GB2371841A - Heat dissipation by leaf springs from hotter regions of a brake disc - Google Patents

Abstract

Thermal equalisation in axially slidable brake discs is provided by leaf springs 54 located between disc-mounting radially-projecting drive keys 32 which slidably engage a central (or external) disc mounting hub. The spring has a flange 62 and gripping portions 58,60 cooperating with the disc and an end portion (66, fig 4) bearing against the hub. The springs 54 may have cooling fins (not illustrated). Thus heat is dissipated by convection/conduction/radiation from hotter zones of the disc identified in accordance with thermal data.

Description

METHOD AND APPARATUS FOR DISC BRAKE THERMAL CONTROL

This invention relates to a method and apparatus for disc brake thermal control, and in particular, but not exclusively, to such method and apparatus applicable to a spot-type automotive disc brake having at least one axially slidable brake disc. Such a brake represents a principal application of the invention, but aspects of it may well find application outside the strict limits of that field.

Our research and development work in relation to disc brakes incorporating axially slidable brake discs has shown that factors worthy of serious investigation and engineering endeavour in relation to such brakes include factors which might have been expected to be relatively minor, yet which are found to be of significance in relation to the provision of brakes offering characteristics which are a real advance in the art.

We have discovered that thermal factors arising from brake constructional features which are inherent in the structure and mounting of parts of the brake mechanism can cause thermal imbalance leading to corresponding inequalities in performance and wear. Specifically, we have identified a thermal imbalance between the central regions between successive drive elements or keys on the brake disc and the regions of those keys or drive elements, the central regions being hotter during braking. To the extent that this imbalance is user-perceptible, it would be better reduced or eliminated, and an object of the present invention is to provide improvements in this regard, or indeed, improvements generally.

According to the invention there is provided a method and apparatus as defined in the accompanying claims.

In an embodiment of the invention described below,

there is provided a method and apparatus wherein thermal equalisation means is provided to offset the effect of positive thermal imbalance at circumferentially spaced os L p locations around the brake disc. The provision of such thermal equalisation means has the effect of neutralising the thermal imbalance caused by various now identified factors including the heat sink and thermal transfer effects of the circumferentially spaced brake disc drive elements which project generally in a radial direction (usually inwardly, but could be outwardly) and which have the effect of creating spaced zones of lower temperature in the disc from the otherwise generally uniformly generated heat energy produced by the frictional engagement between the disc and its associated friction elements during brake use. To put it another way, not all portions of the brake disc are able to lose heat at the same rate and more specifically the portions of the disc which are nearer to one of the drive elements of the disc and which fit into grooves in the hub are able to lose heat by conduction through the drive element into the hub. A further but less significant effect is that in the vicinity of the drive elements there is more metal (the tooth itself acting as a heat-sink) and for this reason also, areas of the disc which are furthest from the drive elements are found to be hotter than areas near to a drive element.

Certain systems for thermal transfer in brake discs are of course well enough known, including the provision of air venting systems within the disc structure. However, such are generally provided in a manner which produces fairly uniform heat loss throughout the entire circumferential extent of the brake disc (or at least that is the intention). However, in the case of the present invention, such uniformity of effect is the exact opposite of our intention, although uniformity of the end result

(meaning thermal balance) of course is our aim, at least in terms of reducing the identified thermal imbalance.

Accordingly, in the embodiments, we provide means at or in the region of those locations where (we have discovered) there tends to be an elevated temperature in the disc during braking or immediately afterwards. At these locations, we provide thermal equalisation means whereby such thermal imbalance can be offset, and this is achieved without the need for otherwise redundant structure, such as thermal drillings in the disc, or indeed, without any additional structure at all, since the thermal equalisation means is in the embodiments provided by resilient means with negligible (so far as cost is concerned) adaptation of same to achieve the required thermal effect.

We have discovered that thermal equalisation means may be provided in the form of resilient means or springs acting between the brake disc or discs and the mounting hub or ring, provided that such are located so that their heat transfer effect is able to act directly upon the thermally elevated portions of the disc.

