Focus on Electronics

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From fly-by-wire to drive-by-wire

Isolated electronic control units (ECU) can be combined to harmonized Integrated Vehicle Control Systems (IVCS), according to TTTech product developers. Click to enlarge

The same factors that drove the fly-by-wire breakthrough in the aerospace industry are now propelling the adoption of drive-by-wire technology in the automotive industry. The substitution of mechanical and hydraulic linkages by purely electrical/electronic systems is due to the limited nature of mechanical systems in the areas of safety and comfort as well as the rapidly improving price/performance ratio of microelectronic components, according to designers at TTTech Computertechnik AG.

It is estimated that, in 2006, at least 25% of the total costs of a passenger car will represent electronic parts; for high-end models it will be more than 35%; however, electronic systems can allow a reduction in overall costs during the complete life cycle of a car. The use of software solutions significantly reduces development and production costs, with an appropriate electronic design helping to solve the expensive differentiation of product variants. The reduced space and weight necessary for electronic systems can lead to reduced fuel consumption. Electronic systems provide new concepts for remote diagnosis and maintenance, and they enable new technologies such as fuel cells and intelligent powertrain control systems.

There are several safety arguments for in-car networks and electronics. Some mechanical components, such as the steering column, represent physical risks to occupants. The replacement of such parts reduces injuries in case of an accident. Electronic control systems enable intelligent driver assistance in dangerous situations and, if inevitable, controlled collision with minimal impact to the occupants. In addition, integrated vehicle control systems can integrate different subsystems into a single, harmonized driver support system, promoting active safety.

In a by-wire car, components for braking, steering, and other functions can be controlled with highly reliable and fault-tolerant communication networks. With increasing size and complexity of these new networks, ease of integration has become a major challenge for design engineers. Additionally, new in-system testing, software upgrade services, and diagnosis capabilities offer new opportunities for after-sales.

A star-coupled time-triggered architecture with TTPIC, TTPIA and a gateway interface. Click to enlarge

The prerequisite for this paradigm shift to by-wire automotive electronic systems has become a fault-tolerant communication architecture that must fulfill real-time requirements. Future control systems will need bandwidth of up to 10 Mbit/s and require a deterministic data transmission with guaranteed latency and minimal jitter. In addition, they must support scaleable redundancy, error-detection and -reporting, and fault-tolerance as well as different physical layers (e.g., fiber optics, wire).

In accordance with these requirements, a time-triggered architecture (TTA) has been developed at Vienna University of Technology in conjunction with industrial partners and other leading research institutions. The cornerstone of the TTA is the Time-Triggered Protocol (TTP). The TTP/C variant refers to the SAE's Class-C classification for fault-tolerant high-speed networks; TTP/A is a low-cost Class-A derivative for smart sensor and actuator networks. The Time Division Multiple Access (TDMA) bus access strategy acts as the basic functional principle of TTP. A defined time schedule controls all activities of this communication system. All "members" of the communication system know their assigned sending slots. A distributed algorithm establishes the global time base with steady clock synchronization. To prevent "babbling idiot" problems and slightly out-of-specification (SOS) failures, TTP/C provides an independent "guardian" that guarantees exclusive access to the bus.

Precisely defined interfaces in value and time domains ensure the composability of TTP-based systems, which means that components can be developed and tested individually since functionalities established and tested at the subsystem level are guaranteed to work at the system level. This dramatically reduces test and validation efforts. The TTP/C protocol contains a membership service to promptly detect node failures and inconsistent states in a distributed control system. It supports different physical interconnection structures, a bus configuration, and a star or multistar configuration that can be applied on fiber-optic as well as electrical physical layers. Based on a known communication schedule, the communication overhead is reduced to a minimum.

TTTech has developed a complete software environment that complements the TTA. The toolset supports all development stages—from simulation to network design, and from data monitoring to download. A fault-tolerant time-triggered operating system, as well as a fault-tolerant communication layer, is available from the company. The first protocol controller chips have been tested by several automakers and Tier 1 suppliers, and protocol controller chips with a transmission speed of up to 25 Mbit/s and data efficiency of more than 80% are now available.

- Kevin Jost

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Bosch, Mechanical Dynamics develop sensor system

Robert Bosch Corp. is working with Mechanical Dynamics, Inc. on a yearlong, $1-million program to develop a sensor that could reduce the risk of injuries caused by airbags in automobile crashes. "Utilizing our expertise in providing engineering solutions through virtual prototyping, we can help Bosch not only achieve its project timeline, but accelerate innovation while reducing the risk involved in developing a significant safety system," said Robert R. Ryan, President of Mechanical Dynamics.

Mechanical Dynamics' consultants are working with Bosch, automotive OEMs, and supplier partners in both the U.S. and Germany to develop and document analytical procedures and perform manufacturing design and analysis. The collaborative process includes conducting finite-element analysis (FEA) studies, correlating test data with the analyses, and optimizing the design.

"Our experience has suggested several keys to success, and Mechanical Dynamics' mechanical design and analysis expertise, along with their knowledge of advanced computer-aided engineering tools, will give us a decided advantage in creating an optimal sensor that meets our development criteria," said Robert Jones, Director of Engineering at Bosch Sensor Systems.

- Kevin Jost

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