Modeling and Simulating a VVT System for Robust Design 2008-01-0901

In order to achieve higher fuel efficiency and lower emissions, the automotive industry introduced variable valve timing (VVT) systems for combustion engines. A common VVT system will adjust the valve timing by changing the phase angle of the cam shafts using cam phasers. Analyzing the behavior of these systems for nominal conditions can be accomplished through many methods, including prototyping. To optimize the robustness of a system, however, its performance should be considered for non nominal conditions. As with all automotive components, manufacturing processes, environmental conditions, and aging all introduce variation to the system. Design of a robust system requires understanding how these sources of variation effect performance. The goal of the engineer is to use this information to develop a system that is tolerant to variation yet not subject to costly over-design. In order to understand the effect of variation acting on a system, hundreds or even thousands of permutations may be required, making hardware prototypes economically unsuitable for the task. Simulation, using a virtual prototype is a vastly more practical and useful alternative due to the time and cost considerations involved when analyzing multiple permutations.

This paper presents a virtual prototyping approach for the robust design of a VVT system. The first step in this approach is to obtain the appropriate models for the system simulation. A number of modeling techniques will be considered that are particularly effective for creating robust systems. The second step in this method is to define the analyses required to evaluate the performance of the system. Proposed will be analysis strategies for understanding behavior as variation is introduced into the system. By using the modeling and simulation strategies presented here, the robustness of a VVT system can be increased while at the same time reducing development time, cost and warranty related system problems.