Design of Cam Phaser for the Formula SAE Racecar

Photo of Michael Dey, Xu Han, Erik Kinzler, Charles Mann Students: Michael Dey, Xu Han, Erik Kinzler, Charles Mann

Sponsor: The University of Texas Society of Automotive Engineers

Date: Spring 2013

Requirements:
The major goal of the cam phaser is to increase torque output of the engine by a minimum of 5%. The cam shaft operation and reliability should not be impaired by implementing the cam phaser system. The cam phaser system must fit inside the free space in the cam housing with a clearance of at least 2 mm between rotating and stationary parts. The system cannot increase the mass of the engine by more than 1kg.

Problem:
Design, fabricate and test a cam phaser system for the YFZ450 engine that achieves the highest torque across the usable engine speed band. The system will be used in the UT Austin Formula SAE vehicle.

Solution:
A Ricardo WAVE simulation was used to determine that a phase angle at the intake of approximately 10-30°(crank) will provide a torque gain of 5-10% until 7000 rpm (near redline). The cam phaser design is based on a centrifugally actuated pin-slot mechanism that pushes on a slot in the camshaft. The centrifugal elements are held together initially via springs and actuated when sufficient rotational speed is reached. The design was prototyped and tested by attaching the cam with a jig to a lathe. The cam was then video recorded rotating at three known speeds (835, 1335, and 2000 rpm) for two sets of springs. The centrifugal elements fully extended using the softer springs at the highest speed. This data agreed with the calculated expected speed for full extension. However, the prototype did not achieve the locking required for cam phasing. The design has been modified and tested using dynamic modeling in MSC ADAMS. The new design achieves locking while achieving a phase angle of 14°(crank) until it exponentially approaches the stock setting at 7200 RPM.

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Photo related to Design of Cam Phaser for the Formula SAE Racecar project
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