A diffuser for a vehicle

Abstract

A diffuser 100 for a vehicle has a body 104 with an outer surface 105. A portion of body 104 defines a cavity 110. An opening 111 extends through body 104 and provides fluid communication with cavity

Description

TECHNICAL FIELD The present disclosure relates to a diffuser for a vehicle. Aspects of the invention relate to a diffuser, to a vehicle, and to a kit of parts. BACKGROUND It is known to provide a diffuser at the rear of a vehicle in order to reduce turbulence and drag. In the case of larger vehicles, for example SUVs, it is advantageous to provide a diffuser inclined at a shallow angle with respect to the floor or undertray of the vehicle so as to minimise upwash. However, a shallow diffuser is detrimental to the off-road capability of a vehicle which requires a much steeper angle with respect to the floor or undertray. One way in which a diffuser inclined at a steep angle has been utilised without being overly detrimental to turbulence and drag is to incorporate a separation trip that extends from an external surface of the diffuser into the flow path of passing air. The separation trip causes flow separation and changes the trajectory of the air leaving the diffuser so as to reduce upwash behind the vehicle. However, the separation trip is often provided as a separate component attached to the diffuser that increases the manufacturing cost and may be subject to damage. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a diffuser, a vehicle, and a kit of parts as claimed in the appended claims. According to an aspect of the present invention, there is provided a diffuser, the diffuser comprising: a body, wherein at least a portion of the body defines a cavity; and an opening extending through the body and providing fluid communication with the cavity; wherein, in use, passing air flowing over the body flows past the opening so as to draw further air from the cavity through the opening and thereby redirect the passing air away from the body. According to a further aspect of the present invention, there is provided a diffuser for attachment to a vehicle, the diffuser comprising: a body having an outer surface, wherein at least a portion of the body defines a cavity; and an opening extending through the body and providing fluid communication with the cavity; wherein, in use, passing air flowing over the outer surface flows past the opening so as to draw further air from the cavity through the opening and thereby redirect the passing air away from the outer surface. In either of the above aspects of the invention, air flowing past the opening may otherwise be referred to as air flowing over the opening or as air flow across the opening. In embodiments of either of the above aspects of the invention, one or more of the following may apply. In the described diffuser, the cavity and opening provide a passive aerodynamic means for redirecting the airflow across a diffuser. This removes the need for a ‘separation trip’ that is often a separate, attached component that extends from the diffuser and which is subject to damage and / or removal in use. Advantageously, the described diffuser provides reduced manufacturing costs and increased reliability whilst still redirecting the air passing over the diffuser. Furthermore, it has been found that the opening provided in the described diffuser allows the ingress of water into, and egress of water from, the cavity and in some cases into and from the internal space defined by the rear bumper of a vehicle. Advantageously, during wading this can reduce the buoyancy provided at the rear of the vehicle as air located within the cavity and the rear bumper can be displaced by water, thereby enhancing the wading capability of the vehicle. In an embodiment the diffuser is for attachment to the rear of a vehicle. Optionally, the diffuser is for attachment to the rear underside of a vehicle. Optionally, the diffuser is for attachment to an exterior of a vehicle, an exterior rear of a vehicle or an exterior rear underside of a vehicle. Advantageously, when the described diffuser is provided at the rear of a vehicle, redirecting the passing air allows the upwash behind the vehicle to be reduced thereby reducing the drag resulting from the turbulent wake. Furthermore, as a result of redirecting the passing air an external surface of the diffuser may extend at a greater angle relative to a horizontal or neutral plane of undertray of the vehicle thereby providing less interference when driving on rugged or off road terrain. In an embodiment, the diffuser is for attachment to the front of a vehicle. In an embodiment, the diffuser is an aerodynamic diffuser. The diffuser may be passive or a passive diffuser. In an embodiment, the diffuser comprises a plurality of openings. In an embodiment the or each opening comprises a slot. Optionally, the or each opening comprises a widthwise extending slot. Optionally, the or each opening comprises a slot extending across at least part of a width of the diffuser. Advantageously, the aerodynamic effect can be experienced across the width of the vehicle to which the diffuser is attached, such that a large portion ora majority of the wake region can be impacted when the diffuser is attached at the rear. It will be appreciated that the expressions width and ‘widthwise in relation to the diffuser mean a width and widthwise direction when the diffuser is in the orientation in which it will be installed on or attached to a vehicle. Optionally, the opening comprises an aperture, a plurality of apertures, and / or perforations. In an embodiment, the diffuser comprises one or more vanes. Optionally, the diffuser comprises one or more vanes extending across the or each opening. Optionally, the diffuser comprises one or more vanes extending across the or each slot. In an embodiment, the one or more vanes are configured to guide or manipulate the further air being drawn from the cavity through the