In recent years, OEMs have added a steady stream of convenience, safety, telematics and entertainment features to their vehicles. At the same time, microprocessor-based technologies are replacing many traditional hydraulic and mechanical systems.

     In this environment, the demand for supporting power and data distribution has multiplied dramatically. The traditional wire harness continues to provide the foundation for the in-vehicle power and data distribution (high current circuits that drive motors, locks, etc., low current circuits that carry information such as speed, temperature, etc.). By adopting a more advanced power and data network (PDN), OEMs can provide the enhanced driving experience customers want, while addressing pressing issues of space, weight and cost.

     PDNs are an evolution in automotive Electrical/Electronic (EE) technology that spans nearly 80 years. New strategies and technologies share the stage with proven approaches to power and data distribution.

     Advances in power and data distribution have not eclipsed previous technologies, but have refined them, adding important options to the engineer’s tool chest. Cost is a major factor in determining how new technologies are implemented. System designers must be able to draw on the best of existing and new approaches to achieve desired results within given cost parameters.

     The challenge is to add greater functionality and more vehicle features, while minimizing or eliminating corresponding increases in physical infrastructure. In many ways, this is as much an art as it is a science.

     A vehicle network incorporates the physical media, electronics and supporting technologies that deliver power and/or data used to activate and control various vehicle functions. In application, this takes the form of a local system of interconnected devices and supporting components such as controllers and gateways. Several sub-networks may be integrated to form the vehicle’s power and data infrastructure. This integration is the job of gateways, which allow data sharing while preventing unwanted interference between dissimilar networks; and bridges, which provide data filtering between similar networks.

     Different PDN architectures are employed to connect the different devices and sub-networks in a vehicle. It is even possible to have two architectures in the same vehicle (a ring architecture could be used for a sub-system that is attached as a node on a bus network).

     Automotive network solutions must satisfy a number of requirements:

     Reliability – The network must be able to perform error-free under adverse conditions for the life of the vehicle.

     Flexibility - Content variation across models and compatibility with aftermarket devices requires network scalability and upgradeability.

     EMC - Unwanted electromagnetic fields can disrupt the network and nearby devices.

     Connector Optimization - Number of connectors, connector size and functional integration are critical variables in network design.

     Cost - Performance and other benefits must be carefully balanced against cost and competitive impact.

     Fault Tolerance - Susceptibility to faults and the need for system redundancy are major issues.

     Modularity - Standardized modules mean shorter design cycles and lower costs.

SAE network classes "SAE network classes"

     In-vehicle networks can be differentiated by data-handling speed. This, in turn, governs the types of devices served and data-communication protocols applied. In general, as network data speed rises, technical sophistication and costs increase accordingly. This is one reason why devices with relatively modest data needs are often networked separately. Class A networks, for example, include devices that operate through simple on/off control of power loads. These copper-based networks generally run at speeds below 10 Kb/s and include devices such as seat controls, power mirrors and trunk releases. Class A data protocols include LIN (Local Interconnect Network) and TTP/A (Time Triggered Protocol).

     Class B networks are designed to allow sharing of basic information between various vehicle devices, thereby eliminating redundant sensors. Operating at 10-125 Kb/s, these networks commonly include instrumentation, emissions systems, speed-control systems and other devices dependent on routine operating data. Protocols applied to Class B networks include J1850 and ISO 9141-2. Class C networks operate at speeds from 125 Kb/s to 1 Mb/s to support large data requirements and/or real-time control. Typical applications include vehicle dynamics and powertrain control. Protocols in Class C include CAN (Controller Area Network) and J1039.

     Class D Networks operate at speeds above 1 Mb/s and are used for safety-critical systems, such as x-by-wire, and high-bandwidth multi-media applications. Class D protocols include FlexRay and MOST in either copper or optical media.

     The 4-Layer Network Infrastructure model recognizes natural network subdivisions based on broad functionality, data transmission speed, and corresponding data protocols. A given layer may be made up of two or more sub networks.

     The energy layer includes power generation, storage and distribution elements (typically an alternator, battery and under hood power distribution center.)

     The safety and mobility layer incorporates airbags, engine control modules, HVAC system, steering, transmission and x-by-wire. These systems are supported by SAE Class C and Class D networks, which provide real-time control, with operating speeds from 125 Kb/s to 1 Mb/s and greater.

     The body layer provides control of lighting, HVAC, door and seat functions and also includes speed control, instrumentation and emissions systems. These functions are supported by low-speed SAE Class A networks operating at less than 10 Kb/s, and SAE Class B networks running at 10-125 Kb/s.

     The infotainment layer includes advanced audio and video devices, wireless phone, voice-activated systems, instrumentation sensing, and other systems requiring SAE Class D data transfer speeds (>1Mb/s). The infotainment layer incorporates an optical fiber network scenario based on the MOST data protocol. The 4-layer model is conceptual, and not intended to suggest physical reality. Rather, its purpose is to help illuminate the challenges, relationships and opportunities inherent in an integrated power and data infrastructure. Application of these concepts plays a central role in the development of advanced PDNs.

