Supermileage Series Hybrid Car

[taylorp035]

I am not sure how many of you guys have seen the Shell Eco-marathon cars or the SAE Supermileage cars, but the idea is to take a stock 3.5hp Brigs engine and make the most fuel efficient car.
The way that most of the cars work is by running the engine for about 10 seconds to accelerate to about 25 mph, then coasting down to 12-15 mph and then running the engine again.

Since I have worked a lot with brushless motors and controllers, I thought that at series hybrid car would allow me to charge a battery pack (LiFeP04 A123 cells) for about a minute or two and then run the car at the efficient 15 mph (minimum speed limit is 15mph).  The road coarse is 9.6 miles long.

Previous cars at my school have run 600mpg, which is not very good.  1st place last year had 2200 mpg.  After running the numbers, it comes out at 600mpg, we were putting 92 watts continuous power on the ground after you took in consideration of the efficiencies.  I firmly believe that starting the car 20-24 times per 9.6 miles is wasting a lot of fuel.

So the reason why I am posting this is because I am not very experienced in generating the power.  My series hybrid would have a generator/alternator on the engine, which would approximately charge a 4s10p A123 pack (23 ah @ 12-14v).  Therefore I could charge the batteries up to 100 amps (4c).  This would require at least 2 hp.  I know the engine is good for rpm's up to 3600.  We do have a dyno and tach. to confirm power output (only relative numbers, no actual hp #'s).  The nice thing would be that a series hybrid with a Watts Up meter would be it's own dyno.

The issue is I am not sure where to start with the generator.  Efficiency is important and cost is not a large sticking point ($1000 would not be out of the question).  Size is an issue (look at pictures below).
I think with the right system and a better tuned engine, we could easily do 1000-1500 mpg.

This is this year's car which is going to compete in 2 weeks.




Here is next year's carbon fiber body that we spent 6 months making and several thousand dollars.  These pictures a pretty old at this point.




 

[TomW]

Interesting.

I think the best part of this approach is you should be able to design an alternator that works "best" at the most efficient speed and output for a given engine.

Your biggest hurdle may be conversion losses. Tweaking the engine run time to allow some "direct electrical drive" to the traction motor while charging. Just off the top here but once you approach full charge you can run the traction motor from the alternator as it tops off the batteries? Lots of things to consider depending on the batteries and how they like a charge.

It seems that diesel electric locomotives direct drive the traction motors which may be another avenue to explore?

Just spitballing.

Tom

[taylorp035]

The batteries will probably never get past 25% full.  We must prove that they are empty ( 2v for A123 cells).  It looks like about 50-60 Wh total for the whole 9.6 miles.

I think the best part of this approach is you should be able to design an alternator that works "best" at the most efficient speed and output for a given engine.

This should also help

The drive motor will probably be a brushless in-runner with a gear box, as I have heard they are more efficient than an out runner.  Wheel rpm is about 260.
The drive motor will need to put out 400 watts minimum for the 1% grade and acceleration requirements.

[zap]

Oh goody... I'll spitball too!

Sounds like mighty fun tinkering to me!
Are you in the Urban Concept class?

Are you married to A123, are they doing some sort of sponsorship?
If not, consider switching chemistry to straight lipo?  A better energy density, smaller/lighter, at the cost of tighter control on the battery management system (BMS)

Or ditch the battery and electric motor and get yourself a good cvt transmisson and flywheel.
http://www.youtube.com/watch?v=4PcIt0FPvWQ=en


Many of the folks over on endless-sphere.com would be all over this project.  You a member?
There are a few friction drive out-runner projects going on right now that are very interesting.

[Bruce S]

Taylor;
Couple questions to help clarify things.
Can you run the engine at idle the entire time or do they shut it off and restart when needed? Do you have a charging system already done for last year's car?
Is whatever being used need to be usable after the race? i.e. does the i.c.e. still have to run the car for say a victory lap?
Here's my reasoning. IF you can run something and it not be in totally working condition after the race then I would go grab the smallest alternator available ( think YUGO) Honda CCx and such or possibly an alternator for a Kubota lawn tractor, some capable of putting out at least 50A set for car voltage of 13.8 and using a pulley on the shaft of the motor and one way undersized so you already driving the Alt at 50% - 75% max RPM , this will allow you to charge the batteries even while i.c.e. is idling and car is coasting. Then when you bring the motor up back up to higher RPMs to get car back up to higher speeds the Alt will continue to charge, plus since you have to start with batts empty you can quickly recharge them.
NOW of course this will load the motor and the Alt is possibly going to be worn out, BUT it should do the job .
Hope this helps
Bruce S
   

[taylorp035]

Are you in the Urban Concept class?

