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Chrysler and EPA to partner on hydraulic series hybrid powertrain for light duty vehicles

Chrysler Group LLC and the US Environmental Protection Agency (EPA) are working together to determine the possibility of adapting a hydraulic series hybrid system for application in large passenger cars and light-duty vehicles. The announcement of the partnership was made at the EPA laboratories in Ann Arbor, Mich., following a meeting with Sergio Marchionne, Chrysler Group CEO, and Lisa P. Jackson, Agency Administrator for the EPA.

The hydraulic hybrid system, developed by the EPA’s lab in Ann Arbor (earlier post), is well known and currently used in industrial applications, including large delivery trucks and refuse trucks across the country. The technology has shown substantial increases in fuel economy when compared with traditional powertrains in the same type of vehicles.

Hydraulic hybrid systems consist of two key components: high pressure hydraulic fluid vessels called accumulators, and hydraulic drive pump/motors. The accumulators are used to store pressurized fluid. Acting as a motor, the hydraulic drive uses the pressurized fluid to rotate the wheels. Acting as a pump, the hydraulic drive is used to re-pressurize hydraulic fluid by using the vehicle’s momentum, thereby converting kinetic energy into potential energy.

Working together, both parties hope to reduce the size and complexity of the hybrid system and produce a technology that is sensitive to the needs of drivers for smooth and quiet operation.

The research project will focus on adapting the hydraulic hybrid system to a Chrysler Town & Country minivan equipped with a 2.4-liter, inline four-cylinder gasoline engine. Components of the hydraulic hybrid system include a 117 cc engine pump, a 45 cc drive electric motor and a two-speed automatic transmission. Fluid for the system will be stored in a 14.4-gallon high pressure accumulator.

The system produces power with engine torque driving a hydraulic pump that charges the high pressure accumulator of up to 5,000 psi (34.5 MPa). The high-pressure accumulator delivers the pressure energy to the axle hydraulic motor, giving the vehicle power to drive the wheels. The gas engine will remain off if the accumulator charge is sufficient to drive the motor.

EPA and its partners announced the world’s first series hydraulic hybrid urban delivery vehicle in 2006. (Earlier post.) In 2004, EPA had combined a full series hydraulic hybrid system with a diesel engine in a 2003 Ford Expedition SUV. This vehicle was announced and displayed to the public in 2004 SAE World Congress. The prototype showed an 85% improvement in fuel economy.

Hydraulic hybrid vehicle technology is one more promising path worth pursuing in the effort to reduce our carbon footprint, and we are excited to partner with the EPA to push forward on this track.

In this hydraulic hybrid project, the Chrysler Group and EPA will evaluate and, hopefully, validate fuel-efficiency gains and greenhouse gas reductions. One of the aims of Chrysler Group’s integration efforts will be to meet driver expectations for smooth and quiet operation, so that Americans will want to buy and will enjoy driving vehicles with this technology.

—Sergio Marchionne

Chrysler Group also will introduce 150 Ram 1500 trucks with a plug-in hybrid electric system in the coming months as part of a project with the US Department of Transportation.




For light duty vehicles I always thought that a turbo diesel along with an hydraulic hybrid train would be teh best solution. Redesign the aero dynamic and you can get a pick up that run at 30MPG


Hydraulic has an inherent efficiency advantage over nearly any other scheme: kinetic energy is produced, stored and used, no phase conversion as with an HEV.
Another point is there's no exotic hardware or technology-all engineering fairly well explored by producers of construction and mining equipment. This should be in production.

Henry Gibson

Please people! Do save a lot of time and money and look up the Artemis web site about their series hydraulic automobile test or the INNAS NOAX website about their proposed series hybrid or just go back to the work leading to the UPS truck that had a series hybrid automobile in its development. Artemis proved their system on the road in a real vehicle. Bosch is keeping it under wraps now, and Artemis is testing (or tilting at) windmills. Series Hydraulic hybrids have been proven to save fuel, and have been retrofitted to existing automobiles. ..HG..


Why research something that has been in production for years?

Why not go ahead and do it and see if it can be sold?

Nick Lyons

Seems like this is a good match for stop-and-go traffic (e.g. garbage truck), but won't it be less efficient for cruising down the highway, especially when compared with a modern downsized, turbocharged drive train? How much energy do you lose with a pumped fluid drive train versus direct mechanical connection driving at a steady 65mph?


The energy storage allows further downsizing, and the hydraulics may give CVT functionality. Running the engine exactly at the minimum BSFC point may offset hydraulic losses; I recall a study a few years ago which found a 2:1 improvement available in a certain application (London taxis?).

I took a quick look at variable-displacement hydraulic pump/motors a while back but don't recall much about the efficiency figures. They weren't terrible but they weren't great either.


If we would have put a fraction of the R&D resources spent on HEV/EV on hydraulic hybrids, we would have had them in production already. As this article indicates, this might start to happen now... Whether hydraulic hybrids have greater potential for reducing FC than kinetic hybrids remains to be investigated.


If they can do it really cheaply, and then roll it out as a standard technology, they could have something.
+ no need to fret abut rare earths or batteries etc.

Even if it isn't quite efficient as an electric hybrid, if millions are sold, we save a lot of fuel.

+ once people get good at building and operating them, they will figure out ways to make them better.

Could you build a PHEV version where you charge a larger accumulator at home from the grid and drive for several miles without any liquid fuel at all?


Hydraulic PHEV isn't practical. The energy capacity of hydraulic accumulators is much too small.

