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Two motors are better than one

Hybrids have received mixed reviews when used in cars and trucks, but new generations are now receiving well-earned attention


Hybrids, vehicles powered by both an electric motor and an internal combustion engine, have received mixed reviews when used in cars or trucks, but new generations are now receiving well-earned attention.

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How would you like to more than double your fuel mileage? That’s exactly what the U.S. Postal Service says can be accomplished by installing a proven hybrid drivetrain into its LLV delivery vehicle. While most applications won’t get anywhere near those savings because they don’t have the light loads and constant stops experienced by the Postal Service, many operations can achieve significant savings.

Back to basics

There are a couple of ways to view hybrid vehicles. First, they can be divided into series or parallel hybrids.

In a series hybrid, a source of energy – usually an internal combustion (IC) engine but sometimes a fuel cell – supplies energy to some kind of energy storage device, usually a battery or hydraulic accumulator. A driving device, some kind of motor – usually electric but sometimes hydraulic – draws energy from the storage device to power the vehicle. At no time does more than one motor drive the vehicle.

In a parallel hybrid, there are two drive units – an electric motor-generator and an IC engine. Designs in this group are further divided into one of two sets: mild or full (some call the latter “strong”) hybrids.


In mild hybrids, the IC engine, either gasoline or diesel powered, is assisted when necessary by an electric motor built into the drivetrain. When the vehicle is operating, even at an idle, the IC engine never shuts down, since the electric motor is not designed to supply motive power to the vehicle independently. Some automobiles use this concept, but trucks, for the most part, do not.

A block diagram of a full hybrid will look the same as its mild counterpart, but the components represented by the various blocks are different. In particular, the electric motor in a full hybrid can power the vehicle on its own under certain conditions. When it does, the IC engine is completely shut off. While some vehicles can launch using only the electric motor, others need both the IC engine and electric motor to launch but can run at slow speeds on battery power, with the IC engine coming on line for necessary power at higher speeds. All of this happens with no input from the driver. Electronics take into account current driving conditions, the position of the gas pedal and the battery’s charge.

So, where does all this energy come from? A hybrid-electric vehicle incorporates a motor-generator in the drivetrain. This is a unit that will generate electricity whenever it’s driven – when the vehicle stops, slows down or goes down a hill. This is the energy that’s stored in an onboard battery pack and is available to the motor upon demand.


Since such a design is actually self contained, it never needs to be plugged in for a recharge. There is, however, another strategy that takes advantage of the fact that many applications have trucks coming home every night. DaimlerChrysler engineers have done just that with the company’s Sprinter van.

“One of our current programs, one that is of particular interest to many people, is our ‘plug-in’ hybrid, which really lends itself to commercial applications,” says Nick Cappa, manager of advanced technology communications for the company in North America. “Plug-in implies that the vehicle returns to a base at night, allowing the driver to plug it in to recharge a large battery pack for six to eight hours. With a Sprinter, you can drive up to 20 miles using only electric power.”

Four such vehicles are being tested and delivering about 25 percent better fuel economy than their counterparts in various applications from newspaper delivery in New York to package delivery in southern California. This product can use various battery types and engines in a variety of combinations. Batteries can be either nickel metal hydride or lithium ion. The engine is either a five-cylinder diesel or a four-cylinder gasoline engine.

Small but big returns

Understanding that regenerative braking provides hybrid electric vehicles with useful energy, it’s easy to see why the Postal Service can decrease its fuel consumption by half in its LLVs on its carrier routes requiring frequent stops.


“Although our main interest in hybrids is fuel economy, we are also looking for maintenance savings in the future,” says Han Dinh, program director for vehicle engineering at the USPS. “It has been estimated that, if fuel goes up one cent per gallon, our operating cost will go up $8 million annually.”

