Turbocharger: Description and Operation

Turbocharger And Components:

The turbocharger is used to increase engine output by providing a denser air/fuel charge to the engine than could normally be attained through natural aspiration. The turbocharger utilizes spent exhaust gas heat and pressure to drive a turbine rotor, which is connected to and drives an impeller wheel in the intake air piping. The impeller compresses the air in the intake manifold according to the amount of turbine revolutions. Only air is compressed, as the fuel is injected at the intake ports by the fuel injection system. However, when the fuel atomizes with the pressurized air, a larger volume "charge" can be forced into the cylinders. Because engine output depends on the amount of air/fuel mixture ignited per unit of time, supplying a larger mixture amount can substantially increase output, without an increase in engine speed.

The turbine speed increases with exhaust gas flow, (approx. equivalent to engine speed times throttle opening), causing intake manifold air pressure to increase, thus increasing engine output (performance). The turbocharger has an operational range of approximately 20,000 to 110,000 rpm. The Turbocharger turbine/impeller shaft rides on two full floating bearings, which are lubricated with crankcase oil under pressure from the engine oil pump. The housing also has coolant passages, which allows engine coolant to cool the turbo.

If Turbocharger pressure gets to high, predetonation (pinging) may occur, causing engine damage and poor performance. To limit turbo pressure, a Wastegate Valve opens in the exhaust passage and bypasses exhaust flow around the turbine. This serves to slow the rotation of the turbine and therefore the impeller. The Wastegate Valve is opened by a pressure diaphragm that senses the pressure in the air intake, prior to the throttle valve. To insure that fuel injection can be metered accurately, the turbocharger is positioned in the piping after the Airflow Meter, therefore data sent to the ECU concerning intake air volume/temperature is not affected by intake charge pressurization.