How does this circuit work?
turbosupra
Posts: 1,088
Apparently it keeps voltage bouncing above and below .45vdc? Just trying to figure out step by step how this happens, and if it'd be worth it to try and emulate on the propeller instead?
Then I can design something on the prop to emulate it I hope.
The first circuit is the stock one, the second is the modified circuit that emulates the stock o2 sensor reading/output.
Post Edited (turbosupra) : 12/28/2009 7:21:47 PM GMT
Then I can design something on the prop to emulate it I hope.
The first circuit is the stock one, the second is the modified circuit that emulates the stock o2 sensor reading/output.
Post Edited (turbosupra) : 12/28/2009 7:21:47 PM GMT
Comments
Black probe connected to the black wire?
Is the black wire connected to ground?
Without the INNER circuitry of what's behind the connector and what's inside the O2-sensor this is hard to say.
What can be said is that the 1 MOhm-resistor causes a voltagedrop across the resistor himself. Following Ohm's law
the voltagedrop depends on the current.
What happends depends on who is the current-source and who is the current-sink
a) the connector is the current-source
If the voltage changes on the connectorside the capacitor will charge/discharge very fast as there is no current-limiting resistor towards the connector
b) the sensor ist the current-source
If the voltage changes on the sensorside the capacitor will charge/discharge pretty slow as the current is limited by the 1MOhm resistor towards the connector
Anyway the 1MOhm-resistor limits the current flowing through the blue wire
From a AC point of view it is a low-pass-filter
like explained here
The mathematical description there is pretty complicated. I ONLY used the fc-formula (cutoff-frequency) to calculate electronic parts.
The most important information to analyse this is how does the sensor work?
Is the basic principle the CURRENT changes with changing O2-values? or is the VOLTAGE changing with changing O2-values?
You seem to have the circuit from somewhere else. Can you post a link? That we can read the additional information?
best regards
Stefan
An Oxygen sensor is a chemical generator. It is constantly making
a comparison between the Oxygen inside the exhaust manifold and air
outside the engine. If this comparison shows little or no
Oxygen in the exhaust manifold, a voltage is generated. The
output of the sensor is usually between 0 and 1.1 volts. All
spark combustion engines need the proper air fuel ratio to
operate correctly. For gasoline this is 14.7 parts of air to one
part of fuel. When the engine has more fuel than needed, all
available Oxygen is consumed in the cylinder and gasses leaving
through the exhaust contain almost no Oxygen. This sends out a
voltage greater than 0.45 volts. If the engine is running lean,
all fuel is burned, and the extra Oxygen leaves the cylinder and
flows into the exhaust. In this case, the sensor voltage goes
lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.
The sensor does not begin to generate it's full output until it
reaches about 600 degrees F. Prior to this time the sensor is
not conductive. It is as if the circuit between the sensor and
computer is not complete. The mid point is about 0.45 volts.
This is neither rich nor lean. A fully warm O2 sensor *will not
spend any time at 0.45 volts*. In many cars, the computer sends
out a bias voltage of 0.45 through the O2 sensor wire. If the
sensor is not warm, or if the circuit is not complete, the computer
picks up a steady 0.45 volts. Since the computer knows this is
an "illegal" value, it judges the sensor to not be ready. It
remains in open loop operation, and uses all sensors except the
O2 to determine fuel delivery. Any time an engine is operated
in open loop, it runs somewhat rich and makes more exhaust
emissions. This translates into lost power, poor fuel economy
and air pollution.
The O2 sensor is constantly in a state of transition between high
and low voltage. Manfucturers call this crossing of the 0.45
volt mark O2 cross counts. The higher the number of O2 cross
counts, the better the sensor and other parts of the computer
control system are working. It is important to remember that the
O2 sensor is comparing the amount of Oxygen inside and outside
the engine. If the outside of the sensor should become blocked,
or coated with oil, sound insulation, undercoating or antifreeze,
(among other things), this comparison is not possible.
In either case, it is fixing a symptom instead of a problem.
