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Hybrids, Hybrids Everywhere

Posted: August 1, 2014 by Rolf Lockwood

Does hybrid power have a future? Judging by the amount of research and development activity that can be seen in every truck maker’s engineering department, and many, many other places, the answer is a very clear ‘yes’. Its appeal is very compelling in some quarters.

Will it necessarily be a combination of electricity and diesel? No. The hybrid world is presently dominated by that setup, but we may see hydraulic/diesel combinations commercialized in a mass way first. Like in 2008. You can get a diesel/electric powertrain in a medium-duty truck now, but it’s not yet exactly a databook option. The hydraulic option could be there sooner (see December’s issue for more on this).

Will it be affordable? Hmmm…tough question. Depends on your perspective. And on how you define “affordable”. There are those who think we’d do better retrofitting older trucks with modern, efficient diesels for a lot less money. Or using biodiesel. Estimates for the added cost of a diesel/electric system are all over the map, if you can find someone to offer an opinion — and a number — at all. We’ve heard $8,000 for simple systems all the way to $40,000 and way beyond, so it’s clear that for the most part only public or government-subsidized fleets can absorb the cost in the short term. The environmental benefits of any hybrid system are real, some more than others, and they may be enough to convince some governments that commercial justification is secondary to the prospect of cleaner air for now.

Even with the prospect of 30-to-60 percent fuel savings, you’d have to run quite a few miles to achieve a payback that would satisfy any sensible accountant in a for-profit operation.

For both public and private fleets, in fact, the need for subsidies is clear. Where they exist, hybrid trucks will flourish even before economies of scale are such that the price premium drops to reasonable levels. For instance, several U.S. school boards in Iowa, New York, and Washington have recently bought International hybrid diesel/electric school buses that cost $200,000 apiece when an ordinary bus costs less than $100,000. They actually only paid the price of that conventional diesel-powered vehicle, the balance being picked up by the states.

The U.S. Energy Policy Act of 2005 does provide tax credits for purchases of medium and heavy-duty hybrid vehicles, ranging from $1,500 to $12,000 depending on vehicle weight and the increase in fuel economy relative to a comparable non-hybrid vehicle. That may not be enough. The Canadian federal government is rumored to be following suit, more or less, in the new year.

The exceptions to this subsidy need are fleets like FedEx, UPS, and to a lesser extent our own Purolator. Nobody in our industry is as far down the hybrid road as those fleets are, and their willingness to be there has as much to do with size as anything else. Fleets that big can afford to look ahead and experiment because the potential savings are monstrous.

To put this in perspective, a few months ago UPS ordered 50 hybrid electric package trucks from both Freightliner and International, but its total buy for 2006 was to be 4,100 ordinary trucks. A drop in the bucket? No, because with 1,500 alternative-fuel vehicles already on the road — diesel/electric, diesel/hydraulic, all-electric, fuel cell — UPS is far and away the leader in this charge.

As for Europe, where we expect high- tech solutions to be accepted more readily, the consensus seems to be that without government incentives — and there are presently none on the horizon — the hybrid idea has a long way to go before being commonly accepted.

In fact, Andreas Renschler, head of the DaimlerChrysler Commercial Vehicles group, wonders aloud if biodiesel might be a better option for Europe unless there are government subsidies or public/private partnerships of the sort that have supported alternative-power transit buses in many North American cities.

“I see that biodiesel is a real possibility in the next 10 or 15 years,” he told me in a private interview at the recent IAA Commercial Vehicles Show in Germany. Some European Mercedes-Benz customers are using 20-30 percent biodiesel blends of rapeseed oil now, he said. Others are taking up the M-B natural gas option, he added, though usage is not high.

Will hybrid power systems be easily maintainable? Another tough question, and the truth is we’re a long way away from knowing the answer. No matter the system in use, there will be new complexities and training demands. And some very high voltage to deal with. That said, the challenge is not likely to be extreme.

