Regulation of Supercharging Pressure
REGULATION OF SUPERCHARGING PRESSUREBASIC 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.
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.
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.
- It means P2 - P1 = constant.
P1: Atmospheric pressure
P2: 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.