GB2510898A

GB2510898A - Wheel guard for a vehicle

Info

Publication number: GB2510898A
Application number: GB1302827.9A
Authority: GB
Inventors: Andreas Kremheller
Original assignee: Nissan Motor Manufacturing UK Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd
Priority date: 2013-02-19
Filing date: 2013-02-19
Publication date: 2014-08-20
Also published as: WO2014129376A1; GB201302827D0

Abstract

A wheel guard 10 is provided for a wheel of a vehicle, the wheel guard 10 defining a cavity for receiving a wheel and comprising a front end with at least one aperture 18,19 to permit airflow through the wheel guard 10 between an engine compartment 23 of the vehicle and the wheel cavity. A protrusion may also be provided at the guard front end to reduce vorticity and pressure oscillations. Apertures may be incorporated in a stepped ladder formation to reduce noise and mud and water ingress. A deflector (14 see fig 8) may be provided to direct outer air away from the cavity. The invention is aimed at reducing shape related resistive forces and increasing fuel efficiency.

Description

WHEEL GUARD FOR A VEHICLE

Field of the invention

The present invention relates to a wheel guard for a vehicle. In particular, the invention relates to a wheel guard for a vehicle which improves, for example, engine cooling and drag effects of the vehicle. The invention also relates to a vehicle fitted or otherwise provided with such a wheel guard.

Background to the Invention

As fuel prices are rising and the requirement for more environmentally friendly vehicles becomes more pressing than ever, it is becoming more and more desirable to increase fuel efficiency.

As 60% of the power required for a vehicle to cruise at high speeds is used to overcome the aerodynamic effects, improving aerodynamics translates directly into improving fuel efficiency. This is done by reducing the drag and lift forces, the main aerodynamic forces opposing vehicle motion, and therefore increasing the power consumption of a vehicle.

The lift and drag forces are the components of the force acting against an object's motion. Lift is the component of the force that is perpendicular to the oncoming flow direction, while drag is the force acting in the direction of the relative flow velocity, which is, in the case of vehicle aerodynamics, opposite to the vehicle's velocity.

Drag increases with speed, and is highly dependent on the object's shape as it increases with the pressure difference between the front and the rear part of the object.

It is therefore an object of this invention to optimise the shape of a vehicle, such that it reduces resistive forces and increases fuel efficiency.

Summary of the Invention

According to one aspect of the present invention there is provided a wheel guard for a wheel of a vehicle, the vehicle having a front vehicle end and a rear vehicle end, the wheel guard defining a wheel cavity within which the wheel is received and comprising a front end towards the front vehicle end which is provided with at least one aperture to permit airflow through the wheel guard between an engine compartment of the vehicle and the wheel cavity.

An embodiment of the present invention comprises a wheel guard for a vehicle permitting airflow between the engine compartment of the vehicle and the wheel cavity to improve engine cooling. Because the air inside the engine compartment usually has a high stagnation pressure with respect to the air in the wheel cavity, a significant pressure drop is created, thus the aperture permitting communication between the engine compartment and the wheel cavity results in an increased flow of air from the engine compartment through the vehicle's cooling radiator, into the wheel cavity.

This effect is especially significant when the vehicle is in use and the stagnation pressure in the front region of the wheel cavity, defined by the front end of the wheel guard, is even lower, and the comparative advantage of the increased flow rate through the vehicle's cooling radiator is even larger.

The wheel guard may advantageously comprise a plurality of openings or apertures to permit airflow through the wheel guard between the engine compartment and the wheel cavity, further increasing airflow from the engine compartment into the wheel cavity.

