Brake rotor assembly

A brake rotor assembly for a dual brake disc braking system includes an annular ring having a plurality of teeth. The teeth are disposed radially about a central axis of the annular ring, and extend inward toward the central axis. The teeth are for slideably engaging a hub (wheel end) having a plurality of channels. The annular ring includes a plurality of pins extending outwardly from the annular ring. A friction disc is disposed radially about the annular ring, and is in interlocking engagement with the plurality of pins. The annular ring and the plurality of teeth are integrally cast from a high strength corrosion resistant material having a tensile strength greater than 260 megapascals to resist fracture during high stress braking conditions and high thermal loads. The friction disc is cast around the annular ring from a grey cast iron.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to a brake rotor assembly for a disc braking system of a vehicle, and further relates to a method of producing the brake rotor assembly.

2. Description of the Prior Art

Disc braking systems for vehicles utilize a brake caliper to urge a pair of brake pads into frictional engagement with a brake rotor (brake disc) to provide a braking force to the vehicle. In order to increase the braking force applied by the disc braking system, it is known to incorporate a second brake rotor into the disc braking system. This may be referred to as a dual disc braking system. The dual disc braking system necessitates that a first brake rotor be slideable along a central axis relative to a second brake rotor. The first brake rotor slides over and rotates with a hub (wheel end or axle). The slideable first brake rotor compensates for wear in the brake pads over time. Accordingly, as the brake pads wear, the first brake rotor slides over the hub along the central axis to compensate for the wear in the brake pads. The slideable first brake rotor typically includes teeth extending inwardly from an inner periphery of the first brake rotor toward the central axis. The teeth are disposed radially about the central axis for engaging channels in the wheel hub for transmitting rotational movement therebetween. The teeth may be integrally cast with the first brake rotor. Typically, the brake rotor and the teeth are cast integrally together from a grey cast iron. However, the grey cast iron tends to fracture under certain high stress braking conditions and high thermal loads generated by the frictional engagement between the brake pads and the brake disc. Additionally, the grey cast iron tends to corrode at the toothed engagement between the teeth of the brake rotor and the groove in the hub, thereby bonding the brake rotor to the hub.

Alternatively, as disclosed in U.S. Pat. No. 4,540,067 (the '067 patent), the first brake rotor may be an assembly wherein an annular ring forms the teeth and is attached to a friction disc by a plurality of bolts. This type of assembly is often referred to as a composite brake rotor. The composite brake rotor, as assembled in the '067 patent, utilizes a portion of the friction disc to attach the annular ring thereto, thereby reducing a contact area between the brake pads and the friction disc and reducing the braking force provided by the disc braking system.

U.S. Pat. No. 5,109,960 (the '960 patent) discloses a method of producing a composite brake rotor. The method includes casting a hub to include a supporting ring extending radially outward from the hub. The hub is bolted to a wheel end, but is not slideable thereon. The supporting ring includes depressions extending across the supporting ring. The hub is placed in a mold, with a pair of parallel friction discs then being cast around the hub. The pair of friction discs include a plurality of webs extending therebetween. The plurality of webs interlock with the plurality of depressions in the supporting ring to interlock the friction discs and the hub. The hub is preferably cast from grey cast iron.

U.S. Pat. No. 5,823,303 (the '303 patent) also discloses a composite brake rotor. The brake rotor of the '303 patent includes a hub having a plurality of pins extending outwardly away from a central axis and disposed radially about the hub. The hub is bolted to a wheel end, but is not slideable thereon. A friction disc is cast around the hub, with the plurality of pins in interlocking engagement with the friction disc. As disclosed in the '303 patent, the hub and the plurality of pins may be integrally cast from gray cast iron. Alternatively, the hub may be formed from steel. When the hub is formed from steel, the plurality of pins may be formed from a high grade steel, such as stainless steel, and connected to the hub by welding or bonding.

Accordingly, there remains a need for a brake rotor suitable for use in a dual brake disc system having a plurality of teeth of sufficient strength to resist fracture while maximizing the contact area between the brake pads and the friction disc.

SUMMARY OF THE INVENTION AND ADVANTAGES

The subject invention provides a brake rotor assembly for a disc braking system. The assembly comprises an annular ring including a plurality of teeth extending inwardly toward a central axis and disposed radially about the central axis for slideably engaging a hub having a plurality of grooves. A plurality of pins is disposed on the annular ring, extending outwardly away from the central axis, and is disposed radially about the central axis. A friction disc is disposed radially about the annular ring, and is in interlocking engagement with the plurality of pins. The annular ring and the plurality of teeth include a material having a tensile strength greater than 260 megapascals.

