GB2317426A

GB2317426A - A disc brake assembly for a motor vehicle

Info

Publication number: GB2317426A
Application number: GB9716310A
Authority: GB
Inventors: Julian Thomas Buckingham
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1996-08-21
Filing date: 1997-08-04
Publication date: 1998-03-25
Anticipated expiration: 2017-08-04
Also published as: DE19736433A1; GB2317426B; GB9716310D0; GB9617547D0

Abstract

The disc brake assembly comprises a brake disc 10 arranged within a heat shield 30 which includes a rotary part 32 mounted, in use, on a vehicle wheel for rotation with the disc 10 and a fixed part 34 mounted, in use, on a fixed part of the vehicle. The rotary part 32 induces centrifugal movement of air through passageways (44, Figure 1), and the fixed part 34 defines a duct 69 through air passes from inlet 64 to outlet 68 on forward movement of the vehicle. Such movement of the air cools the heat shield which can act as a receptor for heat radiated by the disc as well as shielding adjacent components such as the wheel and tyre. The disc 10 may be of reduced thickness or made from a light weight material as heat is readily dissipated by the heat shield 30.

Description

2317426 A DISC BRAKE ASSEMBLY FOR A MOTOR VEHICLE The invention relates to

a disc brake assembly for a motor vehicle.

During braking, the frictional interaction between the disc of a disc brake and the usual brake pads causes the kinetic energy of the moving vehicle to be converted into thermal energy. The thermal energy is stored by the thermal mass of the brake disc which is usually manufactured from a metal such as cast iron. Dissipation of the stored energy occurs by convection and radiation from surfaces of the brake disc to the surrounding air. Considerable temperatures can be generated during braking and the brake disc and brake pads must be capable of performing well over a wide range of temperatures (typically minus 40'C to 880'C) without excessive thermal distortion or loss of structural integrity.

In recent years, vehicle manufacturers have been showing increased interest in using thinner discs or lightweight materials as a replacement for the normal cast iron brake disc. Where there are two or four discs per vehicle, each weighing between 3 and 5 kilograms, a significant weight saving can be achieved by replacement of the conventional cast iron. disc with a thinner disc or a disc of lightweight alternative material.

Temperature is the limiting factor withthinner discs and with many alternative materials and, unfortunately, the temperatures induced by braking can easily rise above the maximum operating temperatures of certain alternative metals such as aluminium alloys. Ceramic materials offer reduced weight but dissipation of generated heat is a particular problem with such materials.

It is known from GB 2 142 103 A to provide a heat shield around a brake disc through which air is induced to flow by centrifugal action when the disc rotates. The amount of heat that can be dissipated in this way is limited by the air flow which can be directed over or through the disc itself and by the maximum temperature of the disc which itself is of generally conventional construction.

An object of the present invention is to provide an improved disc brake assembly which will enable the brake disc to be cooled more effectively than hitherto thereby facilitating the use of thinner brake discs or discs formed from lightweight materials.

According to a first aspect of the invention there is provided a disc brake assembly for a motor vehicle comprising a disc brake caliper assembly and a brake disc arranged within a heat shield, the heat shield comprising a rotary part which is mounted in proximity to one braking surface of the disc for rotation with the disc and a fixed part which is mounted in proximity to 20 the other braking surface of the disc on a fixed part of the vehicle, the rotary part of the heat shield having substantially radial passageways therein which are arranged to induce centrifugal flow of air through the rotary heat shield part and the fixed heat shield part being hollow and defining an inlet, an outlet and a duct for air which is induced to flow from the inlet to the 5 outlet during forward movement of the vehicle.

By forcing air to move over the heat shield, heat radiated from the disc can be dissipated efficiently so that the disc does not require a large thermal mass to store heat generated at the braking surfaces during braking. Therefore, the disc can be made thinner than hitherto to reduce weight or can be made from a lightweight material. Heat dissipation is enhanced by the stationary part of the heat shield being cooled both by the air flow resulting from forward movement of the vehicle and by the centrifugal air flow induced by disc rotation.

