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.
We found that the in-line three cylinder was operated at higher engine speeds even though it was operated at similar acceleration- and load levels like the in-line four cylinder power-train, whereat the off-set of the engine speed shows no correlation with the difference in firing frequency between both engine types. Furthermore, it was revealed that the i3-engine faced gear-up-shift events at higher engine speeds than the i4-engine. Interestingly, the up-shift speeds in the individual gears show good correlation with the individual interior noise level characteristics. Based on the findings, potential countermeasures to enforce drivers of in-line three cylinders to drive at lower engine speeds can be made to ensure that the fuel-economy benefit of i3-engines is accessible even under real-world driving conditions.
