TM 5-3810-300-24&P-3
3.4
BLOWER
The blower, designed especially for efficient Diesel
operation, supplies the fresh air needed for combustion
and scavenging. Its operation is similar to that of a gear-
type oil pump. Two hollow three- lobe rotors revolve with
very close clearances in a housing bolted to the cylinder
block. To provide continuous and uniform displacement
of air, the rotor lobes are made with a helical (spiral)
form, (Figs. 1 and 2).
Two timing gears, located on the drive end of the rotor
shafts, space the rotor lobes with a close tolerance;
is mounted on a double row ball bearing and is driven by
therefore, as the lobes of the upper and lower rotors do
the blower drive shaft by means of a flexible drive hub
not touch at any time, no lubrication is required.
attached to the gear. The drive gear mates with a lower
driven gear (142) that is splined to the lower blower rotor
Oil seals located in the blower end plates prevent air
shaft. Since the lower rotor (timing) gear (14) is also
leakage and also keep the oil used for lubricating the
splined to the lower rotor shaft, it drives the upper rotor
(timing) gear (13).
rotor compartment.
A flexible coupling, formed by an elliptical cam driven by
Lip type oil seals or metal ring type oil seals are installed
two bundles of leaf springs which ride on four semi-
in the blower end plates. Each ring type oil seal consists
cylindrical supports and spring seats is attached to the
of a carrier pressed onto the rotor shaft, a collar pressed
blower drive gear (42) (Fig. 1), and prevents the transfer
into the end plate, and a seal ring contained in a groove
of torque fluctuations to the blower.
of the carrier.
The blower rotors are timed by the two rotor gears (13)
The outside diameter of the seal ring seals against the
and (14) at the rear end of the rotor shafts. This timing
collar to prevent leakage of air or oil. Each rotor is
must be correct, otherwise the required clearance,
supported in the doweled end plates of the blower
obtained by the use of shims behind the gears, between
housing by a roller bearing at the front end and a two row
the rotor lobes will not be maintained.
pre-loaded radial and thrust ball bearing at the gear end.
Normal gear wear causes a decrease in the rotor to-rotor
The blower upper rotor is driven by the blower drive shaft
clearance between the leading edge of the upper rotor
which is coupled to the upper rotor timing gear by means
lobes and the trailing edge of the lower rotor lobes of the
of a flexible drive hub (20) Fig. 1.
standard blower and the small diameter rotor blower. In
the former 71E, 71N and 71T reduction blowers, the
Currently a standard and a small diameter rotor blower
lower rotor is the leading. rotor and the upper rotor is
are used on In-line 71 engines. The small diameter rotor
the trailing rotor; therefore, gear wear will cause a
blower with a 2.00:1 blower to engine speed ratio is
decrease in the rotor-to-rotor clearance between the
employed in the 71E and 71N engines and a 1.95:1
leading edge of the lower rotor lobes and the trailing
blower to engine speed ratio is employed in the 71T
edge of the upper rotor lobes. Clearance between the
engines. When higher pressures are required, such as
opposite sides of the rotor lobes is increased
for bulk unloading, a large bearing 2.00:1 ratio (P) blower
correspondingly.
with metal ring type oil seals is used. The former 71E
and 71N engines used a 1.69:1 ratio blower and the
While the rotor lobe clearance may be corrected by
former 71T engines used a 1.55:1 ratio blower. Early
adjustment, gear backlash cannot be corrected. When
engines employ the 2.00:1 ratio standard blower.
gears have worn to the point where the back-lash
exceeds .004", the gears must be replaced.
The ratio between the blower speed and the engine
speed, and the number of teeth in the blower drive gears
and reduction gears is given in the following chart.
Reduced blower speed on the former 71E, 71N and 71T
reduction blowers is accomplished by the use of an
additional pair of gears mounted on the rotor shafts. The
upper drive gear (140), Fig. 2,
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