How to measure a Bosch LSU 4.9 wideband lambda sensor

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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Fat Freddy » Wed Oct 14, 2015 11:24 pm

I haven't found actual figures but this table shows λ 25.5 in relation to O2. I don't think I'm too far out. Not much point in engineers writing software for above that 25.5 - no point taking it to , it'll take forever.

LambdaPercent[1].gif


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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby KimAndersen » Sat Oct 17, 2015 7:49 am

Hi FF

I agree with you, this specification chart is pretty close or the same as the calculations I did. I found the calculation formula in a datasheet from Bosch where the oxygen vs lambda table is shown.

Based on the document, was I able to make the calculation backwards from the lambda values I got from my test drive.

The lambda reading I got when the car was de´accelerated, were 25,5 which equals to a oxygen percent at 20,087 in the exhaust system.

I must say, that I'm surprised about the high lambda reading I got, but I can't argue against the true facts you have shown me.

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Kim :wink:
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Fat Freddy » Mon Oct 19, 2015 2:50 am

KimAndersen wrote:Hi FF

I agree with you, this specification chart is pretty close or the same as the calculations I did. I found the calculation formula in a datasheet from Bosch where the oxygen vs lambda table is shown.

Based on the document, was I able to make the calculation backwards from the lambda values I got from my test drive.

The lambda reading I got when the car was de´accelerated, were 25,5 which equals to a oxygen percent at 20,087 in the exhaust system.

I must say, that I'm surprised about the high lambda reading I got, but I can't argue against the true facts you have shown me.

Regards
Kim :wink:


Hi

That makes me happy. My formula is a home made reverse engineered effort that seems to work. Well at least get fairly close.
I get 20.118% with atmospheric being 20.94% for 25.5 λ

You can also see why there is no point programming above 25.5. Error will occur. Between 25.5λ and 35.5λ is only 0.232% difference. So any + or - error in % will be minimal but in λ will be huge. :shock:

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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby KimAndersen » Sun Nov 22, 2015 8:56 pm

This time I want to show, how to measure the oxygen content in the exhaust system by first converting the pump current to a voltage signal and then make a lookup table with the oxygen percent vs. voltage signal on the Bosch wideband sensor LSU 4.9.

I know that, the subject has been discussed before by Fat Freddy and that he had some trouble regarding to the accuracy of his test and the same experiences did I, with respect to noise on the signal.

I needed a new approach to tackle this problem to get rid of the noise I was seeing.

The answer to this problem was to use my new precision multimeter current adapter which is called "µCurrent GOLD"
http://www.eevblog.com/projects/ucurrent/.This adapter converts very small current into a milli volt output signal. The only drawback by using the method of measurement is, that you has to break into the circuit, but besides this are there no other drawbacks.

The next step in this process was to make a lookup table based on the technical documentation from Bosch over the wideband oxygen sensor LSU 4.9.This image shows the original lookup table from Bosch´s datasheet with very few data points.

BOSCH_LSU4.9_LOOKUP_TABLE.jpg
BOSCH LSU4.9 LOOKUP TABLE


With these 5 data points have I chosen expand lookup table scaling a lot more exactly to 1601 new data points which is done by some software where it is possible find the correct non-linear curve. The new lookup table have a range from 0 to 21,245178 percent oxygen with an interval at 0,012096 (O2%).

To make this comment short, it´s not a easy task to convert a oxygen percent into a lambda value and then convert this to a milliamp value for then finally to convert this to a voltage value - are you confused - me too !!!.

As mentioned before has this lookup table has range from 0 % oxygen to 21,24, so it is only possible to measure excess oxygen content in the exhaust system as there were no calculation formula which describes the oxygen content below 0 % according to the Bosch datasheet.

The image below show the car during dynamically a road test where the engine are being accelerated to around 3500 - 4000 RPM. The peaks in this scope capture are when the gear changes happens - starting with 4 gear and ends with 6 gear.

BOSCH_LSU49_OXYGEN_CONTENT_ROADTEST.jpg
BOSCH LSU49 OXYGEN CONTENT DURING ROADTEST


BOSCH_OXYGEN_LSU4.9_ROADTEST.psdata
BOSCH_WIDEBAND_SENSOR_LSU49_OXYGEN
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Robski » Mon Nov 23, 2015 12:01 am

.This adapter converts very small current into a milli volt output signal. The only drawback by using the method of measurement is, that you has to break into the circuit, but besides this are there no other drawbacks.

This would depend on what type of coupling scope you're using because the device requires differential coupling as it has a floating ground, I know I have one ..................
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