Optimizing Valve Rotational Speed Using Taguchi Techniques

Abstract

As fuel economy regulations increase and customer preference shifts to smaller, higher power density engines it is more important to effectively cool certain areas of the cylinder head and valvetrain. In order to maximize valvetrain life and increase engine performance it is critical to maintain a near uniform valve seat temperature to enable proper sealing. As cylinder head bridges narrow, and the temperature increases, the water jacket may not be sufficient. An alternative method to ensuring equal temperature distribution across the valve is to promote low speed valve rotation. This will not only aid, cooling the valve seat, as well as cooling and cleaning the valves' seating surface. This paper describes the development and testing of a valve rotation study, utilizing the Taguchi approach in order to determine the most robust design. A test stand was utilized to examine the valve rotation in which the cam was driven directly using a DC motor. The testing was performed on a type II valvetrain, using a donor cylinder head. The Taguchi based project focused on three noise factors: cylinder head machining variability, oil pressure and engine speed, as well as various control factors including valve guide clearance, valve tip surface finish, keeper geometry, valve seal tension, spring shim amount, spring design, rocker arm tab clearance, rocker arm roller radius and rocker arm pad alignment. The testing was conducted using an L18 orthogonal array and a subsequent L9 to further optimize the system.

Analysis of dynamics and friction resistance in the cam-tappet system

“…Excessive amount of valve rotation will result in increased wear of the contacting surfaces, limiting the engine lifetime. In the analysis described in Refalo et al (2010), a minimum engine speed of 3500 rpm was established as a target for valve rotation to begin. Over a typical driving cycle, the valves can rotate at least once.…”