Scalable modular architecturetc "Scalable modular architecture"

     During much of the last century, growing vehicle electrical requirements led to a steady increase in specialized power, diagnostic, control and fault-prevention components. Successful efforts to integrate many of these functions in centralized modules has delivered both cost and performance benefits. However, the advantages of centralization must now be balanced against dramatic expansion of the physical distribution infrastructure to support added energy consumption and data processing.

     The challenge is to deliver the benefits of integrated functionality with a new infrastructure model, one capable of delivering greater capacity and increased efficiency with a compact, cost-optimized physical package.

     Consistent with the 4-layer conceptual model, Yazaki’s Scalable Modular Architecture (SMA) is an instrumental step in this direction. This architectural methodology places multi-functional nodes strategically throughout the vehicle. Each node is fed power from the under hood node and interconnected via a data bus. Power and control of devices are localized in physical zones while leveraging network communications and distributed processing. Each node integrates communications, junction block, gateway, power switching, fault detection, fault handling and body control functionality. This system of nodes provides intelligent, software-driven control, with diagnostics that provide the optimal solution for the vehicle.

     In the Yazaki SMA solution, the primary power distribution and under hood body controls are housed in an integrated power module. The under hood node utilizes bus-bar and printed circuit board technologies and is micro-controller based. The interior nodes are completely solid state, based on a common digital core board design that is deployed in all nodes. smart connectors are also utilized when appropriate for mechatronic based subsystems such as seats and doors.

     Electronics are embedded in these connectors to provide highly localized control of motors, actuators, and sensors. Smart connectors are interconnected via a LIN bus network and are slaves to an interior node master. Interior nodes also provide necessary LIN/CAN gateway functions.

     The SMA methodology can easily be extended beyond 14 volt based systems to 42 volt and hybrid electric vehicle (HEV) applications. This can be accomplished by adding additional functions such as pulse width modulation (PWM), voltage conversion, battery State of Health/State of Charge (SOH/SOC) monitoring and control, jumpstart provisions, and arc detection/prevention to the basic building blocks or “form factors”.

     All SMA nodes are scalable, allowing a single platform design to serve vehicles with differing content profiles. Common hardware form factors can be populated/unpopulated and reconfigured through customized software algorithms. Vehicle features can be added or deleted with minimal impact to the nodes. The result: dramatically reduced development cycles and realization of economies of scale. Other benefits include reduction of wiring, simplified assembly, and intelligent power delivery.

Optical Fiber technology "Optical Fiber technology"

     In certain vehicle network applications, Optical Fiber offers significant advantages over copper. By using pulsed light instead of electrical current, Optical Fiber has the ability to transmit large amounts of data at very high speeds. In addition, Optical Fiber technology permits multiple inputs and multiple outputs to share data simultaneously as members of a common ring network. Optical Fiber can, therefore, meet specific data-handling requirements more efficiently than copper, while saving both weight and space.

     Optical Fiber can also operate successfully in crowded electronic environments, with virtually no degradation of data transmission. Further, it meets strict electromagnetic compatibility (EMC) requirements: unlike copper, Optical Fiber is not susceptible to electrical interference generated by the operation of nearby electronics.

     At speeds above 1Mb/s, Optical Fiber is an efficient and cost-effective medium for use in vehicle PDNs. Its unique operating characteristics and relatively simple architecture make it a strong choice for high-bandwidth applications such as multimedia, telematics and internet access. Equivalent copper-based networks typically require many more connections and a physical layer with considerably greater mass.

     For all its strengths, the current Optical Fiber used in vehicles today has its limitations. Fiber applications are restricted by thermal environment and network configuration. Thermal ratings and optical attenuation of the fiber constrains network architecture design and routing flexibility.

     These issues can be addressed with Polymer Clad Silica (PCS) Fiber. PCS is an advanced material which has minimal optical attenuation and can withstand more demanding environmental conditions. PCS has two more features that make it more attractive than current Optical Fiber: a higher bandwidth, which allows for faster transmission of data (up to 1Gb/s), and greater physical flexibility, which provides optimal packaging solutions for PDN designers.

     Well-designed Optical Fiber networks may be discrete, but they are not isolated. Like other in-vehicle networks, they must be designed as part of the total vehicle infrastructure and optimized with respect to the power networks they parallel. This requires full integration of physical-layer components, software and network architecture – a process best undertaken in the earliest stages of vehicle development.

Wireless technologies "Wireless technologies"

     Today’s PDNs must allow for connecting to the external world like never before. To reach the full potential of telematics, for example, call centers must be able to access information directly from the vehicle’s data bus. This requires precise application of suitable wireless technologies. Similar technical requirements apply to in-vehicle email and internet browsing. Data-interface electronics, based on Wireless Application Protocol (WAP), allow these and other web-based functions to be successfully integrated into the vehicle’s data-management system.

     Hands-free and portable systems also depend on wireless technologies. Yazaki PDNs for vehicles, employing voice-activated cell-phones for data-sharing with PDAs and laptops, use Bluetooth wireless technology interface to achieve efficient connectivity.

Conclusion