Rain Sensor (AIC Automatic Interval Control)

Automatic Interval Control (AIC)

Function
With the aid of a rain sensor, the automatic interval control (AIC) system senses water or dirt on the windshield and activates the windshield wipers accordingly.

The AIC consists of an optical element bonded on the windshield, to which an electronic evaluator is connected.

The system is active as of ignition lock position 1. The wiper/washer switch must be set to the first stage (intermittent wipe setting).

The wiper motor is activated by the general module of ZKE. The electronic evaluator sends the instruction to activate the wiper motor via the K-bus to the general module.

Optical element
The optical element is adhered to the windshield behind the rear-view mirror. It consists of a glass body (prism) which routes the beams emitted by infrared diodes at a defined angle to the windshield. The light beams reflected by the windshield are routed by the optical element to the infrared receivers.The optical element is heated by a heating element to ensure condensation cannot form on it.

The optical element is bonded together with the windshield in a special process such as to guarantee the physical properties of the system. This bonding process cannot be carried out in the workshop. Therefore when replacing the windshield, a special windshield with the optical element already bonded to it must be used.

Electronic evaluator
The electronic evaluator is connected to the optical element by means of a catch mechanism.

It contains the electronic components as well as the infrared diodes and infrared receivers.

The instruction to activate the wiper motor is given via the K-bus interface.

Functional principle
Water on the windshield is detected on the basis of the reflection of infrared beams.







When the windshield is dry, all infrared beams which are emitted by the infrared diodes "S" and which hit the windshield at a defined angle are reflected in full by the windshield and therefore reach the infrared receivers "E" also in full.







A proportion of these beams is deflected by a drop of water on the windshield (in the area of the infrared diodes). These beams no longer reach the infrared receivers "E".

In this way, the extent to which the shield is wet (or dirty) is determined dependent on the light intensity of the infrared beams and, if necessary, an instruction is sent via the K-bus to the general module of the ZKE III to activate the wiper motor.

Operation
To switch on the automatic interval control, the wiper/washer switch must be moved up to the first stage (intermittent wipe) and the ignition lock must be switched to position 1 or 2.

The automatic interval control system then controls the wipe intervals. If the windshield is constantly wet (steady rain) the system activates continuous wiping in stage 1.

The wiper stage 2 can still only be set by way of the wiper switch (third stage).

Automatic interval control remains switched off if terminal R is switched off and on when the wiper switch is set to intermittent wipe. It is not activated before intermittent wipe mode is switched off and on.

The sensitivity of the rain sensor can be varied by means of the knurled wheel on the wiper/washer switch.

NOTE: There is no driving speed-dependent control of the wiper stages (reset of wiper stages when vehicle is stationary). In addition, the automatic fold-back function of the wiper motor has also been omitted on the E38 series (see functional description for windshield wipers).

Operating conditions
The following conditions are necessary to ensure trouble-free operation of the rain sensor:
- The windshield must not be damaged (stone chips, scratches) or must not be heavily soiled (finger marks, streaks, wax film) in the area of the rain sensor.
- The wiper blades must wipe the windshield dry without streaks.

To ensure trouble-free operation, the windshield should be cleaned regularly with a suitable wax-removing cleaning agent. The wiper blades should be replaced regularly.

Initialization
The reflection characteristics of the windshield depend on a large number of factors. In addition these characteristics also change as the windshield ages.

During the initial wipe cycles, a new electronic evaluator determines the degree of reflection of the windshield and stores this data in its non-volatile memory. From this point on, this data is constantly adapted to the windshield which is subject to a certain degree of aging over the course of time.

The stored adaptation values can be deleted with the diagnostic program (service functions). Renewed adaptation (initialization) to the windshield can then be carried out.

The initialization procedure is described in the program sequence.

Initialization is necessary:
- After replacing the windshield
- When a used electronic evaluator is installed in a vehicle