AU702159B2 - A brake disc and method of forming same - Google Patents

Description

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AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: f

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Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: PBR Automotive Pty. Ltd.

Actual Inventor(s): Nui Wang Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: A BRAKE DISC AND METHOD OF FORMING SAME Our Ref 526357 POF Code: 336/336 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1r 2 A BRAKE DISC AND METHOD OF FORMING SAME The present application is a divisional application of Australian patent application 13079/95, the contents of which are herein incorporated by cross reference.

The invention relates to a disc for a disc brake assembly and also to a method of forming the disc. The invention has particular application to disc brakes for use with motor vehicles and it is convenient to hereinafter describe the invention by reference to that application. However it is to be appreciated that the i0 invention has broader application and is not limited to that particular use.

In a typical disc brake assemhly for a motor vehicle, a caliper bridge is arranged to straddle a rotatable disc. The bridge incorporates inboard and .outboard portions each of which incorporates an associated friction pad. The portions are able to move relative to one another to enable the friction pads to engage opposing faces of the disc under the influence of a hydraulic piston cylinder assembly acting on the inboard portion.

i"°The applicant in copending application no. 13079/95, discloses a disc brake assembly which includes a disc including radially outer and inner porticils which are separated by a gap. The brake assembly further includes two pad 20 assemblies which are located on respective opposite sides of the disc and which are interconnected by a draw bar which extends through the gap and is I connected to a piston cylinder arrangement. Actuation of the piston cylinder arrangement imparts a force to the pad assemblies through the draw bar to cause them to move towards or away from the disc to thereby enable actuation and release of the brake assembly.

An aim of the present invention is to provide a disc which is suitable for this disc brake assembly and to a method of forming the disc.

In a first aspect, the invention provides a disc for a disc brake assembly, the disc being rotatable about an Pxis of rotation and including a radially outer portion and a radially inner portion, each of the outer and inner portions having a braking surface on each of two opposite sides thereof and a gap forming a radial 2separation between said outer and inner portions and extending in a continuous EDJHA13079B.DOC 14 April, 1998 3 circle co-axial with said axis of rotation, and connecting means spaced from the braking surfaces and interconnecting the inner and outer portions of the disc, the connecting means being in the form of a bracket located on one side of the disc, the bracket being spaced from the braking surface that side of the disc to form a cavity in which a brake pad assembly is able to be located, the bracket further incorporating at least one passage providing access to the cavity.

The braking surfaces are provided on both the inner and outer portions of the disc. In this way, associated brake pads can be located on opposite sides of the disc with each being arranged to engage both the inner and outer portions of the dsc on actuation of the brake assembly. The brake assembly can be i I interconnected by a force transmitting element such as a draw bar which interconnects the pad assembly and which extends through the gap without inhibiting rotation of the disc.

Preferably there are a plurality of passages formed in the bracket. This arrangement further facilitates installation and removal of the brake pad assembly located against the one side of the disc and also assists in ventilation of the S.assembly to improve heat dissipation from the operative surfaces of the brake pads. Preferably the bracket is adapted to be connected to a hub of a wheel 0 assembly so as to connect the disc to the wheel assembly.

The disc may be formed as a unitary construction or may be cast in sections and subsequently assembled together. Furthermore the inner and otuter portions may be arranged to be fixed to the bracket or in alternative form, at least one of the portions is movably mounted to the bracket so as to enable movement of one portion relative to the other in a directicn parallel to the axis of rotation of the disc.

Preferably the braking surfaces are machined on the inner and outer portion of the disc using a chip producing process.

In a further aspect, the invention relates to a method of forming a disc of the above ,ype. The disc may be formed in one piece or may be formed in separate pieces with the aperture and the contact surfaces machined by any or all of grinding, turning and milling of the disc.

In one form, there is provided a method of forming a disc for a disc brake assembly, the disc being rotatable about an axis of rotation and including a E,\DJH:\13079B.DOC 14 Aprl, 1998 4 radially outer portion and a radially inner portion, each of the outer portion and the inner portion having two opposite sides thereof and a gap forming a radial separation between said outer and inner portion and extending in a continuous circle coaxial with the axis of rotation, the method including the steps of: providing a tool including a central shaft and including at least one cufftting head having a cutting edge radially spaced from, and rotatable about, the shaft; (ii) locating the cutting tool such that the cutting head is on one side of the disc with the shaft being substantially aligned with said gap; (iii) rotating the shaft to cause the cutting head to move in a circular path such that the cufftting edge engages the one side of both the inner and outer portions of the disc on rotation of the shaft to thereby machine braking surfaces on the one side of both the inner and outer portions of the disc.

c Preferably the shaft of the cutting tool is arranged to be parallel to the axis e. dof rotation. Furthermore the cutting tool can be located such that the shaft l 15 extends through the gap in the disc thereby enabling machining of the braking surfaces on both sides of the disc from the one direction.