or each slot or opening. The vane can provide a degree of structural integrity and / or stiffness to the slot whilst also modifying the flow regime. It will be appreciated that the slot can provide laminar flow at the outlet and / or accelerate the flow towards the outlet to impact the effect on the passing air. In an embodiment, the opening comprises a plurality of spaced slots. Optionally, the opening comprises a plurality of slots spaced along the width of the diffuser. The or each slot may extend across at least part of the width of the diffuser. By providing a plurality of spaced slots, the diffuser may have greater structural integrity in comparison with a diffuser having a continuous slot, and the aerodynamic effect of the diffuser can be provided at certain or discrete locations across the width thereof. In an embodiment, the diffuser comprises a duct having: an inlet; an outlet defined by the opening and spaced from of the inlet; and a passage for air between the inlet and the outlet and defined by the cavity; wherein, in use, a portion of passing air flowing over the outer surface passes through the duct and is drawn from the passage through the outlet by passing air that flows past the outlet. Rather than relying on passing air to draw further air from the cavity, a duct provides an inlet for passing air thereby producing air at the outlet with A greater velocity which can redirect the passing air further away from the outer surface of the diffuser. Optionally, the outlet may be located downstream of the inlet. In an embodiment, the passage is fluidly connected between the inlet and the outlet. In an embodiment, the inlet is located at or proximate an end of the diffuser. Optionally, the inlet is located at or proximate an upstream end of the diffuser. By providing the inlet at an end, or an upstream end, of the diffuser a longer passage may be provided to allow more time to modify or guide the flow regime through the duct. It will be appreciated that the expressions “upstream” and “downstream” are in relation to the general flow direction across the diffuser, during normal use, when the diffuser is in the orientation in which it will be installed on or attached to a vehicle and the vehicle is moving forward. In an embodiment, the outlet is defined by an opening as described above. In an embodiment, the passage comprises one or more vanes. Optionally, the one or more vanes are configured to guide or manipulate air passing through the duct towards the outlet. In an embodiment, the diffuser comprises a plurality of spaced ducts. Optionally, the diffuser comprises a plurality of ducts spaced along the width thereof. Optionally, in use, the inlet of the duct is defined between an end of the diffuser and an end of a subframe tray of a vehicle. In an embodiment, the body comprises, or is defined by, an external wall. In an embodiment, the opening extends substantially perpendicularly through the body. In an embodiment, a longitudinal axis or a central axis of the opening extends substantially perpendicularly to a plane extending across the opening. In an embodiment, a longitudinal axis or a central axis of the opening extends substantially perpendicularly to a plane tangent to the body at the opening or an outer edge of the opening. Optionally, in use, the flow direction of further air through the opening is substantially perpendicular to a plane tangent to the body at the opening or an outer edge of the opening. Advantageously, this maximises the impact on the passing air of the further air leaving the opening. The passing air flows substantially parallel to the outer surface of the body. Therefore, the further air will meet the passing air substantially perpendicularly, having the effect that the passing air is moved away from the outer surface of the diffuser. In an embodiment, the diffuser comprises a movable wall portion configured to selectively close the opening. Being able to selectively close the opening allows for an element of control over the aerodynamic effect provided by the diffuser. For example, the opening may be opened and closed in dependence on vehicle speed to adjust the aerodynamic performance of the vehicle. Optionally, the moveable wall portion comprises a flap or a slat. In an embodiment, the diffuser comprises a means for actively providing a feed or jet of air (hereinafter feed of air) from the opening. It will be appreciated that being able to actively provide a feed of air from the opening allows for an element of control over the aerodynamic effect provided by the diffuser. For example, the pressure of the feed of air being tailored to have an effect on the degree by which the passing air is redirected. Optionally, the means for actively providing a feed of air from the opening comprises an air compressor or pump. In an embodiment the means for actively providing a feed of air from the opening comprises a conduit, piping and / or tubing. Optionally, the conduit, piping and / or tubing may be connected to the air compressor or pump and the opening. In an embodiment, the diffuser is formed of a polymeric or plastics material. The diffuser may be formed of carbon fibre reinforced plastic. Optionally, the diffuser is formed of a textile. According to another aspect of the invention, there is provided a vehicle comprising a diffuser as described above. In an embodiment, the diffuser is attached to the rear of the vehicle. In an embodiment the diffuser is attached to the rear underside of the vehicle. Optionally, the diffuser is attached to an exterior of the vehicle, an exterior rear of the vehicle or an exterior rear underside of the vehicle. Optionally, the outer surface of the diffuser extends at an angle of between 10 and 15 degrees with respect to a horizontal plane or neutral plane of the vehicle. Optionally, the outer surface of the diffuser extends at an angle of between 10 and 15 degrees with respect to an undertray or subframe tray of the vehicle. Optionally, a