tolsen

Alternator freewheel pulley - faster gear changes

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Freewheel pulley INA 535005910 viewed next to original solid pulley removed from the 85 Amp Bosch alternator fitted in my 2002 Smart 450 Cabrio Cdi.
INA535005910.jpg

DSC04440.jpg
Note that the grooves are perfectly aligned. No machining is required. Outer groove on the INA pulley is not used.
Bought the INA pulley cheaply on eBay for £15 from someone that had ordered the wrong pulley for his car.

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Summary of benefits by fitting freewheel pulley on alternator on a Smart 450 or 451:

Faster gear changes shifting up.

Smoother idle.

Improved fuel consumption.

Reduced emissions.

Belt tension can be reduced causing less wear on alternator and cooling pump bearings.

Increased life tenfold of auxiliary drive belt.

Faster acceleration.

Improved driving experience.

Allows you to enjoy the Smart as Swatch intended.

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Specified new belt tension for the 450 Cdi 5PK768 alternator/ cooling pump drive belt is 450 N. Same belt on the 54 HP 451 Cdi has new tension 330 N and retension limit 200 N. Corresponding vibration frequency of belt at longest free vibration span for a Contitech belt weighing 59 grams becomes 201 Hz. Retension limit 157 Hz. Vibration frequencies for Gates 5PK768 belt weighing 61 grams are 198 Hz & 154 Hz.

Fitting belt using 54 HP 451 Cdi specified tension results in reduced load on bearings hence increased bearing life.

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Wait, what?

How does putting a sprag clutch on your alternator, and for that matter the time it takes your engine to decelerate, have anything to do with the time it takes to upshift?

Engine speed does not have to be matched to the transmission input shaft in order for power transfer to take place, as a matter of fact, on modern high speed dual clutch transmissions I can assure you the engine cannot change much of it's RPM in only a few milliseconds, rather the extra rotational energy in the engine gets transferred to the wheels (well first whatever cush system is in place in the drivetrain) and you propel forward when the clutch is released.

My VW TDI's have this clutch on the alternator and it helps with NVH from the non uniform crankshaft rotational speed and resulting belt "flapping", but I was able to shift just as fast with or without it. It's a comfort thing, and it weighs more than the typical pulley. More rotational weight = worse acceleration = worse fuel economy (by such a small margin no one could possibly notice).

Dave

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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. Also note that clutch, graph 5, does not engage before engine speed matches transmission speed.

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

That is all folks.

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Hi Tolsen,

I can draw graphs too, my question is: Why does the engine have to drop in speed to prepare for next gear up?

As long as the gear isn't under load while the shifting is taking place, it makes no difference what RPM the engine is at when the power is reapplied. This is the advantage of the dual clutch systems is that the next gear can be shifted because it obviously isn't under load, so the actual shift is just one clutch opening while the other closes, even if the engine itself is several thousand rpm too high for the gear you are shifting in. On smaller bikes we actually hold the throttle open on shifts to bring the engine even higher in RPM so you can use that extra stored energy when you release the clutch. When you only have 10 HP it all helps. :D

I gave this more thought after this morning. I think the real reason you see this alternator sprag clutch unit on other cars and not the Smart Cdi is because the Smart doesn't have a tensioner on the serpentine belt. The VW system would be constantly loading and unloading because of the non-uniform rotational speed of the crank, whereas on the Smart the stored energy from the alternator can go into the crank and vise versa.

In summary, this mod will definitely do one positive thing for your car - It will greatly increase the life of your alternator belt.

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Ask Smart and Getrag why. Getrag, the designer and manufacturer of the transmission made the graph.

The 451 Cdi has a freewheel pulley fitted. Same engine as the 450 Cdi apart from fuel injection system.

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The reason the Smart 450 did not come with any freewheel pulley fitted is the freewheel pulley was not yet invented when the 450 was designed.

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If I read that chart correctly, the ECU isn't waiting for rpm's to match before engaging the clutch. It has already started engaging the clutch a while beforehand, it just waits until they match before fully letting the clutch go. No different than what we do when driving a manual with a clutch. This does nothing to suggest the clutch sprag will speed this process.

