Theory Of Operation; Compressor Side Sealing Mechanism; Waste Gate Modulation - Yanmar 3TNV82A-B Service Manual

Turbocharger Component Functions

Theory of Operation

Normally aspirated engines produce horsepower
that is limited by the atmospheric pressure of the
induction air. The turbocharger is an exhaust gas
pressure driven device that adds to the
atmospheric pressure, resulting in a boost in
pressure at the combustion chambers. This
substantially increases the amount of fuel that can
be injected into the combustion chambers, while
maintaining the proper fuel-to-air ratio. A slight
parasitic loss is imposed on the engine because of
added back pressure in the exhaust system. That
loss is offset by horsepower gains. The net result is
substantially increased overall horsepower over
normally aspirated engines.
The turbocharger consists of two main
components:
• Turbine
• Compressor
Turbine
The turbine is driven by exhaust gas pressure from
the engine and is coupled to a shaft on the
compressor side of the turbocharger.
Exhaust gas velocity is accelerated at the nozzle
portion in the turbine housing where the
cross-sectional area is reduced. As exhaust passes
over the turbine impeller at high linear velocity, the
turbine shaft is rotated at proportionally high rpm.
Compressor
The compressor is driven by a shaft on the turbine
side of the turbocharger and increases the
induction air pressure at the intake manifold.
The compressor impeller draws induction air into
the turbocharger, compresses it and directs it into
the engine at high pressure.
A seal ring and heat insulating plate thermally
isolate heat energy, at the turbine side, from the
bearings and the induction air, at the compressor
side.
TNV DI Service Manual
Bearings
Thrust Bearing
A thrust force is continuously imposed on the
turbine shaft during engine operation. A thrust
bearing prevents the shaft from moving laterally
under this thrust force.
Radial Bearing
A floating radial bearing moves with the turbine
shaft as oil films form on the inside and outside
bearing surfaces. The bearing slipping speed is
slower than the turbine shaft speed, resulting in
higher dynamic stability and reduced mechanical
noise.
Lubrication
The oil pump delivers oil from the engine to the
turbocharger for cooling and lubrication of the
bearings. As oil leaves the turbocharger, it is
returned to the engine.

Compressor Side Sealing Mechanism

A seal ring and a seal plate form a double wall
structure at the rear of the compressor impeller.
The seal ring and seal plate prevent Intake air and
oil leakage.

Waste Gate Modulation

Excessive boost pressure that cannot be
accommodated by the engine can damage the
turbocharger. The waste gate is a component that
monitors intake boost pressure on the compressor
side and diverts exhaust gases around the
turbocharger turbine. The amount of exhaust gas
diverted is varied to limit turbine rpm and maintain
the intake pressure equal to, or less than the
specified maximum level. This improves the
response to load variation in the low to medium rpm
range and minimizes black smoke.
Waste Gate Control
A mechanical pressure sensor in the outlet of the
compressor side of the turbocharger opens and
closes the waste gate to maintain the specified
intake pressure at the intake manifold.
TURBOCHARGER
10-11