Consider this: The weight of a BMW 5 Series after about 40 years of model iterations increased 50 percent. Recently, the electric powertrain in just one model change of the Volkswagen Golf increased the car’s weight 32 percent. What gives? Primarily, added electronics: multiple systems, sensors, wiring, and electrical safety systems to manage and control previously independent and mostly mechanical systems in vehicles, including powertrain, lighting, HVAC, and entertainment.
But weight is not the only thing to consider. “Electrical system complexity is at a tipping point,” says Martin O’Brien, vice president and general manager of the Integrated Electrical Systems Div.at Mentor (mentor.com), a Siemens PLM Software Business. The tipping point is that electrical and electronic (E/E) architecture development can no longer be resolved manually. Explains O’Brien, “Previously independent systems are now tightly interdependent. ‘Rush-to-market’ demands intellectual property re-use and more virtual simulation/verification. The ability to rapidly architect different spins of the electrical system and then to drive those design iterations through the development of the vehicle is critical.”
This where Capital Systems Networks from Mentor comes in. This software tool speeds and simplifies the task of designing in-vehicle controller area network (CAN) communications networks based on the SAE J1939 standard. In simple English, says O’Brien: “What we manage is inside wiring drawings: the signals, the messages, the wiring systems, and so on.”
A standard begets a specialized tool
SAE J1939 is a constrained design standard. It covers in-vehicle communications and diagnostics between electronic controllers and devices in heavy-duty commercial vehicles, such as trucks, buses, and off-road vehicles. It is a higher-layer protocol for communications across a CAN bus, including the messages and conversion rules across the multi-vendor universe of hardware, software, networks, actuators, and related devices in a vehicular E/E system.
A commercial vehicle, according to O’Brien, can have as many as six CAN networks. Each of these connects dozens of electronic control units (ECUs) located throughout the vehicle. And each of these networks may require new designs and rework for every new vehicle model. Besides the obstacles in E/E technology, redesign and rework can be stymied by two other factors. First, isolated data, such as that in spreadsheets, inhibits design reusability, as well as security, scalability, and verification. Second, explains O’Brien, “the new generation of engineers lack adequate access to retained intellectual property.”
Capital Systems Networks, part of Mentor’s Capital tool suite, helps solve all that. The product integrates network and E/E design into one software tool for developing both the functional and physical designs for J1939 networks. Engineers can reuse network designs or use software scripting to create network variants. Throughout the network development process, metrics and key performance indicators (KPIs) provide the analysis needed for validating the design against requirements. Ultimately, the results include higher-quality first-time network designs, shorter design cycles for new products, and faster delivery of mandated, correct-by-construction output.
(A sister product, Capital Networks, is an advanced network design tool for technologies including Ethernet, 4G and 5G, and J1939.)
How it works
An early step in new-vehicle design is defining the E/E architecture, including the quantity, type, and location of the ECUs, sensors, and actuators that monitor and control the various, now predominantly electronic, systems in the vehicle. Engineers start by allocating signals to a functional design of the vehicle. The resulting network design is synthesized to generate KPIs and associated metrics. The metrics are analyzed for suitability to vehicle requirements. Then the network is tweaked for better conformance to requirements. Repeat—until the network is optimized, validated, and matches requirements.
Throughout, Capital can display a physical view of the vehicle in the context of the 3D model. This shows designers the locations of functions in the different ECUs scattered about the vehicle. It also makes designers “aware of lengths, things like that,” says O’Brien. This is useful even though Capital converts the synthesis of the logical definition of the vehicle on-the-fly into physical wiring.
Designers can describe a network at the appropriate level of abstraction: function blocks for hardware, software, sensors, actuators, and so on. Capital can “import black-box functional designs and logic models,” says O’Brien, “further leveraging design data reuse. It is also possible to import an existing platform, complete with properties defined in the 3D CAD environment, or an abstracted logical architecture of the network to use in the architectural platform design view.”
As required, designers can reassign functions from one ECU to another and reroute connectivity when ECUs are merged. Capital will prompt what associated functions and requirements need to be moved, as well. Migrating functions to a new location or network in the architecture—migrating an entire ECU for that matter—may affect performance elsewhere in the system, says O’Brien. “This change in behavior may cascade, causing any number of subsystems or functions to fail. Such changes can completely invalidate the technical implementation of the architecture, driving the re-design of multiple systems.” For all these changes, Capital will analyze the network’s operating characteristics, such as process loading, network bandwidth utilization, and other KPIs, to determine if they fall within predefined acceptable ranges.
As the network design is finalized, Capital creates the wiring harness—live— as well as associated work instructions and vehicle maintenance documentation.
Capital helps in future designs, too. The data model stored in Capital can be extended and modified as new information becomes available, which is a considerable time savings given that most new vehicles are designed from an 80 percent carryover. Capital Systems Network’s data modeling capabilities understand effectivity, configuration management, traceability, and other aspects of managing components and devices. For instance, clicking a pin on any device will show information such as the wire and network connected to that pin (where-used), signal characteristics, and the functions being implemented. If a component is deleted, Capital will automatically list the affected logical designs needing updating.
O’Brien estimates engineers will find vehicular network design development reduced 90 percent. “And it will be right, it will be deterministically correct, and it can be constructed.” Equally important, the optimized design will have been verified against SAE J1939 standards.
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