Time trigger

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Steve Smith
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Re: Time trigger

Post by Steve Smith » Fri Apr 12, 2019 2:41 pm

Hello and thank you for the posts

This can be a challenging one with multiple PicoScope features at our disposal to capture VVT operation. These include Rotation Rulers, Partitions, Deep Measure, Measurements, Advanced Triggers, Persistence Mode and Masks etc. The following link may help here topic18471.html

Focusing upon “ease of use” I have gone with the following option:

Today I have been testing a Toyota Auris Hybrid that has a wonderful feature called “Linear Control” of the VVT Oil Control Valve (OCV) via Techstream (Toyota/Lexus Dealer scan tool)

Having finite control of the VVT system (via the scan tool) does simplify the interpretation of VVT operation as we get to visualize progressive valve timing “advance and retard”.

Depending on vehicle manufacturer and scan tool design, Linear VVT control may not be possible but VVT On/Off (instant advance/retard) is usually an alternative. This can prove challenging if you are trying to capture/visualize this momentary event but using the settings below will most certainly help.

We are going to need a minimum of 3 scope channels:

Channel A Crankshaft.
This signal is fixed and will be used as our “Clock” in which to reference the camshaft signal

Channel B camshaft (Inlet with the Auris above)
This signal is variable depending on VVT Control and timing chain/belt wear

Channel C Ignition cylinder 1 (Petrol) or Injection cylinder 1 (Diesel)
This signal is variable depending on ignition timing control but will allow sufficient stability to provide a synchronization signal every 720° of crankshaft rotation. This will ensure we reference the correct segments of the crankshaft sensor signal in relation to both cylinder 1 ignition event and our chosen camshaft reference point.

Channel D OCV Duty control. This signal is not essential but given we have a spare channel it serves to indicate when VVT control is “active”. We can obtain this information from the speed of the crankshaft (via maths) as VVT “forced” operation is often accompanied with a change in engine speed. With that said, if we have a fault with VVT operation (no fluctuation in engine speed during VVT forced operation) we can confirm the ECU is trying to active the VVT controller by graphing the duty control signal, again via a math channel.

The trigger required is “Simple Edge” falling trigger on the ignition or injection signal (Channel C) as this provides a more defined edge on which to place our time ruler. Ben mentioned a great tip here to use the current clamp around either your ignition or injection signal but once again, on the more defined falling edge.

The time required is a minimum of 20 ms/div as this should provide sufficient time to capture two complete crankshaft revolutions on one screen. This is not always the case depending on how slow the engine is running at idle speed or, if the engine is running unstable (i.e. poor combustion)

The number of samples required at this time frame is fine at 1 million (1 MS)

Another feature that will help here is Bandwidth Limit (active on all channels) for those who own the 4425 version of PicoScope. The following link describes the application of bandwidth limit. https://www.picoauto.com/library/training/filtering

Below we have the capture of the Auris at idle speed with VVT connected but not activated by the scan tool
1 SET UP AND MEASURE.png
Set Up and Measure
Using a single time ruler against the falling edge of our trigger signal (ignition cylinder 1) we can locate a nearby reference point on our camshaft (which just happens to align here with the falling edge of our sync signal) and a reference point on our crankshaft signal (clock)

If we now count the number of crankshaft pulses (teeth) between our chosen camshaft reference point and the missing teeth of the crankshaft (13 here) we have a point of “cam / crank” correlation on which to focus.

Normally, your chosen camshaft reference point would not coincide with the ignition trigger event as it does here, in which case, a second time ruler would be used. One time ruler to remain against your ignition trigger falling edge and one to align your chosen camshaft reference point against your crankshaft sensor signal. See Audi A2 example below using an additional time ruler
2 2nd Time Ruler.png
Audi additional Time Ruler
An important tip here is to choose a camshaft reference point as close as possible to the falling edge of your ignition trigger signal. This will minimize the effects of camshaft phase shift due to normal fluctuations in engine speed

Coming back to the Auris; with a stable capture at idle speed, right click on screen and select “Reference Waveform”. Click on the letter “B” to duplicate the waveform captured on Channel B
3 Reference waveform.png
Reference Waveform
With the reference waveform in place you can now utilize the scan tool to activate the VVT system and monitor the phase shift between the live camshaft waveform and your fixed camshaft “Reference Waveform” whilst also taking note of the live camshaft and crankshaft waveform correlation.

