There is hardly an expression which is more to the point in the engine management. It is, so to speak, the icing on the cake. Although we often buy cars according to their performance, what we actually mean, is their torque, the feeling of being pressed back in to the seat, when we suddenly get the chance to overtake.
In the past and in the case of the petrol driven car, the driver's wishes were satisfied by simply opening the throttle-flap when accelerating, to allow more air into the engine. The rest was then taken care of by the carburettor(s) or later, by the injection system.
With the Diesel it was even worse. Trusting than there was sufficient air coming in, more fuel was simply added. The result was, that often enough the engine gave out more soot instead of more performance. Even with the petrol engine, increasing the torque sometimes remained only wishful thinking.
Nowadays, in the times of E-gas (picture 1 + 2), things are done differently. One tries to justify the driver's longing for more torque more efficiently. However, this requires the determination of the momentary torque provided by the engine. This is also important for the components which must then come to terms with the amount of torque provided.
Not much can be done by simply applying a formula. First of all e.g., a characteristic map is called for. In this case, of the most important parameters like RPM, injection amount, air supply (picture 3 + 4) and amount of exhaust gas (picture 6), the indexed torque is to be determined. This can also be corrected through the momentary temperatures (picture 5) or the cam- and ignition settings (picture 9). This of course, if one can determine the pressure in the cylinder fairly directly.
The determining of the losses is done by moving from the 'indexed' to the 'efficient'. The pressure in the cylinder shows optimum value, indeed, on its way to the drive-wheels some of it is lost. This is what has to be estimated, since the only thing that interests the driver, is the power that he/she can put on the road. One calculates, as it were, from the front to the rear.
Then there is also the so-called torque reserve. Since, what's the point of doing all the calculating, if in the end, the engine just can't produce anything more. Indeed, with this kind of reserve, not the momentary delivered- compared with highest possible torque is meant, this would probably require a different RPM-range.
It's all about the torque that can be quickly generated. In the past that wouldn't have been possible at all. From whence would the engine be able to get that much torque? Sometimes it could be done, in engines having several carburettors mounted quite close to the cylinder head. Indeed, who was fortunate enough to have anything like that? Even turbo-charged engines often reacted with a lag, because their cut-off regulation, when the pressure was too high, was often limited.
Nowadays it's different. Boost-pressure (picture 7+8), can now be generated at shorter notice. The Lambda=1, necessary for the exhaust gas emission control in petrol engines, would also be maintained. There are however, even faster reacting systems, e.g., the ignition. If in this case, one simultaneously controls the pinking and the accompanying circumstances, a fairly spontaneous reaction is possible.
The conversion from layer- to homogenous operation (picture 12) would also be possible, only somewhat slower. There are however, also in this case, reserves available for a quick torque increase. Let's not forget the automatic- or automated transmission. Recently, the automatic changes gear faster because of the constantly engaged lock-up clutch. The dual-clutch gearbox is however, not always as well prepared for the shifting down as it is for shifting up.
While the internal engine possibilities in a petrol engine are split up, the Diesel has, perhaps apart from the boost pressure, only one point which can be addressed, that is the fuel supply (picture 11). Here the dosage and the exhaust gas treatment has become much more efficient. Which modern Diesel engine still belches out smoke when accelerating?
No, the possibilities of generating additional torque have not yet been exhausted. Think only of the number of consumers, which can, at least for a short time, be switched off, perhaps above all the generator (picture 10) or the air conditioner (picture 13). By the way, the torque model refers also to the idling-speed. This can be substantially reduced and increased again only when the clutch is engaged.
Those who give a thought to the future, won't be able to ignore the electric motor. These are, in the first place, small, quick charging motors, which can speed up the turbo charger. Indeed, there are also the larger, slower motors, which may be linked directly with the drive-train. If ever there was somewhere that torque reserve could be found, then here. 05/14