GB2588504A

GB2588504A - Airflow control apparatus

Info

Publication number: GB2588504A
Application number: GB2012826.0A
Authority: GB
Inventors: Patel Paven; Fagg Michael; Ian Mcgeachy Jamie; Parmar Bhavik
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-03-24
Filing date: 2017-03-24
Publication date: 2021-04-28
Anticipated expiration: 2037-03-24
Also published as: GB2588504B; GB202012826D0

Abstract

A vehicle 1 has a rear valance panel 10 including a fairing 17 having an outer surface 18, and also a flow guide 24, providing a permanently deployed surface for guiding the airflow away from outer surface 18, projecting from an exhaust silencer 13. Outer surface 18 and a guide surface of flow guide 24 may each be inclined at an acute angle to a longitudinal axis of the vehicle and these angles may be offset. The guide surface may also be longitudinally and/or vertically offset from outer surface 18 of fairing 17. Part of flow guide 24 may overlap outer surface 18.

Description

AIRFLOW CONTROL APPARATUS

TECHNICAL FIELD

The present disclosure relates to airflow control apparatus. The airflow control apparatus may be configured for use on a vehicle, such as a motor vehicle. In particular, but not exclusively, the present disclosure relates to a rear valance assembly; and to a vehicle.

BACKGROUND

The aerodynamic drag of a vehicle, such as a motor vehicle, is an important design consideration. The vehicle configuration and body type both affect aerodynamic performance.

At the rear of the vehicle, an upper vortex may be formed by the air passing over the vehicle; and a lower vortex may be formed by the air passing under the vehicle. It is known to provide aerodynamic devices to alter the airflow over the vehicle to control the wake formed behind the vehicle. It is known to provide a spoiler to control the airflow behind the vehicle in order to manipulate the wake formed behind the vehicle. In the case of a vehicle having an estate (touring) body style or a sports utility vehicle, a spoiler may be mounted to the top of the tailgate or to the roof of the vehicle. The spoiler may be used in conjunction with a raked profile of the rear of the vehicle, for example formed by an inclined rear screen. In order to control the airflow exiting from under the vehicle, it is known to provide a rear valance assembly at the rear of the vehicle. The rear valance assembly may comprise a fairing to reduce aerodynamic drag.

It is also known to provide a diffuser at the rear of the vehicle. However, the function of a diffuser is different from that of a fairing. In particular, a diffuser is configured to improve dynamic performance of the vehicle. The entrance of the diffuser accelerates the airflow prior to it decelerating as it expands and finally exits from under the vehicle. By accelerating the airflow, the pressure under the rear of the vehicle is reduced and an aerodynamic downforce is generated.

It is against this background that the present invention has been conceived. At least in certain embodiments, the present invention may reduce aerodynamic drag on a vehicle.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a rear valance assembly; to an exhaust silencer; and to a vehicle.

According to a further aspect of the present invention there is provided a rear valance assembly for a vehicle, the rear valance assembly comprising: a rear valance panel comprising a fairing having an outer surface; and at least one flow guide having a guide surface for guiding the airflow away from the outer surface of the fairing. At least in certain embodiments, the at least one flow guide may reduce aerodynamic drag of the vehicle. In use, the at least one flow guide directs the airflow away from the outer surface of the fairing to control the formation of vortices downstream of the vehicle. At least in certain embodiments, the at least one flow guide is operative to control the airflow as it exits from under the vehicle. The at least one flow guide may be arranged to guide the airflow as it exits from under the vehicle and forms a wake behind the vehicle. At least in certain embodiments, the at least one flow guide may reduce upwards turning of the airflow exiting from under the vehicle. The at least one flow guide may direct the airflow in a longitudinal direction. At least in certain embodiments, the outer surface of the fairing is not operative to guide the airflow exiting from the vehicle underbody. Indeed, the at least one flow guide may promote vortex formation at or proximal to the outer surface of the fairing such that the local flow direction may be reversed. The airflow exiting from under the vehicle underbody may be directed away from the rear of the vehicle such that an associated vortex is established further from a rear of the vehicle than an equivalent arrangement which does not include the at least one flow guide. Advantageously, this may also help to reduce soiling of the vehicle caused by dirt being deposited on the rear of the vehicle.

The fairing may be configured such that the outer surface extends in a substantially longitudinal direction or in a substantially vertical direction. Alternatively, the fairing may be configured such that the outer surface forms an inclined surface. The fairing may comprise a ramp which forms the outer surface. The outer surface may be inclined upwardly as it extends towards the rear of the vehicle. The outer surface of the fairing may be substantially planar. Alternatively, the outer surface of the fairing may have a concave profile or a convex profile.

In use, the outer surface of the fairing may be inclined at a first angle relative to a longitudinal axis of the vehicle. The first angle may be an acute angle. The first angle may, for example, be greater than or equal to 5°, 100, 20°,30°, 45° or 60°.

The at least one flow guide may be positioned in front of the outer surface of the fairing. In other words, the at least one flow guide may be disposed upstream of the outer surface of the fairing. The at least one flow guide and the fairing may be at least partially aligned with each other in a transverse direction. The at least one flow guide may be offset vertically from the fairing. In particular, the at least one flow guide may be disposed at a vertical position below the fairing. The guide surface may be disposed below the outer surface of the fairing.

The at least one flow guide may be fastened to the rear valance panel. One or more mechanical fastener may be provided to fixedly mount the at least one flow guide to the rear valance panel. Alternatively, or in addition, the at least one flow guide may be adhesively fastened to the rear valance panel. Alternatively, the at least one flow guide may be formed integrally with the rear valance panel. For example, the at least one flow guide may be an integral feature of the rear valance panel.