In the embodiments, the resilient means is present in any case in order to produce a dynamically stabilising effect on the axially slidable brake disc, this being achieved by means of a generally radially directed resilient action between the brake disc and its associated mounting hub (or mounting annulus in the case of a brake having its caliper at the inner edge of the disc).

Thus the described embodiments enable thermal offset for naturally-occurring thermal imbaiance to be provided by means of the structures of the brake disc mounting system itself (which mounting system is the cause of the imbalance in the first place).

This result is achieved in the embodiments by the adoption of resilient means structured and located so as to

produce a calorific extraction effect at just the locations where such is needed, according to our research. More specifically, in the embodiments the springs engage the discs at or near the half way point between successive disc mounting elements. Engagement between the springs and the discs is over a significant area so that heat is conducted from the disc into the spring in a thermally effective manner. This heat, as received by the spring, is dissipated primarily to the surrounding air and is also conducted through the spring to the hub. The springs are positioned so that they tend to reduce the thermal differentials around the circumference of the disc rather than, as in previous proposals, so that the springs tend to increase the thermal differential by cooling the cooler regions of the disc.

Thus, in the embodiments, we put into practice our discovery that by the use of resilient means at those locations where a temperature inequality by way of a temperature excess in relation to an adjacent area occurs, there can be provided a valuable equalising effect. This effect is maximised by appropriate choice of structure and placement of the resilient means or spring. Usually such spring will be in the form of a leaf spring. The leaf spring may have a form adapted to maximise its exposure to the air as it rotates with the brake disc, thereby to enhance its cooling effect. Likewise, the cooling effect can be further enhanced by taking steps to increase the effectiveness with which heat is conducted into the leaf spring structure for dispersal by radiation or conduction, this entry effect being best improved by enhancing the degree of effective contact between the leaf spring and the disc in terms of both area and face to face loading.

Another feature of the embodiments is that the resilient means or springs are chosen in terms of their

positions so as to be within zones located centrally between successive ones of the circumferentially-spaced disc-mounting elements, the zones extending circumferentially not more than half the circumferential length between two successive mounting elements whereby a spring may be located centrally between the mounting elements or as far from the central position as represents one quarter of the circumferential spacing between the mounting elements. The preferred position for the springs is centrally between the mounting elements or at least in an overlapping relationship with the mid circumferential location.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows for reference purposes a diagrammatic representation of the thermal and related mass aspects and dynamic aspects and general construction of a spot-type disc brake having resilient means adapted to act between a relatively massive hub and a pair of axially slidable brake discs; Figures 2,3, 4 and 5 show a first embodiment of the invention, in views comprising a side elevation view of a portion of a brake disc adapted to co-operate with a complementary hub assembly and with associated resilient and thermal equalisation and general construction means acting therebetween, a plan view of a leaf spring forming one of two resilient and thermal equalisation means, a side elevation view of same, and an elevation view respectively.

In Fig 1 the thermal and related mass aspects, which will be referred to and described more fully below, are indicated by references A to E in which: A refers to the Thermal Differential; B refers to the Relatively Massive Hub;

C refers to the Spring Effect ; D refers to the Uniform Control of Dynamics ; and E refers to the Localised Spot-Type brake effect.

As shown in Fig 1 a spot-type automotive disc brake 10 comprises rotatable brake discs 12,14, a rotatable mounting or hub 15 for the discs 12,14 to permit such rotation and which is adapted to drive the brake discs and to have exerted thereon a braking effect by the brake discs when disc brake 10 is actuated.

Two pairs of friction elements indicated at 16,18 and 20,22 are adapted to frictionally engage braking surfaces on opposite sides of brake discs 12,14 to effect braking on actuation of actuation means 24 therefor. Brake discs 12,14 are axially slidable in use with respect to mounting hub 15 therefor under the action of friction elements 16, 18 and 20,22 and actuation means 24 during braking.

Resilient and thermal equalisation means 26 is provided at circumferentially spaced positions around brake discs 12,14 and is adapted to act between the brake discs and the mounting therefor at said positions. The mounting of the resilient means 26 with respect to the brake disc 12, and on same, is such that the resilient means slides axially with the disc.

