GB2520239A

GB2520239A - Brake Cooling

Info

Publication number: GB2520239A
Application number: GB1317251.5A
Authority: GB
Inventors: Dan Parry-Williams; Arthur Slight
Original assignee: McLaren Automotive Ltd
Current assignee: McLaren Automotive Ltd
Priority date: 2013-09-30
Filing date: 2013-09-30
Publication date: 2015-05-20
Also published as: GB201317251D0

Abstract

A vehicle having a brake rotor 11 attached to a wheel (2, fig 1); a brake calliper 12 having an inboard actuator 26 for pressing an inboard brake pad 24 against the brake rotor 11 and an outboard actuator 27 for pressing an outboard brake pad 25 against the brake rotor 11. An air duct 10 having a first channel 41 for directing air at one or both of the inboard brake pad 24 and the inboard actuator 26 and a second channel 42 for directing air at one or both of the outboard brake pad 25 and the outboard actuator 27. The first and second channels 41 & 42 may be integral or rigidly attached to each other. An inlet 40 to the air duct 10 preferably faces forward with respect to the vehicle. The air duct 10 is preferably fast with the calliper 12.

Description

BRAKE COOLING

This invention relates to cooling a brake mechanism for a vehicle.

Many vehicles have wheels that are equipped with disc brake mechanisms. A typical disc brake mechanism is shown in figure 1. The disc brake mechanism of figure 1 comprises a brake disc or rotor 1 which is rotationally fast with the wheel 2. A brake calliper 3 which is rotationally fast with the vehicle body wraps around the rotor. The brake calliper has brake pads 4, 5 which sit on either side of the brake rotor. In normal operation the brake pads are biased out of contact with the rotor by springs held within the calliper. When the driver wishes to brake he actuates a brake control such as a brake pedal. This increases the pressure in a hydraulic circuit which is coupled to pistons (e.g. 6) in the calliper. The pistons force the brake pads into frictional engagement with the rotor so they resist rotation of the wheel.

When the brake is actuated kinetic energy of the vehicle is converted into heat at the interface between the brake pads and the brake rotor. For a heavy vehicle or a high performance vehicle that is driven with frequent instances of braking this can result in a build-up of heat in the brake system. As the temperature of the brake system increases the effectiveness of the brakes can be reduced through reduced friction at the interface between the pads and the rotor and through overheating of the fluid in the hydraulic circuit. In addition, the rate of wear of the brake rotor and the brake pads can increase at high temperatures. It is therefore desirable to take measures to mitigate the build-up of heat in the brake system.

One way to mitigate the build-up of heat is to increase the size of the brake rotor and/or the brake calliper. Increasing their size and hence their mass reduces the temperature they reach for a given amount of absorbed energy. In a conventional vehicle the rotor is mounted within the wheel rim, as illustrated in figure 1, and ultimately the diameter of the brake rotor is limited by the internal diameter of the wheel.

Another approach is to direct airflow to the brake rotor and the brake calliper by means of a duct as described, for example, in EP 1104370.

Another approach is to provide the rotor with radial through-holes so that it can act as a centrifugal air pump.

Whilst all these approaches are effective, in some situations the performance of a vehicle can still be limited by its braking. For example when a sports car is driven on a twisty track the temperature in its braking system may increase so much that the driver is forced to drive more slowly than the vehicle is otherwise able to go. There is therefore a need to improve the ability of brake systems to cope with high rates of energy absorption.

According to the present invention there is provided a vehicle comprising: a wheel for engaging a running surface of the vehicle; a brake rotor attached to the wheel; a brake calliper rotationally fast with the vehicle, the brake calliper having a body, an inboard brake pad inboard of the brake rotor, an outboard brake pad outboard of the brake rotor, an inboard actuator for pressing the inboard brake pad against the brake rotor and an outboard actuator for pressing the outboard brake pad against the brake rotor; and an air duct having a first channel for directing air at one or both of the inboard brake pad and the inboard actuator and a second channel for directing air at one or both of the outboard brake pad and the outboard actuator.

The first channel and the second channel may be rigidly attached to each other. The first channel and the second channel may be integral with each other.

The duct may comprise an air inlet. The air inlet may be located at a free end of the duct. The first channel may be configured for directing air from the inlet at one or both of the inboard brake pad and the inboard actuator. The second channel may be configured for directing air from the inlet at one or both of the outboard brake pad and the outboard actuator. The inlet may be arranged to face forwards with respect to the vehicle.

