Tech Briefs - Tokyo Motor Show supplier technology
February 2002
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Delphi lithium-polymer battery
 The lithium-polymer battery from Delphi Automotive Systems works by moving lithium ions between the cathode and anode poles without causing any chemical reactions, so it is more efficient than a lead-acid battery. Click to enlarge |
Delphi Automotive Systems touts its lithium-polymer battery as the "ideal" power source for the upcoming generation of hybrid-electric vehicles. The battery is about half the size and weight of a conventional lead-acid battery, according to Gary Cameron, Chief Engineer of Delphi's Energenix center.
Perhaps more importantly for hybrids, the lithium-polymer battery is much more efficient than either lead-acid or nickel metal-hydride ones, so it discharges and recharges more readily than traditional batteries. This efficiency occurs because lithium ions are passed back and forth between the cathode and anode rather than from a chemical change in the battery, said Cameron.
This type of battery is referred to as a "rocking chair" battery because of the way the energy "rocks" back and forth within it. "There are no chemical reactions at either end of the battery, so it has very long life characteristics," said Cameron. "That is why lead-acid batteries tend to fail over time."
Delphi's battery has a specific power greater than 1400 W/kg (0.85 hp/lb), and a specific energy greater than 47 W•h/kg (0.029 hp•h/lb). The operating temperature range for the battery is from -40 to +70°C (-40 to +158°F).
The "polymer" portion of the name refers to the plastic layers within the battery that separate the plates. While most batteries bathe the plates in liquid electrolyte, lithium-polymer batteries separate them with porous polymer soaked in electrolyte. The result is a battery that can not leak corrosive liquid.
Both lead and nickel batteries are resistant to charging, so they get hot as waste energy is dissipated. That inefficiency limits how quickly those batteries can absorb power during regenerative braking. "Lithium polymers can take energy in and out without generating heat or losing energy," Cameron said. That means that hybrids can recover more energy from braking if they are equipped with lithium-polymer batteries.
The catch, as usual, is cost and high-volume production capacity. "Those are the challenges we are trying to take on now," said Cameron. "The lithium industry is fairly young and the supplier base is new."
The company does not want to discuss costs because it is in negotiations with potential customers, but Cameron said that he believes that lithium polymer can be on par with nickel batteries within three to four years after going into commercial production. Delphi's target for commercial production is 2003.
"It will probably never be as cheap as a lead-acid battery," he said. "If you can afford the size and weight and inefficiency of a lead-acid battery, that will always be a cheap solution."
The challenge for potential users is to determine the value of having a smaller, lighter battery that lasts longer. The lithium-polymer battery would probably last five to 10 years instead of only two or three years for a lead-acid battery used in a hybrid-electric vehicle. "You might replace the lead-acid batteries three times over the time you might use one of these," he said.
To boost production volumes, Delphi is looking at applications in non-automotive areas, too. The company is pursuing opportunities in the telecommunications and medical fields as well.
- Dan Carney
Goodyear crosses over with Fortera
 Tire test technician Terry Barrett adjusts Goodyear's Fortera tire on the Flat Trac, a testing device that measures lateral force on a moving tire (above), while technician Jason Thomas adjusts a microphone in Goodyear's anechoic chamber to monitor sounds emitted from the Fortera in determining the tread pattern's noise level (below).  |
Akron, OH-based Goodyear Tire & Rubber Co. has launched a new hybrid that it's calling a cross between a passenger-car and light-truck tire. The Fortera HL (Highway Luxury) Edition tire features a rugged appearance, but delivers car-like road manners. "Fortera HL is a lamb in wolf's clothing," according to Steve Myers, Marketing Manager for Light-Truck Tires. "It's refined ruggedness."
The timing for such a tire is appropriate, said Myers. Crossover SUV models—truck-like chassis built on car platforms—have attracted new customers to SUVs who otherwise might have stayed in a car or minivan. Myers said Fortera HL also is targeted at the growing luxury SUV segment.
Goodyear combined elements of its existing Wrangler truck, Integrity passenger car, and Eagle performance tires, offering what the company calls the "best of the best"—touring, all-season, and on- /off-road performance. Combining elements of existing brands, said Myers, "removes the need for brand extensions that don't quite fit the image" of a crossover SUV.
The company used emerging computational tools to balance competing tire attributes in traction, treadwear, and noise. This use of computer modeling enabled Goodyear to reduce time-to-market by half—to 18 months—for the Fortera and to develop each tire size according to cavity shape, tread design, and footprint geometrics (the hand-sized contact patch where tread and road meet), said Lead Engineer Kevin Legge. Historically, engineers would run these tools on the most popular tire size, then extrapolate the results to other sizes.
Goodyear engineer Karl Sundkvist said studying pressure-sensitive photography of a tire footprint is the first indication of its possible noise levels. Lateral grooves in the tread produce tones, and the tread pattern may compose a pattern noise. The combination of reverberations around a tire then determines its pitch. The engineer's role in tread design, according to Sundkvist, is to vary the size of the grooves and lug voids to produce a wide scale of frequencies that will minimize the chances that an annoying, recurring tone will be produced.
With tires, sound quality is determined inside the vehicle and in Goodyear's anechoic chamber, a room that suppresses echoes or reflections and allows tonal characteristics of noise to be evaluated. Key is engineering a tire that makes no distinct sound without sacrificing other performance characteristics such as ride, handling, and traction. "Because tread grooves are needed for wet traction and to resist slipping, we have to weigh their width and placement very carefully. Tire noise is important, but so is stopping ability and maneuvering on rain-slick roads," said Sundkvist.
 The Fortera tire from Goodyear features a hybrid Aquatred tread compound for improved dry and wet traction, handling, and braking. Full-depth blading and grooving in the tread pattern deliver non-evolving wear. Fortera, which means "strong" (fore) and "Earth" (tera), has a tread design that extends down the sidewall to give the tire a rugged appearance. |
The tire footprint is again used to study stress distributions and determine tread adhesion or slippage on the road surface, said Joel Lazeration, who heads a Goodyear team that studies treadwear. Loss of adhesion can result in loss of vehicle control or in small magnitude slippage that wears the tread.
"As a tire rolls forward, there's virtually no movement of tread in the footprint. But turn the steering wheel and tire slip quickly accelerates," Lazeration said. "Cornering produces considerable slip and wear. In fact, slippage and wear from a severe turn in a parking lot maneuver can equal hundreds of miles of straight-line driving."
Points on the tire tread are not slipping until they leave the footprint, except under extreme cornering, he said. Not surprisingly, the severity of the maneuver determines the rate of wear and the frequency of noise.
"If the tread of a P195/75R14 tire slips 0.025 mm (0.001 in) with each rotation, after 16,100 km (10,000 mi), you'll have 0.2 km (1/8 mi) of slippage; after 96,560 km (60,000 mi), it's 1.2 km (3/4 mi)," Lazeration said. "To me, it's absolutely amazing how long tires do last. Most people don't understand what tires go through."
Lazeration's team used advanced experimental mechanics techniques and modeling tools to analyze Fortera HL's footprint behavior. Test engineers also used the company-proprietary Goodyear Pressure Analysis System (GPAS), which measures pressure changes across the Fortera HL footprint, to identify the highest stress points in the contact area where tread slip may occur. Based on tire slip data, marketers provided Fortera HL with a 96,560-km (60,000-mi) treadlife limited warranty.
The Fortera HL tire is available in 16 sizes and is manufactured at Goodyear facilities in Valleyfield, Quebec, Canada; Union City, TN; and Lawton, OK.
- Jenny R. Hessler