Also shown in Fig 1 at 28 is an indication of the thermal differential which exists between rotatable mounting or hub 15, which has a relatively massive construction, and the brake discs 12,14 at which actuation means 24 causes a localised spot-type braking effect.

Likewise shown in Fig 1 at 30 is the uniform control of dynamics D (in relation to axial movement of the brake discs 12,14), which is a desideratum in relation to the function of resilient means 26 acting between hub 15 and brake discs 12,14, as discussed above. In other words, and in particular in the case of brakes including multiple

discs, it is desirable for the axial movement of the individual discs to be controlled in a uniform manner with the springs providing a uniform effect over the operating range of movement.

Turning to the construction shown in Figs 2 to 5, in this brake 10 resilient and thermal equalisation means is provided by a leaf spring 54, for each key 32 on brake disc 12. The leaf springs each comprise a pair of resilient flanges or tabs 58,60 adapted to grip the disc on opposite sides thereof and a profiled flange 62 adapted to cooperate with the disc, and further comprising a leaf spring end portion 66 to exert the resilient force on hub 15. The flange 62 bears against the disc 12 whilst the leaf spring end portion 66 bears against the hub 15. As shown in Fig 2, one such leaf spring 54 is provided between each key 32 of disc 12 and the next, equally circumferentially spaced therebetween, as more fully described below.

In accordance with the principles of the present invention, the resilient means or springs 54 are caused to engage the brake disc for thermal transfer purposes in a face to face manner, and over at least a moderate minimum zone of contact and heat transfer area. In order to minimise the frictional effect with respect to the relatively fixed hub on which the disc is mounted and on which it slides, if the spring contacts the underside of the disc for heat transfer purposes, then this feature is not allowed to affect the area over which the spring contacts the hub for sliding/thrust transmission purposes (which should minimise friction as far as possible).

In the drawings, the leaf springs 54, are each shown comprising a spring main body portion 70 which is interleaved between the disc and its mounting hub, and locating/radiating portions 58,60 which are located in a gripping (one each side) relationship to the disc so as to

grip same and to be able to dissipate energy therefrom. In this way, the spring portion 70 can efficiently (and using a relatively large area of its surface) engage the inner (radially inwardly-facing) edge surface of the disc, and thereby receives by face to face contact therefrom heat transferred in a conductive manner and effects transfer of same by conduction lengthwise of the leaf spring for subsequent convection and radiation and conduction through the ears or tabs which are located at the other end of the leaf spring. Effectively, the leaf spring functions to provide some degree of heat-transfer function from a zone of relatively high temperature (at which it makes face to face contact with an inner edge portion of the disc) to the hub or to dissipate the heat by convection and/or conduction and/or radiation. Effectively, the area of the disc available for heat dissipation is increased in respect of the zones of higher temperature.

In a modification, not shown, the resilient means or springs are provided with cooling fins to increase their capacity for dissipating heat by convection as the primary heat dissipating effect, due to air passage over the cooling fins.

In the embodiment of Figs 2 to 5, the location at which each spring makes effective face to face contact with the disc is within a central zone extending one half of the circumferential length between successive radially extending drive elements or keys. In other words, one quarter of such circumferential length is available at each end of this latter zone in which (one quarter) the disc temperature is considered relatively too low to be relevant for the heat transfer purposes of the present invention.

In the illustrated embodiment of figs 2 to 5, the zonal contact between the outer face of the spring portion of the leaf spring and the inner face of the brake disc is

profiled and proportioned for such purpose and is located generally centrally within the above-identified (one half circumferential length) heat transfer zone of the disc.

Although in the above embodiments, the invention has been illustrated in terms of the provision of resilient means contacting the disc for heat transfer purposes, it is to be understood that the invention may be embodied in similarly constructed devices, having less resilient action than the anti-tilt springs illustrated. For example, the spring may be a mere anti-rattle spring, or (continuing the same line of modification) the resilient effect of the spring as between the disc and the hub may be negligible or zero in some cases where, for example, the heat transfer may be effectively carried out by a spring-like device but without the need for a spring action since this latter function may be sufficiently performed by other structures in the brake.

