WO2005003586A1

WO2005003586A1 - Brake drum

Info

Publication number: WO2005003586A1
Application number: PCT/US2004/020781
Authority: WO
Inventors: Graham Rex Withers
Original assignee: Cyco Systems Corporation Pty Ltd.
Priority date: 2003-06-27
Filing date: 2004-06-28
Publication date: 2005-01-13

Abstract

A brake drum (10) including an outer rim region (12) defining a circumferentially and axially extending inwardly facing braking surface (15) adapted, to cooperate with at least one brake shoe of a braking mechanism. The outer rim region (12) includes a plurality of circurnferentially spaced, axially and radially extending heat dissipation fins (19). The outer rim region (12) also has outwardly facing peripherally extending surfaces located between the heat dissipation fins (19) located radially inwardly of outer tips of the fins (19). The brake drum is characterized by a reinforcing ring (23) connecting all adjacent fins (19) and is located radially outwardly of the outwardly facing peripherally extending surfaces and radially inwardly of the outer tips of the heat dissipation fins (19).

Description

BRAKE DRUM

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Australian Provisional Application Serial Nos. 2003903272 filed on 27 June 2003 and 2003903406 filed 2 July 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvements in brake drums, particularly of the type having a plurality of brake shoes operating or braking on an inwardly facing circumferential braking surface.

2. Background Art

As is well known with brake drums of the aforementioned kind, the heat developed during a braking operation tends to cause the open axial end of the braking surface to expand to a greater extent than the inner axial end of the surface which is physically restrained by the drum web material extending from its central boss to the outer rim defining the brake shoe cavity and the braking surface itself.

As a result of this differential expansion, braking effect is lost or diminished over the axial width of the braking surface, thus causing a phenomenon known as brake fade. This problem is partially assisted by providing heat dissipation radially through extending fins positioned on the outer surfaces of the brake drum to lower the heat generated at the braking surface. However even with such fins provided, the brake fade phenomenon still occurs with such drums. SUMMARY OF THE INVENTION

One objective of the present invention is to provide a brake drum configuration of the above-discussed type which will further alleviate the problem of diminished braking effect when the brake drum becomes over heated. Accordingly, the present invention provides a brake drum including an outer rim region defining a circumferentially and axially extending inwardly facing braking surface adapted, in use, to cooperate with at least one brake shoe of a braking mechanism. The outer rim region includes a plurality of circumferentially spaced, axially and radially extending heat dissipation fins. The outer rim region further includes outwardly facing peripherally extending surfaces located between the heat dissipation fins located radially inwardly of outer tips of the fins. The brake drum is characterized by a reinforcing ring connecting all adjacent fins. The ring is spaced radially outwardly of the outwardly facing peripherally extending surfaces and radially inwardly of the outer tips of the heat dissipation fins. By providing a reinforcing ring as defined above, the heat dissipation effect of the fms is either not affected at all, or if it is affected, the effect is minimal. Differential expansion of the open outer end of the braking surface is resisted by the provision and location of the reinforcing ring.

BRIEF DESCRIPTION OF THE DRAWINGS One preferred embodiment of a brake drum according to this invention is shown in the annexed drawings, in which:

FIGURE 1 is a perspective view from the brake cavity side of the brake drum;

FIGURE 2 is a perspective view from the other side of the brake drum shown in Figure 1; FIGURE 3 is a front elevation view of the brake drum shown in Figure 1;

FIGURE 4 is a rear elevation view of the brake drum shown in Figure 2; FIGURE 5 is an edge elevation view of the brake drum shown in

Figures 1 to 4;

FIGURE 6 is a cross-sectional view along line A in Figure 4;

FIGURE 7 is an enlarged detail view of detail B in Figure 6; and

FIGURE 8 is an enlarged partial cross-sectional view along line C of Figure 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to the drawings, there is illustrated a brake drum 10 with an optional central boss region 11 and an outer rim region 12 interconnected by a web flange 13 of any conventional type. The web flange 13 is located generally at one axial end of the boss region 11 and outer rim region 12 to define a brake cavity

14 therebetween.

One inwardly facing surface 15 of the outer rim region 12 forms a cylindrical braking surface and defines the radially outer limit of the braking cavity 14. In use, the braking surface 15 is engaged by friction surfaces of at least one braking shoe (typically two opposed braking shoes) during a braking operation. The (optional) central boss region 11 may including a bore 16 to mount bearings and a shaft (not shown) to be braked with the braking shoe or shoes of the brake assembly being mounted to the chassis. The web flange 13 may include reinforcing ribs 17 and a number of bolt holes 18 to enable the drum to be secured to a wheel.

The outer rim region 12 includes a plurality of heat dissipation fins 19 extending radially outwardly from peripherally extending outwardly facing surface sections 20 of the outer rim region 12. The fins 19 extend generally radially and axially, i.e. in a direction parallel to the axis 21 (Figure 4) of the bore 16, for the shaft to be braked. Each fin 19 has a radially outer tip zone 22. A reinforcing ring 23 is formed. This ring 23 connects all adjacent fins 19 roughly midway along their radial length such that the ring 23 is located spaced outwardly from the surface sections 20 and inwardly of the fin tips 22.

