This is all about distance measuring, it doesn't matter whether it's shown in the display or by holding the distance when using cruise-control. The ultra sonic measuring however, is more suitable for short distances, e.g., when parking the car, infra red is for the medium distances of up to 50 meters and electro-magnetic radar or LIDAR is suitable for much greater distances.
The system with distance cruise-control is also called Adaptive Cruise Control, which already brings us to radar (76 GHz). Under 50 meters, radar can, as a rule, not cover the entire width of the road and needs the support of other systems. However, let's first deal with the setting up of this system.
Because three aerials transmit and receive at a certain frequency, and their beam is bundled by an ancillary lens from -5° to +5° horizontally and -1,5° to +1,5° vertically, the required precise basic adjustment of the system is achieved, without which the observation of the traffic lane for a distance of up to 150 meters, would not be possible.
This setting up, is exactly what helps the system shown in the above pictures. In picture no. 1, somewhat older equipment is depicted. Newer diagnostic facilities have several panels, perhaps three or four. As one can see in the further pictures, they're all fitted with spirit-levels, which enables them to be optimally set up.
This ACC-setting up must be done after all and any changes have been made to the suspension, e.g., after an axle-alignment (if an adjustment has been made) and of course, if the car has been damaged in an accident or if the ACC-unit has had to be replaced. It is not orientated on the bodywork but always on the suspension, namely, from the rear- over the front axle towards the wall with the panels.
After that, the following procedure is relatively simple. The system generates a beam in a straight line, then determines the deviation of the returning beam. Depending on the manufacturer, it can be adjusted according to the available data or automatically.
The analysis of the reflected frequencies during driving, can not only give information concerning the distance to the car in front, but also its speed and even about a possible off-set and about further vehicles up front. Together with lane-recognition through other systems any disturbance from vehicles in the other lane(s), can be pretty much excluded.
Possible problems may be aggravated through the ever decreasing braking distances, which in the past, were considered to be 2 meters per second at speeds between 30 and 180 km/h. In the meantime, we've reach the value of 4 meters per second at a speed of between 0 and 200 km/h. In this case the rougher reactions which occur e.g., just before a roadworks, in sharper motorway curves or slipways can be noticed.
As you can see, a precise setting up is of paramount importance. The possibility of irritated braking caused by the system, can be overcome by accelerating slightly, e.g., when overtaking. Actually, the normal use of the indicators when changing lanes, can ease the problem as well. Of course the distance to be kept from the vehicle ahead is variable, however, and for safety reasons, some consider it to be too great ... 10/14