Preferably, air from the rotary heat shield part is arranged to flow into the duct in the fixed heat shield part whereby the fixed heat shield part receives both air which moves centrifugally from the rotary heat shield part and air which is induced into the inlet during forward movement of the vehicle.

The fixed heat shield part may extends across a circumferential edge of the disc.

Conveniently, the fixed heat shield part is substantially annular with a recess for the brake caliper assembly, in which case the caliper assembly may be mounted in front of the disc axis and clearance between the caliper assembly and the fixed heat shield part acts as the inlet. Alternatively, or additionally if two disc brake calipers are provided, the caliper assembly may be mounted behind the disc axis and clearance between the caliper assembly and the fixed heat shield part acts as the outlet.

According to a second aspect of the invention there is provided a motor vehicle having thereon a disc brake assembly according to said first aspect 10 of the invention.

A disc brake assembly for a motor vehicle in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 is an elevation shown partly cut away of a disc brake assembly in 15 accordance with the invention; Fig.2 is a cross-section of the disc brake assembly shown in Fig 1 on the line II - II in Fig 1; Fig 3 is a cross-section of the disc brake assembly shown in Fig 1 on the line III III in Fig 1; Fig.4 shows alternative cross-sectional shapes of a rotary part of the aforesaid heat shield on the line IV - IV in Fig 2; and Fig.5 is a view similar to Fig 1 but without showing the rotary part of the heat shield partly cut away.

Looking at Figs.1 to 3, the disc brake assembly comprises an annular brake disc 10 carried by a top-hat cross-section mounting 12 having a fixing flange 14, an annular drive flange 16 and a cylindrical intermediate portion 18. The fixing flange 14 has four circumferentially spaced apertures 20.

The disc 10 is secured to the drive flange 16 by a plurality of circumferentially spaced headed drive pins 22 which extend through apertures 24 defined by semicircular recesses 26 in the outer periphery of the mounting flange 16 and similar recesses 28 in the inner periphery of the brake disc 10.

The brake disc 10 is housed within a heat shield indicated generally at 30 and comprising a rotary part 32 and a stationary part 34. As will be appreciated from Fig.5, the rotary heat shield part 32 is circular and is axially spaced from but in proximity to the adjacent braking surface of the disc 10. The rotary heat shield part 32 has an inner mounting flange 38 formed with apertures 40 which align with the apertures 20 in the 20mounting 12. In use, the mounting 12 and the rotary heat shield part 32 are connected to a wheel hub (not shown) by studs or bolts which extend through the apertures 20, 40.

The rotary heat shield part 32 has a number of radial vanes 42 which define radial passageways 44. Inlets 46 to the radial passageways 44 are provided at the outer periphery of the of the inner mounting flange 38 and outlets 48 are provided at the outer periphery of the rotary heat shield part 32. Fig 4 shows three different ways in which the vanes 42 can be arranged to define passageways 44 in the rotary heat shield part 32. It will be appreciated that the vanes 42 may be shaped, e.g. volute, to optimise the air flow in the radial passageways 44.

The fixed heat shield part 34 is generally of a hollow L-section, a hollow cylindrical section 50 extending around the outer periphery of the brake disc 10 and a hollow disc section 52 facing and in close proximity to the adjacent braking surface of the disc 10, i.e. on the opposite side of the disc to the rotary heat shield part 32. The fixed heat shield part is suitably mounted on a fixed part of the vehicle adjacent to the brake disk 10, e.g. on a wheel hub carrier. The fixed heat shield part 34 is shaped to define a recess 56 for a brake caliper assembly 54 which comprises a caliper 55 guided by a fixed support 57 for movement parallel to the axis of the disc 10. A piston 58 in the caliper 55 is provided to apply a clamping force to brake pads 60 arranged one each side of the disc 10. An insulator 62 provides a thermal barrier between the piston 58 and the adjacent pad.

