Sensors make cars smarter

October 06, 1997

Under the thin metal skin of a modern automobile, a multitude of sensors gathers information so essential that without it the vehicle won't run. The sensors continuously monitor hundreds of vital signs such as ignition and valve timing; exhaust quality; throttle position; intake air temperature and pressure; wheel slippage; tire inflation; steering-wheel position; and even linear and lateral velocity and acceleration.

Next generation automobiles--those due to hit the road in the next five years--will have sensors that do even more. By the year 2002, as you cruise down the road in your new car, sensors will surreptitiously test the condition of the engine oil and battery charge, measure the real-time combustion pressure in each cylinder, calculate the instantaneous torque of the engine, determine the size and position of front-seat passengers, and even scan the road ahead with radar to look for hazards. Engineers are developing or testing sensors to perform those tasks and more today.

Presented here are examples of a few near-term automotive-sensor developments.

Automobiles present engineers with enormous opportunities for future sensor development.

Chassis controllers. A sensor area receiving a great deal of attention falls under the general umbrella of "vehicle stability enhancement." Cadillac calls its entry into this category Stabili-TRAK. And it includes Systron Donner's (Concord, CA) automotive quartz rate sensor, or AQRS. The sensor incorporates the company's patented Gyro-Chip TM technology to measure the car's yaw rate. By combining this measurement with those for steering angle and lateral acceleration, StabiliTRAK can compare actual vehicle dynamics to the driver's intentions, and then gently apply the ABS and traction-control systems to "nudge" the car back in to the expected line.

The GyroChip consists of a microminiature double-ended tuning fork fabricated via photolithography from piezoelectric quartz. An oscillator powers one of the tuning forks--the drive tines--at resonance. And as long as the GyroChip is stationary, the other set of tines--the pickup tines--do not oscillate. As soon as the chip is rotated, however, the pickup tines respond to Coriolis force and begin to oscillate perpendicular to the drive tines and with a magnitude that is proportional to the rotational rate. An amplifier and demodulator convert the signals from the pickup tines to plus or minus DC voltage that is then used by the StabiliTRAK system.

Systron Donner shipped AQRS sensors for the entire production run of 1997 Cadillacs without a single return from the factory, they say. With quality seemingly solved, the goal now is to cut the price to make the sensor more attractive to less expensive cars. "We've got the leading technology," says Phil Lees, automotive sales engineer, "and we're increasing our factory automation to penetrate further into the market."

They'll face competition along the way. Several other companies are offering or pursuing yaw-rate sensors, including Delco Electronics (Kokomo, IN) which revealed to Design News that its engineers are busy developing a micromachined silicon yaw-rate sensor of their own.

Vehicle stability systems such as StabiliTRAK also need a way to measure steering angle. One such entry into this arena comes from ITT Automotive (Auburn Hills, MI). While it does not

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