The animation below demonstrates this technique where the VVT is activated progressively via the scan tool
TEST 3 VVT OPERATION.gif
Animation of VVT Active Test
The video below includes the use of Techstream to achieve the above results
AURIS VIDEO.mp4
Auris Active Test
(5.96 MiB) Downloaded 73 times
The camshaft timing advancement in terms of crankshaft tooth count is 4 teeth in total, which we could calculate but let’s keep “ease of use” in focus
4 Phase shift.png
Phase Shift
Food for thought on this technique:

Whilst you can see VVT operation by free revving the engine (using the technique above) the increase in engine speed will change the widths of the pulses (reference points) on our camshaft and crankshaft, which by its nature, will introduce confusion.

Where possible, keep the engine speed fixed (to ensure no change in pulse widths) and use your scan tool “Active test” feature to drive the VVT system.

I will add some additional techniques here ASAP using longer time frames and math’s but for now I hope this helps, take care……Steve

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Re: Time trigger

Post by Autonerdz » Fri Apr 12, 2019 3:49 pm

It's way easier than that. We have covered this many times in our webinars. We call it a VVT range and response test. We leave the scan tool in the tool box for this.

Using the technique I described above and a proper capture time, you can measure the amount of total movement and the time it took to get there. Then you can verify the return to home position and also measure the time it took to return. You can capture all this on a single screen.

This method can reveal all sorts of issues with hydraulics and sticky actuators.

Steve Smith
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Re: Time trigger

Post by Steve Smith » Mon Apr 15, 2019 2:40 pm

Hello and thank you for the feedback

Would it be possible to add a link to your webinar as this would assist others with such knowledge and bring about additional diagnostic techniques?

Below is the final capture from Friday’s adventure where an increase in the time span to 20 seconds across the screen (2 s/div) presents an overview of VVT operation
1 OVERVIEW.png
Overview
Whist I have added the math channel “LowPass(60/36*freq(A),8” to graph the RPM, we can clearly see a fall and rise in rpm thanks to the characteristic behavior of an inductive crankshaft sensor during VVT operation (rise and fall in amplitude with rise and fall in rpm)

Using the Negative Duty Cycle math channel “duty-D” we can also see how the change in OCV duty coincides with a change in rpm, so confirming the effects of VVT upon engine speed.

The following links will help here with graphing
topic19271.html
topic21311-10.html#p97972

Below we have VVT at idle speed with no scan tool intervention.
Crank tooth count 13 teeth at 979 rpm with 57.19% OCV Negative duty
2 OVERVIEW IDLE NO VVT.png
VVT at Idle
Now VVT is advanced for the inlet camshaft using the scan tool
Crank tooth count 17 teeth at 767 rpm with 51.75% OCV Negative duty
3 OVERVIEW ADVANCED.png
VVT Advanced
The final image captures the return of the inlet camshaft to the retard position.
Crank tooth count 12 teeth at 1086 rpm with 87.94% OCV Negative duty
4 OVERVIEW ADVANCED.png
VVT Retarded
The Falling Edge Count measurement feature (between the time rulers) will help with a brief indication of “change” of camshaft position (VVT). More information on the Edge Count feature can be found here topic18591.html and applied here https://www.picoauto.com/library/case-s ... -operation

I hope this helps, take care……Steve

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Re: Time trigger

Post by Autonerdz » Mon Apr 15, 2019 3:20 pm

Would it be possible to add a link to your webinar as this would assist others with such knowledge and bring about additional diagnostic techniques?
We have been doing these Group Therapy webinars for 20 years. When the technology evolved to be able to record and preserve them, about 7 years ago, we began archiving them.

There are a few of them covering this technique:

https://www.autonerdz.com/grouptherapy.html

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Re: Time trigger

Post by Liteace » Mon Apr 15, 2019 3:41 pm

Thanks for the response and updates on this, it's back in next week so I'll do reading, make some notes and test again

Thanks again

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Re: Time trigger

Post by Liteace » Tue Apr 16, 2019 9:56 pm

Steve Smith wrote:
Fri Apr 12, 2019 2:41 pm


We are going to need a minimum of 3 scope channels:

Channel A Crankshaft.
This signal is fixed and will be used as our “Clock” in which to reference the camshaft signal

Channel B camshaft (Inlet with the Auris above)
This signal is variable depending on VVT Control and timing chain/belt wear

Channel C Ignition cylinder 1 (Petrol) or Injection cylinder 1 (Diesel)
This signal is variable depending on ignition timing control but will allow sufficient stability to provide a synchronization signal every 720° of crankshaft rotation. This will ensure we reference the correct segments of the crankshaft sensor signal in relation to both cylinder 1 ignition event and our chosen camshaft reference point.

