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The impact of the number of cylinders on two downsized gasoline engines on driving habits in the same passenger-vehicle type was investigated. This was carried out with two similar vehicles, equipped with an in-line three cylinder (i3) and an in-line four cylinder (i4) engine, both having same power, torque and transient-response behaviour. Both engine types were mated to six-speed manual transmissions with same gear-ratios and dual-mass flywheel characteristics. The study was performed by letting a statistically significant number of subjects driving the same route and both vehicles consecutively. The relevant data during driving were recorded simultaneously from either vehicle integrated sensors (CAN), and secondary transducers.

The European Automotive Industry has committed to reduce the emissions. In order to comply with these CO2 requirements, the introduction of fuel efficient technologies is absolutely mandatory. Therefore ‘Downsizing’ is a known way to reduce part load fuel consumption by combining significant displacement reduction with turbocharging to achieve equivalent torque and power levels [1]. To fulfill these demands, an inline gasoline three cylinder powertrain with turbocharged direct injection (SCi Turbo) has been developed. The challenge during the development of such a powertrain is that no degradation on customer demands regarding the key criteria, among others driveability and NVH, is allowed. This paper will show the powertrain components that are affected most by these NVH attributes; this concerns mainly the engine and the power conversion system.

Downsizing of Gasoline Direct Injection engines is a way to reduce greenhouse emissions. A downsized engine will have a much higher specific power density, caused by a significant higher brake mean effective pressure (BMEP). This higher BMEP can be enabled by a turbocharger in combination with gasoline direct injection. In addition, good efficiency is accompanied by fast combustion, i.e. a fast heat release rate. All these factors can lead to an increased level of combustion noise excitation, which means in turn a higher level of radiated noise. Thus a study on impact factors on the combustion noise excitation was carried out on a small I4-gasoline engine, having spray-guided direct injection, combined with a turbocharger. It was found that high intake tumble levels, which e.g. are caused by the intake port geometry or different actuation strategies of the swirl control device, can lead to an increased level of noise and roughness.