Are you married to A123, are they doing some sort of sponsorship?

No, and No.  I am in the SAE Supermileage competition.  As for A123, I have a lot of experience with them in my battlebots and I know they perform to their manufactures' claims and then some.

Here are the rules:
http://students.sae.org/competitions/supermileage/rules/rules.pdf

not, consider switching chemistry to straight lipo?  A better energy density, smaller/lighter, at the cost of tighter control on the battery management system (BMS)

True, lipo's do have much higher power output per pound ( almost 2x of A123), but they don't charge fast, create a lot of heat, don't last long, are very pricey, and the few pounds that I will save is not worth it.

Many of the folks over on endless-sphere.com would be all over this project.  You a member?
There are a few friction drive out-runner projects going on right now that are very interesting.

No, and a friction drive would be much worse than what we currently have.  We are running the special tires that have the 0.0025 rolling resistance coefficient, the best ever made and they are only made once a year by hand by Michelin.

Can you run the engine at idle the entire time or do they shut it off and restart when needed?

We run the engine for 8-12 seconds usually and then shut it off for about 90 sec while we coast.  The series hybrid design would run for about 1-2 min and then stay off for the next 30-35 minutes of the race.

Do you have a charging system already done for last year's car?

No, this is my weak area of expertise.  I am good with the drive motors and the batteries, but I am not good with alternators.

Is whatever being used need to be usable after the race? i.e. does the i.c.e. still have to run the car for say a victory lap?

Well, yes, b/c we run the car for two days, probably 6-15 times, so the alternator would have to last for a while, and we would need to test the car many times before the competition.




From your suggestions, I hear the idea of a small alternator, which 50 - 100 amps would be required, probably closer to 100.  It would have to be in it's efficient range.  I am not sure what the efficiency of a normal car alternator is, but I bet it is better than a permanent magnet motor in the high power output range.  It would be nice not to have any sort of gearing/ pulleys, as this would decrease the efficiency.
If it was more efficient, I could charge my batteries at 150A, but I am not sure if the Brigs would be up to it.  The nice thing is we are running 100 octane (isoctane), so we can pull 4-4.5 hp if we increase the compression.   We have run the engine to 4000 rpm before, but that is past it's redline of 3600.
The battery pack will hold a voltage of less than 14.4v, especially because the pack will be empty.  I have seen people charge these cells to 95% capacity in 4 1/2 minutes, but I would rather charge them at 4C.
One of my far out ideas was to have a large (2-2.5kw) brushless out runner motor do double duty as the starter motor and the generator.  I would have a E.S.C. and the charging circuit hooked up to the three motor wire suing a triple pole, double throw switch.  I talked to a guy at Castle Creations who has made a windmill before using a brushless out runner and some PVC blades.  He hacked a ESC to take the braking power and send it back to the batteries.  Unfortunately, I am not this smart, but maybe he could make one for me

In the end, I am betting that we will only use about 4-5 ah worth of capacity, but the 23ah design allows for faster charging.  As for balancing, I have used A123 made balancers that work quite well.  I would probably end up putting 4 voltmeters on the pack and a light bulb+switch on each to make sure that we can prove to the officials that the battery pack is discharged all of the way (2v per cell) and that all of the energy is coming from the engine (sorry guys, no cheating or sneaky things).  At 100 amps, we would have to run the engine for about 3 minutes.  Obviously we would have to do testing before hand so we would not run out of power on the last lap.

[dnix71]

Some thoughts.

First, B&S engines have a strange HP/torque curve. You better get it and look at it closely. In days gone by the peak torque was at 3600rpm and peak HP was at about 4500rpm. But these engines go on lawn mowers mostly. The energy at the blade tip goes up with the square of the rpm. Lots of people were getting maimed/killed by lawn mowers so the Consumer Product Safety Commission and OSHA demanded changes. One of those changes was to lower to peak of the torque curve so the machines cut grass best at a slower speed. I think it's somewhere around 3200rpm now.

Two, some engines have an intake valve that does not completely close. This "compression relief" allows easier starting but results in intake blowback. I have a Sears brand riding mower with that style engine and it absolutely will not start unless the engine is full choked until it starts. This results in poor start/stop fuel economy.

Also, lawnmowers have poor energy efficiencies because they have lightweight flywheels compared to horizontal shaft engines typically used on gensets and sidewalk edgers. That makes them better at cycling up and down in speed, but results in poor instantaneous torque, since this is a 4 stroke engine, not a 2 stroke.

