It is well known to provide a motor vehicle such as a car or truck with a disc brake to apply a braking effect to a road wheel of the motor vehicle. It is further known that the braking effect produced bv the brake disc results in heating of the brake disc as kinetic energy is converted into heat. This heating effect can be a problem if the temperature of the disc exceeds a certain temperature as it will result in a reduction of braking effect and in severe cases can result in a total loss of braking effect.

It is known to provide a tube extending from a position adjacent to the brake disc to a position in the air passing by the motor vehicle to provide a ram air cooling effect to the brake disc. Such ram air cooling has been used extensively on racing cars for many years but is only really effective at high forward velocities and results in increased drag on the motor vehicle.

It is an object of this invention to provide an improved cooling arrangement for a motor vehicle brake disc.

According to the invention there is provided a motor vehicle comprising at least one wheel rotatably mounted within a wheel cavity defined by a

body structure of the motor vehicle, a brake disc connected to said wheel for rotation therewith, a brake disc calliper to apply a braking effect to said brake disc and a cooling duct for cooling said brake disc characterized in that the cooling duct has a first portion adjacent to the brake disc and a second portion adjacent an outer portion of the wheel such that rotation of the wheel past the second portion causes air to flow through the duct.

Preferably the second portion of said duct is positioned adjacent to a tyre forming part of the wheel.

Preferably the second portion of the duct is adjacent means defining a channel such that air circulating with the wheel will flow through the channel. Desirably the channel is tapered so as to cause acceleration of air flowing through it.

Said means may be arranged to co-operate with the duct so as to form a venturi pump causing air to be drawn through the duct from the first portion to the second portion. In this case the first portion preferably comprises a collector plate having a lip extending around the periphery of the brake disc.

The cooling member preferably extends substantially vertically from the first portion to the second portion such that heat from the brake disc can

cause convection in the cooling duct. This can provide cooling when the wheel is not rotating, i. e. when the vehicle has stopped after braking.

Alternatively the second portion of the duct may include a collector means arranged to channel air into the duct, thereby to urge air through the duct towards the brake disc.

The cooling member is preferably mounted on a part of the suspension or hub assembly which moves vertically with the wheel, such as a suspension strut.

The invention will now be described by way of example with reference to the accompanving drawing of which:- Fig. 1 is a side view of a front part of a motor vehicle according to a first embodiment of the invention: Fig. 2 is a plan view of the same part of the vehicle shown in Fig. 1; Fig. 3 is a front view of part of the motor vehicle of Fig. 1 showing a brake cooling arrangement according to the invention; Fig. 4 is a view in the direction of arrow'X'on Fig. 3;

Fig. 5 is a horizontal section through part of the arrangement of Fig. 3; Fig. 6 is a section corresponding to Fig. 5 but through an arrangement according to a second embodiment of the invention.

Fig. 7 is a view similar to that shown in Fig 4 but showing a third embodiment of the invention : and Fig. 8 is a view in the direction of arrow'R'on Fig. 7 With particular reference to Figs 1 and 2 a motor vehicle 10 has a wheel cover in the form of a front wing 11 defining a wheel cavity 12 in which is rotatably mounted a road wheel 14. During normal forward motion of the motor vehicle 10 the road wheel 14 will rotate in the direction co as shown on Fig. 1.

This rotation of the wheel produces a complex air flow pattern around the front portion of the motor vehicle 10 but in general terms air is dragged by rotation of the wheel 14 from a position at the back of the wheel 14 over the top of the wheel to a position at the front from where it merges with the air passing by the side of the motor vehicle 10.

In general, the effect of this is that the viscosity of the air produces a boundary layer around the wheel which acts as a large rotating torus of air

of varying linear velocity. Adjacent to the surface of the wheel 14 the linear air speed is virtually the same as the linear speed of the wheel, that is to say it is equal to the rotation speed m multiplied by the radius of the wheel 14. and the linear speed of the air reduces as the distance from the surface of the wheel is increased.

With particular reference to Figs 3.4 and 5 the front wing 11 defines a wheel cavity in the form of a wheel arch 12. The road wheel 14 has a wheel member 29 and a tyre member 30. The wheel member 29 is rotatably mounted upon a hub forming part of a wheel hub assembly 17. The wheel hub assembly is supported by a suspension strut 15 and a transverse suspension arm 16. A ventilated brake disc 19 is attached to the hub of the wheel hub assembly for rotation therewith. A brake calliper 20 is mounted upon a fixed part of the wheel hub assembly 17 to provide a braking force to the brake disc 19.

A brake cooling member 18 is attached to the lower part 15a of a suspension strut 15, which moves vertically with the wheel 14, by a fixing means (not shown), and extends substantially vertically from an inlet means in the form of a collector plate 27 at its lower end to an outlet means including an extractor funnel 26 at its upper end. The inlet and outlet means 27,26 are joined by a conduit 28.

The collector plate 27 has an annular central portion 27a that lies close to a side surface of the brake disc 19 and a circumferential lip 27b that extends over the outer peripheral edge of the brake disc 19 for co-operation with radially extending ducts 19a formed within the brake disc 19.

