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Eaton to Begin Production of its Medium-Duty Hybrid Electric System

The core of the system: the Hybrid Drive Unit. Click to enlarge.

Eaton will begin full production this year of its hybrid electric drive system for medium-duty trucks. The Hybrid Electric System (HES), which was seven years in development, is currently deployed in 167 pre-production field units: 93 with FedEx, 50 with UPS, and 24 HTUF utility trucks.

Eaton is primarily targeting the pickup and delivery (P&D) and the utility markets with the HES. In the P&D market, use of the Eaton system provides a 30-50% improvement in fuel economy. In the utility market, the system delivers a 40-60% reduction in fuel consumption, including the fuel that would be otherwise burned to support power generation at the job site.

System diagram for the Utility HEV system. Click to enlarge.

The hybrid system uses a parallel, pre-transmission design. Primary components are the Hybrid Drive Unit (HDU), which combines a clutch, a 44 kW/420 Nm motor/generator and automatically controlled manual transmission; the motor inverter/controller; the DC/DC converter; and a 2 kWh li-ion battery pack.

The basic core of the system (HDU, inverter and battery pack) is the same for both target markets. For the utility market, however, Eaton is providing two additional features: auxiliary power generation and the ability to drive PTO (power take off operations) with the electric motor.

Features of the system include:

  • Electric motor vehicle launch and acceleration assist.

  • Regenerative braking.

  • Charge sustaining battery system.

  • For utility applications, on-board power generation capability.

  • Fall back to engine-only operation in case of hybrid system failure.

A clutch is the interface between the engine and the motor, which is directly connected to the input shaft of the transmission. After startup, the clutch disengages and the vehicle is propelled by the motor. When the battery depletes to a specified state of charge, or when the power demand by the driver exceeds the specified limit, the hybrid control module engages the clutch and begins to blend engine power with motor power for operation. The blending is extremely precise, according to Eaton, and clutch slippage is not an issue.

The engine during driving operation is always on with the Eaton system. That’s due to the lack of electric accessories, according to Matthew Johnson, a member of the Eaton hybrid team who was explaining the system at the SAE Hybrid Vehicle technology Symposium 2007. The engine stays at low idle even in EV drive mode to support the belt loads.

For the utility application, when the driver requests PTO, the engine switches off and the motor powers the tools and hydraulic lift. When the battery is depleted, the hybrid control module restarts the engine, closes the clutch, and recharges the battery. Recharge time is about 5 minutes, and under constant operation, the battery will then support 45 minutes of auxiliary power operation. Since most PTO applications are not constant, however, actual time between charging can be as much as two hours, according to a PG&E user of the hybrid.

Fuel savings in the utility truck vary with the type of mission, which Eaton reduces to two primary forms: more driving with less time on the job site, and less driving, with more time on the job site.



for something like this to be available from Eaton is significant. it means car designers have a complete unit available for fairly high power hybrid applications.

with a bigger battery pack, this motor would be big enough for acceptable performance from a yaris size BEV.

Rafael Seidl

Shaun -

this system is explicitly NOT intended for BEV concepts. It was designed around an ICE in a market in which vehicles are subjected to load cycles that are substantially different from the average passenger car.

Bud Johns

Well put, as usual, Rafael. For delivery trucks and such, I say ABOUT TIME!!

Barry R. Guthrie

I think that this is a good step, but I'm a bit skeptical when I see 40% to 60% reduction in fuel. Especially with a hybrid system. What is the base milage per fuel consumption? You may get type of improvment when your base milaege per fuel consumption is already relatively low. Are we really taking about a 3 to 4 mpg improvment? Albeit this is still a very big improvement for these types of carriers.

Bill H.

It seems to me that Rafael misinterpereted Shaun's staements.

Shaun was referencing the strength of the electric motor in, not the appropriateness of the whole Eaton system for, a Yaris.

Speaking of high-use, mega stopping-and-starting applications, (I'm talking extra-urban here, folks) howza 'bout finally getting around to hybrid school buses and rural letter carriers vehicles? you can bet they're gonna make great use of any regenerative braking they can get.

And how about them aerodynamic boat-tail plates on every semi-trailer? Tha SAE says we're missing a 10% fuel savings there. Do you personally pull the pump nozzle out of your vehicle's fill tube and pour every 10th gallon on the pavement?

SAETechnicalPaperSeries 2000-01-2209 Aerodynamic Drag of Heavy Vehicles (Class 7-8): Simulation and Benchmarking; Government/Industry Meeting, Washington, D.C., June 19-21, 2000.

[If you read it you will see I have used their most conservative estimate of fuel-savings in big rigs from aerodynamic reshaping]

My point is that some dumb flaps of metal on the trailing edges of your boxy trailer give you big savings with
NO mechanical complexity. and this has been known for 7 years at least. {not to put down the Eaton system , bring it on!]


When we see large fuel savings percentages the quote is probably for fuel/power output. To use the drive system may require heavier frames that add weight and cut mileage.

In other words 'what is the weight of this and what it replaces?' Eaton, an adept company, no doubt has it well thought out.

The writer says 'in the P&D market' and again 'in the utility market'. Anyone know if these are standards or just terms?

As far as putting these in school buses. OK by me. But school buses are used about four hours per day and about 180 days a year. And they may not be run at all for weeks. That seems a bad omen for maintenance.

Commerical vehicles look better.


my vacuum cleaner is only used once a week for 20 mins or so and the electric motor seems to do just fine.

school busses should be an early target for hybridization, especially since it will prevent them from running cancer-box diesels near children waiting to board.

my intent about the Yaris was that this precise equipment be installed in a continuous duty BEV app. It'd be absolutely fine and probably experience less stress than in the intermittent duty full load cycle it was designed for, since a yaris will rarely use the full 40kW output.

there would likely be problems like throttle control, efficiency at partial load, etc, but I'd bet they'd be pretty easy to get around.


shaun: my doubts about maintenance on school buses concern the batteries.

I didn't see what Eaton has in the battery pack. But lithium ion, and some other types, are quite finicky about extended storage. Using them in school buses which may sit idle for weeks isn't going to be good for them.

School buses can certainly use them. I just doubt that it is a good early application. But if otherwise, then sobeit.

Eric A & Serena L Knutson

Can some one give us information on where we can find a elecrtic moter " High output " for our Iroc we would like ot make it a Green Car !!!
And also some suggestions on controlers


I'm interested in the type of electric motor that Eaton plans to use in their hybrid drive systems. Does it use permanent magnets or the new electric control optimized system recently patented by Raser Technologies? I understand that te latter increases the efficiency and torque and also has improvements in variable speed operations. I know that UTC is evaluating it for their products such as elevators (Otis) and there are rumors that GM may put it into the VOLT. Any comments?

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