The wheel guard may fuither comprise a protrusion at the front end of the wheel guard which defines an alcove in communication with the main volume of the wheel cavity (i.e. that volume of the wheel cavity housing the wheel). The wheel does not extend into the alcove, but is housed wholly within the main volume of the wheel cavity. The protrusion removes any geometry prone to vortex generation and reduces vorticity in the area. This also results in reduced pressure oscillations in the wheel cavity and improved interactions between the ground boundary layer and the vortex structures, improving the overall drag coefficient of the vehicle, and thus improving the fuel efficiency of the vehicle. Advantageously, the protrusion therefore improves the vehicle's aerodynamics. Typically, because of flow separation around the wheel, the wheel cavity is prone to turbulent flow and vortex generation producing high drag forces and compiomising the overall drag coefficient of the vehicle. The protrusion may be integrally formed with the wheel guard. The advantage of forming the protrusion integrally with the wheel guard is that it improves the structural rigidity of the protrusion and may be placed at the optimal region to improve aerodynamics.

The wheel guard may advantageously comprise at least one opening or aperture which opens into the protrusion. The advantage of this feature is that the aperture allows airflow between the engine compartment and a region of the wheel cavity which, because of the protrusion, has an even lower stagnation pressure, thus achieving a larger pressure drop and increased airflow, improving the engine cooling effect further.

The protrusion of the wheel guard may preferably comprise at least one ladder formation comprising an upper step and a lower step. Such a stepped shape advantageously reduces road noise. The upper and lower steps may be horizontal.

The advantage of such an orientation is that it minimises mud and water ingress through the aperture to the wheel cavity.

At least one of the upper and lower steps of the protrusion of the wheel guard may define an aperture to permit airflow through the wheel guard between the engine compartment and the wheel cavity. In one particular embodiment, both of the upper and lower steps of the wheel guard may define an aperture to permit airflow through the wheel guard between the engine compartment and the wheel cavity.

The protrusion of the wheel guard may advantageously comprise at least two ladder formations arranged side by side. Each of the ladder formations may preferably comprise an upper step and a lower step, each of the steps being provided with an aperture to permit airflow through the wheel guard between the engine compartment and the wheel cavity. Each of the ladder formations may comprise at least two steps.

According to a second aspect of the invention, there is provided a wheel guard for a wheel of a vehicle, the vehicle having a front vehicle end and a rear vehicle end, the wheel guard defining a wheel cavity for housing the wheel, and having a front end towards the front vehicle end, the front end of the wheel guard being provided with a protrusion which defines an alcove in communication with the wheel cavity.

According to a third aspect of the present invention there is provided a vehicle fitted or otherwise provided with a wheel guard. The vehicle therefore comprises a wheel guard in accordance with a first or second aspect of the invention. The vehicle may advantageously comprise a deflector for deflecting airflow away from the wheel cavity. The deflector reduces the stagnation pressure in the front region of the wheel cavity thus increasing the pressure drop between the engine compartment and the wheel cavity and improving the engine cooling effect. It also improves the flow regime in the wheel cavity, therefore improving the drag coefficient of the vehicle.

The deflector is arranged directly in front of a front surface of the protrusion.

It will be appreciated that any of the preferred and/or optional features of the first aspect of the invention can be incorporated alone or in appropriate combination in the second or third aspects of the invention also.

Brief Description of the Drawings

In order for the invention to be better understood, reference will be made, by way of example, to the accompanying drawings in which: Figure 1 is a plan view from the bottom of a vehicle fitted with an improved wheel guard according to an embodiment of the present invention; Figure 2 shows a perspective view from the top of the vehicle fitted with the wheel guard of Figure 1; Figure 3 is a perspective view from the bottom of the vehicle fitted with the wheel guard of Figure 1; Figure 4 is a top plan view of a louvre frame of the wheel guard of Figure 1; Figure 5 is a representation of the vorticity distribution profile of a wheel cavity fitted with a conventional wheel guard; Figure 6 is a representation of the relative pressure distribution profile of the conventional wheel cavity of Figure 5; Figure 7 is a schematic diagram of a side view of the wheel cavity fitted with the conventional wheel guard of Figure 5 and a front part of a conventional vehicle; Figure 8 is a schematic diagram of a side view of the wheel cavity of a vehicle fitted with the wheel guard of Figures 1 to 4; and Figure 9 is a perspective view from the bottom of a vehicle fitted with the wheel guard of Figures 1-3.