The subject invention also provides a method of producing the brake rotor assembly. The method comprises the steps of casting the annular ring from the material having a tensile strength greater than 260 megapascals to form the plurality of teeth integrally with the annular ring; and forming the friction disc radially about the integrally cast annular ring and plurality of teeth.

Accordingly, the subject invention provides an improved composite brake rotor assembly suitable for use in a dual disc braking system. The high tensile strength material, having a tensile strength greater than 260 megapascals and forming the annular ring and the plurality of teeth, permit the brake rotor assembly to resist fracture under high stress braking conditions and high thermal loads. Additionally, the contact area between the friction disc and the brake pads is maximized by casting the friction disc around the annular ring instead of bolting the annular ring to the friction disc. The casting of the friction disc around the annular ring permits the contact area to extend all the way to the annular ring adjacent the plurality of teeth, without loosing any of the contact area to a bolted connection connecting the annular ring to the friction disc.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a brake rotor assembly is generally shown at20inFIGS. 1 and 2. The brake rotor assembly20is utilized in a disc braking system for a vehicle. The disc braking system operates as is known in the art, and includes a brake caliper (not shown) for urging a pair of brake pads (not shown) into frictional engagement with the brake rotor assembly20. The brake rotor assembly20is mounted to a hub22(wheel end or axle) by a splined connection as described below for rotation with the hub22. As is known with the disc braking system, the frictional engagement between the brake rotor assembly20and the brake pads supply a stopping force, transmitted through the brake rotor assembly20to the hub22, to slow the vehicle.

The brake rotor assembly20includes an annular ring24. The annular ring24includes a plurality of teeth26extending inwardly toward a central axis A, with the plurality of teeth26being disposed radially about the central axis A. The hub22includes a plurality of channels28complimentary in configuration to the plurality of teeth26; with the plurality of teeth26slideably engaged within the channels28of the hub22. As best shown inFIG. 4, the annular ring24and the plurality of teeth26are integrally formed together in a casting process.

As also shown inFIG. 3, the annular ring24further includes a rib32disposed around an outer periphery of the annular ring24. The rib32is disposed at an approximate midsection of the outer periphery of the annular ring24. Accordingly, the annular ring24may include a generally thin cross-section near the outer edges of the annular ring24, with the rib32having a larger cross section near the middle of the annular ring24. The rib32increases a bending/shear strength of the annular ring24to help prevent the annular ring24from fracturing during use, while still allowing for the generally thin cross section near the outer edges of the annular ring24.

Continuing withFIGS. 1 through 3, a plurality of pins34is disposed on the annular ring24, and extend outwardly away from the central axis A. The plurality of pins34is disposed radially about the central axis A, with the rib32of the annular ring24extending between the plurality of pins34. Preferably, the plurality of pins34are integrally formed with the annular ring24and the plurality of teeth26during a shaping process. Alternatively, as shown inFIG. 6, a plurality of recesses36are bored in to the annular ring24, through the rib32, and the plurality of pins34are pressed into the plurality of recesses36.

As best shown inFIGS. 1,2,4, and5, a friction disc38is disposed radially about the outer periphery of the annular ring24, and is in interlocking engagement with the plurality of pins34. Accordingly, the annular ring24and the friction disc38are separate components, with the plurality of pins34and the rib32aligning the friction disc38relative to the annular ring24. It should be understood that as the friction disc38is formed around the outer periphery of the annular ring24. The friction disc38also defines a plurality of pockets40for receiving the plurality of pins34. The friction disc38further defines a groove30in interlocking engagement with the rib32of the annular ring24.

As best shown inFIG. 4 through 6, the plurality of pins34and the rib32align and interconnect the friction disc38to the annular ring24, with the friction disc38extending to the outer edges of the annular ring24. Because the brake rotor assembly20does not utilize a bolted connection between the friction disc38and the annular ring24as shown in the prior art, the friction disc38is therefore able to extend around the rib32and into abutting engagement with the relatively thin cross section of the annular ring24. This permits an increase in a contact area between the friction disc38and the brake pads.

The annular ring24and the plurality of teeth26include a high strength material having a tensile strength greater than 260 megapascals, and preferably a corrosion resistance less than 80 milligrams per hour. The tensile strength, as referred to herein, is the greatest longitudinal stress a substrate can bear without breaking. The corrosion resistance is measured by a weight loss during a pre-determined period of time while exposed to saltwater at 25 degrees Celsius. When the annular ring24, the plurality of teeth26, and the plurality of pins34are integrally formed together, the plurality of pins34will also include the high strength material. The high strength material is preferably stainless steel, however it should be understood that some other material meeting the material characteristics described above may also be used to practice the subject invention. It should also be understood that if the plurality of pins34are not integrally formed with the annular ring24and the plurality of teeth26, then the plurality of pins34may not be formed of the high strength material.

