Crank Angle Sensors

[Mik]

Does anyone know how the CAS on the RB engines works?

There is a 120 deg signal and a 1 deg signal. I'm not sure why both of these are needed.

In a 6 cylinder engine, the spacing between cylinder firing is 120 degs, so that singnal makes sense, but what is the 1 deg for?

Wouldn't the 120 deg signal be enough?

Also, does anyone know why there are 2 pins on the ECU for each singnal input?

Thanks

[Sydneykid]

Does anyone know how the CAS on the RB engines works?

There is a 120 deg signal and a 1 deg signal. I'm not sure why both of these are needed.

In a 6 cylinder engine, the spacing between cylinder firing is 120 degs, so that singnal makes sense, but what is the 1 deg for?

Wouldn't the 120 deg signal be enough?

Also, does anyone know why there are 2 pins on the ECU for each singnal input?

Thanks

<{POST_SNAPBACK}>

If there were simply 6 X 120 degree pins, then how would the ECU know when the engine is at TDC on #1? That's what the 0 degree pin does, identify #1. So no, the 120 degree signal would not be enough. I also understand that the 0 degree signal is used for the tacho.

It is my understanding that the 2 X 120 degree signals are for error detection. One is a straight input to the ECU, so it knows when each one of the 6 cylinders is at TDC. The other 120 degree signal is combined with the 0 degree signal to identify #1 and synchronise the other 5 cylinders. So the injectors squirt and the spark plugs fire at the right time for each cylinder.

If the straight 120 degree signal doesn't align with the #1, #2, #3, #4, #5, #6 TDC signals then you get a synchronisation error.

Hope that helps

cheers

[Mik]

If there were simply 6 X 120 degree pins, then how would the ECU know when the engine is at TDC on #1?  That's what the 0 degree pin does, identify #1.  So no, the 120 degree signal would not be enough. I also understand that the 0 degree signal is used for the tacho.

It is my understanding that the 2 X 120 degree signals are for error detection.  One is a straight input to the ECU, so it knows when each one of the 6 cylinders is at TDC. The other 120 degree signal is combined with the 0 degree signal to identify #1 and synchronise the other 5 cylinders.  So the injectors squirt and the spark plugs fire at the right time for each cylinder.

If the straight 120 degree signal doesn't align with the #1, #2, #3, #4, #5, #6 TDC signals then you get a synchronisation error.

Hope that helps

cheers

<{POST_SNAPBACK}>

Thanks.

I've never checked it with a CRO, but I thought 1 deg meant 360 pulses/rev and 120 deg meant 3 pulses per rev. But that can't work. Maybe the 1 deg is 1 pulse per rev just after TDC on #1 and the 120 deg is 3 pulses per rev telling the ECU when to move to the next cylinder??

The error checking makes sense, but I can't see why they don't just split the signal inside the ECU case.

Also, something I just realised, if you adjust static ignition timing by twisting the CAS, you would also change the injector timing, wouldn't you? Does adjusting the global ignition timing on a PFC do this too?

[MonstaS4]

The 1 deg signal gives a pulse every 1 CAMSHAFT degree, not crankshaft. The 120 deg pulse is not identical each time. (Once again it's camshaft degrees - 120 deg x 6 cyls = 720degs = 4 stroke engine cycle) There are 6 unique sized windows 120 degs apart and the ecu counts how many 1 deg pulses are inside each unique "window". The smallest window is 4 pulses wide and they increase by 4's until 24. i.e. 4, 8, 12, 16, 20, 24. So by using these unique windows, the ecu knows exactly where it is in the cycle.

[SteveL]

The 1 deg signal gives a pulse every 1 CAMSHAFT degree, not crankshaft. The 120 deg pulse is not identical each time. (Once again it's camshaft degrees - 120 deg x 6 cyls = 720degs = 4 stroke engine cycle) There are 6 unique sized windows 120 degs apart and the ecu counts how many 1 deg pulses are inside each unique "window". The smallest window is 4 pulses wide and they increase by 4's until 24. i.e. 4, 8, 12, 16, 20, 24. So by using these unique windows, the ecu knows exactly where it is in the cycle.

This is pretty much correct....the ECU needs a unique way to identify each cylinder to work out the firing order and the different width windows for the individual cylinders provides that mechanism, but one edge of the window also provides an accurate position for TDC of the associated cylinder. Once the order is identified and TDC set, it is just a matter of the ECU using the 1deg outer slots to calculate ign firing point. In fact the ECU also calculates the ign timing to fractions of a degree using an algorithm that relies on the fixed angular position of the 1 degree slots. This feature goes back to the original ECCS design used on the L28ET in the 280ZXT, although that used a slotted disk attached to the crankshaft with reluctor pick-up, not optical as used in RBxx engines.

In compasrison, the RB30 CAS has fixed width windows for the CAS cylinder identifier slots.....it has a distributor to take care of the firing order, so the ECU doesn't 'need to know'.