Rev limiter via E-throttle questions

[Pete_89t2]

I'm using a G4+ Fury in an FD RX7 with a DBW throttle. I'd like to use the E-throttle map to act as a rev limiter function, basically by pulling the throttle back to 0% (or near 0%) when the RPMs hit my red line (e.g. 8000RPMs), regardless of accel pedal position.

Currently I have the RPM (x-axis) set up from 0 to 8000 RPM, in 500RPM increments. So as I understand it, setting the throttle to 0% for the entire 8000RPM column would implement a throttle based rev limit at 8000RPM. My question is does the E-throttle table provide interpolated throttle values between the previous 7500 RPM column and the 8000 RPM column? If so, that would be undesirable, as for example at 7900RPM, and at an AP position of 100%, throttle position would be reduced to something close to 0% well before hitting my 8000RPM redline.

Would it be better to add a column at say 8050 RPMs, which would be set to all 0% throttle, and have the prior 8000RPM column track 1:1 with the AP position? That way if interpolation is happening, any AP position above 8000RPM would have its throttle position pulled back to near 0% after RPMs cross the 8000 RPM mark. Am I understanding this correctly?

Thanks in advance!

[Confused]

Yes, it will interpolate between columns.

What you could do, though, is add one extra column before (at 7900) with your 7500 values - it will then only interpolate towards 0 between 7900 and 8000

[Dean]

Would the throttle oscillate too much then? ie. 0 throttle will drop the RPM quickly, then full throttle will increase the revs again etc. etc.

I've had good results with this setup for my e throttle. The throttle starts to close as I reach redline, then it holds steady even if the pedal is flat to the floor.

I can keep the wheels spinning even though the TP says 40% and boost is down to 11psi. If the rpm start to drop, the throttle starts to open more.

.

 

[Pete_89t2]

17 hours ago, Confused said:

Yes, it will interpolate between columns.

What you could do, though, is add one extra column before (at 7900) with your 7500 values - it will then only interpolate towards 0 between 7900 and 8000

Thanks, that confirms what I was assuming. Since I used up all 16 columns for my X axis, I can't add another column, but I can adjust the X axis RPM breakpoints. So now it goes from 0 to 6000 RPMs in 500 RPM increments, then 6000 - 8000 in 1000 RPM increments, which gets to 15 columns, and I made the last column 8100 RPMs for now. So I can use the 8100 RPM column to pull back throttle, and it can interpolate throttle between the 8000 & 8100 values.

8 hours ago, Dean said:

Would the throttle oscillate too much then? ie. 0 throttle will drop the RPM quickly, then full throttle will increase the revs again etc. etc.

I've had good results with this setup for my e throttle. The throttle starts to close as I reach redline, then it holds steady even if the pedal is flat to the floor.

I can keep the wheels spinning even though the TP says 40% and boost is down to 11psi. If the rpm start to drop, the throttle starts to open more.

.

 

That's a great point I hadn't considered, and thanks for sharing what worked for your setup. I haven't fully tuned this car on a dyno yet, but since it's a rotary, I'd expect peak power to fall somewhere in the neighborhood of 6500~7800 RPMs, given its current porting, turbo & exhaust setup. And since rotaries are pretty tolerant of high RPMs, phasing in a softer throttle based rev limit just past where the power peak starts dropping off, similar to your E-throttle map may be a better approach than the more abrupt pull-back I had in mind.