Starting and stopping an engine is wasteful of fuel as well because there is a spring dampened automatic choke connected to a wind vane that also acts as a governor.

You need to do the math carefully. 1 HP is 746 watts. 3.5 HP is 2611 watts. 2611watts/14v is 186.5 amps. 1HP will give no more than 53 amps. That's assuming perfect conversion, which of course doesn't happen.  If your drive motor needs 400 watts minimum you don't need much more than idling power from this engine. You might get better economy by adding some mass to smooth the engine torque and let it idle just above the motor requirements. You know how far you have to go and how long it will take you to get there. If you can regulate the battery charging so that it never gets full, then near the end of the race, shut off the engine and coast home on battery power if that is allowed.

[Bruce S]

OKAY;
 After reading the rules, basically you need the Alt to recharge the batteries for use as an engine starter / electronics device, NOT to propel the car.

Whole different idea then. Go the route of a F150 V6 Alt that is HO rated (bosch comes to mind) These will put out 80 continuous at 2K RPM and up in the 3200 RPM will be up in the 100 Amp range. They are heavy duty rated and will certainly hold up to the entire race from design phase to victory lap and then some.

Use a 1 : 0.5 pulley setup and you should be well suited for the power needed.
Cheers
Bruce S

 

[JW]

(sorry guys, no cheating or sneaky things).

If the batterys have to be dead I just dont see the point, kinda sucks...

Why cant they just give you less than a gallon of gas, compensating for your battery's SOC?

Also,

One of my far out ideas was to have a large (2-2.5kw) brushless out runner motor do double duty as the starter motor and the generator.  I would have a E.S.C. and the charging circuit hooked up to the three motor wire suing a triple pole, double throw switch.  I talked to a guy at Castle Creations who has made a windmill before using a brushless out runner and some PVC blades.  He hacked a ESC to take the braking power and send it back to the batteries.  Unfortunately, I am not this smart, but maybe he could make one for me

Quote
Do you have a charging system already done for last year's car?
No, this is my weak area of expertise.  I am good with the drive motors and the batteries, but I am not good with alternators.

I really feel Flux could give us all a difinitive answer, with the target cut-in speed and constant load figures, for this application, wish he would chime in, on this one.

JW

[JW]

I really feel Flux could give us all a difinitive answer, with the target cut-in speed and constant load figures, for this application, wish he would chime in, on this one.

Or even Rich H.

JW

[willib]

TaylorP may i recommend that you use a good synthetic oil in the vehicle this year.

I mean it does not make any sense whatsoever to throw  a cheap grade of oil in the most important part of your competition car.

The reasoning is , a good synthetic oil is super slippery therefore more MPG's .

Good luck , let us know how things went.

[ghurd]

Oil.
Controversial topic I won't argue about, but I Really like that T-Plus.

First time I used it in a truck, the highway MPG increased by 10% or better.  It doesn't stay that high for many tanks of gas.
Every time I use it for the first time in a vehicle, the temp gauge operates noticeably lower, and that's not something the driver can effect, and can only be attributed to less internal friction.  That is almost permanent, but 1/2 a quart is put in on every other oil change.

The "coolest" thing I did with it was with a mini air compressor.  HF had a sale.  $2.50?  Meaning I came home with a pile of these,
http://www.harborfreight.com/12-volt-250-psi-compact-air-compressor-4077.html
Ran them to break them in.
Removed the plastic housing.
After maybe 10 seconds the cylinder is too hot to hold.
I put some T-Plus in the cylinder from the rod end, turned it by hand to let the rings go over it maybe 20 times, ran it intermittently in short bursts for a bit of conditioning (psychological?).
The 12V amp draw went down some.  Can't recall, maybe 10%?
But can run it 60 seconds or more before the cylinder is too hot to hold.

Just something to think about.
G-

[willib]

Oil.
Controversial topic I won't argue about, ...

Yeah Sorry i felt that i just had to put it out there..

[ghurd]

Sorry.
"Controversial" is about oil containing Teflon.  And in my experience, T-Plus is good stuff.
G-

[willib]

I've never tried T-Plus , but i have tried Mobil 1, and have gotten pretty good milage out of it.

I'm not sure what is in the Mobil 1 , but i was wondering if an oil with graphite or graphene or carbon nanotubes would work better than normal oil..

[JW]

Here's an interesting thread that came up, while I was researching some threads that may or may not help. Fin has done alot of analysis of the alternater designs that are worked on here.

http://www.fieldlines.com/board/index.php/topic,128224.html

JW

[Bruce S]

Guys;
 I too do not want to steal the thread from the poster.
Maybe better for a different or split thread, but, coming in from the race circuit St Louis raceway ( Vega w/350 & '74 Old Omega w/455 both in high 9s )and the likes of trucks and cars w/turbo chargers. Before marriage and kids 

Oil can be an "interesting" subject.

