Nowadays, turbocharging is almost only referred to as 'turbo', which is of course an inadmissible abbreviation, as we will see in the course of this book. However, given the huge proportion, we cannot avoid starting with this type of supercharging here in the introduction as well.

It also sounds so tempting to use the pressure of the exhaust gases of an internal combustion engine to improve its filling. As if all one had to do was insert such a component between the exhaust and fresh gas trains and one could more than dream of increased performance. Yet the turbocharger was first successful in trucks more than 30 years before it was used in cars, so it is not only useful for increasing power.

Also, it was not yet clear how the gases were to enter or leave the respective housings; at that time, the axial design was preferred, later and thus today rather the radial design. Apart from the increase in performance, the reduction of consumption in the transport sector naturally plays the main role, as its costs are the second highest after personnel expenses.

As you can already see from the splendid cut-away part above, turbocharging is much more complex than just driving one wheel with combustion air and sucking in air with the other wheel. You see here, for example, two so- called floods. They are both served by half of the cylinders and come together just before the turbine impeller.

This design can partly replace the one with a double turbocharger. The cylinders are always separated by the firing order, if possible not following each other. Quite simply 1/2 and 3/4 for four-cylinder or 1/2/3 and 4/5/6 for six- cylinder in-line engines. A distinction is made between a large flood on the left and a small flood on the right, from which alone a part of the exhaust gases may be recirculated. This means less weakening of the pressure at low flow rates.

You have probably already heard about it, it is about making the almost only major disadvantage as unnoticeable as possible, the turbo lag, i.e. keeping the gears at speed even when the engine is in overrun mode. For the situation is bound to arise soon that the throttle is opened again and then power or rather torque is required.

We speak of low-end torque, which is the torque at the lowest speed that is usual in driving. Of course, this is much more important in a truck than in a car, which leaves it again after accelerating. Whereby the torque is still not meaningful, because on the test bench you usually give the engine the time to develop it.

As you can see, in the case of trucks it is not so much a question of avoiding turbo lag as of achieving a uniformly high level of efficiency over the entire operating range that is normally used. So, and now we haven't even talked about intercooling, high and low pressure in exhaust gas recirculation, boost pressure control, variability of the supercharger or vanes, and engine braking elements. Stay tuned . . .