Exploring the Stepper Motors on R1200XX

[Ken H.]

So it seems we don't know a lot yet about the TB air bleeder stepper motors on the R1200 series. In particular how to park them when doing TB sync. Which the mfg. procedure would lead you to believe is necessary. (Although many of us have done a sync. without doing so.)

 

So today I pulled one off of our R1200GS in the hopes of learning more.

 

 

Well I didn't really learn much useful. The air bypass plunger is part of the motor itself. It doesn't pull out or separate in any way. Nor could I rotate it by hand. You can feel some sort of mechanism up in it, but I didn't want to force it.

 

There is no manufacturer's name on it. The only markings:

 

"Made in Mexico"

 

7672966

 

D5197

 

Here's hoping this will help someone else dig up more...

[bmwmick]

Ken,

Here is what the RepRom has to say about "synchronisation"

 

"Note that synchronisation does not affect cylinder balance and engine rpm at idle speed.

In order to ensure that the engine operates as smoothly as possible after synchronisation, the BMW Motorrad diagnostic system deletes the adaptation values from the control unit's memory before the throttle valves are synchronised.

In order to ensure that they do not affect synchronisation with the throttle valves slightly open, the idle actuators are held in position by the BMW Motorrad diagnostic system."

 

Mick

[Merch]

Hmmmm, I wonder what position they're held at. Could the same be accomplished by simply disconnecting them????

[Ken H.]

Could the same be accomplished by simply disconnecting them????

No we've tried that already. They just stay wherever they happen to be at the moment. I'm sure they are "driven" back to a specific point by the BMW diagnostic system during service. But how to do ourselves has been the mystery.

[Merch]

I thought about that today while riding....

 

Found this tonight. Certainly not directly applicable, but probably close enough to shed light on theory. Page 3 particularly....

 

http://www.autoshop101.com/forms/h26.pdf

 

I haven't pulled mine....what does the connector look like? (number of terminals, etc)

 

We can DO this!

[Ken H.]

I thought about that today while riding....

 

Found this tonight. Certainly not directly applicable, but probably close enough to shed light on theory. Page 3 particularly....

 

http://www.autoshop101.com/forms/h26.pdf

 

I haven't pulled mine....what does the connector look like? (number of terminals, etc)

 

We can DO this!

Ah, good info. The steppers on the bike have four electrical connections to them.

 

What we really need to figure this out I think is someone with a good portable recording oscilloscope. Then we could monitor the stepper during actual operation and learn what pulse size, width and frequency is used to mover them. Unfortunately it's not me.

[R4ND0M_AX3]

I thought about that today while riding....

 

Found this tonight. Certainly not directly applicable, but probably close enough to shed light on theory. Page 3 particularly....

 

http://www.autoshop101.com/forms/h26.pdf

 

I haven't pulled mine....what does the connector look like? (number of terminals, etc)

 

We can DO this!

Ah, good info. The steppers on the bike have four electrical connections to them.

 

What we really need to figure this out I think is someone with a good portable recording oscilloscope. Then we could monitor the stepper during actual operation and learn what pulse size, width and frequency is used to mover them. Unfortunately it's not me.

If you're gonna go that far you might as well capture the communications between the GT1 and the bike while a tech is doing an actual sync. Then we could just have a box with a sync mode button on it tied to the bikes databus.

[SkidMark]

I am guessing that the numbers on that sensor are not the part numbers, I checked for the part at Max BMW in which they have a parts fiche available for there customers.

 

http://www.maxbmwmotorcycles.com/fiche/fiche.asp

[RFW]

Ah, good info. The steppers on the bike have four electrical connections to them.

 

What we really need to figure this out I think is someone with a good portable recording oscilloscope. Then we could monitor the stepper during actual operation and learn what pulse size, width and frequency is used to mover them. Unfortunately it's not me.

 

NO! That is not how a stepper motor works.

 

There are 2 coils, resulting in 4 wires (one wire at the end of each coil). Pulse SIZE is irrelivant, and so is pulse width. Frequency only controls the speed of the motor (the faster you send the pulse sequences, the faster the steps are, and the faster the motor rotates).

 

The motor is driven by a series of 4 sequences that repeat. Each sequence moves the motor one step.

 

Here is the standard full-step sequence:

 

Step #1... - (coil 1) + - (coil 2) +

Step #2... - (coil 1) + + (coil 2) -

Step #3... + (coil 1) - - (coil 2) +

Step #4... + (coil 1) - + (coil 2) -

 

....then they repeat continuously after that for as many steps as you need.