IF you do use synthetic OIL stay with one type or the other but I would not add anything with either.

For the higher Revs of this particular vehicle I would certainly go with the syn-oil.

Cheers;
Bruce S




 

[taylorp035]

Thanks guys for all of the responses.  I don't have time to think about them right now, but maybe by next week I can do some parts research and the like.  I will discuss the oil with my group members and the power peak being in the high rpm range sounds familiar with some of our test results earlier this year.  I think we hit peak hp past the 3600 rpm mark.  And those who are waiting for performance numbers on my windmill, there hasn't been a 10 mph gust in a week  

[taylorp035]

I was reading a little about car alternators and I found that they only good for about 60% efficiency according to wikipedia  

Efficiency of automotive alternators is limited by fan cooling loss, bearing loss, iron loss, copper loss, and the voltage drop in the diode bridges; at part load, efficiency is between 50-62% depending on the size of alternator, and varies with alternator speed.[7] In comparison, very small high-performance permanent magnet alternators, such as those used for bicycle lighting systems, achieve an efficiency around 60%. Larger permanent magnet alternators can achieve much higher efficiency.[citation needed] By contrast, the large AC generators used in power stations run at carefully controlled speeds and have no constraints on size or weight. Consequently, they have much higher efficiencies, on the order of 98% from shaft to AC output power.

I was thinking that I could get 75-85% efficient.

So then did some searching and found this:
http://www.eco-techalternators.com/pdf/Specificationsheet-14V.pdf

From the graphs of hp usage and output amps, it comes out to about 75% efficient.  Granted, I could never make 7 hp @ 2000 rpm, but that would be the max.

The company also has a 24v version.  It would be ok to have a 24v system since I can get brushless motors, chargers, BEC's, and batteries to do it.  I was thinking that 24v would be more efficient anyways.

One downside to this alternator would be that it weighs a whopping 38lbs, which is more than the whole body/ chassis does....


What I wanted to do was something like this video, where I could use the Brigs to turn a large brushless airplane motor.
http://www.youtube.com/watch?v=1L86_fdsFKY
At 3600 rpm, a 200 kv motor would get you 18v approx. So with very little to no gearing, I could pull 60-100 amps.  I just wish I could find someone else who has done this.  This would be exactly like a normal DIY wind turbine, but with a smaller size.  If I am lucky, I could go to my high school today and test this b/c they have a 530 kv 60 amp motor and a 1130kv 35 amp motor.

[taylorp035]

So I decided to look at brushed PM generators, and I found one that says 94% efficiency and is 72 rpm / volt.

http://www.hydrogenappliances.com/manta.html

Plus, at 22 lbs, it is a lot lighter than the 38 lb model above.

But of course, this is way over kill what I need, so I will keep looking.

[ghurd]

ouch

Might want to search the reputation of a seller before believing anything you read.

Type hydrogen appliances into the search box...
ouch^2

G-

[TomW]

So I decided to look at brushed PM generators, and I found one that says 94% efficiency and is 72 rpm / volt.

http://www.hydrogenappliances.com/manta.html

Plus, at 22 lbs, it is a lot lighter than the 38 lb model above.

But of course, this is way over kill what I need, so I will keep looking.

The yoyo that runs that site has done more to harm RE than any other entity on the internet. Mostly by selling pipe dreams and disseminating insanely inaccurate information. All in the name of greed.

You can only find a higher concentrations of BS in the bull pen at the stock yards.

Believe what you will.

Look around here for info on it.

Tom

[ghurd]

"Look around here for info on it."

2 of my personal favorites?

http://fieldlines.com/board/index.php/topic,142444.0.html

http://fieldlines.com/board/index.php/topic,143050.msg961052.html#msg961052

[taylorp035]

    Thanks, I didn't look at it very hard.

What efficiency do you guys think I could achieve on the generator side?

[taylorp035]

Ok guys, we finally have some video of this year's car running so you have a better idea of what is going on.

http://www.youtube.com/watch?v=Lpa2PYN_rXU
http://www.youtube.com/watch?v=WCgz4Hjru7c
http://www.youtube.com/watch?v=nv0WFsTEpQU&feature=related

None of these videos show the body pieces, but at least you will know what a supermileage car is

[zap]

It certainly looks like a ton-O-fun!

This one (from 2008?) sounded like a 2 stroke?