Detailed Description of the exemplary embodiments

The overall arrangement of a fender protector or wheel guard 10 embodying the present invention is illustrated in Figures 1, 2 and 3.

A wheel guard 10 is the part of a vehicle that frames a wheel cavity and separates the front end of the vehicle and the engine compartment of the vehicle from the wheel cavity. Its primary purpose is to prevent sand, mud, rocks, and other road spray from being thrown in the air by the rotating tyre.

Cooling radiators are used for lowering the temperature in internal combustion engines. This is usually done by passing a liquid (engine coolant) through the engine block where the liquid is heated, then through the radiator itself where the liquid loses heat to the atmosphere, and then back to the engine in a closed loop.

The position and orientation of the wheel guard embodying the present invention is now described referring to Figure 1 which shows a bottom plan view of the front end of a vehicle. The wheel guard 10 comprises a louvre frame 16 having an upper and a lower set of louvres or openings 18, 19. The wheel guard 10 forms an arch which is one of the arches of the front wheels of the vehicle. The vehicle has a tyre deflector 14 located forward of the wheel guard 10 which deflects airflow away from the wheel cavity, in use.

An engine compartment 23 of the vehicle is bounded on either side by the front wheels. A vent or grill 92 at the front of the engine compartment 23 allows airflow into the engine compartment 23 through a radiator (not shown) located within the engine compartment 23. The radiator is located directly behind the grill 92, adjacent to the engine. The grill 92 allows air to flow into the engine compartment and around the radiator, thus increasing the capacity of the radiator to dissipate heat. It follows that an increase in the airflow rate through the radiator results in improved cooling performance.

The frame 16 is protruded on a front surface 24 of the wheel guard 10. As can be seen in Figure 1, the wheel guard 10 has a smaller radius on its inner side 20 adjacent to the engine compartment 23 compared with a larger radius on its outer side 22 which defines a part of the external vehicle surface. As a result, the front facing surface 24 of the wheel guard 10 is a curved surface at an oblique angle to the axis of rotation of the wheel. The frame 16 follows the curved profile of the front facing surface 24. The axis of rotation of the wheel will herein be referred to as the transverse axis 25 of the vehicle, whilst the axis perpendicular to the transverse axis 25, from the front end to the rear end of the vehicle, will be referred to as the longitudinal axis 27.

The tyre deflector 14 is suspended from the bottom of the engine compartment 23, directly in front of the wheel guard 10, at an orientation parallel to the transverse axis 25. Therefore, the tyre deflector 14 is tangential to a forward most point of the frame 16 at the front surface of the frame 16. The frame 16 has an inner end closer to the engine compartment 23 and an outer end towards the external vehicle surface 22. The length of the tyre deflector 14 is such that it is longer than the projection of the louvre frame 16 on the transverse axis of the vehicle 25, for aerodynamic purposes to be explained below, with respect to Figure 8. In the longitudinal direction of the vehicle, the inner end of the tyre deflector 14 lies in front of and is spaced apart from the inner end of the frame 16, while in the transverse direction of the vehicle the outer end of the tyre deflector 14 extends a few centimetres beyond the outer end of the louvre frame 16, closer to the surface 22 of the wheel arch.

Turning to Figures 2 and 3, the louvre frame 16 is integrally formed with the wheel guard 10 at its front surface 24. As can be seen more clearly in Figure 2, on the engine compartment side the frame 16 defines a hollow, broadly wedge-shaped protrusion with a front surface 36 which follows the curved profile of the front-facing surface 24 of the wheel guard 10. The frame 16 forms a ladder formation with two treads or steps in the form of an upper step and a lower step. The frame 16 also includes a lower base 32 at the bottom the engine compartment 23, an upper base 34 parallel to the lower base 32 and two lateral trapezoidal end faces 38 adjoining the two bases 32, 34 and the front facing surface 24 of the wheel guard 10. Figure 3 shows the alcove that the ladder-shaped structure defines at its rear-side. The alcove is internal to the wheel cavity and is integral herewith.

