Crankshaft Position Sensor

The crankshaft position sensor is used to collect real-time crankshaft angle position and engine speed (RPM) data, sending pulse signals to the ECU to determine key control parameters such as ignition advance angle, fuel injection timing, and top dead center (TDC) of the first cylinder. It serves as the “master clock” for modern gasoline/diesel engine control systems. Without a reliable CKP, the engine often fails to start or runs unstable.

Working Principle and Types

Common technical approaches for CKP include:

Magnetoelectric (inductive/magnetic pulse) type: Induced voltage is generated when the coil and core cut through the magnetic field in the tooth ring, with amplitude varying with rotational speed. No external power supply is required, and the structure is simple and resistant to high temperatures and vibrations. However, it is more sensitive to installation air gaps and tooth profiles.

Hall Effect Type (including Magnetic Resistance/MRE Solutions): Internal Hall elements combined with amplification/shaping circuits produce stable square wave digital signals. They offer strong resistance to oil contamination and interference, making them suitable for low-speed identification. Typically require 5 V/12 V power supply (determined by the vehicle's ECU solution).

Optical type: Generates pulses using a light-blocking disk and light-sensitive components, offering high resolution but being sensitive to contamination; rarely used in passenger vehicles.

Engineering note: When high engine low-speed starting performance is required and the wiring harness noise environment is severe, the Hall-effect type is preferred; in extreme temperature/vibration conditions with limited structural space and cost pressures, the magnetic-electric type remains common.

Installation Location and Mechanical Tolerances

Common installation locations: near the front end pulley of the crankshaft, flywheel housing/transmission bell housing, cylinder block near the large flywheel, etc. Rigid fixation and clean ends free of iron filings are required.

Typical Air Gap Range:

• For magnetic-electrical CKP and pulse wheels in general passenger vehicles, the air gap is typically controlled within the range of 0.5–1.2 mm (depending on the vehicle model); excessive or insufficient air gaps may cause phase drift or signal loss.
• Some manufacturer manuals or maintenance guidelines may allow a wider range of 0.5–2.0 mm (subject to specific vehicle models, tooth profile, and magnetic circuit design).
• Industrial/textbook cases also specify a range of 0.5 to 1.5 mm, with final verification via oscilloscope after proper installation.

Vehicle installation checklist: Inspect the CKP tip, gear ring damage/contaminants, air gap, wiring harness shielding, and mounting. Use an oscilloscope to verify waveforms as needed.

SUCH recommends selecting sensors with dustproof and waterproof ratings (e.g., IP67) to withstand humid and sandy conditions (IP rating definitions and meanings refer to IEC 60529).

Comparison of Sensor Types