Vehicle interior aerials and vehicle exterior aerials

Depending on the vehicle equipment, the control unit function for the Comfort Access system may be incorporated in the Car Access System control unit (CAS), the front electronic module (FEM) or the Body Domain Controller (BDC). Comfort Access combines high levels of functionality and comfort. The vehicle can be opened and started without actively using an ignition key.

With Comfort Access, an ID transmitter is required instead of the usual remote control. Alongside the normal functions of the radio remote control, the identifiers have a radio receiver. The radio receiver allows the ID transmitter to reply to a radio signal from the interior aerials and the exterior aerials for Comfort Access. The aerials for Comfort Access are transmitting aerials.

Various aerials are required for communication with the ID transmitter (series dependant):

  • Interior aerials:
    • Interior aerial, centre console, front
    • Interior aerial, centre console, rear
    • Interior aerial, rear window shelf
    • Luggage compartment aerial
    • Driver's side luggage compartment aerial (also called: left luggage compartment aerial)
    • Passenger side luggage compartment aerial (also called: right luggage compartment aerial)
  • Exterior aerials
    • Exterior aerial, driver's side
    • Exterior aerial, passenger's side
    • Bumper aerial

The radio signals from the ID transmitter are received by the remote control receiver and transferred to the CAS control unit or FEM control unit or BDC control unit. Further data processing as well as the corresponding function execution take place in this control unit.

The Car Access System (CAS) or the front electronic module (FEM) or the Body Domain Controller (BDC) controls entry into the vehicle (central locking system) and access to vehicle functions (e.g. key identification, electronic immobiliser, engine start enabling). The CAS control unit or the FEM control unit or the BDC control unit is the master control unit. It is therefore this control unit that issues the release.

The following functions can therefore be performed using Comfort Access:

  • Access authorisation:

    Opening the vehicle or luggage compartment without active use of the ID transmitter

  • Drive authorisation:

    Engine start without active use of the ID transmitter

  • Locking authorisation:

    Closing the vehicle without active use of the ID transmitter

Functional description

A connection between the ID transmitter and the CAS control unit or the FEM control unit or the BDC control unit is established using the exterior aerials and the interior aerials.

Changes in the door handle status are registered by the sensors in the outside door handle electronics and transmitted to the CAS control unit or the FEM control unit or the BDC control unit. The ID transmitter is requested to identify itself via an aerial signal from the CAS control unit or the FEM control unit or the BDC control unit. The aerial signal is transmitted by the CAS control unit or the FEM control unit or the BDC control unit via the exterior aerials.

An ID transmitter belonging to the vehicle must be located in the transmission range of the external aerial in order to respond to the request. The Car Access System (CAS) or the front electronic module (FEM) or the Body Domain Controller (BDC) also checks whether the ID transmitter has access authorisation for the vehicle. If this is the case, unlocking of the doors or boot lid/tailgate is triggered.

The request to open the boot lid/tailgate of the vehicle is triggered by pressing the boot lid/tailgate pushbutton. If the vehicle is locked, a search for an ID transmitter via the exterior aerials then takes place.

When the luggage compartment is closed, authentication is requested from the ID transmitter belonging to the vehicle via the luggage compartment antennas. If an ID transmitter in the luggage compartment replies and no other ID transmitter outside the luggage compartment replies, the boot lid/tailgate is opened again. This prevents an ID transmitter from being accidentally locked in the vehicle. If another ID transmitter is found outside the luggage compartment, the tailgate remains closed. The ID transmitter that is in the luggage compartment is blocked as a possible transmitter when the vehicle is next unlocked.

If the start/stop button is pressed and the brake pedal is operated, the vehicle interior aerials search for an ID transmitter located inside the vehicle. Operation of the aerials is carried out by the CAS control unit or the FEM control unit or the BDC control unit. If an ID transmitter belonging to the vehicle is inside the vehicle, the ID transmitter is authenticated. If the ID transmitter has start authorisation for the vehicle, the CAS control unit or the FEM control unit or the BDC control unit enables starting.

The request to lock the vehicle is activated by pressing an outside door handle. The request is only processed if the driver's door is closed. The door from which the request is being made must also be closed. A search for an ID transmitter is then carried out in the external area of the vehicle via the exterior aerials. If a valid ID transmitter is found outside the vehicle, the vehicle is locked. To implement the lockout safety device function, this is followed by a search for an identifier in the passenger compartment. If the identifier that was authenticated at the outside door handle is also detected in the passenger compartment, the vehicle is unlocked again. Other identifiers belonging to the vehicle can remain in the vehicle.

The assignment of an ID transmitter to a certain interior aerial or exterior aerial of the vehicle is carried out automatically. Here, the aerials of the vehicle are activated successively with delays by radio signals. The time delays create a time window for each aerial in which an ID transmitter found by this aerial can reply. The position of the ID sensor can be assigned to a transmitting antenna via the reply of the ID transmitter during this time window. After receiving a radio signal from the assigned aerial of the vehicle, the ID transmitter returns a coded radio signal via the integrated transmitter. The function is enabled after receiving the correct information in the remote control receiver in the vehicle. In this way, without actuating the remote control, access authorisation and/or start authorisation are granted.

In unfavourable situations, it may not be possible to find the ID transmitter inside the vehicle. In such cases, the CAS control unit or the FEM control unit or the BDC control unit initiates a Check Control Message on the instrument panel. When a corresponding message is received, the ID transmitter needs to be held against the marking on the steering column. This is where the ring aerial can be found. The ring aerial is used for communication between the transponder chip (in the ID transmitter) and the CAS control unit or FEM control unit or BDC control unit. This allows this control unit to issue the start enable after successful identification. Within 10 seconds of placing the ID transmitter against the marking, press the START-STOP button. The engine starts, providing that the brake pedal (automatic transmission) or clutch pedal (manual gearbox) is depressed at the same time.

The following illustration shows an example of an interior aerial.

Index Explanation Index Explanation
1 Interior aerial 2 three‐pin plug connection

The following illustration shows an example of an exterior aerial.

Index Explanation Index Explanation
1 Exterior aerial 2 three‐pin plug connection

Structure and inner electrical connection

The radiation emitted by the interior aerials is spherical in form. This covers the entire interior.

The exterior aerials cover a range of a radius of approx. 1.5 m around the aerials

The aerials transmit on a frequency of 125 kHz.

All the radio signals are encrypted and thus protected against unauthorised access.

All interior aerials and exterior aerials are connected to the CAS control unit or FEM control unit or BDC control unit. Subsequent data processing and appropriate execution of the function takes place on the CAS control unit or the FEM control unit or the BDC control unit.

Unlike the interior aerials, the exterior aerials are equipped with a water spray protected connection.

Index Explanation
1 Interior aerial or exterior aerial

Pin assignments

Pin Explanation
SIG Signal line
SIG2 Signal line 2

Nominal values

Please note the following specified values for the interior and exterior aerials:
Size Value
Maximum signal voltage 56 V
Temperature range -40 to 80 deg C

Diagnosis instructions

Failure of the component

If an interior aerial or exterior aerial fails, the following behaviour is to be expected:
  • Comfort access inoperative
  • Fault memory entry on the CAS control unit or FEM control unit or BDC control unit
  • The engine can still be started

Function check of the component

A function check of the interior aerials or exterior aerials can be carried out using the diagnosis system.

Path: Function structure > Body > Locking and security functions > Comfort Access

 

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