Boost Regulation

PURPOSE
To control turbocharger boost pressure.

LOCATION
^ Wastegate valve:
In turbocharger exhaust turbine housing.
^ Wastegate controller:
On outside of turbocharger.
^ Wastegate control solenoid:
On front of R.F. strut tower.

OPERATION
Basic function of wastegate valve
As the engine speed increases with the opening of the throttle valve, the amount of exhaust gas increases. This leads to increase in the rotational speed of the turbine (approx. 20,000 to 120,000 rpm), the boost pressure and engine output. However, excessive boost pressure may cause engine ping and excessive combustion chamber temperatures leading to piston damage. To prevent this, the system is equipped with a wastegate and controller. By sensing boost pressure, the wastegate bypasses some of the exhaust gas, thereby controlling turbine rpm.

Fig. 1 Turbocharger Full Boost:

When boost pressure remains below a predetermined level, the wastegate valve remains closed so that all exhaust gas passes through the turbine, creating maximum rpm. See Fig. 1

Fig. 2 Turbocharger Full Boost (Close-up):

Since the wastegate controller diaphragm is supplied boost pressure through a rubber hose, it actuates the rod to the wastegate valve when pressure reaches the predetermined level. As the wastegate valve opens some of the exhaust gas bypasses the turbine, slowing the turbine. See Fig. 2

Fig. 3 Turbocharger Partial Boost:

This decreases the turbine rotating energy to keep the boost pressure constant.
It means P2 - P1 = constant.
P1 = Atmospheric pressure
P2 = Boost pressure
See Fig. 3

Concept of wastegate control

Fig. 4 Turbocharger Wastegate Control Solenoid:

The higher the altitude, the lower the atmospheric pressure (P1) and boost pressure (P2). The duty solenoid valve acts as a control to maintain maximum boost pressure (P2) under absolute pressure. See Fig. 4

Fig. 5 Boost Pressure Vs. Altitude Chart:

Max. P2 = Constant (Absolute pressure 161.3 kPa [1,210 mmHg, 47.64 in Hg.]) See Fig. 5