Hydraulic hybrid engines: better than electric hybrids?

Does anyone know more about this system, and why it isn't in use more? Basically it works like a conventional electric hybrid, but instead of electricity stored in a battery, it stores pressurized fluids in a tank during breaking. During acceleration, the pressurized fluids are used for acceleration and reduce gas consumption.


The local newspaper was discussing work college students at the U of MN were doing on engines, trying to convert smaller car and truck engines to hydraulic hybrid drives, and stated you could see a 30% increase in fuel efficiency. They mentioned a 55% increase in the fuel economy of a converted Ford Explorer SUV, to 33 mpg. It seems that hydraulic systems would be more easily implemented than the electric systems currently used in hybrids today, not relying on a battery pack and such. What are the potential cons that are holding hydraulic hybrids back?

And it is so unnecessary. Unless you believe all the spin about how we are not ready for electric cars...the batteries are not good enough...electirc motors are not powerful enough...it is too much trouble to make...bla bla bla.
The first electric car was made in the early 1900s and it worked well. And there is no good reason why we cannot have one now, except that it would burn no gas and thus make all those service stations obsolete.
And the biggest reason is that a photo voltaic panel could charge your cars battery and not even use power off the grid. This is bad news to those that hold coal,gas and oil leases and intend to sell us every drop of it until we choke on the fumes.

They work better for vehicles with large mass: hydrolic systems can absorb more power from braking than current hybrid electric systems, which are limited by the battery C rating (and the motors are usually sized to match that C rating.) Of course integration of ultracaps for burst storage in electric hybrids and use of more powerful motors could alter that.

But hydrolic hybrids are generally "mild" hybrids in that recovering braking energy is all they do -- they do not smooth the engine load during normal driving. So I would not compare those numbers with hybrid mileage numbers -- they are probably for city driving only, and a special kind of city driving at that: (mail truck, trash truck -- many stops.)

One advantage of these, in appropriate applications, may be that they do not require somewhat exotic elements in the drive, such as lithium in batteries, decreasing expense and perhaps increasing the ease of recycling.

All these vehicles are diesel powered and We get Euro quality diesel in the US as of Nov 1, 2006. No bad emissions and we can use efficent EU diesel engines, and bio-diesel is coming!

SOUNDS GREAT TO ME!

:-)

Hydraulic hybrid
A hydraulic hybrid vehicle uses hydraulic and mechanical components instead of electrical ones. A variable displacement pump replaces the motor/generator, and a hydraulic accumulator replaces the batteries. The hydraulic accumulator, which is essentially a pressure tank, is potentially cheaper and more durable than batteries. Hydraulic hybrid technology was originally developed by Volvo Flygmotor and was used experimentally in buses from the early 1980s and is still an active area.

Initial concept involved a giant flywheel for storage connected to a hydrostatic transmission, but it was later changed to a simpler system using a hydraulic accumulator connected to a hydraulic pump/motor. It is also being actively developed by Eaton and several other companies, primarily in heavy vehicles like buses, trucks and military vehicles. An example is the Ford F-350 Mighty Tonka concept truck shown in 2002. It features an Eaton system that can accelerate the truck up to highway speeds.
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Optimal Power Management for a Hydraulic Hybrid Delivery Truck http://www-personal.engin.umich.edu/~hpeng/VSD_from_AVEC_HHV.pdf
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http://www.motorpulse.com/story/view/brown-goes-green-ups-rolls-new-hydraulic-hybrid-trucks

Brown goes green: UPS rolls new hydraulic hybrid trucks www.redorbit.com
Recognize that familiar United Parcel Service truck with the trademark brown paint job? Look twice. The government released its model Wednesday, replete with a new hybrid hydraulic system built for the Environmental Protection Agency by Cleveland-based Eaton Corp (NOTE -not quite true as the developers are International Truck and Engine Corp., Eaton Hydraulics, Parker Hannifin Corp., which specializes in making hydraulic controls, and the U.S. Army).
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http://money.cnn.com/2005/12/21/Autos/hydraulic_hybrids/
EPA invents battery-less hybrid system
Hybrid drivetrain uses compressed fluid instead of electricity. To be tested on UPS trucks.
December 22, 2005: 10:31 AM EST
By Peter Valdes-Dapena, CNNMoney.com staff writer

NEW YORK (CNN/Money) - The Environmental Protection Agency says it can help drivers save fuel. It has said that for a long time, of course, but this time it's not talking about providing fuel mileage data for car shoppers. It's talking about a new invention created in its own Ann Arbor, Mich. research laboratories

Called hydraulic hybrid technology, the system uses energy stored up during braking to help propel a vehicle during acceleration. The energy is stored in pressurized hydraulic fluid, the same sort of fluid used in brake lines and for power steering. <snip>

In the EPA's hydraulic hybrid system, braking pressure is used to power pumps that compress hydraulic fluid. This stores energy in the same way you would if you squeezed a spring with your hands. When needed, the pressure is released and the expanding hydraulic fluid is used to power gears that help turn the vehicle's wheels.

