GENERAL
The intake system consists of an intake duct, a resonator integrated with the air cleaner case, and an air cleaner element housed in the air cleaner case. The resonator, located upstream of the air cleaner case, effectively reduces the intake noise level.
Scheme 34
Scheme 35
- The turbocharger system consists of a water-cooled turbocharger, air-cooled intercooler, waste-gate 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.
Scheme 36
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 opens, the intake air pressure upstream of the turbocharger unit is applied to the wastegate controller. When the solenoid valve closes, the intake air pressure downstream of the turbocharger unit (supercharged air pressure) is applied to the wastegate controller.
Scheme 37
MEMO
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 waste gate valve and its controller are provided. By sensing the supercharging pressure, the waste gate valve controller controls the operation of the waste gate valve to maintain the supercharging pressure at a predetermined level.
Scheme 38
While the supercharging pressure is lower than the predetermined level, the wastegate valve is closed so that entire exhaust gas is directed to the turbine.
Scheme 39
When the supercharging pressure reaches the predetermined level, the wastegate controller lets the supercharging pressure press the diaphragm. This causes the wastegate valve to open through a linkage. With the wastegate valve open, part of the exhaust gas is allowed to flow into the exhaust gas pipe that bypasses the passage to the turbine.
This decreases the exhaust gas pressure that rotates the turbine and keeps the supercharging pressure constant.
Scheme 40
- It means P 2 - P 1 = constant. P 1 : Atmospheric pressure P 2 : Supercharging pressure
CONCEPT OF THE WASTEGATE VALVE CONTROL
At high altitudes, the atmospheric pressure (P1) is low, so that the supercharging pressure (P2) is also low in a conventional system. The wastegate solenoid valve operates in such a way that a constant supercharging pressure (P2) is maintained by acting in response to change in the atmospheric pressure.
Scheme 41
Scheme 42
- Since the intake air having passed through the turbocharger unit is heated to a very high temperature, the air itself expands, resulting in a lower supercharging charging efficiency. The intercooler is provided just before the throttle body to cool down the intake air and improve the boosting efficiency.
- The intercooler is an air cooled type. The air delivered from the air intake duct provided at the engine hood flows through the core and cools the intake air passing through the intercooler.
AIR BYPASS VALVE
When a throttle valve is suddenly closed, a surge may occur due to a sudden rise of the air pressure in the passage between the turbocharger and throttle body. To prevent this, an air bypass valve and air passage are provided. The air bypass valve, actuated by the vacuum created by a sudden closure of the throttle valve, allows the suction air to bypass the turbocharger and flow directly upstream, thus lowering the pressure in the air passage.
