Plastics will survive high-volt jolt

DN Staff

October 1, 2001

8 Min Read
Plastics will survive high-volt jolt

With the transition to 42V electrical systems looming just ahead, the automotive industry may be in for a rough ride as electromechanical components gradually replace mechanical ones throughout the vehicle. But from a plastics standpoint, at least, the road to higher voltages promises to be a smooth one-with just a few bumps as physical property requirements grow more stringent. "We'll test all of our existing materials first," says Susan DeGrood, a materials engineering supervisor for Visteon Corp. (Dearborn, MI). "But we expect that we'll still be able to use many of them."

But even if 42V technology doesn't exactly revolutionize plastics selection, it can still exert some influence. By allowing automakers to pack cars with all kinds of high-power electromechanical systems and accessories, 42V technology threatens to set off a shift toward thermoplastics whose heat resistance exceeds current design standards. And because higher voltage electrical components have an increased chance of arcing, 42V systems will also put some upward pressure on dielectric-strength and flame-resistance requirements.

By fostering a range of new electromechanical systems, 42V technology opens up new design opportunities and may help speed the pace of metal-to-plastic conversions.

Heating up. Of the three material properties affected by 42V, heat resistance poses the biggest hurdle for current crop of underhood thermoplastics. In theory, bumping up the voltage of automotive electrical systems could reduce amperage. "From a pure electrical standpoint, temperatures should drop," says Jim Puscas, automotive manager for GE Plastics (Southfield, MI). In a 14V system, current already contributes to as much as "a 40C lift" above the underhood temperatures that plastic parts have to withstand, Puscas continues. "If environmental temperatures stay the same in the 42V, this temperature rise due to current will be less," Puscas says.

But many electrical components will never see that current reduction, according to Phil Chapekis, Visteon's manager of higher voltage vehicles. "Once you add all that power to vehicle, people will find a way to use it," he explains. "That drives the current back up." Indeed, the reason for going to 42V in the first place is to enable high-power electromechanical systems that will eventually handle the steering, braking, heating, cooling, and power-generation tasks. The hungriest of these systems need about 3 kW of power, significantly driving up the amperage-and, by extension, the temperature requirements.

As OEMs phase in more and more of these high-power systems, the temperatures requirements for underhood plastic components will "inch up gradually," says John Solenberger, a development planning manager for DuPont Engineering Thermoplastics (Wilmington, DE) and the company's representative to the MIT 42V Consortium. What's more, Solenberger adds the 42V technology fosters a shift toward electromechanical systems that are not only powerful but also smaller than their mechanical predecessors. "As a general principle, smaller and more powerful means hotter," he says.

With those two factors in mind, Solenberger foresees temperature requirements moving up as much as 20C, so that components today engineered for temperatures up to 155C would ultimately see increases to as high as 175C. DeGrood, too, sees the temperature requirements for a growing number of plastic components creeping up to 175C.

Some of the new electromagnetic vehicle systems with 42V don't need to go under the hood. As an example, electric air-conditioning units don't access to the engine, so they can be located anywhere.

A couple of factors could mitigate temperature increases. Components already stepped down to low voltages will experience the current reduction Puscas mentioned, reducing heat requirements. "There will be a few areas where the current goes down," Chapekis agrees, citing 3V automotive electronics as one example. Keeping a lid on heat can also be a design objective, one that avoids the need to switch to pricier plastics for the sake of heat performance. "We work hard to limit temperature increases to contain costs," DeGrood notes.

Aside from increasing temperature requirements, the move from 14V to 42V systems will require materials that help reduce the threat of arcing. "We need to look at materials with improved dielectric strength," says DeGrood. This need for electrical insulation will be especially pronounced if 42V reduces wire diameters and ushers in smaller, thin-walled connectors, according to Puscas.

Some materials developments have already addressed this need for electrical property improvements. GE, for example, has recently developed new PBT grades with enhanced dielectric strength. DuPont has recently introduced a new translucent nylon aimed at 42V fuse applications. "It has better electrical properties and higher temperature resistance than PES," reports William Hsu, DuPont's technology vice president. And Solenberger cites a more general move from straight nylon to the company's Zytel DMX, which has better dielectric strength.

Yet the need for dielectric strength improvements at this point remains more of an incipient trend than a specific requirement. One reason is that 42V's much-touted potential to halve wire diameters may not come to pass in every electrical application. Chapekis maintains that "a significant number of wires are already at their mechanical limit for bonding," which in turn limits further reductions in connector size. What's more, Solenberger says the fight against arcing also relies as much on the connector's mechanical design-which can promote tighter physical connection to keep sparks at bay-as the material's electrical properties.

The fight against arcing may also ratchet up automotive industry's demand for flame resistant materials. Today's 14V systems use these materials sparingly-on a few power distribution boxes, Puscas reports. "But if there's higher potential to spark, there's more need for flame retardant materials," he says. On the downside, flame retardant materials cost as much as 10 to 20% more than comparable standard resins.

Better properties? No sweat. Despite its influence on physical property requirement, 42V technology probably won't trigger any sweeping changes in plastics selection since current off-the-shelf or modified plastics can surmount gradual up-ticks in property requirements. After all, automotive applications-whether 42V or the current 14V-hardly represent the worst case for engineering thermoplastics: A wide range of industrial components have long had more stringent requirements for life cycle, heat performance, dielectric properties, and flame resistance. "A lot of the development and systems testing work has already been done for more challenging industrial applications," Solenberger notes. Puscas agrees: "42V doesn't represent a huge stretch for existing plastics portfolios. We have the ability to borrow some resins from non-automotive portfolios and modify others."

Where current materials do fall short, the solution will be more a matter of grappling with cost rather than developing brand new materials. DeGrood foresees an increasing reliance on costlier high-performance materials-such as high-temperature nylon, and even LCP in place of standard nylon and PPS. "Right now, we use LCP precision parts for its combination of flow and mechanical properties. If temperature requirements creep up, we might end up using it for heat resistance too," she says.

As much as changing property requirements matter, the biggest influence of 42V technology may come in the form of new applications. All the brand new designs for steering, braking, and power-generation systems favor metal-to-plastic conversions that aren't feasible in retrofits. And the inherent design freedom of plastics ties into the ability to move some of the new electromechanical vehicle systems-like air conditioning units, for example-out of the engine compartment. "There will be many opportunities for plastics," DeGrood says.

More material effects

Plastics won't be the only materials affected by the move from 14 to 42V. Susan DeGrood, an engineering materials supervisor for Visteon, points out that the heat, electrical, and ignition property requirements that affect plastics will also have a similar effect on adhesives, wire coatings, and thermal management materials too. Forty-two-volt technology's reliance on high-frequency electromechanical systems places a different set of demands on magnetic materials.

"New types of motors, fast solenoids, alternators, and motor-generators must be able to operate with minimum energy losses at high frequencies in order to achieve critical power densities," says Dr. David Lashmore, technology vice president at Mii Technologies (West Lebanon, NH). But high-energy losses associated with traditional magnetic material technologies have traditionally limited operating frequencies. "The major energy loss mechanism in the more traditional electromagnetic devices, at higher frequencies, is heat dissipated by the eddy current generation," Lashmore explains.

To address the high frequency needs of 42V systems, Mii recently developed new magnetic materials. This family of alloys consists of spheroidal particles encapsulated with an inorganic ferrite type insulator for very high frequencies, a new ceramic encapsulated flake material for bush dc motors and alternators to replace laminations, and sintered products for the lower frequency applications.

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