1) How can the ACC determine the current speed of the vehicle? The radar provides closing speed but not the speed our car is actually travelling.A query can be sent to the Engine Control to determine current speed of ACC car. 2) Does the radar also send a "target lost" signal? If not, how can the ACC determine when the target is no longer ahead?
See Answer 1 on 9/21/01 listing. 3) What is the range of the radar - 400ft or 500ft? The constraints say 500ft, but the answer to question 5 from 9/22 states 400ft.
You should go with the more conservative value (e.g., 400 ft.) 4) How often does the radar update its information?
See Answer 2 for 9/19/01 questions. (Hardware and Radar are being considered synonymously.)
1. As soon as a lead vehicle is detected, and there is a positive closing speed, apply maximum braking power until the speed of the lead vehicle is matched. In other words, brake immediately.
2. As soon as the lead vehicle is detected, calculate the deceleration required to bring the car to a speed matching the lead vehicle at a point at least 2 seconds behind the lead vehicle. In other words, brake gradually just hard enough to end up at the 2 second distance.
3. When the lead vehicle is detected, calculate the distance from the lead vehicle that some deceleration less than maximum, says 9 ft/sec-sec, will bring the car up behind the lead vehicle something slightly more than 2 seconds behind the vehicle. In other words, don't brake until you have to. Maybe the lead vehicle will speed up or turn.
Choice 1 is probably not very good because it will result in the brakes being applied frequently and hard. Choice 2 seems OK, and is probably most safe if the deceleration required is constantly reevaluated, but leaves open the chance that another driver will cut in front of the system car. This occurs because the car is gradually slowing down quite a distance from the lead vehicle.
Choice 3 most closely mimics what a human would do, but is least safe. Once the distance for braking is set, if the lead vehicle slows significantly, the system may not have enough braking power to adjust.