Going to start a Hydraulic hybrid project
 

I've decided to build a hydraulic hybrid out of a Geo Metro. Been thinking about doing this for several years now.

The donor car is the mule for the Cornell XPrize team, I'm going to look at it tomorrow. My primary concern at this point is the car has power brakes so if I have an engine kill switch for pulse and glide the brakes won't work. If I have hydraulic on the rear transmission maybe its not that big of a deal though. The mule was built to test bed electric motors and batteries so it is built up with extra springs in the rear and it looks like the mounting plate for the electric motor on the transaxle is pretty beefy.

I laid in bed last night doing rough calculations in my head and got so angry that my crappy American made car has cost me over $20,000 in gas to go 160,000 miles in 10 years. It should have cost less than 1/4 of that. This country is so wasteful and I am obsessed with energy efficiency. The thought of paying $30,000 for a Prius so I can only double my mileage seems obscene to me. There has to be a better way. The XPrize really opened my yes to the advantages of very light cars and aerodynamic efficiencies. The technology is already here and the price is very affordable but big oil, big companies and big govt don't really want us driving around in cars that get 75-100mpg.

Batteries are just too heavy and too expensive. I've gone over and over it and even with Lith Ion unless you use an ultracap you need batteries that are way too big and too heavy just to get 100 miles of range. Ultra cap are too expensive and too dangerous to work with. High voltage electric systems are also dangerous and quirky to deal with.

I have traveled to about 40 countries and in a lot of countries farmers ride around on single cylinder diesel engines (tractors) with not transmissions, just straight drive trains. We are so wasteful here in the US it's insane.

Like I said my goal is to spend <$5000 for everything on the 1st gen car and to get a car that will get between 60 and 70mpg. I believe I can do it.

My first gen car will likely be just the Metro with a rear train power assist hydraulic passive system and an auto-on-off for the engine. I plan on regearing the tranny to make the gears tall so it will do <1000rpm at 55mph in the highest gear. There will also be extensive Aero modding, a plexiglass tadpole tail, wheel covers, no mirrors and a ground effect skirt made out of rubber that will be less than 2 cm from the highway surface. I expect to get constantly harassed by the cops, but damn decent milage.

The 2nd gen car will be a plug in hybrid with high density batteries and the hydraulic hybrid system that work together. The hydraulic will be used for accl/dec and the batteries will be used for high speed cruising. The gas motor will only be used when the batteries are depleted. There will be no regen braking system for batteries, all regen braking will go to hydraulic system. You lose too much energy with regen braking going to the electric system. Hydraulic is way more efficient from the standpoint of transmission losses. This car should get close to 80+mpg. It's likely that this car will also be the metro. The electic motor will mate with the rear axle. This configuration should work well on dry roads, less well on wet roads and not at all in snow and ice.

My 3rd gen car (not the geo, something different) would be a hydraulic drive car (off the shelf hydraulic drive train system not homebuilt like the first one) with a tiny diesel engine mated with a small generator and a battery pack. Plug in extended range EV similar to Volt but with a hydraulic drive train. All regen braking would go to hydraulic system not to batteries. This one would need to be ultra-lightweight and aerodynamic. I have an all Aluminum Prowler I would really like to use for this project, but not till the current engine in it dies :) Currently it has over 80,000 miles so maybe another couple of years it will be ready. It will require some aero modding on the wheels and front susp members but otherwise should work well. The front bumpers and grill will have to go as well.

Right now the issues I'm thinking about are

-Accumulator size (10 Gal?)

-Spring for lightweight accumulator or get cheap one from the junkyard

-What motors will minimize leakage losses and not use too many GPM at high RPM

-How to arrange the valving mechanisms. I'm thinking of putting them where the Ebrake is and the engine kill switch on the top of the gear shifter.

- Should I put the motors in the hub or just mount one on the axle for starters

-Should I buy the hydraulic stuff new or just get old parts from a junkyard

-Minimizing losses on the hydraulic system when the motors are free spinning and the car is running on gas power.

-System by which I can refill the accumulator before I leave the house, maybe an air wrench tuning the motor manually before I leave so I can leave the house with a full hyro accumulator

- What size accumulator to use, I'm thinking 10 Gal. That should be enough to capture the energy from several stops.

Any input is always welcome.

Karl

You mentioned that batteries are "too heavy and expensive". What's the energy density of hydraulic? You could spend your entire budget on high pressure control valves if you were really pushing the limit...

I've heard of hydraulic hybrid systems for city use in large trucks. I think they are high power but relatively low efficiency, and I really doubt they have enough capacity for long-term assist at high speed.

Of course the shortest route to 100mpg on the highway is aerodynamics and a very efficient small engine (see: aerocivic, Edison2, Avion).

If you really want to build a hybrid, by all means, tear into it! But there had better be a damn good reason to make it more complex than a small engine & good aero if you want to get it done and put enough miles on it to justify the work.

gridlok -

Good luck on your project. I don't think anyone has tried to build a HyHybrid(?) on Ecomodder. How did you come by the Cornell Metro Mule?

