GB2057609A

GB2057609A - Thermally Balanced Rotors

Info

Publication number: GB2057609A
Application number: GB8023625A
Authority: GB
Original assignee: Kelsey Hayes Co
Current assignee: Kelsey Hayes Co
Priority date: 1979-07-18
Filing date: 1980-07-18
Publication date: 1981-04-01
Also published as: FR2461847B1; CA1156568A; GB2057609B; JPS5618130A; MX148253A; DE3026354A1; IT1131711B; BR8004438A; SE8005143L; JPH0158779B2; IT8023519A0; DE3026354C2; FR2461847A1

Abstract

A (solid) brake disc 100 or (vented) brake rotor 14 has a rotor portion 16 engaged by brake pads and a mounting portion 22, wherein heat generated in use tends to flow from portion 16 to portion 22, wherein there is provided heat sink means which tend to control even temperature distribution in the rotor portion 16 caused by the heat sink effect of the mounting portion 22 to thereby reduce radial temperature gradients. This heat sink means may be provided as follows:- (i) By means of additional mass of material e.g. same as and/or integral (e.g. cast) with rotor or disc; see e.g. Figures 3,4 where wall 18 of portion 16 of rotor 14 is tapered; see also Figures 6-9 where disc 100 has additional portions of various shapes outside swept area. (ii) There may be a reduced area of frictional engagement 108 with the pad(s) on one or both sides of the disc or rotor. <IMAGE>

Description

SPECIFICATION Thermally Balanced Rotors The invention relates generally to disk brakes and more specifically to disk brakes having a thermal balancing mass disposed on the rotor or disk. The thermal mass functions as a heat sink to balance the heat sink provided by the support and mounting structure which is utilized to secure the rotor or disk to the wheel hub.

The frictional heating and heat dissipation function of disk brakes in vehicle service is accurately described as cyclical. The brakes are intermittently and often relatively infrequently activated to stop the associated vehicle and this duty cycle provides substantial intervals during which the frictionally heated components may cool. The mass of a solid disk brake represents a substantial and accessible heat sink into which heat generated along the walls of the disk by frictional engagement with the brake pads may be transferred. Nevertheless, the support structure which represents a substantial heat sink generally adjacent to the inner edge of the disk having no corresponding or compensating heat sink on the outer edge of the disk will generate a radial temperature gradient across the disk.

Prolonged application of disk brakes, of course, produces substantial quantities of heat which may be better dissipated by incorporating a plurality of radially disposed venting passageways within the disk which is then designated a rotor.

(Although the term "disk brake" is commonly used generically to refer to both solid and vented rotor brake assemblies, it should be noted that the term "disk" is properly used to refer only to a solid assembly and the term "rotor" is used in reference to a vented assembly. This distinction is generally maintained throughout the following specification except where repetition of "disk" and "rotor" would be obviously redundant or where the term "disk brake" is used generically to refer to a brake having a rotating circular planar member frictionally clamped by a pair of opposed brake pads). The radial passageways provide additional heat transfer surface and air circulation within the rotor. A vented rotor will thus generally dissipate heat into the surrounding air more rapidly than a solid disk due to its greater heat transfer surface and air circulation.In contrast to the unified mass of a solid disk, the inner and outer walls of a vented rotor represent thermal masses which exist in different thermal environments inasmuch as they are separated by a plurality of radial ribs or webs. Furthermore, the rotor hub and/or mounting structure is generally fabricated with or secured to at least one of the two rotor walls and represents a substantial thermal mass or heat sink. Thus, a vented rotor is also subject to radial thermal temperature gradients in the wall adjacent or connected to the mounting and support structure.

The invention provides a brake or rotor comprising a rotor portion which can be engaged by brake pads and a mounting portion by means of which the rotor portion can be mounted on a rotatable member to be braked, wherein in use heat generated by friction between brake pads and the rotor portion tends to flow from the rotor portion into the mounting portion and wherein there is provided heat sink means which, in use, tends to counteract the uneven temperature distribution in the rotor portion caused by the heat-sink effect of the mounting portion.

