Mechanics
By adding a turbocharger to an automobile, an engine of a given size can have
the horsepower increased by up to 40%, sometimes even more. Horsepower is
the amount of work that the engine is able to do. By increasing this amount
and holding the engine size constant, the efficiency and performance of the
vehicle increases. As can be seen in the diagrams on the preceding page, a
turbocharger consists of mechanical parts moving at very high speeds in relation
to each other. The operation of the turbocharger consists of two connected
turbines spinning at high speeds. This brings up the idea of friction and
inertia. The spinning turbines are acted on by the force of the exhaust gasses
in a positive direction, and the effects of internal friction acting to oppose
motion. Because the performance is dependent on the high speed of the turbine,
the friction forces would ideally want to be eliminated to allow faster acceleration
of the turbines for quicker response. With connecting shafts spinning sometimes
as high as 150,000rpm's, there is obviously a large amount of friction, and
therefore heat in the turbocharger. To minimize this, shafts are supported
in fluid bearings, which is just a constant supply of oil around the shaft,
or in more efficient chargers highly advanced ball bearings are used to minimize
friction. Those that use ball bearings are also able to use smaller, lighter
shafts, which have less inertia, and are therefore able to spin up quicker.
Inertia is the other property affecting the performance of the turbocharger.
Using lighter turbines will allow the charger to accelerate much faster, however
the turbines must be able to tolerate exposure to high heat, and large changes
in air pressure. The best material currently for this is ceramic, which is
lighter than the traditional steel construction, and has less inertia allowing
there to be less lag. Lag is the time that it takes for the turbo to be acted
upon by the exhaust gasses, reach its effective speed, compress the air, and
cause a noticeable increase in performance. This is the main drawback to turbochargers,
so any decrease in friction or inertia also decreases lag, and is very desirable.