The second channel may have an inlet inboard of the brake rotor. The second channel may extend between the brake rotor and the wheel. The second channel may extend between the upper surface of the brake rotor and the wheel. In the region of an inlet of the second channel the cross-section of the second channel may be elongate in the Z axis of the vehicle. Where the second channel extends between the upper surface of the brake rotor and the wheel the cross-section of the second channel may be elongate in the X axis of the vehicle.

The duct may be fast with the brake calliper.

The first channel may have an outlet configured to direct air flowing in the first channel to play on to at least a part of the inboard actuator. The inboard actuator may be located inboard of the brake rotor. The mechanism may be configured so that when the inboard actuator is not actuated a part of the inboard actuator is exposed between the inboard brake pad and the body of the brake calliper. The outlet of the first channel may be configured to direct air flowing in the first channel to play on to that part of the inboard actuator.

The second channel may have an outlet configured to direct air flowing in the second channel to play on to at least a part of the outboard actuator. The outboard actuator may be located outboard of the brake actuator. The mechanism may be configured so that when the outboard actuator is not actuated a part of the outboard actuator is exposed between the outboard brake pad and the body of the brake calliper. The outlet of the second channel may be configured to direct air flowing in the second channel to play on to that part of the outboard actuator.

One or both of the inboard and outboard actuators may be hydraulic pistons.

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: Figure 1 shows cut-away view of a wheel with a conventional disc brake mechanism.

Figure 2 shows a disc brake mechanism with a cooling duct from below, inboard and behind.

Figure 3 shows the disc brake mechanism of figure 2 from above, inboard and in front.

Figure 4 shows a cross-section through the disc brake mechanism of figures 2 and 3 on the horizontal plane indicated by line A-A' in figure 3.

The disc brake mechanism of figures 2 to 4 incorporates a duct 10. Duct 10 is arranged to receive an air flow when a vehicle to which the disc brake mechanism is fitted is in motion. Duct 10 wraps around the brake rotor 11. As a result it can deliver airflow to both sides of the rotor in order to effect cooling of the rotor 11 and/or calliper 12. In particular the air flow may be arranged so as to preferentially cool hydraulic components of the calliper and thereby help to cool hydraulic brake fluid.

In more detail, the braking mechanism of figures 2 to4 comprises a rotor carrier 13.

Brake rotor 11 is attached to the rotor carrier 13 so that it is rotationally fast with the rotor carrier. The brake rotor and the rotor carrier could alternatively be formed as a single component.

As shown in figure 4, the rotor carrier and a wheel 14 are attached to an axle 15 of a vehicle so that they are rotationally fast with the axle. Threaded stub bolts 16 on the axle pass through both the wheel 14 and bores 17 on the rotor carrier 13. The wheel and the rotor carrier are fixed to the stub bolts 16 by nuts 18. Alternatively, the rotor carrier could be attached to the axle by one set of couplings and the wheel could in turn be attached to the rotor carrier by a separate set of couplings.

The wheel 14 comprises a hub 19, by means of which it is attached to the axle 15, radially extending spokes 20 and a rim 21. The rim 21 extends in an axial direction with reference to the rotation of the wheel. A tyre 22 is attached to the periphery of the rim.

The brake calliper 12 comprises a rigid outer housing 23 which wraps around the brake rotor 11. The brake calliper is attached to the vehicle so it is rotationally fast with the vehicle. Typically the vehicle will have a suspension mechanism that permits at least vertical motion of the wheel relative to the vehicle, and conveniently the brake calliper will be attached to the suspension mechanism so that it can move in bump etc. with the wheel. Within the housing 23 of the calliper are two brake pads 24, 25 and two brake pistons 26, 27. One brake pad is located on each side of the brake rotor. The brake pads are biased away from the brake rotor by springs (not shown) so that in normal operation the brake pads are not in contact with the brake rotor. The pistons are connected to a hydraulic circuit that is coupled to a driver-operable brake control of the vehicle, for example a brake pedal. Each piston bears on the rear surface of a respective one of the brake pads, which may be constituted by a back plate of the pad, and when the pressure of the hydraulic circuit is raised the pistons act against the springs to push the brake pads towards the brake rotor. In this way, the brake pads clasp the rotor and so the brake can function to retard the vehicle when the brake pads make contact with the brake rotor.

The duct 10 generally comprises an inlet 40 and first and second channels 41, 42 separated by a mid-section 43. The first channel 41 extends from the lower region of the inlet to an inboard outlet 44 for directing cooling air to the region of the inboard brake pad 24. The second channel 42 extends from the upper region ot the inlet to an outboard outlet 45 for directing cooling air to the region of the outboard brake pad 25.

The inlet is located inboard of the vertical plane of the brake rotor and so the second channel includes a cross-over portion shown at 46 which passes across the brake rotor, between the outer rim of the brake rotor and the wheel rim 21.