Also, just as a gasoline-electric hybrid's gas engine can charge the batteries directly during highway cruising, the hydraulic hybrid's engine can also pump up the pressurized fluid tanks as the vehicle drives. <snip>

There is a major advantage to the EPA's new system and one major disadvantage, the agency said. The advantage is its simplicity and relatively low cost. The system would cost an estimated $600 to install on a mass-production basis, the agency estimates, compared to $3,000 to $6,000 for an electric hybrid system.

The disadvantage is the system's weight, the EPA says. According to a 2004 EPA report, a hydraulic hybrid SUV would weigh about 190 pounds more than a conventional SUV. That means the EPA's system is most applicable to trucks where the added weight would make a smaller overall difference, the agency said. The added weight of the system is similar to the weight of an electric hybrid system, although the EPA itself cites weight as a disadvantage. <snip>

The UPS truck could get as much a 70 percent increase in fuel efficiency in city routes, the EPA estimates, and the added cost of the trucks should be paid off in fuel savings in about 2.5 years. <snip>

...of the mileage claims, and of their projected cost claims.

But yes the technology is a welcome contestant. The more the merrier.

I caught a Countdown comment but was sleepy and did not get the whole thing.

I can't imagine they were running at a speed above 10mph.

:-)

which is why hydraulic systems work. If you exert pressure on one end of a line, that pressure is transferred intact by the fluid in the line to an equivalent pressure at the other end.

You might be thinking of air, which you CAN compress.

Cars that run on pressurized air are being developed. Filling up would mean rolling up to a compressor and pumping your tank full of air at several atmospheres. That air would run the same sort of piston and valve system we have now.

This would seem to be an ideal arrangement. Electric power would be used to compress the air, but that power could conceivably be from renewable resources or a closed PVC/fuel cell setup.

The oil boys would hate it.

It would seem to me that you would pretty much have to have a rolling pressure tank to get any real range out of such a system. Look at your average garage style air compressor. It has a tank about 2 or 3 feet in diameter and 4 or more feet tall. Fill it to it's max safe pressure and the compressor kicks on shortly after you start using anything you hook up to it.

Perhaps i am not keeping up with modern motive technology enough.

The internal combustion engine has a LONG way to go as far as efficiency is concerned. We shouldn't kid ourselves, gasoline engines are here to stay for as long as any of us will be around. One of the biggest wasters of fuel in the U.S. is the automatic transmission. Engine control systems that shut the engine off at stop lights, for example and start up again when you depress the accelerator (anyone who has ever driven a gas powered golf cart has experienced this) would save millions of barrels alone even without any other changes to the design of the primary motive power (the engine).

I just don't see how an automobile that could run off compressed air could be practical.

never mentions putting this type of drive in a personal or mid-size passenger vehicle such as a mid-size sedan.

What I have read is that the hydraulic drive is intended for large vehicles that make frequent stops. The smallest vehicle tried was a Ford Explorer, I believe, but I think that the best applications will be for even larger vehicles commonly used in commercial or public transit applications.

used for local trips, which is what 95% of us do 95% of the time. Alternate vehicles could possibly be rented for road trips.

Compressing the air using deceleration might extend the range somewhat, but you're right, there would have to be sizeable tanks, probably in the undercarriage.

Liquefied gases might be another thing to consider, but the power required to compress atmospheric gases to liquid would make such a system prohibitively expensive unless we found a very cheap, environmentally friendly power source. You could pop out a relatively small empty tank and swap it for a full tank and be on your merry way quite easily.

Oil simply isn't going to last forever, nor should it. We see how fossil fuels are starting to damage the environment, and when they're gone, the environment will have a chance to readjust. We do need to start thinking outside the oil can for alternatives, though, and playing with this stuff is essential.

:-)

turned up the mechanism, an onboard tank filled with nitrogen gas. As a regenerative braking system forces the hydraulic fluid into the tank, the GAS is compressed.

Now that makes more sense.

The bad news is that the machinery for this is pretty bulky, and the smallest vehicle being considered is a huge Ford Explorer. This technology would seem to be better suited to delivery trucks and city buses, large vehicles that make frequent stops.

http://www.greencarcongress.com/2004/10/eaton_and_peter.html

:-)

The accumulator is a cylinder filled with nitrogen, and is connected to the line between the hydraulic pump and the system. Hydraulic fluid is forced into the cylinder, compressing the air and when the hydraulic pressure drops to less than the pressure in the cylinder, the fluid is forced out again.

Accumulators are on any hydraulic system in use today, and are used to smooth out pressure spikes and to maintain system pressure (invariably the pump can't meet demand instantly so the accumulator picks up the slack and 're-charges' during the low demand periods).