The invention provides a brake rotor or disk having thermal balancing mass disposed thereon to act as a heat sink to compensate for the mass, and thus heat sink, provided inherently by the rotor or disk mounting structure. As will become apparent, the balancing mass may be integrally cast with the rotor or disk or secured to the rotor or disk at any convenient step in the fabrication process by any suitable fastening means.

Furthermore, the material of the balancing mass may be but need not be the same as the material of the disk or rotor itself.

The invention also provides a disk brake assembly including a brake disk or rotor according to the invention. For example, if space were a consideration, a material of a high heat capacity (specific heat) could be employed. In other applications, a lightweight material might be desirable. All such variations which provide heat sinking mass to balance the heat sinking mass of the rotor or disk support structure are deemed to be within the scope of the invention.

In a vented rotor, the balancing mass may be so disposed on the wall of the rotor most proximate to the support means, generally the outer wall, that the outer wall thickness increases with increasing radial distance from the rotor centre. Alternatively, the heat sink mass may be disposed along a rotor wall in any fashion which achieves the desired heat sink balance with that of the rotor support structure and tends to minimize radial temperature gradients.

Alternatively, the vented rotor, or solid disk, may include mass or material about the periphery which is not acted upon by the brake pad. This may be accomplished by either reducing the area of frictional engagement between the brake pad and the rotor or disk wall by diminishing the pad's radial width thereby providing an unswept annular surface about the outer periphery of the rotor or disk which functions as a heat sink or by adding additional material about the periphery of the disk in any convenient configuration. The distribution (that is to say, the axial cross-section) of the peripheral mass may be adjusted to conform to particular space and thermal balancing requirements.

It is an object of the invention to provide a brake rotor or disk which exhibits a low radial temperature gradient.

It is a further object of the invention to provide a vented brake rotor exhibiting a low radial temperature gradient which may be manufactured by conventional and common manufacturing techniques.

Various forms of disk brake, brake rotor and brake disk constructed in accordance with the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a disk brake; Figure 2 is a fragmentary cross-sectional view taken along the line 2-2 of Figure 1; Figure 3 is a fragmentary, perspective view of a first form of vented brake rotor; Figure 4 is a fragmentary, perspective view of a second form of vented brake rotor; Figure 5 is a cross-sectional, diagrammatic view of a portion of a vented brake rotor; Figure 6 is a fragmentary, cross-sectional view of a first form of solid brake disk; Figure 7 is a fragmentary, cross-sectional view of a second form of solid brake disk; Figure 8 is a fragmentary, cross-sectional view of a third form of solid brake disk; and Figure 9 is a fragmentary, cross-sectional view of a fourth form of solid brake disk.

Referring to Figure 1 of the accompanying drawings, a disk brake assembly is indicated generally by the reference numeral 10. The disk brake assembly 10 includes a caliper assembly 12 and a rotor assembly 14. The rotor assembly 14 includes a rotor section 1 6 having generally planar and parallel outer and inner walls 18 and 20, respectively. The rotor assembly 14 further includes a frusto-conical support structure or hat section 22 which is generally cast integrally with the rotor section 16. The hat section 22 defines a plurality of openings 24 which co-operate with a plurality of lug bolts 26 and other components of a wheel hub 28 to secure the rotor assembly 14 to the wheel hub 28 in a conventional fashion.

The support structure for the rotor section 16 and the means for connecting it to the wheel hub 28 may also take many forms and be produced by various manufacturing processes other than those described and illustrated. For example, the support structure may consist of a planar, inward extension of a rotor or disk axially slidably mounted upon a spindle or axle shaft by means of a fluted interconnection, a distinct insert which is secured to the rotor or disk by any appropriate means including integral casting, or a structure having a U-shaped cross section which attaches to the periphery of the disk or rotor. A brake disk or rotor according to the invention may be provided with any of the foregoing and many other mounting configurations.