I expect everything to go electric in the long term, but hydraulic or air hybrids still make tons of sense in the mean time.


A bank of ultra-capacitors can store the equivalent energy for 1,000,000+ short burst of energy (like hydraulics) when required. The main difference is that hydraulic is cheaper but much less efficient. All energies lost must be replaced by the on-board power source.

For certain specific applications (garbage trucks etc) requiring short burst of energy/power, hydraulic may be the preferred solution.


There is no conspiracy to stop hydraulic hybrids and they don't need any research. They exist, are fairly simple and cheap.

They have advantages (price mostly) and disadvantages (efficiency) compared to an HEV with supercaps or a flywheel.

It's very simple, each type can be produced and customers (mostly fleets with city focused vehicles) do a TCO evaluation, takes a bribe from their "favorite" and then writes up an RFP to favor the one who bribed them (or their brother-in-law, etc.)

:-) I wish I was only kidding here.

They all work, which one gets purchased depends more often on the dirty side of the political system.


Hydraulics make more sense the heavier and larger the vehicle...because those vehicles would require much more costly batteries or supercaps to be HEV.

I think Chrysler looked at the market and said, "We're number three for pick up trucks and mileage requirements and gas prices are going up...hydraulic hybrids sound tough like a fork lift, we can sell this for cheap and gain market share..."

I wonder how large an accumulator they would need to do a saw-tooth stop-start pattern where the engine only spends about half the time on, running at its most efficient RPM?


Healthy Breeze,
You'd be surprised at how little energy it actually takes to stop/start even the largest vehicles in city traffic.

According to the NYT studies done the last couple of years, the average speed of their buses is about 13 mph. Even when they come to a complete stop from say 25mph, a 40,000lb bus only needs about 280Wh of energy storage (after mechanical losses) for regen braking...and then using that same regen to start up again and get mostly back up to speed.

That's only a few kg of Li batteries or maybe 30-40kg of supercaps.

It's just not that much or that expensive considering that city bus costs $400,000+ to start with.

And of course, it's a trade off. If they want to be able to cover speeds with total regen, say up to 60mph (about 1.65kWh), then you start getting a much bigger battery/supercaps/hydraulics/flywheels, whatever. But it's a simple ROI on the additional energy capacity vs the number of times that particular vehicle will actually get up to those speeds on their daily routes and come to a full stop.


Conspiracy? I have been watching several governmental committees in Europe, who decide on public funding for hybrids. Electric hybrids get all the money and nothing goes to pneumatic, hydraulic or kinetic hybrids; isn´t that conspiracy? Well maybe not, after all, since there are so few (good) proposals on the "alternative" hybrids. Or maybe the conspiracy worked already in the phase before the proposals were made, so none of the alternatives were supposed to have a chance for receiving funding. Thus, nobody will come up with a project proposal in this field. The result might be that we will have electric hybrids on the near and medium future and one or two of the alternative hybrids (whichever wins the race…) on the long term, when electric hybrids will not be competitive any more. That is on the condition that some of the alternative hybrids will prove to be superior technology (in spite of that they will have to live on scraps for funding in the near future).


Europe may have realized that electrified vehicles will eventually replace all those mechanical contraptions. EU (and many others) may be on the right track.


"Eventually". But right now, we need to improve the stuff rolling off the lines whether it's electric or not.


Yes, HEVs, PHEVs and BEVs seem to put enough pressure on manufacturers to come up with more efficient ICE units. It will not be long for the first 60+/mpg HEV to come to the market.


irregardless of improvements seen, we can always improve the gas engine section of hybrid systems to make them more efficient, I have developed one possible way:

Aside from that, this looks very promising, certainly better than the pneumatic systems that have been proposed, although I imagine such as system has a relatively low MTBF, and high maintenance cost.


Since kinetic and hydraulic hybrids show a potential for both better fuel economy and lower cost than electric hybrids, we should not neglect them as some of you propose. Instead, I would be in favor of equal terms when it comes to government funding.

BTW, the first 60+ ICE vehicles have been on the market for quite long. VW Lupo 3L and Audi A2 3L both could do 80 mpg (diesel).

Fred H

Too bad the VW Lupo 3L and Audi A2 3L were discontinued after several years of low sales.

Around the same time, the first generation Prius was also on the market and didn't sell very well either. But instead of discontinuing it, Toyota improved it, and soon sold enough to run an assembly line at full capacity.

If Chrysler actually does bring a hydraulic hybrid to market, will they abandon it if it is not immediately successful?

Henry Gibson

Many of you have not read the literature about the actual Artemis hydraulic hybrid that was built and tested and had at best double the efficiency of the same model car with the same size engine in a standard test. The hydraulic losses were recovered, in all cases, by more efficient running of the engine. A smaller engine would have given even better performance. INNAS NOAX, has several devices to increase hydraulic efficiency, has also an interesting proposal for a electric-hydraulic-hybrid, which I had been keeping secret, now on their website. A cheap battery and a cheap low power electric hydraulic pump for constant operation combined with their hydraulics or engine hydraulics for a much cheaper long range electric hybrid.

Empty air pressure tanks are much cheaper than super capacitors and their electronics for the same power density which is why a UPS company uses air tanks and a turbine to keep their cheap small flywheel going until engines can start. Hydraulic hybrids avoid the cost and complexity of high-power electronics. ..HG..

CyberPine Educational Media

No expensive Battery? What's the life span of the two components and presuming they can be eventually repaired when they wear down.

Such an exciting technology... Oil company lobbiest get to work to make sure this never sees it's way to consumer vehicles.

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