[rbhawaii]

My students and I have begun a "new" type electric car project!
It will be brutally simple.
We have replaced the rear axle on a '91 Geo Prism, with the rear axle from a Subaru Justy. The Subaru rear suspension is especially well suited for this format. The Subaru rearend is floating with CV axles, and the springs are separate from the struts. The Prism has struts with springs, so the rear of the car will have double springs to support the added weight of the "three football players" in the back seat!
We are powering the rearend with a 17hp motor bolted right up to the pumpkin. No clutch, no gear reduction, just direct drive.
We have calculated the vehicle speed to be about 70 mph at maximum motor rpm.
The theory is to run the ICE up to about 20 mph, then simply turn on the motor, put the car in neutral, and turn off the ICE.
If or when the batteries run low, just restart the ICE!

Simple enough?

What do you think?

We're doing it on a shoe-string budget.
Fortunately, we've gotten some help from Bob Dewitt at American Electric Company in Honolulu. They are sponsoring a 17 hp kit from CloudEV.
We have received everything except the motor, which will take a while to ship.
We still need to decide on the battery set-up. 12 volt batteries will take up half the space of 6 volt batteries, but there seem to be some trade-offs involved.

Any thoughts?
Please chime in.

 

[madderscience]

What you are describing is called a parallel hybrid design. though in your case, probably without the regenerative braking capability that the commercial units like the prius have.

Somebody in seattle did a similar thing with a geo metro though their somewhat goofy but totally functional setup involved a literal 5th wheel that could be dropped down between the two rear wheels and retracted when not in use. This was more or less the back half of a motorcycle but powered via a 6HP electric motor and direct drive with gear reduction. Otherwise it was basically the same idea, use the engine for accleration and the electric for cruising and/or an assist. The setup worked and with careful driving he claimed he could reduce fuel consumption in the car by about 50% until the batteries ran down, which with that setup was about 20-30 miles on (if I remember correctly) 120 volts in a single string of 12V batteries.

The 12V vs. 6V tradeoff is simple: battery weight is roughly proportional to range in an EV. Assuming you are talking about the same type of batteries (flooded, say) for a given voltage pack, making one out of 12V trojan T-1275 batteries will weight about 2/3 of what one made out of 6V T-105 batteries would weigh. You will generally get more cycles out of a bigger pack due to reduced peukert effect and shallower cycling of the pack.

Given your setup I'd use a fairly small pack and just keep the cycles low, meaning probably pretty minimal range. eight T-1275s would give 96V and weigh about 600lbs. If you then keep the EV-only driving to around 15 to 20 miles the cycles shouldn't go too deep.

One of the observations the person I mentioned above had was it was rather complex to try and manage two drivetrains simultaneously and also keep an eye on the road. So Depending on what your goals are for this, it may make more sense to go pure EV or to just buy an insight, prius or one of the many other commercially manufactured hybrids that are out there now.

Good luck.

 

[vgslimo]

hey sounds cool. i live here on oahu and would love to be able to check it out. let me know if this is possible and maybe where you guys plan on showing it.

 

[This is Bill]

I think this project is a great idea for the students...

It can be done in time and the car won't require top of the line electronics.

Also, your car will be sort of backwards from what manufacters offer. What I mean by that is usually the electric is used for slow speeds and the ICE for higher speeds. I guess this is because the electric effecieny diminishes as the rpm increases and also the ICE can be matched at a more optimum rpm.

It would be neat to compare it's new gas mileage to the current.

 

[SamM]

I absolutely love this idea. My thought is to get something like a Subaru WRX. Why not make it a real looker. EVs don't have to be plain looking! Remove the rear driveshaft and install an electric motor in the rear. There are quite a few of the WRXs being used in drifting. If it can be converted to run in RWD only, then it should be able to be run in FWD only. Add the motor to the rear axle and mount the batteries into the rear seat area. 95% of my driving is solo during my commute to work. I don't need the rear seat so that's the most logical location for the batteries. 12 batteries should fit in there nicely. The car could be run in EV mode but if extended range was needed the ICE could be used for battery charging or driving it as a regular gasoline powered vehicle.

A better vehicle choice would be a VW Diesel Golf that already gets 50mpg. Get the vehicle up to speed, switch the engine off and then enjoy the electron ride to work. The diesel engine could also be used to charge the vehicle during the trip (if needed), with the vehicle in neutral with a hand type throttle mounted on the dashboard. Again, you would have the option of running on pure Diesel or Bio-Diesel for extended trips. I see this as the answer to my future automotive needs. I hate buying gasoline. Making my own fuel would be a blast. Forget the WRX, I want the Diesel Golf.

Thanks rbhawaii, you may have just helped me decide what my first EV project will be!

 

[Xringer]

Your project sounds a little like mine. I drive a 1999 Honda CRV and since it's only got 33,000 miles on the ICE, I want to keep it for a few more years.

