Automotive Electronics


When I did research on Analog IC companies I discovered that the automotive segment was a significant and growing market. It has often been said that the electronic percentage of an automobile has been growing rapidly. This was brought home to me on my way home from Easter diner. A temperature warning light began flashing and my “on-board computer” said that I needed to add coolant. I pulled off the highway to a service station and did as advised. Back on the highway the system was acting funny so I pulled over and called AAA for a tow to prevent any major damage. This week's commentary gives an overview of automotive electronics in the areas of safety, theft deterrent, telematics, GPS and so forth.

Safety When we are driving we should be concerned about our safety, the safety of our passengers and the safety of others whether driving, cycling or walking. According to the National Highway Traffic Safety Administration (NHTSA) motor vehicle fatalities are the leading cause of death in age groups 3 through 33. The table below shows the ranking of motor vehicle crashes as the cause of death compared to 68 other categories.
The graphs below show the fatalities and injuries due to motor vehicle crashes. Motor vehicle fatalities account for 94% of transportation deaths which includes planes, boats, and trains.
Some interesting statistics: In 2003 occupants of cars accounted for 46% of fatalities, occupants of light trucks 29%, motorcyclists 9% and pedestrians 11%. In 2003 occupants of cars accounted for 60% of injuries while occupants of light trucks accounted for 30%. Alcohol was involved in 40% of all fatal crashes. 34% of the time blood alcohol concentration was above 0.08. Fatal crashes as function of speed limit was 20% for 65 mph and higher, 32 percent for 55 mph and 18% for between 45 mph and 55 mph. More accidents occurred on Saturday and on Sunday than on any weekday. More accidents occurred in the afternoon than other times of day. In 40% of fatalities another car was hit, 31% of the time a fixed object was hit and 16% of the time a moving object such as a pedestrian.

As depressing as these absolute numbers are, the situation has been improving. The number of fatalities per 100 million VMT (Vehicle Miles Traveled) has dropped 73% from 4.74 in 1970 to 1.48 in 2003. Similarly the fatality rate per 100,000 population, per 100,000 licensed driver and per 100,000 registered vehicles has dropped 43%, 57% and 65% respectively over the same period. The number of injuries per 100 million VMT (Vehicle Miles Traveled) has dropped 41% from 169 in 1988 to 100 in 2003. Similarly the injury rate per 100,000 population, per 100,000 licensed driver and per 100,000 registered vehicles has dropped 29%, 30% and 35% respectively over the same period.

Seat Belts

Although seat-belts are principally mechanical systems there is an electronic component that alerts the driver by beeping and flashing a symbol on the dashboard that signal a passenger has not buckled their seat belt. The history of the seat belt goes back to the 1800s. However the three point seat belt (shoulder and lap belt) goes back only to 1958.

In 1966, the Highway Safety Act and the National Traffic and Motor Vehicle Safety Act were passed. The legislation authorized the federal government to set and regulate motor vehicle and highway standards, and also created the National Highway Safety Bureau, which later became the National Highway Traffic Safety Administration (NHTSA). In 1968 this led to the publication of the first Federal Motor Vehicle Safety Standards (FMVSS) which established a minimum safety code which all vehicles sold in the U.S. must meet.

In 1970, a Federal Motor Vehicle Safety Standard proposed that all vehicles manufactured after January 1, 1973 be equipped with an automatic restraint mechanism (air bag or seat-belt). The auto industry fought against the regulations and the rule was eventually rescinded by NHTSA in 1981. In 1984, NHTSA proposed that automatic restraint systems be required in new vehicles unless two-thirds of the U.S. population was covered by a mandatory seatbelt law by September 1989. This came to pass well before the time limit expired.

NHTSA currently coordinates a national campaign to increase seatbelt and child safety seat use called "Buckle Up America" and recently coordinated "Click It or Ticket," a high-profile law enforcement activity that relied on increased checkpoints and citations to increase seatbelt use.

In 1986 when I was a citizen of Massachusetts, the state government passed a mandatory seat-belt law. Citizens including a popular radio talkshow host campaigned on Libertarian grounds to put the issue on the ballot. There were also concerns that seat-belts would prevent people from escaping if their vehicle went underwater or caught on fire. The law was soundly defeated. After a period the legislature passed another mandatory seat-belt law but classified enforcement of that of that law as a “secondary enforcement” whereby an officer must pull you over for another traffic violation first, before enforcing the seat belt law. Most states have similar “secondary enforcement” laws. In May 3003 the Massachusetts Legislature, by a tie vote, refused to upgrade the seatbelt law to a primary offense. Neighboring New Hampshire is the only state with no mandatory seat-belt law. According to a recent survey, the national rate of seatbelt use is 79 percent, but in Massachusetts it is only 62 percent. Massachusetts placed 47th of 47 states surveyed.


Airbag patents go back to the 1950s. In the 1970s both General Motors and Ford placed airbags into a small fleet of automobiles. Throughout the 1980s, manufacturers resisted installing airbags. They argued that safety did not sell vehicles and were worried about the additional costs. In the early 1990s Lee Iaccoca changed his opinion and promoted the use of airbags in a TV campaign. By 1992, most manufacturers had airbags on the driver side and by the mid-1990s most had airbags on the passenger side as well. Side air bags and head curtain airbags are becoming increasingly popular.

Airbags have been found in rare instances to cause serious or even fatal injuries when someone is very close to, or in direct contact with an air bag module when the air bag deploys. Such injuries may be sustained by unconscious drivers who are slumped over the steering wheel, unrestrained or improperly restrained occupants who slide forward in the seat during pre-crash braking, infants in rear-facing child seats, and even properly restrained drivers who sit very close to the steering wheel. The recommended margin of safety between driver and airbag is 10 inches. In 1998 NHTSA authorized vehicle owners to get on/off switches installed for one or both air bags in their car if they (or other users of their car) fell into one or more of specific risk groups, e.g. vehicle has no back seat. Federal Motor Vehicle Safety Standard (FMVSS) 208 now requires that manufacturers certify their airbags would not inflict certain “injuries” to a 5'9” dummy (both belted and unbelted) in a crash test into a solid barrier at speeds up to 30 mph and frontal angles up to 30 degrees.

Airbag systems consist of a crash detector, an igniter, an inflation system, the bag itself and a diagnostic system to test system readiness. Air bags are designed not to activate during sudden braking, while driving on rough or uneven pavement or in the event of a minor collision. Sensors detect a crash by measuring deceleration, the rate at which a vehicle slows down. One of the simplest designs employed for the crash sensor is a steel ball that slides inside a smooth bore. The ball is held in place by a permanent magnet or by a stiff spring, which inhibit the ball's motion when the car drives over bumps or potholes. However, when the car decelerates very quickly, as in a head-on crash, the ball suddenly moves forward and turns on an electrical circuit, initiating the process of inflating the airbag. Today sensors are more likely to use a MEMES accelerometer. For example Analog Devices manufactures an inertial sensor which converts differential capacitance into voltage.

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