This is a 16 valve engine with 2 cams sensors, 1 sensor per cam shaft, what I wanted to do was actuate / activate each cam individually with the scan tool to see, with the rulers on screen, the cam timing change and also see if the degrees given on the scan tool (Tech2) corresponded with the pico data, Ive tried triggering off all 3 channels and nothing.

I remember looking at Pico live data / waveform many years ago on a Nissan almera that had a stretched chain, triggered off the crank, it all sat there as smooth and anything, you could see the cam trace wondering and could even work out the degree's

I dont know if my scope is broke, its to sensitive or the software has changed but its not like it used to be, I'll keep battling on as need a result

Thanks

Liteace
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Re: Time trigger

Post by Liteace » Tue Apr 16, 2019 10:00 pm

Liteace wrote:
Tue Apr 16, 2019 9:56 pm
Steve Smith wrote:
Fri Apr 12, 2019 2:41 pm


We are going to need a minimum of 3 scope channels:

Channel A Crankshaft.
This signal is fixed and will be used as our “Clock” in which to reference the camshaft signal

Channel B camshaft (Inlet with the Auris above)
This signal is variable depending on VVT Control and timing chain/belt wear

Channel C Ignition cylinder 1 (Petrol) or Injection cylinder 1 (Diesel)
This signal is variable depending on ignition timing control but will allow sufficient stability to provide a synchronization signal every 720° of crankshaft rotation. This will ensure we reference the correct segments of the crankshaft sensor signal in relation to both cylinder 1 ignition event and our chosen camshaft reference point.

This is a 16 valve engine with 2 cams sensors, 1 sensor per cam shaft, what I wanted to do was actuate / activate each cam individually with the scan tool to see, with the rulers on screen, the cam timing change and also see if the degrees given on the scan tool (Tech2) corresponded with the pico data, Ive tried triggering off all 3 channels and nothing.

I remember looking at Pico live data / waveform many years ago on a Nissan almera that had a stretched chain, triggered off the crank, it all sat there as smooth and anything, you could see the cam trace wandering and could even work out the degree's

I dont know if my scope is broke, its to sensitive or the software has changed but its not like it used to be, I'll keep battling on as need a result

Thanks

ben.martins
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Re: Time trigger

Post by ben.martins » Tue Apr 30, 2019 1:15 pm

Hello Liteace,

Sorry to hear you're still having problems getting the setup to work for you.

Lets step back and re-look at the advanced trigger option and see if we can get the setup right to see if that can help stabilise the image. We can have both the cams and the crank present on the screen and may be worth while using an ignition source as well just to give us an idea of cylinder 1.

In order to get this correct we need to set the trigger on a CAM that isn't going to be actuated or better still disconnect the OCV to prevent it from moving in relation to the CRANK. If I use capture you sent into us to get some values then you should be able to set this up accordingly.

To start with you need to identify what 'pulse' you would like to trigger from. I'm going to suggest using the pulse width trigger but under the condition use the Greater than option. The reason being if you were having trouble with ignition energy causing an incorrect trigger then I would look for the pulse bigger than this to eliminate it. Looking at the CAM pattern you have there are two small pulses and two larger pulses and using the greater than condition we would like to trigger on the biggest pulse. This means we need to measure the next smallest pulse down in order for our trigger to look for a pulse that is bigger. Measure both the two larger pulses to determine this but also make a note of the long they are.

In your capture we have a pulse of 31.63ms and 31.28. I've set a crossing point for the trigger at 3V but anywhere on the crossing line would be ok and then you can zoom right in to where the waveform crosses this point and place your time rulers at this intersection. This will give you a very accurate measurement. From the above measurements we would like to place a trigger that is looking for a pulse greater than 31.28ms, which hopefully will mean the only one left to trigger on is the next pulse up at 31.63ms.
Advanced trigger.png
Selecting the advanced trigger options icon from the toolbar select the Pulse Width option. If we are still using your capture I've used Channel C as my source, the direction is Negative, Condition is Greater Than, Thereshold set to 3V and time is 31.3ms. Hysteresis can be kept low as it's a fast edge on this sensor and I just found the Negative option seemed to be more stable. This should hopefully give you a good trigger on one of the CAM sensors where you can now drive the other with your scan tool to see its movement. I've tried this using your CAM image and a waveform generator and it does work but I've not had the opportunity to try this live on a car.

I hope this helps and please let us know how you get on.

Kind regards

Ben

Liteace
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Re: Time trigger

Post by Liteace » Mon May 06, 2019 6:41 pm

I'll give this a go when its back in

Thanks all for the help up to now

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