Patent Application
20060027429
The subject invention relates to a composite brake drum with a metal matrix composite liner that provides a less corrosive wear surface.
A brake drum is formed as a cylindrical component having an outer surface and an inner surface defining an internal cavity. The inner surface provides a braking surface, also referred to as a wear surface, which is selectively engaged by a brake shoe assembly. The brake shoe assembly is mounted within the internal cavity and includes a pair of shoes, each of which supports a brake lining. During normal vehicle operation, the brake drum is rotating while the shoes are non-rotating. In response to a braking command, the shoes are moved into engagement with the wear surface to slow or stop rotation of the brake drum.
Typically, brake drums are formed from cast iron and include a ferrous wear surface. This type of brake drum is heavy and the ferrous wear surface has a tendency to corrode. Corrosion significantly degrades the wear surface, which can adversely affect brake operation and brake lining wear.
In order to improve fuel economy, some brake drums are formed from a lightweight material. These brake drums must also provide a long lasting wear surface. One type of lightweight brake drum includes an outer cylindrical component having an outer surface and an inner surface with an inner component attached to the inner surface. The outer cylindrical component is formed from a metal matrix composite, which is much lighter than a conventional cast iron brake drum. The inner component is formed from a ferrous material that provides a ferrous wear surface.
While this configuration provides a lighter brake drum, the problem with corrosion still exists. With this type of brake drum, corrosion can affect adhesion of the brake linings on the shoes to the ferrous wear surface.
Thus, there is a need for a brake drum that has a less corrosive wear surface.
A composite brake drum includes an outer cylindrical component and an inner liner. The outer cylindrical component has an outer surface and an inner surface that defines an internal cavity. The inner liner is mounted within the internal cavity and is attached to the inner surface to provide a braking or wear surface. The outer cylindrical component is formed from a first material and the inner liner is formed from a second material that is less corrosive than the first material.
Preferably, the second material is a metal matrix composite. In one example, the metal matrix composite includes silicon carbide aluminum (SiCAl). In one disclosed embodiment, the first material is cast iron and the inner liner is either press-fit or cast into the internal cavity of the outer cylindrical component. In another disclosed embodiment, the first material is stamped steel and the inner liner is cast or press fit into the internal cavity of the outer cylindrical component.
In one disclosed embodiment, the outer cylindrical component includes a plurality of protrusions formed on the inner surface. The plurality of protrusions provides a good attachment surface for a cast inner liner. In one example, the plurality of protrusions is formed as a plurality of ribs with each rib having a generally trapezoidal profile.
The subject invention provides a composite brake drum with improved lining-to-drum adhesion characteristics. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A brake drum, shown generally at 10 in
The brake drum 10 also includes an inner component 24 that is mounted within the internal cavity 22, and which is attached to the inner surface 16 of the outer component 12. The inner component 24 provides a braking surface 26, which is also referred to as a wear surface. A brake shoe assembly (not shown) includes a brake lining that is selectively moved into engagement with the braking surface 26 in response to a braking command.
The outer component 12 is formed from a first material and the inner component 24 is formed from a second material that is less corrosive than the first material. The first material is preferably a cast iron or stamped steel material, however, other materials could also be used. The second material is preferably a metal matrix composite material. One example of a metal matrix composite material is silicon carbide aluminum (SiCAl), however, other metal matrix composites could also be used.
In one example, the outer component 12 is a cast iron brake drum and the inner component 24 is a liner. The inner surface 16 can be machined out by a predetermined amount, such as six (6) millimeters, for example, and the liner can be press-fit into place within the internal cavity 22. The press-fit generates a sufficient retaining force between the cast iron brake drum and the liner to permanently attach the liner to the cast iron brake drum. Dowel pins or some other shear retainer may also be required to permanently attach the liner to the cast iron brake drum.
In another example, the outer component 12 is a cast iron brake drum that includes a plurality of protrusions 30 formed on the inner surface 16 (see
Preferably, the protrusions 30 are formed as a plurality of ribs 34 with each rib 34 having a trapezoidal profile (see
In another example, the outer component 12 is formed from a stamped steel material and the inner component 24 is formed from the metal matrix composite material. The metal matrix composite material is cast or pressed into the outer component 12, as described above. The outer component 12 formed from stamped steel material may or may not include protrusions. In this configuration, the metal matrix composite might be formulated to minimize thermal expansion, to better match the ferrous material forming the outer component, while also providing superior wear properties compared to traditional cast iron. This formulation process is within the knowledge of one of ordinary skill in the art.
In each of these configurations, the metal matrix composite provides a less corrosive wear surface than would be provided by a traditional ferrous wear surface. This significantly reduces the propensity for the brake lining to adhere to the wear surface.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