As can be seen in Figures 6 and 7, the ring 23 conveniently has a generally rectangular cross section and may have an axial length slightly greater than that of the braking surface 15. In the embodiment illustrated in Figure 7, the axial length of the reinforcing ring 23 is less than that of the fins 19. In other arrangements, the reinforcing ring 23 may extend to the full axial length of the fin 19 or beyond. It is preferred that at least a portion of the ring 23 is located at but radially outwardly of the open face 24 of the braking cavity 14. As further can be seen in Figures 6 and 7, a portion 25 of the fins 19 may be arranged to extend radially inwardly of the braking surface 15 while extending also in an axial direction. This may be achieved by angling a portion 26 of the rearwardly facing surface 27 of the web flange 13 in an axial direction between the fins 19. If desired, a mechanism for an automatic braking system (ABS) speed control for the brakes is cast as an integral unit. A proximity sensor reads the speed of the road wheel RPM. It is circular, i.e. in a radius or on a pitch circle diameter, central to the bearing housing. An involute gear tooth pattern may be provided on the end of the bearing housing. A proximity sensor may produce an electrical signal from the tooth pattern. The signal is communicated to an electronic control unit (ECU) as a function of the speed at which the brake drum is turning. As the wheel is attached to the drum, this allows the ECU that operates the ABS to know at what speed (RPM) the wheel rotates. Alternatively, a series of the equally spaced lugs may be provided on a desired pitch circle diameter that is located on the inner face of the wheel mounting flange of the brake drum. These lugs are used to trigger a motion detector which is mounted on a stationary brake backing plate to generate an electronic signal for the ABS computer controller. One advantage is to produce a low cost, compact, accurate means for determining the angular velocity of the brake drum during the operation of a braking system.

One preferred method and apparatus that will produce the brake drum disclosed herein is the subject of U.S. Patent Application Serial No. 10/753,651, filed January 8, 2004, the disclosure of which is incorporated here by reference. That patent application discloses a method and apparatus for the production of metals and/or metal-based materials and/or metal matrix composite materials. They are characterized by a fine globular or spherical microstructure.

Accordingly, in one aspect, the present invention provides a method of producing semi-finished or finished brake drums from such metal-based materials. The method includes the steps of:

(i) . maintaining a metal-based material in a mixing furnace in a thixotropic semi-solid state (a liquid-like slurry);

(ii) subjecting the material to a continuous shearing and mixing action and a centrifugal force while in a thixotropic semi- solid state within the mixing furnace to form a fine, globular microstructure (down to about 0.5 microns in diameter); (iii) delivering the material involutely from the mixing furnace while in the thixotropic semi-solid state to a delivery site, such as a casting head or into the introduction chamber of a molding machine; and (iv) transporting the material in the thixotropic semi-solid state into a mold or die cavity of the molding machine from the delivery site to form the semi-finished or finished brake drum.

Optionally, a low density foam core may be used, such as that shown in USPN 5,992,500 (incorporated herein by reference) and then the desired light metal is die-cast over it. Suitable light metals include aluminum, magnesium, metal- mineral composites and alloys thereof. Alternatively, the foam may be used as an insert to reduce the amount of solid metal in the central boss region. This methodology reduces weight and reduces the amount of aluminum in the casting, but still has the necessary strength in the hub area.

The problems associated with noise, vibration and harshness (NNH) resulting from the brake friction linings are ameliorated by the foam/aluminum combination and should assist in reducing transmission noise.

Optionally, the aluminum housing may be extended out to a larger diameter.

It is desirable to exclude moisture or water from the internal components of the brake drum to avoid the brake "freezing up" or locking due to the formation of an ice coating between brake friction linings and the brake drum. Unless prevented, the freezing may occur when the vehicle is stationary or parked overnight in subzero temperatures. Unless prevented, such an ice coating could be formed between the rotating surface of the inner brake drum and the non-rotating brake shoes. To address this concern, a "U"-shaped cross section groove can be provided in the bore of the open end of the brake drum. Into this groove is fitted a sealing ring (such as a Teflon^® or an "O"-ring made of suitable polymer). The sealing ring remains in contact with the stationary back plate peripheral surface. The brake drum assembly is then sealed by the O-ring located in the U-shaped groove, thereby preventing the entry of water or moisture into the braking chamber. The brake drum wheel bearing is usually cast integrally and is attached to the axle spindle by a self-locking, threaded nut. The wheel bearing is usually fitted into a solidified brake drum casting by first machining an accurate stepped bore into the hubbed brake drum, into which is pressed a low friction sealed roller or ball bearing assembly. An improved lower cost method involves placing the bearing (usually by a robotic arm) which may be preheated to control the amount of solidification crush into a die cavity which clamps the bearing in place when the casting die closes. A semi-solid aluminum-mineral metal composite (usually preferred) is injected into the closed die. This causes the metal to flow around the periphery of the outer bearing casing. Metal shrinkage then locks the bearing in place. In some instances or applications, the casting die can be changed to allow the metal to form shoulders or mini-flanges to give greater (or higher) locking values for the retention of the bearing in the aluminum hub section of the brake drum. This casting process is facilitated by a very low latent heat value of the casting material. This reduces the machining costs needed and eliminates the cost of preventing the brake drum from creeping or walking under extreme axial loads imposed upon the brake drum. These loads would be imposed by abrupt turning or cornering of the vehicle or colliding into a stationary object such as a curb.

