According to an ancient proverb it is not possible to have the barrel full and the wife drunk. In our industry, designers are called upon to choose and the relative frequency between opposing needs, and then impossible, then to meet at the same time, in the best of ways. Working to improve things in a sense, it worsens the situation in the other. In other words, if you earn from a part, you lose the other, and vice versa. As obvious, the solution that is eventually adopted is always a compromise.
The examples about are not lacking.
At the level of the characteristics of the materials used to make the various components begin to present themselves to the designer the important choices. A high hardness provides better wear resistance by sliding (and also to the abrasive). However, it is usually associated with greater brittleness, which obviously is disadvantageous. Therefore, it is necessary to mediate carefully. The material must have sufficient hardness but at the same time a sufficient toughness. This is typically achieved not by changing the alloy that is used but “balancing” it in a timely manner to the heat treatment to which the component is subjected. In the drawings this is carefully indicated, together with the dimensions and machining tolerances that must be respected. In some cases it is necessary to have a high surface hardness, but maintain a considerable toughness in the central part of the component. This is for example the case of the gears, in which in correspondence of the contact between the teeth to reach pressures high. If you indurisse each tooth for the whole of its thickness it would be too fragile. In the internal zone (that is, “heart”, as they say in the technical, it must stay tenacious! In this case, as in others similar, you use a treatment that allows you to harden only the outer layer of metal, such as carburizing or nitriding. Also important is the surface hardening (flame or, more often, induction), widely used for the pins of the crankshafts. Of course, it is always necessary that the material used not only has adequate mechanical properties but is also of a type that lends itself to be subjected to the treatments in question.
As for the crankshafts, it is interesting to observe what has happened in the last few years. In the four-cylinder engines in line-already some time ago had been a gradual move from three to five main bearings. This was made necessary by the increase in performance. An increase in the number of media, as well as an increase in the diameter of the pins of the tour, ensures an increase in stiffness (decrease in deflections), and allows you to withstand greater stress. There is, however, a downside, which consists in both cases, by an increase in friction, which causes a deterioration of the mechanical efficiency of the engine, what is deleterious for the purposes of the specific consumption. Each horse is obtained by burning a greater amount of fuel! For this reason, given that the three media of course you can’t return to, the technicians are striving to adopt the pins with a diameter as much as possible, content, without, however, get off so much to not affect the stiffness, far more than by the needs of robustness and durability, however, fundamental.
Well when it comes to volumetric efficiency, engine sucked in some compromise at the level of choices you need. To get a faster combustion it is indispensable to impart to the charge (i.e. the fuel-air mixture) an adequate turbulence. Very important is the one called tumble, vortex, with its axis of rotation perpendicular to that of the cylinder. Unfortunately you do not get your own free, but at the expense of the breathing of the engine. When you initiate the intake air in the cylinder, a turbulence of this type has place in a certain loss of load (which increases with the increase of the intensity of the turbulence itself). Engines very fast sometimes you have to give up something in terms of filling to increase the tumble and thus prevent the progress of the front of the flame may be too slow in relation to the time available for the performance of the combustion.
Staying on the subject of aspirated engines from the competition, it is interesting to remember that when the regulation of Formula One has started to ask the durations of the motor considerably superior to the previous ones (which typically consisted of only one race more tests and were of the order of 400 km), the designers are due to run for cover even change some of the technical choices. There have been those who had to abandon the development of a tree, working on roller bearings instead of bushings (solution that would have allowed a slight increase in performance, thanks to better mechanical performance) for just this reason. But also with regard to the materials with low-friction bushings, there have been problems and in some cases, it was necessary to develop new ones.
Often the process of obtaining the best performance at the expense of durability, and vice versa. A typical case is constituted by the brakes. If you pads with a high coefficient of friction, capable of ensuring deceleration powerful and suitable to satisfy even the most demanding pilots, even in track use, their useful life will inevitably be less than that of pills less powerful, used in similar conditions (but of course the results are significantly lower, in terms of performance). And as is logical the opposite happens if you use brake pads with a friction material designed to have the maximum duration. A similar discourse applies also to the tyres, as anyone can easily ascertain by simply attending a Formula One race.