tolsen

Alternator freewheel pulley - faster gear changes

71 posts in this topic

A freewheel pulley allows the alternator to continue spinning on its own inertia whilst engine is slowing down in preparation for a gear change. This results in less load on auxiliary drive belt and faster gear changes. Some claim they also improve fuel consumption.

DSC04431.jpg
Pulley on the left is original pulley from my 2002 Smart 450 Cabrio Cdi and now very much worn. Pulley on the right came from a Renault, unsure which model and year. This pulley is a freewheel pulley made by INA. Original pulley has 5 grooves. This INA pulley has 6 grooves. No real problem, only have to ensure belt is in right grooves and correctly aligned.
Diameters measured over top of ridges: Original pulley when new 54.2 mm. This INA freewheel pulley 55.7 mm.
I had to machine the new pulley to make it align crank shaft pulley. Removed 1.1 mm where pulley faces alternator.
Nowhere in WIS could I find any torque specification for alternator pulleys. Google also no good for same so I checked Renault Dialogys and found specified torque is 8.2 daNm.

DSC04433.jpg
Freewheel pulley fitted on alternator. Protective cap fitted. Existing belt was in a poor state so I fitted an older used belt in a slightly better condition.

Road test:

Noticably faster gear changes shifting up. No change shifting down.


Why faster gear changes shifting up?
The high inertia of a fast spinning alternator with standard pulley will slow down (resist) speed changes of the wee Smart engine.
A freewheel pulley allows alternator to continue spinning on its own inertia because decoupled from engine when engine slows down. Engine can therefore reduce its rotational speed faster.

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Does it click like a bicycle freehub?

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Does it click like a bicycle freehub?

Clickless like Continental style freehubs.

Anyway, this is a mod I strongly recommend. Combined with a good and correctly pleloaded clutch actuator, good thermostat and restrictor plug you can enjoy motoring just like swatch intended.

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INA 535005910 is a perfect fit for any Smart 450 Cdi with Bosch alternator. No machining is required.

INA535005910.jpg

Spacer under existing pulley is reused. Tightening torque 8.2 daNm. Outer groove on pulley is not used.

Above pulley can be sourced for about £28 in the UK.

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Good idea! Any way of posting comparative data for data-junkies like me?

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No, how the car actually performs, i.e. fuel consumption, oil analysis, torque, HP. I don't suppose you have baseline numbers on the car prior to the mod?

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I am not convinced a clutch pulley will save fuel as claimed by some manufacturers.

Car performance has definitely improved. Got no figures to back that up and do not intend to produce any.

Have been out enjoying Smart motoring every spare hour since I fitted the freewheel pulley. That ought to suffice as far as comparative data is concerned.

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Fair enough. In theory it would definitely make some improvement; and usually the butt-dyno is sufficient for enthusiasts. Still, a good idea, these little engines need relief from any parasitic load that can be be mustered. I'm still looking to buy one, but I'm not sure if I can hide it in the garage so my wife won't see it :)

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Faster gear changes shifting up should result in faster acceleration time. I could therefore time my Smart from zero to 80 km/h. The only problem is I did not time it before fitting the freewheel pulley and reinstating old pulley is several hours work. Subframe must be lowered and alternator must be unbolted and preferably removed but possible to do with alternator loose from its mounts but attached to the wiring.

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Zero to 80 Km/h acceleration tests. Flat road. Nil wind. Ambient temperature 6 C. Tests done with transmission in automatic.

With freewheel pulley: 12.5 seconds, This is average of four runs.

Without freewheel pulley: 14 something seconds. This is from memory. Measured on same stretch of road.

Car: 2002 Smart Cabrio 0.8 Cdi. Running on original map. Standard wheels all around. Only driver in car when testing. No passenger, no baggage. Towbar fitted, no trailer. 1/2 fuel tank. Engine at operating temperature. Headlights on. Heater fan on low speed.

Improvement around 1.5 seconds which is 0.5 seconds per gear change. Not bad in my book.

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I hate to ask, but can't you out the other pulley back on to do a measured test? ;)

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Better if one of you guys do it so we get independent tests. Original pulley is made out of aluminium so there will be many well overdue for replacement. Order the INA freewheel pulley referenced in one of my previous posts. Do acceleration test, change pulley and repeat.

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By the way, I am now really enjoying this Smart. Fitted new rear £23 each Sachs shocks same time as replacing alternator pulley. New shocks made quite a difference on the ride. I suppose my 14 year old shocks were years overdue for replacement.

