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Transportation Technology

How Chrysler's Battery-Less Hybrid Minivan Works 347

thecarchik writes "Chrysler announced Wednesday that it would partner with the US Environmental Protection Agency to build and test prototypes of a different kind of hybrid vehicle, one that accumulates energy not in a battery pack but by compressing a gas hydraulically. The system in question, originally developed at the EPA labs, uses engine overrun torque to capture otherwise wasted energy, as do conventional hybrid-electric vehicles. The engine is Chrysler's standard 2.4-liter four-cylinder, the base engine in its minivan line. But rather than turning a generator, that torque powers a pump that uses hydraulic fluid to increase the pressure inside a 14.4-gallon tank of nitrogen gas, known as a high-pressure accumulator."
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How Chrysler's Battery-Less Hybrid Minivan Works

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  • FTFA:

    That compressed gas, stored at pressure as high as 5,000 pounds per square inch, represents energy waiting to be released.

    Not sure I'd want to be an a 1.0 version consumer vehicle with that much pressure without some serious discussion about the safety precautions to prevent or mitigate "unexpected pressure drops".

    Can someone who's got more experience with the fluid mechanics add to this?

    • More dangerous than riding around with a tank of explosive liquid?

      • Correct me if I'm wrong, but this would be in addition to a tank of explosive liquid.
      • by jdogalt ( 961241 )

        More dangerous than riding around with a tank of explosive liquid?

        You've been watching too much (or some) action fiction on tv and in the movies, and not enough mythbusters. It's basically near impossible to get a tank of gasoline to explode. I'm pretty sure it took actual explosives for the MB crew to get that to happen.

    • by perpenso ( 1613749 ) on Monday January 24, 2011 @09:37PM (#34989484)


      That compressed gas, stored at pressure as high as 5,000 pounds per square inch, represents energy waiting to be released.

      Not sure I'd want to be an a 1.0 version consumer vehicle with that much pressure without some serious discussion about the safety precautions to prevent or mitigate "unexpected pressure drops". Can someone who's got more experience with the fluid mechanics add to this?

      Scuba divers drive around with aluminum cylinders containing air at 3,000 PSI. Safety "burst" discs are built into the regulator of the cylinders so that if over pressurization occurs they rupture. The results are frightening and embarrassing but its only air and not shrapnel since the cylinder remains intact. I expect there are similar technologies in the pressure vessels in these cars.

    • by SuperBanana ( 662181 ) on Monday January 24, 2011 @10:13PM (#34989782)

      For those who are not into car repair et al, Audi used hydraulic pressure accumulators for power brake assist. It's a great system, particularly for turbocharged cars, which spend a considerable amount of time in normal driving with low or no manifold vacuum (which is created by the pistons trying to draw air past a restriction, aka, the throttle vane. That big round thing your brake master cylinder comes out of? That's the vacuum servo. It uses surface area to multiply force from the vacuum.) Citroen used the same idea to power the extensive hydraulics used in their famous suspension systems. Mercedes did as well for their cars which had hydraulic power windows (!!), door-closers, and suspensions. Nowadays, the idea of hydraulic assist has largely gone by the wayside, with auxiliary electric vacuum pumps used where necessary. It's a shame, because the hydraulic system had a HUGE amount of reserve; you could pump the pedal hard almost thirty times.

      The reservoirs are lovingly nicknamed "the bomb" by enthusiasts and owners of mid-80s-to-early-90's Audis, strictly on appearance; they look sort of like a large-ish cartoon bomb. I have NEVER heard of one exploding or failing (in terms of the pressure vessel, say, by cracking) in any way, and they've been in use for almost thirty years.

      The way they DO fail, very predictably, is via the internal bladder that separates the nitrogen charge from the hydraulic fluid. Eventually the bladder fails, or the nitrogen simply diffuses through the bladder. Also, hydraulic systems are pretty horribly unreliable; with age, everything rubber fails eventually. Citroen did a pretty good job of proving that too, but on Audis, pretty much all the hydraulic hoses eventually fail. The hazard, in this case, is that when this system fails, it'll dump gallons of very slippery hydraulic fluid all over the road. If you're lucky, it won't also spray it all over, say, your hot exhaust. Atomized oil is pretty damn flammable.

      Another danger: with the Audi system, all you had to do was pump the brake pedal until it was hard, and the system was safe to work on. This system would involve higher pressures and larger quantities of fluid...and it would become a real danger for anyone working on the car to do so with the system charged, as fluid over a certain pressure will either break skin or worse. I imagine they'll develop an easy way to discharge it, but people are still idiots.

      The thing is also going to be a total bitch in a fire; I'm sure they'll put a pressure relief on the nitrogen side, but even then, you've got 10-15 gallons of flammable oil to deal with.

      I really don't see Chrysler having any incentive to make the thing more durable than Audi/VW/Citroen did. It'll be made so it lasts about 60-70K, and then you'll be looking at replacing a huge, high-pressure tank. Expect the hilarity 3-4 years from whenever they go on sale, probably sooner.

      • "Citroen used the same idea to power the extensive hydraulics used in their famous suspension systems"

        Yeh they sure did. My dear late friend Harry had a big Citroen Pallas, and when the hydraulics failed he ran up the back of the same car twice. Once originally and again when they pulled over to exchange details, the car in front braked too quickly AGAIN and Harry ran up the back of it once more!


  • by fluffy99 ( 870997 ) on Monday January 24, 2011 @09:19PM (#34989310)

    The amount of energy you can store in a 14 gallon hydraulic accumulator is pretty small. Even if they're cranking the pressure up to 6-7,000 psi the energy density is around 50kw-sec/gallon or somewhere around the equivalent of a car battery.

