Two kinds of
oil pumps are in general use - the gear type and the rotor type. Each is
usually driven from the camshaft or the crankshaft. The gear type oil pump
involves two meshing gears which draw oil from the sump into the spaces
between the rotating gear teeth. When the teeth come together, oil is forced
out under pressure.
The rotor type oil pump has an inner and an outer rotor in one cylinder.
Oil fills the space between the two rotors when drawn from the sump. As
in the gear type oil pump oil is forced out under pressure to the engine.
In cold conditions, oil pressure required to push it through the small clearances
in the bearings could be excesive enough to damage the pump. A pressure-relief
valve is provided inside the pump to reduce pressure. The valve opens under
excess pressure and leaks some of the oil back to the sump.
Crankcase ventilators also called breathers are provided to allow gases
that get past the piston into the crankcase to escape. These can pollute
the atmosphere, if released into the air. Modern systems ensure these are
vented back into the air intake.
Basic Types of Oil Pumps
pump: A pair of gears mesh with each other and revolve in a
close fitting housing. Oil fed in at one side is carried out
round the edge and out the outer side.
pump: An inner rotor meshes with the outer one which has one
more lobe. Having different axes of rotation the spaces vary
in size, causing oil to be drawn in and forced out.