Referring now to Figures 1 and 2 of the drawings, the caliper assembly 1 2 is generally Cshaped and includes a caliper bridge 30 interconnecting an outboard leg 32 and an inboard leg 34. The caliper bridge 30 extends across the rotor section 1 6 and is there positioned and retained by guides (not shown) disposed parallel to the axis of the rotor assembly 1 4 which are in turn secured to an anchor plate 35. The guides provide a floating mounting for the caliper assembly 12 according to conventional disk brake practice. The inboard leg 34 of the caliper assembly 12 defines a cylinder 36 within which is disposed a mating piston 38. According to conventional practice, to apply the brake pressurized hydraulic fluid is supplied to the cylinder 36, advancing the piston 38 toward the rotor section 16.Adjacent to the mouth of the cylinder 36, an annular groove 40 provides seating for an annular seal means 42 disposed therein. The annular seal means 42 is preferably fabricated of an elastomeric material such as rubber and prevents loss of hydraulic fluid from the cylinder 36. The piston 38 includes an annular groove 44 which provides a retaining means for correspondingly shaped portion of a dust boot 46.

The dust boot 46 comprises an integral, onepiece seal moulded of elastomeric material such as rubber. The folded, bellows-like dust boot 46 provides a protective seal about the exposed end of the interface between the piston 38 and the caliper assembly 12 while permitting substantial relative axial motion between them. An outboard disk brake pad assembly 48 and an inboard disk brake pad assembly 50 are slidably disposed on the anchor plate 35 and frictionally engage the outer wall 1 8 and the inner wall 20, respectively, of the rotor section 1 6.

The invention does not reside in the caliper assembly 1 2 and associated components, and the foregoing description is intended only to be representative of the possible componentry with which a brake disc or rotor according to the invention may be combined. The invention may be successfully used with widely varying caliper assembly and piston configurations as well as with other motive energy sources such as pneumatic, mechanical or electrical devices. The structure and function of the caliper assembly 12 and associated components will not be further described.

Referring now to Figures 2 and 3, the first form of rotor section 1 6 includes an outer wall 18 and an inner wall 20, as has been previously expiained. The rotor section 16 is vented and, as such, includes a plurality of radially extending passageways 54 and an equal number of ribs 56 which extend transversely between the outer wall 18 and the inner wall 20 of the rotor section 1 6.

The inner wall 20, or, more broadly, the wall further from the mounting structure or hat section 22 and separated from it by the ribs 56, has a uniform wall thickness. The outer wall 18, or, more broadly, the wall of the rotor section 1 6 nearer to, and connected to, the mounting structure or hat section 22, however, increases in thickness with increasing distance from the centre of the rotor assembly 14. The wedgeshaped mass of the outer wall 1 8 thermally balances the mass of the hat section 22 and thus minimizes radial temperature gradients across the outer wall 18 of the rotor section 1 6.

Referring again to Figures 2 and 3, it is apparent that the increasing thickness of the outer wall 1 8 produces a corresponding reduction in the axial width of the air passageways 54. If the circumferential lengths of the inlet and outlet of the passageways 54 were equal, such a reduction in the width of the passageways would result in an outlet substantially smaller than the inlet and choke or impede the flow of air through the passageways 54. The choking of the air flow may, of course, be eliminated by making the area of the air passageway outlets approximately equal to or greater than the area of the air passageway inlets.

By adjusting the cross-sectional area of the ribs 56, a substantially constant or radially increasing cross-sectional area of the air passageways may be maintained. Thus, thermal balancing of the heat sink of the mounting structure and good air flow through the radial air passageways may both be achieved.

Referring now to Figure 4, it should be apparent that a vented rotor such as the rotor 1 6 need not incorporate substantially rectangular ribs nor substantially rectangular air passageways in order to practise the invention. In this regard, the second form of rotor 60 includes an inner wall 62 having a constant thickness at its thinnest portion, and an outer wall 64 having an outwardly increasing thickness. The rotor 60 includes air passageways 66 having a generally elliptical cross-section. The major axes of the elliptical passageways 66 at the outer surface of the rotor 60 are aligned circumferentially about the periphery of the rotor 60.The major axes of the elliptical passageways 66 at the inner surface of the rotor 60 are parallel to the axis of the rotor 60 and thus at right angles to the major axes of the elliptical passageways 66 at the outer surface of the rotor 60. It should be noted that such a configuration may also have air passageways of constant or radially increasing cross-sectional area in addition to the heat sinking mass and can also achieve very low radial temperature gradients in the wall of the rotor 60 nearer to the mounting structure while maintaining good air flow in the elliptical passageways 66.

