(1) The engine oil used for the engine equipped with the turbocharger is used for not only lubricating the engine but for lubricating and cooling the turbocharger. As the engine oil is exposed to the heat of the turbocharger, its temperature rises easily. For this reason, the engine oil and engine oil filter maintenance should be carried out faithfully. Otherwise it causes the turbocharger to damage. If the recommended engine oil is not used, it causes the bearings of turbocharger to be damaged. Therefore, be sure to use the recommended engine oil.

HINTRefer to the Owner’s Manual or Maintenance Schedule as the replacement intervals of the engine oil and oil filter vary by the model or condition under which the vehicle is used.

(2) Since the bearings are not sufficiently lubricated just after starting a cold engine, racing or sudden acceleration of the engine causes damage to the bearings.

(3) After the engine is placed under heavy loads, such as after high-speed driving or long distance driving, allow the vehicle to idle for a few minutes before shutting it off.

NOTICE

The turbocharger temperature does not rise too high while driving as the turbocharger is cooled by the oil and coolant. When the engine is stopped immediately after high-speed driving, etc., circulation of the oil and coolant stop. This causes the turbocharger to remain uncooled, leading to damage such as sticking. Thus, it is necessary to idle and cool the turbocharger.

2. Precautions on maintenance

(1) Do not start the engine with the air cleaner or air cleaner case removed. Otherwise it will allow foreign particles to enter causing damage to the compressor wheels and turbine.

(2) In the case that the turbocharger malfunctions and must be replace, first check the following items for the cause of the problem and remedy as necessary.

Engine oil level and quality

Conditions under which the turbocharger was used

Oil lines leading to the turbocharger

(3) When removing the turbocharger, plug the intake and exhaust ports and oil inlet to prevent dirt or other foreign materials from entering the system.

(4) When removing and reinstalling the turbocharger, do not drop it, bang it against anything, or grasp it by easily deformed parts, such as the actuator or rod.

(5) When replacing the turbocharger, check for the accumulation of carbon sludge in the oil pipes, and if necessary, clean out or replace the oil pipes, too.

(6) When replacing the turbocharger, put the oil into the turbocharger oil inlet and turn the compressor wheel by hand to spread oil on the bearings.

(7) When overhauling or replacing the engine, cut the fuel supply after reassembly and crank the engine for 3seconds to distribute oil throughout the engine. Then idle the engine for 6seconds.

Operation

At low speed

As the nozzle vane passage becomes narrow (closes), the flow speed of the exhaust gas flowing into the turbine wheel becomes faster and the turbine wheel operates more efficiently. In this way, as the exhaust gas pressure applied to the turbine wheel is increased, the increase of boost pressure becomes faster, and engine output is increase even at low speeds.

At high speed/heavy load

As the nozzle vane passage becomes wide (opens), the boost pressure is controlled because the flow direction of the exhaust gas changes and the efficiency rate of the exhaust gas, which is activated on the turbine wheel, decreases. However, the excess rotation of the turbine wheel is prevented with improvement of the fuel consumption and engine output because the boost pressure is controlled to the specified pressure.

The turbocharging indicator lights are built into the combination meter, and inform the driver about operating condition of the turbocharger with green and amber LEDs (Light-emitting diodes). When the turbocharger operates the specified boost pressure, the green LED is turned on. The amber LED is turned on when the turbocharger exceeds the specified boost pressure.

2. Pressure switches

Two switches are used to sense boost pressureLowpressure switch and high-pressure switch. The difference between these two switches is the strength of the springs. When the boost pressure applied to the diaphragm exceeds a certain level, the switch is turned on.

(1) Control when the boost pressure is below the specified value When the boost pressure is below the specified pressure, the actuator does not operate. All the exhaust gas is therefore routed into the turbine wheel because the waste gate valve remains closed.

(2) Control when the boost pressure is above the specified value When the engine speed rises and the boost pressure supplied by the turbocharger exceeds the specified value (intercept point), the actuator diaphragm is depressed. This causes the waste gate valve to open and part of the exhaust gas bypasses the turbine wheel. By allowing part of the exhaust gas to bypass the turbine wheel, the rotational speed of the turbine wheel is regulated so that the boost pressure becomes within the specified value.

HINT:

With some gasoline engine, the boost pressure is also controlled in accordance with the octane rating of the fuel used (premium or regular gasoline).

Relationship between Boost Pressure and EngineSpeed

The relationship between the boost pressure and engine speed when the accelerator pedal is fully depressed, is shown on the left. The relationship between the boost pressure and engine speed varies according to the load placed on the engine.

Engine oil is supplied from the oil inlet pipe to lubricate and cool the full-floating bearings inside the center housing. After that, the oil passes through the oil outlet pipe and returns to the oil pan.

2. Cooling system

The turbocharger is cooled by the engine coolant. The engine coolant is introduced into the coolant channel inside the center housing via the coolant inlet pipe. The engine coolant returns to the water pump via the coolant outlet pipe after cooling the turbocharger system.

1. Mechanically controlled type

With a diesel engine, the boost compensator increases the maximum fuel injection volume in accordance with the boost pressure. (Refer to the chapter of the diesel injection pump in the book of diesel engine, for details.)

2. Computer-controlled type

The computer-controlled engine detects the intake air volume with the air flow meter and the intake manifold pressure with the turbo pressure sensor, and increases the maximum fuel injection volume with the engine ECU. (The fuel injection volume is determined by the injection duration.) Although the illustration on the left shows the diesel engine, the fuel injection volume is increased in proportion to the volume of the intake air in a gasoline engine.

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.

Center housing

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.

Full-floating bearings

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.

1. Charging efficiency

The engine’s ability to draw air in is called charging efficiency. The charging efficiency of a conventional engine is about 65-85% due to the resistance of the intake system and the exhaust gas remaining in the exhaust system. However the charging efficiency of an engine equipped with a turbocharger or supercharger can be more than 100%.

2. Compression ratio

The gasoline engine has a greater tendency of knocking as the compression pressure is increased. Since air is compressed to a pressure greater than the atmosphere pressure and is fed to the cylinders of a turbocharged or supercharged engine, the compression pressure becomes higher than that of the conventional engine and knocking occurs more easily. Therefore the compression ratio of a turbocharged or supercharged engine is set lower than that of a conventional engine to prevent knocking.

Mass of air actually taken in

Charging efficiency(%) = —————————————– X 100

Mass of air in cylinder under standard conditions

*Standard conditionsStandard atmosphere pressure at 2C(68 F)