Sensor measurements relative to crankshaft position

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Sensor measurements relative to crankshaft position

Postby Fast_Moto on Wed Aug 06, 2014 9:05 am

Is there any possibility to take the value measured by an input at a particular crankshaft position (or at any point within a range). The value would remain the same until the same crankshaft position has been reached again. Specifically, I would like to measure the manifold pressure of individual cylinders relative to a particular crankshaft position (or an average over a range). Obviously, the ECU does this for some of the outputs (ignition, injection). Any recommendations?
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Re: Sensor measurements relative to crankshaft position

Postby Holmz on Sat Aug 09, 2014 4:16 pm

That is a very interesting question.
I am not sure that ignition or injection are inputs.

Are looking for resonance? or just wanting a smoother pressure input?
For the later, all the cylinders can be hosed into a chamber to low pass filter the ensemble.

On pg92 of the "ECU Installation April2010.pdf it mentioned variable cam input.

I think that the only inputs that are referenced to the crank are the cam position inputs. So if one was looking at a rising or falling edge...The it may work.
At one point I convinced myself that I could measure the start of the coil's dwell by using a that input.

And external knock sensor would need to know the crank position, so it must be on the CAN stream(?).

If you were lucky enough to know where you wanted the measurement, and that it was near one of the rising or falling edges of the coils or the injectors, then a sample and hold could be used.
Otherwise the only way I know of doing that is to use a separate data acquisition system.

If you figure it out I would like to know.
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Re: Sensor measurements relative to crankshaft position

Postby stevieturbo on Sun Aug 10, 2014 8:37 am

Max-Torque over on Pistonheads is doing this with a goldbox.

How he has achieved it though I do not know, but he mentioned it a couple of years ago.

He's an electronics/automotive guy, so he may well have designed his own box to do it in conjunction with the Motec.

http://www.pistonheads.com/gassing/prof ... &mid=27545

Link below off topic, but it's a thread he posted, so you might be able to get his attention there

http://www.pistonheads.com/gassing/topi ... %283%29%29
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Re: Sensor measurements relative to crankshaft position

Postby Scott@FP on Sun Aug 10, 2014 1:26 pm

RPM Synchronous sampling has been around in the OEM world for quite awhile, if the input channel has a fixed sampling frequency not sure how you are going to accomplish that.
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Re: Sensor measurements relative to crankshaft position

Postby Fast_Moto on Wed Aug 13, 2014 1:51 pm

The reason I think this may be possible is because the low side ignition output also can work as an absolute voltage input. If there is a hardware mechanism for outputing a signal relative to crank position, it seems possible (at least theoretically) to do a measurement relative to crank position. Maybe this would require some low level programming of the pins. Maybe Motec could chime in and provide their perspective.
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Re: Sensor measurements relative to crankshaft position

Postby Scott@FP on Wed Aug 13, 2014 7:34 pm

At some point you are going to be RPM limited due to cylinder count (if common plenum) and response time of the most common abs pressure sensors, which is in the 1.0-1.5 mS range, or go to a high speed pressure sensor. if you want to experiment on the cheap with the concept of crank synchronous MAP sampling a 300 dollar Microsquirt (2 ign, 2 inj channel) will do it.
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Re: Sensor measurements relative to crankshaft position

Postby David Ferguson on Thu Apr 29, 2021 10:23 am

I found this thread while looking for this exact thing. It would be really great to have an event that runs at a specific crank angle, or perhaps a new input class for "cycle position sampled inputs", where you would specify a cycle position to sample the sensor input. I would also like to use that for capturing other channels, such as Engine Speed Reference Instantaneous.
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