Every automaker is looking for ways to improve the fuel economy of its vehicle fleet to meet the EPA greenhouse gas regulation, which translates into 2025 Corporate Averaged Fuel Economy of 54.5 mpg. Engine Stop Start technology will improve the fuel economy of the vehicle by shutting down the engine when the vehicle is stationary. While this is an established technology in Europe, it is beginning to gain momentum in North America, where NVH refinement is a stronger consideration. To utilize the fuel economy benefits of Stop Start technology in the North American market, the technology must be seamlessly incorporated into the vehicle.
This paper gives an overview of characterizing an auto start based on the features of a few Powertrain-system-level metrics. Following the fundamentals of NVH, (Source, Path and Receiver) the receiver touch points will be less perceptible to vibration, if the powertrain-system source is made smoother. Tangential components, which are functions of cylinder pressure and crank angle, are the dominant forces during auto start. Six powertrain-system-level metrics that will define an auto start are developed: engine ramp rate; engine jerk during initial combustion; engine flaring; vibration dose value from the active side of the engine mounts; starter engagement time based on battery voltage; and near field sound level measured 15 cm away from starter. This paper recommends that all of these metric values be reduced to obtain better customer subjective and objective ratings. This paper also correlates these powertrain-system metrics with driver tactile and audible sensory response points.