Claims (12)

1. A method of mounting a brake disc in a spot-type disc brake, the disc brake comprising : a) at least one rotatable brake disc; b) a rotatable mounting for said brake disc to permit such rotation and which is adapted to drive said brake disc and to have exerted thereon a braking effect by said brake disc when the disc brake is actuated ; c) at least one pair of friction elements adapted to frictionally engage braking surfaces on opposite sides of said brake disc to effect braking on actuation of actuation means therefor; d) said brake disc being axially slidable in use with respect to said mounting therefor under the action of said friction elements and said actuation means therefor during braking; e) resilient means being provided at circumferentially-spaced positions around said brake disc and adapted to act between said brake disc and said mounting therefor at said positions; characterised by said method comprising : f) providing said resilient means comprising mounting means therefor adapted to mount said resilient means at said circumferentially spaced positions on said at least one brake disc, and choosing said positions in accordance with thermal data identifying regions of higher disc temperature during use of said brake; and g) the method further comprising the step of causing said resilient means to cool said regions when said disc is heated during use of said brake.

2. A method of axially slidably mounting a brake disc in a disc brake comprising providing resilient means adapted

to act between said brake disc and a rotatable mounting therefor at circumferentially spaced positions around said disc, and providing mounting means for said resilient means, and the method comprising causing the resilient means to be mounted on the disc at said spaced positions and choosing said positions in accordance with thermal data identifying regions of higher disc temperature during use of said brake.

3. A method according to claim 1 or claim 2 characterised by the step of choosing said positions within zones located centrally between successive circumferentially spaced mounting elements mounting said disc on said rotatable mounting, said zones extending circumferentially not more than half the circumferential length between two successive mounting elements.

4. A method according to claim 3 characterised by choosing said positions at least overlapping with the mid circumferential point between two succesive mounting elements.

5. A spot-type disc brake comprising : a) at least one rotatable brake disc; b) a rotatable mounting for said brake disc to permit such rotation and which is adapted to drive said brake disc and to have exerted thereon a braking effect by said brake disc when the disc brake is actuated; c) at least one pair of friction elements adapted to frictionally engage braking surfaces on opposite sides of said brake disc to effect braking on actuation of actuation means therefor; d) said brake disc being axially slidable in use with respect to said mounting therefor under the action of said

friction elements and said actuation means therefor during braking ; e) resilient means being provided at circumferentially spaced positions around said brake disc and adapted to act between said brake disc and said rotatable mounting therefor at said positions characterised by f) said resilient means comprising brake disc mounting means for said resilient means which mounts said resilient means at circumferentially spaced positions on said at least one brake disc and chosen in accordance with thermal data identifying regions of higher disc temperature during use of said brake, whereby in use said resilient means cools at least one of said regions when said disc is heated during use.

6. A disc brake comprising at least one rotatable brake disc and a rotatable mounting therefor, characterised by cooling means mounted on said brake disc and adapted to exert a cooling effect by conducting heat therefrom at positions chosen in accordance with thermal data identifying regions of higher disc temperature during use of said brake.

7. A disc brake according to claim 5 or claim 6 characterised by said positions being within zones located centrally between successive circumferentially spaced mounting elements mounting said disc on said rotatable mounting, said zones extending circumferentially not more than half the circumferential length between two successive mounting elements.

8. A disc brake according to claim 7 characterised by said positions at least overlapping with the mid

circumferential points between two succesive mounting elements.

9. A disc brake according to claims 5 or 6 characterised by said resilient means being adapted to engage said disc between projecting drive keys or elements formed on said disc to cooperate with keyways or grooves formed in said rotatable mounting for said brake disc.

10. A disc brake according to any one of claims 5 to 9 characterised by said resilient means comprising a leaf spring adapted to grip said disc between resilient flanges formed on said resilient means.

11. A method of mounting a brake disc in a disc brake substantially as described herein with reference to the accompanying drawings.

12. A disc brake substantially as described herein with reference to the accompanying drawings.