The turbocharger is a device which uses the energy of the exhaust gas to rotate the turbine wheel at high speeds. There is a compressor wheel on the same shaft as the turbine wheel which compresses air into the cylinders when it is rotated. In this way, engine output is increased. The waste gate valve and actuator prevent the boost pressure from rising too high. Some models are equipped with an intercooler to lower the temperature of the compressed intake air and improve the charging efficiency ratio.
NOTICECaution is necessary for handling vehicles because the turbocharger becomes extremely hot due to the exhaust gases. Also, it is necessary to faithfully replace the engine oil at the determined replacement interval. Refer to the Precautions for Turbocharger for more information.
Components of Turbocharger
The turbocharger consists of the turbine housing, compressor housing, center housing, turbine wheel, compressor wheel, full-floating bearings, waste gate valve, actuator, etc.
Turbine and compressor wheels
The turbine wheel and compressor wheel are mounted on the same shaft. When the turbine wheel rotates at high speed due to the pressure of the exhaust gas from the exhaust manifold, the compressor wheel on the same shaft also rotates, compressing the intake air into the cylinder. The turbine wheel must be heat resistant and durable because it is directly exposed to the exhaust gas and becomes extremely hot and rotates at high speeds. Therefore it is made of an ultra-heat resistant alloy or ceramic.
The center housing supports the turbine wheel and compressor wheel via the shaft. There is an oil channel in the housing to supply engine oil to lubricate and cool the shaft and bearings. Also, engine coolant is circulated through the coolant channel that is built into the housing in order to prevent the engine oil temperature from rising and the engine oil from deteriorating prematurely.
Since the turbine and compressor wheels turn at speeds of up to 100,00rpm, the full-floating bearings are used to ensure the absorption of vibrations from the shaft and lubrication of the shaft and bearings. The full-floating bearings are lubricated by the engine oil and rotate freely between the shaft and housing to reduce friction, thus allowing the shaft to rotate at high speed.
Waste gate valve and actuator
The waste gate valve is built into the turbine housing. The waste gate valve opens and bypasses part of the exhaust gas to the exhaust pipe in order to stabilize the boost pressure when the boost pressure reaches the specified value, approx. 7kPa (approx. 0.7 kg/cm2). The opening and closing of the waste gate valve are controlled by the actuator.
Two-way Twin Turbo
Two-way twin turbo features two turbochargers installed in one engine. When the turbochargers are operated efficiently under light loads or low speed, engine responsiveness such as acceleration is improved. When the turbochargers are operated efficiently under heavy load and high speed, high power output can be attained. When there is only one turbocharger, it is difficult to attain efficient operation for both heavy loads and light loads. In this case it is only possible to attain efficiency one way or the other. However, the twin turbo controls the exhaust gas control valve and exhaust bypass valve. It operates one turbocharger under light loads, and two turbochargers for high speeds and heavy loads in order to improve engine response in all speed ranges and attain high power. The illustration at left shows 2JZ-GTE engine produced in 1993-1999.