The guide surface of the at least one flow guide may be inclined upwardly as it extends towards a rear of the rear valance assembly. In use, the guide surface of the at least one flow guide may be inclined at a second angle relative to a longitudinal axis of the vehicle. The second angle may be an acute angle. At least in certain embodiments, the at least one flow guide may be configured such that the guide surface is inclined upwardly as it extends towards a rear of the vehicle. Thus, the outer surface comprises a divergent (diverging) surface. In use, the outer surface may form an expanding volume at the rear of the vehicle. In a variant, the at least one flow guide may be configured such that the guide surface is inclined downwardly towards a rear of the vehicle.

The second angle may be less than or equal to 5°, 10°, 15°, 30°, 45° or 60°, for example. The second angle may be greater than or equal to 0°, 10, 2°, 3° or 5°, for example. In certain embodiments, the second angle may be substantially zero (0 / such that, in use, the guide surface of the at least one flow guide extends substantially parallel to a longitudinal axis of the vehicle.

The at least one flow guide may be configured to guide the airflow in a substantially longitudinal direction (i.e. substantially parallel to a longitudinal axis of the vehicle).

The fairing and the at least one flow guide may be configured such that there is an angular offset between the outer surface and the guide surface. The angular offset corresponds to the angular difference between the first and second angles. The second angle may be less than the first angle. The angular offset may be greater than or equal to 5°, 10°, 15°, 25° or 45°, for example.

The guide surface of said at least one flow guide may be substantially planar. Alternatively, the guide surface of said at least one flow guide may be curved in a longitudinal direction. For example the guide surface may be concave or convex.

A portion of the at least flow guide may project in a rearwards direction spaced apart from the outer surface of the fairing. The guide surface of the at least one flow guide may be offset longitudinally and/or vertically from the outer surface of the fairing. At least in certain embodiments, the longitudinal offset and/or vertical offset may prevent the flow from reattaching to the outer surface.

A portion of the at least one flow guide may overlap the outer surface of the fairing. The portion of said at least one flow guide may overlap the outer surface in a longitudinal direction.

The at least one flow guide may have a length which is greater than or equal to lOmm, 20mm, 30mm, 50mm, 70mm or 90mm. A greater length is preferable to improve the aerodynamic efficiency of the at least one flow guide. However, at least in certain embodiments, the at least one flow guide is configured so as not to affect the departure angle of the vehicle.

The at least one flow guide may be configured to promote separation of the airflow from the vehicle body, thereby reducing the ability of the airflow to follow the profile of the rear of the vehicle. The at least one flow guide may be configured to promote separation of the airflow from the rear valance assembly and to guide the airflow to prevent reattachment of the detached airflow to the rear valance panel.

In certain embodiments, the at least one flow guide may function as a flow separation device for promoting flow separation. The flow over the rear valance assembly may be an attached flow and the at least one flow guide may promote flow separation. The at least one flow guide may comprise a geometrical discontinuity that causes the attached flow to separate from the surface. The geometrical discontinuity may, for example, comprise one or more of the following: a sharp radius, a change in angle, a step, a backwards facing step (i.e. a step facing in the opposite direction to the flow direction), a sharp corner, on offset or step change, and a trailing edge of the geometry.

The at least one flow guide may comprise a rear (trailing) edge. The rear edge of the at least one flow guide may form a separation edge for promoting flow separation. The separation edge may comprise a clearly defined geometrical discontinuity that may cause or promote flow separation. The geometrical discontinuity may be sufficiently marked that even a favourable pressure gradient could not maintain flow attachment. The separation edge may be in the form of a sharp edge, for example formed by another surface joining the guide surface at an oblique angle. The separation edge may be arranged substantially perpendicular to the guide surface, or at an oblique angle to the guide surface. Alternatively, or in addition, a lip, protuberance or other projection may be provided at the rear edge of the at least one guide member to promote separation of the airflow.

At least in certain embodiments, the guide surface of the at least one flow guide is operative to guide the airflow away from the outer surface of the fairing such that reattachment of the airflow downstream of the at least one flow guide may be prevented. The at least one flow guide may guide the airflow such that flow reattachment to the outer surface of the fairing or any other surface of the vehicle does not occur, even in the presence of a favourable pressure gradient which may draw the airflow back towards the outer surface of the fairing.

At least a portion of the exterior of the outer surface of the fairing may be concave. In certain embodiments, the concave profile may prevent reattachment of the flow downstream of the at least one flow guide.

A vertical offset between the guide surface and the outer surface of the fairing may prevent (or suppress) reattachment of the flow to the outer surface of the fairing or any other surface of the vehicle. The at least one flow guide and the rear valance panel may have a stepped or 7-shaped profile in longitudinal section. The guide surface and the outer surface may be offset from each other in a vertical direction (and optionally also a longitudinal direction) to form said stepped or 7-shaped profile. The guide surface and the outer surface of the fairing may be arranged substantially parallel to each other.

A channel may be formed between the at least one flow guide and the rear valance panel. The channel may be open in a rearwards direction. The channel may, for example, be V-shaped. The channel may promote formation of a vortex in the region formed between the airflow diverted by the at least one flow guide and the outer surface of the fairing.

The fairing may comprise a front section and a rear section. The outer surface of the fairing may be inclined upwardly from said front section to the rear section. The at least one flow guide may be positioned proximal to the front section. The at least one flow guide may be positioned in front of the front section of the fairing. The at least one flow guide may be configured to direct the flow away from the front section of the fairing.

The at least one flow guide and/or the fairing may be centred on a centreline of the vehicle. The at least one flow guide and/or the fairing may extend across a central region of a vehicle underbody, for example extending transversely across the region between the wheels of the vehicle.