 

To translate, in step 1, Coil 1 has negative on its "left" end and positive on its "right" end. Coil 2 is the same.

 

Then in step 2, the polarity of coil 2 is reversed (positive on its left and negative on its right end).

 

In step 3, the polarity of coil 1 now reverses, and the polarity of coil 2 changes back to what it was in step 1.

 

Finally, in step 4, the polarity of coil 2 reverses again, so both coil 1 and 2 have positive on their "left" ends and negative on their "right" ends.

 

Step 5 is a repeat of step 1, and so on.

 

As you can see, the steps are similar to counting in binary numbers 0 to 3 (that is, 00--->01--->10--->11).

 

That is all there is. Nothing very complicated.

 

Bob.

[Merch]

Assuming we would want to park the motors at their mid point, we need to know a few things.

 

First of course, is the number of steps from one extreme to the other.

 

Knowing that, could we just drive the motor in one direction some maximum number of steps to ensure fully entended or retracted, then drive the other direction 1/2 that amount.

 

The fly in that logic would be if there is no 'end point' to the steps....the pintle would just extend/retract...ending up where it started after the max number of pulses were applied.

 

Just thinking out loud here.

[RFW]

Assuming we would want to park the motors at their mid point, we need to know a few things.

 

First of course, is the number of steps from one extreme to the other.

 

Knowing that, could we just drive the motor in one direction some maximum number of steps to ensure fully entended or retracted, then drive the other direction 1/2 that amount.

 

The fly in that logic would be if there is no 'end point' to the steps....the pintle would just extend/retract...ending up where it started after the max number of pulses were applied.

 

A stepper motor has no idea "where" it is. It certainly has no "clue" where its mid point is. It just "steps". Therefore, as you point out, a means is needed to know where it is (in absolute terms).

 

There are two ways this is normally done....

 

1. Include a rotary or positional encoder to feed back locational information. This is clearly not done in this case, because there are only the 4 motor wires. Besides, this would be very costly and gross overkill for such a simple mechanism.

 

2. Advance the motor enough upon startup that it is certain to reach a defined mechanical stop (no matter where it started from). Then step it a defined number of steps to reach a predefined "nominal" setting, from which further incremental steps can be made under software control.

 

The second method makes the most sense here. The cumulative accuracy of X number of steps is very high, so if the stepper starts from a known position, then after (say) 20 steps, its position will also be accurately known.

 

You should should be able to pull it out of the bike, then switch the ignition (not starting the bike) on and watch the device. You will probably see it "zeroing" itself in a similar manner as described.

 

You can also hook up a logic analyser or a storage scope to the coils, and watch what is happening there. This will tell you where it positions itself (number of steps) at startup.

 

Bob.

[Merch]

I will see what I can find out during powerup. It will be several days before I'll have time, but this is doable. The quest to understand these not withstanding, there may be an easy way to perform the 'park' prior to sync.....

 

From the description of the operation during powerup, couldn't we satisfy the need to park the stepper motors before a TB sync by powering up (without starting the engine), allowing the steppers to move to whatever startup postion is programmed, disconnect them then start the engine?

 

Seems like this approach will satisfy the need to have the steppers in a fixed location while performing the TB sync and not having them 'chase' the sync adjustment that's being made.

[FlyingFinn]

A stepper motor has no idea "where" it is. It certainly has no "clue" where its mid point is. It just "steps". Therefore, as you point out, a means is needed to know where it is (in absolute terms).

 

All this talk about a machine (or a part of one) "knowing where it is" reminded me of this little gem.

An informative description of a missile guidance system

Missile Guidance

 

--

Mikko

[Ken H.]

From the description of the operation during powerup, couldn't we satisfy the need to park the stepper motors before a TB sync by powering up (without starting the engine), allowing the steppers to move to whatever startup postion is programmed, disconnect them then start the engine?

I think it's a good thought, but I've never seen anything to make me think they return to a set position at each start up. Rather, the Motronic learns over time the best position for them to be in and only make minor adjustments from there as needed. Until connected to the BMW diagnostic system for the factory sync procedure. Then it sets them to some predetermined position.

 

Still, trying it as mention (turn on the bike with one removed but connected) would lend some clue to this question. Let us know your results please.

[RFW]

Rather, the Motronic learns over time the best position for them to be in and only make minor adjustments from there as needed.