It should further be noted that neither the evenly tapering wall 1 8 of the first form of motor adjacent to the hat section 22 and its generally rectangular air passageways 54 nor the scalloped, tapering wall 64 of the second form of rotor and its generally elliptical air passageways 60 are to be construed as limitations of the scope of the invention. Rather, any configuration of the walls of a rotor or disk which provides a heat sinking mass for balancing the mass and heat sinking effect of the rotor or disk mounting structure in order to reduce radial temperature gradients within the rotor or disk falls within the ambit of the invention.

An example of the thermal balance that may be achieved by disposing mass on a wall of a vented brake rotor to balance the inherent heat sink provided by the rotor mounting structure and thus reduce radial temperature gradients within the rotor will now be given. It should be appreciated that the following calculations are illustrative and exemplary in nature and are provided only to clarify and explain the invention. The accuracy of the results of such calculations is commensurate with the apparent complexity and sophistication of the mathematical analysis used. The result of the present calculation should be considered only as a first approximation which can be improved upon by more sophisticated mathematical and empirical analysis as well as experimental testing such as dynamometer testing.

Figure 5 illustrates an outer rotor wall and hat section similar to that which might be utilized in a heavy duty vehicle brake. The ribs and inner wall of the rotor are illustrated in phantom lines for reference purposes only and are not included in the following calculations, their heat transfer and temperature gradient characteristics being deemed to have a negligible effect on the radial heat transfer and temperature gradient characteristics of the wall of the rotor adjacent to the mounting structure. As has been noted, the hat section of the rotor, designated as elements 1, 2 and 3 in Figure 5, provides a heat sink for the frictional heat generated on the surface of and absorbed into the adjacent outer wall of the rotor which is designated as element 4.Element 5 of Figure 5 represents a tapering mass disposed on the rotor wall which, with the mass of element 4, balances the heat sink provided by elements 1,2 and 3 of the hat section.

The following calculations quantify this balancing relationship and determine an approximate width or thickness T for the triangular element 5 for given dimensions of elements 1, 2, 3 and 4 of the hat section and rotor section, respectively. The radii and other dimensions of the elements of the hat section and rotor are those illustrated in Figure 5. The Theorem of Pappus which states that the volume of a solid of revolution is the product of the generating area and the distance travelled by the centroid of the area is used to calculate the volumes of the various elements and thus implicitly the mass and heat capacity of these elements since it is assumed that the density and specific heat of the rotor are uniform.

For element 1 of the hat section, the area (A,) equals .5Rx2.4R or A1=1.2R2, the centroid radius (Y1) equals 1.5R+1.2R orY1=2.7R and the distance travelled by the centroid (D,) is 5.4 no. According to the Theorem of Pappus, the product A1D, equals the volume (V1) of element 1 and A,D1=6.487rR3. Likewise, for element 2, the area (A2) equals .5Rx2.0R or A2=1 .0R2, the centroid radius (Y2) equals 3.9R+.25R or Y2=4.15R and the distance travelled by the centroid (D2) is 8.3 7do. The product A2D2 equals 8.3 nR3, which is the volume (V2) of element 2.Again for element 3, the area (A3) equals .5Rx1.2RorA3=.6R2, the centroid radius (Y3) equals 3.9R+.6R or Y3=4.5R and the distance travelled by the centroid (D3) is 9.0 7to. The product A3D3 equals 5.4 R3 and is the volume (V3) of element 3. Finally, the total volume (and proportionately mass) of elements 1, 2 and 3 (V,23) equals ÀD or 6.48 R3+8.3 7tR3+5.4 R3-20 18 R3.

Performing these same calculations for elements 4 and 5 of the rotor section, the area of element 4 (A4) equals .5Rx2.6RorA4=1 .3R2, the centroid radius (Y4) equals 5.1 R+ 1.3R or Y4=6.4R and the distance travelled by the centroid (D4) is 12.8 my. The product A4D4 equals 16.6 R3.

Likewise for element 5, the area (A5) equals .5x2.6RxT or A5=1 .3RT, the centroid radius (Y5) equals 5.1 R+.667x2.6R or Y5=6.8R and the distance travelled by the centroid (D5) is 13.67or. The volume (V5) of element 5 equals the product A5D5 or 17.7 7cR2T.

