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 (approximately 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 wastegate valve and its controller are provided. By sensing the supercharging pressure, the wastegate valve controller controls the operation of the wastegate valve to maintain the supercharging pressure below a predetermined level.

Fig 1: Basic Function Of Wastegate Valve (1 Of 3)

Courtesy of SUBARU OF AMERICA, INC.

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.

Fig 2: Basic Function Of Wastegate Valve (2 Of 3)

Courtesy of SUBARU OF AMERICA, INC.

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

  Fig 3: Basic Function Of Wastegate Valve (3 Of 3)

  Courtesy of SUBARU OF AMERICA, INC.