Automobile transmission - Impact on vehicle consumption

In our first article, [BM 2 582] , we saw why a gearbox was essential, and how it could complement the engine to ensure the vehicle's propulsion by adapting to the conditions of use.

A second article [BM 2 583] highlighted the gearbox's direct contribution to vehicle performance, whether in terms of top speed, acceleration or crossing ability...

But in these years of the global problem of CO ₂ emissions, the question of motor vehicle consumption is crucial, as is that of the polluting emissions for which it is partly responsible.

While the role of the engine in this area is fairly intuitive for everyone, that of the gearbox and, more generally, the powertrain is undoubtedly less so. Yet the latter plays a major role in vehicle fuel consumption.

For a given driving condition, gearbox ratios determine engine speed/load operating points, which are more or less favorable in terms of fuel consumption and pollutant emissions.

In addition, the gearbox, through its own efficiency, adds a load to the engine, degrading the consumption balance directly linked to driving conditions.

These aspects are discussed in detail in this article, which draws on concrete examples wherever possible to illustrate the point.