For a static thermal balance to exist, the volume (and mass) of elements 1,2 and 3 should be approximately equal to the volume (and mass) of elements 4 and 5 or V1 +V2+V3rV4+V5 20.18 R31 6.6 'uR3+1 7.7 nR2T 3.58 7tR31 7.7 'rR2T .2RT Thus a maximum width T of the triangular element 5 of the rotor section of .2R is a first approximation of the mass thickness which achieves a thermal balance in a rotor assembly of the stated proportions.

The foregoing description referring to Figures 1 to 5 of the drawings has been directed to vented rotors having generally radially oriented air passageways disposed between the walls of a brake rotor. The concept of the invention, however, which is the placement of mass on the brake disk or rotor to compensate for the inherent heat sinking characteristic of the mounting structure, may also be applied to solid brake disks.

The concept of the invention also includes either a specifically formed peripheral extension to the disk or, alternatively, providing a brake pad on the side of the disk nearer to the mounting structure, or on both sides, which does not frictionally engage the entire side wall of the disk but leaves a peripheral band unswept. So configured, this area of the disk, rather than being a source of heat from the frictional contact of the brake pad, becomes merely an additional mass which functions as a heat sink to balance the inherent heat sinking characteristic of the mounting structure.

Figures 6, 7, 8 and 9 show four solid disk profiles according to the invention. Specifically, Figure 6 shows a solid disk 70 which is secured to an integrally cast hat section 72. The frictionally engaged portion of the disk 70 corresponding to the effective radial width of the brake pads (not shown) is designated by the brackets 74. It is apparent that the disk 70 extends radially outwards beyond this swept area. Specifically, the outer edge of the disk 70 is obliquely formed and defines a pointed, triangular section 76 about its periphery. The triangular section 76, having a majority of its mass disposed adjacent to the side of the disk 70 nearer to the hat section 72, provides slightly greater heat sinking to this side of the rotor than to the opposite side and thermally balances the disk 70.

Similarly, Figure 7 illustrates a disk 80 having a hat section 82 and swept rotor surfaces 84.

Again, mass 86 is disposed on the disk 80. In a fashion similar to that of the solid disk 60 illustrated in Figure 6, the mass 86 is nonuniformly disposed about the outer surface of the disk 80 and provides somewhat greater heat sinking to the side of the disk 80 nearer to the hat section 82.

Since by its nature a solid disk will tend to have a more uniform temperature than will a vented rotor, applications may exist where a thermally balancing mass should be uniformly added to the periphery of a disk. Furthermore, a mounting structure such as the radially extending planar structure described previously, if secured substantially symmetrically about the axial midplane of the disk, will generally be optimally balanced by a correspondingly disposed heat sink mass. Referring to Figure 8, a solid brake disk 90 is formed with an integral planar mounting 92 as described above. The frictionally engaged area of the disk 90 is designated by brackets 94. An annulus 96 having a generally rectangular crosssection is uniformly disposed about the periphery of the disk 90. The annulus 96 may be integrally cast with or subsequently secured to the disk 90 and may be fabricated of the same material as the disk 90 or of a different material. It should be apparent that the mass of the annulus 96 will function relatively uniformly as a heat sink with regard to the left and right faces of the solid disk 90 as will the planar mounting 92 due to the uniform distribution of material about the axial midplane of the disk 90.

Figure 9 illustrates a solid disk 100 having a mass 104 disposed about its periphery to thermally balance the inherent heat sink represented by an integrally cast hat section 102.

The additional mass 104 is formed in a triangular section and tends to absorb and dissipate heat uniformly from both surfaces of the disk 100 in a similar manner to the annulus 96 of the disk illustrated in Figure 8. It should thus be apparent that additional mass, incorporated into either a solid disk or a vented rotor, may be disposed about the periphery of the rotor in any fashion consistent with the goal of thermally balancing the inherent heat sink created by the mounting structure af the rotor. Once the required thermal balance heat transfer characteristics have been established the specific material, heat capacity, mass, cross-section or thickness may be selected with regard to such considerations as casting and manufacturing techniques, cost or energy conservation.

