Where can CANs go next?

Computer-aided data networks speed up the flow of information and enhance the reliability and service lives of commercial vehicles.

By Dr Klaus Schubert, MAN Nutzfahrzeuge AG

Electronics and computer-aided data networks are becoming an integral part of the structure of heavy vehicles. In the late 1980s, electronic components were used primarily to perform functions that could not be carried out mechanically or pneumatically. Today, comprehensive computer-aided data networks are being implemented and are opening up a new world of opportunities. Data buses that link a variety of electrical and electronic components via just one line are replacing the traditional cable harnesses, which can be as thick as a man's arm. The new controller area network (CAN) bus technology cuts costs while enhancing reliability and safety. Ideally, it will also extend the vehicle's service life indefinitely.

CAN

Controller area network is the new transmission medium. It does away with the numerous lines, plug contacts and connections previously required for transmitting signals and information in a vehicle. Digitised data is sent via a single cable and is made available to different control units simultaneously. The networking of completely separate functions, therefore, makes the varied use of electronic components possible. CAN functions according to the multimaster principle, simultaneously transmitting all data from the sender to the various receivers. Measuring sensors perform the role of the sender while control units act as the receivers.

It is important to ensure that messages that have been dispatched arrive at the correct receiver. Consequently, each is sent with a tool that decodes it according to its significance for individual control units and prioritises them according to urgency. When the line is free, each and every station can send its own messages. However, if several pieces of information are being sent at the same time, those that are deemed high priority will be given precedence. The other stations will then repeat their attempt to transmit their messages as soon as the line is free. So that long waiting periods can be avoided and important messages sent swiftly, individual messages come in a limited-length data frame. The shorter the message, the higher the priority.

Safety first

Electronics are gradually being applied in components for enhancing road safety. Anti-lock and anti-slip systems are those that merit close examination. Just because a truck or bus brake is fitted with ABS does not necessarily mean that its braking distances will be shorter. What is most important is that vehicles stay manoeuvrable and retain their tracking stability.

In diesel engines, the electronic system helps to reduce exhaust emissions, and the electronic control of retarders and gearboxes both enhances safety and relieves the driver of numerous manual tasks. Today, it is unthinkable that these developments should come to fruition without the incorporation of electronics.

Rapid advances in the sphere of semiconductor technology are providing developers of commercial vehicle electronics with increasingly powerful microcontrollers and output stages, and larger memory capacity in control units (which yield further application possibilities). Integrated ABS/ASR systems, electronically controlled air suspension, automated gearboxes and electronic diesel injection systems are but a few examples.

Initially, the application of CAN bus technology in commercial vehicle construction was limited to the driveline system. Its task was to enable a quick exchange of information between the electronic diesel control system (EDC), the gearbox and the ASR. An analysis of the entire electronic system in a commercial vehicle reveals that in the future, two or three independent CAN systems will be installed. Nowadays, all suppliers offer at least one variant control unit that has a CAN interface. So that variations in the design of the CAN bus do not proliferate excessively, physical interfaces are standardised in the SAE J1939 according to data and transmission formats. Most European manufacturers of commercial vehicles use these standards as a yardstick.

Networking benefits

Other facets of modern electronics are the increased temperature stability and vibration resistance. If hybrid technology is used, the direct attachment of devices to units will be possible. For example, an electronic control unit for an automated gearbox can be installed within the gearbox cover. The development and tool costs involved in this procedure are critical should the unit numbers in the commercial vehicle industry prove to be low.

The spread of electronics integration and the simultaneous CAN networking of systems are steps that show further opportunities for cost cutting and enlarging the functional spectrum. The electronic brake system (EBS) is a pertinent example. So-called pressure control modules - that have integrated electronic systems fitted to the wheel brake cylinders and axles - are linked to the core piece and central control unit in the cab with a CAN data bus. These modules also receive the set nominal value from the bus.

In future, the driveline control units, retarder, automatic gearbox, running gear control, electronic air preparation system and electronic brake will all be connected to a vehicle master computer (FFR) and vehicle control unit in a similar way. From here, they will receive their set-point values, general processing information and sensor values (measured at other points) as well as have the option of transmitting their own values or requirements to it.

For technical reasons, the electronic injection system is as close to the engine as possible and receives its set-point values from the FFR via an engine CAN bus. The FFR processes this information centrally and, depending on operating conditions and the driver's request, calculates the necessary set-point variables. These include the required gear or requested driving and braking torques that are regulated - via CAN - by locally installed electronic systems.

Such an example shows that great emphasis will be placed on CAN networking in order to enhance reliability and vehicle availability. Commercial vehicle developers will have to make special efforts to meet the specifications for electromagnetic compatibility, interference or short-circuit stability and reliability. To do this, they must take account of longer lines, higher mass offsets and cable harness routeing patterns (which vary greatly).

Since much of the cable harness and numerous components found on control units with multipole plug connections are located outside the vehicle, the availability and longevity required of commercial vehicles can be guaranteed only through the use of single-load seals and high-quality contacts.

As a result of networking, traditional function and component allocations are lifted. In the past, cruise control functions were automatically allocated to the EDC unit. The Bremsomat function, meanwhile, was linked to the retarder control unit. Today, a combined cruise control/Bremsomat function can be built into the FFR. EDC and retarder controls are reduced to intelligent elements.

System and function development must now be pursued with a larger number of tasks in mind. Following this, more responsibility is being apportioned to the commercial vehicle manufacturer. If the FFR is regarded as a co-ordinating point within the driveline system, it becomes clear that further vehicle-specific functions can be integrated there. From power take-off and working speed control to clutch and gearbox functions, and vehicle-specific engine control, all can be combined meaningfully.

Other CAN benefits

However, CAN bus technology is not restricted to the driveline and its periphery. It brings about changes in traditional electrics and bodywork electronics. Functions previously performed with relay and cabling technology in conjunction with miniature electronics will eventually be amalgamated in a central, on-board computer. Lighting control, headlight beam regulation, flame starter control, wipe/wash control, headlight cleaning, sensor monitoring, comfortable interior space management and so on, can also be integrated into the computer in an economic and controlled manner. Ultimately, central on-board diagnosis will take over the gateway functionality between the driveline CAN system and the instruments, as well as co-ordinate the information to be gathered.

Depending on allocation, maintenance and wear calculations can be carried out by one of two vehicle-specific computers. The driver can call them up via the instruments and central on-board computer. Such a function can be implemented more economically with a central system. The reason decentralised systems are used in buses is because of space restrictions and the variety of functions required. It is here that the multiplex interface comes into play. The many different versions of, and equipment options for, buses require a high degree of flexibility. Locally fitted control units, which are directed from one central knot via CAN, maintain this flexibility.

Intelligent electronic architecture

It is easy to predict that intelligent electrics and electronics will contribute enormously to the evolution of the commercial vehicle industry. A new electronics architecture, whose development potential cannot yet fully be fathomed, is on the horizon. In this context, it must be highlighted that, despite these changes, innovations in the field of individual systems will not cease. Electronic air suspension, for instance, will be accompanied by electronic damping control. The airbag will become a standard feature in trucks, and systems such as the adaptive cruise control have already reached pre-series maturity. Consequently, commercial vehicles will continue to evolve rapidly.

The truck industry's objective must be to build trucks and buses that show standards comfort, reliability and operational safety that are currently only seen in high-end, middle-market cars. Networked electronic components are an inextricable part of this goal.

Author

Dr Klaus Schubert is chairman of the executive board of MAN Nutzfahrzeuge AG.
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