PDC (Park Distance Control)
PDC (Park Distance Control)
An active PDC system is used in the MINI. It features four sensors in the rear bumper with the control unit and acoustic transmitter located in the right side of the luggage compartment.
Purpose of the System
The PDC system assists the driver during parking maneuvers and helps to avoid damage to the MINI when parking in tight or awkward spaces. Despite the PDC assessing obstructions it is still the responsibility of the driver to make proper decisions especially when detection of objects approaches the physical limits of the system.
System problems may occur even under optimum preconditions. It is possible that a nonexistent obstruction is signaled or an existing obstruction is not signaled.
System Components
The PDC system consists of:
- PDC Control Unit.
- Active Ultrasonic Sensors (4).
- Audio Generator.
PDC Control Unit
The control module is located in the rear right hand quarter panel. The control module is the microprocessor that controls and monitors all of the functions of the system.
The primary tasks of the control unit are:
- Actuation of the ultrasonic sensor and reception of the echo.
- Monitoring the sensor for correct function.
- Evaluation of the echo pulses received.
- Interference suppression.
- Actuation of the audio generator.
- Monitoring the lead wire of the audio generator.
- Evaluation and monitoring of the control inputs.
- Monitoring the power supply.
- Management of the diagnostics and test function.
- Bus communication.
- Control of the echo threshold values.
The PDC control module is linked via the K-bus with the other control modules connected to this bus.
Active Ultrasonic Sensors
By means of a digital signal, the ultrasonic converters are set by the control module to either a combined sending and reception operation or to a pure reception operation:
- In the combined operation, the converter first sends out a packet of ultrasonic pulses and then receives the echoes which are reflected by an obstruction within its reception range. These echo signals are amplified and compared with a threshold that is programmed specifically to the vehicle.
- In the area of pure reception, the converter receives the pulses that have been emitted by the adjacent converters of the same system.
By the evaluation of these signals in the control module, the location resolution and the physical shape of the obstruction are better recorded.
Audio Generator
The audio generator acoustically reports the distance to the obstruction to the driver and warns him/her of a potential problem.
Principle of Operation
With the ignition ON the microprocessor of the control module performs a self-test and checks the peripheral components for correct functioning. If the microprocessor does not recognize any faults, the system is operational after approximately one second. After a successful self-test the PDC control unit is ready to function, and will be switched on when reverse gear is selected for longer than one second. The system is automatically deactivated when the transmission is taken out of reverse gear.
The microprocessor specifies the chronological time frame of the clearance measurements:
- PDC control unit transmits a "send" command via the signal lines to the sensors in accordance with a fixed specification.
- The sensors then send an ultrasonic oscillation packet.
- The echo, which has been reflected from an obstruction, strikes the sensor after a time period that is proportional to the clearance.
- The echo signals are amplified in the sensors and changed into digital signals. These signals are then sent back to the microprocessor in the PDC unit via the signal line.
- The echo transmission times are determined and the clearances of the individual sensors to the obstruction are calculated from this.
The quartz frequency of the microprocessor serves as the time basis for the measurement of the echo transmission time. The clearance between the converter and the obstruction is calculated from the transit time between the beginning of the transmission and the output of a low signal (echo reception). The position of the obstruction and the minimum clearance between the vehicle and the obstruction are derived from the calculated clearances of the individual converters and from the measured clearances by the 2 respective adjacent converters.
An acoustical warning is provided via the acoustical transmitter if the vehicle is in reverse gear and it approaches an obstruction to within 0.6 m for the outer sensors and 1.5 m for the center sensors. The clearance message consists of audio pulses with a duration of 75 ms. The pause between the audio pulses becomes shorter in proportion to the distance as it diminishes. Below the minimum clearance of 0.25 m, the audio sequence converts to a continuous tone. If the clearance to the obstruction remains constant, the center converter maintains the last actuated audio repetition frequency. For the outer converters, the clearance warning is switched off after 3 seconds in this event in order to indicate that the vehicle is moving next to a wall and not approaching an obstruction.
Diagnosis
Faults, which are determined, are filed in the fault memory and may be read out by means of the DISplus. The fault memory is formed by means of the EEPROM of the microprocessor so that the filed data is also maintained when the system is in an inactive status.