The transmission gets to proper RPM faster than the engine because, no surprise, the moment the gear is actually selected the transmission input shaft has to be rotating the new speed (it is coupled to the tires/road surface), it is mechanically decelerated (via syncro) to that speed which no engine could ever match. The clutch is what brings the engine speed back to the transmission speed, you can literally see the moment the clutch starts to rub on the flywheel and the engine rpm starts changing drastically. If it were actually waiting for the engine speed to match only by the natural deceleration of the engine alone, that line would be perfectly linear. I'm not convinced that the clutch is slowing the alternator faster than the alternator would all by itself at that rpm.

When I was building a human powered helicopter for a competition a few years ago I built a recumbent bicycle that had a VW Bosch alternator attached to it as a means to produce a certain amount of power over a certain time. When it kicked in it wasn't like riding up a hill, it was like hitting a brick wall (It was really funny really to watch people try to ride it). The brutal force it takes to run an energized alternator is more than enough to slow it down all by itself, trust me on this one. I've experienced this directly. If anything that alternator will slow the engine down FASTER if it is connected, actually now that I remember that bike setup, I'm positive it would.

The idea of a sprag on the alternator was already being implemented on VW TDI's back in the late 90's, so the pulley was invented already, unless the original OM660 sat on a shelf for over half a decade before they decided to use it. I have a locked up pulley in my basement now off a 1999 ALH, they are both Bosch alternators, I wouldn't be surprised if it is similar in dimensions.

Just the saving on wear and tear on the belt may warrant the switch itself, if a guy had one laying around. My belt on this smartie I've torn apart is pretty toast, and the car didn't even have all that many miles on it. This sprag isn't for faster gear changes, it's to help NVH from high frequency cycling of the power/compression pulses.

Not a performance mod at all, only a comfort mod.

Dave

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With a freewheel pulley, there is less parasitic load on engine hence improved fuel consumption.

AltShaftSpeed.png

A freewheel pulley decouples alternator's inertia from torsional vibrations (negative angular acceleration) from the three cylinder engine.
A freewheel pulley increases alternator rotational speed.
A freewheel pulley extends life of auxiliary drive belt.
A freewheel pulley eliminates any belt slippage or squeal at engine deceleration such as when shifting up in gear.
In case of the Smart 450 and 451, fitting a freewheel pulley will increase gear change speed. (Note that some models like the 451 Cdi already have the freewheel pulley fitted).

Benefits summary:

Faster gear changes shifting up.
Smoother idle.
Improved fuel consumption.
Reduced emissions.
Increased life tenfold of auxiliary drive belt.
Faster acceleration.
Improved driving experience.

Allows you to enjoy the Smart as Swatch intended.

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GearChangeGraph.png

I think we may agree on this one: Clutch starts to bite approximately from the point where red curve 2 crosses green curve 5.

Alternator spins 3 times faster than engine hence acts as a flywheel effectively slowing down time it takes for engine dropping in speed.

Of course I have already checked this out by observing alternator spinning around after engine has come to a standstill. Got to rev engine then turn off to see this so can only be verified with the help of an assistant.

Unlike castrating your air intake by delipping, something many fools did to their Smarts years ago, fitting a free wheel pulley is a mod that actually provides benefits. Well worth it especially if your pulley needs replacing due to wear anyway.

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You said you determined that the engine will stop while the alternator is still spinning by shutting off the engine. I wonder, by shutting off the engine are you de-energizing the alternator? Maybe?

One thing I absolutely know for sure is that when an alternator is made to work, it takes all the effort I have to keep it spinning at all. I don't have the gear ratio I was using though... but it was intended to keep it spinning around the same speed it would in a car at lower engine RPM. Once it gets to a low enough speed it shuts off and spins but that is slower than it will see with the engine running.

I think the clutch starts to bite a little sooner than that crossing point in the graph, basically when the almost linear deceleration starts to take a dive.

Adding the clutch doesn't hurt anything, that much is certain.

