This material is addicted to the course of technical english. British or American accent is required.
Without the aid of the friction, an automobile could not move itself. Excessive
friction in the automobile, however would mean rapid destruction. We cannot eliminate internal friction, but we do reduce it to a controllable degree by the use of friction reducing lubricant. These lubricants are usually made of the same crude oil from which we obtain gasoline.
The petroleum oils are compounded with animal fats, vegetable oils and other ingredients to produce satisfactory oils and greases for automobile use. Lubricating oils and greases are also manufactured from silicones and other materials and have no petroleum products in them.
Lubricating oil in an automobile engine has several tasks to perform:
1) to reduce the friction between the moving parts of the engine and thus to reduce the amount of destructive heat generated by excessive friction and to conserve the power that I would otherwise be wasted in overcoming excessive friction;
2) to act as a seal and thus to prevent leakage between parts such as pistons, rings and cylinders;
3) to flow between friction generating parts and thus to carry away much of the heat;
4) to wash away the abrasive metal worn from friction surfaces. The engine oil must function whether the temperature is below zero or above 100 deg.F.
This is contrary to the nature of petroleum products as they tend to thicken at low temperature and thin out at high temperature. The oil therefore goes through many processes during manufacture to reduce this tendency to "stiffen" or "thicken" at low temperatures. Light oil facilitates cold starting and attains circulation sooner than a heavier oil. At the same time it is not desirable to use an oil so light that it cannot maintain a film of protection between the moving parts.
The moving parts in the engine are subjected to speed and pressure as well as heat. The pressure has a tendency to squeeze the oil out and permits the bearing surfaces to contact each other and produce friction and wear. The oil is required to form a film thick enough to hold these surfaces apart. The film may contain several layers of oil molecules.
One layer rolls over another with a minimum of friction and also these layers hold the two surfaces apart against the pressure tending to force them together. The oil may be supplied to the moving parts of the engine by splashing or by pump pressure. Pressure feed is the most widely used system for automobiles. Some engines use a combination of both types.