The lower base 32 is relatively large, of broadly rectangular shape, having a front edge and a rear edge, its rear edge adjoining the front facing surface 24 of the wheel guard 10.

The upper base 34 is relatively small, of broadly rectangular shape and has a front and a rear edge, its rear edge also adjoining the front facing surface 24 of the wheel guard 10 a few centimetres above the lower face 32. The upper base 34 constitutes the top tread of the ladder-shaped structure and accommodates an upper set of louvres or apertures formed of three adjacent apertures 40a spaced apart equidistantly by intermediate sections 42 of the top base 34.

The shape of the upper base 34 can be best described with respect to Figure 4, which shows a top plan view of the frame 16. The front edge of the upper base 34 takes a castellated form, to define a set of channels 44 and ridges 46 formed on the front facing surface 36 of the louvre frame 16. The channels 44 and ridges 46 extend approximately vertically. Rectangular protrusions 48 of the castellated front edge of the upper base 34 are formed in front of the intermediate sections 42 separating the apertures 40a. Each protrusion 48 serves as a small upper base for one of the hollow wedge-shaped ridges 46. For structural integrity, the front-facing surfaces of all the ridges 46 have the same slope, lying on the plane defined by the front edges of the trapezoidal end faces 38.

For each channel 44, an upper riser 50 between the upper and lower treads of the ladder-shaped structure defines the surface which forms the back of the channel 44. The riser 50 is parallel to the front facing surface 24 of the fender, as opposed to the front edges of the trapezoidal faces 38, so that the channels increase in depth with the distance from the smaller upper base 34. Each channel 44 only extends from the upper base 34 to a few centimetres above the lower base 32.

This way, the channels 44 are shorter than the ridges 46, and the back of each channel 44 has a steeper slope than the ridges 46 at the front-facing surface 36.

At the lower end of each channel 44, a lower set of louvres or apertures 4Db is provided, forming the second set of apertures formed within the lower tread of the ladder-shaped structure. A lower riser 51 extends between the lower tread and the bottom of the engine compartment of the vehicle 23 for each channel.

The frame 16 therefore forms a two-tread vent structure, connecting the interior of the engine compartment with the wheel cavity, allowing air to flow from the former to the latter.

The rotation of the wheel causes the flow to separate very early, which creates a large wake behind the wheel. This turbulent wake and the presence of strong vortices produces high drag and lift forces compromise the vehicle's aerodynamics and consequently fuel efficiency. The configuration of the wheels and the wheel cavities is therefore important to the aerodynamics of a vehicle, as the contribution of the wheels to the overall drag and lift coefficients of a vehicle is usually significant. The drag coefficient is a common dimensionless metric used to quantify the resistance (drag) of a vehicle in motion.

The vorticity and relative pressure distributions in the wheel cavity of a vehicle fitted with a conventional wheel guard are shown in Figures 5 and 6. The conventional wheel guard, lateral sides of the wheel and the lower front and back surfaces of the wheel guard are denoted by reference numbers 10', 52', 60' and 62' respectively. Strong vortex formations are present not only on the lateral sides of the wheel 52', but also on the lower front and back surfaces 60', 62' of the conventional wheel guard 10', as will be described below with more detail with reference to Figure 7. The main vortex relevant to the present invention is that coming up the front surface 62' of the conventional wheel guard 10' (labelled in Figure 5 as "A").

Turning to Figure 6, the relative pressure profile of the wheel cavity of a vehicle fitted with a conventional wheel guard is illustrated. Overall, the pressure in the wheel cavity region contiguous to the conventional wheel guard 10' is slightly raised in comparison to the environment in a hornogenous fashion, apart from areas in the lower front 60' and the back surfaces 62' of the conventional wheel guard 10', where a significant increase with respect to the pressure in the rest of the wheel cavity is observed. This local pressure increase in the lower front surface of the wheel cavity 60' will be explained with more detail below, with reference to Figure 7.

