Turbocharger Control System Description - Control
The turbine in the turbocharger is turned by the exhaust gas, compresses the fresh intake air with the compressor mounted coaxially
with the turbine, and discharges the air into the charge air cooler. The fresh intake air gets hot when compressed, is cooled in the
charge air cooler, then enter the cylinders.
The turbocharger equips with the turbocharger wastegate control valve and the turbocharger bypass control valve to control the
system pressure and gas flow rate. The turbocharger wastegate control valve is actuated by an electric actuator.
To control the boost pressure, the PCM changes the turbocharger wastegate control valve open ration using the duty control of the
stroke of the turbocharger wastegate control actuator.
When the turbocharger wastegate control valve closes, all the exhaust gas flows from the exhaust manifold to the turbine and serves
the driving force for turning the turbine. This increases the turbine shaft speed and increases the compression pressure of the fresh
intake air, causing the boost pressure to increase.
When the turbocharger wastegate control valve opens, some of the exhaust gas bypasses the turbine and flows directly into the
catalytic converter mounted downstream of the turbocharger. This decreases the turbine shaft speed, causing the boost pressure to
decrease. This mechanism prevents the boost pressure from increasing excessively, and protects the engine and turbocharger.
The turbocharger bypass control valve consists of a diaphragm, a return spring, and a valve and is connected to the turbocharger
bypass control solenoid valve for control.
Normally, the turbocharger bypass control solenoid valve is kept ON by the PCM. Because equal pressure is applied to the both sides
of the diaphragm, the turbocharger bypass control valve is kept closed by the return spring.
When the throttle valve is closed from the supercharged condition, the PCM turns OFF the turbocharger bypass control solenoid
valve. At this time, the negative pressure in the downstream of the throttle valve, which has passed through the solenoid valve, is
applied to the solenoid side of the diaphragm, causing a pressure difference between the both sides of the diaphragm. The differential
pressure overcomes the return spring force and the valve opens, causing the fresh intake air which has passed through the
compressor to leak into the upstream of the compressor. This adjusts the system internal pressure and at the same time prevents the
intake air drag in the compressor from increasing and the turbine shaft speed from decreasing, which provides improved response at
the time of re-acceleration.
Engine Output Control
The turbocharger wastegate control actuator is an electric type, which enables flexible and precise control of the turbocharger
wastegate control valve open ratio regardless of the operating condition of the engine. This enables the turbocharger wastegate
control valve to function as an engine output control device in cooperation with the throttle valve.
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