Fifth whell vs belt driven additional engine
 

I am currently driving Italian fiat Idea, with 1.3 diesel, getting close to 55 mpg. Sometimes dream about full EV conversion. But it add problems with mot in my country. So, only one option - hybrid drive. My road to work is 50/50 urban/extra urban ~ 50 km. If I put electric motor 3-4 kw as fifth wheel or as add-on with belt to the main engine, i could get 30-40% better mpg. And I will need 4-5 optima yellow top 12 volt@ 55 ah. Weight addition would be only 100 kg for batteries, 15-20 kg for motor. A little bit more than additional passenger.

So question. With fifth wheel i could get independent propulsion without ic, but without gear-box, i would need more powerful motor, or I will be limited to some speed interval. More or less - lower efficiency or not enough power.

With e-motor added by belt to main ic engine, I could get clean parallel hybrid, needed smaller motor, could use main gear-box. An also could get poor-man regenerative braking.

Conclusion - fifth wheel would be more suited for constant speed application like extra urban or slow driving in city stuck traffic.

But add-on motor will get just better mpg, regardless of speed, but would be needed to run ic all the time.

Ar my conclusion correct ?

Stanislav

Welcome to ecomodder.

Not bad with 50% city driving.

5 HP isn't very much.
A 5th wheel adds weight (not good in the city) and drag when it's being used.
You need to have a mechanism that can lower and raise the 5th wheel (more weight) with enough power to transfer the electric power to the road, while it still needs a suspension to deal with the road.
Something like that gets complicated quickly.


Another technique is to add an electric assist motor to the rear wheels .
(the Idea is front wheel drive IIRC ?)
The rear wheels are already there, they have suspension, and you're not adding drag and weight for a 5the wheel .

This is something that's already been done.


That gets rather complicated as you need a clutch mechanism to detach the normal engine from the electric engine.
It's not something that's easy to do.

Rear wheel drive electric makes your car all wheel drive :)

Thank you for answer. 5 Hp - I am not going to get 100% e-assist, only add on to existing engine. And if taking not more than 100 kg of lead acid batteries - i will have only 2.5-3 kwh of energy. I have seen implementation of fifth wheel on honda insight. With careful driving it is ok. But the lack an ABS on it, which in winter could make some serious problem. Traction is problem also.

Yes, it is front wheel, mix of fiat panda/fiat punto. Yes, i know about rear axle e-drive, used in some Nissan and Mitsubishi. But as far, as I know - it works only till 40 km/h. Correct me, if I am wrong. Better option would be from hybrid lexus... But is way out from my budget.

As i was (or sometimes still in) car-tuner, fitting supercharger is quite simple. I don't see big difference between fitting sc or add-on motor. And some of sc was with built in clutch. Like ones from Mercedes slk. Or just from A/C pump.

But still - will it get better mpg ?

Better than 55? How many miles do you put on?

Totally ? I have this car for ~ 9 month, has driven ~12 000 miles for now.

And if some-one going to buy car with 1.3 jtd, for best mpg, i would rather go for fiat punto. Slightly less weight, better aerodynamic than idea or panda.

If I have this right, you are not really planning on any all-electric operations whether it's 5th wheel or engine-assist- either way the diesel will be running.

How did you come up with the potential 40% fe gain?

A few numbers:
16,000miles/year @ 60miles/day, 5 days/week
1.30 euros/liter diesel in Italy= $1.72U.S./liter
1 liter= .264gallons U.S.
$1.72/l= $6.52/gallon
55mpg(U.S.?)
16000/55=291g/year= $1897/year or $158/mo.

Were you able to achieve +40% fe- 77 mpg- that'd result in 208g/year=$1356 and you'd save $45/mo on fuel, but would have to spend some of that on the conversion and electricity...

Yes, You are absolutely right. In my country it is close to impossible to register full electric car. But hybrid is allowable. And if I can take 100-120 kg of lead acid acu on board, this should give 30-40% of total energy needed for my trip.

Ic engine is left in place. It should give adequate acceleration with even small e. motor.

And more - simple way to do such an upgrade, run alternator as a motor with some kind of brushless controller. Again - it does not need to start from zero rpm. Going alternator less, got 7-8 % of better mpg in my case. By running it as a motor - we could double it. So it should be more like 14-16 % in my case..

You should also consider adding the electric drive to the front axels near the differential, i could be a relatively easy install using belts and pulleys. Also i think that 5hp is plenty, you could perhaps drive this car 60km/h(possibly a lot more in even the slighest down slope) with pure electric and turning the ICE off completely.

No, it is not so easy. Ideal way would be get 4x4 panda, and use it gearbox. When I should get easy access to front wheel. But for idea whose gearbox a too week.