Figure 7 is a schematic diagram of the side view of the wheel cavity of a vehicle using a conventional wheel guard, and the area directly in front of the wheel guard.

The bottom of the engine compartment, the axis of rotation of the wheels and a tyre deflector are denoted in Figure 7 by reference numbers 23', 25' and 14' respectively. The bottom of the engine compartment 23' is typically at a level below that of the axis of rotation of the wheels 25'. A conventional wheel guard 10' forms an arc concentric to the wheel of the vehicle, contiguous to the bottom of the engine compartment 23'. As the centre of the arc of the wheel arch lies above the bottom of the engine compartment 23', the conventional wheel guard 10' meets the bottom of the vehicle at an oblique angle 80', which due to its shape causes the formation of the area of increased stagnation pressure and vortex generation 60' of Figures Sand 6. In addition to this, with the conventional wheel guard 10', the tyre deflector 14' is typically suspended a few centimetres in front of the corner 80' between the conventional wheel guard 10' and the bottom of the engine compartment 23'.

These two features, the distance between the tyre deflector 14' and the conventional wheel guard 10', and the sharp feature formed due to the oblique angle 80' the wheel arch forms with the bottom of the engine compartment 23', result in a geometry prone to vortex generation, as it facilitates flow separation.

The resulting flow regime around the rotating wheel inside the wheel cavity is characterised by unsteadiness and strong vorticity, giving rise to the high pressure regions in the lower front surface 60' and lower back surface 62' of Figure 6. The arrangement therefore results in an increased drag coefficient, and subsequently decreased fuel efficiency, a problem addressed by an aspect of the present invention, as will be explained with reference to Figure 8.

Figure 8 is a schematic diagram of the side view of the wheel cavity of a vehicle fitted with the improved wheel guard 10, and the area directly in front of the wheel guard. Comparing and contrasting with the conventional wheel guard 10' of Figure 7, the advantages of the invention become apparent.

The tyre deflector 14 of Figure 1 and 3 can be seen in side view suspended directly in front of the louvre frame 16 at a right angle to the engine compartment 23, and provides a more efficient wind receiving surface, deflecting the windflow away from the wheel cavity better than the conventional tyre deflector 14' of Figure 7, as it is located closer to the wheel cavity.

The overall step-shaped structure of the frame 16 described with respect to Figure 3 above, can also be seen in this side view. One advantage of the invention is that it replaces the sharp convex corner 80' created between the conventional wheel guard 10' and the engine compartment 23 of the vehicle of Figure 7, which is a crucial factor contributing to the vortex generation at this area.

This optimised shape, in combination with the tyre deflector 14 of Figures 1 and 2, which can be seen here in side view, results not only in reduced vorticity, but also reduced pressure oscillations in the wheel cavity and improved interactions between the ground boundary layer and the vortex structures in the wheel cavity, therefore reducing stagnation pressure in the wheel cavity. As a result of the improved flow regime the overall drag coefficient of the wheel guard 10 is decreased, improving aerodynamics and fuel efficiency. Computational simulations and wind tunnel testing have demonstrated that the use of the improved wheel guard 10 improves the overall drag coefficient of the vehicle by 0.2%.

Another factor contributing to this improved flow regime is the air flowing from the engine compartment, through the apertures 40a and 4Db of Figure 2 and into the wheel cavity, as indicated by the schematic streamline 82. The reduced stagnation pressure achieved by the step feature of the louvre frame 16 and the improved tyre deflector 14 results in a low pressure region behind the tyre deflector. The air inside the engine compartment usually has a higher stagnation pressure, therefore a significant pressure drop is created, increasing the flow of air from the engine compartment (high pressure) to the region behind the tyre deflector (low pressure because of the improved tyre deflector 14), and therefore increasing the airflow rate through the vehicle's radiator. Computational simulations and wind tunnel testing have demonstrated the airflow flux through the radiator to have increased by 10.5% when using the improved wheel guard 10 of the present invention.

