Stupid question...radiator fans...ac or dc input?

[MadMark]

Great thread I learned a lot, two questions:

The new pulse width modulated fans, are they stepper motor driven?

And why is an O2 sensor called a lambda sensor?

Thanks guys

 

[Stick]

Great thread I learned a lot, two questions:

The new pulse width modulated fans, are they stepper motor driven?

Normal DC motors. Speed is controlled through PWM and duty cycle.

And why is an O2 sensor called a lambda sensor?

Lambda is when fuel/air mixture is ideal, or a lambda of 1.0. An o2 sensor is just a switch who's midpoint is at lambda. Greater than lambda (1.01 or higher), and fuel is cut. Less than lambda (.99 or less), and fuel is added.

Some manufacturers call it a lambda sensor because it's technically a more accurate term than "oxygen sensor", because they don't actually sense oxygen.

 

[Stick]

The bottom line is that you can measure it with a DC DVM in the millivolt range, and get useful info on it...

I think it's more that the PCM is looking at the DC voltage output of the sensor to determine what to do, and not worrying about the fact that the voltage varies slightly. As far as the PCM is concerned, an O2 sensor is a switch. You're either above stoichiometric, or below it, and that's what the PCM is worried about.

 

[Vvmvbb]

Normal DC motors. Speed is controlled through PWM and duty cycle.



Lambda is when fuel/air mixture is ideal, or a lambda of 1.0. An o2 sensor is just a switch who's midpoint is at lambda. Greater than lambda (1.01 or higher), and fuel is cut. Less than lambda (.99 or less), and fuel is added.

Some manufacturers call it a lambda sensor because it's technically a more accurate term than "oxygen sensor", because they don't actually sense oxygen.

Just to clarify a little. lamda control is a feedback loop that adjusts the pulse width for the fuel injectors such that there is exactly enough fuel to just completely burn in the amount of air comming in as measured by the air flow sensor (MAF or AFM). At that balance it turns out that the air to fuel ratio = 14.7. For simplicity, that balance is also defined as lamda = 1. So the injected pulse width is adjusted so that lamda = 1. When lamda > 1, there is too much air for the fuel injected (lean). When lamda < 1, too little air (rich).

 

[Outlawmws]

That DVM when set to DC should give you the DC component and when set to AC should give you the AC component. Always good to check both when looking at a signal with a DVM and not an oscilloscope.

Good dvm can show both ac+ dc at the same time. My fluke 189 does.

Sent from my Galaxy Nexus using Tapatalk 2

Yeah verifying the presence of the AC component should be a very good thing to do when troubleshooting O2 (lamda) control, heh? It would tell you that the the control loop is at least trying to work (out of open-loop mode and making fuel adjustments). Next time I change out an O2 sensor I'll grab a scope trace before and after for kicks.
DC coupled probe, of course ;-).

I think it's more that the PCM is looking at the DC voltage output of the sensor to determine what to do, and not worrying about the fact that the voltage varies slightly. As far as the PCM is concerned, an O2 sensor is a switch. You're either above stoichiometric, or below it, and that's what the PCM is worried about.

For what I'm after, none of this matters... All I care about is if the voltage is between about 200mv and 750 mv, and because of the slope it reads (look at the chart in my original post) it has the proper A/F mix. Anything else and something is hosed and I need to do something.

The idea is that in a pre OBD vehicle (Or even a motorcycle) you can install an O2 sensor and use it to tune the carb and KNOW if the AF mix is where you want it. You can wire the DVM in, hang it on the dash and monitor it while driving.

 

[Vvmvbb]

For what I'm after, none of this matters... All I care about is if the voltage is between about 200mv and 750 mv, and because of the slope it reads (look at the chart in my original post) it has the proper A/F mix. Anything else and something is hosed and I need to do something.

The idea is that in a pre OBD vehicle (Or even a motorcycle) you can install an O2 sensor and use it to tune the carb and KNOW if the AF mix is where you want it. You can wire the DVM in, hang it on the dash and monitor it while driving.

For that you might consider a wideband O2 sensor. Much wider dynamic range. A traditional narrow band sensor will respond over air/fuel ratios of ~14.5 ~ 15 or something. The wide band from ~5 ~ 22. If you measure your narrow band and you are in range, you are good as you say. But if you are off, the wideband can help you know how the adjustments you are making are moving you towards the nominal 14.7. Needs a controller unlike the narrow band.

 

[magova1104]

Thanks to Outlawmws, Stick and Vvmvbb. I really enjoyed and learned a lot in this thread.