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EPA and Partners Unveil Diesel-Hydraulic Series-Hybrid Delivery Truck

The UPS hydraulic hybrid

The US EPA and its industry partners today unveiled the world’s first diesel-hydraulic series-hybrid delivery truck. (Earlier post.) The hydraulic hybrid offers an improvement in fuel economy of up to 60-70% and a reduction in CO2 emissions of 40% or more compared to a conventional diesel-powered truck.

The hydraulic series hybrid uses an 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.

The hydraulic hybrid vehicle (HHV) offers features comparable to an electric hybrid for maximizing fuel efficiency:

  • Regenerative Braking. 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.

  • Optimum Engine Control. The engine pump pressurizes and transfers fluid from the low pressure reservoir to the rear drive pump-motor, and under certain operating conditions, to the high pressure accumulator. As in other series hybrid designs, the engine operates at its maximum efficiency sweet spot to achieve optimum vehicle fuel economy.

  • Shutting Engine Off When Not Needed. The engine can be completely shut off during certain stages of operation, to be activated by the controller only when it is needed. As a result, in stop and go urban city driving engine use is cut almost in half.

The hydraulic hybrid powertrain. Click to enlarge.

The powertrain. A high-pressure accumulator stores energy as a battery would in a hybrid electric vehicle using hydraulic fluid to compress nitrogen gas. A low-pressure reservoir stores the low pressure fluid after it has been used by the pump/motor.

The engine pump-motor pressurizes and transfers hydraulic fluid to the rear drive pump/motor and/or high pressure accumulator. The rear drive pump-motor converts the pressure from the hydraulic fluid into rotating power for the wheels, and recovers breaking energy which is stored in the high pressure accumulator.

The hybrid controller monitors the driver’s acceleration and braking, and commands the hybrid system components.

EPA estimates that the added costs for the hybrid components, produced in high volume, for a package delivery vehicle have the potential to be less than $7,000, which would be recouped in less than three years by the lower fuel and brake maintenance costs.

In today’s dollars, the net lifetime savings over this vehicle’s typical 20 year lifespan are estimated to be more than $50,000. If fuel prices continue to increase at a faster rate than inflation, the lifetime savings would be even greater.

EPA and UPS plan to evaluate the demonstration vehicle in on-the-road service during 2006.

EPA is also developing a second UPS demonstration vehicle in a second phase of this partnership in order to explore the cost effectiveness of a different full hydraulic hybrid system configuration under a variety of load and driving cycle conditions.

EPA also plans to install an EPA Clean Diesel Combustion (CDC) engine in the phase 2 vehicle. (Earlier post.) The CDC engine does not need NOx aftertreatment to achieve 2010 NOx standards.

Eaton played a key role in developing this HHV with EPA. The other organizations that contributed to the development of the UPS hydraulic hybrid demonstration vehicles are UPS, International Truck and Engine Corporation, and the US Army-National Automotive Center. Major technical support was provided by FEV Engine Technology, Inc., Southwest Research Institute and Morgan-Olson.



I think they should start an ad campaign--

"Brown goes green" !

Max Reid

Wonderful, there is good competition for the Battery based hybrid. I guess EPA/UPS share this technology with GM & Ford for their vehicles.

This will finally force automakers like Toyota & Honda to strip the extras and offer a Battery based hybrid for < 20K.


The UPS trucks are built by Grumman Olsen Industries. If the past Grumman has had a reputation of not sharing anything. They have earned the rep of "does not play well with others". Reportedly Grumman holds over 1600 patents on just how the UPS truck looks.

Charles S.

Max Reid:

I think if you step back a little, you may see the bigger picture here.

First, Ford had already demonstrated a hydraulic-hybrid in a concept truck back a few years ago. This technology isn't exclusive to EPA, but rather, automotive industry just didn't have any motivation to put it into production... until now.

Second, hydraulic systems require a lot of space. That is why batteries would always be a better choice compare to hydraulics for cars.

Third, hybrids are expensive not just because of the batteries alone. Labor, development, etc. are other costs that need to be factored into the price tag. Toyota and Honda has already promised that the next gen hybrids will be cheaper than current models. Whether you believe in the promise or not, both of those companies have long said that the future of hybrids lies in bringing the costs down.

With all that said, while the cost for the manufacturers will come down, the final price tag of hybrids may not really decrease as rapidly as we all may hope. As long as price of oil remains high *AND* fuel-efficiency remains low among all the automotive manufacturers, then hybrids will continue to command a premium.


Charles -- Good Post -- A little Robin Hood economics of take from the gas guzzler and give to the fuel efficent (aka tax incentives for hybrids) would go a long way towards leveling the playing field.

Max Reid


I am big time supporter of battery based hybrids as well and have read about Toyota and Honda planning to bring down the cost of hybrids.

Toyota and Honda put the blame on battery cost, buy why not they just remove some of the extras and reduce the cost. If Honda can apply the hybrid system on Civic-LX model, it could come to 18K, but they dont.

Honda set a wrong foot with Insight (Sold < 20,000 units worldwide) and Accord which sold somewhat better last year and poorly this year with its V6 engine.

Amidst this, if some other company can sell a hybrid for lesser cost, that would be better.

I hope atleast the Vue-Hybrid which will cost just 2K more than regular Vue sells better.

Rafael Seidl

Hydraulic hybrids are strictly for trucks, especially those that need to make frequent stops but generally travel slowly. Think courier services, mail trucks, garbage trucks, school buses, city buses etc.

The system is cheaper than an electric hybrid and potentially suitable for retrofitting to stinky legacy diesels. You'd have to replace the mechanical accelerator wire with a computerized hybdrid controller, though, to fool the old engine.