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The high inertia of a fast spinning alternator with standard pulley will slow down (resist) speed changes of the wee Smart engine.

A freewheel pulley allows alternator to continue spinning on its own inertia because decoupled from engine when engine slows down. Engine can therefore reduce its rotational speed faster.

I would have thought that the drag of the alternator would make the engine slow down faster. Are you saying it acts like a motor on the over-run?

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Yes, fast spinning alternator is acting like a giant flywheel. Note that these pulleys are also called overrun pulleys.

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Our wee Smart engines have same size alternator as much larger normal engines. Those larger engines are less affected by the "flywheel effect" of the fast spinning alternator. Therefore, the smaller the engine the greater the benefit from fitting an over run (freewheel) pulley.

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I think we need to consider what Tolsen is not saying. The alternator is not a giant rotating mass that takes several minutes to coast down to stop; but there is a moment during RPM changes when the engine will have to slow down the alternator. I doubt that this lasts more that a fraction of a second to a second, but it would certainly add that buffering affect. You may actually even get a softened re-engagement.

Certainly, the rest of the time the alternator acts as a brake, especially when you're using a lot of electricity to run accessories.

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Smart could have been smarter if they had switched on a high load such as the electric heater to brake alternator just at the right time when engine is slowing down preparing for next gear shift up.

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Here we have some solid proof that time for engine to slow down is important for speed of gear changes.

GearChangeGraph.png
Above chart is copied from:
7.Aachener Kolloquium Fahrzeug- und Motorentechnik 1998, Das hochintegrierte, automatisierte 6-Gang Schaltgetriebe für den smart,
Dipl.-Ing.(FH) Günter Rühle, Dipl.-Ing.(FH) Peter Tillmann Dipl.-Ing.(BA) Henning Diel, Dipl.-Ing.(FH) Michael Hackenjos, GETRAG, Ludwigsburg.

The chart depicts various variables covering gear change from 2 to 3.
For simplicity, just look at graph 1 transmission speed and 2 engine speed. Units are RPM on Y-axis, time on X-axis.

Note how quickly transmission changes its speed whilst engine takes a considerable time.

Fitting a freewheel pulley reduces the time it takes for engine to drop in speed in preparation for the next gear up.

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That's interesting. Do you know how much time is elapsed on the x-axis?

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That's interesting. Do you know how much time is elapsed on the x-axis?

I think Getrag intentionally left out time markings on x-axis.

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A freewheel pulley allows the alternator to continue spinning on its own inertia whilst engine is slowing down in preparation for a gear change. This results in less load on auxiliary drive belt and faster gear changes. Some claim they also improve fuel consumption.

DSC04431.jpg

Pulley on the left is original pulley from my 2002 Smart 450 Cabrio Cdi and now very much worn. Pulley on the right came from a Renault, unsure which model and year. This pulley is a freewheel pulley made by INA. Original pulley has 5 grooves. This INA pulley has 6 grooves. No real problem, only have to ensure belt is in right grooves and correctly aligned.

Diameters measured over top of ridges: Original pulley when new 54.2 mm. This INA freewheel pulley 55.7 mm.

I had to machine the new pulley to make it align crank shaft pulley. Removed 1.1 mm where pulley faces alternator.

Nowhere in WIS could I find any torque specification for alternator pulleys. Google also no good for same so I checked Renault Dialogys and found specified torque is 8.2 daNm.

DSC04433.jpg

Freewheel pulley fitted on alternator. Protective cap fitted. Existing belt was in a poor state so I fitted an older used belt in a slightly better condition.

Road test:

Noticably faster gear changes shifting up. No change shifting down.

Why faster gear changes shifting up?

The high inertia of a fast spinning alternator with standard pulley will slow down (resist) speed changes of the wee Smart engine.

A freewheel pulley allows alternator to continue spinning on its own inertia because decoupled from engine when engine slows down. Engine can therefore reduce its rotational speed faster.

Is this where you removed 1.1 mm from the pulley?. To accommodate pulley alignment?

Would you know if there is a cross over number for SKF instead of INA? SKF is more common here in Canada.

https://www.youtube.com/watch?v=rXehCcNzq_A

post-15911-0-53144800-1460846830.png

Edited by GRP151

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Around a 1 second improvement in acceleration would be worth it if it is only around $56 CDN. I found a cross reference

SKF VKM 03302 or GATES OAP7080

It looks like it was used on lots of smaller diesel engines. Nothing looks like it was available in Canada or the US but very possibly Mexico.

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