IIn one form, the cutting tool includes first and second cutting heads which are radially spaced apart along the shaft. In this way simultaneous machining of both sides of the disc can be undertaken by locating the cutting heads on respective opposite sides of the disc with the shaft extending through the gap.

Preferably the depth of the cutting of the cutting tool can be varied by movement of the tool in a direction parallel to the axis of rotation of the disc.

Preferably the disc is rotated about its axis of rotation to provide feed for the cutting tool. Furthermore preferably the surface finish on the breaking suface may be varied by varying the speed of rotation of the disc relative to the speed of rotation of the cutting tool shaft.

It will be convenient to hereafter describe various embodiments of the invention in greater detail with reference to the accompanying drawings. The SIparticularity of these drawings in the related description is not to be understood as Sii; 30 superseding the generality of the preceding broad description of the invention.

i rIn the drawings: E:\DJHA13079B.DOC 14 April, 1998 -~-sC31~1a r.Th 5 .Ud Figure 1 is an exploded perspective view of a sub assembly for a disc brake assembly including a disc according to a first embodiment of the invention; Figure 2 illustrates a variation of the sub assembly of Figure 1; Figure 3 is a sectional view of the first embodiment of a disc for use in a disc brake assembly of Figure 1; Figure 4 is a sectional view of a second embodiment of a disc for use in the disc brake assembly of Figure 1; Figure 5 is a variation of the disc of Figure 4; Figure 6 is a perspective view of a disc brake assembly including the sub assembly of Figure 1; Figure 7 is a sectional view along section line VII-VII of Figure 6 and i illustrating a full cast disc according to a further embodiment of the invention; Figure 8 is a perspective view of a variation of the brake pad assembly for use in the sub assembly of Figure 1; Figure 9 illustrates a machining tool for preparation of the braking surfaces of the disc of the disc brake assembly according to an embodiment of the invention; S: Figure 10 is a variation of the machining tool of Figure 9 incorporating two I cutting heads; and "2 Figure 11 is a schematic view of the braking surfaces on a disc using the machining tools of either Figure 9 or Figure 1 illustrates a sub assembly 10 of a disc brake assembly 100. This !figure is an exploded view to more clearly disclose the various component parts.

The sub assembly incorporates inboard and outboard friction pad assemblies (11 and 12 respectively), each of which incorporates a :upport plate (13, 14) and a friction pad (15, 16). Typically, each friction pad is bonded or riveted to its respective support plate to transmit shear load.

An anchor bracket 17 is adapted to be mounted to a motor vehicle through mounting holes 18. Guide rails 19 extend along opposing sides of the bracket to support the inboard and outboard assemblies. Cooperable slots 20 are located on the respective inboard and outboard assemblies 11, 12 and receive the guide rails enabling the assemblies to be slidably mounted on the anchor 17 in a j direction away or towards each other. It should be appreciated that the pad i EADJH:13079B.DOC 14 April 1998 .t 6 assemblies may be secured to the anchor bracket 17 in other ways, such as with slideways located on the anchor bracket arranged to receive respective ends of the assemblies, or by a pin guided arrangement.

Two cylinder piston assemblies (22, 23) form the actuating means 21 of the sub assembly 10. Each cylinder piston assembly includes a cylinder 24 mounted to the inboard pad assembly through bracket 25, and piston 26. In each cylinder piston assembly, the piston 26 is slideable within the cylinder 24 along a movement axis 71 (Figure 7) and movable in a direction away or towards the support plate 13 of the inboard assembly 11 under hydraulic pressure. A seal 27 (Figure 7) is located between the piston 26 and cylinder 24 and a boot (not shown) is located on the cylinder on the inboard side of the seal 27. It should be i realised a single cylinder could be used and that the number of cylinders in the Sassembly 10 may vary depending on the size of the assembly as well as the specific torque output required. Furthermore, the cylinders may be secured to the support Fiate 13 in any suitable form including integrally forming the cylinders with the support plate. Furthermore, it may be desirable to have only a reduced contact area between the cylinder and the plate and this arrangement is illustrated in Figure 7.