I would love to see hydraulic hybrid trucks. Each Monday and Thursday, a huge old garbage truck drives by every home in this city. The driver slams on the breaks, throws in the garbage and then floors it again, while he travels 40 to 75 feet to the next house.

What a waste! I often see skid marks on the street after he leaves, though that may be from the recycle truck, which drives the same way, but once a week.


Note that “fuel efficiency” measured in MPG is better by 60-70%, while CO2 emissions (which are directly proportional to “fuel efficiency” measured in l/100km at same fuel) is lower only by 40%.

General formulae is : Y = X/(1+X), Where:

Y – PER CENT of fuel efficiency improvement, calculated using L/100km measurements;

X –PER CENT of fuel efficiency improvement, calculated using MPG measurements.

In our case 0.65/1.65 = 0.394.. or approximately 40%

P.S. Carbon content of gasoline is 2.421 kg per gallon, and carbon content of diesel fuel is 2.778 kg per gallon, or 15% higher then gasoline:

So, oddly enough, diesel vehicle having 18% higher MPG then gasoline one emits same amount of CO2 per mile traveled.

shaun mann

the cost of hybrids has virtually nothing to do with the extras. the hybridization makes the car expensive. in order to increase the value of the car for little extra cost, they throw in the extras so people won't gasp at the idea of paying $7000 for just fuel economy. this makes their hybrids much less profitable than comparably equipped vehicles, but more palatable to consumers.

Rafael Seidl

Andrey -

x MPG US = (235.21/x) L/100km
x L/100km = (235.21/x) MPG

1 L/100km gasoline = 24 g/km CO2
1 L/100km diesel = 26.5 g/km CO2
(difference is due to fuel composition)

Ergo, if you double your fuel economy in MPG, you halve your fuel usage in L/100km and also halve your GHG footprint.

In US units:
x [MPG US] = 235.21/x * 24 * 1.609 = 9083/x [g CO2/mi]

10 MPG US = 908 g/mi CO2
20 MPG US = 454 g/mi CO2 (454g = 1 lb)
30 MPG US = 303 g/mi CO2
40 MPG US = 227 g/mi CO2
50 MPG US = 182 g/mi CO2
60 MPG US = 151 g/mi CO2


Thomas Pedersen


Fun post :-) I bet the garbage truck makes a helluva noise as well!

In my subjective experience, diesel engines emit most during heavy acceleration (even brand new TDIs let out black smoke when the driver floors it). Removing the strain on the engine by such a hybrid system would really take away a lot of the noise and smoke from diesel engines in city traffic.

Luckily, busses and trucks are a lot less noisy here in Europe than in USA IMO, but I would still love to hear less of them.

I know pneumatic compression systems have been tested in Denmark some 10-15 years ago without much luck. But maybe modern computer controls and better hydraulic motors make the difference.

This sounds like a great system. Let's hope it works and gets implemented soon.

Thomas Pedersen


If a diesel engine emits 15% more CO2 per gallon than its gasoline equivalent, then it needs to drive exactly 15% longer to balance that - not 18%!

It's not complicated, it's simple! ;-)


Rafael, Thomas:
Not my point. Read the article above: 60-70% increase in MPG and only 40% decrease in CO2. Why? I did direct calculations and came up with formula to convert one to another. Remember, per cent calculations could be very tricky.

Rafael: I used data from EPA document

It indicates CO2 emissions from 1 liter of gasoline as 2.325 kg, from 1 liter of diesel 2.668 kg, or difference of 14.75 (calculated compared to gasoline). Your data lead to 10.4% difference. Which data is more accurate – I do not know.

Now the table, calculated according to my formulae:

MPG increase,% CO2 per km decrease, %

10 9
20 17
30 23
40 29
50 33
60 38
70 41
80 44
90 47
100 50
E.I. double the MPG, halve CO2, as you rightfully pointed out.

fyi CO2

"Brown goes green" !>

Andrew, did you come up with the yellow E85 Tshirt concept, tooo?
One truck does not constitute a groundswell - UPS is just covering their brown ars, attempting to play catch up. I see nothing about their phase in term, except
"EPA and UPS plan to evaluate the demonstration vehicle in on-the-road service during 2006."
On the other hand, the other delivery co. has been driving greener 6 years now...

Rafael Seidl

Andrey -

simply don't use percentage changes related to MPG. Its a reciprocal of actual fuel use, and therefore inherently nonlinear.



That’s what I always prefer to do – operate with actual numbers, not with per cent points. Too bad there are two different gallons, two different miles, two different hp, three different tons, etc.


Good comments about the CO2 output of these trucks. But like more and more companies are doing now (the mass transit system just did it here in Utah), switching to a blend of biodiesel (B20 for instance, which is 20% biodiesel) will lower the net CO2 output of these trucks by 20%. That would more than make up for the other numbers that have been stated. Because biodiesel came from plants that got it from the air and the truck is putting it back into the air, the CO2 balance is maintained if you burn it. In fact, it wouldn't surprise me if UPS and FedEx, et al were already running a mixture of biodiesel in their fleet. If that were the case (and that's hypothetical) then all the stated numbers in this thread would be incorrect if the big picture is taken into account.



I have a way to cut CO2 emissions from garbage collection in half in you area - go to once a week garbage collection!



It seems to me that this form of energy capture, storage, and application would work well in another set of cars that could benefit from being even greener: railroad cars. Utilizing this technology on engines and cars on traditional railroad, subway, and commuter engines and cars would make an already greener choice for transportation even better for the environment. I wonder if canola oil works as the hydraulic fluid?

hampden wireless

I saw a segment on this truck on the news. While I like it, the system can only store 2000 hp seconds of power. Or 100hp for 20 seconds. While that is alot of power quickly its not alot of total power.

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