SKF AB (Sweden; Stockholm: SKFA) has introduced a new type of rotation-sensing bearing for hybrid automotive applications.

SKF's bearing employs a fixed magnetic field, offering a continuously variable signal to the electronics monitoring it. The sealed units are designed to operate at high temperatures and high speeds and are built into the drivetrain rather than the wheel ends. In contrast, most speed monitoring is currently accomplished by deploying Hall-effect sensors in the wheel bearing hub units.



The bearing from SKF was developed to interface with Valeo's StARS (Starter Alternator Reversible System), which is a micro-hybrid propulsion design centering around a Stop-Start function -- cutting off the engine when the vehicle slows to a crawl or stops in neutral. StARS then restarts the vehicle when the driver lifts off the brake or engages the clutch. This all accomplished via the combination starter/alternator unit and a standard 12 volt system.

In inverter mode, the starter/alternator takes 12 volts DC from the battery and changes it into three-phase current to work as a starter motor. In rectifier mode, it works as a high-efficiency 180 amp alternator.

Approximately 60 engineers from Valeo and PSA Peugeot Citroën Group have been working on the micro-hybrid drive system in partnership since 1998. PSA's name for the system is Stop & Start. Valeo designed the electrical equipment, power and control electronics. PSA Peugeot Citroën handled drivetrain integration, defined the operating parameters, and the human interfaces. PSA also designed a hydraulic-damped belt drive system strong enough to tie the starter/alternator to the crankshaft.

In dense urban traffic, StARS -- a relatively simple system which does not require major drivetrain changes -- can offer up to 25% boost in fuel economy and reduce emissions by the same amount. PSA Peugeot Citroën claims 8% to 15%.

SKF Automotive President, Tryggve Sthen, said: "This new bearing solution is a successful step in our strategy to be a partner to the automotive industry in delivering energy efficient vehicles. The Valeo StARS system is a good example how new technology and joint development can achieve significant CO2 emission reduction."

The StARS / Stop & Start system is now being offered in several production vehicles -- the Citroen C2 and C3 Stop & Start, Smart with Micro Hybrid Drive, and Mercedes A Class and B Class models equipped with Blue Efficiency.

SKF's magnetic sensor bearings are being manufactured by SKF France.

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