Roots superchargers usually have a bypass valve that is open at idle.

I want to start playing with the electric bypass valve that came with my Mercedes kompressor
(mentioned here: thread71-205859: Sound suppression for Lysholm compressor with blow-thru throttles )
and I am wondering which strategy to choose. I can make it TPS or MAP dependent.

I was wondering when it should close.
Should it close gradually from above a certain level of inlet pressure on, or does it shuts close over a fairly short stroke of throttle, located somewhere above the cruise position?

Is this a turbocharged and blown engine?  I am familiar with a bypass arrangement on the old 2 cycle Detroits where at cruising speeds the turbo would put up more air than the blower could pass so there was a spring loaded bypass around it to let the extra air get into the airboxes.  Only when the pressure between the turbo and the blower started building up would the spring pressure be overcome but what you are describing and wanting to do is diametrically opposite to that situation.

If one absolutely must put the blower upstream of the throttle, you may do well to copy the throttle body setup as used by VW on the G60 engine.  (The G60 used a remotely mounted positive displacement supercharger)

They employed a bypass throttle that was mechanically coupled to the standard throttle plate.  When the throttle is closed, the bypass is wide open, and vice-versa.  It also appears that the butterfly is biased to blow open with pressure, if the linkage should disconnect.  Certainly, they trusted its operation enough to put it into mass production.

My experience on similar systems (Mini Cooper S) has shown that the bypass (operated on purely manifold vacuum with no active control) is continually variable so even at part load there is still some positive pressure effect from the S/C. On the Siemens system used on Mini this was compensated for by using a MAP sensor before and after the S/C which then fed back into the ETC control and torque model. This prevented any drivability/surge issues as the balance of low pressure/high pressure changed through the engine speed and load range.

We tried implementing electronic bypass control in the interests of pursuing part load fuel economy and improving response but the cost out-weighed the benefit and it never made it into production.

Pat makes a good point in saying that OE's spend a lot of time/effort/money getting these systems to work so unless you're prepared to have the potential of some significant compromise you maybe better off focusing your efforts on something

So far, the bypassvalve starts closing at about 60% TPS and is fully closed around 75% TPS, this means that it's position is dependant of TPS.
I had a look at my logfiles and found out the following: the boost builds up over a much smaller TPS range than over which the valve is closing.
This makes engine operation feel jerky and somewhat uncomfortable because boost always build up at the same point, independent of RPM and driving conditions (uphill-downhill).

So, I'll have to extend the TPS range over which the valve closes or go for the other approach.
That will be to drive the valve(ball valve) so as to deliver a certain boost dependant of TPS.
I'm tending to go for that second one, and in the mean time I'll foresee the necessary wiring for all the relevant parameters to be logged by one device and not by two separate like now, because that makes it awkward and unprecise to reconstitute te dat.

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