# FWD car & engine with RWD diff + elec. motor = DIY Plug in hybrid?



## RS3RS (Jun 14, 2008)

OK, here's my thinking. I have a Ford Focus SVT, which is a front wheel drive 4 cylinder.

There are several kits made for people who want to convert it to a rear wheel drive V8 or something, which includes a ford rear end differential with all the brackets and the like you need to hook it up.

Now, what would happen if I were to leave the existing drive train alone, but hook up a rear end diff, with an electric motor running direct drive to the rear end, some batteries in the trunk, with a controller and the like?

Basically, you could drive on the electric motor around town and during your daily commute, but if you needed high speeds, or wanted to go on a spur-of-the-moment road trip, just fire up the gas motor.

I know it would weigh alot, but I wouldn't need much battery power. A 20 mile range would be plenty, and it wouldn't even have be able to go freeway speeds. 45 mph top speed on electric would be about right.

You could even incorporate regenerative braking for a 100% true plug in electric hybrid.

Is this a stupid idea?


----------



## Corvettemike (Jun 1, 2008)

Sounds cool to me. Im a newbe so my expertise is very limited. Is your car a manual tranny? Manual tranny may be better for your idea.


----------



## RS3RS (Jun 14, 2008)

Corvettemike said:


> Sounds cool to me. Im a newbe so my expertise is very limited. Is your car a manual tranny? Manual tranny may be better for your idea.


Yeah, it's a manual. Should be easy enough to leave it in neutral and just drive along.

I'm a newbie too, I'm really just talking theoretically for the time being. I'm definitely doing an EV conversion at some point, but I'm not really sure what the project will be. I think the availability of a gas engine as needed would be very convenient though.


----------



## MrCrabs (Mar 7, 2008)

What is the GVWR (gross vehicle weight rating) of the car? What is the curb weight? The difference is the amount you can add safely (per the manufacture).

By the time you put a big enough electric motor and batteries in you would most likely be over the weight rating, and wouldn't be able to carry any passengers at all (that means no driver)

With the stock ICE not running you wouldn't have power steering or power brakes, and would be draining your starting battery by powering your lights, and starting batteries aren't meant to be discharged very much.

You would need some way to send a throttle signal to the controller, but keep the gas pedal stock to control the gas engine.

This would be a very complicated conversion to attempt.


----------



## fshagan (Jun 4, 2008)

Great minds think alike ... check out this kit that does basically what you've suggested (although with a biodiesel engine in front and electric motor driving a single wheel in back):

http://www.rqriley.com/xr3.htm


----------



## RS3RS (Jun 14, 2008)

MrCrabs said:


> What is the GVWR (gross vehicle weight rating) of the car? What is the curb weight? The difference is the amount you can add safely (per the manufacture).
> 
> By the time you put a big enough electric motor and batteries in you would most likely be over the weight rating, and wouldn't be able to carry any passengers at all (that means no driver)
> 
> ...


Good point, I'm not sure of the gross vehicle weight rating - I'll google it and see what I can find. 

Draining the battery isn't much of a problem to me - I'll just switch it over to a deep cycle, or throw in a switch to run it all off of the same batteries as the motor, should be easy enough.

Also, with the gas engine off, pressing the accelerator won't have any effect - and vice versa when the battery system is turned off, so it seems like it should be just fine. Should just be able to wire the controller straight up to the pedal AND have the pedal hooked up to the throttle body as usual.

The power steering / brakes could be a bit more complicated, but should still be solvable without much more difficulty than a regular EV conversion. Maybe upgrade the alternator on the gas engine to a higher output model, and simply run the power steering & brakes (and maybe even a/c) off of a small aux. electric motor all the time.

Really, I'm seeing weight as being my only real limiting factor here. I'm about to head out the door, but later this afternoon when I have some time I'll crunch the numbers and get back to you guys. 

edit: Oh, and thanks for the link fshagan - if I cut out the rear diff and just hooked up the motor to one wheel I could save a lot of weight!


