ROTARY BRAKE CALIPERS 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 calipers on a brake disc. In a traditional mode of operation, the brake disc is mounted on a wheel axle or wheel hub, and is arranged to rotate at the same angular velocity as the wheel. A set of calipers is arranged about the brake disc, and does not rotate. The brake disc thus moves relative to the calipers at a speed which is proportional to the vehicle speed.

When braking is required, a compressive force is applied by the calipers to cause brake pads mounted on the calipers 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 applied is proportional to the compressive force. The present invention relies on the realisation that, in addition, the braking force varies with the speed of the brake disc relative to the brake pad.

The present invention seeks to provide a brake which increases the braking force available by increasing the relative speed of the brake disc relative to the brake pad. SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a braking device for a rotating member, 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 arranged to rotate about the axis in a direction opposite to that of the rotating member. This has the effect of increasing the speed of the rotating member with respect to the braking member, and thus increasing the frictional force applied by the braking member.

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

The braking member may be arranged to rotate at a fixed angular velocity. Alternatively, the braking member may be arranged to rotate at an angular velocity proportional to that of the rotating member. 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 braking member is arranged to rotate at an angular velocity which is between 10% and 50% of the angular velocity of the rotating member. 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. This means that the time taken to slow the rotating member to a desired speed is reduced. 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 side view of a braking device in accordance with the present invention; Figure 2 is a front view of the braking device of Figure 1 ; and

Figure 3 is a perspective of the braking device of Figure 1. DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the figures, there is shown a braking device 10 mounted on a wheel axle 12. The braking device 10 includes a brake disc 14, and a set of brake calipers 16.

The brake calipers 16 are mounted onto a gearing arrangement 20. The gearing arrangement comprises a sun gear 22 which is mounted onto the wheel axle 12; three planetary gears 24 which are mounted around, and engaged with,

the sun gear 22; and a carrier gear 26 which is centered on the axle 12 and mounted around and engaged with the three planetary gears 24. The three planetary gears 24 are located on respective axles 28, which are fixed with respect to the wheel axle 12. The calipers 16 are mounted on the carrier gear 26. The arrangement is such that rotation of the wheel axle 12 causes rotation of the sun gear 22, and counter rotation of the planetary gears 24. This counter rotation of the planetary gears 24 about their respective axles 28 causes the carrier gear 26 and thus the calipers 16 to rotate about the wheel axle 12 in the opposite direction to the rotation of the wheel axle 12. The gearing ratio between the sun gear 22 and the carrier gear 26 is in the order of 1 :4. As a result, the angular velocity of the brake calipers 16 is about 25% of that of the wheel axle 12 and brake disc 14.

The braking device also includes a backing plate 30, which provides a bearing for both the wheel axle 12 and the planetary gear axles 24. In use, the gearing arrangement causes the set of brake calipers 16 to counter-rotate with respect to the brake disc 14. As a result, the angular speed of the brake disc relative to the brake calipers 16 is about 25% greater than the actual angular speed of the brake disc, for instance as measured relative to the backing plate 30. When braking is required, a clamping force is transferred to the brake calipers 16. This may be done through an appropriately sealed hydraulic fluid path (not shown), or may be performed in response to an electronically transmitted signal or other non-contact means. The calipers 16 then apply a frictional force to the brake discs 14 in a known fashion. The degree of frictional force, being dependent on relative velocities of the contacting surfaces, will be higher than that which would result from the same compressive force applied by a stationary set of brake calipers.

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 ratio of between 1 :2 and 1 :10 is likely to be particularly useful. Alternatively, the brake calipers 16 may be caused to rotate independently of the

brake disc 14. The counter rotation may also, it is envisaged, be controlled by electronic control.