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Eaton and Peterbilt to Produce Hydraulic Hybrids

Peterbilt and Eaton Corporation are jointly developing refuse trucks using Eaton’s parallel hydraulic hybrid system—Hydraulic Launch Assist (HLA). Peterbilt plans to build and evaluate a production version of the vehicle during the next year.

The hydraulic launch assist system uses regenerative braking to capture the energy otherwise lost in braking. Unlike its electric cousins which use regenerative braking to generate electricity to store in a battery for use with an electric motor, the hydraulic hybrid system recovers the energy in the form of pressurized hydraulic fluid.

The HLA system uses a reversible hydraulic pump/motor coupled to the drive shaft through a clutch and two accumulators. When a driver steps on the brake, the pump/motor forces hydraulic fluid out of a low-pressure accumulator into a high-pressure accumulator, increasing the pressure of nitrogen gas stored there to 5,000 psi.

During acceleration, the HLA system switches from pump mode to motor mode. The nitrogen gas forces the hydraulic fluid back into the low-pressure accumulator, and the pump/motor applies torque to the driveshaft through the clutch.


(The diagram at right is a conceptual sketch of the hydraulic launch assist configuration, from an EPA update on the technology. More on the EPA below.)

The hydraulic hybrid truck uses the hydraulic power for the intimal acceleration boost, then blends in the engine. This results in a significant reduction in fuel consumption and improved acceleration due to the high power density of hydraulics.

Eaton estimates that the HLA can provide a 25–35% percent improvement in fuel efficiency, with 25–35% reductions in emissions and some 50% reduction in brake wear.

With a version of HLA Eaton developed with Ford, the engineers found that approximately 80% of the initial kinetic energy was returned to the vehicle.

“The system stores approximately 380 kJ of energy,” says Brad Bohlmann, a mechanical engineer and business development coordinator in Advanced Technology at Eaton’s Fluid Power Group. “With that much energy, we can accelerate a 10,000-lb vehicle from a dead stop to between 25 and 30 miles per hour with no assistance from the vehicle’s combustion engine.”

The HLA system can provide high torque very quickly, even at very low speeds, and is well-suited for heavy vehicles that do a lot of stop-and-go driving—vehicles like a refuse truck or heavy delivery truck. Or, hmm, maybe even a large urban SUV.

The technology could have a significant impact on improving the operating costs of customers involved in stop-and-go applications, such as refuse. Hydraulic Launch Assist can be quickly tailored for maximum fuel economy or enhanced productivity through quicker acceleration and shorter cycle times. Additionally, the system increases brake life and reduces engine and transmission wear, potentially extending component life and lowering service costs. It is also more environmentally friendly by decreasing exhaust emissions and noise.

—Peterbilt Chief Engineer Craig Brewster


Earlier this year, Ricardo Automotive presented to H-TUF the results of a simulation of fuel economy comparing hybrid electric systems to a hydraulic hybrid in a refuse collection vehicle. According to HTUF, Ricardo found significant potential for fuel economy improvement for all hybrid route vehicles where the duty cycle involves significant stop-and-go driving.

Using the assumptions in the Ricardo model, the hydraulic launch assist architecture provided the most consistent and highest average fuel economy improvement, improving fuel economy by roughly 48% in simulation over the measured driving cycle. Half the improvement came from the hydraulic launch assist plus the effect of engine downsizing. Idle stop and a near term “dual clutch” transmission also played a significant fuel-saving role.

Eaton is one of the leaders in working with hydraulic hybrid systems, but is not alone. Eaton worked with Ford and the EPA on the technology, and in 2002, Ford introduced an F-350 prototype using the HLA system.

The EPA continues to push forward with its hydraulic hybrid research. The agency has produced a test chassis (frame and powertrain, no skin) weighing 3,800 pounds that indicates that the hydraulic hybrid approach could triple the fuel economy of conventional vehicles (to up to 80 mpg)for a midsize sedan.

According to the EPA, it has made breakthroughs in designing hydraulic accumulators and pump/motors to be more efficient, smaller, and lighter for motor vehicle applications, which will also help improve fuel efficiency. The agency currently has cooperative research and development agreements with several private sector partners (such as Eaton) to further the development of hydraulic hybrid systems.

Permo-Drive, an Australian company, is another leader in hydraulic hybrid technology, and is working with its partner Dana Corporation on the FMTV (Family of Medium Tactical Vehicles) project for the US Army.

A company called SHEP, Inc. is working with Pi Technologies on light-duty hydraulic hybrids, targeting a Jaguar X-series as a prototype.


meshack A. O.

make clear indication of the diagram and its principle of oprations.

Walter J Mentzell

I would like to be up on your progress as I belive the hyd is the way to go,I have been working with a project as a hobby in my garage,trying to put the motor into the wheel,in doing so I had to re invent the electric motor which needed done useing an encoder to feed computer info to its opperation of one wheel and could sum up the operation of all 4 wheels,the motor I desiged is an electric hydrulic,which increases the efficency.I have to run for now,hope to hear of any new Ideas your co is working on keep up the good work.Jerry Mentzell


im going to be blonde and i want you too call me 836....

D.R. Hogue

I have been keeping up with this technology along with the Starrotor technology, thanks to Popular Science Magazine. Both are the answer to the gasoline problems we have today. Hydrogen, Batteries and corn fuel is not and will never be.