Force transmitting means 28 in associated with the actuating means 21 to provide at least part of an interconnection between the pad assemblies such that the inboard assembly responds to movement of the outboard assembly towards O or away from the disc. In the first embodiment, the force transmitting means 28 is in the form of rods 29 associated with each cylinder piston assembly and which extend coaxial with the movement axis. In Figure 1 the rods are integrally formed with respective piston 26. 1l1 an alternative arrangement (not shown) each piston is connected to the rod through any appropriate coupling means such as a screw thread arrangement. Rods 29 pass through apertures (30, 31, 32) in the respective cylinders 24 and pad assemblies 11 and 12 and are secured to the outboard support plate 14. The rods 29 are slideable within the apertures 30 and 31 enabling the rods to be movable relative to the cylinders 24 and the inboard pad assembly 11. A seal 33 (Figure 7) is provided in the respective apertures to seal between the respective rods 29 and the cylinders 24.

E:\DJH:\13079B.)OC 14 April, 1998 -I I-~i 7 While the rods 29 may be secured to the support plate 14 in any suitable way, in the illustrated arrangement of Figure 1, each rod incorporates a threaded stud 34 on its outer und which is arranged to receive a cooperable nut Furthermore, the rod 29 is keyed to the support plate 14 to prevent relative rotation thereof during tightening of the nut 35 by a portion 36 located adjacent the stud 34 and having a rectangular or any other non-circular shape crosssection which is received in the suitably shaped aperture 32 in the outboard support plate. Furthermore, the rods 29 are positioned across the support plate 14 at a position to optimise the load distribution induced on the plate 14 by the rods 29. In this arrangement, as there are two rods, the friction pad 16 may be divided notionally into two regions with each rod connected at a centre of a respective one of the regions. To evenly distribute the load across the plate the 0 size of each region would be proportional to the expected actuation load induced by each rod. In the illustrated case as each rod is expected to transmit half the actuation load, the size of these regions is approximately the same.

In an alternative arrangement shown in Figure 2, each rod 29 incorporates ;an enlarged T-shaped head portion 37 and each aperture (31, 32) in the pad assemblies is elongated to accommodate entry of the respective head portions.

The rods 29 are arranged to be secured to the outboard support plate 14, once the respective heads have passed through apertures 32, by rotating the rods through 900. The heads are biased towards support plate 14 to minimise rattle by some form of spring clip (not shown). At the same time this clip also acts as an antirotational device for the head. In this arrangement, the rods are typically connected to the pistons via screw threads (not shown).

The friction pad (15, 16) of each pad assembly (11, 12) provides a operative surface (38, 39) which in use is arranged to engage respective sides of a disc (Figure While the friction pad may be unitary, in the illustrated arrangement, the operative surface of the respective pad assemblies incorporates channels and 41 which divide each operative surface into four discrete parts. One channel 40 extends longitudinally across each pad assembly and incorporates the respective apertures (31, 32) to receive respective rods 29. The other channel 41 EADJM13079B.OOC 14 Aptil, 1998 extends substantially transverse to this channel 40. Other arrangements of channels may be provid.J if required.

As illustrated in Figure 8, a quick release pad assembly 42 is provided comprising a support plate 43 and friction pad 44. Apertures 45 are formed through the plate and pad which are arranged to receive respective rods 29.

Each aperture is in the form of a radial slot which extends preferably from the radially lower edge 46 of the pad assembly 42 to enable quick release of the pad assembly from the brake sub assembly.

Figure 3 illustrates a first embodiment of the disc 50 which may be used in j association with the sub assembly 10 to form the disc brake assembly 100.

The disc 50 is arranged to rotate about an axis of rotation 51 and rotate with the motor vehicle. The disc has an inboard side 52 and an outboard side 53 and incorporates a radially inner portion 54 and a radially outer portion 55 which are J separated by gap 56 extending in a continuous circle coaxial with the axis 51 of the disc.

Each prrtion (54, 55) has a respective inboard and outboard braking surface ij (57, 58, 59, 60) located on opposite sides of the disc 50. These braking surfaces provide the engagement surfaces for the operative surfaces (38, 39) of the respective pad assemblies.