Will we see hybrid powertrains in over-the-road trucking? Not in the short term. Maybe not in the medium term either. Hybrids are really about urban transport needs — P&D trucks, courier vans, garbage packers, especially utility trucks. And, of course, both school and transit buses.

What’s a Hybrid?

What exactly do we mean by ‘hybrid’ vehicle? Simply, it’s one that uses two different power sources to make the wheels go round. But there’s more. You can have both ‘series’ and ‘parallel’ hybrids.

This U.S. Air Force refueller is built on a Mack RD 6×4
chassis with a prototype diesel/electric powertrain.

If both the diesel engine and electric (or hydraulic) motor are connected to the drive wheels at least some of the time you have a ‘parallel’ system. It maintains conventional drivetrain design, augmenting the diesel’s output with the electric motor’s. The diesel engine — usually smaller than would normally be spec’d — and a small electric motor together replace a larger conventional engine. They may both be used to get the truck moving, but once cruise speed has been reached the electric motor is shut down. That leaves the smaller diesel to maintain speed, but of course it will do so more efficiently than a larger engine would. At the same time, the diesel will spin the electric motor, which has become a generator, to recharge the on-board batteries.

In a ‘series’ hybrid system, on the other hand, there’s a generator connected directly to the diesel engine but the driving is done by the electric motor alone, which drives traction motors at the wheels ends. There’s no mechanical link between the engine and the drive axle. The diesel is operated in a constant-speed mode that allows for maximum efficiency. Unlike the parallel system, there’s no redundancy — if the electric motor is out, you’re stopped.

One of the very biggest advantages of a diesel/electric hybrid is regenerative braking via the electric motor, which can create torque in reverse as well as forward ‘gear’. In that mode it’s a generator being turned by the rotational force of the driving axle and thus generating electric energy for storage in the battery. At the same time it’s slowing the vehicle down with the resistance of the electric motor. Normal brakes are still required, but they’re used far less — really only in very hard stops — so brake shoes will receive much less wear, extending their life and reducing maintenance costs.

It’s all very efficient, relatively speaking, capturing some of the braking energy that would normally be wasted as heat and saving it for acceleration purposes. Stop-and-go city driving is ideal for such a system — and vice versa — because the cycle of acceleration followed by deceleration brings a high energy-recovery ratio.

The Utility Truck

Aside from courier operations, the first mass users of hybrid trucks might well be utility fleets. Development is well advanced, thanks in part to a major pilot test begun a year ago. Organized and sponsored by WestStart’s Hybrid Truck Users Forum, it’s been field-testing 24 International utility trucks with a diesel/electric power-train jointly developed by the truck maker and Eaton Corporation. Some 14 fleets are involved, including Hydro Quebec.

The drive system is a parallel hybrid configuration, with the permanent magnet motor mounted directly in front of the transmission, behind the engine and clutch. The engine powers a conventional drivetrain directly or drives the electric motor to create electrical energy that’s stored for use as needed. Electric and diesel torque can be ‘blended’ to improve vehicle performance and to operate the engine in the most fuel-efficient range for a given speed. The truck can also be run with electric power only, and it features regenerative braking. The truck can operate the utility bucket in electric-only mode, with the engine off, significantly contributing to improvements in fuel economy. Not to mention emissions and noise reductions.

Each test truck, along with an additional baseline non-hybrid vehicle, is equipped with International’s ‘Aware’ vehicle intelligence system. It sends continuous information to everyone involved in the test, data that will be invaluable in helping fleet owners understand the impact of hybrid-electric vehicles in their operations. Early tests indicate that fuel use can be cut by 40 to 60 percent.

Utility fleets aren’t the only market for a medium-duty truck of this general sort, of course, so this test will help others to make sensible hybrid decisions — applications with frequent start-and-stop operations or significant idle time, for instance, such as food, beverage, and retail delivery. The military is keenly interested too.

There are many more examples of hybrid power systems than we have space for here, so look for a second installment next month. We’ll examine the diesel/hydraulic idea and other variations on the diesel/electric theme, including battery developments.

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