Testing Shows Connaught Retrofit Mild Hybrid System Reduced CO2 Emissions By Up to 24.7%
UK Consortium Developing ZEV Retrofit for Commercial Vans

UPS to Purchase 7 Hydraulic Series Hybrid Vans; Prototype Showed 45-50% Improvement in Fuel Economy

The hydraulic system provides a high power-density energy storage option. Click to enlarge. Source: EPA

After two years of road-testing of a prototype, UPS has placed its first order for hydraulic diesel series hybrid delivery vehicles (HHV), becoming the first in its industry to do so.

Disclosing the results of its road testing on Detroit routes for the first time, UPS and the US Environmental Protection Agency (EPA) said the prototype vehicle had achieved a 45-50% improvement in fuel economy compared to conventional diesel delivery trucks. UPS believes similar fuel economy improvements and a 30% reduction in CO2 are achievable in daily, real-world use.

The hydraulic series hybrid, originally developed in a laboratory of the US Environmental Protection Agency (EPA), uses a diesel engine/pump to pressurize and transfer hydraulic fluid to the rear drive pump/motor and/or high pressure accumulator. The hydraulic drivetrain replaces the conventional drivetrain and eliminates the need for a conventional transmission.

Hydraulic series hybrid truck configuration. Click to enlarge. Source: EPA

The hydraulic system also handles regenerative braking and energy storage. When stopping the vehicle, the hybrid controller uses the energy from the wheels by pumping fluid from the low pressure reservoir into the high pressure accumulator. When the vehicle starts accelerating, this stored energy is used to accelerate the vehicle. This process recovers and reuses more than 70% of the energy normally wasted during braking. (Earlier post.)

UPS is ordering seven HHVs. The company will deploy the first two in Minneapolis during the first quarter of 2009. Eaton, which helped develop and refine the vehicle’s hydraulic hybrid power system, will monitor the vehicle’s fuel economy performance and emissions in the Minneapolis area. The additional five HHVs will be deployed later in 2009 and early 2010.

The EPA estimates that when manufactured in high volume, the added costs of the hybrid components can be recouped in less than three years through lower fuel and brake maintenance costs.

Eaton began working with the EPA in October 2001 under a Cooperative Research and Development Agreement involving hydraulic hybrid systems and components. As part of Eaton’s role in designing and developing hybrid technologies, the company’s engineers were co-located at the EPA’s Ann Arbor facility. Eaton also earned a number of hybrid power system patents and continues to work on a number of other hybrid vehicles initiatives with UPS and others.

The EPA believes the technology can perform equally well in other applications such as shuttle and transit buses and refuse pick-up trucks. In 2007, the agency launched a project to develop hydraulic series hybrid systems for Class 6 port yard hostlers—the heavy-duty diesels that move goods and products from ships to trucks at ports. (Earlier post.)

For the longer term, the EPA is interested in exploring a number of different high-efficiency engines for use in the series-hybrid architecture, including optimized diesel or spark ignition engines with biofuels; HCCI gasoline engines; and free-piston engines.



Joe L.

Halleluyah! Let's hope a publicly-available hydraulic hybrid retrofit kit is not far behind. My 17 MPG Isuzu Trooper could really use one. Supposedly Czero out in Colorado is working on such a kit.


45% improvement - it sounds fantastic!
What's the catch ?
Cost ?
Maintenance ?
Safety ?
or you just need to re-engineer a huge amount of the machine.
Can they do this for smaller vehicles or is it only worthwhile for largish ones ?

Hybrid fan

No catch, but it is hydraulic tech, and therefore HEAVY. As such this system can best be used in large city vehicles that do a lot of stop and go driving: delivery trucks, garbage trucks and urban buses.

Light duty vehicles, not so much. Battery electric tech is a MUCH better solution for them.


Progress. But terribly slow progress. Two vehicles in 2009, five more by 2011?

But if they have it right the pace will increase. Better to have a good vehicle in two years than crap today.

Retrofit kits don't often work out economically. Static and expensive things such as factories, office buildings, jet engines and ocean liners get serious rebuilds and overhauls. Cheaper items do not.

Bentleys get rebuilt. Troopers?

Most vehicles are not quite small and cheap. But they are not quite static and expensive either. A big retrofit probably wouldn't pay. But sometimes people just like to do things for themselves.


Results from real world testing of the prototype in Detroit sound excellent.
The pdf file also mentions on page 22 that the prototype is carrying at least 1300 lbs extra of mountings to enable body-off testing, so EPA are expecting even better results in future pre-production versions:

"45 to 50% initial in-service mpg improvement using prototype hardware. More mpg is coming through:
- 2nd generation engine-off power brakes & steering
- More efficient EPA engine pump
- Advanced engine-off control strategy
- Lower weight
(eliminate prototype mountings for body-off testing)"

Initial lab results using EPA City cycle show up to 74% potential improvement in mpg from 10.4 to 18.1 mpg.