As has been previously noted, the inventive concept may also be practiced by reducing the amount of surface on the side of the disk or rotor nearer to the mounting structure or on both sides of the disk or rotor that is frictionally engaged by the brake pad or pads. Referring briefly to Figure 9, the conventional brake pad swept surface is illustrated on the right by the bracket 106. On the opposite side of the disk 100 a reduced area of frictional engagement designated by the numeral 108 may be used in a disk brake according to the invention inasmuch as the non-engaged area designated by the bracket 110 is no longer a source of frictional heat but in fact represents an area and associated mass which functions as a heat sink. It should be noted that the radial width and thus the frictionally engaging area of both brake pads may be reduced thus providing heat sinking on both faces of the brake disk or rotor.

Claims

1. A brake disk or rotor comprising a rotor portion which can be engaged by brake pads and a mounting portion by means of which the rotor portion can be mounted on a rotatable member to be braked, wherein in use heat generated by friction between brake pads and the rotor portion tends to flow from the rotor portion into the mounting portion and wherein there is provided heat sink means which, in use, tends to counteract the uneven temperature distribution in the rotor portion caused by the heat-sink effect of the mounting portion.

2. A brake disk or rotor as claimed in claim 1, the rotor portion of which is generally planar and extends radially outwards from the mounting portion.

3. A brake rotor as claimed in claim 2, wherein the rotor portion comprises first and second spaced apart walls and radially disposed air passageways in the rotor portion and the heat sink means is disposed along at least one of the said walls.

4. A brake rotor as claimed in claim 3, wherein the thickness of the heat sink means in an axial direction increases with increasing distance from the axis.

5. A brake rotor as claimed in claim 4, wherein the rotor portion comprises a first circular wall secured to the mounting portion and a second circular wall spaced apart axially from the first wall, and a plurality of rib means interconnecting the first and second walls, the two walls having inner and outer surfaces coaxial with the axis of the rotor, the inner and outer surfaces of the first wall being so obliquely disposed with respect to one another that the first wall increases in thickness with increasing distance from the axis.

6. A brake rotor as claimed in claim 5, wherein the first wall, the second wall and the rib means define radial air passageways of substantially uniform cross-sectional area.

7. A brake rotor as claimed in claim 6, wherein the rib means have a substantially uniform crosssectional area along their radial length.

8. A brake disk as claimed in claim 1 or claim 2, wherein the rotor portion is solid and the heat sink means includes material disposed generally adjacent to the outer periphery of the rotor section.

9. A brake disk as claimed in claim 8 when dependent upon claim 2, wherein the mounting portion extends axially to one side of the rotor portion.

10. A brake disk as claimed in claim 9, wherein the heat sink means is disposed asymmetrically about the plane of the rotor portion, at least most of the heat sink means being on the same side of the disk as the mounting portion.

11. A brake disk as claimed in any one of claims 8 to 10, wherein the said material is in the form of a solid of revolution about the axis of the disk.

12. A brake disk as claimed in claim 11, wherein the generant of the solid of revolution is a triangle.

13. A brake disk as claimed in claim 11, wherein the generant of the solid of revolution is a rectangle.

14. A brake disk as claimed in claim 11 when dependent upon claim 10, wherein the maximum radius of the area of the surface of the rotor portion that in normal use is swept out by the brake pad on one side of the disk is greater than the maximum radius of the area swept out by the pad on the other side of the disk.

1 5. A brake disk or rotor substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 3, or Figure 4, or any one of Figures 6 to 9 of the accompanying drawings.

16. A disk brake assembly, which includes a brake disk or rotor as claimed in any one of claims 1 to 15.

17. A disk brake assembly as claimed in claim 16, wherein the brake disk or rotor is as claimed in claim 1 and the heat sink means is formed by a part of the rotor portion of the disk or rotor adjacent to a part of one face of the rotor portion that is situated outwardly beyond, in a radial direction, the part of the face that, in use, is engaged by a brake pad or pads.

18. A disk brake as claimed in claim 17, wherein the brake pad or pads that, in use, engage the said one face of the rotor portion, engage the rotor portion only over an area of which the radially outer boundary is located radially inwards with respect to the radially duter boundary of the area of the other face of the rotor portion that, in use, is engaged by a brake pad or pads.