Hall effect cam sensor

[John Appel]

I am using a Link G4 storm on a twin cylinder motorcycle engine of our own construction. It is a parallel twin with 360 degree crankshaft and therefore has equally spaced firing intervals. I am running sequential injection using a Hall effect sensor on the overhead exhaust camshaft. I believe these sensors can be sensitive to heat and can fail. If the sensor were to fail and give no signal at all can the Link be set so that it reverts to batch fire and injects and sparks every revolution . The engine would probably run just as well under normal operating conditions but maybe would not idle so well due to the very short pulse width when using the batch fire system.

 John

[Simon]

If the sensor fails while the engine is running it will continue to run on just the crank signal.

However it will not restart once stopped.

[Simon]

I think that could work. The risk is that if it gets a trigger error off the crank then it will not correct itself.

Using the MAP signal is how a lot of current factory motorbike systems do it.

[Adamw]

John,

While I agree with Simon that many OEM's sucessfully use the map sensor sync strategy, in my experience it is a lot less successful in the aftermarket world.  I think the issue you will find is that the 'location' of the sync pulse (in reference to TDC) will vary/drift significantly depending on things like cranking speed, air density etc.  If it only moves within a small window of degrees and you can get it always happen between the same two teeth on the crank wheel then you should be golden and it will work fine, if however this sync pulse drifts so that its crosses over a crank tooth or even just happens too closely to a crank tooth pulse then you will start to see trigger errors and odd timing events.

Personally I would be looking much harder at a more traditional cam sensor if you want something that will work easily from day 1 and continue to be reliable.  There are many ways to do it, my first choice is always a sensor pointing at either a bolt or hole or notch on the cam drive sprocket, but I have even done things like poke a sensor through a hole in the rocker cover and have it see a cam lobe/rocker arm/bolt/lug/notch etc. The old 1GT101DC is a really good sensor for this type of thing because they trigger off almost anything ferrous and over quite big gaps - it seems to be reliable even when fitted inside the engine.

[John Appel]

 

Thanks for that Adam. As I understand it all timing comes from the crankshaft teeth and in particular the reference tooth which is the first one after the gap.When you fill in the details on the cam sensor it asks whether it is inductive type or Hall effect but it does not ask for a degree position of the sensor relative to TDC.  With an even firing 360 degree twin there is one ignition pulse and one injection pulse every turn of the crank. The purpose of the cam sensor is only to direct the pulse to the right cylinder and the left cylinder alternately. when we first tried to start our engine running sequential and using the cam sensor it would not start. We then swapped over the plug leads and injection wires and it started immediately.  Simon says that it only needs the sync pulse on start up. As soon as the engine starts it does not need the sync pulse any more. I think that if I used a pulse from a MAP sensor on one port it also would not matter exactly when the pulse occurred.  As you say the exact timing of this pulse may vary slightly and may cross over one of the crank teeth. My feeling is that it would not matter as long as it does not cross from one side of the reference tooth to the other side.

 If it did cross the reference tooth I think that the degree timing figure would be the same but everything would be displaced one turn and in effect the right cylinder would become the left and vice versa.

 I have looked at the Modern Triumph Bonneville twin and there is no cam sensor. One of the wires going to the injectors has a tag on it labeled Cyl one. This would indicate that the engine is running sequential because if it was batch fire it would not matter if you swapped the injector wires. The ignition is waste spark using one twin lead coil and so this cannot go wrong. The only way I can think of how to differentiate one cylinder from the other is from a MAP pulse.

 The W800 Kawasaki is also a 360 twin and does not have a cam sensor. Does anyone have any further detailed information on how they do this.

[Adamw]

Probably if you can set it up so that your sync pulse is nowhere near your missing tooth it may work.  I have only been asked to tune a couple of aftermarket ECU's that used the map type sync and neither of them would stay synced for long (not links).  I definitely can confirm however that the link will stay 720 synced when using a missing tooth crank if you completely remove the cam pulse while running - I'm just not sure if it will be happy if the cam pulse is still connected and drifting around a lot.

For the other bike engines you mentioned I suspect they would use the map sensor method as that seems common on bikes.  It works fine with OEM's however because they design their whole trigger logic to work with the variable map pulse location.  Aftermarket ECU trigger logic needs to be much more generic as they have to work with a huge range of trigger types so they will never be as robust when it comes to rejecting errors from these odd sync types.

Here's a bit of useless info for you just since you seem interested in odd sync strategies... The Zytek ECU's used in F1 & touring cars in 80's & 90's were sequential without any cam sensor (from memory they didn't even have a missing tooth crank wheel).  They would just try firing on the first TDC event that it saw, if it didn't start after about 5 seconds then it would switch to the next TDC and would continue doing that until the engine started.  Once it saw the RPM increase above cranking speed it would lock to the correct TDC just by counting teeth.