WGDC Deadband

I'm currently completing open loop boost control tuning on an application with an internal wastegate and electronic control. The process I have followed is to log, adjust the Compressor Power Output Table so that the base value is close to the actual. Once happy, I increase the torque request and repeat the steps.

I'm now at the point at which I'm hitting a WGDC of circa 93% at redline (100% = wastegate closed).

How do I ascertain when/if I've gone to far and I'm operating in the wastegate deadband?

Shaun,

If you request higher WGDC and boost doesn't increase under like conditions (same engine speed and load, ambient conditions, exhaust temp, gear, etc.), then the gate is likely either closed, or being forced open by high exhaust pressure.

At 93% it's unlikely you'll get a lot more out of it by going to 100%, perhaps no change at all, but that's a quick test.

In terms of deciding when you've gone too far, that depends on many factors.

At high wastegate duty you're likely at high exhaust temperature and pressure, perhaps high turbo shaft speed, and potentially generating very high compressor outlet air temperature. With sensors for these items, you can make a more educated decision.

A dyno also helps determine whether you're getting a meaningful gain out of an increase in boost pressure, or if the increase in exhaust pressure and intake temperature is preventing you from making significantly more power. Also, when there's a need to retard timing advance as boost increases to avoid knock, that may negate the gain from an increase in air mass.

Thank you Mike. That helps a lot.

Can wastegates be forced open by high exhaust pressure when using electronic boost actuators?

Depends on the type of actuator. The Turbosmart "Poppet" style will not move unless being driven as they are on a worm gear that locks into place when the motor is not adjusting the position. The DBW style units are supposed to be balanced on either side so they see equal load on the plate and shouldn't be able to be blown open. (see Steve Morris's video on this, he used the dbw style units for cold side boost control and snapped a throttle blade with the boost spike)

I have seen some of the OEM style electronic WG's blown open by back pressure.

+1 for Stephen's great comments, which mirror my experience.