Cornell Chronicle: Cornell 100 MPG Team to compete
http://www.news.cornell.edu/stories/May10/car.jpg

CarloSW2

Hydraulic hybrids are meant to have enough hydraulic reserve for acceleration, but not for cruise. They are set up to keep a smaller engine running in an efficient part of its load curve most of the time.

Great idea! I like to see people trying new things in search of the best fuel economy. Your idea reminds me of the old PTO (Power take off) on a tractor engine. Sometimes used to run added equipement or a Hydraulic pump.

Just a thought here about the cost of added weight and cost of hydraulic valves, hoses, and motors.

Would it be a more cost effective solution to use compressed air rather than hydraulics as a storage medium?

I have seen the compressed air powered cars do quite well in short haul applications. And pnuematic parts are lighter and much less expensive.

Here's a good link to Hydraulic Hybrid "How stuff works"
HowStuffWorks "Parallel and Series Hydraulic Hybrids"

Good luck with your project :)

You will need to make some serious aero mods to drive your Metro 55mph at 1000 rpm. And I doubt the engine is at it's peak efficiency at that rpm either. The VW TDI engine is at it's most efficient nearer to 2000 rpm, with naturally aspirated gassers usually little higher.

I think this may be the car he's looking at:

http://ecomodder.com/forum/showthrea...aca-15334.html

gridlock, I would be happy to help.

What are your fabrication capabilities beyond your budget?

regards
Mech

Yes the hydraulic part is for the acceleration and regen braking not for driving. I have watched my OBD2 meter carefully for the last 2 years and most of the gas is used up in accelerating, much less cruising at speed. If I can use the hydraulics for getting it up to speed then use the gas engine to cruise that would be what I want. The RPM may be more than 1000 but I want it less than 2000 in the top gear at 50-55mph.


As for fabrication I have access to a shop and one of my good friends is a machinist who can make me whatever I need for cheap. I built a kit plane several years ago so I have the skills to pay the bills.

I looked at the Metro today. I was a little disappointed. It is not what I would consider to be particularly 'safe'. The mods the cornell team did were temporary and not really meant for a daily driver. Still debating on whether I want my 11 year old son riding around in it. Have to think about it a little more. It's the perfect donor car for this job and about 100 hrs of work have already been done in the right direction I want to go but the car has 200,000 miles on it not 20,000 like advertised so it makes it much less sweet of a deal.

What I meant were that lead acid are pretty heavy, lith ion are too expensive and you can't really but just one large powerpack right now.

I have to decide it I want to get an old insight and do major aeromods to it to try to get 60+mpg or mess around with the metro which may or may not ever get close to that.

Decisions, decisions. The insight would be safer and should easily get 55+ with <$1000 worth of aeromods (boattail, wedgenose, bottom pan, catamram wheels). It would also be very reliable and very safe. Also it is made out of aluminum so I can drill into the body panels with relative impunity for rust. The problem is the interior cargo space, I need room for my kites and snowboard/skis and the insight just doesn't have it. The metro does. If I built a decent boattail out of aluminum sheeting I could throw one or two more kites in the trunk which would make it just enough room I think.

The metro is way cheaper, but at 200,000 miles for an american car it will likely die soon. I have a pt cruiser with 160,000 miles that has not passed inspection for over 8 months, it will never pass (computer is wacked) and I have a Honda Oddessey with 170,000 that is acting like it will easily go another 100,000 miles.

If a deal seems too good to be true, it probably is. That was kind of the deal with the Cornell mule. I'm going to see now if they will sell some other equip like a 3 phase AC motor and controller with it, if not I'm not sure I want it. Decisions, decisions.

The question is really what direction do I want my energy to go. Is the statement

Dammit Detroit build a hybrid that is more efficient with current technology?

or

Dammit Detroit build a car that is VERY lightweight and VERY aerodynamic ?

That is the question. Right now its feeling more like the latter.

Karl

I have looked into using hydraulics for a couple projects, primarily for an outboard motor for my ski boat, so I can ditch the 2-stroke and use an inboard 4-stroke engine. Another one is to use hydraulic wheel motors as a way to put motors at the wheels without all the unsprung weight of electric motors.

What I've been told, and come to agree with, is that the efficiency is not very good for hydraulics. All the components are very heavy to handle the high pressure. The pump to create the high pressure generates a lot of heat in the fluid that must be removed.

Electric is just a lot more efficient. For a hybrid like the Prius that just uses battery power to accelerate, you can use a very small battery that is not very expensive. Frankly, the Prius is a very efficient and well-designed approach for a hybrid, I don't think any DIY approach can surpass it.
You can replace the NiMH battery with Lithium to reduce its weight, and use the drivetrain in a smaller lighter car for 2-people rather than 4.

You can purchase a wrecked Prius for about $3-5K, take the drivetrain, and put it in a Geo Metro, or maybe even a smaller car, and for under $10k (and a LOT of your labor) you could have a higher mileage hybrid. That would be my suggestion. Otherwise, a used Prius for $10k will get you 60mpg if driven like an old lady.