 

Clearly there must be SOME kind of feedback mechanism involved here, in order for the Motronic system to "know" what the "best" position is. Although I know quite a bit about stepper motors and their control, I don't know much about this specific implimentation. I'd be curious to hear exactly what this part is really doing on the bike (balancing the 2 cylinders at idle and low throttle openinsgs, I believe), and how the system would "know" when adjustment is needed and when it is optimum. I've torn the motor down completely on my K100, but have only a little experience with boxers.

 

Bob.

[Ken H.]

Clearly there must be SOME kind of feedback mechanism involved here, in order for the Motronic system to "know" what the "best" position is.

Yeah, that's also been a separate subject of some speculation. The two leading theories that I have heard is it based on what the knock sensor "hears", or that it is based on the feedback from the two oxygen sensors in the exhaust. The later being the most likely to me. Monitoring the position of the stepper itself would be rather useless because it is the amount of air that the variable bypass port let's through that impacts engine performance. You need to monitor something post-combustion so to speak.

[RFW]

The two leading theories that I have heard is it based on what the knock sensor "hears", or that it is based on the feedback from the two oxygen sensors in the exhaust. The later being the most likely to me. Monitoring the position of the stepper itself would be rather useless because it is the amount of air that the variable bypass port let's through that impacts engine performance. You need to monitor something post-combustion so to speak.

 

I don't think it is either of these. If I understand the purpose of this stepper-controlled air valve correctly, it is intended to balance the 2 cylinders. That is, to ensure that at low throttle openings and at idle (the only conditions when balancing is important), the amount of fuel/air entering each is the same.

 

Certainly, the knock sensor cannot possibly have any way of determining how well balanced the cylinders are, since balancing only applies at low throttle or at idle, which are conditions where no preignition occurs anyway. Besides, the presence or absence of preignition has nothing at all to do with balancing the inlet charge to each cylinder.

 

The Oxygen Sensor also cannot possibly sense balance either. O2 sensors are there to detect mixture problems; all they do is sense the amount of oxygen in the exhaust and adjust the FUEL (not the air volume) being delivered to the cylinder to ensure it is at the exact 14.7:1 Stoichiometric point.

 

So there must be some other feedback mechanism that can sense "balance". This is getting intriguing!

 

Bob.

[CMWingfield]

Not to steal the thread as I'm very interested in this topic albeit a complete Doofus regarding this stuff, but, don't ya just love it when smart people talk about electronic doohickys!

 

Keep it up guys, you'll get to the bottom of the stepper motor thing. I've got confidence in ya!

 

Mike

[russell_bynum]

The Oxygen Sensor also cannot possibly sense balance either. O2 sensors are there to detect mixture problems; all they do is sense the amount of oxygen in the exhaust and adjust the FUEL (not the air volume) being delivered to the cylinder to ensure it is at the exact 14.7:1 Stoichiometric point.

 

Can you go into more detail with this, please? It seems to me that if one O2 sensor is getting a different reading than the other, then there must be an imbalance. Assuming the other factors are the same, like the combustion chambers are both the same, the spark plugs are both the same, and both injectors are the same, then the only explanation for a difference would be a different amount of air getting in on one side vs. the other. And you could fix that by using the stepper motors to let more or less air in to a particular side.

 

What am I missing?

[RFW]

Can you go into more detail with this, please? It seems to me that if one O2 sensor is getting a different reading than the other, then there must be an imbalance. Assuming the other factors are the same, like the combustion chambers are both the same, the spark plugs are both the same, and both injectors are the same, then the only explanation for a difference would be a different amount of air getting in on one side vs. the other. And you could fix that by using the stepper motors to let more or less air in to a particular side.

 

What am I missing?

Well, start with a motor that is perfectly balanced and operating "closed loop" (O2 sensors are up to temperature and the mixture is dead-on stoichiometric).

 

The volume of air-fuel going into each cylinder is identical (hence the intakes are balanced), and the exhaust of each cylinder has zero oxygen content (exactly enough O2 was in the intake charge to burn all the gas, with no O2 left over).

 

Note that in actual operation, the system "dithers" several times per second between very slightly lean and very slightly rich. In engineering terms, where Lambda=1 is the perfect stoichiometric air-fuel mixture, a properly operating motor must operate between Lamda=0.995 and 1.005 in order for a 3-way catalytic converter to operate. So for all intents and purposes, it can be said that there is just enough oxygen in the mixture to burn all the fuel, with essentially none left over.