A bracket 61 is located on the outboard side of the disc 50 and interconnects ;the inner and outer portions (54, 55). The bracket 61 is secured to the inner and outer portions and is spaced from the inner and outer portion outboard braking surfaces (58, 60) to provide a cavity 62 in which the outboard assembly 12 is located, enabling the operative surface 39 of the outboard assembly to engage the outboard braking surface (58, 60) of the inner and outer portions.

A second embodiment of the disc 50 is illustrated in Figure 4. This disc is similar to the disc of Figure 3 and incorporates the radially inner and outer portions (54, 55) separated by the gap 56. However in this arrangement, the disc forms part of the wheel assembly 63. The wheel assembly includes a hub 64, a rim 65, and a plurality of spokes 66 interconnecting the hub and rim. In Figure 4, the inner and outer portions are bolted, or otherwise rigidly connected, to the wheel assembly 63. This arrangement is feasible for use where the wheel incurs E:DJHA13079B.DOC 14 April, 1998 ~pa~a~ -a~ap sl 9 little side loading (eg. in cornering) and therefore, is not subjected to bending of the rim relative to the hub. An example of such a situation would be with a motor cycle.

A variation of this disc 50 is illustrated in Figure 5 which may be used in motor vehicles where cornering loads could deflect the rim relative to the hub. In this case, the inner portion 54 is fixed to the hub 64 and the outer portion is attached to the rim 65 or spoke 66 in a manner that allows limited movement in the axial direction such as through a spline 67 as illustrated, or through correct alignment of the inner and outer portions, the inner portion is movable relative to the hub in an axial direction, while the outer portion is fixed, or both the I inner and outer portions are movable in the axial direction with the sub assembly o °being fixed to form a datum surface. A further embodiment of the disc is illustrated in Figure 7 which comprises a fully cast disc 50. This disc is arranged to be connected solely to the hub and therefore deflection of the rim relative to the A: hub does not cause misalignment of the inner portion relative to the outer portion.

Figures 6 and 7 illustrate the disc brake assembly 100 incorporating the sub assembly 10 and disc 50. The inboard and outboard pad assemblies (11, 12) are .supported on the anchor bracket 17 and are located on opposing sides of the disc 50 with the guide rails 19 of the bracket 17 extending through the gap 56. The outboard pad assembly 12 ocated in the cavity 62. The disc 50 includes a series of passages 68 which are formed in the bracket 61 to provid= access to the cavity 62 and also improve ventilation around the disc. The cylinders 24 are connected to the inboard assembly 11 and the rods 29 are connected to the respective pistons 26 and extend through the gap 56 and are connected to the outboard pad assembly 12. The movement axis 71 of each piston relative the respective cylinder is substantially parallel to the axis of rotation 51 of the disc and each piston 26 is arranged to move away from the inboard assembly in operation of the brake along the movement axis 71 with the rods 29 acting as a draw bar which dr, ws the outboard assembly towards the inboard assembly causing the operative surface 39 to be drawn into engagement with the outboard I braking surface (58, 60) of the disc 50. As the inboard assembly 11 is movable E:\DJH:\1379B.DOC 14 April. 1998 on the anchor bracket 17, on continued movement of the pistons 26 away from the inboard assembly 11, the inboard pad assembly is caused to move on the guide rails 19 on the bracket 17 to move the operative surface 38 of the inboard assembly 11 into engagement with the inboard face (57, 59) of the disc An advantage of the disc brake assembly 100 is that each rod 29 is much better able to accommodate the loads induced in operation of the assembly than prior art caliper bridge arrangements by virtue of the location of each rod relative to the operative surfaces and to the axis of movement of the respective pistons.

In this arrangement, the loads induced at these operative surfaces are transferred substantially along each rod with little bending moment being applied with any drag load or torque induced at the respective pad assemblies being transferred to the anchor bracket through their point of contact on the guide rails 19. As a result, the brake assembly provides a much stiffer arrangement with deflection of I •the brake assembly due to operational loading being substantially reduced. As a result, the operative surface of the pad assemblies on the disc will not change under increased loading thus enabling the brake assembly to give a more consistent specific torque output under different loadings. Furthermore, with the stiffer construction, the pad assemblies may include larger surfaces and the piston cylinder arrangement is more efficient requiring a lower fluid displacement.

