24-11-2012, 06:20 PM
TURBOCHARGER SYSTEM
02. Turbocharger System.pdf (Size: 228.68 KB / Downloads: 120)
Turbocharger System
GENERAL
The turbocharger system consists of a water-cooled turbocharger, air-cooled intercooler, wastegate
control solenoid valve, etc.
The turbine rotated by exhaust gas pressure rotates the compressor.
As a result, the intake air is compressed by the compressor before it is delivered to the intake
manifold.
This turbocharger system controls the supercharging pressure according to changes in the atmospheric
pressure. Even at a high altitude, therefore, the system offers stable performance without
being affected by variations in atmospheric pressure.
TURBOCHARGER UNIT
The turbocharger is water-cooled. It utilizes a wastegate valve to adjust its supercharging pressure
to an optimum level. The turbine is housed in a lightweight, thin-wall, heat-resistant casting. The
compressor housing is made of thin-wall, aluminum alloy casting. The shaft for turbine and compressor
is supported by a full-floating metal bearing system.
LUBRICATION OF TURBOCHARGER
The turbocharger is lubricated by engine oil branched out from the oil pump. To cope with very high
speed of the turbocharger turbine and the compressor shaft which may reach a maximum of several
hundred thousands of rpm, full-floating type bearings are used which can form adequate oil films
on their inside and outside during running.
Further the oil supplied to the turbocharger also plays a role of cooling the turbine so that heat from
exhaust gas does not transmitted to the bearings.
COOLING OF TURBOCHARGER
The turbocharger unit is cooled by engine coolant, which enhances the reliability and durability of
the unit. The engine coolant from the coolant drain hose located under the cylinder head is led by
a pipe to the coolant passage provided in the turbocharger bearing housing. After cooling the bearing
housing, the engine coolant is led into the coolant filler tank through a pipe.
WASTEGATE CONTROL SOLENOID VALVE
The wastegate control solenoid valve switches the intake air pressure passages to the wastegate
controller in response to signals from the ECM. When the solenoid valve is closed, the intake air
pressure upstream of the turbocharger unit is applied to the wastegate controller. When the solenoid
valve is opened, the intake air pressure downstream of the turbocharger unit (supercharged air
pressure) is applied to the wastegate controller.
BASIC FUNCTION OF THE WASTEGATE VALVE
When the engine speed increases as the throttle valve opens, the amount of exhaust gas increases.
This increases the speed of the turbine (approx. 20,000 to 150,000 rpm), the supercharging pressure
and the engine output.
If the resultant supercharging pressure is extremely high, however, it may cause knocking and an
excessively high thermal load on such engine components as pistons. In the worst case, the engine
may be damaged or broken. To prevent this, the wastegate valve and its controller are provided. By
sensing the supercharging pressure, the wastegate valve controller controls the operation of the
wastegate valve to maintain the supercharging pressure below a predetermined level.