 

Now, assume an intake imbalance. This is essentially the same as one throttle butterfly being open slightly more than the other.

 

The result is that the slightly increased air volume being admitted into that cylinder is sensed by the air mass sensor, and a corresponding increase in fuel is injected to burn with the excess air. If there is any initial error in the increased amount of fuel. the O2 senor detects the problem and fine-tunes the fuel being injected to keep the (increased) intake charge pefectly stoichiometric again.

 

So what the result of this imabalance is, is that one exhaust pipe will have a slightly increased volume of exhaust as compared with the other one. But BOTH will still have 100% combustion with zero O2 left over.

 

The O2 sensors cannot detect exhaust VOLUME. They can only detect O2 content. Since the O2 content is effectively zero in both cases, there is no way the oxygen sensors can detect any difference between one cylinder and the other that can be used as a basis to determine if the intakes are balanced or not.

 

Bob.

[Boffin]

Bob,

that would hold true if the motronic varied each cylinders charge independantly, however it does not. The boxer squirts the same amount of fuel into both intakes at the same time, both the cylinder on the intake stroke and the one on the firing stroke. So an imbalance cannot be corrected by varying the fuel, as one side would always be leaner than the other - although both sides would be oscillating between leaner/richer. This leaves just the idle air adjust to correct balance.

 

Cya, Andy

[Ken H.]

The result is that the slightly increased air volume being admitted into that cylinder is sensed by the air mass sensor, and a corresponding increase in fuel is injected to burn with the excess air. If there is any initial error in the increased amount of fuel. the O2 senor detects the problem and fine-tunes the fuel being injected to keep the (increased) intake charge perfectly stoichiometric again.

A point in addition to what Andy said (no independent left to right fuel injection control) the boxer engine doesn't have a air mass sensor to sense differences / changes in intake air volume. So given a fixed fuel charge (left to right anyway) the only way I see to vary maintain (near) perfect stoichiometric air-fuel mixture is to vary the air flow. Which bring us back to the air by-pass valve and the stepper motors.

 

I think.

[russell_bynum]

The result is that the slightly increased air volume being admitted into that cylinder is sensed by the air mass sensor, and a corresponding increase in fuel is injected to burn with the excess air. If there is any initial error in the increased amount of fuel. the O2 senor detects the problem and fine-tunes the fuel being injected to keep the (increased) intake charge perfectly stoichiometric again.

A point in addition to what Andy said (no independent left to right fuel injection control) the boxer engine doesn't have a air mass sensor to sense differences / changes in intake air volume. So given a fixed fuel charge (left to right anyway) the only way I see to vary maintain (near) perfect stoichiometric air-fuel mixture is to vary the air flow. Which bring us back to the air by-pass valve and the stepper motors.

 

I think.

 

That's my understanding as well...though you fellers have definitely spent more time mucking around in there than I have.

[RFW]

A point in addition to what Andy said (no independent left to right fuel injection control) the boxer engine doesn't have a air mass sensor to sense differences / changes in intake air volume. So given a fixed fuel charge (left to right anyway) the only way I see to vary maintain (near) perfect stoichiometric air-fuel mixture is to vary the air flow. Which bring us back to the air by-pass valve and the stepper motors.

 

I think.

 

Aha. I stand corrected. That makes this quite a bit more complicated. So what happens with a new K-bike, where there are 4 (not just 2) separate butterflies that need synchronizing. Surely they don't have 3 or 4 stepper controlled air volume adjustment valves. On a car, there is only one common butterfly, but if the new K-bikes are anything like my old K100, there are 4 butterflies and 4 inlet tracts to balance.

 

One also might ask why the R-bikes have 2 oxygen sensors (one for each cylinder) if there is no way to individually adjust the fuel injected to that particular cylinder. It would seem that the suggested method of correcting the mixture to one cylinder using this valve, would involve a series of successive approximations, since more variables are involved.

 

My assumption (perhaps incorrect) was that the balancing valve was intended to simply make the bike run smoother, the same way that it used to be done by balancing with a vaccuum gauge until both left and right inlet manifolds had the same vaccuum (and hence the same air being drawn into the cylinders).

 

Bob.

[russell_bynum]

Aha. I stand corrected. That makes this quite a bit more complicated. So what happens with a new K-bike, where there are 4 (not just 2) separate butterflies that need synchronizing. Surely they don't have 3 or 4 stepper controlled air volume adjustment valves. On a car, there is only one common butterfly, but if the new K-bikes are anything like my old K100, there are 4 butterflies and 4 inlet tracts to balance.

