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Old 01-24-2015, 02:53 AM   #1 (permalink)
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"ADDING" a rear engine to a FWD car to run at the same time.

Hi. I'm new here, so I hope I picked the best sub forum for it.

I have been researching this stuff for days, but the only posts that I can find date back to 2011 and earlier, which is very old in the world of electronics. With the takeoff of Tesla motors, I got an idea that I want to run by some people who know wayy more about this than I do.

There is a TL;DR at the bottom.

Background: I am an Electrical/Computer Engineering major and really like fast cars. I managed, barely, to convince my parents to get me a 2006 Chevy Impala SS, which is a pretty fast car, as my first car. I managed it because, although it is fast, it looks pretty docile, actually isn't too bad on the fuel economy, isn't too high in miles, is moderately cheap, well reviewed, FWD, safe, and the exhaust is pretty quiet. So basically, I managed to follow all of the "rules" for a young male's first car, while also getting a 5.3L V8 rated at 303 HP and 327lb.ft torque. The car gets EPA 19 City and 29 HWY. I actually get more like 16 city and 32 Hwy. It has Displacement on Demand(now known as "Active Fuel Management) which shuts off 4 of the cylinders while cruising, which is why there is such a huge gap between city and highway mileage.
My dream car, however, it the Tesla Model S P-85D. All electric, but insanely fast. Too bad I will probably never be able to afford that one. Either way, I would love to own a Tesla one day. I am in the process of convincing my mom to get a Volt as her next car, but it doesn't look too hopeful.

So anyway, I have an idea, but I wont be able to act on it for several years. I need to know now if it is practical, because, if something happens to this car, I need to know if I should bother keeping it or selling/scrapping it for a different car. It is perfect for the idea that I have. Funny thing is, the reason it is perfect for this idea is also the big "issue" with the car in the first place- the fact that it is a big V8 in a FWD car. When you gas it hard, weight goes to the back tires, leaving the front tires without good traction. I'm sure you guys all know about that. Either way, it is a very fast car... once it gets going.

On to the idea.

Idea: I want to add an electric engine to back of the car which will work at the same time as the front engine. This works out perfectly in my head, because the torque curves of the electric and gas engine crossfade almost perfectly. The car will be AWD, but the back wheels will do most of the work until the gas engine gets in to the torque band.
At the very least, I want to have the car become a straight-line beast, but I am waaaay more hopeful that I can actually really get into this to make a true, daily-driven hybrid. Based off the way the Tesla Model S looks, the rear engine doesn't seem to take up much space. At most, it looks like I'll lose my extra wheel space. I am going in to electrical engineering, but I am not shy when it comes to welding, fabricating, and coding. So I don't care if i have to do any of that to bring it all together. This will probably be a weekend hobby for months or years if I go for it. I obviously wont start until I have a different car to drive in the meantime.
The full plan goes like this: By the time I'm ready to do it, I hope to be able to actually take a 400HP electric motor out of a wrecked Tesla Model S, as they will hopefully be more popular in a few years. If I do manage to find a wrecked model S with the back in tact, I may just take the whole thing and see if I can use the entire rear drive train assembly. Then set it up in the car, most likely with completely custom rear axles and what not. I want it to be fully functional with regenerative braking for the back wheels and everything. I would probably start with a small battery. If it can do 10 miles, it would be perfect. I would set it up to charge off of the gas engine, which will always be on. The reason, I assume, that the gas engine would always be on is because it would be even more work to get the car to work properly without the engine on, but I'm not sure yet. I think this is a good idea anyway, because I can maybe find a way to get the Active Fuel Management(AFM) to stay on all the time. The gas engine on 4 cylinders, combined with the electric engine, should be powerful enough to accelerate the car with hardly any effort. The gas engine would also constantly charge the battery, which would make that low 10 mile range into maybe 20-30. Once the battery is totally done, I just turn the electric engine off for a while, turn AFM off, and the V8 takes on all the work like it normally would.
If i can get it to work out like this, then the next step would be to get the biggest, reasonably-sized battery and get the car to work fully electric.
I guess the car would be kind of like a Prius, but still probably less efficient, 5 times the horsepower, and with an extra 1500 Pounds to lug around.

The goal is to be a complete sleeper. Amazing fuel economy, luxurious ride(which is kinda already has... kinda), and then, when the time comes, a ridiculous amount of horsepower from all 4 wheels.