The rear valance assembly may consist of one flow guide. Alternatively, the rear valance assembly may comprise a plurality of said flow guides. The flow guides may be positioned in a side-by-side arrangement, for example on opposing sides of the vehicle. Alternatively, the flow guides may be offset from each other in a longitudinal direction. In this arrangement, the airflow exiting from under the vehicle underbody may be controlled in multiple stages.

According to a further aspect of the present invention there is provided a vehicle comprising a rear valance assembly as described herein. The vehicle may be an electric vehicle (EV) having one or more electric traction motor for generating torque to propel the vehicle. Alternatively, the vehicle may have an internal combustion engine for generating torque to propel the vehicle. Alternatively, the vehicle may be a hybrid electric vehicle (HEV), for example comprising an internal combustion engine and one or more electric traction motor.

The vehicle may have at least one exhaust silencer (also known as a muffler). The at least one flow guide may be disposed behind said at least one exhaust silencer. The at least one flow guide may be disposed between said at least one exhaust silencer and the rear of the vehicle. The at least one exhaust silencer has a lower silencer surface. In use, the lower silencer surface is exposed to the airflow under the vehicle and forms part of the vehicle underbody. The at least one flow guide may form a continuation of the lower silencer surface.

The flow guide may be spaced apart from the lower silencer surface in a longitudinal direction and optionally also a vertical direction. The at least one flow guide may be configured to promote flow separation.

It will be understood that the at least one flow guide may be shaped and/or oriented so as to provide the appropriate clearance around an exhaust system and/or the at least one exhaust silencer.

According to a further aspect of the present invention there is provided a vehicle comprising: a rear valance panel comprising a fairing having an outer surface; and at least one flow guide having a guide surface for guiding the airflow away from the outer surface of the fairing. The vehicle may be an electric vehicle (EV) having one or more electric traction motor for generating torque to propel the vehicle. Alternatively, the vehicle may have an internal combustion engine for generating torque to propel the vehicle. Alternatively, the vehicle may be a hybrid electric vehicle (HEV), for example comprising an internal combustion engine and one or more electric traction motor. The at least one flow guide may be configured to promote flow separation.

The outer surface of the fairing may be inclined upwardly as it extends towards a rear of the vehicle. The outer surface may be inclined at a first angle relative to a longitudinal axis of the vehicle. The first angle may be an acute angle. The first angle may, for example, be greater than or equal to 30°, 45° or 60°.

At least in certain embodiments, the at least one flow guide may be configured such that the guide surface is inclined upwardly as it extends towards a rear of the vehicle. In a variant, the at least one flow guide may be configured such that the guide surface is inclined downwardly as it extends towards a rear of the vehicle.

The guide surface of the at least one flow guide may be substantially parallel to a longitudinal axis of the vehicle. The guide surface of the at least one flow guide may be inclined at a second angle relative to a longitudinal axis of the vehicle. The second angle may be an acute angle. The second angle may be less than or equal to 5°, 100, 15°, 30°, 45° or 60°; and/or greater than or equal to 0°, 1°, 2°, 3° or 5°.

There may be an angular offset between the outer surface of the fairing and the guide surface of the at least one flow guide. The angular offset may be greater than or equal to 5°, 10°, 15°, 25° or 45°.

The guide surface of the at least one flow guide may be offset longitudinally and/or vertically from the outer surface of the fairing. At least in certain embodiments, the longitudinal offset and/or vertical offset may prevent the flow from attaching to the outer surface.

A portion of the at least one flow guide may overlap the outer surface of the fairing. In particular, a portion of the at least flow guide may project in a rearwards direction beyond a portion of the outer surface of the fairing.

In certain embodiments, the at least one flow guide may function as a flow separation device for promoting flow separation. The at least one flow guide may promote separation of the flow from the surface of the rear valence assembly. At least in certain embodiments, the guide surface of the at least one flow guide is operative to guide the airflow away from the outer surface of the fairing such that reattachment of the flow downstream of the at least one flow guide may be prevented. The at least one flow guide may comprise a rear (trailing) edge. The rear edge of the at least one flow guide may form a separation edge for promoting flow separation. The separation edge may be in the form of a sharp edge, for example formed by another surface joining the guide surface at an oblique angle. The separation edge may be arranged substantially perpendicular to the guide surface, or at an oblique angle to the guide surface. Alternatively, or in addition, a lip, protuberance or other projection may be provided at the rear edge of the at least one guide member to promote separation of the airflow.

The vehicle may comprise at least one exhaust silencer. The at least one flow guide may project from said at least one exhaust silencer.

According to a further aspect of the present invention there is provided an exhaust silencer for a vehicle, wherein the exhaust silencer comprises at least one flow guide having a guide surface for guiding the airflow as it exits from under the vehicle. The at least one flow guide provided on said exhaust silencer may function as an aerodynamic trip for controlling the airflow exiting from the vehicle underbody. The at least one flow guide may promote separation of the flow from the surface of the exhaust silencer. The at least one flow guide may be configured to promote separation of the airflow from the exhaust silencer and to guide the airflow to prevent reattachment of the detached airflow.

At least in certain embodiments, the at least one flow guide may be configured such that the guide surface is inclined upwardly as it extends towards a rear of the vehicle when the exhaust silencer is fitted to the vehicle. In a variant, the at least one flow guide may be configured such that the guide surface is inclined downwardly as it extends towards a rear of the vehicle when the exhaust silencer is fitted to the vehicle.

The exhaust silencer may comprise a housing. The at least one flow guide may project from said housing. The at least one flow guide may be mounted to said housing; or may be integrally formed with said housing.