I was thinking that the hydraulic load may have represented an ideal rpm/ load with regards fuel economy, hence finding a cheat.

More likely any electric or hydraulic hybrid will not yet have realised the potential from engine design tuning to a narrower power rpm band to increase fuel efficiency and emissions towards practical near 30% improvements.

The load would need to be compatible.


This result is expected. If you look at the low average speeds, you end up having very high potential MPG without stops. Recovering all the energy at high efficiency allows the city drive to exceed highway mileage greatly.

Again, totally expected.


"hydraulic tech, and therefore HEAVY"

Hybrid fan, you did not notice plot showing that the Specific Power is almost 10 times better than NiMH? Since no one has designed and built a sensible scaled down version for cars, there is no reason to believe it will not be as lightweight (Specific Power).

The 1st priority for hybrid systems is energy recovery (Specific Power). This technology allows almost doubling mileage without the massive weight penalty. Note that "Prius batteries weigh 600 pounds and cost over 5000 dollars". And that only allows 30kW of power without killing the battery life.

2nd priority, going to plug-in etc for energy storage adds so much weight that it negates the mileage benefit somewhat.

What is ironic about all this is it could have been done 50 years ago, perhaps for little extra up vehicle cost (simplified transmission and downsized simpler engine).


Where do you get your facts from. The toyota prius battery pack weighs a couple hundred pounds not "600" pounds. And last i heard it costs less than $3000 to replace not $5000. Who were you quoting?


Perry, the Prius battery pack only weighs about 100 lbs, not a couple hundred.


sounds great, but really, 7 vehicles in 2 years? what's wrong with them?

Bob Bastard

Joe L, I have a better idea. Instead of waiting for an expensive and heavy retrofit kit to install on your already weighty and aerodynamically-challenged Trooper, why not spend less money and buy an older model Civic, or similarly fuel efficient vehicle and use that as your primary commuter vehicle? Even if the kit provided a 45% increase in fuel economy, that is still only 24.65 mpg. For a lower upfront cost than what the hydraulic hybrid kit would likely cost, you could easily have >35 mpg, and keep the miles off of your Trooper, saving it for those occasions when you actually need it for off-roading and such. If you find that the amount of time you actually need the additional utility of the SUV does not justify the expenses of registering and insuring an additional vehicle, you could get rid of the Trooper and rent or borrow on those occasions when you need 4-wheel drive or a little extra cargo space.

Henry Gibson

Up till now there has been a lack of updated information about the UPS hydraulic hybrid truck. It is interesting to see that the performance is very good, but that it did not cause a large follow up order that might have made such trucks economical even though they comment that it requires large numbers of such trucks to make them economical. It is clear that there must be a federal requirement for high efficiency trucks just like there is one for water heaters and refrigerators no matter the cost.

With modern computer design, hydraulic transmissions can be both cheap and efficient. A French steam locomotive designer created steam locomotives that had double the power and higher efficiency by careful consideration and design of steam passages. The management did not let him build another because he had shown that the high power electric locomotives and electricfication that they were promoting was not necessary.

Roger Waller has demonstrated that some diesel fueled steam locomotives and ships can have overall lower operating costs and better revenue than the diesel engine powered ones. It is probably the time now for him to build lokomotiven that use air bearing Capstone turbines for the draft and a little bit of traction as long as he is burning oil anyway.

Steam and hydraulics are very similar because they involve the movement of fluids through channels. To make the devices efficient the channels must be large enough and well constructed.

The wide use and variety of air powered tools shows that they are superior for many uses than electric tools. More than a century ago, a steam forging machine was demonstrated that could break an egg in a wine glass without breaking the glass.

Hydraulic hybrids can be as efficient as electric ones even for cars, and the UPS system was first demonstrated in a car. Artemis also demostrated an automobile series hybrid system in a commercial car with double the operating efficiency in city traffic. Some birds have air channels in their bones, and hydraulic hybrids could have air pressure tanks as part of the frame.

At any hydroelectric station the turbines weigh less than the generators. With hydraulics one is dealing with mechanical energy at all times and there is no conversion necessary. The weight of the transistorised drive electronics alone and the cost are far higher than a high power hydraulic motor.

The highly neglected INNAS NOAX Chiron free piston hydraulic pump eliminates many moving and stationary parts from an internal combustion engine. It can have high enough compression to ignite any fuel including hydrogen and methane and propane and there are no bearings to be damaged by high pressure. No starting motor is needed and low NOX is produced. A tiny hydraulic turgo powered alternator can supply as much electricity as is needed for the car. Exhaust heat can boil water for a connected steam piston that increases the efficiency. Such a machine can burn any liquid or gaseous fuel and can operate in the high efficiency low pollution Homogenious-Charge-Compression-Ignition(HCCI) mode.

