Home made hybrid (using access to 5th gear on FWD transaxle)
 

I've had an idea of a home made hybrid. It will not be greatly powerful, and only be an assist motor for a hybrid conversion using the 5th gear extension on the gearbox's mainshaft (as I think the Metro also has?).
The mainshaft rotates continuously and feeds power through the differential directly, so this would be a gearless motor system that would be independant of the engine and gears.

There's a steel pan extension to the side of the gearbox that houses the 5th gear. It would be possible to add a drive to the gearbox main shaft through this pan using a belt drive system, and locate the motor above the gearbox.
A belt drive like a cam belt system would do the job.

The shaft ends with a nut holding the 5th gear cog on. My theory is to replace this with a threaded driveshaft that can be torqued onto the shaft as the nut is currently, then dowelled in place to ensure it does not move. This would then serve as the mating shaft for the toothed drivewheel driven by the motor that is located above it.
The steel pan will need to have a shaft seal on it the same as a crank oil seal, but I don't see this as a big job.

First diagram below shows the gearbox
Second shows the approximate positions of the 5th gear & shafts
Third shows where the motor would locate above the gearbox, next to the engine.

Any comments??

This is the motor I would be considering

http://cgi.ebay.co.uk/DC-12-24V-ELEC...QQcmdZViewItem

Thanks for posting this! It's exactly what I was considering when I asked what was beneath that cover on the end of my transaxle.

Potential challenges:

1. With an offset belt / chain / gear driven setup, there will uneven loading on the bearings on the driven shaft. Enough to be a problem? Don't know.

2. That motor would be adequate in terms of power, but it's got a crummy output shaft. (Looks like a pump motor shaft.) Makes it difficult to couple to a cog to drive your belt.

This is very exciting - are you seriously considering pursuing this?

If you're going to drive the differential directly, you'll need some serious reduction in your belt drive. (Of course you've thought of that already.)

Another thought: rather than having the motor spin continuously (ie when the engine is driving the vehicle), ideally a freewheeling clutch could be used.

Or an AC clutch

Yup. Or a motorcycle type of freewheel.

1) Yeah, I thought of this too. The extension, in combination with the required belt tension, may well cause too great a bending moment and therefore high load on the shaft bearing. I'm guessing some kind of external bearing on an extension from the gearbox may be in order?

2) The output shaft does look poor, I'd have to take a look at what I could do with it in terms of fitting a coupling to it.

I was going to use a 2:1 reduction ratio, driving through a 3.765 axle to 13 inch wheels with a circumference of 1.77m. This would equate to 8.75mph/1000rpm. Is that enough reduction??

Also would the motor be able to handle higher voltages?? Estimated power output of motor? Top speed of a (currently) 1500 lb car?

I like the motorcycle auto clutch idea :)

Yes, I'm seriously considering doing this...... long term :)

The car has to remain driveable through all the work.

Probably mount something on the modified stamped steel cover and you'd be OK.

I can't really say with any confidence. I only know enough to say that it's something that needs to be considered.

Probably. If the rating on the motor tag is continous, then you can absolutely feed it higher voltage/current for shorter periods. If you want to exceed its rated voltage/current for an extended period, you'd have to add forced air cooling however.

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Here's another question/thought: does the 5th gear cog have its own shaft, or are there other gears on it, inside the transmission case?

If there are lower gears on a shared shaft, I'd consider driving that one instead of the output shaft to the differential, because it would give you the option of multiple ratios. (Although the tradeoff would be that you'd have to have the clutch depressed to keep from spinning the engine via the transmissions "input" shaft while driving electrically.)

This idea fascinates me...

It looks to me that this is rated at around 23 HP for 2 minutes. Typical derating would be about 1/2 that for 5 minutes (400 amps/22v) and another 1/2 for a 1/2-hour rating (200 amps/22v). Rough estimates. That's about 5.8HP, which is good for about 25 MPH (eventually...) in a 1500 pound car on a level road. Again, this is a rough estimate, and depends on many other factors.

At 25 MPH the motor will be turning about 2870 RPM and IMHO the top speed available with this setup/HP. It will probably be relatively slow to accelerate, but would be good to hold a speed once it is accelerated there by the IC engine. Under load the compound motor may not be able to attain much more than 3000 RPM - they tend to self-limit - and you are wise to consider some sort of mechanism that will prevent the vehicle from overspeeding the motor.