As for the rest of the claims, especially faster acceleration, I think we need more isolated data. (Such as my MyChron data logger keeping all aspects the same except that pulley).

Belt life tenfold is tough to prove.

Improving the smart driving experience? While we are already at the very peak of adrenaline and excitement? How can this be? :icon_smile:

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Should be easy to confirm whether alternator is generating if turning when ignition is off. A voltmeter will tell us.

Quicker gear changes means faster acceleration. I have published acceleration times on thesmartclub, with and without freewheel pulley.

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Here is a video showing my standard 450 Cdi with free wheel pulley accelerating from 0 to 100 km/h in auto:
 

 

Please notice the super slick gear shifts and whisper quiet engine. Of course still running on the original exhaust. Only 15 years old and clocked 216,000 km.

Edited by tolsen
1 person likes this

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After seeing that video of the gear changes on a stock map cdi, I am convinced this is a really interesting modification to do. Looks to me about 15-16 seconds to get to 100 kmh. That is almost as fast as some of the remaps.

 

Imagine a remap PLUS a freewheeling pulley. I'm doing it!

 

 

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The best mod I have done so far. Easy and cheap if you go for the INA pulley. Smart’s own, the one fitted to alternator on the 451 Cdi, is far too expensive. 

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I like the looks of the INA you've identified, I am probably going to source a couple, as I know this mod is going to get done on a couple cars already! ;)

 

I will sift eBay for the INA 535005910 and grab a best deal on a couple and send them into my USA address to save a bit of tax and duty. Look to be about $40 USD each

 

Ordering three at least - one for me, one for Izzy, and a spare for someone else's car, or my next extra car ;)

If you are local, or near local to me and want one, speak up now! Shipping is hardly anything extra for multiples.

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OK, question as I'm always interested in a HP gain of any kind...lol...damn and i thought I could stay away from it with this car.....augh!!!!!

 

I only manual shift ....up just under 3000rpm and down close to 2000 maybe 1900rpms...simply to get the best fuel consumption rates....and stay under 90 kph on secondary roads.....I can easily get the fuel consumption rate down to 3.6 maybe 3.5 LPHK

 What will this mod do when shifting in manual mode and shifting carefully?  I see it soley for wear and tear on the belt..?  I have never seen a worn out altenator pulley like the one shown.....perhaps they were all steel pulleys?  Why are they alluminium, simply for weight savings or speed to turn the small pulley?  I'm also on the fence about it making much difference if you are making the altenator work in any way. Just spin one by hand and then draw a load from it, it'll drag very quickly and depending upon the load it'll be very hard to turn by hand I bet!  So it's a catch 22 imho, yes it may work if you are not using the altenator as it'll spin freely but if you are demanding power from said altenator then it should help slow the motor down some....imho.....and after saying all this I could also be completely wrong, but this is how my old brain see's it. sorry.

Now, what if you decreased the dia of said pulley? Then what?  Just a thought?

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This is a mod to get quicker shifting. I do not think you will be able to measure fuel economy differences, at least not any that anyone else will believe. They will want A-B-A-B and lots of controlled runs of each, and that's just too much work to justify the mod. The mod is to get quicker shifting, and up to speed quicker.

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We need to lessen the weight of moving parts if you want quicker spool up speeds....lol.  OR more HP and THAT is a very very slippery slope and never worth the funds spent, ask me how i know...lol    Hense I'm trying NOT to step onto that slope!

It's bad enough I bough a spare Smart just to have cheap spares etc...lol.  Now i need a STAR machine...lol Who's got one..?  I need it...lol

 

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I've done the search for power etc etc with my bike and Truck and  well let's face it every vehicle toy I've owned!    You always get the people who simply need testing and charts, specs etc etc, and then when asked they never have any desire to do any of said mods, they just like the arguement to try and diswade you and anyone from doing these mods.  It's the reason i stopped visiting the bike forums, I was even an admin and own one of the heavily modded machines in Canada.  It's now been un modded and up for sale...lol next!  Mods are soon for sale seperately.....the only way to get any of your money back...lol.

 

 

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