Most automotive vehicles currently produced have disc brakes on at least the front wheels. Additionally, many automotive vehicles including trucks now include disc brakes on the rear wheels. The majority of disc brakes include a rotor which is attached to the vehicle wheel via a hub. Extending radially outward from the hub is a braking portion. The braking portion typically includes two discs. A inner disc is typically directly connected to the hub along its inner diameter. An outer disc is spaced away from the inner disc and is connected to the inner disc by a plurality of radial ribs. The ribs have two functions. First, to connect the outer disc to the inner disc, and second, to provide a flow path between the discs to allow for air cooling of the rotor. The first and second discs provide opposed surfaces first and second friction faces. The friction faces are engaged by inner and outer brake pads. The brake pads engage the friction surfaces in response to a fluid actuated brake caliper. The brake caliper is supported by the vehicle suspension system to be adjacent to the rotating rotor.
Since the rotor is attached to the wheel, it is required that the rotor be balanced. Many rotors are fabricated by a gray iron casting process. Therefore most rotors require a balancing correction after finish machining. To balance the rotor, typically the peripheral outer diameter edges are machined. The machining of the disc rotor causes the friction faces of the rotor to have a non-constant radius outer diameter.
To achieve aerodynamic efficiency, the hood and roof heights of automotive vehicles have been reduced. Accordingly, the space envelope between the top of the wheel well and the disc brake caliper has been minimized. To achieve maximum brake pad wear life, the engagement surface area of the brake pads should be as large as practically possible. However, from a noise wear and vibration standpoint, the engagement surface area with the brake pads should be constant regardless of the angular orientation of the rotor. When the rotor has been balanced by circumferentially machining off a part of its perimeter at the outer diameter of the rotor, the brake pads will have the situation of fluctuating engagement area with the rotor depending upon the rotor's angular orientation. This situation of non-constant area engagement can be a generator of undesirable wear and noise. The noise parameter is especially critical in providing a commercially attractive product.
One way to avoid shaving off the perimeter of the rotor to achieve balancing is to add weights to the rotor. The addition of weights is undesirable due to the possibility of their breaking off after prolonged periods of use. Additionally, it is difficult to weld on weights or add weights by virtue of a weld bead due to the metallurgical properties of many of the rotors. Accordingly, it is desirable to provide a method of balancing disc brake rotors while providing friction surfaces which have a constant radius outer diameter with a radial center coterminous with the axis of the rotor without requiring the connection of additional weight to the rotor.