 

The difference is that the 4 butterflies on your K-bike were linked with a rod and basically didn't ever go out of sync. You sync it once and don't have to touch it again unless you have to take the thing apart. With the boxer, each butterfly is controlled by a cable. In the case of the Oilhead, there's one cable that goes from the grip to a junction box, then two short cables from there...one going to each butterfly. As each of those short cables stretches at slightly different rates, the TB's go out of sync. I'm assuming the Hexhead has a similar throttle cable setup.

 

One also might ask why the R-bikes have 2 oxygen sensors (one for each cylinder) if there is no way to individually adjust the fuel injected to that particular cylinder. It would seem that the suggested method of correcting the mixture to one cylinder using this valve, would involve a series of successive approximations, since more variables are involved.

 

I would agree with that...but isn't that how it would work using your air mass sensor method? i.e. the system sees that there's a difference, makes a change, goes back and checks again, adjusts again, etc. Right?

 

My assumption (perhaps incorrect) was that the balancing valve was intended to simply make the bike run smoother, the same way that it used to be done by balancing with a vaccuum gauge until both left and right inlet manifolds had the same vaccuum (and hence the same air being drawn into the cylinders).

 

I think that's the intent, but they're just doing it by looking at what's coming out of the exhaust rather than looking at what's going down the intake.

[smiller]

I'm just brainstorming, but what about the crank position sensor? In many automobiles minute changes in the rotational speed of the engine over a small range of crank degrees can be detected and reported by the ECM (typically as a cylinder misfire event) and I wonder if this same technique couldn't be used in this case, i.e. comparing crank acceleration during the power stroke of each cylinder and using the steppers to try to keep them equal?

[Ken H.]

I'm assuming the Hexhead has a similar throttle cable setup.

It does. It's an all new junction, "Bowden" box design with much shorter Bowden to TB cables, but the basic concept remains.

[RFW]

The difference is that the 4 butterflies on your K-bike were linked with a rod and basically didn't ever go out of sync. You sync it once and don't have to touch it again unless you have to take the thing apart.

 

Well, they did go way out of synch, but that was thanks to a previous owner's diddling with the adjustments. Had to set up a vaccuum pump to resynch them. But I see the point about the long cables connecting the boxer's throttles.

 

I would agree with that...but isn't that how it would work using your air mass sensor method? i.e. the system sees that there's a difference, makes a change, goes back and checks again, adjusts again, etc. Right?

 

Well, with the way I thought it worked, it would be a lot more deterministic. There would only be one variable; if the mixture was out on one cylinder, the O2 sensor would sense it and directly change the mixture to it. The other cylinder would not be affected. But the way it is, with a common air mass sensor, things are more complex.

 

Suppose the mixture was out on the cylinder that did not have the air valve, but OK on the one that does. It is almost certain that there isn't any INDIVIDUAL fuel volume control for EACH injector. So what would have to happen would be that the Motronic system would adjust the mixture to correct the problem on the cylinder without the valve. That may correct THAT cylinder's problem, but now the one WITH the valve (that was previously OK) will be wrong. That will be sensed by ITS O2 sensor, and that problem will be corrected by the valve adjustment. Successive approximation ...sort of.

 

Of course, that assumes that each O2 sensor can be "read" and reacted to individually (as opposed to the two of them just being averaged).

 

All conjecture, of course.

 

Bob.

[russell_bynum]

Suppose the mixture was out on the cylinder that did not have the air valve, but OK on the one that does.

 

Hmm...I was operating under the assumption that there was one air valve per side. If that's not the case, then I see your point.

[big-t]

 

 

Has anyone actually confirmed that this is a batchfire system.?? Batchfire is antique by todays standards and O2s on each cylinder would indicate the fuel mixture is adjustable for each cylinder.

[Ken H.]

But the way it is, with a common air mass sensor, things are more complex.

Back up, back up please. Where on the R1200 series have you found any air mass sensor??? I've studied the schematic and the intake system on the bike itself quite a bit and I don't find an air mass sensor anywhere. Only input air temperature sensor in the air box.

[Ken H.]

 

Has anyone actually confirmed that this is a batchfire system.?? Batchfire is antique by todays standards and O2s on each cylinder would indicate the fuel mixture is adjustable for each cylinder.

It was certainly the case on the R11XX series. I myself haven't actually confirmed this on the R12XX series yet. Gives me something to do this weekend though!