To inhibit binding of the piston within the cylinder without compromising the efficiency of the assembly, a portion 70 of the cylinder wall between seals 33 and 27 is relieved. In this way, the possibility of binding of the piston 26 can be reduced without compromising the effectiveness of the sealing arrangement between the piston 26 of the cylinder 24 or rod 29. A neat fit is provided between the cylinder and the piston or rod on either side of respective seals 33, 27. This ensures that extrusion of the seals does not occur which would otherwise increase fluid displacement. While the rod 29 takes very little bending movement, any side loading on the rod reacts against cylinder 27 at the location adjacent the seals 27, 33 which provide a bearing surface for the piston or rod.

Furthermore, as each rod is more efficient in accommodating the stresses induced in the assembly, and as a caliper bridge is no longer required, the brake assembly can be of lighter construction and manufacturing costs can be reduced.

E'.\DJH:\13079B.DOC 14 Apri, 1998 ic usa~ I~ PB~~"LI 11 Furthermore, as it is not required to provide space for a caliper bridge on the radial extremity of the disc, a larger diameter disc is possible which provides a larger heat sink for the brake assembly, and a larger effective radius.

In addition the brake assembly 10 is well equipped to effectively dissipate heat in operation of the assembly. In relation to the disc, with the radial separation there is more surface area in the disc and vents 69 formed between the braking surface are shorter. Furthermore, the longitudinal channel 40 in each pad assembly is arranged to be located over the gap 56, providing a gap which allows air flow around the contact surfaces. The transverse channels 41 further ,i assist in encouraging the air flow. Furthermore, with this arrangement, there is no caliper bridge or other structure to shield heat dissipation.

A further advantage is that the brake assembly may be more easily removed from the disc. As a caliper bridge is not required, once the rods are disconnected from the outboard pad assembly, the brake assembly may be withdrawn from the disc by being moved in the axial direction. Furthermore, the pad assemblies may be changed without removal of the wheel. For example, in the brake assembly shown in Figure 2, the rods are released from the outboard pad assembly by being rotated through 900, and this c&n be effected from the outboard side of the disc through passages 68. The inboard pad assembly and piston cylinder arrangement is then withdrawn from the disc in the axial direction and the outboard pad assembly is removed through the spokes in the wheel provided an adequate gap exists between adjacent spokes. A similar operation can be undertaken to install the new pad assemblies.

Further benefits can be realised in the disc brake assembly 100 by the design and method of manufacture of the disc The disc 50 may be formed in one piece or may be cast in separate pieces and assembled later. In one embodiment, the bracket 61 forms part of a centre support 76 which is secured to an axle for rotation witn the vehicle. Typically the centre support is made from steel and is fabricated or pressed or formed from a combinati-' thereof. The inner and outer portions (54, 55) of the disc are cast or otherwise formed on to the bracket. Each portion may be formed as a single Y piece or may be formed from a plurality of interfitting segments These portions EADJHA1307.B.DOC 14 Apil 1998 12 may be cast from any suitable material inclUding aluminium, metal matrix composition or cast iron. Alternatively, the bracket and inner and outer portions may be cast from a single material and integrally formed together as shown in Figure 7.

To prepare the necessary inboard and outboard brakina surfaces (57, 58, 59, the portions may be machined using a chip producing process including grinding, turning and milling. The surfaces usually need to be planar and have a suitable surface texture to expedite burnishing of the friction pads.

Figure 9 illustrates a suitable machining tool located in the disc 50 to provide the outboard braking surfaces (58, 60). The machining tool 77 incorporates a A head 78 mounted on a rotatable shaft 79. Cutters 80 (which may include single point or multiple point cutting edges) are secured to the head and are spaced from the axis of rotation 81 of the -haft and are separated by an angle which is approximately 1800. The spacing determines the depth of the respective braking 15 surface of the inner and outer portions.

To prepare the outboard braking surface, the tool is inserted in through the gap 56 within the disc 50. To facilitate insertion of the head 78 in through the gap 56, the machining tool 77 is of suitable shape, such as substantially T-shape as Fillustrated with the cross piece being arcuate to enable insertion into the gap 56 or in an alternative embodiment (not shown), of a substantially L-shaped configuration. To machine the face, the cutters 80 are located against the disc aif: surface and the tool 77 rotates about the shaft causing the cutters to move against the disc surface. To vary the depth of the cut, relative axial movement between the tool and the disc is provided. Tne disc 50 is also caused to rotate to provide feed for the tool 77.

