RPM ringing "boioioing" on low RPM tip in
#1
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The thread on CKP trigger wheels got me thinking about how much error it might get when the crank is accelerating or decelerating quickly.
Out of curiousity I examined the characteristics of driveline windup and ringing in my datalogs. Wondering how much acceleration it had. See below. I floored the throttle at ~2000 RPM to have a look.
The RPM trace shows the characteristic ringing which sounds and feels like a sort of "boioioing".
Here's what I found. The ringing is at 6 Hz, and the effect on RPM is around 240 Hz peak-to peak. IOW if you start at 2000 RPM and floor it, for the first few cycles it will peak at 2120 RPM, dip to 1880, repeat, until it dies out. The peak rate of change appears to be close to 1000 RPM/sec, on top of the 300 or so from accelerating the car (3rd gear, ~100 kPa).
I ran some math assuming sinusoidal frequency modulation of the RPM trace.
If you modulate RPM at 6 Hz, and the driveline lash is 3° is either direction, I get very close to 240 RPM peak to peak, and 700 RPM/sec peak acceleration.
FWIW decelerating in neutral with my 11 lb flywheel is around 1500 RPM/sec.
So the engine appears to rock 3° in each direction.
More later on the resulting error in crank angle...
Upper trace is RPM, lower is TPS.
Horizontal scale is 1 sec per division, I rolled the throttle in in about 0.5 sec.
Out of curiousity I examined the characteristics of driveline windup and ringing in my datalogs. Wondering how much acceleration it had. See below. I floored the throttle at ~2000 RPM to have a look.
The RPM trace shows the characteristic ringing which sounds and feels like a sort of "boioioing".
Here's what I found. The ringing is at 6 Hz, and the effect on RPM is around 240 Hz peak-to peak. IOW if you start at 2000 RPM and floor it, for the first few cycles it will peak at 2120 RPM, dip to 1880, repeat, until it dies out. The peak rate of change appears to be close to 1000 RPM/sec, on top of the 300 or so from accelerating the car (3rd gear, ~100 kPa).
I ran some math assuming sinusoidal frequency modulation of the RPM trace.
If you modulate RPM at 6 Hz, and the driveline lash is 3° is either direction, I get very close to 240 RPM peak to peak, and 700 RPM/sec peak acceleration.
FWIW decelerating in neutral with my 11 lb flywheel is around 1500 RPM/sec.
So the engine appears to rock 3° in each direction.
More later on the resulting error in crank angle...
Upper trace is RPM, lower is TPS.
Horizontal scale is 1 sec per division, I rolled the throttle in in about 0.5 sec.
![](https://www.miataturbo.net/attachments/ecus-tuning-54/31612d1326474499-rpm-ringing-boioioing-low-rpm-tip-rpm-boioing.gif)
#2
Tour de Franzia
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It's cool to know that while I'm at home, alone, in the cold, pretending the cat understands me while I drink beer and play a video game with a steering-wheel clamped to a coffee table, there is a team of engineers on Miataturbo working around the clock to make my car faster, more reliable, and writing it at a 3rd grade level so I can interpret it. It would have been nice if you guys could have done all this four years ago so I don't have to waste my precious time doing things twice.
#8
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It's cool to know that while I'm at home, alone, in the cold, pretending the cat understands me while I drink beer and play a video game with a steering-wheel clamped to a coffee table, there is a team of engineers on Miataturbo working around the clock to make my car faster, more reliable, and writing it at a 3rd grade level so I can interpret it. It would have been nice if you guys could have done all this four years ago so I don't have to waste my precious time doing things twice.
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#10
Boost Pope
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It's cool to know that while I'm at home, alone, in the cold, pretending the cat understands me while I drink beer and play a video game with a steering-wheel clamped to a coffee table, there is a team of engineers on Miataturbo working around the clock to make my car faster, more reliable, and writing it at a 3rd grade level so I can interpret it. It would have been nice if you guys could have done all this four years ago so I don't have to waste my precious time doing things twice.
![big grin](https://www.miataturbo.net/images/smilies/biggrin.gif)
(I am finding, for some reason, that the hysteresis of the circuit is not meeting published specs. Not quite sure what's up with that yet...)
#11
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Jason, what's the effect with, say, a 4000RPM tip-in? I know that I avoid lugging like the plague. However, the engine rock would still be there at about the same frequency at high RPM -- and because that's a higher torque area, I'd expect the rock to have higher amplitude. To lazy to do the math myself.
Plus, I'm still using a CAS, so now I have to factor in the timing belt. Darn it, you're going to keep me up nights!
Plus, I'm still using a CAS, so now I have to factor in the timing belt. Darn it, you're going to keep me up nights!
#13
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I have been experimenting all morning with different circuit topologies for trigger input decoders. Picked up a handful of CD40106es earlier in the week, and I'm doing variants on the JasonC schmitt-trigger circuit at this very moment. ![big grin](https://www.miataturbo.net/images/smilies/biggrin.gif)
(I am finding, for some reason, that the hysteresis of the circuit is not meeting published specs. Not quite sure what's up with that yet...)
![big grin](https://www.miataturbo.net/images/smilies/biggrin.gif)
(I am finding, for some reason, that the hysteresis of the circuit is not meeting published specs. Not quite sure what's up with that yet...)
I am going to use JasonC's schmitt-trigger circuit to feed my MS3 running my vvt engine.
-Raj
#14
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It's cool to know that while I'm at home, alone, in the cold, pretending the cat understands me while I drink beer and play a video game with a steering-wheel clamped to a coffee table, there is a team of engineers on Miataturbo working around the clock to make my car faster, more reliable, and writing it at a 3rd grade level so I can interpret it.
For some reason, we have a lot of these people on MT.net. It's why I'm addicted to it.
Of course, there is also newb buggery.
#16
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Jason, what's the effect with, say, a 4000RPM tip-in? I know that I avoid lugging like the plague. However, the engine rock would still be there at about the same frequency at high RPM -- and because that's a higher torque area, I'd expect the rock to have higher amplitude.
As for timing errors, it will always be proportionally worse at low RPM. E.g. say you have 2° error doing this at 1000 RPM, it will be 0.5° at 4000 RPM. This is also why if you do the throttle-blip-in-neutral timing test where you set the ECU to do constant timing, you will see the most error initially at low RPM, and it diminishes as RPMs rise.
#18
Boost Pope
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In fairness, I have a handful of the 40106s sitting here and I've only tested one gate of one chip so far. I'm going to go through the rest of them and see what kind of spread I find.