tangent to the outer surface of the diffuser extends at an angle of between 10 and 15 degrees with respect to a horizontal plane or neutral plane of the vehicle. Optionally, a tangent to the outer surface of the diffuser extends at an angle of between 10 and 15 degrees with respect to an undertray or subframe tray of the vehicle. In an embodiment, the cavity is defined between the body of the diffuser and a portion of a rear bumper of the vehicle. According to yet another aspect of the invention, there is provided a kit of parts comprising diffuser as described above and a subframe tray for a vehicle. In an embodiment, an end of the subframe tray comprises a lip configured to guide passing air into the inlet of the duct of the diffuser, in use. Optionally, the lip may be located at a downstream end of the subframe tray. Optionally, the lip may be located at a rearward end of the subframe tray. 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 invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematic representation of a diffuser for attachment to a vehicle in accordance with an embodiment of the invention; Figure 2 shows a bottom view of a vehicle including a diffuser in accordance with the arrangement of Figure 1; Figure 3 shows a lower perspective view of the vehicle of Figure 2; Figure 4 shows a lower perspective view of the rear of the vehicle of Figure 2; Figure 5 shows a cross-sectional view through a longitudinally extending mid-plane of the vehicle of Figure 2; Figure 6 shows a cross-sectional view through a longitudinally extending plane at the rear of the vehicle of Figure 2; Figure 7 shows a schematic representation of a diffuser for attachment to a vehicle in accordance with another embodiment of the invention; and Figure 8 shows a vehicle in accordance with an embodiment of the invention. DETAILED DESCRIPTION A diffuser 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 1 to 6. Figure 1 is a schematic showing the general operation of the diffuser 100 in use and Figures 2 to 6 illustrate how the diffuser 100 may be attached to a vehicle 500. Figure 2 shows a longitudinal axis (or x axis) 501 and a lateral axis (or y axis) 502 of the vehicle 500 and Figure 6 shows a vertical axis (or z axis) 503 of the vehicle 500. The diffuser 100 also has a longitudinal axis 101, a lateral axis 102 and a vertical axis 103, of which the longitudinal and vertical axes 101,103 are shown in Figure 1 and the lateral axis 102 is shown in Figure 2. When the diffuser 100 is attached to the vehicle 500, the longitudinal axis 101, lateral axis 102 and vertical axis 103 of the diffuser 100 are parallel with the longitudinal axis 501, lateral axis 502 and vertical axis 503 of the vehicle 500, respectively. The vehicle 500 has a front end 504 and a rear end 505 spaced from one another along the longitudinal axis 501. The diffuser 100 is attached to, and extends laterally across, a portion of a rear underside 506 of the vehicle 500 rearward of a rear axle 507 and between wheels 508. More specifically, the diffuser 100 is attached to an underside of the rear bumper 509 in this embodiment. It will be understood that references to a width of the diffuser and a widthwise direction are hereinafter defined by the direction of the lateral axis 502 of the vehicle 500 and the lateral axis 102 of the diffuser 100. The diffuser 100 includes a body 104 formed from a polymeric material in this embodiment and has an outer surface 105 over which passing air flows as the vehicle 500 moves, in use. The outer surface 105 has an upstream end 106a that is located adjacent an end of a subframe tray 510 of the vehicle 500 and a downstream end 106b spaced along the longitudinal axis 101 from the upstream end 106a. As will be appreciated, the upstream end 106a is located closer than the downstream end 106b to the front end 504 of the vehicle 500 and air will flow over the outer surface 105 from the upstream end 106a towards the downstream end 106b during forward motion of the vehicle 500. As is shown in Figure 6 in particular, a tangent to the outer surface 105 is inclined relative to the subframe tray 510 and a horizontal plane or neutral plane P (hereinafter horizontal plane) of the vehicle 500, as shown in Figure 6. The outer surface 105 has a first portion 107 located closer than a second portion 108 to the front end 504, and the first and second portions 107, 108 are separated by a step 109 (not shown in Figure 1). Furthermore, a tangent T to the outer surface 105 in the first portion 107 is less inclined relative to the subframe tray 510 or horizontal plane P than a tangent T’ to the outer surface 105 in the second portion 108, as is shown by the dashed lines in Figure 6. As is shown in Figures 1, 5 and 6 in particular, a cavity 110 is defined between the body 104 and the rear bumper 509 of the vehicle 500 and an opening 111 extends through the body 104 in the first portion 107, and provides fluid communication with the cavity 110. The opening 111 is defined by two widthwise extending slots 112, 113 in this embodiment. The slots 112, 113 are identical, and are a mirror image of one another about a centreline C of the vehicle 500. The slots 112, 113 are each located on a respective side of the centreline C of the vehicle 500 and are separated by a blank portion 114 of the outer surface 105. Furthermore, each slot 112, 113 has a first portion in which the size of the opening is constant along its width and a second portion in which the size of the opening narrows or reduces towards an end thereof. The diffuser 100 includes a plurality of vanes 115 extending across each slot 112, 113 that are configured to guide air being drawn from the cavity 110, in use. It will be appreciated that the vanes 115 may also provide a degree of structural integrity and / or stiffness to each slot 112, 113. In this embodiment the provision of the vanes 115 extending across each slot 112, 113 means that each slot 112, 113 is