An air inlet 64 is formed at the leading edge of the fixed heat shield part 34 and extends for about one quarter of its outer circumference. An angled inlet lip 66 is provided so that when the vehicle is travelling forwards (indicated by arrow F in Fig. 1) air is constrained to enter the inlet 64. An air outlet 68 is formed at the trailing edge of the fixed heat shield part 34 diametrically opposite the air inlet 64 and also extends for about one quarter of its outer circumference. In that way, air entering the inlet 64 is induced to flow through a duct 69 formed by the hollow interior of the fixed heat shield part 34 and to exit through the outlet 68 as indicated by the arrows in Fig.3.

An annular inlet 70 in the fixed heat shield part 34 is aligned with the outlets 48 in the rotary part 32. During rotation of the disc 10, the rotary heat shield part 32 induces centrifugal flow of air through the passageways 44 from the inlets 46 to the outlets 48. Air leaving the outlets 48 enters the annular inlet 70 and mixes in the duct 69 with air which has entered through the inlet 64. All of the air leaves the fixed heat shield part 34 through the outlet 68.

The cylindrical section 50 of the fixed heat shield part 34 has a peripheral lip 72 which slightly overlaps the outer periphery of the rotary part 32 to reduce air leakage between the rotary and fixed heat shield parts 32, 34 and to limit ingress of dirt and water.

The air passing through the heat shield 30 has a significant cooling effect on the heat shield so that the heat shield acts as a receptor for heat radiated from the braking surfaces of the disc 10, such heat being readily dissipated by the air flowing through the heat shield. This makes it practicable to use a disc of lightweight material or a considerably thinner disc than has hitherto been normally used as it is possible to dissipate the heat which would be stored in a conventional cast iron disc which relies on its mass for such heat storage. As well as leading to an overall weight reduction, a thinner disc is advantageous from a packaging point of view.

It should be noted that the disc brake assembly in Fig.1 is drawn with the brake caliper assembly 54 at the 12 o'clock position at the top of the Figure. In use, it is likely that the brake caliper assembly 54 will be positioned instead substantially where shown at 54a or 54b in Fig.1, i. e. at the 9 o'clock position in front of the disc axis or at the 3 o'clock position behind the disc axis. Where the brake caliper assembly is in the 9 o'clock position at 54a, sufficient clearance between the caliper assembly and the recess 56 may be provided to allow this to act as the inlet 64. Similarly, where the brake caliper assembly is in the 3 o'clock position at 54b, sufficient clearance between the caliper assembly and the recess 56 may be provided to allow this to act as the outlet 68.

Claims

-10CLAIMS

1. A disc brake assembly for a motor vehicle comprising a disc brake caliper assembly and a brake disc arranged within a heat shield, the heat shield comprising a rotary part which is mounted in proximity to one braking surface of the disc for rotation with the disc and a fixed part which is mounted in proximity to the other braking surface of the disc on a fixed part of the vehicle, the rotary part of the heat shield having substantially radial passageways therein which are arranged to induce centrifugal flow of air through the rotary heat shield part and the fixed heat shield part being hollow and defining an inlet, an outlet and a duct for air which is induced to flow from the inlet to the outlet during forward movement of the vehicle.

2. A disc brake assembly according to Claim 1 in which air from the rotary heat shield part is arranged to flow into the duct in the fixed heat shield part whereby the fixed heat shield part receives both air which moves centrifugally from the rotary heat shield part and air which is induced into the inlet during forward movement of the vehicle.

3. A disc brake assembly according to any preceding Claim in which the fixed heat shield part extends across a circumferential edge of the disc.

4. A disc brake assembly according to any preceding claim in which the fixed heat shield part is substantially annular with a recess for the brake caliper assembly.

5. A disc brake assembly according to Claim 4 in which the caliper assembly is mounted in front of the disc axis and clearance between the caliper assembly and the fixed heat shield part acts as the inlet.

6. A disc brake assembly according to Claim 4 in which the caliper assembly is mounted behind the disc axis and clearance between the caliper assembly and the fixed heat shield part acts as the outlet.

7. A disc brake assembly for a motor vehicle constructed and arranged substantially as described herein with reference to the accompanying drawings.

8. A motor vehicle having thereon a disc brake assembly according to any preceding claim.