April 2021

APRIL 2021 AFTERMARKET 25 For accuracy of data transfer, the following conditions must be met. For a recessive bit, the LIN voltage must be greater than 80% of the battery voltage. For a dominant bit, the LIN voltage must be less than 20% of the battery voltage. See Fig.6. The slew rate or transition time between a high bit and a low bit is critical too for data transfer. Vehicle charging systems One particular system which has utilised LIN bus communication is the vehicle charging system. Fig.7 shows a conventional charging system layout fitted to an older vehicle. The D+ terminal is used as an exciter current for the rotor field winding. The rotor field winding is wired in series with the charge warning light. The W terminal was used for measuring engine speed by tapping off a stator phase. A layout of a modern system using LIN bus is shown in Fig.8. The internals of the alternator are fundamentally the same: Rotor poles Rotor field winding Stator Rectifier (used to convert Alternating Current to Direct Current) The exception being the Engine Control Module uses the LIN bus to control a transistor which varies the current flow through the rotor field winding to control the output voltage of the alternator. Next issue: In part two, Damien will address CAN Bus communication networks Fig 7 Fig 8