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In regards to a two cylinder motorcycle; if the CAM sensor sends the ECU the cylinder position what does it use the crankshaft sensor for? How are they related to the timing for each cylinder?
Thanks,
The cam sensor is often just a single pulse, so the ECU knows the phase of the 4-stroke cycle. For every 360 degrees of crankshaft revolution, there is only 180 degrees of camshaft rotation. So a single trigger can tell you if cylinder 1 is at TDC compression stroke(valves closed), or TDC exhaust stoke (valve(s) open).
On variable camshaft engines, there may be more than one trigger (cam angles are determined relative to the crankshaft "home" or missing tooth position"), but not enough to determine the crankshaft position with any accuracy (required for ignition timing).
In the ECU, there is a programmed relationship (ie. degrees, or number of teeth) between the crankshafts "home" position, and the TDC of Cylinder 1, TDC of Cylinder 2. The teeth on the crank trigger wheel allows the ECU to track the crankshaft position (in degrees) and speed, so it can time the injection and ignition events correctly.