The duct 10 is rigidly attached to the brake calliper 12. The duct 10 includes brackets 47 which are attached to the wheel upright, the housing of the wheel bearing or the housing 23 of the brake calliper. When the duct 10 is mounted so that it is fast with the brake calliper the duct can move with the calliper during suspension travel and even during steering motion if the wheel is a steerable wheel. This helps to maintain alignment between the outlets of the duct and the calliper.

The duct 10 is formed of sheet material. It could be formed of plastics material such as polyethylene or ABS (acrylonitrile butadiene styrene) or of a fibre reinforced composite such as carbon fibre reinforced polymer (CFRP). As can be seen from the figures it can be formed from multiple moulded parts that can be clipped, welded or screwed together.

In this example the inlet 40 is configured to face forwards when the vehicle is in motion.

In this way air flow though the duct is enhanced through a ram effect. Other arrangements are possible. Air flow could through the duct could be actively driven, e.g. by an electrically-powered fan. The inlet 40 is located inboard of the brake rotor.

This is convenient since the spokes 20 of the wheel are conventionally outboard of the brake rotor and might otherwise clash with the inlet.

The first channel 41 starts at the lower region of the inlet 40. In this example the inlet is located forward and inboard of outlet 44 and so the first channel extends rearwards from the inlet and then outwards from the centreline of the vehicle (i.e. with a component in the Y axis of the vehicle) before reaching outlet 44. Outlet 44 is located close to the inboard brake pad 24, so the channel 41 directs cooling air from the inlet to the inboard brake pad. This allows the cooling air to cool the inboard brake pad and the region of the calliper 12 that is adjacent to the inboard brake pad particularly effectively.

The second channel 42 starts at the upper region of the inlet 40. This is advantageous because it is convenient for the cross-over portion 46 of the second channel to be located above the brake rotor, so as to keep it away from the road or other running surface of the wheel. By having the second channel start at the upper region of the inlet 40 the length of the second channel and correspondingly the mass of the duct is reduced. The cross-over portion could alternatively pass in in front of, behind or below the brake rotor. Since in this example the inlet is located forward and inboard of outlet and the cross-over portion is located above the brake rotor the second channel extends from the inlet rearwards, upwards and outwards from the centreline of the vehicle to reach the cross-over portion 46. The cross-over portion extends outwards from the centreline of the vehicle. The second channel then extends downwards and forwards to reach outlet 45. Outlet 45 is located close to the outboard brake pad 25, so the channel 42 directs cooling air from the inlet to the outboard brake pad. This allows the cooling air to cool the outboard brake pad and the region of the calliper 12 that is adjacent to the outboard brake pad particularly effectively.

It can be advantageous for one or both of the outlets 44, 45 to be arranged so as to direct air flow to the rear surface, e.g. a back plate, of the respective brake pad. In particular, it can be advantageous for one or both of the outlets 44, 45 to be arranged so as to direct air flow to the region of a hydraulic piston 26, 27 that engages the respective brake pad. The air flow from each channel can usefully be directed so that it plays on to part or all of the respective piston. This enables the air flow from the duct to cool the hydraulic pistons particularly effectively, reducing the build-up of heat in the hydraulic fluid of the brake circuit. One way to help achieve this is to locate one or both of the outlets 44, 45 adjacent the rear surface of the respective brake pad, and particularly adjacent the interface or if present the gap 60, 61 between the rear surface of the respective brake pad (i.e. the surface facing away from the brake rotor) and the neighbouring inner edge of the brake calliper. Another way to help achieve this is to have one or both of the outlets directed into the respective such interface or gap: that is to have the duct(s) arranged so that the direction of the air flow at the outlet(s) is towards the respective interface or gap.

The channels 41, 42 are separated by a mid-section 43 which resists or prevents air flow between the channels. This can be advantageous because it helps to control the amount of air that is directed to each of the outlets 44, 45 in the manner described below. The mid-section also contributes structural rigidity to the duct.