In use, the guide surface of the at least one flow guide may be inclined at an angle relative to a longitudinal axis of the vehicle, the angle being an acute angle. The angle may be less than or equal to 15°, 30°, 45° or 600; and/or greater than or equal to 3°, 5°, 10° or 15°.

The at least one flow guide may have a length which is greater than or equal to 5mm, lOmm, 15mm, 20mm, 30mm or 40mm.

The at least one flow guide may extend in a transverse direction.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 shows a schematic representation of an underside of a vehicle incorporating a rear valance assembly having a flow guide member in accordance with an embodiment of the present invention; Figure 2 shows a sectional view of the rear valance assembly shown in Figure 1 along a centre line of the vehicle; Figure 3 shows a rear perspective view of the rear valance assembly shown in Figure 1; Figure 4 shows a rear perspective view of an underside of the rear valance assembly shown in Figure 1; Figure 5 shows a sectional view through the rear valance assembly shown in Figure 1; Figure 6 shows a schematic representation of the orientation of a fairing provided on the rear valance assembly and the flow guide member shown in Figure 1; Figure 7 shows computational fluid dynamic (CFD) analysis of the airflow along a longitudinal centreline of the vehicle shown in Figure 1; Figure 8 shows an enlarged view of the CFD analysis of the airflow along a longitudinal centreline of the vehicle shown in Figure 1; Figure 9 shows a schematic representation of an underside of a vehicle incorporating a flow guide member in accordance with a further embodiment of the present invention; Figure 10 shows a perspective view of the exhaust silencer incorporating the flow guide member in accordance with the embodiment illustrated in Figure 9; and Figure 11 shows a side elevation of the exhaust silencer shown in Figure 10.

DETAILED DESCRIPTION

A vehicle 1 incorporating a rear valance assembly 2 in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying figures. The vehicle 1 in the present embodiment is a motor vehicle having a sports utility vehicle (SUV) body type. It will be appreciated that aspects of the present invention are applicable to motor vehicles having other body types.

The vehicle 1 has a reference frame comprising a longitudinal axis X, a transverse axis Y and a vertical axis Z. The longitudinal axis X is coincident with a longitudinal centreline CL of the vehicle 1.

The term "forward" is used herein to refer to a normal forward direction of travel of the vehicle 1. The term "rearward" is used herein to refer to a direction opposite to the normal forward direction of travel of the vehicle 1. The term "front" is used herein to refer to the portion of the vehicle which faces in a forwards direction. The term "rear" refers to the back or tail end of the vehicle. The terms "upwardly" and "downwardly" are used herein to define orientation in relation to the longitudinal axis X of the vehicle 1.

A departure angle is the maximum angle the vehicle 1 can achieve when transitioning to an incline without the rear of the vehicle 1 contacting the ground. The departure angle is defined with reference to a departure line (or plane) which extends tangentially from a contact point of the rear wheel(s) of the vehicle 1. The vehicle 1 comprises a reference line called the ground line which is parallel to the road surface. The ground line extends parallel to the longitudinal axis X and is coincident with the lowermost rigid part of the vehicle underbody.

As shown schematically in Figure 1, the vehicle 1 comprises a vehicle body 3 and four (4) wheels 4-n (where n indicates the location of the wheel) mounted to the vehicle body 3 by separate suspension assemblies (not shown). An internal combustion engine 5 is provided to generate torque to drive at least some of the wheels 4-n. An exhaust system 6 is connected to the internal combustion engine 5. A vehicle underbody (denoted generally by the reference numeral 7) is formed on an underside of the vehicle 1. The vehicle underbody 7 is defined by the components on the underside of the vehicle body 3 which are exposed to airflow under the vehicle 1 (the airflow under the vehicle 1 being illustrated by an arrow AF in the Figures).

In certain embodiments, one or more panels may be mounted to the underside of the vehicle body 3 to define the vehicle underbody 7. The vehicle underbody 7 comprises a front section 7A, a mid-section 7B and a rear section 7C. The front section 7A and the mid-section 7B are arranged substantially parallel to the longitudinal axis X of the vehicle 1. The rear section 7C is inclined upwardly as it extends towards the rear of the vehicle 1. A central region of the vehicle underbody 7 extends between the wheels 4-n of the vehicle 1. The wheels 4-n are disposed on opposing sides of the central region and, when the vehicle 1 is in motion, air flows along said central region. It will be understood that the wake generated by the rotation of the wheels 4-n affects the airflow under the vehicle 1.

The vehicle body 3 has a rear surface 8 which is disposed at the rear of the vehicle 1 and faces in a rearwards direction. In the illustrated body type, at least a portion of the rear surface 8 extends upwardly in a substantially vertical direction. In the present embodiment, at least a portion of the rear surface 8 is defined by a top-hinged tailgate (not shown) which can be opened to provide access to a load bay of the vehicle 1. The rear valance assembly 2 in accordance with the present embodiment is mounted at the rear of the vehicle 1. The rear valance assembly 2 provides a transition from the vehicle underbody 7 to the rear surface 8.

As shown in Figure 2, the rear valance assembly 2 comprises a rear valance panel 10; and a first flow guide 11. When the vehicle 1 is in motion, the rear valance assembly 2 guides the airflow exiting from under the vehicle underbody 7. The rear valance assembly 2 helps to control the airflow at the rear of the vehicle 1 and thereby affects the wake formed behind the vehicle 1. The profile of the rear valance panel 10 and the first flow guide 11 are described herein in greater detail.

The exhaust system 6 is operative to convey exhaust gases from the internal combustion engine 5 to a tailpipe 12 mounted at the rear of the vehicle 1. The exhaust system 6 comprises an exhaust silencer 13 (also known as a muffler) comprising a housing 14 which forms a resonance chamber through which the exhaust gases pass before exiting through the tailpipe 12. The housing 14 extends in a transverse direction (parallel to the transverse axis Y of the vehicle 1) and is mounted at the rear of the vehicle 1 in front of the rear valance assembly 2. The exhaust silencer 13 is suspended from the vehicle body 3 by one or more hangers 15.

