Powertrain and vehicle technology is rapidly changing to meet the ever increasing demands of customers and government regulations. In some cases technologies that are designed to improve one attribute may impact others or interact with other design decisions in unexpected ways. Understanding the interactions and optimizing the transient performance at the vehicle level may require controls and calibration that is not available until late in the vehicle development process, after hardware changes are no longer possible. As a result, an efficient, up front, CAE process for assessing the interaction of various design choices on transient vehicle behavior is desirable. Building, calibrating and validating a vehicle system model with full controls and a mature calibration is very time consuming and often requires significant experimental data that is not available until it is too late to make hardware changes. This paper presents a simplified CAE method for vehicle system modeling using GT-SUITE as the CAE platform with a fairly simple vehicle model together with a detailed engine model and simplified controls. The method involves the transient modeling of engine, transmission and vehicle as well as simplified vehicle controls and calibrations that can be used early in the vehicle development process. This paper provides an example of assessing the impact of intake cam duration, VCT lock position and VCT response on vehicle launch performance. Typically an engine’s intake cam duration would be chosen based on the assessment of part load Brake Specific Fuel Consumption (BSFC) and the peak torque performance curve, both achieved under steady state operating conditions, not based on a transient vehicle maneuver. In order to demonstrate this new methodology, several intake cam durations and cam actuation types were chosen to evaluate their impact on vehicle launch performance. The launch performance from both engine idle speed and engine-off conditions were evaluated. Results showed that the method was very useful in assessing vehicle performance sensitivity to design changes and actuator response in vehicle system optimization.
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