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Integration of Engine Start/Stop Systems with Emphasis on NVH and Launch Behavior
Abstract:
Automatic engine start/stop systems are becoming more prevalent and increasing market share of these systems is predicted due to demands on improving fuel efficiency of vehicles. Integration of an engine start/stop system into a “conventional” drivetrain with internal combustion engine and 12V board system is a relatively cost effective measure to reduce fuel consumption. Comfort and NVH aspects will continue to play an important role for customer acceptance of these systems. Possible delay during vehicle launch due to the engine re-start is not only a safety relevant issue but a hesitating launch feel characteristic will result in reduced customer acceptance of these systems. The engine stop and re-start behavior should be imperceptible to the driver from both a tactile and acoustic standpoint. The lack of masking effects of the engine during the engine stop phases can cause other “unwanted” noise to become noticeable or more prominent. Other comfort related criteria like a stable 12V board supply during the engine start phase or A/C usage during the engine stop phase need to be considered as well.
This paper provides an overview of start/stop systems and starter concepts. The requirements for different transmission types and the associated start/stop challenges are described. The phases of an engine start are described in detail, and their influence on the vehicle vibration investigated. NVH related metrics for describing the engine start/stop and vehicle launch are introduced. Key design parameters of the powertrain and driveline on the start/stop NVH behavior are studied. In addition, the impact of engine start on the vehicle's launch behavior is analyzed. Comparisons of different start/stop systems are conducted and results from case studies on the influence to launch delay and “change-of-mind” engine restart are provided. Finally, the effect of missing masking noise during the engine stop phases is discussed.