The hangers 15 are adapted at least partially to decouple the housing 14 from the vehicle body 3 to reduce the transmittal of vibrations into the vehicle body 3. It will be understood, therefore, that the exhaust silencer 13 is movable in a limited range relative to the vehicle body 3 and the rear valance assembly 2. To accommodate this relative movement, the rear valance assembly 2 is spaced apart from the exhaust silencer 13. A gap G is formed between the housing 14 and the rear valance assembly 2 to maintain this separation.

As shown schematically in Figure 1, the housing 14 has a lower silencer surface 16 which forms a portion of the rear section 70 of the vehicle underbody 7. The housing 14 is configured such that said lower silencer surface 16 is inclined upwardly as it extends towards the rear of the vehicle 1. As shown in Figures 2 to 5, the rear valance panel 10 comprises a fairing 17 which is inclined upwardly towards the rear of the vehicle 1. The fairing 17 has an outer (external) surface 18 which is inclined upwardly as it extends towards the rear of the vehicle. The outer surface 18 forms a diverging (divergent) surface. The fairing 17 in the present embodiment comprises a ramp which forms the outer surface 18. The fairing 17 is formed integrally with the rear valance panel 10, but could be formed by an insert or other member mounted to the rear valance panel 10. The fairing 17 is disposed in a rearmost portion of the rear section 70 of the vehicle underbody 7. The fairing 17 is centred on a centreline of the vehicle 1 and extends transversely across a majority of the width of the vehicle 1. In the present embodiment, the fairing 17 extends across the central region of the vehicle underbody 7 between the rear wheels 4-3, 4-4. In the present embodiment, the fairing 17 is substantially planar, but may be curved in a longitudinal direction and/or a transverse direction. For example, the fairing 17 may be curved in a transverse direction to match the lateral portions of the rear valance panel 10. As shown in Figure 6, the outer surface 18 is inclined at a first angle al (°) relative to the longitudinal axis X of the vehicle 1. The first angle al is an acute angle (al <90°). In the present embodiment, the first angle al is approximately 45°, but the first angle al may differ in other applications. The rear of the rear valance assembly 2 forms a rear bumper 21 (also known as a fender) or other trim panel at the rear of the vehicle 1.

As shown in Figures 2 to 5, the first flow guide 11 extends transversely across a majority of the width of the vehicle 1. In the present embodiment, the first flow guide 11 extends across the central region of the vehicle underbody 7 between the rear wheels 4-3, 4-4. The first flow guide 11 may also extend transversely beyond the central region of the vehicle underbody 7 into a region behind the rear wheels 4-3, 4-4. For example, the first flow guide 11 may have a width substantially equal to the tyre track of the vehicle 1. The majority of the airflow exiting from under the vehicle underbody 7 flows over the first flow guide 11. The first flow guide 11 is arranged to direct the airflow away from the outer surface 18 of the fairing 17. In the present embodiment, the longitudinal position of the first flow guide 11 is between the housing 14 and the rear valance panel 10. The first flow guide 11 comprises a first guide surface 19 having a leading edge 19A and a trailing edge 19B. The leading edge 19A is positioned proximate to, but spaced apart from, the housing 14. The trailing edge 19B is offset vertically from the fairing 17. In particular, the trailing edge 19B is positioned below the fairing 17 in an overlapping arrangement. The first guide surface 19 and the outer surface 18 have a generally Z-shaped profile in longitudinal section. The first guide surface 19 and the outer surface 18 are offset from each other in a vertical direction to form said Z-shaped profile. A V-shaped channel 20, open to the rear of the vehicle 1, is formed between the fairing 17 and the first flow guide 11. The trailing edge 19B of the first flow guide 11 is configured to define a discrete edge along which the airflow separates from the first guide surface 19.

As shown in Figure 6, the first guide surface 19 is inclined at an angle relative to the outer surface 18 of the fairing 17. The first guide surface 19 is inclined upwardly at a second angle a2 (°) relative to the longitudinal axis X of the vehicle 1. The second angle a2 is an acute angle (a2<90°). The second angle a2 is less than the first angle al (a2<a1). The magnitude of the second angle a2 may, for example, be less than or equal to 45°, 300, 15°, 10° or 5°. In the present embodiment, the second angle a2 is approximately 0°. An angular offset (Ac) between the outer surface 18 and the first guide surface 19 is approximately 45° in the present embodiment. The orientation of the outer surface 18 and/or the first guide surface 19 is/are vehicle specific so the angular offset (Ac) may vary depending on the vehicle type and/or configuration. It will be understood, therefore, that the angular offset (Ac) may be less than or greater than 45°. The first guide surface 19 is arranged to direct the airflow away from the fairing 17 of the rear valance panel 10. In the present embodiment the first guide surface 19 is substantially planar, but in a variant the first guide surface 19 may be curved in a longitudinal direction. For example, the first guide surface 19 may have a concave profile or a convex profile in a longitudinal direction. Similarly, the profile of the first guide surface 19 could change in a transverse direction, for example to modify the airflow at each end thereof.

As outlined above, the rear surface 8 of the vehicle 1 is defined by a top-hinged tailgate. As can be seen in Figure 7, the tailgate in the present embodiment comprises a raked section 22 which is inclined at an angle relative to the longitudinal axis X of the vehicle 1. The raked section 22 may for example comprise a rear windscreen of the vehicle 1. An upper spoiler 23 is mounted to the tailgate to control the flow of air as it passes over the top of the vehicle 1. The upper spoiler 23 may be inclined downwardly as it extends towards the rear of the vehicle 1. When the vehicle 1 is in motion, the upper spoiler 23 may control the formation of an upper vortex core VC1 which is established in the wake behind the vehicle 1, as shown in Figure 7.

