Components of a turbocharger (typical example)
(1) Air inlet
(7) Turbine housing
(2) Compressor housing
(8) Turbine wheel
(3) Compressor wheel
(9) Exhaust outlet
(10) Oil outlet port
(5) Oil inlet port
(11) Exhaust inlet
A turbocharger is installed between the exhaust and intake
manifolds. The turbocharger is driven by exhaust gases which
flow through the exhaust inlet (11). The energy of the exhaust
gas turns the turbine wheel (8). Then, the exhaust gas flows
out of the turbine housing (7) through the exhaust outlet (9).
The turbine wheel and the compressor wheel (3) are installed
on the same shaft. Therefore, the turbine wheel and the
compressor wheel rotate at the same rpm. The compressor
wheel is enclosed by the compressor housing (2). The
compressor wheel compresses the inlet air (1). The inlet air
flows into the engine cylinders through the inlet valves of the
The oil from the main gallery of the cylinder block flows through
the oil inlet port (5) in order to lubricate the turbocharger
bearings (4) and (6). The pressurized oil passes through the
bearing housing of the turbocharger. The oil is returned
through the oil outlet port (10) to the oil pan.
Some turbochargers have a wastegate. The wastegate is
controlled by the boost pressure. This allows some of the
exhaust gases to bypass the turbine rotor at higher engine
speeds. The wastegate is a type of flapper valve that
automatically opens at a preset level of boost pressure in order
to allow exhaust gas to flow around the turbine. The
wastegate allows the design of the turbocharger to be more
effective at lower engine speeds.
The wastegate is controlled by a diaphragm which is open to
the atmosphere on one side and open to the manifold pressure
on the other side. The wastegate normally opens at
approximately 74 kPa (10.7 psi). The relief valve opens at 150
kPa (21.8 psi).
An air/fuel ratio control is installed between the turbocharger
and the fuel injection pump. The air/fuel ratio control performs
the following functions:
The fuel is limited on acceleration in order to prevent an
The generation of black smoke is reduced.
The fuel efficiency i s improved and emissions are
reduced at low boost when the fuel rack is limited for
low power output.
The air/fuel ratio control is a nonserviceable part. Adjustment
and repairs should only be done by a Caterpillar Dealer.
Cylinder Head And Valves
The valves and the valve mechanism control the flow of the air
and the exhaust gases in the cylinder during engine operation.
The cylinder head assembly has two valves for each cylinder.
Each valve has one valve spring. The ports for the inlet and
exhaust valves are on the right side of the cylinder. Steel valve
seat inserts are installed in the cylinder head for both the inlet
and the exhaust valves. The valve seat inserts can be
The valves move along phosphated steel guides in order to
reduce friction and wear. The valve guides can be replaced.
The exhaust valve guide has a counterbore in order to prevent
the seizure of the valve stem. The seizure of the valve stem is
caused by a buildup of carbon under the head of the valve.