Communication Systems in Automotive Systems

Communication Systems in Automotive Systems

Piet De Pauw (BVBA De Pauw, Belgium)
Copyright: © 2013 |Pages: 37
DOI: 10.4018/978-1-4666-2976-9.ch002

Abstract

Communication networks in general, can be divided into 4 different classes: Ring (one directional or bidirectional), Star (active or passive), Tree, and Bus (passive). These 4 classes of communication networks are also used in transport systems. The main properties of these networks are overviewed. Then, the most important automotive networks are discussed: LIN, CAN, MOST, Ethernet, and Flexray, as well as their implementations in cars. For the MOST and Ethernet networks, different physical layer implementations are possible. The different factors determining the choice of a network are discussed. Cost is a major driver for automotive networks. For avionics networks, different standards for the network protocols and the physical layer implementations exist. In most cases physical layer implementations are proprietary, although, due to cost reduction pressure, more and more standardization is ongoing, and a tendency exist to adapt automotive network standards, and for the pressurized part of the airplane, also automotive physical layer implementations.
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Introduction

Automotive Industries, 2005

In the past 30 years, the automotive industry has changed dramatically. The former, purely mechanical systems have been replaced by a combination of mechanical and electronic devices.

The main drivers for improvements in cars are:

  • Increase of Safety: (Not only passive safety e.g. seat belts, but mainly by electronic means: air bags, anti-lock braking system (ABS from German: Antiblockiersystem), Electronic stability control (ESC), Blind Spot Detection (BSD), Adaptive Cruise Control (ACC), Lane Change Assist (LCA).

  • Fuel Consumption Reduction: Electronic Power Assisted Steering (EPAS), Replacement of belts by electronics, Lambdasonde, Motor Control Units (MCU).

  • Increase of Comfort: MOST network.

Electronics is the key enabler for progress in the automotive industry. More than 90 percent of the innovation in a car is in electronics, and electronic devices comprise more than 30 percent of the car manufacturing cost of today’s luxury and mid-range cars.

Among the increasing amount of electronics in cars, data communication networks are penetrating into cars as well. Nowadays, an average car has 10 to 20 intelligent electronic devices.

Why networks have been developed? No network is needed, when devices are directly connected to each other. If there are N electronic devices in a car, the connecting each device with each other requires N x (N-1)/2 connections. Therefore, as the number of nodes increases linearly with time, the number of connections to be made increases quadratically, making networks more and more attractive. A bus network for N devices also only needs N connections. Therefore cost is the main driver for the development of automotive networks.

Because of the largely different requirements, four different categories of networks emerge: low speed, medium speed, high speed and safety critical networks.

One of the first electrical networks to be developed for cars is the controller area network (CAN), which was developed by Bosch in 1984 and made an appearance in high-end Mercedes cars in 1992. CAN has been standardized by the International Standards Organization as ISO 11898 for high and low-speed/fault-tolerant versions. High-speed CAN runs up to 1 Mbit/s and is used for engine control and power-train applications. Low-speed/fault-tolerant CAN reaches 125 Kb/s and is used for body and comfort devices. CAN is a very popular bus standard for the automotive industry, supporting in-vehicle communication and industrial automation applications.

As the data throughput reaches more than a few megabits per second, EMI issues with the current electrical automotive buses become the main concern. In addition, the introduction of hybrid cars and electrical cars has obliged car manufacturers to significantly increase the Radiative immunity requirements from 100 to 150 V/m for cars with combustion engines to 600 V/m for hybrid and electrical vehicles.

Since the applications connected to each node of the network require electrical signals, optical networks (Optical Physical Layer or oPHY) always require electrical to optical and optical to electrical conversion. These conversions add to the cost of optical networks. On the other hand, optical connections are fully immune to electromagnetic disturbances from outside.

Although electrical networks (Electrical Physical Layer or ePHY) have difficulties coping with EMI issues, they do not need the conversions between electrical and optical signals.

This situation makes that in automotive network there is always a competition between implementations of the network as an electrical physical layer, or as an optical physical layer. The precise values of the EMI specs play an important role in the decision which physical implementation of the network to choose.

The number of network nodes is increasing year after year. In 2012 about 1.4 billion nodes are expected to be manufactured. This means the average car has about 20 nodes, while high end cars have 60 to 80 nodes.

As requirements on cars are still increasing: CO2 emission, safety, connectivity to the outside world, infotainment… the number of nodes in automotive networks is expected to continue to rise the coming years.

As electronic drivers and receivers become complex, struggling to transfer high speed data via low bandwidth electrical wires. To overcome these problems, the automobile manufacturers have introduced fiber optic systems in addition to the networks based on copper wires. The benefits for car manufacturers are higher bandwidth, immunity to EMI, low weight, and increased transmission security (see Table 1). Compared to electrical broadband wirings, large-core optical fiber may also offer advantages in ease of handling and installation.

Table 1.
Comparison between consumer and automotive transceiver ICs
Consumer ICsAutomotive ICs
Lifetime in the field>5 years>20 years
Production lifetimea few years10 to 20 years
Production volume per chipset10 to 50 million/yr100k to 5 million/yr
Immunity to
radiated
electromagnetic
disturbances
3 V/m for
80/230 MHz-1 GHz
(CISPR 14-2/EN 55014-2: 1997)
or
10 V/m for
80 MHz-14 Hz (IEC 61000-6-2: 1999)
150V/m (cars with combustion engines)
or
600 V/m (hybrid cars and electrical cars)
Operational Temperature range[0C, 70C][-40C, +85C to +125C]
Maximum failure rate in the field<1000 ppm/year<1 ppm/year

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