Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
A vehicle start/stop engine system is investigated with focus on human perception of discomfort. The FRF between engine rotational acceleration around the neutral torque axis (NTA) and seat rail acceleration with the specific interest in start up and shut down events is estimated from measurements, using a shaker torque excitation. The inverted torque sensitivity formulates a frequency dependent target of powertrain torque related to seat rail acceleration.
The main rotation direction for the transversally mounted engine is the pitch-direction, yielding high acceleration levels in both longitudinal x-, and vertical z-direction compared to the lateral y-direction. Specific weighting functions are used to normalize these accelerations to human perception. Acceleration levels in x-, and z-direction at the seat rail are similar after weighting curves have been applied.
The amount of discomfort experienced by a person depends on vibration amplitude, frequency, direction and time duration. However, there is no evidence on in what way a specific time dependence affects the perceived comfort.
The NTA around which the engine as a rigid body rotates is experimentally estimated and verified by comparing to the reference CAD NTA. The powertrain mounting system center of gravity is assumed to be known from the CAD model.
The seat rail is found to be a more convenient measurement position to use in order to achieve reproducible results rather than the seat cushion. This, since the acceleration at the cushion also depends on several other factors such as person size, weight and body posture and also on the non-linear properties of the seat foam padding.
2011. , 65 p.