OMEM710 Hardware Manual 2v11
57
Boost pressure is regulated by the turbo wastegate which is opened at a boost pressure set by the
actuator. To increase the boost pressure at which the wastegate is opened, the actuator needs to
see a lower pressure than actually exists in the manifold. The ECU is able to control a solenoid to
lower the pressure that the actuator sees, therefore increasing the boost pressure at which it opens
the wastegate. The ECU can therefore never reduce the maximum boost to below that of the
actuator setting, it can only be increased.
As the solenoid is a PWM device, the map describes the duty cycle of the solenoid against engine
load (boost pressure) and engine speed. A value of zero would not activate the solenoid, and a
value of 100 would have the solenoid open fully.
Normally, the engine would be first mapped without the boost control activated. The fuel and ignition
values can then be guessed for the load sites not yet reached. The Wastegate Duty map is used to
increase the boost to the required level, then these sites can be fully mapped.
The Wastegate Duty map is engine load (boost pressure) vs engine speed. At the engine speeds
where extra boost pressure is desired, the solenoid may be opened just before the boost reaches
the maximum permitted by the actuator to allow the engine to boost to the desired pressure. At
boost pressures above the desired pressure, the solenoid should be closed again to prevent
overboost.
To Next Page
Loading...
