Pickup Rotor Length: The Language of Ignition Timing
In modern electronic fuel injection (EFI) systems, the ECU needs to know the precise position of the crankshaft at all times. The pickup rotor's protrusion (or tooth) passing by a sensor is the signal that provides this information. Calculating the exact length of this protrusion is a critical step in calibrating the engine's trigger system and ensuring accurate ignition and injection timing.
From Angles to Linear Length
The calculation essentially translates the angular width of the pickup on the small-diameter magnet to a linear length on the larger-diameter target rotor.
1. Find the Angular Width
First, we calculate the angle (in degrees) that the pickup protrusion covers on the original magnet's circumference.
2. Convert Angle to Target Length
Then, we apply that same angle to the circumference of the larger target rotor to find the final, scaled-up protrusion length.
Why is This Measurement So Critical?
Accuracy in the trigger system is paramount for a well-running engine.
ECU Trigger Settings
Standalone ECUs need to know the exact length of the trigger signal (in degrees or mm) to correctly interpret the engine's position. An incorrect value can lead to timing drift, misfires, or a no-start condition.
Ignition Timing Accuracy
The ECU uses the rising and falling edges of the pickup signal as reference points. The physical length of the protrusion directly affects the timing of these edges. Precise measurement ensures that when the ECU commands 30 degrees of timing, the engine receives exactly 30 degrees.
