Alternator clutch

[Denni]

G'day

I'm wondering if anyone can help with a question.

I've had to have the clutch on the alternator replaced on my 2009 ATX - thankfully at no cost.

Does anyone know what the purpose of having a clutch fitted to the alternator is?

The dealer seems to think that perhaps it is stop the alternator from running when it is required, in a similar fashion to the A/C compressor.

Does anyone actually know what purpose the clutch serves?

Just to satisfy my curiosity.

Great forum.

Thanks

Dennis

[CONROD]

Mate I think this is what you are referring too. Hopefully someone like ADAMSY would be a grateful and fully inform you on the matter as he would know first hand if it has or hasn,t got a clutch in the drive pulley

cheers CONROD

A serpentine belt drive system for an automotive vehicle in which the sequence of driven assemblies includes an alternator assembly comprising a housing and an armature assembly mounted in the housing for rotation about an armature axis. A hub structure is carried by the armature assembly outwardly of the housing for rotation therewith about the armature axis. A coil spring and one-way clutch mechanism is disposed in operative relation between the alternator pulley and the hub structure for (1) transmitting the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the armature assembly is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient rotational movements in opposite directions with respect to the alternator pulley during the driven rotational movement thereof and (2) allowing the hub structure and hence the armature assembly to rotate at a speed in excess of the rotational speed of said alternator pulley when the speed of the engine output shaft is decelerated to an extent sufficient to establish the torque between said alternator pulley and said hub structure at a predetermined negative level.

[450HP/tonne]

Summary of the above:

The one-way clutch allows the alternator to free-spin when you shift up a gear (which can be at high rpm / high shock loading). The inertia of the alternator allows it to produce energy until belt and alternator speeds match.

[01 VEY]

The initial purpose of fitting the freewheeling clutch pulley and de-coupler pulleys was to assist in preventing "belt wrap". This happens when the rotor which is usually spinning at well in excess of 10,000 RPM and the engine speed drops dramatically. The rotor continues to spin and this can shred the polygroove belts. Some inventive vehicle manufacturers have made another application of the alternator over-running.

It seems to be used for the computer, ECU or the Body Control Module to calculate the engine speed versus the actual vehicle speed. By doing this parity or disparity comparison Toyota have, on some Hi-Ace models, somehow managed to incorporate this into the airbag deployment mechanism in order to set the airbag off when the vehicle comes to a sudden stop. IE an accident. If the clutch pulley is replaced with a solid steel one this has been known to cause the deployment of the airbags where there is a passenger sitting if the vehicle stops suddenly.

In Mercedes Limo style vehicles there has also been a case reported where the computer thinks the engine is about to cut out under heavy braking and then opens the throttle even though the driver has his foot firmly planted on the brake pedal.

Gotta love the new age of computers and fly by wire engine control systems.