Novel Three-Cylinder Engine Solutions Offering Low Noise Vibration and Harshness for Range-Extender and Hybrid Electric Vehicles

In recent years, automotive manufacturers have introduced an increasing array of in-line three cylinder engine solutions with the objective of providing efficient low CO₂ emission power train solutions for small vehicles and in some cases to address down-sizing targets. At the same time, three cylinder engines have seen recent introduction in range-extender and hybrid electric vehicles such as the BMW i8. Unfortunately in-line three cylinder units present serious challenge to engineers in terms of noise, vibration and harshness and this often yields criticism from customer perceptions. The in-line three-cylinder arrangement however does offer an attractive packaging solution for vehicles and an effective method of reducing overall vehicle cost. This paper presents analysis and modelling of a high durability three-cylinder two-stroke cycle engine, which could offer advantages in this competitive and challenging sector for small automotive power plants particularly from a noise, vibration and harshness perspective. The engine uses segregated scavenging to overcome the durability problems of conventional two-stroke cycle engines. Configurations are presented with and without balance shaft and compared with a four stroke engine solution. The novel ability to combine the balance shaft with an integrated rotary valve system controlling gas exchange whilst simultaneously countering the problem of the pitching couple that three cylinder engines traditionally suffer from. Modelling of the benefits of the technology to address NVH issues are presented and discussed.