[taylorp035]

You are probably right ZAP.  That was from Shell Eco-Marathon, which did not have a specific engine requirement.  Ours requires that we all use the same 3.5hp Brigs engine.

If we did not have an engine requirement, I would use one of those model airplane nitro motors 

[willib]

What efficiency do you guys think I could achieve on the generator side?

At least for an axial flux machine , where output / input power is controllable more or less , your input power is your Briggs .

Your output power is determined by your magnet strength and your stator. and of course the  layout of the machine.

You are going to have to decide whether you want to run the car off of electricity or the Briggs , i'm not sure it can be both at the same time. Maybe it can i'm just not sure how it could be done..

If i was to run it off of electricity , i would build a charging alternator and a alternator/motor and power it off of super capacitors with an RC type three phase controller .

For batteries i would use super-caps or ultra caps because you can charge them quicker than batteries.

And with Super Caps , every electron that goes in,  can come out.

So you would be balancing the energy stored in the caps , for the duration of the run.

If the caps are full let off on the Briggs, If the caps need power rev the Briggs.

[ghurd]

Bigger alternators tend to be more efficient, I think.

Seriously.  
I would test a motor before and after being treated with T-Plus, which will lead to using it.
And multi electrode plugs.

Us old farts put a lot of importance on porting and polishing the intake and exhaust ports and manifolds.
Like a hydro system, it is difficult to make power if the 'stuff' can't get in and out of the cylinder fast and easy.
Rules look like they accept and expect that type of thing.

Running excessively lean is very hard on a motor, but the MPG goes up.
You ain't going to California with that piston, are you?

I did not see anything ruling out NOS.
It is non flammable so it can not be a fuel.  
G-

[Bruce S]

What efficiency do you guys think I could achieve on the generator side?

At least for an axial flux machine , where output / input power is controllable more or less , your input power is your Briggs .

Your output power is determined by your magnet strength and your stator. and of course the  layout of the machine.

You are going to have to decide whether you want to run the car off of electricity or the Briggs , i'm not sure it can be both at the same time. Maybe it can i'm just not sure how it could be done..

If i was to run it off of electricity , i would build a charging alternator and a alternator/motor and power it off of super capacitors with an RC type three phase controller .

For batteries i would use super-caps or ultra caps because you can charge them quicker than batteries.

And with Super Caps , every electron that goes in,  can come out.

So you would be balancing the energy stored in the caps , for the duration of the run.

If the caps are full let off on the Briggs, If the caps need power rev the Briggs.

Willib;
 I like your idea of lowering the weight by using super-caps. Unfortunately he cannot use the electric for motion, rules say only ICE can be used, the charge is to restart motor after coasting as many laps as possible. Since the Caps would give him the instant power needed to restart motor that would safe weight by pounds rather than ounces.

This could be a very good way to go.

Bruce S
 

[taylorp035]

I know that the rules say that only the ICE can be ued, but it has been determined by the officials that it would be ok to build a series hybrid, as long as all of the energy comes from the fuel.

As far as the super capacitors go, I see no advantage to using them since my batteries will charge/ discharge as much power as the brigs can put out.  Plus, A123 cells are over 99% efficient, which I have verified myself.

From my research with in hub motors for the drive, I have found that most of them are 36v, not 24v, and that they are all sensored brushless 3 wire motors.  The issue with this is that my speed controllers are only good for 24v, and castle creations only makes one sensored controller.  There are a few 24v versions out there, but the performance would be sub par.  I was wondering if any of you guys have experience with in hub motors on bikes, and how much power they draw under use.  The car that this will go in will be about 200lbs with the driver, so it should be easy to move.

In the videos that I posted, I am betting that the motor never put out more than 1.5hp.

Hopefully I will get to test out our new homemade speedometer tonight, and maybe a few performance figures will get calculated   Also, we will most likely test our brakes ( we need 0.25g's ).

[TomW]

If the battery is just for starting the Briggs why not use an extended rope and the recoil  starter? route it to the cockpit and eliminate much weight and complexity?

Just a thought. I did not read the rules.

Tom

[willib]

Us old farts put a lot of importance on porting and polishing the intake and exhaust ports and manifolds.
Like a hydro system, it is difficult to make power if the 'stuff' can't get in and out of the cylinder fast and easy.

I did not see anything ruling out NOS.
It is non flammable so it can not be a fuel.  
G-

Wow Glen with that Nitrous he could do a quarter mile in nine flat.

http://en.wikipedia.org/wiki/Nitrous

what do yall think about removing the stock muffler ? I think the engine can breathe better without any restriction to the exhausting process , or is that not allowed?

I agree that polishing the the intake and exhaust ports is a good idea.