Gateways

Gateways

Introduction

A gateway (GW) is an interface. It connects different bus systems within the vehicle's electrical system. It provides a means of ensuring the exchange of information in spite of differences in the rates of data transmission on the individual bus systems. Diagnostic access to the individual control units from a central point is made possible by the gateway.

The gateway modules used in the E65/E66 are the Car Access System (CAS), Control Display (MCGW-MOST/CAN gateway) and the Central Gateway Module (ZGM).

Method of Operation







The data transmitted by the various bus systems is received by the gateway. At this point, transmission rates, data and priority levels of the individual messages are filtered and temporarily stored if necessary. This requires a non-volatile memory.

Using gateway rules and conversion tables, the gateway converts the messages as required by the various bus systems concerned. The messages are then passed to the various bus systems via which they reach their ultimate destinations (recipient control unit). If necessary, messages that are relatively less important are held in the gateway's memory and sent later.

Overview of E65/E66 gateways




Examples of the Function of the Central Gateway Module (ZGM)







The DME and DSC control units both place messages on the PT-CAN. Those messages are received by the Central Gateway Module from the PT-CAN. The buffer memory on the Central Gateway Module temporarily stores the messages from the PT-CAN.

They are converted by the Central Gateway Module according to specific gateway rules and conversion tables for the K-CAN System Bus. As the K-CAN System Bus is slower than the PT-CAN, the two messages are joined together and are sent out as one message. The messages reach their destinations (IHKA/Kombi) via the K-CAN SYSTEM bus.


Electronic Fuel Pump Control

The DME calculates the delivery rate of fuel required on the basis of the vehicle's operating status. The figure calculated is sent in the form of a message to the SBSR (right B-pillar satellite).

The original message (PT-CAN signal) is converted by the ZGM to a byteflight message (fibre-optic signal). From the ZGM, the message is passed via the byteflight to the SIM, which passes it to the SBSR.

The electronic evaluation unit integrated in the SBSR converts the signal to a PWM signal. That PWM signal controls the electronic fuel pump (EKP).The required fuel delivery rate can now be provided by the electronic fuel pump.







Windscreen Wiper Function







The driver operates the windscreen wiper switch (SWS) to initiate a wiper system function. The wiper switch is plugged directly into the Steering Column Switch Center Module (SZL).

The SZL module analyzes the signals from the wiper switch and calculates which wiper system function has been selected by the driver. That information is placed on the byteflight in the form of a message.

The Safety Information Module (SIM) receives the driver's instruction from the SZL and passes it on to the ZGM via the byteflight. The ZGM receives the message from the SIM and passes it on in its role as "gateway control unit" to the Wiper Module (WIM) via the K-CAN S. The wiper module performs the action requested by the driver (e.g. wipe or wash).

Optimum Charging Controlled by Power Module (PM)







In order to drain as little energy as possible from the battery (particularly in the winter), the idling speed is increased at an early stage. This ensures that the battery charge level is kept high. If the charge level falls below the minimum required to be able to start the car, the idling speed is increased.

The PM detects that the battery charge level is low and places a message to that effect on the K-CAN P. The Car Access System (CAS) passes the message on to the K-CAN S. The ZGM receives the message from the CAS and passes it on via the PT CAN in its role of "gateway control unit".

The DME module receives the request to increase the engine speed over the PT-CAN. The DME passes that request on via the LoCAN to the Valvetronic control unit (VVT). The Valvetronic control unit controls the output stage for the valvetronic motors to increase the engine idle speed accordingly.

Examples of CAS Gateway Function

Seat Adjustment







The driver operates the seat adjustment switch. The command is processed by the switch block and passed via a 3-core data line to the Center Console Control Center Module (BZM).The BZM places the message on the K-CAN S for the Car Access System (CAS).

The CAS passes the message on in its role as "gateway control unit" to the driver's seat module (SMFA) via the K-CAN P. The seat module activates the required seat adjustment motor via its output stages.

Electric Windows (FH) and Sunroof (SHD)







Using the convenience open function, the windows and sunroof can be opened by pressing the open button on the remote control. The commands from the remote control are received by the Car Access System (CAS).

The CAS places the message on the K-CAN P and the K-CAN S. All 4 door modules (TM...) receive their messages from the K-CAN P, while the sunroof receives its message from the K-CAN S. The modules then activate their output stages to open the windows and sunroof. If the button on the remote control is released while the operation is still in progress, it is then immediately halted. In order to re-activate the convenience open/close function, the appropriate button on the remote control has to be pressed again.

Example of CD Gateway Function

PDC







The audible PDC warning is output via the audio system speakers. If the car gets close to an obstacle when the PDC is active, this is signalled by the relevant sensor to the PDC control unit via the bi-directional data line. The PDC control unit calculates the distance from the obstacle and places that information on the K-CAN S.

The Control Display (CD) receives the message and passes it on in its role as "gateway control unit" to the MOST bus. The Audio System Controller (ASK) receives the message from the CD and calculates from it the required signal tone and frequency. On the basis of that calculation, the ASK activates the mid-range speaker in the appropriate corner of the vehicle. The audible signal is superimposed (mixed) over the current audio sound (radio, CD, etc..).