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In-vehicle networking is creating a quiet revolution in automotive technology—over the past two decades it has eliminated the unwieldy wiring harnesses once used for control circuits, and increased vehicle safety and reliability. Networking has made possible dozens of comfort and convenience features such as antilock braking systems (ABS), airbags, engine and transmission control, and electric power steering.
Before in-vehicle networks, point-to-point control was the rule, which meant that every system was connected to its control point by a separate wire. Each new wire added complexity and potentially decreased reliability.
In the future, automobile networks will simplify the operation of control systems and simultaneously expand features by attaching more and more control modules into high-speed data networking backbones. Networks will provide drivers with operational data such as lane departure warning systems and (slippery) road condition advisories that will make them better drivers. At the same time, networks will allow drivers and passengers to enjoy their journey more than ever before with entertainment and area information.
Hybrid car needs
In-vehicle networking is a mission-critical component of environmentally friendly automobiles such as hybrids, which would not be possible without fast, reliable inter-communication between hybrid-drive components. Hybrids include a battery system, which means battery charging and management. The architecture also requires precise coordination between the electric motor and the gasoline engine—adding up to a lot more control and a lot more communication. In-vehicle networks are the only answer.
Networking basics
In-vehicle networks provide fast, reliable, and efficient communications for the control of virtually all mechanical and electric automotive systems—everything from windshield wipers to braking and suspension, to heating and air conditioning systems. Networks also deliver information from all over the vehicle to the dashboard where drivers can check fuel level, engine temperature, and other indicators at a glance.
Instead of a thick wiring harness composed of dozens of wires (and weighing 50 kg (over 100 lbs)), networks implement a "common carrier" approach by sending control information for numerous systems over just a few wires.
Like any network, the information stream is organized according to a network protocol to assure that a particular system actuator can identify which data packet is intended for it and act accordingly. From a functional perspective, the four basic components of an in-vehicle network are:
The transport medium—usually copper wire
Transceivers—integrated circuits (ICs) dedicated to the critical task of transmitting and receiving information
The network protocol—software that provides identification criteria and rules for exchanging information
Microcontrollers (MCUs) —execute the network protocol and continuously provide and receive information via the transceivers
In reality, an automobile network is far more complex. It includes other components to assure the high reliability and safety required by automobile manufacturers.
LIN, CAN, and FlexRay
Although many network protocols have been proposed over the years, the most significant are LIN (Local Interconnect Network) and CAN (Controller Area Network). First used in vehicles in 1994, CAN handled networking functions until LIN—more cost effective but lower performance—was introduced in 2002. The newest automobile network, FlexRay, has only recently appeared in cars.
LIN can be implemented at low cost and is perfectly suited for local control operations such as actuating door locks and electric window controls. LIN's low data rate (20 kbps) prohibits its use in more sophisticated and data-intensive applications such as motor control, braking, and suspension systems. That market is dominated by CAN, which comes in three flavors: Fault-tolerant CAN, high-speed CAN, and single-wire CAN, which is used primarily by General Motors.
Cars are becoming more sophisticated every year, however, and network technology has to keep pace.
So within the next year or two, FlexRay will begin its significant market penetration. FlexRay is a high-speed (10 Mbps) network well-suited for time-critical applications. It has been in development since 1999 and is now in use in some high end vehicles.
Below is illustrated the bus speed of each network with representative applications for each.
The next figure illustrates the market segmentation for in-vehicle networks over the next few years in terms of individual network connections, or nodes. Each node is the connection point on the network for an ECU (Electronic Control Unit) that supervises and controls some mechanical system.
It is worth noting that the overall market for automotive networking will grow at a 10% annual rate through 2011. Driving this trend is the introduction of more electronics in every vehicle, and that accounts for the much faster annual growth rate than the auto industry's 2 to 3%.
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