Design of a Cam Phaser System for the UT Formula SAE Racecar

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Sponsor: The University of Texas Society of Automotive Engineers

Date: Spring 2011

Requirements:
Our project is designed to raise the torque curve below 8,000 RPM's by 5% on average. It should do this with 50 psi hydraulic pressure supplied by the engine oil. The cam phaser should fit inside the existing geometry of the valve cover and engine head. Additionally, the system should be designed for greater than 100 operating hour service intervals.

Problem:
The University of Texas at Austin Formula SAE racecar utilizes a motorcycle engine that is optimized for high-end horsepower at the expense of low-end torque. On a formula car this degrades acceleration and cornering performance. Striving to get any edge possible, our team is designing a cam phaser system that will vary the timing of the intake valves on the engine to enhance the torque curve, particularly in the lower end.

Solution:
Our team continued on the work produced by previous semesters' teams. The previous teams designed a system with a rotor attached to the cam shaft. This rotor sits inside the stator where oil pressure controls the rotor's position relative to the stator that is attached to the sprocket and timing chain. Our team improved the manufacturability of the previous design. The design integrates the back cover plate into the rotor to reduce complexity and eliminate seals. Additionally, the existing bolts can be used to attach the cam phaser to the camshaft. This avoids machining and heat treating the camshaft. Lastly, we widened the oil passages in the stator and increased the radius of the fillets, allowing us to machine the cam phaser using 1/8" mill bits instead of 1/16" mill bits. This leads to faster manufacturing time and with higher tolerances.

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