The lubrication should provide a load-bearing film of lubricant, reduce friction in gliding parts, redirect warmth to the oil sump, hold impurities in suspension, seal, protect polished metal parts against corrosion and, in
addition, reduce the level of mechanical noise..
The picture below shows an oil pump from the middle of the last century. At that time there was only one sort of oil available and one viscosity for summer and another for the winter period. Instead of an electric pump
there was a hand crank.
The engine and the automatic gearbox are each lubricated by a pump. In the manual gearbox (motor car) and final drive the gearwheels dip into the oil and swirl it, in the form of fine
droplets, to all the points to be lubricated. The two-stroke engine works with a mixture of fuel and oil. In the four-stroke combustion engine the lubricant is filtered, because here, together with the abrasion from other components, the road dust which is taken in, despite filtering, can still enter the engine, this creates heat and
residues when being burnt. Particularly when cold-starting the petrol engine the fuel components with
a high boiling point cause the oil to become thinner.
Lately, oil-thinning also appears in Diesel engines when, for the purpose of regeneration, a post-injection takes place. Under normal circumstances, in the
Diesel engine, the soot
rather causes oil thickening.
This doesn't generally occur in the sliding bearings of the vehicle, because either the bearings are installed with lubricant or else oil residue is still present. Nevertheless, in this type of friction, the forces are the
This is the situation between dry- und liquid friction. Here the sliding friction surfaces are seperated by an oil film, but there are still points of contact. Mixed friction can occur under unfavourable conditions like e.g., high
stress and hot oil which has taken on a low viscosity.
This is the normal condition of the sliding bearings. Liquidity seperates the two friction surfaces by hydrostatics (higher oil-pressure) or by hydrodynamics (adapted RPM). 11/11
|Mechanical Reporter . . .|