Field of the Invention

The present invention relates to brakes, particularly those used in conjunction with vehicle wheels. The invention finds its primary application in relation to disc brakes.

Background to the Invention

It is known to apply a braking force to a vehicle wheel by the application of brake callipers on a brake disc. In a traditional mode of operation, the brake disc is mounted on the wheel axle or wheel hub, and is arranged to rotate at the same angular velocity as the wheel. A set of callipers is arranged about the brake disc, and does not rotate. The brake disc thus moves relative to the callipers at a speed which is proportional to the vehicle speed.

When braking is required, a compressive force is applied by the callipers to cause brake pads mounted on the callipers to come into contact with the brake discs. The frictional force applied acts to slow the rotation of the discs, and hence the vehicle wheels. Braking of the vehicle is thus effected.

In most modern vehicles, the compressive force is applied by hydraulic means.

The braking force generated is proportional to the compressive force applied and the properties of the contacting disc and pads. For a given wheel speed and momentum, and in the presence of a constant applied brake force, the efficiency of the braking operation can be measured or quantified by the linear distance travelled by the vehicle before coming to a stop. This linear distance travelled can also be converted to a number of wheel revolutions, which can be further reduced to the fundamental parameter of the swept distance. This is the amount of contact, measured as a distance, the pads travel over the disc during the braking action.

It will be apparent, therefore, that if one could cover the swept distance required for a particular braking operation in a shorter period of time, this will result in a proportional increase in braking efficiency. The present invention seeks to provide a brake system which increases the braking efficiency by increasing the speed of the brake disc relative to the vehicle wheel.

Summary of the Invention

In accordance with the present invention there is provided a rotating member for a braking device, the rotating member being arranged to rotate about an axis, the braking device including a braking member which is arranged when activated to provide a frictional force to the rotating member, wherein the braking member is fixed in position and the rotating member arranged to rotate about the axis. Through the arrangement, the rotating member is made to rotate in the same direction as the vehicle wheel, but at an increased angular velocity. The braking benefits associated with this increase in velocity of the rotating member relative to the vehicle wheel are thereby realised.

In a preferred embodiment of the present invention the rotating member is a brake disc, and the braking member is a set of brake callipers.

The rotating member may be arranged to rotate at a fixed angular velocity. Alternatively, the rotating member may be arranged to rotate at an angular velocity proportional to that of the vehicle wheel. This may be achieved, for instance, by the use of a gearing arrangement such as an arrangement of planetary gears. In a preferred embodiment, the rotating member is arranged to rotate at an angular velocity which is between 1 10% and 150% that of the vehicle wheel.

It will be appreciated that, all other things being equal, the operation of the braking device of the present invention will provide a greater braking effect than would otherwise be the case. When the invention is applied to a vehicle wheel, it will be apparent that the stopping distance of the vehicle will be reduced in a corresponding fashion.

Brief Description of the Drawings

It will be convenient to further describe the invention with reference to a preferred embodiment of the braking device of the present invention, being one where the invention is applied to a vehicle wheel. Other embodiments are possible, and consequently, the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention. In the drawings:

Figure 1 is a front view of a braking system in accordance with the present invention;

Figure 2 is a cross-section through line A-A of the braking system of Figure 1 ; and

Figure 3 is a perspective of the braking system of Figure 1 .

Detailed Description of Preferred Embodiments

Referring to the Figures, there is shown an assembly comprising of a brake disc 10, a gearing arrangement 12, 14, 16, 18 and a wheel hub 20.

The gearing arrangement comprises of a sun gear 18, four planetary gears 16, a planetary gear carrier 14 and an outer ring gear 12.

In this embodiment, the sun gear 18 is fixed in position and restrained from experiencing any rotational motion. The planetary gears 16, which are engaged with the sun gear 18, are supported by the planetary gear carrier 14. The wheel hub 20, to which the wheel (not shown) is attached via the wheel studs 22, is fixed to the planetary gear carrier 14, such that rotation of the wheel results directly in proportional rotation of the planetary gear carrier 14. Through this action, and engagement with the planetary 16 and sun 18 gears, the ring gear 12 rotates in the same direction as the wheel but at an increased rate. In this embodiment of the invention, the brake disc 10 is attached to the ring gear 12 such that rotational movement is transferred to the brake disc 10. In the preferred embodiment, the sun gear 18 possesses sixteen teeth and the ring gear 12 has forty teeth, producing a gearing ratio of 0.71 : 1 . This is an overdrive ratio whereby the ring (output) gear 12 rotates with an angular velocity approximately 41 % faster than the planetary gear carrier 14 (input). When braking is required, a clamping force is transferred to the brake callipers (not shown). This may be done through an appropriately sealed hydraulic fluid path (not shown), or may in theory be performed in response to an electronically transmitted signal or other non-contact means. The callipers then apply a frictional force to the brake disc 10 in a known fashion. The degree of frictional force, of which the relative velocities of the contacting surfaces is a factor, will be higher than that which would result from the same compressive force applied to a more slowly rotating brake disc.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. For instance, the gearing ratio may be selected to achieve a particular result. It is anticipated that a gearing over drive ratio of between 0.7 : 1 and 0.9 : 1 is likely to be particularly useful. Alternatively, the brake disc 10 may be caused to rotate independently of the vehicle wheel. The rotation may also, it is envisaged, be controlled by electronic means.