The upstream end 48 of the mid-section divides the inlet 40 between the first and second channels 41, 42. The position of the upstream end 48 in the inlet helps to control the relative proportions of the air passing through the inlet that are directed to the outlets 44, 45. By locating the upstream end so that the inlet end of the first channel is bigger, proportionally more air will be directed to inlet 44, and vice versa. It is desirable for substantially equal air flows to be directed to both sides of the brake rotor. This can help to cool the brake pads and calliper uniformly. When the brake pads are cooled uniformly each brake pad can develop a similar braking torque and so the brake pads are more likely to wear evenly. The aerodynamic conditions around the inlet 40 and in the first and second channels 41, 42 can be measured or modelled and the upstream end 48 of the mid-section positioned to achieve a desired balance of air flows through the first and second channels. In general, it can be advantageous to locate the mid-section such that the cross-sectional area (perpendicular to the air flow) of the inlet to the channel 41 that serves the inboard side of the brake rotor/calliper is smaller than the cross-sectional area (perpendicular to the air flow) of the inlet to the channel 42 that serves the outboard side of the brake/calliper. This can allow any additional air resistance in channel 42 relative to channel 41 to be overcome and the flows to outlets 44 and 45 to be nevertheless substantially equal. That additional air resistance could result from (a) channel 42 being longer than channel 41 due to having to loop around the brake rotor and/or (b) channel 42 being constricted where it passes between the outer rim of the brake rotor and the wheel The upstream end 48 of the mid-section acts as a splitter to split the air flow reaching the inlet 40 into flows for the first and second channels 41, 42. It is desirable for the splitter to be somewhat downstream of the outermost part of the inlet 40, so there is an inlet channel upstream of the splitter, as shown most clearly in figure 3. This improves air flow around the nose of the splitter.

The mass of air exiting the outlets 44, 45 in unit time will depend on the speed of the vehicle and other aerodynamic conditions around the duct. Conveniently the duct is configured so that the mass of air exiting one outlet 44 is substantially equal to the mass exiting the other outlet 45 over at least the mid-part of a working speed range of the vehicle in question: for example between 70 and 120mph.

The duct may be equipped with aerodynamic elements 49 external to the channels 41, 42 for influencing air flow around the wheel, for example to reduce drag or increase downforce.

It will be appreciated that in order for the second channel 42 to be of an effective size there must be a significant gap between the outer rim of the brake rotor and inner surface of the wheel rim in order to accommodate the cross-over portion 46. The gap can conveniently be greater than any of 40mm, 50mm, 60mm, 80mm or 100mm. This means that the brake rotor may be substantially smaller than could otherwise be accommodated in that wheel. As indicated above, a conventional way of improving cooling performance is to increase the size of the brake rotor. However, the applicant has found that reducing the size of the brake rotor in order to accommodate a channel that can direct cooling air to the outboard side of the brake rotor/calliper can in at least some situations improve brake perfornace further than would be achieved with a larger rotor. Using a smaller rotor has the additional advantage that the smaller brake rotor has lower mass.

As indicated above, it is convenient for the duct to be arranged so that when the vehicle is in motion air is forced through the duct and hence through the first and second channels, in the direction towards the outlets.

The first and second channels and their outlets can conveniently be arranged so that when air flows through each of the channels it plays on to any one or more of: the rear surface of a brake pad, a part of a brake piston (conveniently a part of the piston that is exposed between the calliper body or housing and the rear surface of the brake pad) and a region of the calliper body or housing that surrounds the piston. In this way the air can effectively reduce the transmission of heat from the friction interface between the pad and the rotor to the hydraulic fluid in the piston. Each of the channels serves a respective side of the calliper, so the air from the inboard channel is directed to that or those components on the inboard side of the calliper and vice versa. Air from the inboard channel may be directed to components of a different type from those to which air from the outboard channel is directed. The channels may behave as set out above when the vehicle is in motion at a suitable speed, for example 60mph, 80mph or 100mph.

A convenient packaging arrangement for the second channel 42, which serves the outboard brake pad, is: (a) for it to be arranged so that in the region of its inlet end it is taller (in the vehicle's Z axis) than it is wide (in the vehicle's Y axis) and/or (b) for it to be arranged in the region where it intersects the plane of the brake rotor and/or where it passes most closely between the brake rotor and the wheel rim so that it is wider (in the vehicle's X axis) than it is tall (in the vehicle's Y axis).

In the case of a steerable wheel these criteria can be judged when the wheel is facing straight ahead. This arrangement can allow the cross-sectional area of the channel to be maintained whilst reducing the requirements for space in a wheel arch (by virtue of criterion (a)) and between the rotor and the wheel rim (by virtue of criterion (b)).

In the embodiment of figures 2 to 4 the duct 10 is formed as an integral unit including the first and second channels 41, 42. This makes it particularly convenient to mount the duct to a vehicle and helps to make the duct more robust than if the channels were distinct units.

The vehicle may be a road vehicle such as a car, especially a sports car. Alternatively it could be an aircraft or motorbike. If the wheel is not set to the side of the vehicle, either side of the wheel may be considered the inboard side and the other side considered the outboard side. When the wheel is set to the side of the vehicle it can conveniently be located in a wheel arch. The wheel arch should offer sufficient clearance to avoid clashing with the duct throughout the suspension and steer travel of the wheel.