Dinh explains how USPS determined the possibility of such a large fuel savings. “A few years ago, we did a simulation of the fuel savings offered using a Toyota Prius power train to power an LLV. The results indicated that we would more than double fuel mileage – a 100 percent improvement – with fewer emissions. We then put a Prius through a 24,000-mile accelerated durability test, which it passed with flying colors. We’ve subsequently purchased 10 Ford Escape hybrids. While these are currently under test, and we do not yet have data for analysis or final numbers, both the fuel savings and maintenance savings appear to have been very good.”

The USPS also is studying the value of hybrids in larger vehicles.

“We’re also working with a company based in Vancouver, B.C., to convert one of our step vans into a parallel hybrid electric vehicle,” Dinh says. “Although this was accomplished, the supplier decided to partner with Ford and has taken the vehicle back to replace some components with Ford technology.”


The USPS’ use of hybrid vehicles is being curtailed by current law. It’s required by EPACT to use substantial numbers of alternative fueled vehicles, but hybrid electrics do not qualify as such under current law. While legislation has been introduced to change this, it may take a long time.

Another light-duty program

General Motors debuted hybrid electric drive trains in its Sierra and Silverado full-size pickups some years ago, but those early designs never delivered satisfactory performance. As a result, their production ceased this past summer. The company, however, has not walked away from hybrids and is now delivering second-generation models.

“Our goal has always been to provide a broad portfolio of hybrids, starting with the highest volume models,” says Rob Minton, communications director for GM fleet and commercial operations. “Earlier this year, we introduced the Saturn Vue Greenline, a full hybrid that delivers a 20 percent improvement in fuel economy. The first truck platforms to be introduced with new hybrid packages will be the Tahoe, Yukon and Escalade SUVs.”

These trucks also will feature GM’s displacement on demand cylinder deactivation technology, which allows the engine to run on either four or eight cylinders. Together, the technologies are expected to achieve a fuel economy improvement of about 30 percent.


“GM’s strategy is to go after the highest fuel-consuming vehicles first,” says Thomas G. Stephens, group vice president, GM Power-train. “We believe this strong hybrid on a full-size truck will save twice as much fuel per mile as a comparable small hybrid vehicle.”

The current program builds on knowledge from the development of the GM Allison parallel hybrid electric system for buses. These city transit buses have been achieving fuel savings of up to 60 percent.

Bigger trucks too

Several manufacturers of medium-duty vehicles already have presented, or are testing, hybrid versions of their products. For example, independent test results involving an International Truck and Engine Corp. utility truck in field tests, when measured against driving and work cycles typical of the utility industry, showed a decrease of 40 to 60 percent in the amount of fuel used, as well as emissions-reduction benefits. The program, sponsored by WestStart’s Hybrid Truck Users Forum (HTUF), a project bringing together truck fleet users, truck makers, technology companies and the U.S. military, will field test 24 utility trucks with hybrid power trains jointly developed by International and Eaton Corp.

“Early results are very promising,” says Bill Van Amburg, senior vice president at WestStart. “While we will need to test these trucks on a larger scale and over a longer period of time, we continue to see indications that these vehicles are commercially viable and will deliver real value to customers.”


“The initial findings support our vision of making diesel-electric hybrid trucks a viable option," says George Survant, director of fleet services for Florida Power and Light Co. and the chairperson of the HTUF Utility Working Group. “The other benefits we expect, such as extended maintenance intervals and fewer brake changes, further illustrate the promise of this technology.”

Early this year, Freightliner introduced a prototype utility truck and discussed the company’s plans to bring medium-duty hybrid vehicles to the market. It is a full-parallel hybrid with regenerative braking and electric-launch capability. The company used a Business Class M2 106 model with a 33,000-lb. GVWR chassis powered by a 230-HP MBE 900 engine. By incorporating a 44-kilowatt, 59-HP electric motor, the vehicle can achieve 290 HP and 860 lb.-ft. torque when the electric and diesel motors are paired. According to the company, simulations and testing have shown significant fuel economy improvements over conventional diesel engines.