The first flow guide 11 extends into the flow of air passing along or proximal to the vehicle underbody 7. The first flow guide 11 in the present embodiment is a rigid, inflexible member. In a variant, the first flow guide 11 may be resilient, for example to accommodate relative movement of the housing 14. The first flow guide 11 is operative to control the airflow exiting from under the vehicle 1. As the vehicle 1 is in motion, the first flow guide 11 controls the airflow as it exits from under the vehicle underbody 7. When the vehicle 1 is in motion, the first flow guide 11 may control the formation of a lower vortex core VC2 which is established in the wake behind the vehicle 1, as shown in Figures 7 and 8. More particularly, the first flow guide 11 may control the air exiting from under the vehicle underbody 7 to move the lower vortex core VC2 in a rearwards direction further away from the rear of the vehicle 1 (compared to an arrangement without the first flow guide 11). The base static pressure (i.e. the pressure at the rear surface 8 of the vehicle 1) may be increased, thereby reducing aerodynamic drag on the vehicle 1.

The first flow guide 11 is operative to control the airflow under the vehicle underbody 7 when the vehicle 1 is travelling in a forwards direction. Unless specified to the contrary, references herein to the vehicle 1 being in motion refer to the vehicle 1 travelling in a forwards direction. The operation of the first flow guide 11 will now be described in more detail with reference to Figures 7 and 8 which show Computational Fluid Dynamics (CFD) analysis of the airflow above and below the vehicle 1 along a vehicle centreline. The streamlines and the associated flow direction are illustrated in Figures 7 and 8; and the shading indicates the localised flow velocity. The CFD analysis models the flow of air when the vehicle 1 is in motion on a fixed, flat surface R. The flow of air past the vehicle 1 is modelled at the rear of the vehicle 1. The formation and interaction of the upper and lower vortex cores VC1, VC2 are illustrated in Figures 7 and 8.

A portion of the air incident on the vehicle 1 is directed under the vehicle 1 and flows through the volume formed between the road R and the vehicle underbody 7. The front section 7A and the mid-section 7B of the vehicle underbody 7 are substantially parallel to the longitudinal axis X such that the volume between the road R and the vehicle underbody 7 is substantially uniform. The rear section 7C of the vehicle underbody 7 is inclined upwardly such that the volume between the road R and the vehicle 1 expands (increases), thereby decelerating the flow of air towards the rear of the vehicle 1. Thus, the airflow is decelerating as it travels over the lower silencer surface 16 and the rear valance panel 10 disposed at the rear of the vehicle underbody 7. In an arrangement in which the first flow guide 11 is omitted, the airflow would be split such that some of the airflow would be entrained into the void behind the housing 14.

In the present embodiment, the first flow guide 11 at least partially closes the gap G between the housing 14 and the rear valance panel 10, thereby reducing the entrainment of air into this void. The first flow guide 11 also helps to re-direct the airflow in a rearwards direction away from the fairing 17 of the rear valance panel 10. As a result, the lower vortex core VC2 is displaced in a rearwards direction further away from the rear surface 8 of the vehicle body 3.

The lower vortex core VC2 may also be displaced downwardly relative to the vehicle 1. The displacement of the lower vortex core VC2 may cause an increase in the base static air pressure which helps to reduce aerodynamic drag on the vehicle 1. By diverting the airflow downstream, the first flow guide 11 may also help to reduce the deposition of material suspended in the air onto the rear surface 8 of the vehicle body 3. Thus, at least in certain embodiments, soiling or contamination of the vehicle 1 may be reduced.

The first flow guide 11 has been described herein as a separate element which is fastened to the rear valance panel 10. It will be appreciated that the flow guide could be formed integrally with the rear valance panel 10.

In the embodiment described herein the first flow guide 11 is shown as being offset vertically from the fairing 17 in an overlapping arrangement. In particular, the first flow guide 11 projects in a longitudinal direction over a front region of the outer surface 18. Alternatively, or in addition, the first flow guide 11 may be offset longitudinally from the fairing 17. The first flow guide 11 may be disposed upstream of the fairing 17. The first flow guide 11 and the fairing 17 may be juxtaposed to each other. The first guide surface 19 and the outer surface 18 may intersect along a discrete, sharp corner which forms a geometrical discontinuity which causes flow separation. As described herein, the first guide surface 19 of the first flow guide 11 and the outer surface 18 of the fairing 17 are inclined at an angle relative to each other. The angular offset (Aa) between said the outer surface 18 and the first guide surface 19 may be sufficient to cause the airflow to separate at the trailing edge of the first flow guide 11. The angular offset (Aa) could, for example, be greater than or equal to 45°, 60°, 75° or 90°. The fairing 17 could comprise a concave profile to promote flow separation and/or to prevent reattachment of the flow downstream of the first flow guide 11. In particular, the exterior of the outer surface 18 of the fairing 17 may have a concave profile. Alternatively, or in addition, the interface between the first flow guide 11 and the fairing 17 may be configured to promote separation of the airflow.

For example, a lip or a groove may be formed between the first flow guide 11 and the fairing 17 to promote separation of the airflow.

In the embodiment described herein, only the lower surface of the first flow guide 11 is exposed to the airflow under the vehicle underbody 7. In a variant, the first flow guide 11 may be spaced apart from the vehicle underbody 7 such that the upper and lower surfaces are exposed to the airflow under the vehicle underbody 7.