But, I would like to add some e-boost to the drive system.

Since I've removed the rear-wheel-drive components, I have a choice
of driving the transfer case to assist the engine,
or drive one or both of the rear wheels directly. (No EV only mode).

The system would be a Weak plug-in Hybrid using a 5-10 HP motor
and a pack that would provide assist power to the ice for about 10 miles,
before going off line to await for charging.

My main problem is going to be delivering low RPM power to the wheels..

My goal (besides having fun) would be 30 MPH city and 40 MPH highway..
Pretty modest (I think) and maybe even cheap to do..

 

[Bowser330]

I like the dual drive idea and want to continue this discussion....

I was thinking something similar to the last member, about sometype of "boost" system...

So, keep the metro or civics 30mpg motor and add a RWD suspension setup mated to a sepex 84V 425A (max) 25HP ~50ftlbs...mate the motor to the final drive (but what ratio?)...

I would think that the controller and the ICE Ecu would need to talk to one another so that both sets of wheels were spinning at the same speed, otherwise one is dragging on the other...so the way i see the electric motor would need zero interface with you, the ICE motor would tell it what RPM to spin at, and if that RPM happens to be low and you are giving 425Amps then you will get an extra 50 ftlbs out of it....

in theory this setup will completely compliment a small 4 cyl turbo motor (which has a stronger power band in the higher rpm range)...

the electric motor would ofcourse shutdown automatically once the batteries were at whatever DOD% you setup, the cool part about using the sepex motor(s) would be the regen, they would be turned off for power but not regen, they could slowly recharge up and then be ready to "assist" again...

Please someone help me refine the plans stated above!

Thanks!

 

[Xringer]

I like the dual drive idea and want to continue this discussion....

I was thinking something similar to the last member, about sometype of "boost" system...

So, keep the metro or civics 30mpg motor and add a RWD suspension setup mated to a sepex 84V 425A (max) 25HP ~50ftlbs...mate the motor to the final drive (but what ratio?)...

I would think that the controller and the ICE Ecu would need to talk to one another so that both sets of wheels were spinning at the same speed, otherwise one is dragging on the other...so the way i see the electric motor would need zero interface with you, the ICE motor would tell it what RPM to spin at, and if that RPM happens to be low and you are giving 425Amps then you will get an extra 50 ftlbs out of it....

in theory this setup will completely compliment a small 4 cyl turbo motor (which has a stronger power band in the higher rpm range)...

the electric motor would ofcourse shutdown automatically once the batteries were at whatever DOD% you setup, the cool part about using the sepex motor(s) would be the regen, they would be turned off for power but not regen, they could slowly recharge up and then be ready to "assist" again...

Please someone help me refine the plans stated above!

Thanks!

I think my idea of a manually controlled Assist system only needs to know the MPH
(which is proportional to the transfer case RPMs) to work with the ICE.
I would want a RPM sensor/lock-out, since I don't want to engage the assist motor at low speeds.

Read about the 'Auto Mode' of this new bicycle.
http://www.sanyo.com/news/2008/12/01-1en.html
I think some of those Sanyo ideas might be applicably to a weak-hybrid car..
Their control & sensor system sounds pretty neat..

 

[Bowser330]

why dont you want to engage the electrical motor at low speeds? dumb question...

 

[Xringer]

why dont you want to engage the electrical motor at low speeds? dumb question...

The Mars ME0709 motor that I'm looking at, does not work real well at low RPMs.

 

[JRP3]

Unfortunately using the ICE at low speed and the E motor at high speed seems to be the least efficient way to work the setup. The ICE is least efficient at low speed operation and most efficient at higher steady speeds. Might be better to find some gearing setup that allows the E motor to accelerate the vehicle.

 

[Bowser330]

Unfortunately using the ICE at low speed and the E motor at high speed seems to be the least efficient way to work the setup. The ICE is least efficient at low speed operation and most efficient at higher steady speeds. Might be better to find some gearing setup that allows the E motor to accelerate the vehicle.

Good point.

In all the "electrical assist" type articles I have read, they all seemed to agree that the best way to assist an ICE would be at the moments of acceleration, especially the acceleration from a stopped position. That way you keep the ICE from having to demand/process more fuel and thus have it give off less emissions.

How would the acceleration pedal be setup in the car? Would you have to create a "dead zone" for it? or would you just leave all that alone have the electrical motor match the rpm/speed of the vehicle?

 

[Xringer]

Unfortunately using the ICE at low speed and the E motor at high speed seems to be the least efficient way to work the setup. The ICE is least efficient at low speed operation and most efficient at higher steady speeds. Might be better to find some gearing setup that allows the E motor to accelerate the vehicle.

I wish there was a cheap and easy way to get good efficiency.