Additionally, while at an elevated temperature, a single (or multi) groove(s) may be ground or machined into the periphery of the bearing casing to assist in the locking action of the bearing in the hub.

The integral casting of the brake drum wheel bearing is usually attached to the axle spindle by a hexagonal self locking threaded nut. The wheel bearing is usually fitted into the solidified brake drum casting by first machining an accurate stepped bore in the hub of the brake drum, into which is pressed a low friction sealed roller or ball bearing assembly. In using the disclosed brake drum, significant weight savings are obtained over conventional cast iron brake drums which, excluding the weight of bearings, may weigh about 5.3 kilograms. In contrast, the disclosed brake dram

(prepared with an alummum-mineral metal composite material) may weigh about 2.2 kilograms.

The foregoing description is intended to relate to a preferred embodiment of the invention but variations and modifications thereof are possible within the scope of the annexed claims.

Claims

WHAT IS CLAIMED IS: 1. A brake drum including an outer rim region defining a circumferentially and axially extending inwardly facing braking surface adapted to cooperate with at least one brake shoe of a braking mechanism, the outer rim region including a plurality of circumferentially spaced, axially and radially extending heat dissipation fins, the outer rim region further including outwardly facing peripherally extending surfaces located between the heat dissipation fins located radially inwardly of outer tips of the fins, the brake drum being characterized by a reinforcing ring connecting all adjacent fins and located radially outwardly of the outwardly facing peripherally extending surfaces and radially inwardly of the outer tips of the heat dissipation fins.

2. A brake drum according to claim 1 wherein a web flange connects a central boss region to the outer rim region adjacent one axial end of the central boss region, thereby defining a braking cavity with one wall of the cavity being formed by the braking surface.

3. A brake drum according to claim 2 wherein each of the heat dissipation fin extends radially inwardly from the outer tips to a position intermediate the braking surface and the central boss region.

4. A brake drum according to claim 3 wherein each of the heat dissipation fin extends axially from an outer surface of a radially outer region of the web flange.

5. A brake drum according to claim 1 wherein the reinforcing ring has an axial length substantially equal to that of the heat dissipation fins.

6. A brake drum according to claim 1 wherein the reinforcing ring has an axial length less than that of the heat dissipation fins.

7. A brake drum according to claim 1 wherein the reinforcing ring has a generally rectangular cross section.

8. A brake drum according to claim 1 wherein the reinforcing ring has an axial length that exceeds that of the inwardly facing braking surface.

9. A brake drum according to claim 2 wherein the reinforcing ring extends radially outwardly from a wall of the braking cavity.

10. A brake drum according to claim 1 wherein at least some of the fins extend radially inwardly of the braking surface.

11. A brake drum according to claim 10 wherein a portion of the fins extends also in an axial direction, the portion being disposed at an angle in relation to a rearwardly facing surface of the web flange in an axial direction between the fins.

12. A brake drum according to claim 1 further including an automatic braking system speed control that is cast as an integral unit.

13. A brake drum according to claim 12 further including a proximity sensor that generates a signal as a function of wheel rotation speed.

14. A brake drum according to claim 12 urther including an involute gear tooth pattern that is provided on an end of a bearing housing, the proximity sensor producing an electrical signal as a function of tooth pattern, the signal being communicated to an electronic control unit (ECU) in proportion to the speed at which the brake dram turns.

15. A brake drum according to claim 1 wherein the outer rim region includes a foam core.

16. A brake drum according to claim 1 wherein the central boss region includes a foam core.

17. A brake drum according to claim 15 comprising a shell formed from a light metal.

18. A brake drum according to claim 6 wherein the axial length of the reinforcing ring approximates but is greater than the axial length of the braking surface.

19. A brake assembly including a brake drum according to claim 2, further including at least one brake shoe mounted at least partially within the braking cavity, each brake shoe having a friction surface that is engageable with the braking surface.

20. A method for making a brake drum comprising: providing an outer rim region with a circumferentially and axially extending inwardly facing braking surface that is adapted to cooperate with a brake shoe; providing circumferentially spaced, axially and radially extending heat dissipation fins; disposing outwardly facing peripherally extending surfaces between the heat dissipations fin, the surfaces being located radially inwardly of the outer tip fins; and providing a reinforcing ring that connects all adjacent fins, the reinforcing ring being located radially outwardly of the outwardly facing peripherally extending surfaces and radially inwardly of the outer tips of the heat dissipation fins.