GB2416817A - Vehicle braking system - Google Patents

Abstract

A vehicle braking system comprises a wheel 2 including a brake ring 3 to which braking force is applied, and a brake calliper 6 for applying the braking force to the brake disc 3. The annular brake disc 3 may be detachably attached to the wheel rim 2, or may be integral with the wheel 2. Typically, the brake disc 3 would have its (outer) periphery attached to the wheel rim with the inner circumference free of attachments. The calliper 6 is preferably positioned radially inwardly of the brake disc3. Said calliper is preferably pivotally mounted (ie. it can rotate about axis A-A) to facilitate the removal of the wheel 2 from its associated axle. The invention aims to improve heat dissipation characteristics and improve air flow by providing the above braking system. The braking system is intended to be used in cars, railway, buses, etc.

Description

1- 2416817 Brak Meg Systems This invention concerns braking systems

particularly but not exclusively for vehicle wheels.

Braking systems for vehicle wheels generally function by converting kinetic energy into heat energy using a braking system which includes a surface with a high coefficient of friction to slow down the wheels. The problem is that if the generated heat is not dissipated, the braking efficiency of the systems becomes less and less, and eventually the brakes fail through so-called brake fade.

Drum brakes are particularly vulnerable to brake fade because more of the drum is heated by the friction generating shoes than is available to dissipate heat by convection to the surrounding air.

Disc brakes are generally more efficient than drum brakes because they enable greater pressure to be applied by a calliper squeezing brake pads on to a brake disc attached to the associated wheel hub than can be applied to the internal surface of the drum of a drum brake. The area of heating contact between the friction pads of disc brakes and their associated - 2 - discs can therefore be substantially reduced compared with that of brake shoes with their associated drums for the same braking effort. Typically, 20% of the surfaces of the discs of disc brakes are intensely heated by disc pads, with 80% of the disc being available to dissipate heat by convection to the surrounding air within the confines of the associated wheel.

The dissipation of heat from disc braking systems by convection from steel discs is, however, very inefficient due to the limited surface areas of the discs themselves and the fact that the discs tend to act as a plug which restricts air flow through the wheel even when the latter is spoked.

In an attempt to improve their vehicle braking systems, manufacturers have been increasing the internal diameters of the wheels of their vehicles so that larger diameter discs and larger brake callipers can be fitted. This can enable the braking leverage of braking systems to be increased as a result of the increased disc radius. However, the larger radius of these larger discs means that the associated calliper has to be considerably longer than with the conventional smaller discs to cover the depth of the discs.

The longer so-called "beam" callipers used with these larger discs are generally of four or six pot construction, and this adds considerably to their complexity and cost of production.

In addition, they greatly reduce the area of the brake disc which is exposed for cooling by convection to air inside the wheel, and they can also worsen the "plug" effect by reducing the air space available to cool the discs by convection to air inside the associated wheel.

The main inherent problem with both drum and disc braking systems is, therefore, that heat dissipation from them by convection through the air alone is generally insufficient to prevent brake fade. Furthermore, the very designs of the braking systems themselves tend to reduce their efficiency by disrupting airflow over surfaces which should serve to cool these surfaces. 3 -

According to the present invention there is provided a vehicle braking system comprising a load bearing wheel including a brake ring to which a braking force is applied to brake the vehicle and a brake calliper for applying a braking force to the brake ring.

Vehicle braking systems in accordance with the present invention have substantially reduced the above problems associated with disc braking systems which have a disc attached to an axle of the vehicle. This results from the use of a brake ring connected to the rim of the wheel.

In addition, particularly high leverage can be applied to the brake ring via an associated brake calliper because the ring can be substantially the diameter of that of the wheel with which it is used.

Particularly high ratios of heat dissipating to heat producing areas of braking surface can be obtained.

High air flows through associated wheels can be achieved, thereby providing particularly good cooling by convection.

In addition to cooling by convection, braking systems in accordance with the present invention allow cooling to take place by conduction, in particular from the braking ring to the wheel to which it is attached. This can be particularly good when the wheel is made of high thermal conductivity materials such as aluminum.

The brake rings are preferably detachably attached to the wheel, but they can be integral with the wheel.

In general, the brake calliper will in use be positioned radially inwardly of the brake ring. 4 -

In use, the brake calliper will in general be mounted pivotally to facilitate removal of the wheel from its associated axle.

An embodiment of braking system in accordance with the present invention will now be described with reference to the accompanying drawing which is a vertical section through a vehicle wheel including the embodiment of braking system.

The illustrated vehicle wheel is substantially conventional in that it has fixing holes 1 for securing it to an axle of the vehicle and a rim 2 for receiving a pneumatic Lyre (not shown).

However, it differs from conventional vehicle wheels in that it includes an annular brake ring 3 which is secured in an annular recess 4 in the rim 2 by countersunk bolts 5.

Braking forces can be applied to the ring 3 using a calliper 6 which is attached to the vehicle suspension and can be operated hydraulically in conventional manner via an hydraulic hose (not shown) to force hydraulic pistons 7 against brake pads 8, and the latter into frictional engagement with the disc 3.

Removal and replacement of the wheel from the vehicle can be effected in substantially conventional manner by first releasing and then rotating a portion of the calliper 6 about the line A-A so that it can be moved to the position indicated by broken lines in the drawing, and then removing and subsequently replacing the fixing nuts or bolts which hold the wheel on the vehicle axle.

Vehicle braking systems in accordance with the present invention can be used on a variety of vehicles. They can be used on road vehicles, for example cars, buses, lorries and road vehicle trailers, and they can be used on vehicles which run on rails or tracks, for example railway carriages, railway wagons and trams. - 5

Claims (6)

1. Claima 1. A vehicle braking system comprising a load bearing wheel

   including a brake ring to which a braking force is applied to brake the vehicle and a brake calliper for applying a braking force to the brake ring.
2. 2. A braking system according to claim 1, wherein the brake ring is detachably attached to the wheel.
3. 3. A braking system according to claim 1, wherein the brake ring is integral with the wheel.
4. 4. A braking system according to any of the preceding claims, wherein the brake calliper in use is positioned radially inwardly of the ring.
5. 5. A braking system according to any of the preceding claims, wherein the brake calliper in use is mounted pivotally to facilitate removal of the wheel from its associated axle.
6. 6. A vehicle braking system substantially as herein described with reference to the accompanying drawings.