Operation
Operation
PDC System Operation
When the ignition switch is in position II and reverse gear is selected, the PDC sensors are automatically activated. The PDC ECU only activates the system if reverse is selected for more than 1 second. This avoids nuisance audible warnings when the gear selector lever is being moved between Drive and Park on vehicles with automatic transmission.
When the system is activated, the PDC ECU illuminates the indicator LED in the PDC switch, switches on the ultrasonic sensors and generates a single chime on the PDC sounder to indicate the system is active. If an object is range of the sensors when the system is activated, a series of audible warnings are emitted by the PDC sounder immediately.
If PDC operation is not required, it can be suspended temporarily by pressing the PDC switch. When reverse is deselected and subsequently reselected, PDC will automatically become active again.
Sensor Operation
The PDC ECU processes the distance readings from the ultrasonic sensors to determine if there are any objects within the detection areas. If there are no objects in the detection areas, there are no further audible warnings. If an object is detected, repeated audible warnings are produced on the PDC sounder.
The maximum detection range is 2000 mm (78.7 in). When an object is detected, the time delay between the audible warning tones decreases as the distance between the detected object and the vehicle decreases until, at approximately 370 mm (14.5 in), the audible warning tone is continuous.
After the initial detection of an object, if there is no decrease in the distance between an object and the central sensors, the time delay between the audible warnings remains constant. If an object is detected by one of the corner sensors only, the audible warnings stop after about 5 seconds if there is no change in the distance between the object and the corner sensor.
Detection Calculation
When operating in the combined transmitter and receiver mode, the sensor outputs a number ultrasonic pulses and receives the reflected echo signal. The ECU amplifies the received echo signals and compares them with a pre-programmed threshold to calculate the distance to the object. This is achieved by determining the elapsed time between the transmission and reception of the ultrasonic signal.
When operating in receiver mode, the sensor receives echo signals transmitted by an adjacent sensor. This mode is used to improve the accuracy of the system.
The detection cycle consists of the ECU operating one sensor in the combined transmitter and receiver mode and transmitting a number of ultrasonic pulses. The ECU then switches the transmitting sensor and the adjacent sensor(s) to receiver mode. After a short time delay, this sequence is repeated using a different sensor to transmit the ultrasonic pulse and continues until all four sensors have output an ultrasonic signal. This sequence is completed in 100 ms. The ECU uses several measurements of the same sensors to remove errors from the calculation.
If the object is directly behind a sensor, the distance is calculated using the time between the transmission and reception of the signal. If the object is positioned between two sensors, the ECU uses both signals to determine the correct distance using triangulation.
To perform the triangulation calculation, the ECU must know the distance between the individual sensors in the bumper. This information is stored in the ECU memory. From the received distance from each sensor and using the known distance between adjacent sensors, the ECU can calculate the minimum distance from the vehicle to the object.
When approaching several objects, the ECU recognises the distance from the vehicle to the nearest object.