicle.

Images