[big-t]

 

 

I really gotten into the 1200s yet,but it seems like I saw a post on adjusting the valves and there was a cam position sensor showing in the picture.If thats the case you can bet its multi point injection, which explains the o2s on each cylinder.Cam position sensor used in conjunction with the crank sensor determines which cylinder is firing and also can be used to tell if the engine is misfiring.

[Ken H.]

 

I really gotten into the 1200s yet,but it seems like I saw a post on adjusting the valves and there was a cam position sensor showing in the picture.If thats the case you can bet its multi point injection, which explains the o2s on each cylinder.Cam position sensor used in conjunction with the crank sensor determines which cylinder is firing and also can be used to tell if the engine is misfiring.

I just took a look at the schematic a bit closer and unlike the R11XX series the R12XX does indeed have independent connections from the Motronic to each fuel injector. They were wired in parallel on a single connection on the R11XX series. So it is possible they are opening each one independently. I still want to put a scope on it sometime to see if they are in-phase or not when I get a chance.

 

Back to the original question of what the system uses as a reference point to adjust the steeper motors, I just noticed there are two separate knock sensors also (I was thinking previously there was only one). Something in my head still makes me think what they are reading could be used to compare combustion balance between each side. There is also independent cyl. head temp. sensors. Perhaps the system is using inputs form all three sources? I don't know...

[RFW]

 

Batchfire is antique by todays standards and O2s on each cylinder would indicate the fuel mixture is adjustable for each cylinder.

 

The Motronic system does not adjust fuel volume to individual cylinders. Nor is there any need to do this as long as they are close and the average of all cylinders is "neutral". Besides, the Motronic system is basically an automotive device, and attempting to adjust fuel volume for each injector on a car would require one sensor per cylinder, and would be totally impractical. Bosch did not design a complete new Motronic system for the relatively few BMW motorcycles being sold.

 

For example, on a 2-cylinder motor for the sake of illustration, if one cylinder has a small amount of residual oxygen in its exhaust (i.e. it is running slightly lean), and the other has a slight amount of CO/HC (running slightly rich), then what happens is this....

 

The exhaust passes through the oxidation catalyst and it "burns" the CO/HC with the residual O2, eliminating both in the process. The reduction catalyst (that eliminates the NOx component) cannot work in an oxidizing environment (which is the entire reason for using O2 sensors and very tight process control). Since the residual CO/HC from one cylinder was just "burned" off with the residual O2 from the other cylinder by the oxydation catalyst, the there is no longer any residual oxygen and the reduction catalyst now has a non-oxidizing environment and can effectively eliminate the NOx.

 

So it is not important that EACH cylinder has a perfectly neutral exhaust. Within reasonable limits, it is only important that they average out.

 

Bob.

[big-t]

Back to the original question of what the system uses as a reference point to adjust the steeper motors,

 

 

RPM...based on the TPS voltage the ecm knows the engine should be at idle.All the parameters for air,fuel,timing at that particular idle speed are preprogramed into the ECM,so all it has to do is run the stepper motors in and out to keep it at the target rpm.The ecm at the same time is adjusting the A/f ratio to keep it within the parameters for idle.

 

Using the cam position sensors is a much more accurate way to keep track of rpm and engine timing rather than just using a crank sensor for these duties,as the ecm has to allow for slop in the cam chains when just using the C/S

[Ken H.]

Back to the original question of what the system uses as a reference point to adjust the steeper motors,

 

RPM...based on the TPS voltage the ecm knows the engine should be at idle.All the parameters for air,fuel,timing at that particular idle speed are preprogrammed into the ECM,so all it has to do is run the stepper motors in and out to keep it at the target rpm.The ecm at the same time is adjusting the A/f ratio to keep it within the parameters for idle.

 

Using the cam position sensors is a much more accurate way to keep track of rpm and engine timing rather than just using a crank sensor for these duties,as the ecm has to allow for slop in the cam chains when just using the C/S

So if I read you correctly your thought is that all the stepper motors are for is control of idle speed? Not idle sync? Certainly possible, but that would be contrary to everything BMW has said about the system so far. They have been quite specific that the stepper motors control side-to-side idle synchronization, thus the only sync adjustment needed is the above idle one.

 

Knowing what RPM the engine is at with crankshaft or camshaft position sensors is easy. Knowing how the two sides are in balance to each other, now that's the question.

[RFW]

So if I read you correctly your thought is that all the stepper motors are for is control of idle speed? Not idle sync?