provided by a plurality of apertures separated by the vanes 115 and arranged to form the shape of the respective slot 112,113. Also in this embodiment, the vanes 115 are a part of the body 104 of the diffuser 100 and an outer surface of each vane 115 provides a part of the outer surface 105 of the body 104. Referring now to Figure 1 in particular, as the vehicle 500 moves forward in use, passing air 120 flowing over the outer surface 105 flows from the upstream end 106a to the downstream end 106b and past (which may instead be referred to as over or across) the opening 111. By ‘past’ it will be appreciated that air flows from a forward side of the opening to a rear side of the opening, when the vehicle moves forwards, in use. Air 121 located within the cavity 110 has a higher pressure than the passing air 120, and is therefore drawn from the cavity 110 through the opening 111. The air 121 drawn from the cavity 110 redirects the passing air 120 away from the outer surface 105 such that it has an angle of incidence relative to the subframe tray 510 or vehicle horizontal plane P less than the angle of inclination of a tangent T” to the outer surface 105, as is shown by the flowlines F in Figure 1. Therefore, the upwash behind the vehicle 500 is reduced. A diffuser 300 in accordance with another embodiment of the present invention is described herein with reference to the accompanying Figure 7. The diffuser 300 of Figure 7 is similar to the diffuser 100 of Figures 1 to 6, and like features are denoted by like reference numerals incremented by ‘200’. Figure 7 is a schematic showing the general operation of the diffuser 300 in use. It will be appreciated that the diffuser 300 may be attached to a vehicle 500 (Figure 8) in a similar manner to the diffuser 100 described above. The diffuser 300 also has a longitudinal axis 301, lateral axis 302 and vertical axis 303, of which only the longitudinal and vertical axes 301,303 are shown in Figure 7. It will be appreciated that the lateral axis 302 is as per the lateral axis 102 of the diffuser 100, described above. When the diffuser 300 is attached to a vehicle 500, the longitudinal axis 301, lateral axis 302 and vertical axis 303 of the diffuser 300 are parallel with the longitudinal axis 501, lateral axis 502 and vertical axis 503 of the vehicle 500, respectively. The diffuser 300 is configured to be attached to, and extend laterally across, the rear underside of the vehicle 500. More specifically, the diffuser 300 is attached to an underside of the rear bumper 509 in this embodiment. The diffuser 300 includes a body 304 formed from a polymeric material in this embodiment and has an outer surface 305 over which passing air flows as the vehicle 500 moved, in use. The outer surface 305 has an upstream end 306a that is configured to be located adjacent an end of a subframe tray 510 of the vehicle 500 and a downstream end 306b spaced along the longitudinal axis 501 from the upstream end 306a. As will be appreciated, the upstream end 306a is located closer than the downstream end 306b to a front end 504 (Figure 2) of the vehicle 500 and air will flow over the outer surface 305 from the upstream end 306a towards the downstream end 306b during forward motion of the vehicle 500. A tangent T to the outer surface 305 is inclined relative to the subframe tray 510 and a horizontal plane or neutral plane P (hereinafter horizontal plane) of the vehicle 500, as shown in Figure 6. In this embodiment, instead of there being a cavity defined between the body 304 and a rear bumper 509 (Figure 3) of the vehicle 500, there is a cavity 316 that forms part of a duct 317. The duct 317 has an inlet 318, an outlet 319 spaced along the longitudinal axis 301 from the inlet 318 and a passage for air between the inlet 318 and the outlet 319 and defined by the cavity 316. An end of the subframe tray 510 is provided with a lip 510a that is arranged to guide passing air 320 into the inlet 318 of the duct 317. It will be appreciated that the diffuser 300 may include a pair of ducts 317, each having an outlet similar to the slots 112, 113 of the diffuser 100 described above. The outlet 319 may also include one or more vanes in a similar arrangement to the vanes 115 of the diffuser 100. The diffuser 300 may also include a second cavity defined between the body 304 and the rear bumper 509 of the vehicle 500. The second cavity is defined in part by an inner part of each duct 317, the inner part being a part which faces the rear bumper 509 in use. The second cavity may be in fluid communication with the cavity 316 formed by the duct 317 and / or passage. As the vehicle 500 moves forward in use, a portion 321 of passing air 320 flowing over the outer surface 305 from the upstream end 306a to the downstream end 306b is guided into the inlet 318 of the duct 317 by the lip 510a. Furthermore, the remaining passing air 320 flows past the outlet 319, and the air 321 located within the duct 317 has a higher pressure than the passing air 320. Therefore, the air 321 is drawn along the cavity 316 / passage and out of the outlet 319. The air 321 drawn from the cavity 316 redirects the passing air 320 away from the outer surface 305 such that it has an angle of incidence relative to the subframe tray 510 or vehicle horizontal plane P less than the angle of inclination of the tangent T to the outer surface 305, as shown by the flowlines F’ in Figure 7. Therefore, the upwash behind the vehicle 500 is reduced. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A diffuser for attachment to a vehicle, the diffuser comprising:a body having an outer surface, wherein at least a portion of the body defines a cavity; and an opening extending through the body and providing fluid communication with the cavity;wherein, in use, passing air flowing over the outer surface flows past the opening so as to draw further air from the cavity through the opening and thereby redirect the passing air away from the outer surface.

