Distance measurement and indication: Notes
The control module receives information from the DICE when reverse gear is selected. The control module accordingly activates the distance sensors. The sensors emit and receive ultrasound signals, sent in a preset pattern, see DISTANCE SENSORS .
Continuous data from the sensors regarding the closest object is processed by the control module so that the correct signal is sent to the SID, to then be sent to the driver. The information is sent to the SID over the I bus.
The driver receives information from the SID regarding the closest object behind the vehicle in the form of pulses of sound of varying frequencies. The first indication is given when there is an object 1.8 m behind the vehicle. The frequency of the signal is then 2 pulses per second.
The frequency of the signal increases the closer to the object the car comes. The signal changes as follows:
- 1.8 - 1.3 m: 2 pulses/second
- 1.3 - 0.9 m: 3 pulses/second
- 0.9 - 0.3 m: from 5 to 12 pulses/second in close steps
- 0.3 m: continuous tone
If the driver reverses at a speed greater than 1.8 m/s (6.5 km/h), the SPA is of no benefit since the indication of distance is limited to 1.8 m behind the car. The driver has therefore only 1 second to react and bring the car to a halt. In addition the braking distance must be taken into account. For the SPA to be of benefit, moderate speeds must be maintained.
If the distance sensors are covered by ice, snow or dirt, their function will be impaired. In such cases the distance sensors should be wiped clean.
When reversing on a surface that is highly reflective to ultrasound, the system can indicate the distance to the ground instead of the closest object behind the car. This can occur, for example, on unmade roads or other uneven surfaces. Testing of the function of the SPA must be carried out on an even surface with no objects placed on the ground.