----------



## MrCrabs (Mar 7, 2008)

RS3RS said:


> Also, with the gas engine off, pressing the accelerator won't have any effect - and vice versa when the battery system is turned off, so it seems like it should be just fine. Should just be able to wire the controller straight up to the pedal AND have the pedal hooked up to the throttle body as usual.


I would research into the vehicle to make sure this is true. You will need the key in the on position to unlock the steering column, but that will also enable the fuel pump. You would need to make sure pressing the accelerator with the key on won't try and inject any fuel into the gas engine.


----------



## BrianWillan (Feb 22, 2008)

RS3RS said:


> Now, what would happen if I were to leave the existing drive train alone, but hook up a rear end diff, with an electric motor running direct drive to the rear end, some batteries in the trunk, with a controller and the like?
> 
> Basically, you could drive on the electric motor around town and during your daily commute, but if you needed high speeds, or wanted to go on a spur-of-the-moment road trip, just fire up the gas motor.
> 
> ...



I have the same idea, and I was also looking at the Riley XR3 too. That until I came across this website while cruising the cleanmpg.com forum (EV sub forum) and found the Poulsen Hybrid Power Assist System. 

http://www.poulsenhybrid.com/poulsen.html

It is a pair of wheel motors mounted to the rear wheels of a FWD vehicle with the controller and 72Volts of batteries mounted in the trunk. If the pricing is to be believe on the site, the system, Lead Acid batteries and installation come out to $5K USD.

This solution has now shot to near the top of my list on how to get the through the road parallel hybrid that I want. ;-)

Cheers

Brian Willan
Oshawa, Ontairo


----------



## slow (Jun 9, 2008)

There is little room under the chassis once you do the RWD conversion with the solid axle. I am fairly sure you need to run a fuel cell for the stock ICE, since the RWD 8.8 axle takes the place of the stock fuel tank. This takes up more of the mimimal storage capacity the interior of that chassis. 

Ryan


----------



## Manntis (May 22, 2008)

very, very complicated for little gain, IMHO.


----------



## JeffPritchard (Jun 10, 2008)

I think the trick here is to have the ICE engine on and idling while using the electric motor.

Sure, you mpg is no longer infinite, but it will certainly be a whole lot better than normal. Probably better than a non-plugin hybrid (just a guess).

The beauty of it is that you still have AC, and power everything. The trick, I think is to come up with an auxiliary accellerator pedal that mounts on top of the ICE gas pedal. You push on the electric pedal to go slow, and if you want to go faster, or if your juice has been used up, then you push harder and you make the ICE gas pedal move.

Probably you would have to keep the ICE tranny in N when using electric, so you're not working against the ICE back pressure. If you want to have fun, leave it in gear and hit the gas for a few added horsepower from the electric addition.

My question is, if you're doing this with an ICE pusher (i.e. normally RWD), and you are putting your electric stuff on the front wheels...what would happen if you only powered one of the front wheels????

jp


----------



## RS3RS (Jun 14, 2008)

MrCrabs said:


> I would research into the vehicle to make sure this is true. You will need the key in the on position to unlock the steering column, but that will also enable the fuel pump. You would need to make sure pressing the accelerator with the key on won't try and inject any fuel into the gas engine.


Problems like that are incredibly simple to solve though. The fuel pump is electric, nothing a switch can't take care of.


----------



## Manntis (May 22, 2008)

RS3RS said:


> Problems like that are incredibly simple to solve though. The fuel pump is electric, nothing a switch can't take care of.


that's minor compared to no brakes or steering


----------



## Vwbeamer (Jun 16, 2008)

I also had an idea for a Plug in hybrid, i posted this on another furum, didn't get much feedback.