“Freightliner has been testing hybrid vans for some time through our Freightliner Custom Chassis business unit,” says Michael Delaney, senior vice president of marketing. “This prototype is an important step toward future production of a medium-duty hybrid commercial vehicle. We are bullish on hybrid technology and its future in the commercial marketplace.”


Freightliner said it is considering implementing the hybrid system in a variety of medium-duty trucking segments, including beverage, school-bus and pick-up-and-delivery applications.

Peterbilt displayed a hybrid electric medium-duty truck outfitted with a fully integrated bucket lift body at the HTUF National Meeting in San Diego recently. The hybrid Model 335 will be in limited production in 2007.

“There is increasingly strong demand for hybrid vehicles as customers recognize the bottom-line benefits of reduced fuel use and service requirements, as well as the civic impact of responsible environmental practices,” says Dan Sobic, Peterbilt general manager.

According to Peterbilt chief engineer Landon Sproull, the truck, powered by the new PACCAR PX-6 2007-compliant engine, uses a parallel hybrid system that was developed with Eaton Corp.

“We expect the hybrid Model 335 will result in a 30 to 40 percent reduction in fuel use through the combined improvement of on-road fuel economy and stationary job site operation,” Sproull says. “The fuel savings, combined with reduced maintenance requirements, will significantly impact our customers’ bottom line.”

The reduced maintenance requirements result from less wear on the engine as its workload is supplemented by the electric engine and the brakes, since charging of the batteries retards the motion of the vehicle, Sproull says.


Mitsubishi Fuso also has a hybrid electric cabover work truck called the Canter Eco hybrid. This is a full parallel hybrid and will be available this year in the Japanese commercial market. The company has not announced when the truck might be available in the United States.

While the hybrid layout is a new development, the individual components in it are all proven designs, according to the manufacturer. The 123-HP turbocharged diesel engine is the same one that has been used in conventional medium-duty truck service in Japan for several years. This is coupled with a 47-HP brushless, permanent-magnet synchronous electric motor-generator. It, too, has been field proven in a number of applications, according to the company. Finally, power from both the diesel and electric drives is carried through a Mitsubishi Fuso Inomat II automated mechanical transmission similar to those used in Fuso Class 8 trucks for a decade.


It’s not difficult to see the results of work done by Eaton. Hybrid electric vehicles require an unprecedented level of integration and partnership between truck OEMs, the engine manufacturer and the suppliers of the drivetrain and major electrical components. Eaton says its strategy includes early and significant collaboration with truck OEMs, engine manufacturers and key technology/component suppliers. The results are clear.


“We provide hybrid electric systems to include an automated transmission with an electric motor-generator behind an electrically operated clutch, says Mark Lloyd, market development manager for hybrid electric products at Eaton Corp. “We also provide the controller for the motor, the battery system and the hybrid control module, which has supervisory control over the engine and hybrid functions, including the transmission. We utilize the engine’s CAN data link (like J1939) so we can get information from the engine’s electronic control unit. One of the key aspects of our product, which is focused on the medium-duty market, is the fact that the system is fully integrated into the drive train. It is not an add-on device.”

There’s no doubt that hybrid electric trucks are coming to the commercial trucking industry. Should you consider them? Probably. Should you buy them? Only if they’re likely to save you money.

A hybrid package costs about $50,000, but that figure is expected to come down. They offer up to 90 percent reduction in emissions, 25 to 50 percent better fuel economy, improved driveability, quieter operation and reduced maintenance using the same fuel in use now.


Hybrid Checklist

                    If it: Conventional vehicle

Mild Hybrid

Full Hybrid Plug-in Muscle
shuts off the engine at stop-lights and stop-and-go traffic * * * * *
Uses regenerative braking and operates above 60 volts * * * *
Uses an electric motor to assist a conventional engine * * * *
Can drive at times using only the electric motor * * maybe
Recharges batteries using clean electricity from the wall plug and has a range of at least 20 miles on electricity alone * maybe
Sacrifices fuel economy to achieve extra acceleration performance maybe *
Chart supplied by the Union of Concerned Scientists.


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