BMW Valvetronic evaluation

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Steve Smith
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BMW Valvetronic evaluation

Post by Steve Smith » Fri Oct 04, 2019 3:01 pm

Cutting a long story very short:
BMW 114i (N13) suffered a vacuum pump seizure due to oil starvation. This resulted in “locking” of the exhaust camshaft that consequently “spun” the exhaust Vanos unit until the securing bolt sheared and the rest as they say, is history.

Post engine repair I saw a great opportunity to measure the control signals to the Valvetronic unit (responsible for adjusting the inlet valve lift) which utilizes a 3-Phase DC brushless motor.

It is worth mentioned here that Valvetronic (VT) is predominately about reducing fuel consumption and includes many beneficial side effects such improved engine efficiency with a reduction in exhaust emissions. VT operation allows the throttle plate to remain in a fixed position under a variety of engine operating conditions where air intake is controlled by varying intake valve lift!

With the VT actuator disconnected the engine can run as normal utilizing the throttle plate for conventional air intake control with a fixed valve lift (set to maximum)

Below we have engine rpm plotted against throttle plate position and manifold pressure (No VT operation) Here we can see a typical response from the MAP sensor as throttle plate opens to introduce atmospheric pressure followed by an increase above atmospheric thanks to turbo charger activity

IMAGE 1.png
Image 1
Below we have an overview of engine speed, throttle plate position and MAP sensor activity during engine speed increase from idle to medium speed, then WOT. (No VT operation) The fluctuations in the MAP sensor and the throttle plate indicate air intake control is via throttle plate operation only and not the VT assembly. This capture can be used as evidence that VT is inactive
IMAGE 2.png
Image 2
Moving now to a WOT test with VT connected and active

The additional channels at the bottom of this capture are connected to the VT motor which I will go through later. Notice the completely different signature from the MAP sensor during the WOT event given there is very little change in manifold pressure until approx. 26.03 seconds where the throttle has reached its maximum position at 4.47 V. Here we use a combination of varying valve lift and throttle plate control. (N.B Max power demanded by the driver will result in WOT regardless of VT active or inactive)
IMAGE 3.png
Image 3
Below we have an overview of engine speed, throttle plate position and MAP sensor activity during engine speed increase from idle to medium speed, then WOT. (with VT operation) Focusing on the MAP sensor from idle through to medium engine speed we have minimal fluctuations by comparison to image 2 above (VT inactive) thanks to a combination of throttle plate control in combination with variable intake valve lift. This capture can be used as evidence that VT is active
IMAGE 4.png
Image 4
Concentrating on MAP sensor voltage, there is virtually no change in manifold pressure until we go to WOT. The voltage here is fixed at 1.775 V regardless of engine speed which is quite impressive when you think that the MAP sensor reads 1.859 V at atmospheric with ignition on engine off! The manifold pressure is held purposely below atmospheric to enable purging of the fuel tank via the EVAP system. I have also included a number of measurements that highlight throttle position & MAP sensor rise time/rise rates to bring home how the different air intake control strategies influence these values.

Looking now at the Valvetronic motor control, below I have included the channel labels to assist with identification of each channel
IMAGE 5.png
Image 5
Below we focus on MAP sensor activity with VT active during the transition from WOT to over-run. I chose this area of the waveform rather than idle to WOT due to the noise present on all waveforms thanks to Ignition/injection and 3 phase activity.

Note the current flow through each phase of the VT actuator accompanied with one of the 5 hall effect position sensors confirming rotor activity/motion
IMAGE 6.png
Image 6
To assess the electrical integrity of the VT actuator we can compare phase current for repeatability, uniformity and peak to peak values, which should theoretically be near equal. Below we have some variance in the peak to peak value of channel G (“U” Phase). Whilst the vehicle has no running errors, I may revisit this value to check for a possible measurement error such as current clamp drift!
IMAGE 7.png
Image 7
Note below how the 3 phases align perfectly with each current peak (120° apart) using the rotation rulers to denote 0-360° then partitioned by 3 to reveal the three phases. I know as the years go by this measurement will become more frequent than 0-720° partitioned by 4! Take a look at the “U” phase voltage fixed at approx. 14.58 V (CH D) & how the “U” phase current increases in proportion (CH G) both highlighted in yellow
IMAGE 8.png
Image 8
Finally, to add a clearer view of events we can use maths and filtering to bring about clarity.
IMAGE 9.png
Image 9
To graph the RMS of the VT actuator 3 Phase current please see the “Maths is cool" post here

I will try to add more on those VT Actuator position sensors ASAP

Following on from the previous comment regarding 5 Hall Effect position sensors integrated into the VT actuator, please find below all 5 position sensors in action with “Channel Labels” for reference. Here we move the VT actuator from idle to WOT, back to idle then ignition off. Note how they all differ with regards to output and orientation
IMAGE 11.png
Image 11
Below we have zoomed in at the point of WOT followed by releasing the gas pedal. (MAP sensor CH C starts to fall towards end of capture)
IMAGE 12.png
Image 12
The final capture below looks at all 3 phase voltages during the shutdown (passive discharge period)
We had previously looked at Phase current (images 6 and 7 above) in order to evaluate the electrical integrity of the VT actuator. Comparing phase current for repeatability, uniformity and peak to peak values, which should theoretically be near equal (here each phase is under load)

Monitoring the 3 phase voltages at the point of “vehicle power down” allows us to record the voltage decay during the passive discharge phase, which once again should be near equal without “drop out” across the expected decay time. This delay time is not specified and so we refer to the capture below at approx. 26 seconds as a typical example (Here each phase is off load)
IMAGE 10.png
Image 10
I hope this helps....
Take care……..Steve

wohcfets
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Posts: 4
Joined: Tue Feb 18, 2020 3:47 am

Re: BMW Valvetronic evaluation

Post by wohcfets » Thu Feb 20, 2020 4:58 am

Awesome analysis!
It would be even better if digging deeper into 5 hall effect sensor waveforms. I don't understand why using 5 sensor for monitoring motor position.

Rfmotors1
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Posts: 6
Joined: Fri Aug 31, 2012 8:14 am

Re: BMW Valvetronic evaluation

Post by Rfmotors1 » Sat Feb 22, 2020 5:40 am

Hello Steve,

This is really excellent deep analysis, not only demonstrate the picoscope ability but it's also highly educational.
I just imagine the 3 current clamps on the harness that is difficult to reach, break out leads..... very nice 👌.

This also explains why the engines which have this valve lift system malfunctioning due to faulty ignition coils and DTC regarding this valve lift, valvetronic. I imagine that coil makes interference resulting in corrupted Hall sensors signal.

Really very nice and valuable info, thank you very much for sharing it.

Regards,
Roman

leonardorj
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Posts: 4
Joined: Tue Mar 24, 2020 1:32 pm

Re: BMW Valvetronic evaluation

Post by leonardorj » Tue Mar 24, 2020 1:52 pm

Bacana a analise !

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