Understanding Automotive Multiplex Networks: CAN Bus and LIN Bus Explained
Automotive Multiplex Networks
Introduction to Networks and Protocols
A network consists of terminals connected by transmission routes and rules for communication. Key elements include sender, receiver, language, and transmission channel. A protocol is a set of established rules that both senders and receivers must understand for communication within a network.
Bus Systems in Vehicles
A bus system facilitates information transmission and is categorized by its data transmission speed. Common bus systems in vehicles include:
- CAN bus: A 2-wire bus operating at 5V or 12V, used for various functions like comfort and infotainment.
- LIN bus: A single-wire bus operating at 12V, often used for simpler tasks like windshield wipers.
- Other buses: Additional buses with varying speeds and functionalities may be present depending on the vehicle.
Multiplex Networks in Vehicles
Multiplex networks are digital communication systems where connected elements share a single line (bus) for data and signal exchange. The typical configuration involves a central unit connected to multiple buses with varying speeds based on real-time requirements. Comfort and body elements utilize slower buses, while driving-critical elements (traction and safety) and information systems use high-speed buses for faster response times.
Bus Communication and Interconnection
Communication occurs via one or two electrical cables or optical fibers, minimizing the need for extensive wiring. Electronic control units with microprocessors interpret messages and control associated sensors and actuators. Real-time data exchange protocols ensure efficient communication.
Interconnecting different networks through multiplex control units enables information exchange between stations while reducing wiring complexity. High-speed networks manage traction and motor systems, while medium or low-speed networks handle comfort and body functions. This system optimizes strategies, enhances reliability, and reduces cabling costs.
Multiplex Systems for Comfort and Convenience
Comfort and convenience devices are typically managed by a central unit interconnected with the multiplex network. Information sharing across the network determines the activation of various actuators. Since different systems operate at different speeds, power electronics ensure compatibility. A unit called UCH or gateway, often integrated into the instrument cluster, connects to the main CAN bus lines.
CAN Bus (Controller Area Network)
CAN bus is a serial communication protocol for digital information exchange between electronic control units. It operates serially, transmitting data bits one after another. The transmission functions as a multi-master system, where all subscribers have equal rights to send data to the bus.
CAN Bus Applications:
- Coupling Control Units: Real-time applications like engine control units and ESP (Electronic Stability Program) regulate vehicle movement with transmission speeds between 125 kbit/s and 1 Mbit/s (High CAN).
- Body and Comfort Electronics: Multiplex applications control and regulate body and comfort components like air conditioning, central locking, and seat adjustment with speeds ranging from 10 kbit/s to 125 kbit/s (Low CAN).
- Mobile Communication: Communication with components like GPS navigation, telephone, or audio equipment with central display and control units aims to minimize driver distraction with speeds up to 125 kbit/s.
LIN Bus (Local Interconnect Network)
LIN bus operates at a maximum speed of 20 kbit/s and connects actuators or sensors to corresponding control units. Orders are transmitted unidirectionally from the master control unit to the slave sensor or actuator. LIN bus systems are typically localized within a specific area (e.g., roof) and are also referred to as “local subsystems.”
Data exchange between different LIN bus systems occurs via a control unit using the CAN bus. LIN bus utilizes a single-wire bus configuration.
Current CAN and LIN Bus Lines in Vehicles:
- CAN Bus: Traction, comfort, infotainment, and diagnostic box.
- LIN Bus: Steering wheel, windshield wipers, and alarm.
The transmission speed for CAN bus traction and diagnosis is 500 kbit/s, while infotainment and comfort operate at 100 kbit/s.