Slide-to-Roll Ratio in Automotive Valve Train Cam and Oscillating Roller Follower
The objectives of this investigation were to experimentally and analytically evaluate the performance of a valve train cam and oscillating roller follower mechanism. Of particular interest was the effect of operating conditions on the slide-to-roll ratio (SRR) of the roller follower. In order to experimentally measure the SRR at the cam-roller contact, a valve train test rig (VTTR) was utilized. The VTTR contained a section of a heavy-duty diesel engine valve train that was instrumented with encoders and Hall effect sensors to measure the camshaft and roller follower angular velocities as a function of operating parameters. To corroborate the experimental with analytical results, a numerical model for the cam and oscillating roller follower was developed. In this modeling approach, the roller angular velocity was determined via a torque balance between the frictional torque of the pin-roller follower and cam-roller follower interfaces. The pin-roller friction was obtained by developing a time-dependent hydrodynamic journal bearing model with variable speed and load. Friction maps were developed for the cam-roller follower interface using a ball-on-disk EHD2 rig to capture the friction behavior across a range of entraining velocities, contact pressures, and SRRs. Additional areas of investigation included thermal effects and wear in the pin-roller contact. Overall, good agreement was obtained between the experimental and analytical roller follower angular velocity, with the normalized RMS errors less than 7%, across all operating conditions investigated. The analytical investigation determined that thermal effects in the pin-roller contact are insignificant for the typical operating conditions. However, it was shown that the pin-roller friction torque is critical in causing roller follower slip, as the SRR greatly increases once the pin-roller friction torque is greater than the cam-roller friction torque. Finally, pin-roller local wear was demonstrated to have detrimental effects on the SRR of the roller follower once a critical wear depth was reached.
- Master of Science in Mechanical Engineering
- Mechanical Engineering
- West Lafayette