A further embodiment of the present invention will now be described with reference to Figures 9, 10 and 11. Like reference numerals are used for like components. This embodiment of the present invention comprises a second flow guide 24 for controlling the flow of air towards the rear of the vehicle 1. The second flow guide 24 in the present embodiment functions as an aerodynamic trip. The second flow guide 24 may be used instead of, or in addition to the first flow guide 11 described in the previous embodiment.

The vehicle 1 in accordance with the present embodiment comprises a modified exhaust silencer 13. The second flow guide 24 is integrated into the housing 14 of the exhaust silencer 13. In particular, the housing 14 is modified such that the second flow guide 24 is fastened to the lower silencer surface 16. The second flow guide 24 projects outwardly from the lower silencer surface 16 into the flow of air passing along or proximal to the vehicle underbody 7. In the present embodiment, the second flow guide 24 extends approximately 9.5mm from the lower silencer surface 16. The second flow guide 24 is substantially planar and extends in a transverse direction substantially parallel to the transverse axis Y of the vehicle 1. In the present embodiment, the second flow guide 24 extends across the width of the housing 14 and is coincident with the central region of the vehicle underbody 7. The second flow guide 24 comprises a second guide surface 25 which is inclined at a third incline angle (a3) relative to the longitudinal axis X of the vehicle 1. The second guide surface 25 extends downwardly as it extends towards the rear of the vehicle 1. The third incline angle (a3) is an acute angle (i.e. less than 90°). In the present embodiment the third incline angle (a3) is approximately 60°. The second flow guide 24 is positioned on the lower silencer surface 16 in front of the gap G formed between the housing 14 and the rear valance panel 10. The second flow guide 24 is configured so as not to affect the departure angle of the vehicle 1. In the present embodiment, the positioning and size of the second flow guide 24 is such that it does not extend beyond the departure line defined as a tangent between a contact point of the rear wheels 4-3, 4-4 and the rear of the vehicle 1.

The second flow guide 24 is operative to direct the airflow exiting from the vehicle underbody 7 away from the rear of the exhaust silencer 13 and the rear valance panel 10. In particular, the second guide surface 25 directs the airflow downwardly such that the lower vortex core VC2 is established further behind the rear of the vehicle 1. The lower vortex core VC2 may also be displaced downwardly relative to the vehicle 1. Thus, the second flow guide 24 is operative to modify the wake formed behind the rear surface 8 of the vehicle 1. The displacement of the lower vortex core VC2 may cause an increase in the base static air pressure which helps to reduce aerodynamic drag on the vehicle 1. By diverting the airflow behind the vehicle 1, the first flow guide 11 may also help to reduce the deposition of dirt and other material suspended in the air onto the rear surface 8 of the vehicle body 3. The second flow guide 24 may promote separation of the flow from the lower silencer surface 16. At least in certain embodiments, the reattachment of the detached flow may be prevented. In use, the second flow guide 24 may prevent the flow from attaching to the rear valance assembly 2.

As outlined above, second flow guide 24 may be used in conjunction with or instead of the first flow guide 11 described in the previous embodiment. The second flow guide 24 could be incorporated into the rear valance assembly. For example, the second flow guide 24 could be provided in front of the fairing 17. In this arrangement, the second flow guide 24 would be operative to divert the airflow away from the fairing 17 as it exits from under the vehicle underbody 7. The second flow guide 24 has been illustrated as projecting from the lower silencer surface 16. In a variant, the second flow guide 24 could be incorporated into the profile of the lower silencer surface 16. For example, the second flow guide 24 may comprise a fairing incorporated into the lower silencer surface 16. The fairing may define a guide surface which is inclined downwardly as it extends towards the rear of the vehicle 1.

It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the invention. The first flow guide 11 has been described herein as being permanently deployed. In a variant, the first flow guide 11 may be deployable selectively. For example, the first flow guide 11 may be deployed when the vehicle speed is greater than a predefined speed threshold. One or more actuator may be provided to deploy and/or retract the first flow guide 11.

The rear valance assembly 2 has been described with particular reference to a vehicle 1 comprising an internal combustion engine 65. It will be understood that the rear valance assembly 2 may be used in a vehicle 1 which does not include an internal combustion engine. For example, the rear valance assembly 2 may be used in an electric vehicle (EV) having one or more traction motors for generating torque to propel the vehicle. The rear valance assembly 2 may be used in a hybrid electric vehicle (HEV).

Example embodiments of the present invention may be characterised by the following paragraphs: 1. A rear valance assembly for a vehicle, the rear valance assembly comprising: a rear valance panel comprising a fairing having an outer surface; and at least one flow guide having a guide surface for guiding the airflow away from the outer surface of the fairing.

2. A rear valance assembly according to paragraph 1, wherein, in use, the outer surface is inclined at a first angle relative to a longitudinal axis of the vehicle, the first angle being an acute angle.

3. A rear valance assembly according to paragraph 1 or paragraph 2, wherein, in use, the guide surface of the at least one flow guide is inclined at a second angle relative to a longitudinal axis of the vehicle, the second angle being an acute angle.

4. A rear valence assembly according to paragraph 3, wherein the second angle is less than or equal to 5°, 10°, 15°, 300, 450 or 60°; and/or greater than or equal to 0°, 10, 2°, 3° or 5°.

5. A rear valance assembly according to any one of paragraphs 1 to 4, wherein there is an angular offset between the outer surface of the fairing and the guide surface of the at least one flow guide.

6. A rear valance assembly according to paragraph 5, wherein the angular offset is greater than or equal to 5°, 10°, 15°, 25° or 45°.

7. A rear valance assembly according to any one of the preceding paragraphs, wherein the guide surface of the at least one flow guide is offset longitudinally and/or vertically from the outer surface of the fairing.