But, I'm not sure it's possible with the direct-connection I'm thinking of using.
I want to connect the Mars motor directly to the transfer case (where the old rear-wheel drive shaft was),
to give the ICE a little 'push' once the RPMs of the transfer case (or e-motor) are up around 1000..

My guesstimates of the transfer case / motor RPMs are:
MPH --RPM
20 = 647
31 = 1003
35 = 1133
40 = 1294
50 = 1618
60 = 1941
65 = 2104
70 = 2265

Here's the motor curves at some lower voltages.
(I would like to see them at the 72 volt range)..
http://www.electricmotorsport.com/store/images/EV_Parts/motors/ETEK-RT Performance Data.pdf

So, if I had an RPM detector set to enable the E-motor at 1000 RPM,
I think it might be in the more efficient range of the motor.?.
(Or, am I interpreting the charts wrong??)

Once turned on, the assist would operate anytime the CRV exceeded 31 MPH.
I could preset the max current limit to allow the pack to last for a 10 mile or 20 mile trip etc.
Just enough to get around town with better MPG..

Right now, the ICE is doing about 30 MPG on a flat road at 30-35 MPH..
So, if it had a little 50 amp E-kick going, it might just jump up to 40 MPG..
That would be sweet!!

 

[Bowser330]

Let me understand something please...

When we are talking about efficiency of the electrical motor, we mean when it gets the best power output and lowest amp draw = best efficiency....

In an electric car this is crucial to be able to extend the range and use of the battery pack...however in a Hybrid design, I do not see the efficiency of the e-motor being as important as the efficiency of the ICE, anything to increase the ICE efficiency saves both more money and more emissions...

Accroding the the graphs I have, If i run 2 sepex motors to the rear wheels from a stop, 0rpm, I will demand 100-ftlbs at 425A draw at 84V...from 0rpm till 2000rpm (speeds are taken from the graphs) I know that the efficiency is only 70% and wont increase to a decent 85% till around 3500 RPM...but that 100ftlbs is what Im looking for, given a "dead zone" pedal setup, you could use the E-motor for 0-2000rpm jolts of power to accelerate the vehicle and use the ICE to keep it moving.

Xringer,

What made you choose that e-motor? Which others have you considered?

 

[JRP3]

Right now, the ICE is doing about 30 MPG on a flat road at 30-35 MPH..
So, if it had a little 50 amp E-kick going, it might just jump up to 40 MPG..
That would be sweet!!

No way will you see that sort of increase with the setup you are talking about. Think of it this way, if the ICE never had to accelerate the vehicle it might be able to get 35mpg by holding a steady speed, but you aren't going to be helping acceleration with your setup. You might see a couple mpg the way you are doing it, not worth it in my opinion. You could get the same or better by doing aero mods like a flat belly pan and wheel covers for less effort and money.

 

[JRP3]

In an electric car this is crucial to be able to extend the range and use of the battery pack...however in a Hybrid design, I do not see the efficiency of the e-motor being as important as the efficiency of the ICE, anything to increase the ICE efficiency saves both more money and more emissions...

As long as the high amp draw doesn't overheat the motor you're basically correct.

 

[Bowser330]

JRP3 makes a good point. All DIY EV'ers or DIY Hybrid'ers should consider aeromods and low rolling risistance tires, like many of the members of ecomodder.com do.

These techniques along with hypermilling have netted these members 40-50mpg easy...

 

[Xringer]

Xringer,

What made you choose that e-motor? Which others have you considered?

It's small, not too heavy, has pretty good output between 1000 & 2000 RPMs, and since it's a PM, it can work with a regen controller.

And, when I sell the car, that motor might be good on a motorcycle..

I did look at Bushless and decided there wasn't a lot of advantage
in this application.

 

[Xringer]

No way will you see that sort of increase with the setup you are talking about. Think of it this way, if the ICE never had to accelerate the vehicle it might be able to get 35mpg by holding a steady speed, but you aren't going to be helping acceleration with your setup. You might see a couple mpg the way you are doing it, not worth it in my opinion. You could get the same or better by doing aero mods like a flat belly pan and wheel covers for less effort and money.

I've been thinking about a belly pan, but I'm not sure what kind of gain
it would bring..

Maybe I should just stop carrying big boxy stuff on my roof racks??


Anyways, with just a slight bit of down hill grade, I can hit 40 MPG easily.
So, I'm wondering what 2 or 3 HP of assist would do for it..
I'm pretty sure the assist system would propel it's own weight and then some.. (I hope it would)!
If I was just going down to the store (4 miles round trip), maybe I could turn up the juice to 4 or 5 HP for the trip..

 

[JRP3]

If you can do a full belly pan you'd be smoothing out the largest area of the vehicle. Plus I'd do full wheel covers in the back. I'd also say remove the luggage rack but it looks as if you might actually need it