 

If there is only one of them feeding one cylinder only, then it obviously cannot control idle speed. If there are two, then it is possible to contol both idle speed and synch. I was under the impression that there is only one of these things, however.

 

Bob.

[big-t]

Batchfire is antique by todays standards and O2s on each cylinder would indicate the fuel mixture is adjustable for each cylinder.

The Motronic system does not adjust fuel volume to individual cylinders.

 

 

 

No argument,I should have said "monitered" instead of "adjustable".

[Ken H.]

I was under the impression that there is only one of these things, however.

There is on on each side. You may be thinking of the throtle position sensor that is on the left side only.

[BeemerBerg]

OK. After reading all the above posts, I still don't get it.

 

Last nite I did a throttle body balance on my 13,000 mile R 1200 Rt. I used my trusty BMWSportTouring model 7100 $4 water manometer (actually the advanced version, using Kool-Aid rather than water, for better visibility).

 

Wasn't so worried about where the balance was at idle, since I don't spend much time there anyhow. Locking the throttle at about 4,000 RPM, I found that the levels were about 4" apart. Loosened the lock adjuster, and got 'em within an inch of each other on the manometer, snugged it down & put the tupperware back on.

 

Should I even worry about stepper motors, or what the balance looks like at idle?? Don't the stepper motors control the TPS at idle, taking the place of the BBS (big brass screw) that's on the older oilheads? Or does the stepper motors try to "balance" the throttle bodies at ALL rpms??

 

What am I missing??

[steveknapp]

What am I missing??

 

The joys of being an anal/compulsive type who frets about such things!

 

If your bike ran like crap, I could see worrying. But it doesn't, does it? Runs fine, right?

[steveknapp]

that would hold true if the motronic varied each cylinders charge independantly, however it does not. The boxer squirts the same amount of fuel into both intakes at the same time, both the cylinder on the intake stroke and the one on the firing stroke. So an imbalance cannot be corrected by varying the fuel, as one side would always be leaner than the other - although both sides would be oscillating between leaner/richer. This leaves just the idle air adjust to correct balance.

 

Andy, true for an oilhead, not true for a hexhead.

 

The hexhead added a cam sensor, allowing the strategy to know engine phase. It's got seperate injection control as well. Even the four plugs can be fired independently.

 

From what I understand, each jug is managed as it's own motor.

 

Idle balance can be obtained from the crank posistion sensor, just like any other vehicle. You can see crank acceleration from each firing pulse, and try to balance them out. It's not hard at all actually.

 

Seth hit the nail on the head:

"I'm just brainstorming, but what about the crank position sensor? In many automobiles minute changes in the rotational speed of the engine over a small range of crank degrees can be detected and reported by the ECM (typically as a cylinder misfire event) and I wonder if this same technique couldn't be used in this case, i.e. comparing crank acceleration during the power stroke of each cylinder and using the steppers to try to keep them equal? "

 

You think that's why it got a higher resolution crank possition sensor (36 tooth I think)? It's not as interesting as some of the other theories, but it is the most likley. Oh, and the changes are as "minute" as you might think.

 

 

I still think it's all moot.

[BeemerBerg]

It didn't run like crap before--but there was a little more vibration than I thought there should be (I figgered cause of a slight TB difference.)

 

Does it run better? Don't know yet. Too darn cold in the AM to tell.

 

Anal retentive--yea, But Tinkering helps me "bond with my bike" and overcome cabin fever. Besides, if it ain't broke, I can make still make it better

[Ken H.]

2. Advance the motor enough upon startup that it is certain to reach a defined mechanical stop (no matter where it started from). Then step it a defined number of steps to reach a predefined "nominal" setting, from which further incremental steps can be made under software control.

 

The second method makes the most sense here. The cumulative accuracy of X number of steps is very high, so if the stepper starts from a known position, then after (say) 20 steps, its position will also be accurately known.

 

You should should be able to pull it out of the bike, then switch the ignition (not starting the bike) on and watch the device. You will probably see it "zeroing" itself in a similar manner as described.

So I did just that today. And you are quite right, upon turning the key on the steppers move to a position where the air bleeder piston is fully retracted. That is - with the air bleeder at full open, max. air bypass. Or what I assume is fully retracted. Definitely much more retracted/open that at the key off position. Which is another interesting observation - as I turn the bike off the piston is moved by the stepper to fully extended, then it retracts it just a bit. I'm thinking that when mounted in the TB it extends to where the air bypass passage is fully closed, then opens it a fixed amount. Is this the so called "parked" position that the dealer diagnostic system puts the system in for synchronization? Who knows?