My thinking is if it only takes 15 hp or so to go 60 mph, let's use a 15 hp motor. The extra HP we have in our cars is need to accelerate. That where the electric motor comes in.

let the electric do what it does best, short trips, low speeds, and the ICE do what it does best, long steady high speeds.

My plan was to get a dual shaft EV motor. The extra shaft would be driven by a 9-10 hp ICE. I plan on using a simple Horizontal shaft air cooled single cylinder engine like used on tiller or lawn tractor.. These are light and inexpensive. Life is about 1000 hours or about 50,000 miles.

The ICE would be coupled to the electric motor with a belt driven torque converter. This set up would allow the engine and motor to turn at different rpms. This will also allow the ICE to idle with out spinning the EV Motor, since the converter doesn't lock up until the ICE spins about 1300 rpm .

The other advantage to the Torque converter is a torque multiplier and allows the small ICE to develop more torque at low EV Motor shaft speeds.

I want to control the ICE throttle with a control servo. Ideally, i would like to keep the motor at 80% load, since this is will allow the most range extension without harming the ICE and also is the most efficient load for the ICE. Then in actual practice, the EV Motor will provide all the power needed to go faster than the speed attainable with the gas motor alone. It will also assist in acceleration at lower speeds.

The car I want to use is a vw squareback. it is geared stock so that 3rd gear would be good for electric only and short trips. Fourth gear would be for combined power. The torque converter on the IC and high torque of the electric motor combined should allow a starting from a dead stop to highway speeds without shifting out of fourth. 

Even though this is a manual tranny car, it would be driven as an auto. The driver places the tranny in third for electric only and in fourth for ICE assisted. 

My rough math and from what I have learned so far, with 8 100ah lead acid batteries and a 96 volt motor, i should have a range of about 40 miles on batteries alone and a speed of about 60 mph. 

With gas assist, range should increase to about 100 miles ( highway) and speed I will limit to 75 mph. Should get about 70-80 mpg. This is very rough math and by no means I'm an expert.orzonal shaft air cooled single cylinder engine. These are light and inexpensive. Life is about 1000 hours or about 50,000 miles.

The ICE would be coupled to the electric motor with a belt driven torque converter. This set up would allow the engine and motor to turn at different rpms. This will also allow the ICE to idle with out spinning the EV Motor, since the converter doesn't lock up until the ICE spins about 1300 rpm .

The other advantage to the Torque converter is a torque multiplier and allows the small ICE to develop more torque at low EV Motor shaft speeds.

I want to control the ICE throttle with a control servo. Ideally, i would like to keep the motor at 80% load, since this is will allow the most range extension without harming the ICE and alos is the most efficient load for the ICE. What i plan on doing is figuring the top speed that the ICE alone running at 80% load will get the car up to. Then I will simply have a servo to pull that throttle open to the 80% load at that speed. Then in actual practice, the EV Motor will provide all the power needed to go faster than the speed attainable with the gas motor alone. It will also assist in acceleration at lower speeds.

The car I want to use is a vw squareback. it is geared stock so that 3rd gear would be good for electric only and short trips. Fourth gear would be for combined power. The torque converter on the IC and high torque of the electric motor combined should allow a starting from a dead stop to highway speeds without shifting out of fourth.


----------



## Ioku (Sep 27, 2007)

I think for something like this it would be better to use a car that comes with an AWD and FWD option rather than trying to add some new axle that was never designed to be there. Something like a Subaru or Volvo could work well.


----------



## RS3RS (Jun 14, 2008)

Manntis said:


> that's minor compared to no brakes or steering


No brakes or steering can still be overcome.

I mean, we're talking about a DIY plug-in hybrid vehicle that is built at home in your own garage. 

Something that can commute daily, cost pennies to recharge, and still go from New York to LA on a whim if needed.

Of course it's not going to be easy! There are challenges to overcome every step of the way.

Anyway, my point is that just because it's not a common-place problem, doesn't mean a little creativity can't work around it. Everything is relative - having to come up with a new PS or braking system is a walk in the park compared to the concept of building a gasoline/electric hybrid in your garage.