    • by Caerdwyn ( 829058 ) on Monday January 24, 2011 @09:31PM (#34989440) Journal

      Perhaps not pointless. In the city, it's the start-stop aspect which is the mileage killer. Regenerative systems capture some of the energy used to decelerate, and use it to re-accelerate later. This is responsible for a large part of the efficiency of electric hybrids in city usage. I'm not sure if the hydraulic system described in TFA is linked to braking, or would by nature of its design capture energy during deceleration, but if so it would definitely help in city use. In fact, that may be the only place in which it shows gains, but let's not underestimate that. Most minivan use IS city use.

      There is also the advantage that it's not based upon rare earths or lithium, which have their own political "sourcing" issues and their own limitations on how much is available. In short- to medium-term timeframes, that could be more important than ultimate efficiency comparisons with electric hybrids.

      The safety concern is a serious one. Unlike present applications mentioned in TFA (garbage trucks, busses), there is much less structure in a minivan-sized platform to protect the pressure vessel. Anyone remember the Pinto problem []? This is solvable, though it will require more structure (meaning more weight) to protect it. Overall, the hydraulic subsystem + the weight of the protective structure are probably less than the weight of the electric subsystem including its batteries, so that may be a net gain over electric hybrids, but we won't know til we see specs.

    • It would indeed be pointlessly small if the intention was to charge up the reservoir and use it to drive around with.

      However that isn't the intention. I will confess that I glanced at the summary. Perhaps you - and the assclowns with mod points - should try it?

  • by slimjim8094 ( 941042 ) <slashdot3@just[ ... t ['con' in gap]> on Monday January 24, 2011 @09:51PM (#34989588)

    I routinely work with compressed gases (~2500psi, medical oxygen on an ambulance). The tanks are tremendously well-built, and if you drop one you're worried about the valve because it protrudes - not the tank itself. And by my envelope calculations, there's something like 603k pounds trying to turn my tanks inside out.

    Yes, I'd want to be damn sure I knew what that tank was doing, and how well it was built - but we're pretty good at making pressure vessels that won't rupture on their own, and equally good at making ones that are solid enough to withstand impacts.

    Frankly, 15 gallons of gasoline worries me more. The kind of impact that would rupture a tank would aerosolize the gas, and I'd rather be in an explosion than an explosion with fire.

    • by S.O.B. ( 136083 ) on Monday January 24, 2011 @10:08PM (#34989736)

      Finally someone who has something intelligent, constructive and relevant to say rather than the myriad of knee-jerk, living in mom's basement, I watch Discovery Channel experts.

      Are you on the right site?

      • Re: (Score:2, Funny)

        Is it discovery channel that everyone migrated over to? Dammit! I'm still watching "The Learning Channel" and learning that having 19 kids is suicidal.
        • I thought they officially changed their name to the letters "TLC" and haven't been "The Learning Channel" for quite some time. Now back to go watch more Spike TV...........
    • I don't know anything about Chrysler's tanks, but I do know that MDI has got tank storage figured out [] for their own purposes.

  • I don't believe it's quite the same thing, but this group [] has been working on a similar idea for a few years now. Only problem is I don't think the latter vehicle would be so splendid in the snowy North.

    • I, for one, will not drive at any speed in a tricycle vehicle with the single wheel in front. They are proven unstable in cornering.

      Even bicycle-type tricycles: those that go at any significant speed have a single drive wheel in the back and two wheels up front.

      I'm not saying that a "standard" tricycle will tip over at the drop of a hat, but they are less stable when cornering, especially when braking while cornering. The two-wheels-in-front configuration is provably more stable.
  • by Anonymous Coward on Monday January 24, 2011 @10:01PM (#34989670) []
    The compressed air car has been under development for a long time. It shows great promise but nobody yet has been able to make a practical vehicle.

    The advantage of a hybrid vehicle is that it doesn't have to store enough energy for a complete trip. In particular, it stores energy (thereby heating the engine) and releases energy (thereby cooling the engine) over a short period of time. The pure compressed air vehicle has the problem that the engine is permanently in cooling mode. If the engine is hot, because it has just been compressing gas, it is far more efficient. The longer it operates as an engine, the less efficient it becomes.

    The advantage of compressed gas for short time energy storage is that the storage is simple and does not take much sophisticated material as compared with batteries.

    People raise the problem of a tank of gas stored at very high pressure. The hybrid vehicle doesn't need as big a tank. Also, they've been working on this for a long time. The problem is basically solved. It isn't nearly as much a problem as a tank of gasoline.

  • KERS []

  • Tata is making subcompacts in India which use this exact method as a propulsion source to get around. However, what works over there might not work over here.

    But, if the technology makes it over, just the fact that it can keep a vehicle running with the gasoline or diesel engine off at idle to low speeds in city traffic would save a good amount of fuel.

  • This sounds reminiscent of the starting system used in the good old Yakovlev Yak-52 aircraft. They first started flying them in 1976 according to Wikipedia .... ah well, what is old is new again.

  • by Anonymous Coward

    This engine is a split-cycle four stroke air hybrid that fires After Top Dead Center (ATDC) effeciently. The engine already holds far more pressure than standard combustion engines and reduces NOx by up to 80% and CO2 emissions by ~30% over similar hybrids and standard combustion engines - without the need of an ancillary system for power management (an electrical system for example). The engine presses out nearly 100% of the gas from the exhaust piston which leads to

  • Whatever happened to flywheels for energy storage? Popular Science couldn't shut up about them 40 years ago. Example: []

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