SKF
Magnetic Trigger Wheels
SKF magnetic trigger wheels are multi-pole magnetic rings integrated into engine seals (typically the rear main seal assembly) to provide crankshaft position and speed data to the engine control unit (ECU). The magnetic ring is bonded to a metal carrier or directly onto the seal assembly, and it operates reliably in the engine oil environment. By integrating the trigger wheel into the seal, SKF eliminates the need for a separate target wheel mounted on the crankshaft, reducing parts count, assembly time, and potential corrosion points. The magnetic pattern is precisely encoded to match the specific ECU requirements (number of pole pairs, reference marks). This solution is widely used in modern engines where space and reliability are paramount. SKF ensures the magnetic field strength remains stable over temperature and after exposure to oil and metal debris.
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Integrated Crankshaft Position Encoding
Replaces separate tone wheel.
Pole Pair Count
Precisely matched to engine ECU requirements (e.g., 60‑2 pattern).
Temperature‑Stable Magnetism
Maintains signal strength from cold start to full engine load.
Oil‑Resistant Embedding
Magnet material fully encapsulated to prevent corrosion.
Assembly Simplification
One component instead of bearing seal + separate tone wheel.
Reduced Engine Length
Saves axial space in the engine block.
How a Magnetic Trigger Wheel in the RMS Works
The rear main seal’s PTFE lip extends to form a carrier for a precisely magnetised rubber ring. As the crankshaft rotates, the magnetic poles sweep past a Hall‑effect sensor mounted in the block, generating a clean square‑wave signal that the ECU uses to time fuel injection and ignition.
The Cost of a Faulty Trigger Wheel Signal
An intermittent signal from a cracked or demagnetised trigger wheel causes the ECU to lose crankshaft position, resulting in engine misfires or a no‑start condition. SKF’s 100% production‑line magnetisation and signal testing prevents this field failure, guaranteeing a reliable timing signal.