Automotive engineers look to 42V architectures

DN Staff

March 12, 2001

7 Min Read
Automotive engineers look to 42V architectures

Detroit- Some day, vehicles may drive themselves. They'll autonomously watch for obstacles, control the throttle, pump the brakes, and even steer clear of collisions.

Automakers who share that vision, however, are convinced that it can't happen without the development of new electrical architectures. Most agree on a 42V platform that offers about three times as much electrical punch as today's venerable 12V systems.

Still, the changeover to higher voltages is fraught with obstacles. Many engineers are unconvinced of the need. Others fear that the costs of the technology will outweigh the benefits. And many have expressed concerns over implementation issues, such as safety and availability of compatible components.

Proposed 42V architectures could support flywheel-based integrated starter-alternators, which would provide more electrical power for vehicles.

That's why automotive engineers have formed consortiums to explore the issues, and eventually bring higher voltage systems into production vehicles. MIT's Consortium on Advanced Automotive Electrical/Electronic Components and Systems has teamed with automakers, and with the United States Council for Automotive Research to help standardize the emerging 42V architecture. "If everything looks good, and if we can show that 42V is beneficial, then we plan to have a totally 42V system in place by 2006," says Michael Matouka, staff development engineer for GM's Electrical Center. "But if we run into problems, it could be a lot later than that."

Debating the need. Proponents of the 42V system tout its multitude of advantages over 12V systems, inherently serving as a foundation for the use of flywheel-based, integrated starter-alternators. These devices can serve as an abundant source of electrical power for use by power-hungry features such as steer-by-wire, brake-by-wire, active suspension, electromechanical valve actuation, so-called "start-stop" systems, and heated seats and windshields.

Engineers view drive-by-wire as the most critical to the future of the automobile. "By-wire systems are an enabler for autonomous vehicle control," says Mark DePoyster, chief engineer for advanced chassis systems for Delphi Automotive (Dayton, OH). "They're a stepping stone to allowing vehicles to do things independent of the driver."

For automotive designers, however, by-wire technology represents a huge technical challenge. To make them a reality, engineers say they've got to convert from conventional hydraulic-based steering and braking systems to electric motor-based units.

As they look to the future, automotive engineers say that the power dilemma posed by by-wire and other up-and-coming technologies is so great that it eventually won't make sense to stick with today's 12V architecture. Engineers say that drive-by-wire vehicles could easily have peak power requirements in excess of 5 kW, especially if they use catalyst heaters or windshield heaters, in addition to the usual array of lights, fans, and multimedia devices.

That's a big problem for the vast majority of today's vehicles, which use generators or alternators that typically produce only about 1-2 kW. For that reason, most automakers say they are looking at employing integrated starter-alternators (also known as integrated starter-generators) from such companies as Siemens Automotive, Bosch Automotive, and Delphi Auto- motive Systems. Such systems claim to boost a vehicle's electrical power by a factor of seven to ten times, ultimately supplying as much as 12 kW.

The systems are accompanied by higher costs, in several forms. "Power is not free," says Matouka of GM. "A 42V system enables you to handle power, and control it more efficiently. But the power still has to come from your fuel tank."

Matouka points out that every additional 350 watts used by the vehicle results in a loss of about one mile-per-gallon of fuel economy. As a result, automakers want to tread lightly in the realm of higher power and make sure that consumers really want it.

Carmakers' current plans call for incorporating their first 42V systems in dual-voltage schemes, in which some of a vehicle's features would use 42 volts, while most others would still work off the 12V battery.

The issues. Even as they plan dual-voltage systems, however, engineers are puzzling over the solutions to the accompanying technical issues. Key among these is the standardized development of components, such as connectors, fuses, and semiconductor devices.

Even more important, consortium members are concerned about safety during the changeover from 12V to 42V systems. "Most of today's systems are protected against 24V jump-start, but not a 42V jump-start," says Paul Nicastri, project leader for 42V architecture and drive development for Ford.

As a solution, engineers are trying to standardize the design of 42V cables and battery terminals that can't be connected to 12V systems-even by the most determined consumers.

At the same time, the consortia are working with semiconductor makers on standardized logic and power devices. But, engineers say that the effort has a long way to go. "The convergence from 12V to 42V is not yet clear," notes Jim Spangler of ON Semiconductor. "We will build, but they have to tell us what they need."

However, most members of the automotive technical community are convinced that the changeover will occur eventually. The 12V system, they say, has served for more than a half-century, and most engineers doubt that it could serve for more than another decade, especially as the industry begins to consider vehicle autonomy. DePoyster of Delphi says, "I can put a 12V system in a drive-by-wire vehicle and make it work, but it's debatable whether I can do it economically and practically. That's why 42V systems will probably be a requirement for tomorrow's vehicles."

Tomorrow's electrical loads

Today's best luxury vehicles typically offer about 2 kW of electrical power, while more economical vehicles offer less. If automakers add some of the following features, tomorrow's vehicles will need to generate more power.


Peak power draw (kW)

Electric AC


Electromechanical valve actuation


Catalyst heating


Windshield heating




Heated front seats




Power seats


Rear defrost


Electric fan


Power windows




ABS pump


Engine coolant pump


Table courtesy of Vishay Siliconix.

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