The real problem with them is this... you have to get the exact resistance value right... otherwise the computer will be getting bad data... remember GIGO. If you get a value that tells the computer that it is too rich, it will lean it out, which is the worst thing you can do. It can give you better mileage temporarily, but will kill the engine very quickly by running it hot. Burnt valves and pistons often is the result.
All I am saying is be careful with a device like that. $75 for a new O2 sensor is a lot cheaper than a new engine. Leaving it alone is better than a fix like this. (By the way, the other two leads are for the heating element in the O2 sensor.)
Bill
Dave
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Dave Andreae
Parallax Tech Support·
I believe the basic principle is voltage, but I can measure voltage values and current values and report back. All of the manual diagrams and such indicate voltage as the variable.
Kwinns description is correct about how it is described to operate though, as a voltage oscillation.
If you are asking whether the sensor delivers or absorbs current, the sensor is provided voltage, and it outputs between 0 and 1v. I believe the white wire is a reference voltage, and the two black wires are supply + volts, 1 being for the heater and one for the sensor itself.
I'm trying to calculate how just the resistor effects it, if it were at 1v constant output, and I'm doing something wrong [noparse]:)[/noparse] cause the calcs are way off. e = i * r, so volts = 20mA * 1000000 . But that's wrong obviously? It seems that if it just had that resistor inline, it would read the same 1v on one side as the other side of the resistor, correct?
What makes it a low pass filter, but not a high pass? I would think you'd need both for this type of circuit?
I don't have any more information on the original circuit (the image was posted on a web forum), then those pictures. I have what the factory manual says the signal should look like on an oscilloscope though, which is pictured below.
Post Edited (turbosupra) : 12/28/2009 7:05:57 PM GMT
I can make measurements tonight to determine, what would you like to see?
The question to begin with here is what are you trying to do? Do you just want to know what the cap and resistor do, or are you trying to modify the oxygen sensor output?
There are 2 basic types of oxygen sensors, narrow-band and wide-band. It looks like your data comes from a narrow-band.
The narrow-band oxygen sensor sweeps up and down in voltage from about 0.1 to 0.9 volts, sometimes higher sometimes lower. The frequency is slow enough that you can see it on a voltmeter that has a needle on it. The vehicles ECU is looking for about .5 volts to keep the air/fuel mixture at 14.7 to 1. The narrow-band oxygen sensor is really nothing more than a switch to the ECU. The ECU reads the oxygen sensor as either rich or lean and makes adjustments in fuel trims to maintain 14.7 to 1.
If you are looking to modify your oxygen sensor output to make the mixture richer or leaner than there is a device called an EFIE that can do that.
Again if I knew more what your goal is I could help you more.
Alex
It's definitely a narrow band.
This circuit is something that has been tested on my vehicle and shown to work quite well in keeping the check engine light off when a n/a car is turbocharged. This circuit keeps the stock ecu quite happy.
I'd like to diagnose exactly how it works, and then try and emulates it's operation with a propeller.
Glad to hear that works for you. I work a lot with supplemental hydrogen, HHO, Brown's Gas, whatever you want to call it. Some people who get into it have no idea that an EFIE device is available to lean out the mixture for mileage gains with the supplemental hydrogen. I see them trying to reinvent the wheel by trying to build such a device when it has already been designed and works with a solid history of results.
I would guess that with a turbocharger you have to add more fuel for everything to work well.
Alex
I went through a turbo everything phase myself I put one on my Outlander 800 ATV we tried to mess with the O2 sensor to add mroe fuel but it just didn't cut it I ended up getting a power commander but would like to build my own controller with a prop
I have the front end program if you want a copy but have not started on the circuit yet
I'd love to see the program! Can you post it here?
I need something to compliment the piggy back management I have, and keep my stock ecu happy, and so I'd like to have a signal conditioner with the props extra outputs
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MOORE'S LAW: The capabilities of electronics shall double every 18 months.
cloyd's corollary: Hardware is easy, software is hard.