System Activation Logic; Principle Of Distance Measurement; Obstacle Distance Information - Fiat TIPO Handbuch

S
YSTEM ACTIVATION LOGIC
At key-ON, the system is ready for operation in less than 0.5 seconds. Park assist functionality is
activated at Key ON and engine running and Reverse Gear engaged.
P
RINCIPLE OF DISTANCE MEASUREMENT
Measurements are timed by the ECU. The ECU controls the sensors, which generate a sequence of
ultrasonic pulses.
Upon being reflected by an obstacle, the signal is captured by the sensor, amplified, converted into a
digital signal and transmitted in this form to the ECU.
The ECU compares the signal coming in with the one given out and determines the time elapsed
between signal emission and echo reception (Time of Flight). This value is converted into distance and
communicated to the driver in the form of audible/visible signals.
Time of flight is measured by means of ECU clock frequency. The ECU is fitted with a counter whose
value is recorded both at the start of the measuring process and when the echo signal is received. The
difference between these two values gives the time taken by the pulses to reach an obstacle and
return to the ECU. Since the sound propagation speed in air is known, it is possible to determine the
distance of an obstacle from this difference, with an accuracy of ±1 cm.
Each sensor has a dedicated counter register.
System operation is checked during each measuring cycle. If the echo signal is not disturbed, the ECU
determines the shortest time of flight among the measures of all sensors. This is compared with the
previous measurements to determine whether the vehicle is moving closer to or away from an
obstacle.
Position and type of obstacle are determined on the basis of each measuring process performed and
the distance between sensors. Due to this information, actual distance is determined with greater
accuracy in critical conditions.
Ground reflections are ignored unless they have the characteristics of an obstacle.
System have to monitor the occlusion of the sensor by snow, mud or Ice. If an occlusion is detected,
ECU communicates to the costumer the not available status of the system.

Obstacle distance information

The ECU processes the information supplied by the 4 sensors and consequently activate the
acoustical warning and the display to inform the driver of the presence of obstacles.
The tone emitted by the loudspeaker/radio speaker informs the driver that the vehicle is approaching
an obstacle beginning with the first approach distance (the distance at which the system starts
producing intermittent signals).
The time duration of the tone is fixed, while the pauses between tones are directly proportional to the
distance from the obstacle: pulses emitted in a quick succession indicate the presence of a very close
obstacle.
A continuous tone tells you that the obstacle has reached the second approach distance (the distance
at which the signal becomes continuous).
Distances are measured along the perpendicular to the bumper.
The audible signal is cut out immediately if the distance increases with more than the hysteresis
distance (10-15 cm).
The tone cycle remains constant if the distance measured by the inner sensors is constant, while if
this condition occurs for the external sensors, the signal is cut off after 3 seconds (stopping of warning
during manoeuvres parallel to walls).
Warnings are not emitted in the presence of a trailer.
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