Brakes – Elements – Brake wheels
Reexamination Certificate
2001-03-30
2002-09-10
Butler, Douglas C. (Department: 3683)
Brakes
Elements
Brake wheels
C188S073200, C188S25000B, C188S2640AA, C188S071600
Reexamination Certificate
active
06446770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to rotors, especially to brake rotors used in high performance vehicles. The invention also relates to ventilated brake rotor assemblies including a pair of spaced brake pad contact surfaces separated by a plurality of vanes.
2. Description of Related Art
Conventional brake assemblies include a brake rotor with a brake pad contact surface for contact with brake pads associated with a vehicle wheel to effect braking. The brake pad contact surface can be an annular ring that engages with the brake pad, which is typically a high friction material, to stop rotation of the brake rotor, which is connected to a hub of a wheel assembly.
High performance vehicles require superior braking power to effect braking at high vehicular speeds and to quickly stop rotation of the vehicle wheel hub assembly. Conventional rotors typically have a smooth brake pad contact surface, which does not provide sufficient friction required for high performance vehicles and heavy duty vehicles. Some prior art rotors have been designed to increase friction by modifying the surface of the rotor to provide some texture.
However, another problem associated with brake rotors, particularly in high performance applications, is the high heat generated across the brake pad contact surface during braking. Heat generation, particularly with increased friction, results in an uneven thermal gradient, thermal distortion of the brake pad contact surface and heat stress that deteriorates the rotor disc. Such heat effects can result in increased replacement and maintenance costs for high performance brake rotor assemblies. None of the prior art assemblies provide a high friction surface that can handle the stresses imposed by heat generated during braking in high performance vehicles.
One known way to handle the heat generated during braking is to use a ventilated brake rotor. This type of brake rotor includes a pair of brake pad contact surfaces spaced from each other, generally by a plurality of spaced vanes or ribs. The vanes or ribs allow air to circulate under the brake pad contact surface for cooling.
However, ventilation alone does not remedy problems associated with non-uniform heat distribution across the brake pad contact surface that can create thermal distortion and frictional instability. Ventilated brake rotors have uneven temperature gradients over their brake pad contact surfaces. This is due to the heat sink capability of the vanes underneath the brake pad contact surfaces. Heat generated on the brake pad contact surfaces on the areas that overlap a vane is directly transferred to the corresponding vane. Heat generated during braking on the brake pad contact surfaces on the areas between vanes is not directly transferred to a vane. Accordingly, the temperature of the brake pad contact surfaces in the areas between vanes is higher than in the areas that overlap a vane. This non-uniform temperature gradient contributes to thermal distortion on the rotor brake pad contact surfaces. The thermal distortion results in non-uniform contact between brake pads and the brake pad contact surfaces which further increases the thermal gradient, causes premature rotor and pad wear, and increases thermal judder and vibration. Thermal distortion further results in thermal checking in the rotor and decreased rotor life.
Further, conventional ventilated rotors do not provide sufficient friction for high performance applications.
SUMMARY OF THE INVENTION
One aspect of the embodiments of the invention is to provide a rotor with a brake pad contact surface that offers superior braking power and performance. The surface can increase friction and stopping power while maintaining frictional stability throughout the braking application.
Another aspect of the embodiments of the invention is to provide a rotor with a brake pad contact surface that reduces the non-uniform temperature distribution (thermal gradient) across the brake pad contact surface during automobile braking. Accordingly, thermal distortion and the numerous problems associated with thermal distortion is minimized.
An additional aspect of the embodiments of the invention is to provide a rotor with a brake pad contact surface that performs with reduced vibration and thermal judder during braking, especially due to the decreased thermal distortion. Accordingly, a decrease in thermal distortion contributes to smooth braking.
A further aspect of the embodiments of the invention is to provide a rotor with a brake pad contact surface in which the thermal gradient across the surface is reduced, resulting in decreased thermal checking and an increase in rotor life.
Also, the embodiments of the invention provide a rotor in which uniform contact is promoted between the rotor and brake pads. Non-uniform contact typically results from thermal distortion. Uniform contact can result in a decrease of taper and radial wear on the pads and an increase in pad life. Uniform contact also can decrease uneven wear. Uniform contact also minimizes undesirable frictional variability between the pads and the brake pad contact surface.
The embodiments of the invention further provide a cleaning characteristic to the brake pads. This cleaning characteristic further decreases the occurrence of a transfer layer on the brake pad contact surface. The cleaning characteristic also cleans pad wear debris from the brake pad contact surfaces. A transfer layer, and pad wear debris contribute to undesirable frictional variability between the pads and the brake pad contact surface. The transfer layer includes brake pad and rotor particles that have been deposited on the brake pad contact surface.
The various design possibilities and optimal design for each particular braking application can be established using finite element analysis based on computer simulations. Goals of the ultimate design can include increasing friction between brake pads and the brake pad contact surface, and decreasing the thermal gradient and thus decreasing thermal distortion on the rotor.
Other aspects, advantages and objects of the invention will become apparent with the description herein, especially when taken in conjunction with the detailed description and drawings.
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Stock Car Racing Magazine, Feb. 1997, p. 74, 188/268XL.
Burgoon Donald L.
Killeen Seen E.
Qian Wenqi
Butler Douglas C.
Performance Friction Corporation
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