The cooling airflow is more clearly illustrated with respect to Figure 9. The cooling airflow 90 enters the engine bay through the grill 92, as in a conventional vehicle, and exits at the front region of the wheel cavity.

In addition to the aerodynamic and engine-cooling effects of the invention, the step-like shape of the louvre frame 16 results in reduced road noise and splash noise, while the approximately vertical orientation of the apertures 40a and 40b minimises mud and water ingress.

It is these aerodynamic and engine cooling effects which dictate the dimensions of the louvre frame, which are selected to achieve the optimal trade-off between improvement in aerodynamics and engine cooling (which increases with the size of the apertures and the step feature), and structural integrity (as the smaller the apertures the more robust the part). In an embodiment of the present invention the dimensions of the features of the improved wheel guard 10 were chosen such that the overall height of the louvre frame 16 is approximately 530mm, the length and width of an aperture 40a or 4Db is 45mm and 15mm approximately, and the width of an intermediate section 42 of the upper base is approximately 20mm. The aforementioned 10.5% increase in the cooling airflow and 0.2% decrease in the drag coefficient were obtained experimentally using a model with the above dimensions.

Claims

Claims: 1. A wheel guard for a wheel of a vehicle, the vehicle having a front vehicle end and a rear vehicle end, the wheel guard defining a wheel cavity within which the wheel is received and comprising a front end toward the front vehicle end which is provided with at least one aperture to permit airflow through the wheel guard between an engine compartment of the vehicle and the wheel cavity.
2. A wheel guard as claimed as Claim 1, comprising a plurality of apertures to permit airflow through the wheel guard between an engine compartment of the vehicle and the wheel cavity.
3. A wheel guard as claimed in Claim 1 or Claim 2, comprising a protrusion at the front end of the wheel guard which defines an alcove in communication with the wheel cavity.
4. A wheel guard as claimed in Claim 3, wherein the protrusion is integrally formed with the wheel guard.
5. A wheel guard as claimed in Claim 3 or 4, wherein the at least one of the apertures opens into the protrusion.
6. A wheel guard as claimed in any of Claims 3 to 5, wherein the protrusion comprises at least one ladder formation comprising an upper step and a lower step.
7. A wheel guard as claimed in Claim 6, wherein the upper and lower steps are horizontal.
8. A wheel guard as claimed in Claim 6 or Claim 7, wherein at least one of the upper and lower steps defines an aperture to permit airflow through the wheel guard between the engine compartment and the wheel cavity.
9. A wheel guard as claimed in Claim 8, wherein each of the upper and lower steps defines an aperture to permit airflow through the wheel guard between an engine compartment and the wheel cavity.
10. A wheel guard as claimed in any one of Claims 6 to 9, wherein the protrusion comprises at least two ladder formations arranged side by side.
11. Awheel guard as claimed in Claim 10, wherein each of the ladderformations comprises an upper step and a lower step provided with an aperture to permit airflow through the wheel guard between the engine compartment and the wheel cavity.
12. A wheel cavity as claimed in any of Claims 6 to 11, wherein each of the ladder formations comprises at least two steps.
13. A wheel guard for a wheel of a vehicle, the vehicle having a front vehicle end and a rear vehicle end, the wheel guard defining a wheel cavity for housing the wheel, and having a front end towards the front vehicle end, the front end of the wheel guard being provided with a protrusion which defines an alcove in communication with the wheel cavity.
14. A vehicle comprising a wheel guard as claimed in any of Claims ito 13.
15. A vehicle as claimed in Claim 14, further comprising a deflector for deflecting airflow away from the wheel cavity.
16. A vehicle as claimed in Claim 15, wherein the deflector is arranged directly in front of a front surface of the protrusion.
17. A wheel guard substantially as herein described with reference to the accompanying Figures 1,2,3,4,8 and 9.
18. A vehicle substantially as herein described with reference to the accompanying Figures 1, 2, 3,4, 8 and 9.