JOHN W. EVERT | Mechanical Engineering Technology
Requirements
Dimensionality
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Design is constrained so that it must function as replacement for a conventional circle track racing car design of 11.75” x 1.25” rotor sourced from an early 1970’s Chevrolet Impala, 3rd generation Corvette or 2wd full-size pickup of that era.
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Rotor body must mount to a dedicated hub bearing carrier assembly with eight 5/16” fasteners on a 7-inch bolt circle. This hub is a components-off-the-shelf assembly utilizing 2.0-inch inside diameter tapered roller bearings and serves as the conventional means for which the rotor is mounted by design to modern racecar.
Off-car testing
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Removal of 20% of the static mass from the assembly.
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Confirm an existing manufacturer’s claim of 34% reduction in the moment of inertia in a similar product.
On-car testing
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Rotor assembly must be able to resist the forces created by an angular velocity of 315 rad/sec
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Rotor must be able to dissipate the heat generated from 125 kilowatts of kinetic energy if mounted on the front axle of the racing car
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Rotor must be able to resist the torque provided by the linear deceleration rate of 8 m/s2
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Provide an experimental means to confirm the assumed forced convection constant.
ENGINEERING MERIT
In order to design the brake rotor to fit the stated design requirements several equations will be used. Equilibrium equations are necessary to determine resultant forces and moments about the X and Y axes. Determinants of the thermodynamic properties such as coefficient of expansion, theoretical temperature increase, and theoretical rate of thermal dissipation are all necessary to provide a baseline in the selection of the proposed materials. The dimensions are limited by the design constraints set forth by the conventional design. However, there is design latitude in part thicknesses considering dissimilar materials are being used so provided overall width, outside diameter, and rotor mounting bolt pattern limitations are observed. Direct shear stress, τavg=V/A, is necessary to determine the diameter and number of fasteners that will attach the friction surfaces to the rotor body. The number of fasteners and their diameter mounting the rotor body to the hat is established by the manufacturer of the unit. However the width of the body material surrounding the fastener is subject to analysis since the mechanism is in single shear and will place pressure along a semicircular area of the fastener length in the Y-axis. Finally, normal stress σ=F/A, is necessary to determine the amount of clamping force is present in the braking moment.
SCOPE OF EFFORT:
The scope of the project will involve the mechanical components of a vehicle’s hydraulic braking system. The evaluation is only of the mechanical aspect of a hydraulic braking system. The caliper, pads, rotor carrier, and bearings have already been produced by manufacturers and are not subject to evaluation. Due to a multitude of different concepts involving the braking system’s friction surface, slight alterations may be made to the rotor body and friction surface dimensions in order to work within the constraints set forth by the initial design criteria.
SUCCESS:
The objective of this project is to design a lighter rotor that maintains comparable structural performance to rotors that are currently commercially available. The success criteria are a direct result of the design requirements. Thus, for the brake rotor to be one hundred percent successful, it must meet all of the standards set in the success criteria listed below. Answers requiring numerical test data values will be included along with a pass/fail listing and an explanation supplement.
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Removal of 35% of the total rotating mass.
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Maintain similar, or improved, braking characteristics than that of a conventional design.
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Concentrate on maintaining rigidity around the central pad contact area
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Friction surfaces must be replaceable in order to reduce cost of wear components
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Corrosion resistance of the friction surface will be advantageous to later generation automobiles with regenerative braking as a safety device in emergency braking incidents.
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Subsequent designs may employ variations in friction surface materials to improve frictional and thermal braking characteristics.
However, for the device to be a functional part, it must be able to withstand the forces generated by 4000 revolutions per minute and have the necessary thermodynamic properties to dissipate 125 kilowatts of energy in the form of radiant heat and the integrity to withstand a moment about the hub center axis of which 1300 Newton-Meters are applied.