VVT minimum MAP

[y8s]

I know I love to post new threads about random little features... so here's a new one!

When I was originally playing with the VVT in my Miata / MX-5 with another EMS, one of the issues I had setting it up was severe oscillation of the system at low loads. 

In other words, during free revving or light cruise, as the cam dipped into the low advance range, the setting would oscillate like crazy.  The end result was that the car couldn't hold a constant RPM (say 3000 rpm) because the engine torque kept changing.

I managed to fix this issue pretty easily because the system was 3D MAP vs. RPM based.  I simply set the advance to the minimum (full retard) up to, say 70 or 80 kPa (because who cares about maximizing power when you're not full throttle?) and it stopped the oscillation.

I haven't had a chance to play with the VVT setup in the Adaptronic yet, but:

1. has this been an issue for anyone yet?

2. if it has, can it be implemented?

It may be that the other system just had a terrible feedback methodology and the control loop was unstable at that particular load/rpm, but who knows.

[Nick_R]

Well the e420c uses a PID controller for continuous VVT and anyone who has studied control theory will tell you that an unstable system is almost certainly the result of bad PID gain values. Unless the system itself is inherently unstable, or you don't have enough control authority, it should be possible to choose PID values that don't cause oscillation. In addition, you can choose a whole new set of PID values for each RPM band. This is needed because the engine oil pressure at the actuator changes with RPM.

Cheers,
-Nick (Adaptronic)

[y8s]

the previous system was a PI only.  To be honest, I had never changed the P and I values when I had it because they were in a strange place in the settings.  In retrospect, you make a very obvious point.