The series hybrid allows for a smaller engine which by itself increases the efficiency. The loss of efficiency, caused by the transmission, is compensated for by there being no need to operate a large engine at low efficiency and low speed to get high acceleration torque from stops. Even a lawn-mower engine can charge up air reservoirs enough to get superfast starts from stops.

Flywheels may also be used for longer term power as they are in Parry People Movers' rail vehicles that are now being used to train operators for daily service. These two vehicles are far more efficient and far quieter than the vehicles that they replace. ..HG..


Who is making the conversions? Is it Hybra-Drive Systems? Eaton? The press release isn't very clear. Maybe they are just buying the vehicles that were used in the study, and this is (yet again) another b*llsh*t press release....


This is the fraud - the work was done by Vince Carmen -


Vincent CARMAN

Inertial Storage Transmission

Can This Transmission Really Double Your Car's Mileage? (Mother Earth News, November/December 1977 )
Dominic Muren: Prototype: Vincent Carman's Inertial Storage Transmission (treehugger.com)
Scott Burns: Energy Saving Invention Being Suppressed by Snafu (Boston Herald American, Monday, April 25, 1977 )
Vincent Carman: Patents List
V. Carman: US Patent # 4441573 -- Fuel-Efficient Energy Storage Automotive Drive System
V. Carman: USP # 4350220 -- Automotive Drive System
V. Carman: USP # 4227587 -- Automotive Drive System

Mother Earth News (November/December 1977)

Can This Transmission Really Double Your Car's Mileage?

Carmen's Inertial Storage Transmission is the key to greater car mileage.

Lots more at RexResearch.com - PanaceaUniversity.org

The progress is slow because ??




If this is a fraud, so is the Prius. That concept was invented in 1974 by TRW in the US. Doesn't really matter who invented it, it matters who gets it into high volume production.

The hydraulic system is best suited to delivery van type of drive cycles. I'm not sure it would be as beneficial to a typical personal vehicle. City taxis, airport buses, trash pickup, etc., would be great applications.

Way to go Eaton. Keep up the good work.


The chart they present is seriously misrepresenting reality to skew things in their favour!

They are claiming that the power density of their system (3,000 W/kg) is the key to their viability, and suggest in their chart that lithium-ion batteries can only manage about 800 W per kg at around 5 Wh/kg.

This is total rubbish, as many cells beat this by a country mile, such as A123 with 3,000 W/kg and 100 Wh/kg, or Altair with 5,000 W/kg and 85 Wh/kg.

70% braking energy recovery is typical of hydraulic losses, whereas today's lithium-ion cells are at around 98% coulombic efficiency.

Thor Windbergs

Industrial competition is always good, Eaton against BoschRextroth everyone wins. No more loud garbage trucks, city bus or school buses..

A big plus for both operators and the environment - fuel savings of up to 25%

Tightened environmental legislation and political guidelines demand alternative concepts. The HRB hydraulic hybrid from Rexroth helps meet strict environmental regulations, while at the same time ensuring appreciable reduction in operating costs through fuel savings!

An HRB pays for itself quickly: For fleet operators of refuse trucks and shuttle buses, construction companies, municipal governments with school and city buses, container handling facilities, port operators...

Rexroth develops HRB in two versions:

HRB parallel for vehicles without hydrostatic transmission
HRB series for vehicles with hydrostatic transmission
Learn more about…

... Hydraulic and electronic hybrid drives
... Applications where HRB is used
... the benefits of HRB

Fact Sheet HRB
Press information: Refuse collection vehicle with hydraulic hybrid drive from Rexroth


Joe L.

Bob B.,
You're right! That's why my 45mpg Jetta TDI is my main driver. The Trooper is my testbed vehicle for hybrid research. (And for hauling stuff that won't fit in my Jetta.)
Your logic is sound, but thousands are now losing their homes or stuck with an SUV they can't sell for half its former value. Would be nice to have a cheap SUV retrofit option -- buying a new car is now out of the question for them.
P.S. Aerodynamically challenged is right! I'll never fix that on the Trooper!

Michael McMillan

This is ancient news, but the 70% number if the amount of energy put back in the tank stop sign to stop sign assuming a cruzing speed 35mph, 2 city blocks between stopsigns, and the vehicle being a UPS brown delivery van with an average load of packages.

15% to 18% of those losses are due to aerodynamic and rolling losses. The remaining 12% to 15% are all in the hydraulic drive train. But I challenge anyone to find a drive train engine to differential which only looses 12% or less. And I include the clutch or Torque converter.


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