4-Cylinder Engine and Multi-Cyclinder Engines Torque Fluctuation

In today's engine specifications, noise and vibration are just as important as performance and fuel consumption. This is why the study of variations in the instantaneous torque delivered by the engine under different operating conditions ("acyclism") is fundamental, not only to quantify the phenomenon, but also to find the most effective palliative solutions.

A detailed analysis of the single-cylinder engine was given in the previous article [BM 2 588] . By definition, a multi-cylinder engine is a more or less complex combination of single-cylinder engines. The acyclism of a multi-cylinder engine is therefore defined on the basis of the acyclism of the single-cylinder engine. To do this, we need to take rigorous account of the parameters that enable us to switch from one to the other, in particular the number of cylinders and the time intervals between ignitions. But there's more to it than that, as the latter depend on other factors such as cylinder layout, crankshaft shape and ignition sequence.

Acyclism is dealt with here in a general way for the multi-cylinder engine, using a rigorous approach to arrive at robust formulas useful for determining orders of magnitude essential for the design or test engineer. Emphasis is then placed on the in-line 4-cylinder engine, still the most widely used in the automotive world. All aspects relating to the phenomenon of acyclism applied to multi-cylinder engines in general, and to four-cylinder engines in particular, are formulated in a precise and progressive manner.