Ir The relative speed of the rotation of the disc compared to the tool 77 determines the finish on the surface. If the disc rotates more slowly than the tool, a milling process occurs at the surface. If the disc rotates at a faster speed than the .ool, then a process similar to a turning process occurs though the rake angle of the cutter would not remain constant as in an ideal turning process due to the rotation of the cutter shaft. t "l'.d130798.OC 14 ApA, 1998 I'!;sraeadth ol7 oae bottesatcuig h utr omv r0 U V .i: I0 0 I*004 0* L. 0 0000~r

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The milling process is preferred because the resultant finished texture is of a cris-cross pattern 84 (which is illustrated in Figure 11) which is believed to be better for burnishing the surface than the pattern produced by a turning process, which is similar to a spiral.

To prepare the inboard braking surface, a similar tool (not shown) is used except the cutters face outboard rather than inboard as in the tool 77. The inboard suiface may be prepared separately or simultaneously with the preparation of the outboard surface. In the latter arrangement, the two machining tools would typically be spaced circumferentialiy about the disc.

An alternative tool 82 is illustrated in Figure 10. This tool is substantially the same as the tool illustrated in Figure 9 except that an additional head 83 is incorporated on a concentric shaft 85 in a position spaced from the head 78. In this arrangement, cutters are located on opposing faces of the heads 78 and 83 and as in the earlier embodiment, the cutters on each head are radially spaced 15 from the axis of rotation of the shaft and separated by an angle which is approximately 180°, though other angles may be used. For example the angle may be 90° which may assist in minimising vibration. The concentric shaft 85 is provided to enable axial displacement between each head and the disc to enable the depth of cut to be varied.

With the tool 82 the inboard and outboard braking surfaces can be processed simultaneously thereby enabling the processing time to be further redil'ed. In other respects the tool 82 processes the faces on the disc in the same way as the earlier embodiment. In yet another alternative, two heads are provided spaced along the axis of the shaft with each head only having a single cutter which is arranged to cut a respective one of the opposing inboard and outboard faces. :n this arrangement, each cutter is radia'jly spaced from the axis of rotation of the shaft with the angle between the cutters about the axis of rotation being typically zero such that the cutters are arranged to straddle a particular portion of the disc, or at approximately 1800 such that one cutter is arranged to engage the inner portion of the disc while the other cutter engages the outer portion or at any other relative angular position.

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t EAfJKM3o798.DOC 14 Apria. I9M8 14 In an alternative arrangement (not shown) the first portion of the disc may be formed separately from the second portion and may be processed individually, or assembled, and then processed simultaneously. Each of these pieces may be formed in one uniform material or may be composite or incorporate inserted portions.

In the manufacture of the disc either as a single piece or in separate pieces, each portion may be solid or ventilated or the disc may be formed with one portion ventilated and the other solid depending on the performance characteristics required.

It will be appreciated from the foregoing description that the disc brake assembly, sub assembly, disc and method of forming same in accordance with the invention provides an arrangement which is better able to accommodate the loads involved in operation of the brake assembly while being of light weight construction, being relatively inexpensive and effective in dissipating heat.

S Finally it is to be understood that various alterations, modifications and/cr additions may be introduced into the construction and arrangements previously described without departing from the spirit or ambit of the invention described.

E;ADJH\M3079B.OOC 14 AprX 1998

Claims (5)

1. A disc for a disc brake assembly, the disc being rotatable aoout an axis of rotation and including a radially oiter portion and a radially inner portion, each of the outer and inner portions having a braking surface on each of two opposite sides thereof and a gap forming a radial separation between said outer and inner portions and extending in a continuous circle co-axial with said axis of rotation, and connecting means spaced from the braking surfaces and interconnecting the inner and outer portions of the disc, the connecting means being in the form of a bracket located on one side of the disc, the bracket being spaced from the braking surface on that side of the disc to form a cavity in which a brake pad assembly is able to be located, the bracket further incorporating at least one passage providing access to the cavity.

02. A disc according to claim 1, wherein the bracket includes a plurality of passages.

3. A disc according to either claim 1 or 2, wherein the bracket is adapted to be connected to a hub of a wheel assembly so as to connect the disc to said o owheel assembly.

