The growing challenge
As electronic systems in cars become more complex, reliability becomes harder to achieve. The more complex a system, the more failure points it offers--and today's separate systems are being networked together in ever more complicated arrangements. With point-to-point wiring giving way to control and power buses, the possibility of massive failures that affect the whole car, not just individual functions, arises. New functions often require new technologies, which in the beginning may be less reliable than more developed ones.
The growing reliance on software raises more issues. As every computer user knows, software is far more likely than hardware to fail, and rebooting is hardly practical in a sharp downhill turn. Then, too, automotive software modules must communicate and coordinate with one another.
For hardware, too, the environment is more demanding. Space constraints place circuits near heat sources. Sensors may be bathed in transmission fluid at peak temperatures nearing 165 degrees centigrade.
"Back in the 1980s, before antilock braking systems, the highest junction temperature we had to rate for was 150 degrees centigrade," said Randy Frank, an automotive marketing manager at International Rectifier (El Segundo, Calif.). But those systems required higher reliability, so makers of power semiconductors began qualifying their products for 175 degrees centigrade to prevent gradual shifts in operating parameters or failure of internal wire bonds, he explained.
Underhood temps may rise further, driving semiconductor makers toward devices qualified for 200degrees centigrade operation. Should even higher temperatures be required, liquid-cooling systems may be added to electronic modules. As a last resort, device makers may shift from silicon semiconductor materials to more costly silicon carbide, because of its stability at higher temperatures.
Nor is that all. More electronics means more risk from externally generated electromagnetic interference (EMI) and from EMI generated by systems in the vehicle that are adjacent or interconnected. The effects can be quite serious: on certain highway overpasses in Europe, the engines of some vehicles have been shut off when their control units encountered high EMI levels from, among other things, high-voltage lines beneath the roadway, reported David Ladd. He is communications manager at Siemens VDO Automotive (Auburn Hills, Mich.), which operates an electromagnetic compliance testing lab. "These problems must be identified and corrected before the vehicle goes into production," he emphasized.
Because of these risks, the auto industry is re-evaluating its requirements and testing for new sources of EMI. Suppliers are increasingly relied upon to develop expertise in managing potential risks during the early stages of engine control unit development, noted Ladd. And the growing use of optical-fiber databuses is eliminating one possible source of EMI problems.
Voltages will rise in the next decade or so, as vehicles move up from 14 V provided by today's 12-V car battery to 42 V from a 36-V battery, or to dual voltage systems. But voltage spikes, surprisingly, may become less troublesome.
Today's worst spikes are load dumps that occur if connection is suddenly lost between the alternator and battery. Rare as they are, the resulting transients must still be guarded against. In 12-V systems "today, with MOSFETs, we may use 55-V devices," said Frank. Tomorrow's 42-V alternators will incorporate transient suppressors, probably avalanche diodes, permitting the use of 75-V or 100-V devices. Fuses and relays may have to be redesigned. Connectors certainly will need redesigning, because disconnecting loads from a running system, which causes only brief sparks at 14 V, can cause sustained arcing at 42 V, and so erode contacts and even start fires.
Cost constraints add to the interest of an engineer's life, too. When you're deploying devices by the millions, saving a few nickels per car can make you a hero--as long as those savings don't up the expense of warranty service.
Longer warranties, owed in part to the increased use of electronics, make reliability still more important. But the electronics also can make repair more difficult, encouraging vehicle owners to have more of their service done by authorized agencies, who will report defects to the carmakers.