Preferably, the friction disc38is formed from a gray cast iron material. However, it should be understood that the friction disc38may also be formed from some other material suitable for use as a brake disc in the disc braking system, such as a ceramic material.

The subject invention also provides a method of producing the brake rotor assembly20. The method comprises the steps of shaping the annular ring24from a material having a tensile strength greater than 260 megapascals to form the plurality of teeth26integrally with the annular ring24. The step of shaping the annular ring24may include a casting process, a forging process, or a machining process. It should be understood that some other manufacturing process may also be utilized to shape the annular ring24.

As discussed above, the plurality of pins34may be integrally shaped with the annular ring24and the plurality of teeth26. The high strength material used to shape the annular ring24, the plurality of teeth26, and if desired the plurality of pins34includes a tensile strength greater than 260 megapascals. Preferably, the high strength material also includes a corrosion resistance less than 80 milligrams per hour, wherein the corrosion resistance is measured by a weight loss during a pre-determined period of time while exposed to saltwater at 25 degrees Celsius.

If the plurality of pins34is not integrally shaped with the annular ring24and the plurality of teeth26, then the method further comprises the step of placing the plurality of pins34on the annular ring24. The step of placing the plurality of pins34into the annular ring24further comprises the steps of drilling a plurality of recesses36into the annular ring24, and pressing the plurality of pins34into the plurality of recesses36. Alternatively, the plurality of pins34may be bonded or otherwise affixed to the annular ring24.

The method further comprises the step of forming the friction disc38radially about the integrally cast annular ring24and the plurality of teeth26. When the friction disc38is formed from the ceramic material, the method further comprises the step of curing the friction disc38formed about the annular ring24. The curing process will vary dependent upon the type of material utilized for the friction disc38. When the friction disc38is formed from the gray cast iron material, the step of forming the friction disc38radially about the annular ring24is further defined as casting the friction disc38about the annular ring24.

The method further comprises the step of heating the annular ring24and the plurality of pins34prior to casting the friction disc38to pre-stress the annular ring24. In this manner, the annular ring24and the plurality of pins34will be hot when the friction disc38is formed. Heating the annular ring24and the plurality of pins34causes the annular ring24and the plurality of pins34to expand due to thermal expansion. The annular ring24remains in the expanded state as the friction disc38is formed around the annular ring24. Accordingly, both the annular ring24and the plurality of pins34shrink during cooling, reducing a compressive stress that the friction disc38exerts on the annular ring24, i.e., because the annular ring24is in the expanded state when the friction disc38is cast, the relative difference in the amount that the annular ring24and the friction disc38shrink is reduced, thereby reducing he compressive stress exerted on the annular ring24by the friction disc38as the friction disc38shrinks during cooling. It should be noted that the plurality of pins34extend radially outward from the annular ring24along a straight path. This allows for the radial expansion of the friction disc38when heated during use, without stressing the annular ring24or the plurality of pins34further.

The method further comprises the step of heating the assembly20after casting the friction disc38around the annular ring24to relieve any internal stresses in the assembly20. The internal stresses in the assembly20may lead to fracture of the annular ring24during use. Heat treating processes for relieving the internal stresses present in the assembly20are well known in the art, and not described in detail herein.

The method further comprises the step of milling the plurality of teeth26, a first side surface and a second side surface of the friction disc38to a final shape. Milling the first side surface and the second side surface of the friction disc38is further defined as turning the first side surface and the second side surface of the friction disc38. The final shape is milled after the rotor assembly20has been heat treated to relieve any internal stresses.FIG. 4shows the friction disc38before the milling process, with the first side and the second side of the friction disc38extending past the annular ring24.FIGS. 5 and 6show the friction disc38after the milling process, with the first side and the second side of the friction disc38milled flush with the annular ring24. Preferably, the plurality of teeth26is milled to the final shape after the first side and the second side of the friction disc38has been milled to the final shape. The plurality of teeth26must be precisely shaped. Therefore, it is important that the teeth26are milled after the first and second side surfaces of the friction disc38have been milled to avoid altering the final shape of the plurality of teeth26. Alternatively, it should be understood that the plurality of teeth26may be milled before the first and second side surfaces of the friction disc38. Milling and turning processes are well known in the art and are not described in detail herein.

The foregoing invention has been described in accordance with the relevant legal standards; thus, the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiments may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.