The extractor funnel 26 comprises a tapering funnel portion 26a defining a tapering channel 25 and is situated adjacent to an outlet part 26b forming the top of the conduit 28. The outlet part 26b has an outlet opening 26c which communicates with the tapering channel 25 at a position near to its position 25a of minimum cross-sectional area. The extractor funnel 26 is located in the wheel arch between the body of the vehicle and the tyre, approximately at the highest point of the tyre, and is spaced apart from the tyre 30 by a small distance'G'but is located as close to the tyre 30 as is possible to maximise the collection of air rotating with the wheel 14.

It will be appreciated that because the brake cooling member is attached to the lower part 15a strut 15 it will rise and fall with the wheel 14 and that therefore the collector plate 27 and extractor funnel 26 will remain fixed in relation to the axis of rotation of the wheel 14 and brake disc 19.

Operation of the cooling mechanism is as follows. When the vehicle moves in a forward direction the wheel 14 rotates in the direction shown by the arrow co on Fig. 1 causing the brake disc 19 to be rotated in the same

direction due to its attachment to the wheel hub. Rotation of the brake disc 19 causes air to be drawn into the inner end of its radially extending ventilation ducts 19a and thrown outwardly towards the outer periphery of the brake disc 19, the brake disc forming a centrifugal air pump in substantially known manner.

The rotation of the wheel 14 causes the tyre 30 to be rotated within the wheel arch 12 causing air to be rotated in the same direction as the wheel 14. Some of the rotating air is collected by the funnel portion 26a and because of the reducing cross-sectional area of the tapered channel 25 the speed of the air is increased as it travels through the channel 25. At the juncture with the outlet opening 26c of the outlet part 26b the velocity of the air is considerably increased This produces a region of low pressure near the outlet opening 26c which causes air to be sucked out of the outlet opening 26c by a venturi pump effect, thereby creating a flow from the collector plate 27 through the conduit 28. The air flowing through the gap 'G'which is also accelerated also contributes to this pumping effect.

The cooling member 18 therefore acts as a duct taking hot air exiting the outer rim of the brake disc 19 away from the brake disc 19. Because of the flow produced by the cooling member 18 the efficiency of the pumping effect of the brake disc 19 is increased and so the result is that more air is drawn through the ducts 19a for a given rotational speed.

When the wheel stops rotating after a significant brake application the brake disc will still be at a high temperature. Because of the lack of rotating air the venturi pump action will cease. However, because of its vertical orientation, the cooling member then acts as a cooling stack producing a strong convection current up through the conduit 28 which draws air from around the brake disc, and also out through the radially extending ducts 19a in the brake disc 19.

With reference to Fig. 6 a second embodiment of the invention is in many respects the same as the first. Corresponding parts are shown by the same reference numerals preceded by a'1'. The extractor funnel 126 has a funnel portion 126a which, together with the wheel 130, forms a tapered channel 125: and an outlet part 126b which is connected to the channel 125 via an outlet opening 126c. Once again the flow of air through the channel 125 forms a venturi effect sucking air out of the outlet part 126b through the outlet opening 126c. The main difference between this embodiment and the first is that in this case the outlet part 126b is nested in front of the strut 115 rather than behind it.

Also according to the invention, either as an alternative to the venturi arrangement described above or in addition to it, the ram effect of the rotating torus of air around the wheel can be used to directly cool the brake disc, using a duct or conduit leading from a position near the tyre to the

inner circumference of the brake disc. Figs 7 and 8 show a third embodiment of the invention in which both ram air and suction is used to cool the brake disc. Similar parts to those in the first embodiment have the same reference numeral preceded by a'2'.

The wheel hub assembly 217 is supported by a suspension strut 215 and a transverse suspension arm 216. A ventilated brake disc 219 is attached to the hub of the wheel hub assembly 217 for rotation therewith. A brake calliper 220 is mounted upon a fixed part of the wheel hub assembly 217 to provide a braking force to the brake disc 219. A brake cooling member 218 is provided corresponding exactly to that shown in Figs. 3 to 5.

An air collector duct 240 extends radially, and approximately horizontally, outwardly from a position adjacent to an inner periphery of the brake disc 219 to a position adjacent a tyre 230, at approximately the rearmost portion of the tyre. The air collector duct 240 has an inlet orifice 241 at its outer end, shaped so as to collect passing air from the torus of air rotating with the wheel, and an outlet orifice 242 at its inner end to supply air from the duct 240 to the centre portion of the brake disc 219.

The air collector duct 240 is circumferentially spaced some distance away from the brake cooling member 218 so as not to interfere with the pumping effect of the cooling member 218. To prevent disruption of the

convection flow produced in the cooling member 218 when the vehicle is stationary and the brake disc 219 is at an elevated temperature the air collector duct extends substantially horizontally.

The air collector duct 240 is mounted on a steering arm 245 which is fixed in relation to the hub and therefore also moves vertically with the wheel.

The combination of the brake cooling member 218 and the air collector duct 240 provides a positive pushing and pulling of air through the brake disc 219 and therefore maximises the amount of cooling provided to it.