Abstract This study presents the NVH characteristics of a passenger vehicle with a three-cylinder engine and a Continuously Variable Transmission (CVT) and an optimization procedure to achieve balance between fuel economy and NVH. The goal of this study is to improve fuel economy by extending the lock-up area of the damper clutch at low vehicle speed and to minimize booming noise and body vibration caused by the direct connection of the engine and transmission. Resonance characteristics of the chassis systems and driveline have been studied and optimized by the experiment. NVH behavior of the vehicle body structure is investigated and modifications for refinement of booming and body vibration are proposed by simulation using MSC NASTRAN. Calibration parameters for CVT control are optimized for fuel economy and NVH. As a result, the lock-up clutch area has been extended by 300RPM and the fuel economy has been improved by about 1%, while the NVH characteristics of the vehicle satisfy the targets. Introduction A low weight, compact and high efficiency engine are important to meet the demands of consumers for fuel economy and high performance. With the reduced size of the three-cylinder engine, efficiency and carbon emission can be improved, but greater noise and vibration is generated due to the increased unbalanced inertia forces. Continuously Variable Transmissions (CVT) are able to provide clutch lock-up of the torque converter at lower vehicle speed than automatic transmissions, thereby improving fuel economy. However, by engaging the lock-up clutch at low speed, the isolation of the transmission from the high engine torque fluctuation is reduced. The increased torsional vibration in the driveline increases vibration and booming noise in a passenger vehicle.This study focuses on the extension of the lock-up clutch area at low engine speed for fuel economy, the required optimization of the chassis and body systems and the calibration parameters of the CVT control. The goal is to improve the refinement of booming noise and body vibration of a small passenger vehicle incorporating a 1000cc three-cylinder engine and a CVT. The following development goals were established for the improvement of fuel economy and minimization of noise and vibration. 1. Understanding the characteristics of a vehicle with three- cylinder engine and CVT. 2. Decreasing lock-up booming and vibration via experiment and simulation to optimize front suspension system and body structure. 3. Optimization of the calibration parameters of CVT control to improve fuel economy and NVH. Understanding the Characteristics of a Vehicle with Three Cylinder Engine and CVT The engine is generally the main source of noise and vibration in a passenger vehicle, so it is important to understand the dynamic characteristics of the engine mechanism. The noise and vibration of the engine are generated by the combustion pressures within cylinders and the inertial forces due to the motion of the pistons and crankshaft. Kwon et al. presented the balancing of a three-cylinder engine with a balance shaft and investigated the characteristics of a three-cylinder engine [ 1]. Figure 1 shows the in-line array of the reciprocating piston and crankshaft crank pin, having a 120 degree separation for the three-cylinder engine.Understanding 3 Cylinder CVT Vehicle for Improving Fuel Economy and Reducing Noise and Vibration2016-01-1294 Published 04/05/2016 Jonggyu Kim, Pyoung Beom Kim, YoungChan Lee, Sunghee Jung, and Byeong-Ug Choi Hyundai Motor Company CITATION: Kim, J., Kim, P., Lee, Y ., Jung, S. et al., "Understanding 3 Cylinder CVT Vehicle for Improving Fuel Economy and Reducing Noise and Vibration," SAE Technical Paper 2016-01-1294, 2016, doi:10.4271/2016-01-1294. Copyright © 2016 SAE InternationalDownloaded from SAE International by Univ of California Berkeley, Monday, July 30, 2018Figure 1. Piston and Crankshaft in-line Array of a Three-Cylinde