Collision Avoidance and Parking Assist Systems: Description and Operation

Park Distance Control 2 (active PDC)

Function
The Park Distance Control supports the driver on maneuvering into and out of parking spaces. It helps to avoid damaging the vehicle when parking in tight or awkward spaces.

The control module measures cyclically the distances between each converter and a possible obstruction.

On approach, the distance between the vehicle and the nearest object is signaled to the driver proportionally by means of a tone signal generator. The shorter the distance to the obstruction, the faster the tone sequence. A distance below approx. 25 cm is signaled by a continuous sound.

The acoustic signal is switched on when driving alongside a wall in order to avoid a long continuous sound. The distance warning is reactivated if the vehicle moves closer to the obstruction.

While driving, the electronic control module monitors correct operation of all ultrasonic converters.

Diagnosis takes place via the I-bus/K-bus.

The reversing gong is controlled by the PDC control module.

Components

PDC2 control module
The PDC2 control module activates the ultrasonic converters and evaluates the received echoes. It monitors the converters to ensure they are functioning correctly and controls the tone signal generator.

Active ultrasonic converters
In the PDC2 system, the converters are active, i.e. an electronic module is fitted in each converter. Each converter has its own power supply and its own additional data link to the PDC control module.

The converters operate both as transmitters as well as receivers. The received echoes are converted into a digital signal in the converter which is then sent via the data link to the PDC2 control module.

All converters are electrically and mechanically identical. Special retaining fixtures at the mounting locations ensure the converters are properly adapted to the bumper.

If the minimum detectable distance increases impermissibly, a fault code is stored in the fault memory. This may also be attributed to dirt, water, ice, snow.

IMPORTANT:
- Particular care must be taken before starting extensive troubleshooting to ensure that the converters are fitted correctly in their retaining fixtures and are free of dirt. During troubleshooting there should be no obstruction closer than 40 cm to the converter.
- On vehicles like the R50 with automatic transmission, the status of the reverse gear is not transferred via the bus in the emergency driving program. This means that the PDC is not automatically activated on reversing. Before troubleshooting, check the automatic transmission.

Tone signal generator
The tone signal generator signals the distance to the driver acoustically and provides a warning if faults occur.

Series E38/39/53: Speaker
Series E46: Gong

Reversing gong
An acoustic signal is output via the gong (Japanese version) for as long as reverse gear is engaged. This signal is interrupted immediately if the PDC detects an obstruction within its measuring range and issues a distance warning.

Vehicle signals
The control module receives the following information on the current status of the vehicle via the I-bus/K-bus: Vehicle speed, reverse and trailer operation.

System-related characteristics

IMPORTANT: For this reason, the assessment of obstacles, even with PDC, is the responsibility of the driver, particularly when detection of objects approaches the physical limits of ultrasonic measurement.

System-related problems may arise even under optimum preconditions. It is possible that a nonexistent obstruction is signaled or an existing obstruction is not signaled.

In the following situations it is possible that the PDC signals an obstruction although one does not exist:
- heavy rain
- converters extremely dirty, iced up or when they are covered with snow
- in the case of ground echoes from extremely rough road surfaces, grasses
- in large closed rectangular rooms with smooth walls (e.g. underground car parks)
- when the converters are not fitted correctly in their support brackets

In the following situations it is possible that the PDC does not signal an obstruction:
- low objects with corners and sharp edges
- When the acoustic signal is switched off while driving alongside a wall while parking. This also applies when the vehicle approaches an obstruction - but further away - at a different angle.