TL;DR. I am majoring in electrical engineering. I am not a professional engineer yet, but I am about mid-way, so don't be afraid to talk to me with fancy terms relating to the motor. I have a FWD Impala SS with a 300HP V8 engine in the front. In the future, I want to add a 400HP Tesla motor(or some other powerful electric motor) to the back and set the car up to run like a true hybrid for amazing efficiency, but also be able to run both engines at once for insane power. I don't want to have a massive battery, because I like my trunk space, so the V8 stays. This is one of few cars that have such a powerful engine while only being FWD, so that is why I want to try it. I'm down to make custom shafts, axles, and other various fabrication.
My main question is whether or not this idea is plausible. I will not be able to act on it for a few years, but I need to know if I should keep the car around or not.

Thanks!


Last edited by ciano22; 01-24-2015 at 03:09 AM..
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Old 01-24-2015, 03:36 AM   #2 (permalink)
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This is often talked about but rarely accomplished. The easiest way to do it is to take a FWD car with a AWD option, add the AWD rear subframe and add a motor to that.

The main issue is interfacing the two drive systems. With an auto that's fairly easy, but that means the engine has to be idling all the time in EV mode or you'll kill the tranny. It may be possible to add an electric pump to circulate fluid while the engine is off, but I have yet to see this actually done.

If the engine has to be idled all the time, you'd probably get better results from a manual conversion and EOC.

But yes, I'd love to do this to my VW T5, add a big electric motor (no need to use a Tesla motor, plenty exist off the shelf), and have 800NM plus great economy from a 2ton AWD van It has an AWD version so the conversion is fairly straight forward. However, it's a manual and it's very hard to come up with a fool proof way to interface the electric motor with a manual trans.
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Old 01-24-2015, 04:01 AM   #3 (permalink)
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I've thought about something like this for my Civic Wagon. There was an AWD option, so adding the rear drive would be easy. Having an EV mode and assist climbing hills would be great. And I'd likely never get stuck in snow again! But the extra drag of the system (CV axles, differential) would surely hurt my highway MPG.
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Old 01-24-2015, 04:40 AM   #4 (permalink)
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Lol no snow or hills to worry about where I live. lots of rain though... and potholes.

The car has no AWD counterpart,so I guess I'll have to find or build a subframe for it, but it is auto! I figured that there would be issues trying to get the gas motor to turn off completely, but I'm ok with just leaving it on. Like I said, running the gas engine in 4-cyl mode and just using the electric motor to assist would be great. The 4 cyl engine can keep the car going up to 75 mph at less than 2000rpm before the car turns the other 4 cylinders back on. With the engine loaded by the recharge mechanism, it may be a little harder though.

If I could find a way to do simple edits on the afm of the gas engine and out put of the electric motor, I think I could interface them for 3 modes.
1. Gas mode. The electric engine is just completely off and charging.
2. Econ mode. The car is only in 4 cyl mode and the electric motor only engages when the gas engine reaches 1900 rpm. This would be kinda tricky, but if I could limit the gas engine to 2000 rpm, and have only the electric engine respond to any further throttle, that would be amazing. I might have to set up something on the physical gas pedal for that. Basically, the electric engine will just help accelerate the car and leave the gas engine to cruise.
3. Sport mode. Well, more like drag mode. Car is in V8 mode only and the electric engine is on. This one would be set up so that I floor it, the electric engine immediately applies a ton of power, which i Will have to dial in, and then, as the gas engine begins to take over, the electric engine stops.

This is all theory though. Figuring out how to do this is gonna be fun. These are the easy modes too. Gas engine off mode and prius mode would take waaaay more work.

I looked around for some electric motors for sale, and the ones that I found were not very powerful and were very expensive. I found one with 138hp that costs $4k. As of today, you can buy a scrapped model S for $20K. I am optimistic that I will be able to get the tesla back end for less than 10k by the time I want to do this. The battery is the most expensive part of those cars, not the motor.

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Old 01-24-2015, 05:59 AM   #5 (permalink)
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Quote:
2. Econ mode. The car is only in 4 cyl mode and the electric motor only engages when the gas engine reaches 1900 rpm. This would be kinda tricky, but if I could limit the gas engine to 2000 rpm, and have only the electric engine respond to any further throttle, that would be amazing. I might have to set up something on the physical gas pedal for that. Basically, the electric engine will just help accelerate the car and leave the gas engine to cruise.
I confuse easily.

What you describe is a 'through-the-road' hybrid. I have no comment on the front half, but for background you might review the 5 years of [semi-weekly] back episodes at EVTV Motor Verks - Electric Car Conversion Videos.

Also look at http://ecomodder.com/forum/showthrea...mgr-29878.html. That is about Toyota Synergy Drive parts. The Toyota Highlander and Lexus LX400h have a subframe and motor-generator in the back, supplementing a V-6 and 2ea MGR in the front. It uses high-voltage AC, so you get the regen; and a buried magnet rotor that does some engineering magic to reduce back-EMF at higher RPMs.