In fact, I think it should be relatively easy to create a system to power the P/S and power braking systems.


----------



## Manntis (May 22, 2008)

RS3RS said:


> No brakes or steering can still be overcome.


yes they can - but you're the one proposing keeping the entire stock ICE up front, which makes for little room to power your brakes and steering off something that a) doesn't require the ICE to be on; b) fits in between everything, and c) can withstand the heat and vibration of being located right near the ICE, for those occasions you turn it on.



RS3RS said:


> I mean, we're talking about a DIY plug-in hybrid vehicle that is built at home in your own garage. Something that can commute daily, cost pennies to recharge, and still go from New York to LA on a whim if needed.


...which is why most people start with hybrids and add the plug. Easier to do as a running vehicle for a lot less engineering than you're proposing 



RS3RS said:


> Of course it's not going to be easy! There are challenges to overcome every step of the way.


challenges take time and money to overcome. The more challenges, the longer your project will take before you can drive it and the bigger the hit to your pocketbook. A straight EV conversion can easily cost $15,000+, and that's without many of the problems you're making for yourself.



RS3RS said:


> In fact, I think it should be relatively easy to create a system to power the P/S and power braking systems.


see comment one, above.

The fact is, you're proposing a hybrid hauling around ICE, electric motor, and a small battery pack, yes? That's what the Prius, Escape, etc. already do. And they can be converted to plug-in.

It's tempting to look at what they've done and think "I could make one of those", but then all the little details that need to be solved, each seeming "a walk in the park", connect together to make that walk a cross-country hike.

If you have the time and money to plow into it, have at it. It'll likely cost you as much as buying an Escape Hybrid and converting it to plug-in, though.


----------



## RS3RS (Jun 14, 2008)

Manntis said:


> yes they can - but you're the one proposing keeping the entire stock ICE up front, which makes for little room to power your brakes and steering off something that a) doesn't require the ICE to be on; b) fits in between everything, and c) can withstand the heat and vibration of being located right near the ICE, for those occasions you turn it on.
> 
> 
> 
> ...


Very good points.


----------



## judebert (Apr 16, 2008)

The one problem nobody has mentioned yet: max electric motor speed. The wires in the motor are either wound together or epoxied on. For an ADC 9", you don't want to get it above 6K, or the commutator bars could fly off! (Really. It happened to me.)

If you leave the motor permanently affixed to the rear diff, it will regulate the max speed of the entire car. If you use a gear ratio sufficient to get you up to high speeds, then your motor will need a powerful controller providing a lot of current to get the torque it needs at low speeds. If you use a gear ratio for lower speeds, then you can't go too fast, or your electric motor will disintegrate.

A clutch or transmission would be necessary to achieve both. 

Not impossible, mind you, just a pitfall you should consider.


----------



## Bowser330 (Jun 15, 2008)

judebert said:


> The one problem nobody has mentioned yet: max electric motor speed. The wires in the motor are either wound together or epoxied on. For an ADC 9", you don't want to get it above 6K, or the commutator bars could fly off! (Really. It happened to me.)
> 
> If you leave the motor permanently affixed to the rear diff, it will regulate the max speed of the entire car. If you use a gear ratio sufficient to get you up to high speeds, then your motor will need a powerful controller providing a lot of current to get the torque it needs at low speeds. If you use a gear ratio for lower speeds, then you can't go too fast, or your electric motor will disintegrate.
> 
> ...


So lets say you used an AC Induction motor (like the one electric motorsports sells) direct drive (1:1)...45hp 110ftlbs torque...i think it can rev up to 7500rpm...which if (1:1) 5000rpm = 65mph then (1:1) 7500rpm = 97mph...fast enough i would say for a safety margin...

peak torque from 0-2000rpm, (1:1) = (0-26mph)....

yay or nay?


----------