 

One think I believe is certain though based on experience with the oilheads, the amount of air bypass will effect more than just idle sync. You can demonstrate that by twisting a LBS while doing an above idle speed sync on an oilhead. The higher RPM sync will change.

 

I would think the exact same situation has to be occurring on the hexhead. The stepper position, and thus the amount of air bypass has to be effecting higher RPM sync. After all, if it didn't, why would there be a dealer service procedure at all to park them in some (unknown to us) position when doing a high speed sync? But what is the position?

 

What we need is a dealer person who hangs out here who would be willing to connect their diagnostic system to a hexhead and with a stepper pulled out of the TB observe it when doing the "parking" procedure. Then report back here as to what that position is.

 

I'm betting it is the key off partially retracted/opened position, but who knows?

[Ken H.]

Bob (and everyone else),

 

Two parts to this puzzle we're trying to figure out -

 

1) How to move the steppers without the dealer's BMW diagnostic system.

 

2) Once we can move them, were to for a starting position for sync?

 

Toward the first goal, I bought a hobby stepper motor controller kit and I can now step a 6-wire (two coils each with a center tap) stepper motor around to my heart's content. But how to interface a 4-wire stepper like is on the bike? Any clues anyone?

 

As to the second question, I still don't have a guess?

 

I think if we keep chipping away, just like bleeding ABS systems a couple of years ago, we can conquerer this thing! Any input is appreciated.

[Marty Hill]

Do I smell smoke!

[CMWingfield]

This is the best thread in a long while!! Sort of like watching "Monk" on T.V. You guys are great!!! I can't wait for the pictures on that stepper motor gizmo!!

Mike

[RFW]

Bob (and everyone else),

 

Two parts to this puzzle we're trying to figure out -

 

1) How to move the steppers without the dealer's BMW diagnostic system.

 

2) Once we can move them, were to for a starting position for sync?

 

Toward the first goal, I bought a hobby stepper motor controller kit and I can now step a 6-wire (two coils each with a center tap) stepper motor around to my heart's content. But how to interface a 4-wire stepper like is on the bike? Any clues anyone?

 

As to the second question, I still don't have a guess?

 

4 and 6 wire motors are essentially the same thing. The difference is only that it is electrically more convenient to drive a 6 wire motor, because there is no need to reverse the current flow through a motor winding.

 

The magnetic field MUST be able to be reversed, for each coil, but the way it is done with center tapped coils (6 wire motors) is as follows...

 

12V (+) is generally connected to the center tap. Then each end of the coil is connected to a transistor (essentially acting as a simple switch) that connects to ground. Only one of these transistor "switches" is conducting at any one time. To have one polarity of magnetic field in the coil, the transistor switch at one end of the coil is turned "on". To reverse the polarity of the magnetic field, that switch is turned "off" and the opposite one is turned "on". The net result is that at any one time, only half the coil is used, but with one switch turned "on". current flow (and hence magnetic poarity) is opposite from when the other switch is turned "on".

 

With a 4-wire motor, there is no center tap. As a result, current must actually be reversed in the coil when the magnetic field needs to be reversed. This is a bit more inconvenient.

 

To do this, one must have a so-called "H-Bridge" for each coil. With an H-Bridge, imagine the letter "H". See the attached (very crude) diagram.

 

In operation, either "switches" 1 and 4, OR "switches" 2 and 3 are closed. If 1 and 4 are closed, current flows through the coil from left to right, establishing a magnetic field in one direction. If switches 2 and 3 are closed, current flows throught the coil from right to left, reversing the magnetic field.

 

Technically, is is slightly more difficult (when transistors are used instead of mechanical switches) to drive the "upper" switches (1 and 2), so that is why center tapped 6 wire motors are popular.

 

It is perfectly possible (albeit rather tedious) to drive the coils using real switches. Obviously, the speed of stepping will be really absurdly slow! If this is done, it is absolutely CRITICAL to remember to switch OFF one pair BEFORE switching ON the other pair. Otherwise, a straight short from +12 to ground will result.

 

As for the actual starting position, I cannot hazard a guess without seeing these things in action.

 

Bob.

[steveknapp]

You can find ICs. A quick google turned up these at $3 per.

 

http://www.alltronics.com/download/1330.pdf

 

Two of those, a PIC, and some glue, you could manually control the motors.