Cars are getting smarter and smarter. For example, the 1996 Cadillac
Concours, Oldsmobile LSS, and Chrysler LH platform cars all have substantially
more electronic content than the 1995 versions. But the head of the class is
arguably the 1996 Lincoln Continental. Smart features include a sound system
that shuts down when the voice-activated cellular phone is in use and a personal
protection system that uses global satellites to summon emergency aid.
As a whole, the car's electronics system is faster than that of an Intel 486DX microprocessor-powered PC, according to Ford officials. The electronic engine-control module (EEC-V) can execute 1.7 million instructions per second.
The Continental's smarts come from microprocessors and microcontrollers. (A microcontroller is a microprocessor with added peripherals such as on-chip memory.) One or more of these chips is in each of the car's modules, which control one or more subsystems.
A module is a system of integrated components and assemblies that workers can install as a unit. The Continental's modules include a variety of microprocessors and microcontrollers from different manufacturers. They also contain memory to record failures or impending failures, such as a misbehaving sensor or an open circuit.
Cars aren't necessarily gaining more and more processors and modules. Designers are using more powerful processors and using them to control more than one function. "In most cases the microprocessor isn't being used all the time, so we're able to combine functions, such as the antilock-brake and traction-control systems," says Lincoln-Mercury Project Design Engineer Susan Young. "The benefit is you're fully utilizing a very powerful microprocessor, and you're reducing cost and packaging space. You're also saving wiring and weight and using fewer components."
Take the bus. Another way microprocessors let designers save weight and improve reliability is by communicating via a bus.
The Multiplex Communication Network (MCN) is the multiple-module operating system of the Continental. It consists of a common 2-wire bus that interconnects all the modules. The bus is redundant, so if one of the two wires breaks, the other wire will let the system continue to operate. Modules communicate via the Ford-proprietary Standard Corporate Protocol (SCP), which complies with SAE's J1850 industry standard. Messages can contain control, status, or diagnostic information, as well as operating parameters.
"We have over 200 signals that go between 10 modules," says Young. One benefit is reduced wire count, which improves reliability because you have fewer hard-wired connections. "We share signals between the modules on the 2-wire bus. By doing that you eliminate the wire that the signal represents."
The bus controls features ranging from dimming the instrument panel to a sophisticated traction-control system. Designers tried to utilize the bus as much as possible and make it as efficient as possible to get the full benefit. In fact, the technology let them excise 150 wires weighing about 8 pounds.
Other bus advantages:
Because sensor data is shared, there is no need for multiple sensors performing the same function.
A data link connector under the steering column serves as the diagnostic interface. Through this port, a service-station computer uses the bus to talk to and interrogate all the modules.
The Continental's modules control so many functions that we don't have the space to list them all here. Instead, here in a nutshell is what the major modules control:
Lighting Control Module--interior and exterior lighting, automatic lamp shut-off, panel dimming, anti-theft features, chimes, trunk release, and battery saver.
EEC-V Powertrain Control Module--electronic fuel pump, limited-return fuel system, shifting, ignition coils, hydraulic-fluid pressures, and more.
The audio system modules have their own protocol--the audio corporate protocol, or ACP. This protocol is local and runs on this smaller network because the audio system is so interactive. The controls are up front on the dash, but the electronics and amplifier are in the back of the car along with an optional CD player and cellular phone. The network connects to the SCP through the Front Control Module.
"The radio is like a gateway between the protocols. It lets you do diagnostics of the audio system," notes Young.
Satellite safety. The 1996 Continental's RESCU (Remote Emergency Satellite Cellular Unit) system includes a microprocessor in the car's trunk. The system is linked to the cellular phone through the audio bus. Pushing a button on the overhead console automatically places a call to summon roadside assistance; pushing another button calls for help in cases of crime or medical emergencies. The system pinpoints the car's location within 100 feet through a network of satellites called the Global Positioning Satellite (GPS) system and sends that data as part of the cellular call. The processor receives GPS data from an antenna and is linked to the cellular phone.
Ford Automotive Components Division developed Lincoln RESCU, which it claims is a worldwide auto manufacturer first. Look for this safety feature--as well as many of the microprocessor-controlled "Gee whiz" features--to proliferate in the years to come.
Electronics will rule the road
Today, 10 to 12% of the total value of a car is in its electronics, estimates David Cole, director of the Office for the Study of Automotive Transportation at the University of Michigan. "By the early part of the next decade, we expect the figure to be up in the area of 20%. That's considerable growth."
These electronic components include microprocessors and microcontrollers; sensors, which detect some kind of variable; and actuators and transducers, which take a signal from the processor and convert it into an action.
Microcontrollers in cars will increase in power and take on more functions, says Cole. But engineers are also looking at putting some of the intelligence right into actuators and transducers. An example is Analog Devices' ADXL50 micromachined accelerometer, which is essentially a completely specified acceleration-measurement system on one silicon chip. The device is a popular choice for front-seat air-bag deployment modules.
The chip has a surface-micromachined movable element as the sensor. Because the sensing element measures less than 0.5 mm2, the chip has plenty of room for signal-conditioning and self-test circuitry. The complete chip takes up only about 9 mm2.
Another place electronics will be going is into transmissions. "By 2005, we expect 95% of transmissions to use electronic control; versus about 65% in 1994," says Cole.
Still another growth area for electronics is multiplexing, which is using one bus to handle the signals for a car's entire electronics system. Cole's preliminary data predict an increase in multiplexing systems from about 3% of today's vehicles to 25% of 2005-model-year vehicles.
"The advantage of multiplexing is the potential for increasing simplicity," he notes. "For example, you may have 50 wires going in and out of the driver's door--rear-view mirror, seat controls, power window control. With multiplexing, you could have just a couple of wires to transmit the signals." As multiplexing catches on, look for designers to consider using fiber-optic cable instead of twisted-pair wire to implement buses.