Cruise control has evolved
By Brad Bergholdt
Published: Friday, Oct. 18, 2013, 9:07 p.m.
Question: How about a tutorial on the GM adaptive cruise control system? Specifically, I'm curious as to whether the GM system uses engine or mechanical braking, or combinations thereof, in decelerating vehicles when encountering slower traffic. When decelerating, the brake lights are not activated. Doesn't this pose a hazard to following traffic?
Also, I understand other manufacturers use a laser system rather than millimeter-wave radar. Are other technologies involved? I have a 2008 Cadillac DTS and love it.
— Roland Marquis
Answer: We've come a long way from the first cruise control system found on the '58 Chrysler. Conventional cruise control systems use throttle only to try to balance operator-desired speed versus actual vehicle speed. On downgrades, vehicle speed may overrun the desired set speed.
Adaptive cruise control can have many names and is typically found on luxury vehicles, because of its fairly high cost. It is trickling down and may become standard equipment on all vehicles, given time. Adaptive cruise control, or ACC, uses radar, LIDAR (laser) and cameras to perceive vehicles ahead and their behavior. Should you come upon a slower-moving vehicle with ACC engaged, engine throttle is reduced and, if need be, brakes are applied to maintain your desired following distance. Brake lights are deployed when your deceleration rate reaches a calculated threshold.
ACC employs a complex network of vehicle modules to manage things smoothly. Your Caddy uses a distance-sensing cruise control module, located behind the grille, to ping the roadway ahead and classify objects. A yaw sensor tells the system whether you are driving straight or turning. Brake and accelerator pedal sensors indicate possible override input, and your selection of desired following distance is considered. Participating modules include the engine control module, transmission control module, electronic brake control module, instrument panel module and radio amplifier. The system is smart enough to predict brake temperature and downshift the transmission as needed for engine holdback. Should the radio amplifier not work, ACC will stand down, because audible warnings wouldn't be available.
Radar-based systems are the most popular by a wide margin. In some cases, cameras provide additional object classification, coupled with GPS to determine road and intersection characteristics. These super-smart systems can predict the car ahead with a flashing turn signal will probably turn off at the exit — yikes!
Collision mitigation is a logical spinoff of ACC capabilities and is available on many systems. Even with cruise control disengaged, these systems will detect threats ahead and warn you, disengage throttle and apply brakes as needed to avoid a collision.
Let's hope drivers don't become complacent; no system can be expected to function perfectly every time.
In the future, we'll move from autonomous to cooperative systems, where vehicles will communicate with each other. This will allow tightening of following distances and less reactive stop-and-go maneuvering, speeding traffic along more smoothly.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Email him at email@example.com.
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