My effort has stalled out temporarily, but I have the MGR and subframe. I hope to use The Lear 2.3kW charger from a Chevy Volt or Smart EV. Power inverter and batteries to be determined.

OEM junkyard parts are the way to go—I paid $650 for the MGR and the charger goes for about $400. The parts are there but nobody knows what to do with them. Smart, and probably Tesla, won't be any help—they actively thwart reuse of their components.
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Old 01-24-2015, 03:01 PM   #6 (permalink)
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Love your future project!!!

First here's a picture I took from this last years SEMA of a Tesla floor pan with the rear motor.

You should be able to zoom in on the photo bucket page and get a closer look?

I've been thinking about adding a electric motor also to my AWD Talon in a couple years. I haven't decided which way to configure it though???

My car is a AWD Auto right now that makes over 600+ WHP, so I would want to match the performance of what I have now but run the rear axles with an electric Tesla motor? My thought were to run a FWD transmission. I just haven't figure out if I should run a auto or manual yet??? So I'm defiantly up for suggestion's?

Anyway glad to see your post and will be watching closely.
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Old 01-24-2015, 04:24 PM   #7 (permalink)
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Already been done back in 1966 -- with V8 engines -- in an Oldsmobile Toronado chassis:

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Old 01-24-2015, 05:25 PM   #8 (permalink)
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Can you guys recommend some powerful electric motors for me to look at? I may be able to do this sooner than I thought. If i am going to do this, I want to do it big, so a little 138HP motor is not going to be worth it, especially if that engine is $4000. Once I get the electric engine working, then I will begin mods on the gas engine to get that engine to be more powerful as well. There is the possibility of having 2 electric motors working together in the back as well. Basically, I want the back motor(s) to at least match the power of the front engine, but hopefully actually be higher.

As far as tesla not letting people re-use their stuff, I'm sure that there will be a way to isolate JUST the electric motor and get it to work myself. I already do stuff like that in lab classes, although not nearly as large and complicated as a 400HP electric car motor. Hopefully it isn't that complicated though. Tesla releasing all their patents makes me hopeful that they aren't the kind of company to go out of their way to stop the re-use of their equipment, but business is business I guess. No matter how nice they are, they still want to make some money as well.
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Old 01-24-2015, 05:29 PM   #9 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
Already been done back in 1966 -- with V8 engines -- in an Oldsmobile Toronado chassis:
Yes, I've known of things like this for years, but this is going to be much more complicated, because one of the engines is going to be fully electronic. Having the 2 engines interface with each other is going to be the hard part. You dont even need a computer to have 2 gas engines work together. Just get the throttle to work simultaneously on both engines and they pretty much just work.
Also, the electric motor is so small, that I can still use my trunk once this is done!
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Old 01-24-2015, 05:33 PM   #10 (permalink)
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Quote:
Originally Posted by freebeard View Post
I confuse easily.
Sorry. I probably didn't explain clearly. The car already has a system which allows for 4 of the cylinders to be shut down, making it go from a V8 to a V4(or inline 4?). My goal for econ mode is to have the car stay in 4 cyl mode constantly, and then use the electric motor to help the small 4 cylinder engine accelerate the car without straining too much. Then, the electric engine will turn off. I don't want the 4-cyl engine to have to work too hard, so I want to create a way for the electric motor to automatically kick in when the gas motor approaches a certain RPM. Then, somehow, get the gas motor not to exceed that RPM and have the electric motor use more power if I continue to push the gas, basically giving me more power without increasing the RPM of the gas engine.

Here's a model of it in my head.
The car Idles at 800 RPM, so, once the engine goes down to 1000 RPM or lower, the electric motor turns on and prepares to accelerate.
I hit the gas to accelerate.
Both engines work to accelerate the car.
Once the gas engine reaches 2000 RPM, it stops increasing in RPM, but the electric motor keeps applying power.
Once I'm at cruising speed, the electric motor turns off and stays off until the RPMs of the gas engine either fall below 1000, or try to exceed 2000. So, basically, the electric motor will only help accelerate the car. Econ mode will obviously accelerate and react pretty slowly, but that's fine, because when I am "mentally" in econ mode, I drive like a grandma anyway.

Another great way to do it would be to simply use the car's built in method for kicking the V8 engine back on to trigger the electric motor instead. Anytime the car would normally want to engage the V8, it will engage the back engine instead.

Quote:
Originally Posted by freebeard View Post
What you describe is a 'through-the-road' hybrid.
Wow. That is actually very helpful, because that is pretty much exactly what I want. I cant believe I didn't think to load the back wheels themselves during cruise instead of the front engine. That makes things even easier!
I can't do it today, but I'll definitely check out all those links you gave. I glossed over them really quickly and they seem to be very helpful.
Thanks a lot!


EDIT: I really like your username and picture! LOL


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