Hybrids get a second look

DN Staff

April 7, 1997

13 Min Read
Hybrids get a second look

Let's begin by acknowledging that the concept of a hybrid car breaks no new ground. But electric cars powered by batteries or fuel cells seem unlikely to perform well enough to please both consumers and regulators in the foreseeable future. Given this reality--and the pressure now being exerted on the U.S. automotive industry by federal and state governments to cut tailpipe emissions--hybrid technology appears more and more attractive to engineers and scientists.

Take another look. In the not-too-recent past, most design engineers saw hybrids as excellent student projects, but rather impractical real-world vehicles. A hybrid, after all, requires two energy sources instead of one. If things go a bit wrong, a design can combine the disadvantages of both systems and turn out as a true clunker. But times change.

First, consider the different propulsion system arrangements lumped together in the hybrid category. In a series hybrid system, a heat engine drives a generator. The generator either charges a battery pack, powers an electric motor that spins a flywheel (a mechanical battery), or delivers energy directly to an electric motor (or motors) to power the vehicle's wheels. Most projects now underway use batteries, though flywheel technology is the subject of a lot of research. Drive motors either take power from the battery pack, or from the generator. When the battery pack powers the drive motor, the generator engine shuts down.

Because the engine can operate intermittently, and because the vehicle speeds up or slows down without regard to engine speed, the engine can operate in a narrow and efficient speed range. When the engine shuts down, the vehicle produces true zero-emissions performance.

A parallel hybrid also uses an en-gine/generator set and a battery pack. But in this configuration either the engine or the batteries can produce motive power. For short trips, the system can function as an electric-only vehicle. For longer trips, the heat engine takes over and propels the car. Both sources of energy can provide power to propel the car during high-energy-demand events--for example when climbing a hill.

Further variations on this theme involve power-assist, range-extender, and dual-mode configurations. Typically a parallel system, a power-assist hybrid uses a relatively large heat engine and a smaller battery pack that can deliver extra power when needed. Range-extender setups employ a lot of battery storage capacity and a smaller engine, and are generally series hybrids. The engine enables the vehicle to limp home if the batteries get drained, and it can perform onboard battery recharge. Dual-mode systems balance both design approaches and enable the vehicle to run on all-electric or all-engine power, or a combination of the two.

How can hybrids help automakers improve mileage and cut emissions? Well, hybrids use smaller engines than those that equip today's auto fleet, so they inherently burn less fuel. And the smaller engines operate intermittently. Result: less fuel consumption and lower emissions. Also, regenerative braking makes it possible to capture some energy normally lost as heat and store it as electricity or mechanical energy (in a flywheel), further improving fuel economy.

Chrysler talks hybrid. Early in 1996 Chrysler Corporation and the U.S. Department of Energy signed a cost-shared, four-year, $85 million contract to develop a hybrid system. It's early days for Chrysler on the new contract, but the company believes that both series and parallel hybrid configurations have potential to meet program goals. So Chrysler engineers will evaluate both approaches.

"We've been doing the vehicle simulation work, which is really the cornerstone of the program," says Project Engineer Robert Lawrie of Chrysler. Before Chrysler starts building expensive hardware, design engineers will analyze and simulate various hybrid vehicle configurations. Simulations will cover performance and fuel economy, and do optimization and tradeoff studies. "The milestone we have is that this fall we'll have a hardware decision," says Lawrie, "and what we're calling our Generation One vehicle will be constructed by the end of 1997."

The Department of Energy has hybrid vehicle technology development contracts with all of Detroit's Big Three. "There's a collaboration agreement between Ford, GM, and Chrysler," explains Lawrie. "There's an effort to reduce duplication of work between the Big Three. GM is focusing on a gas-turbine series hybrid; Ford Motor Company is focusing on a parallel-diesel hybrid; and Chrysler has the task of developing a series hybrid with a diesel engine." But today, Chrysler sees its task as one of analyzing both the series and parallel configurations.

After completing a good deal of simulation work, Chrysler engineers can decide if the company is ready to build the series hybrid, and whether or not that represents the best configuration. "I'd like to think it's a little too early in our program for us to say we're going to build either the series or the parallel," states Lawrie. "There is an understanding that we'll build a series hybrid in the collaboration agreement. But of course it has to make technical sense."

