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."
Boom! (Score:1, Insightful)
Pointlessly small amount of storage. (Score:5, Insightful)
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.
Perhaps not so pointless (Score:5, Insightful)
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 [wikimedia.org]? 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.
Re:Boom! (Score:4, Insightful)
If you have ABS, you already have something like this in your car. It's a little (1qt) metal sphere with a rubber diaphragm in it. It holds about 3,000PSI of Nitrogen in order to cycle the ABS when it activates.
As for the safety...well... how safe is it to carry around 20 gallons of highly flammable gasoline?
Scuba tank's burst disc ... (Score:5, Insightful)
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?
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.
Re:Boom! (Score:3, Insightful)
Now there's an idea! If crushed in a wreck, it would be holding more energy. Storing the energy of wrecks could become the new eco-friendly feature in cars.
Compressed gases aren't *too* bad (Score:5, Insightful)
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.
Re:Phenomenally bad idea (Score:1, Insightful)
Re:Perhaps not so pointless (Score:2, Insightful)
Well, 80% of the US population lives in urban areas and 20% in rural. So that means slightly more than one urban family needs to own a minivan for every four rural families that do in order for the majority of minivans to be owned by urban dwellers.
If you think the ratio is that far skewed, the onus of proof is on you.
Re:It's worse then that. (Score:3, Insightful)
TFA refers to using the "engine overrun torque". Presumably they're referring to the situation where you take your foot off the gas pedal and engage a lower gear, thus causing the momentum of the vehicle to drive the engine - colloquially referred to as "slowing down using the gears".
I see three problems with this. One, most US cars are automatics. Two, your typical minivan driver thinks one or the other pedal has to be pressed flat to the floor at all times. Three, your typical minivan driver doesn't understand what gears are. And four (I'll come in again) even if she did understand what gears are, she'd have to put her cellphone/pizza/lipstick down in order to move the lever (point two notwithstanding).
Re:Boom! (Score:4, Insightful)
This will be tested up the wazoo, and then some.