8. A rear valance assembly according to any one of the preceding paragraphs, wherein a portion of the at least one flow guide overlaps the outer surface of the fairing.

9. A rear valance assembly according to any one of the preceding paragraphs, wherein a rear edge of the at least one flow guide forms a separation edge for promoting flow separation.

10. A rear valance assembly according to paragraph 9, wherein the separation edge is arranged substantially perpendicular to the guide surface, or at an oblique angle to the guide 30 surface.

11. A rear valance assembly according to any one of the preceding paragraphs, wherein the at least one flow guide and the rear valance panel have a stepped or Z-shaped profile in longitudinal section.

12. A rear valance assembly according to paragraph 11, wherein the guide surface and the outer surface are offset from each other in a vertical direction and optionally also a longitudinal direction to form said stepped or Z-shaped profile.

13. A rear valance assembly according to any one of the preceding paragraphs, wherein the fairing comprises a front section and a rear section, the at least one flow guide being positioned proximal to the front section of the fairing.

14. A rear valance assembly according to any one of the preceding paragraphs, wherein the at least one flow guide is configured to extend in a transverse direction across a central region of a vehicle underbody. . 15. A vehicle comprising a rear valance assembly according to any one of the preceding paragraphs.

16. A vehicle according to paragraph 15 comprising at least one exhaust silencer, wherein the at least one flow guide is disposed behind said at least one exhaust silencer.

17. A vehicle according to paragraph 16, wherein the at least one exhaust silencer comprises a lower silencer surface, the at least one flow guide forming a continuation of the lower silencer surface.

18. A vehicle according to paragraph 16, wherein the flow guide is spaced apart from the lower silencer surface in a longitudinal direction and optionally also a vertical direction.

19. A vehicle comprising: a rear valance panel comprising a fairing having an outer surface; and at least one flow guide having a guide surface for guiding the airflow away from the outer surface of the fairing.

20. A vehicle according to paragraph 19, wherein the outer surface is inclined at a first angle relative to a longitudinal axis of the vehicle, the first angle being an acute angle.

21. A vehicle according to paragraph 19 or paragraph 20, wherein the guide surface of the at least one flow guide is inclined at a second angle relative to a longitudinal axis of the vehicle, the second angle being an acute angle.

22. A vehicle according to paragraph 21, wherein the second angle is less than or equal to5°, 10°, 15°, 30°, 45° or 60 °; and/or greater than or equal to 0°, 1°, 2°, 3° or 5°.

23. A vehicle according to any one of paragraphs 19 to 22, wherein there is an angular offset between the outer surface of the fairing and the guide surface of the at least one flow guide.

24. A vehicle according to any one of paragraphs 19 to 23, wherein the angular offset is greater than or equal to 5°, 100, 15°, 25° or 45°.

25. A vehicle according to any one of paragraphs 19 to 14, wherein the guide surface of the at least one flow guide is offset longitudinally and/or vertically from the outer surface of the fairing.

26. A vehicle according to any one of paragraphs 19 to 25, wherein a portion of the at least one flow guide overlaps the outer surface of the fairing.

27. A vehicle according to any one of paragraphs 19 to 26, wherein the vehicle comprises at least one exhaust silencer, wherein the at least one flow guide projects from said at least one exhaust silencer.

28. An exhaust silencer for a vehicle, wherein the exhaust silencer comprises at least one flow guide having a guide surface for guiding the airflow as it exits from under the vehicle 29. An exhaust silencer according to paragraph 28, wherein the exhaust silencer comprises a housing; and the at least one flow guide projects from said housing.

30. An exhaust silencer according to paragraph 29, wherein the at least one flow guide is mounted to said housing; or is integrally formed with said housing.

31. An exhaust silencer according to any one of paragraphs 28, 29 or 30, wherein, in use, the guide surface of the at least one flow guide is inclined at an angle relative to a longitudinal axis of the vehicle, the angle being an acute angle.

32. An exhaust silencer according to paragraph 31, wherein the angle is less than or equal to 15°, 30°, 45° or 60°; and/or greater than or equal to 3°, 5°, 10° or 15°.

33. An exhaust silencer according to any one of paragraphs 28 to 32, wherein the at least one flow guide may have a length which is greater than or equal to 5mm, lOmm, 15mm, 20mm, 30mm or 40mm.

Claims

Claims 1. A vehicle comprising: a rear valance panel comprising a fairing having an outer surface; and at least one flow guide arranged to be fixedly mounted to the vehicle to provide a permanently deployed guide surface for guiding the airflow away from the outer surface of the fairing wherein the vehicle comprises at least one exhaust silencer, wherein the at least one flow guide projects from said at least one exhaust silencer.
2. A vehicle as claimed in claim 1, wherein the outer surface is inclined at a first angle relative to a longitudinal axis of the vehicle, the first angle being an acute angle.
3. A vehicle as claimed in claim 1 or claim 2, wherein the guide surface of the at least one flow guide is inclined at a second angle relative to a longitudinal axis of the vehicle, the second angle being an acute angle. C\I
4. A vehicle as claimed in any one of claims 1 to 3, wherein there is an angular offset CD between the outer surface of the fairing and the guide surface of the at least one flow guide.
5. A vehicle as claimed in any one of claims 1 to 4, wherein the guide surface of the at least one flow guide is offset longitudinally from the outer surface of the fairing.
6. A vehicle as claimed in any one of claims 1 to 5, wherein the guide surface of the at least one flow guide is offset vertically from the outer surface of the fairing.
7. A vehicle as claimed in any one of claims 1 to 6, wherein a portion of the at least one flow guide overlaps the outer surface of the fairing.