As this article went to press, Chrysler engineers already had basic series and parallel configurations assembled in simulations. Major tasks still facing them involved: getting all the input data needed to accurately characterize components; defining all losses or inefficiencies in the modeled system; defining steady state calculations for fuel economy and emissions; placing thermal transients in the simulations; modeling thermal behavior; and modeling accelerating transients and trying to find their impact on performance and fuel economy.

Engineers at Chrysler don't lack experience in working with hybrid vehicles. The company's Dodge Intrepid ESX employs a series hybrid configuration. In that vehicle, a 1.8-l three-cylinder turbodiesel drives an alternator that feeds 300V to electric motors mounted in the car's rear wheels. A pair of spiral-wound lead-acid battery packs from Bolder Technology, Wheat-ridge, CO, store energy and capture energy from the car's regenerative braking system. They also provide extra power for instant acceleration.

Lawrie describes the design of the ESX's battery pack as quite a technical challenge. "The batteries that we picked were available as two-volt cells," he explains, "and so we wound up stringing 150 together in a series string to build up to 300V. Then we combined four of those strings in a matrix connection to get the energy that we wanted for the vehicle. And that process of building up the battery pack had a lot of technical challenge in terms of balancing the cells and the maintenance of that pack and its state of charge."

By taking advantage of experience gained during the company's 1994 Neon Lite program, Chrysler engineers developed an aluminum unibody for the ESX that weighs about 2,800 lbs, some 600 lbs lighter than comparable conventional steel-bodied vehicles.

Basically a packaging exercise, Dodge Intrepid ESX enabled Chrysler engineers to become more familiar with some of the technologies needed for hybrid vehicles. They particularly sought to understand the vehicle integration issues that define the personality of the vehicle, rather than to evaluate specific component technology. "The major effort was in packaging and control strategy development, and it was very successful," says Lawrie. "We wound up with a working vehicle that we were able to drive around and demonstrate to people, and we learned quite a bit about integration issues."

Engineers also learned a great deal about the interactions of components in short time frames, and the response times of diesel engines versus their emissions characteristics. "We learned a lot about the compromises of making the engine/alternator/electric motor and batteries work together as a system so that it's transparent to the driver. And that's what we tried to do," Lawrie remarks.

GM's choices. Teams from General Motors and Ford have been working on hybrid technology since 1993 under contract to the U.S. Department of Energy. This program ends in 1998, and aims to produce a vehicle with twice the fuel efficiency of today's conventional vehicles. Engineers at GM's Research and Development center lead the GM hybrid team. The $151 million contract with GM set the goal of developing a production-feasible hybrid with a fuel efficiency 100% greater than that of a conventional car. After investigating the technical alternatives, the GM engineering team decided to develop a series hybrid. "GM is very interested in a low-emissions hybrid vehicle," explains Program Manager Larry Oswald, "and the easiest way to get low emissions is with a series hybrid drive." Both turbine and Stirling engines are candidates for GM's hybrid program. "They're both continuous combustion engines, and inherently very clean without aftertreatment," says Oswald.

Two test vehicles, Gen 1-1 and Gen 1-2, will help GM evaluate hybrid technology. Gen 1-1 uses a gas turbine, Gen 1-2 a Stirling. "I refer to both of them as powertrain mule vehicles," says Oswald. "They're Chevrolet Luminas. We've installed a new powertrain. Other than that there's not much change to the cars."

Optima Batteries Inc. of Denver, CO, supplies spiral-cell lead-acid batteries for use in GM's hybrid vehicles. Consisting of 60 six-volt batteries, the packs offer high power in a relatively small package. The batteries are improved versions of Optima's deep-cycle marine batteries. "We looked into both bipolar lead-acid and spiral-wound lead acid. This thin-cell lead acid from Optima is quite ideal for our battery pack," comments Oswald. "It's got some special additives and the geometry has been tweaked a bit to give us what we need. The additives give us the cycle life we need. And you can go to Optima and buy them. That's not true of a lot of other batteries."

Delco Electronics Division of General Motors supplies hardware for engine control, while the team at the GM R&D center does software and algorithm development. "You've got to be into that, otherwise you don't have control over your program," says Oswald.

Vehicle performance doesn't present a problem. In terms of vehicle acceleration, Oswald describes performance as identical to that of conventional cars or slightly better. The minimum fuel economy improvement objective is 50%. "But the goal of the program is to actually double the fuel economy of the Lumina. So we're trying to get a 50 mpg composite fuel economy vehicle before it's over," says Oswald. "Right now I'd say we're about halfway there."

