Jump to content

Airbox sensor?


R1100RSpurist

Recommended Posts

what does the oxygen sensor in the air box do?

There is no oxygen sesnor in the air box! Even if there was, it could never work. O2 sensors need to reach several hundred degrees before they can function. O2 sensors are in the exhaust.

 

What you are seeing is probably an air inlet temperature sensor.

Link to comment
R1100RSpurist

oh ok that makes sense, and then the motronic would adjust the amount of fuel based on the density of the air?

Link to comment
oh ok that makes sense, and then the motronic would adjust the amount of fuel based on the density of the air?

The motronic system takes a number of factors into consideration to modify the basic "fuel map", including ambient air temperature (using the airbox sensor), and engine temperature (at least two sensors in different places in the engine). Then once the basic memory map driven values are calculated (and modified accordingly by temperature and other factors), the system looks at the exhaust oxygen content (using the O2 sensor) and adjusts these values a little based on the feedback it gets from the O2 sensor. All this happens many time a second.

 

But with regards to your question, the airbox sensor is a temperature sensor. Temperature sensors cannot measure density. Some engine management systems are able to indirectly sense density and correct for it, and others are not. Air mass sensors that use the principle of inlet airflow offer a hot wire, are able to sense air density and correct for it. Others, for example those that use throttle position only to determine airflow, are not.

Link to comment

I believe that the Motronic has an internal pressure sensor and can determine air density (I would think it would have to, since throttle position and air temperature alone wouldn't be enough data.) But as Bob noted it is not the sensor in the airbox, that is for temperature.

Link to comment
I believe that the Motronic has an internal pressure sensor and can determine air density (I would think it would have to, since throttle position and air temperature alone wouldn't be enough data.) But as Bob noted it is not the sensor in the airbox, that is for temperature.

Actually, other than the original 1968 Bosch Jetronic system, which had an aneroid as a means of determining butterfly opening (and which inherently corrected for altitude/density), most successive systems including the electromechanical K-Jetronic, and analog L-jetronic (used on all K-bikes from 1083 until the early '90s) had no way to sense air density caused by altitude changes. So it is clearly not an absolute requirement to sense density changes caused by altitude.

 

Density changes resulting from temperature are of course taken care of by the temperature sensor. The most successful way to deal with this is the use of a hot wire air mass sensor, but I believe this is not used on any BMW bikes.

Link to comment
what does the oxygen sensor in the air box do?

 

Owen, as mentioned that sensor in the top of the air box is the AIT (air inlet sensor).. It basically tells the Motronic (fueling computer) what the temperature is of the air entering the throttle bodies..

 

Probably the most important job of that AIT sensor is for cold engine starting fueling requirements..

 

It is also used by the Motronic to figure air density as it needs to know the air density to know how much oxygen is in the intake air so it can add the proper amount of fuel.. The AIT by itself will not give air density but used in conjunction with the absolute pressure sensor inside the Motronic will give a fairly accurate representation of air density..

 

The AIT would basically be a minor sensor as the engine management system can use speed density (RPM vs throttle opening angle) to bridge around the AIT if needed..

 

In fact once the fuel management goes into closed loop & uses the 02 for fueling control it could care less about the AIT.. But as soon as the throttle is moved, or RPM comes up past mid RPM range, or it goes back into open loop it then uses that AIT to kind of fine tune the basic open loop fueling map (or maps) for current ambient conditions..

 

The prime sensors that your fuel management system uses are engine RPM, TPS (throttle position sensor), absolute pressure, & engine oil temperature, the AIT is more of a fine tuner (the bike will run fairly good with it disconnected as the computer defaults to a fixed air temp (not sure on the Motronic system but probably around 70°f or so)..

 

Twisty

Link to comment
Joe Frickin' Friday
...So it is clearly not an absolute requirement to sense density changes caused by altitude.

 

If you're going to run at a wide range of altitudes, the computer's gotta be able to tell how much air mass is getting in the cylinder. The oilhead bikes run flawlessly from sea level up to the top of Pikes peak without any manual adjustments; this would be impossible if they were not measuring (and adjusting the map for) ambient pressure.

Link to comment
R1100RSpurist

where do you guys learn so much about the motronic system...where can i learn? smile.gif, thank you for your answers, and maybe someone could tell me the difference between closed and open looped FI and what all this means?

Link to comment
If you're going to run at a wide range of altitudes, the computer's gotta be able to tell how much air mass is getting in the cylinder. The oilhead bikes run flawlessly from sea level up to the top of Pikes peak without any manual adjustments; this would be impossible if they were not measuring (and adjusting the map for) ambient pressure.

I agree that it is A Good Thing and certainly necessary for optimal running, but my point was only that an entire generation of fuel injected cars that used the K, KE, L and LE Jetronic systems (including nearly 10 years of K-bikes) and had no way to sense the pressure drop at higher altitudes. My old K100RT (with its LE Jetronic system) runs just fine in the mountains, albeit no doubt not optimally.

Link to comment
Clive Liddell

Hi Bob,

According to Charles O Probst's FI book most "higher end" K and KE systems did/do accomodate "altitude". I am still using one ('91 M-B) ;>)

Link to comment

The early K-bikes also had a jumper to set for high altitude use, so even though their altitude signal was binary (jumper on/jumper off) they still had a altitude signal.

Link to comment
ShovelStrokeEd

Bob,

It, your old K bike, really had a primative form of mass air flow sensor in that flapper valve. With mass air flow measured, it is not necessary to compensate for changes in altitude, it is done for you.