4. A disc according to any preceding claim, wherein at least one of the inner

900. or outer portions is formed from a plurality of segme its. 5. A disc according to any preceding claim, wherein the inner and outer portions and the bracket are formed as a unitary construction 6. A disc according to any one of claim 1 to 4, wherein the inner and outer portions are connected to the bracket. 7. A disc according to any preceding claim, wherein the inner and outer portions are fixed to said bracket. 8. A disc according to claim 6, wherein at least one of the outer or inner portion is movable relative to the other of the outer or inner portion in a direction substantially parallel to the axis of rotation of the disc. 9. A disc according to any preceding claims, wherein the inner and outer portions are formed from different materials. A disc according to any preceding claim, wherein the braking surfaces are machined on the inner and outer portions using a chip producing process. ;jz_ 16 11. A method of forming a disc for a disc brake assembly, the disc being rotatable about an axis of rotation and including a radially outer portion and a radially inner portion, each of the outer portion and the inner portion having two opposite sides thereof and a gap forming a radial separation between said outer and inner portion and extending in a continuous circle coaxial with the axis of rotation, the method including the steps of: providing a tool including a central shaft and including at least one cutting head having a cutting edge radially spaced from, and rotatable about, the shaft; (ii) locating the cutting tool such that the cutting head is on one side of the disc with the shaft being substantially aligned with said gap; (iii) rotating the shaft to cause the cutting head to move in a circular path such that the cutting edge engages the one side of both the inner and outer portions of the disc on rotation of the shaft to thereby machine braking surfaces on the one side of both the inner and outer portions of the disc. 12. A method according to claim 11, wherein the shaft of the cutting tool is parallel to said axis of rotation. 13. A method according to either claim 11 or 12, further including the step of: locating the cutting tool relative to the disc such that the shaft extends through said gap. 14. A method according to any one of claims 11 to 13, further including the steps of: providing the tool with a second cutting head having a cutting edge radially spaced from the shaft, the second cutting head being spaced from the first cutting head along the shaft; (ii) positioning the cutting tool such that the shaft extends through said gap and that the cutting heads are located on respective opposite sides of said disc; and (iii) rotating the shaft to cause both the cutting heads to move in a circular path such that the cutting edges engage respective ones of the sides of both the inner and outer portions of the disc on rotation of the shaft to thereby simultaneously machine braking surfaces on both sides of both the inner and outer portions of the disc. E0DJIA13079B.DOC 14 Apil, 1998 iN *1 17 A method according to any one of claims 11 to 14, further including the steps of: moving at least one of the cutting edges in a direction substantially parallel to the axis of rotation of the shaft to thereby vary the depth of cutting of that cutting edge on machining of the braking surfaces. 16. A method according to any one of claims 11 to 15, further including the step of: providing the tool with the or each cutting head including a plurality of cutting edges angularly spaced around the shaft. 17. A method according to any one of claims 11 to 16, further including the step of: t ol rotating the disc about the axis of rotation to provide feed for the cutting; I ti too l. 18. A method according to claim 17, further including the step of: varying the speed of rotation of the disc relative to the speed of rotation of 0 o the shaft to vary the surface finish on the braking surfaces. 19. A disc for a disc brake assembly substantially as herein described with reference to the accompanying drawings. 20. A method of forming a disc substantially as herein described with reference to the accompanying drawings. DATED: 14 April, 1998 PHILLIPS ORMONDE FITZPATRICK Attorneys for SPBR AUTOMOTIVE PTY LTD L E:DJH:\13079B.DOC 14 April, 1998 ABSTRACT A disc brake assembly 100 is disclosed which includes a disc 50 having axis of rotation 51 and including a radial inner portion 54 and a radial outer portion 55 separated by a continuous circumferential gap 56. Pad assemblies 11, 12 are located on respective sides of the disc 50 and each is engagable, on respective sides of the disc, with both the inner and outer portions. A piston cylinder assembly 22, 23 having a piston 26 and a cylinder 24 is provided for movement of the pad assemblies into engagement with the disc. The cylinder 24 is connected to the inboard pad assembly 11 and a draw bar 29 is provided which extends co-axially with the axis of movement of the piston cylinder assembly through the gap 56 to connect the piston 26 to the outboard pad assembly 12. S* i 0 99 9 a e E E EADml13079B.DOC