Ford's way. Late in 1993, Ford Motor Company began a cost-shared, five-year $120 million hybrid propulsion systems development contract with DOE. Given its agreement with the other members of the Big Three, and the goal of improving fuel efficiency to twice that of a current production vehicle, Ford set out to study parallel hybrid prototypes.

Bradford Bates, manager, alternative power source technology, at Ford, explains that the deliverable vehicle for the hybrid program will be a modified Mondeo (the European version of the Contour). The car will be tied into Ford's work on the industry/government program called the Partnership For A New Generation of Vehicles (PNGV), which aims at producing cars capable of 80 mpg performance. "The hybrid vehicle program started here before the PNGV program," says Bates. "But once the PNGV program hit, we said the sensible thing to do is to target the powertrain size for that, not for a full-size, full-weight vehicle." Thus the decision to use a Mondeo rather than, for example, a Taurus.

Ford intends to use spiral-wound lead-acid batteries as the storage medium in its hybrid. Ultracapacitors and flywheels, in Bates' view, remain interesting research projects, not usable products. As for the diesel power plant, it will be a brand-new engine designed by Ford for the hybrid. Bates describes it as a conventional four-cylinder, direct-injected, compression-ignition engine. Ford is also developing its own control algorithms and software for the hybrid.

While outsiders can raise many questions about hybrids, Bates sees cost of components as the major hurdle. "You've got a real problem when you're trying to take the costliest subsystems in the vehicle and put two of them together. Cost, size, weight, and packaging," he remarks, "really constitute the greatest challenge."

What then lies in the future for Ford's hybrid program? "If you're pretty innovative about how you put some of this technology together, and get a few breaks in the technical world, it could be a cost-effective product that customers would love to have," says Bates.

Ford brought a non-driveable concept car to the 1996 Detroit Auto Show that embodies some of the work done to date under this contract. The series-hybrid Synergy 2010 used a rear-mounted 1.0-l diesel to drive a generator. Permanent magnet motors in all four of the vehicle's wheels would provide motive power, while a composite flywheel was set up to act as the energy storage system. Regenerative braking would capture energy and store it in the flywheel.

So where will these programs go? Hybrid technology may lead to production vehicles, or prove the automotive equivalent of a dry hole. Although hybrids aren't a new type of vehicle, the work now underway by the Big Three's talented engineers, and their subcontractors, will stimulate new technical developments. With the racetrack in mind, let's consider the hybrid a long shot, but worth a bet. After all, if this horse comes home first, the payoff could be lovely.

Driving Intrepid ESX

Charles J. Murray Senior Regional Technical Editor

From the moment I turn the ignition key of the Dodge Intrepid ESX I know I've entered another era in automotive history. It's impossible to miss the differences between this hybrid and conventionally powered vehicles. First, there's the rattle and whir of the car's pumps and fans. The ESX employs a pair of fans--one for the intercooler, another for the oil cooler. And it uses an oil cooler pump. The pump and fan noises aren't loud, and would certainly be eliminated in a production version of the vehicle. But they serve as a reminder that the ESX is a hybrid, simply because they are not initially drowned out by the roar of an inertial combustion engine.

When I shift the car into gear, the powertrain doesn't deliver a familiar purr. Instead, it whines. A pair of 125-hp Zytec electric motors propel the ESX, and they emit noise at a much higher pitch than does an IC engine. These two motors deliver surprising power, however. Chrysler engineers programmed the vehicle to go no faster than 50 mph during development. But its 0 to 50 mph acceleration seems competitive with that of many production vehicles.

After I grow accustomed to the sounds and feel of a hybrid, my spin around Chrysler's Arizona test track is uneventful--until the diesel engine suddenly kicks in. It starts on its own, without warning, and I can't help but feel surprised. Most drivers aren't prepared to hear the sound of a cranking engine while they're tooling along at 30 mph. But the ESX's diesel engine must run approximately 80% of the time to maintain the 300 to 320V bus voltage needed to power the motors.

Of course ESX's engineers aren't expected to do extensive Noise Vibration and Harshness (NVH) work on a concept vehicle. Undoubtedly the noises I heard will be dramatically reduced if a hybrid ever reaches production status at Chrysler.

But the driving experience, with or without extensive NVH, is undeniably different. The Intrepid ESX serves as a portent of the vast changes that may lie ahead for the auto industry.

Sign up for the Design News Daily newsletter.

You May Also Like