2. A diffuser according to claim 1, wherein the diffuser is for attachment to the rear of a vehicle.

3. A diffuser according to claim 1 or claim 2, wherein the opening comprises a slot.

4. A diffuser according to claim 3, comprising one or more vanes extending across the slot.

5. A diffuser according to claim 3 or claim 4, wherein the opening comprises a plurality of spaced slots.

6. A diffuser according to claim 1, comprising a duct having:an inlet;an outlet defined by the opening and spaced from the inlet; anda passage for air between the inlet and the outlet and defined by the cavity;wherein, in use, a portion of passing air flowing over the outer surface passes through the duct and is drawn from the passage through the outlet by passing air that flows past the outlet.

7. A diffuser according to claim 6, wherein the inlet is located at an end of the diffuser.

8. A diffuser according to claim 6 or claim 7, wherein the outlet is defined by an opening according toany one of claims 3 to 5.

9. A diffuser according to any one of claims 6 to 8, wherein the passage comprises one or more vanes configured to guide air passing through the duct towards the outlet.

10. A diffuser according to any one of claims 6 to 9, comprising a plurality of spaced ducts.

11. A diffuser according to any preceding claim, comprising a movable wall portion configured toselectively close the opening.

12. A diffuser according to any preceding claim, comprising a means for actively providing a feed of air from the opening.

13. A diffuser according to any one of claims 1 to 10, wherein the diffuser is passive.1014, A vehicle comprising a diffuser according to any one of claims 1 to 13.

15. A kit of parts comprising diffuser according to claim 6 and a subframe tray, wherein an end of the subframe tray comprises a lip configured to guide passing air into the inlet of the duct, in use.12

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