The equipment shown in figures 2 to 4 is for a left-hand wheel. Mirror image equipment could be installed on a right-hand wheel. It is advantageous for opposite wheels of a vehicle to be fitted with analogous equipment so that their cooling performance is matched. Equipment as shown in the figures could be attached to the front and/or rear wheels of a vehicle. Equipment as shown in the figures could be attached to steerable and/or non-steerable wheels of a vehicle. As indicated above, the duct 10 is conveniently attached to so it moves with the brake calliper. It could be mounted to equipment that supports the brake calliper and/or to suspension components or directly to the body of the vehicle. In that latter case, it is advantageous to provide a mechanism for keeping the outlets 44, 45 aligned with the calliper during suspension movement.

The cooling arrangement described above can be particularly effective when the brake rotor and/or the brake pads are made of material(s) capable of providing effective braking performance at particularly high temperatures, for example greater than 400°C, 500°C or 600°C. In contrast Examples include materials that comprise ceramic one or more ceramic components, e.g. in the form of powder or fibrous filler. Examples include materials comprising carbon, e.g. in the form of carbon fibre. Examples include ceramic composite and carbon composite materials, notable carbon ceramic material. Brake rotors of such materials have higher effective operating temperatures than, for example, conventional steel discs. With such materials braking performance is typically limited by the build-up of heat in the hydraulic fluid rather than by overheating of the solid brake components. A build-up of heat in the hydraulic fluid can ultimately cause it to boil. Therefore having a means of effectively cooling the hydraulic brake fluid directly at the brake piston or more generally at the brake calliper is especially effective. With the arrangement illustrated in figures 2 to 4 the brake rotor and the brake pads may reach significantly higher temperatures than the brake fluid.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. A vehicle comprising: a wheel for engaging a running surface of the vehicle; a brake rotor attached to the wheel; a brake calliper rotationally fast with the vehicle, the brake calliper having a body, an inboard brake pad inboard of the brake rotor, an outboard brake pad outboard of the brake rotor, an inboard actuator for pressing the inboard brake pad against the brake rotor and an outboard actuator for pressing the outboard brake pad against the brake rotor; and an air duct having a first channel for directing air at one or both of the inboard brake pad and the inboard actuator and a second channel for directing air at one or both of the outboard brake pad and the outboard actuator.
2. A vehicle as claimed in claim 1, wherein the first channel and the second channel are rigidly attached to each other.
3. A vehicle as claimed in claim 2, wherein the first channel and the second channel are integral with each other.
4. A vehicle as claimed in any preceding claim, wherein the duct comprises an air inlet, the first channel is configured for directing air from the inlet at one or both of the inboard brake pad and the inboard actuator and the second channel is configured for directing air from the inlet at one or both of the outboard brake pad and the outboard actuator.
5. A vehicle as claimed in claim 4, wherein the inlet is arranged to face forwards with respect to the vehicle.
6. A vehicle as claimed in any preceding claim, wherein the second channel has an inlet inboard of the brake rotor and extends between the brake rotor and the wheel.
7. A vehicle as claimed in claim 6, wherein the second channel extends between the upper surface of the brake rotor and the wheel.
8. A vehicle as claimed in claim 7, wherein in the region of an inlet of the second channel the cross-section of the second channel is elongate in the Z axis of the vehicle and where the second channel extends between the upper surface of the brake rotor and the wheel the cross-section of the second channel is elongate in the X axis of the vehicle.
9. A vehicle as claimed in any preceding claim, wherein the duct is fast with the brake calliper.
10. A vehicle as claimed in any preceding claim, wherein the first channel has an outlet configured to direct air flowing in the first channel to play on to at least a part of the inboard actuator.
11. A vehicle as claimed in claim 10, wherein when the inboard actuator is not actuated a part of the inboard actuator is exposed between the inboard brake pad and the body of the brake calliper and the outlet of the first channel is configured to direct air flowing in the first channel to play on to that pad of the inboard actuator.
12. A vehicle as claimed in any preceding claim, wherein the second channel has an outlet configured to direct air flowing in the second channel to play on to at least a pad of the outboard actuator.
13. A vehicle as claimed in claim 12, wherein when the outboard actuator is not actuated a part of the outboard actuator is exposed between the outboard brake pad and the body of the brake calliper and the outlet of the second channel is configured to direct air flowing in the second channel to play on to that part of the outboard actuator.
14. A vehicle as claimed in any preceding claim, wherein one or both of the inboard and outboard actuators are hydraulic pistons.
15. A vehicle substantially as herein described with reference to figures 2 to 4 of the accompanying drawings.