Up to this time all my thoughs were stuck on the engage/disengage of a motor/generator using a battery at each wheel.
I like this style of thinking, definitely outside of the box.
How come I have not heard of this before? Also, how come there is no publicity on this unit?


this site sucks nuts


The idea is not new. Over 35 years ago a high school shop teacher built a hydraulic drive car by replacing the I.C. motor with a hydraulic motor and used an 18HP lawn mower engine to recharge the hydraulics in a Bradley bodied VW. Gave 70 MPG and zero to sixty in seven seconds with this crude setup.
Northrop's "Swords to Ploughshares" electric hybrid bus only increased fuel economy by 1% using electric regenerative braking due to the inefficiency of electric motors/batteries. Reducing the weight from 32,000 lbs to 25,000 lbs was the major factor in increased economy. Hydraulics is more efficient over a wider range of speeds.

Louis Delarosbil

My name is Louis and i leave in canada..So i read lot of thing about hydraulic car and i want to make it on my own!!!
How can i do that .I need pump how much have 200hp do you know the formula to transforme it???
Do you have any drawing or blue print for all the system i want to built etc etc etc......

Thank to answer all my questions...

I speak french to if you have any french conection to find the plan just tell me pls...


Best regard


deepak sanan

The hydraulic hybrid system could be well suited for city buses in large metro areas. Has there been any economic analysis of this application? I am very interested in applying this system for buses in developing countries.

Thank you.


This is a public relations / investor scheme. 4 yrs since the article and no hydraulic hybrid system in sight. Even ford dumped its so called 60 MPG hydraulic F150. Peterbuilt currently offers a hybrid but it is electric.

Conclusion: No matter how good you think you are, you can not change the laws of physics. Fluid power has never been a efficient mode of energy conversion and never will.

Henry Gibson

Big pipes, large openings and smooth surfaces and bends plus a few other things allowed Chapelon to double the horse-power of steam locomotives without increasing the size. Porta did the same and added more efficient combustion for his Argentinian locomotives. These were fluid power devices.

The UPS is testing its hydraulic hybrid.

Roger Waller at DLM builds steam locomotives that give equal service to diesel locomotives burning the same amount of fuel with fewer repairs. He has also built efficient quiet Steam ferry engines that need only one man operation and very simple maintenance. His main contribution was efficient insulation of all hot parts. Also he sells external heaters that can keep the boiler hot or quickly bring it to operating temperature without smoke.

A steam turbine locomotive, TURBOMOTIVE, ran in Great Britain for more than ten years, including WWII, and had better efficiency than its piston equivalents. I have discovered, not invented, a very simple reduction gearing set that would have allowed TUBOMOTIVE full power in reverse as well.

Fluid power of a liquid type can also be engineered to be at least as efficient as diesel-electric and far less costly. The Chinese were, at one time, building steam locomotives that cost one eighth the price of equivalent diesel locomotives.

Hydraulic transmission of power was available in a few places including London where large steam engines pumped water into high pressure pipes and small shops would use water-motors to run all kinds of mechanical equipment. The waste water was run into the river through the sewers.

Modern materials and devices would allow the the construction and long use of steam buses. There is plenty of room for condensers. Efficient glass foam insulation is available. Electric heaters would keep the boilers hot. Fluid hydraulic gas pressure systems could be added if regeneration was desirable.

ROGER WALLER of DLM! One of your next machines should be a steam bus. You know how to build steam machines.


Ankush Aggarwal

No alternatives are are easy to match the IC engine but I see a huge promise in hydraulics application in automotive industry. The amount of energy density, rate of release of energy, rate at which energy can be absorbed (Breaking) far exceeds that of an electric drive.
Wish good luck to all developers



This will work. I see the name Peterbilt and I know it has the proper backing but I looked at the design and I need to be honest, I am scratching my head.. They are thinking different than me. Doesn't mean it won't work, it just means they are coming at it from a whole other angle. I would have put everything in front of the tranny but maybe I am missing stuff already tested and failed.

J. B. Brown

i believe that you are going in the right direction i also believe that a hydraluic car can run without the use of gasoline elimitating our dependence on oil

where can i get hydros cuz i want sum. i live i canada even there not aloud in canada i have a 1987 cady


Why does the system use Nitrogen gas instead of some other gas/fluid?

dhange pradeep

hi,i m a final year student of mechanical engg.i have iterest in automobile so i wanted to do project on hydrualic launch assist.Can you help me by providing all importent information.

ukoje celestine

i have been working on a hydraulic motor system dat re-utilizes the pressurised fluid,so that the engine operates without any external can contact me on this number for more information 08029837144 or08034273506 or mail me

ukoje celestine

i have been working on a hydraulic motor system dat re-utilizes the pressurised fluid,so that the engine operates without any external can contact me on this number for more information 08029837144 or08034273506 or mail me

ukoje celestine

i have been working on a hydraulic motor system dat re-utilizes the pressurised fluid,so that the engine operates without any external can contact me on this number for more information 08029837144 or08034273506 or mail me

marco ponce

hi everybody i just finish mi 12 cilinder motor i will install in mi dodge ram 1500 this motor dont need gas no batteries no water no steam no pollution no noise only change the oil may every 6 monts this is mi prototype for sale we can install in any car truck trailer train mecanical amusement generators etc

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