 

The later Motronic systems, at least as they are configured for our bikes calculate air density from a barometric pressure sensor located on the Motronic circuit board itself and from inlet air temperature. The one thing that isn't compensated for is the amount of water vapor in the air allowing the engine to run a bit rich under conditions of high humidity. Of course, closed loop operation, for those bikes equipped with an O2 sensor, takes care of that.

Link to comment
If you're going to run at a wide range of altitudes, the computer's gotta be able to tell how much air mass is getting in the cylinder. The oilhead bikes run flawlessly from sea level up to the top of Pikes peak without any manual adjustments; this would be impossible if they were not measuring (and adjusting the map for) ambient pressure.

I agree that it is A Good Thing and certainly necessary for optimal running, but my point was only that an entire generation of fuel injected cars that used the K, KE, L and LE Jetronic systems (including nearly 10 years of K-bikes) and had no way to sense the pressure drop at higher altitudes. My old K100RT (with its LE Jetronic system) runs just fine in the mountains, albeit no doubt not optimally.

 

RFW, it’s been a long time since I have messed with the older Bosch K, KE, L or LE Jetronic systems so don’t know if ALL those systems use the flapper door air (AFM) meters? I know the later ones did as well as the early BMW K bikes..

 

I know the K jetronic (constant injection) used an air meter system as that system for sure needed to know air mass..

 

Those systems that used (AFM) flapper door system used that to determine air flow same as the modern FI systems use the mass air flow sensor (MAF).. If you have mass air flow, TPS, & AIT you have your air density if you throw in MAP (manifold absolute pressure) you then have redundant air density monitoring..

 

The BMW Motronic 2.2 & 2.4 doesn’t have either a (MAF) or (AFM) or a (MAP) so how would they determine air density without a pressure sensor?????? Air density is a MUST if you want to have decent runability at altitude & a MUST HAVE to meet emission regulations at altitude..

 

Even the first simple automobile speed density FI systems used a (MAP) & some of them even used an additional altitude compensator.. As long as you have a MAP you have air density as that compares manifold negative pressure to atmospheric pressure..

 

Twisty

Link to comment

ShovelStrokeEd, sorry for posting about the same thing as you, it looks we were both going to the same place at the same time here..

 

Twisty

Link to comment
so which does the R1100RS have? or does it use the air temp sensor for everything?

 

Owen, the R1100RS is a simple basic Alpha-N system (engine RPM & throttle position).. It’s primary fueling control is engine RPM & TPS (throttle position).. By knowing how fast the engine is spinning & how far you have the throttle opened it can pretty well judge how much fuel is required.. It would run with just the above but really needs more to be able to cold start & operate properly at all ambient temps, engine temperatures, & altitudes..

 

The air sensor (AIT) in the air box is used to help determine the air temperature entering the engine so the fuel injector squirt time can be fine tuned for air temp, altitude, & it helps with air density determination..

 

There is an oil temperature sensor on the engine to tell the fueling computer how hot the engine is so it can fine tune the injector squirt time & spark map for basic engine operating temperature..

 

There is sensor mounted on the L/H throttle body (TPS) that tells the fueling computer how far you have the throttle opened.. That is a fundamental sensor that the computer MUST HAVE to determine how much air is entering the engine.. It also must know how fast the engine crankshaft is turning as the faster it turns the more air the engine takes in.. Both the engine RPM & throttle opening are a MUST HAVE to allow proper operation..

 

There is a basic atmospheric pressure sensor inside the fueling computer & that is used to determine air density along with the air temperature sensor.. A manifold absolute pressure sensor would probably a better option but with just two cylinders the vacuum pulses would be pretty wild so it would be difficult to obtain a quality manifold negative pressure signal (probably why the system doesn’t use one)..

 

There is also a (heated) oxygen sensor mounted in the exhaust system.. When the engine gets hot & the throttle is held steady or at low to mid throttle openings the fueling computer goes into CLOSED LOOP & uses that input to hold the fuel air mixture to about 14.7:1.. That is needed to help the catalytic converter operate effectively & help keep emission levels low.. Even though that 02 sensor is technically called a sensor it really operates more like an oxygen switch.. It’s purpose is to monitor the amount of oxygen in the exhaust gas that’s leaving the engine as that gives an indication of how complete the combustion process.. The 02 sensor compares the amount of oxygen that is in the exhaust gas & compares that to the amount of oxygen that is in the air outside the exhaust.. In doing so it produces a voltage & the fueling computer looks at the 02 voltage compared to a basic voltage of about .45 volts.. In actuality it really looks at what side of .45 volts the 02 is at then adds or subtracts fuel until it flips over that .45v center (the other side or .45 volts).. When working correctly the computer will keep adding or subtracting fuel to keep the 02 sensor toggling back & forth across that .45-.5 volt threshold..

 

Simple as that (well sort of) as there are internal computer fueling maps,, internal spark maps,, CCP to force the computer to use certain basic fueling & spark maps, the computer also monitors system voltage as the system voltage has an effect on injector squirt amount..

 

Twisty

Link to comment

Minor correction:

There is an oil temperature sensor on the engine to tell the fueling computer how hot the engine is so it can fine tune the injector squirt time & spark map for basic engine operating temperature..

On the R1100 and R1150 series the oil temp sensor is used strictly for the oil temp gauge. The info is never sent to the Motronic engine management computer.
Link to comment
On the R1100 and R1150 series the oil temp sensor is used strictly for the oil temp gauge. The info is never sent to the Motronic engine management computer.
Correction to your correction, yes it does... connected to pin 7 of the Motronic. It would kind of have to be... how else would the ECU know when to come off of cold enrichment?
Link to comment

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...