A set of gerotor pumping elements is shown
output pressure of the pump by bypassing oil back
in figure 5-7. Each set of gerotors is separated by
to the pump inlet. Also notice the location of the
a steel plate, making each set an individual
shaft shear section, which will allow the shaft to
pumping unit. Each set consists of an inner
shear if the gears should seize.
element and an outer element. The small star-
GEROTOR OIL PUMP.-- The gerotor pump
shaped inner element has external lobes fitting
usually has a single element for oil feed and several
within and matching with the outer element,
which has internal lobes. The small element
elements for scavenging oil. Each of the elements,
pinned to the pump shaft acts as a drive for the
pressure and scavenge, is almost identical in
outer free-turning element. The outer element fits
shape. However, the capacity of the elements is
within its steel plate, having an eccentric (not
controlled by varying the size of the gerotor
having the same center) bore. In some engine
elements. The pressure element has a pumping
models, the oil pump has four elements, one for
capacity of 3.1 gpm (gallons per minute) com-
oil feed and three for scavenging. In other models,
pared to a 4.25-gpm capacity for the scavenge
elements. So the pressure element must be smaller
pumps have six elements, one for feed and five
for scavenge. In each case, the oil flows as long
since the elements are all driven by a common
as the engine shaft is turning.
shaft. Engine rpm determines oil pressure, with
a minimum pressure at idling speed and maximum
PISTON OIL PUMP.-- The piston lubrica-
pressure at maximum engine speed.
tion pump is always a multiplunger type. Output
of each piston supplies a separate jet. Oil drained
from the points of lubrication is scavenged by a
separate pump element. The piston-type pump
(fig. 5-8) is used less than either of the other types.
Valves
Valves control the pressure and flow of oil in
the lubrication system. There are three types of
valves common to oil systems that are discussed
in this text. They are relief valves, check valves.
Figure 5-7.-Gerotor pumping element.
and bypass valves.
Figure 5-8.-Axial piston pump.
5-11
