Picture the hallways of a fast-growing company’s building—jammed with people barely slipping past each other to get to work assignments. It’s time for the company to reorganize work flow, relocate people who work together, perhaps even move to a larger place. There’s an analogy to the electronic feature content in automobiles today.
Major increases in electronic function call for improvements in data flow—that is, the ability to move more messages and get responses more quickly along the large "hallways" represented by CAN (controller area network) buses. However, it all has to be done without adding a lot of cost, and car manufacturers have been implementing major changes to accomplish these aims.
At Chrysler, there now is a new electronics architecture called PowerNet, which was introduced on three 2011 Chrysler products as the start of an across-the-board phase-in. The architecture makes its debut on the Chrysler 300, Dodge Charger, and the Dodge Journey crossover. It retains the single 500-kb/s high-speed CAN but replaces the 83.3-kb/s low-speed CAN with a pair of 125-kb/s medium-speed CAN data buses, one for interior functions and a second just for telematics. As many as 40 computers may be on a PowerNet vehicle.
The most visible symbol of the new telematics bus is the 8.4-in center-stack touch-screen command center. The screen, presently the largest in the industry, works with the latest version of Chrysler’s hands-free Uconnect for smartphones. It enables the motorist to control the audio, climate control, and navigation, and with Sirius Travel Link, it adds the ability to check weather and gasoline prices anywhere in the U.S., sports scores, and movie listings.
This is the basic layout. As in all automotive CAN systems, the 500-kb/s CAN is primarily for control of powertrain, four-wheel-drive, and safety systems—and for Chrysler, also electrohydraulic steering. The 125-kb/s interior bus covers HVAC, lighting, and other interior comfort and convenience features.
Both buses connect to a new central body computer, which serves as the gateway, transferring data back and forth. The 125-kb/s telematics bus is connected separately to the interior bus through a gateway in the Chrysler Telematics Platform (CTP)-radio module, which also is the command center for telematics. The result of the two 125-kb/s bus layout is a lot of additional bandwidth to cover electronics requirements.
The heart of PowerNet is the new central body controller/gateway, and it’s the same module for all PowerNet vehicles. This body module handles the gateway functions previously shared by a front control module (dropped completely) and the cabin compartment node (CCN). The CCN, a module that performed instrument cluster and a number of body module functions, now is just a simple instrument cluster module (primarily for display) and is on the 500-kb/s CAN bus. There are up to three specific instrument cluster modules per vehicles, so keeping the overall function simple makes each module easier to design and lower in cost.
Locating the instrument cluster module on the 500-kb/s bus may raise eyebrows, but if the cluster module were on the interior bus, the high-speed CAN messages would have to go through the gateway, a more difficult transfer, as was pointed out by Martin Yagley, Director, EE Architecture, Chrysler. And the message list includes powertrain and safety—important information for the driver.
Another possibly surprising module location is the radio frequency (RF) hub on the 500-kb/s CAN. However, more than just unlocking the door, the RF hub first must take the signal from the key fob and perform an instant electronic handshake with the engine computer, Yagley explained. Then it can transmit a request through the body computer gateway to unlock the door. The 500-kb/s CAN location also permits starting the engine if there is a problem on the interior bus.
There are some low-speed messages that have to go from the 125-kb/s interior bus through the gateway to the 500-kb/s bus, such as HVAC and infotainment, but they do not raise a traffic issue, he said.
The 500- and 125-kb/s interior buses tie into seven LINs (local interconnect networks), sort of narrower feeder “hallways” that operate at a leisurely 19.5-kb/s for low-data-rate sensors, switches, and lighting. LINs, serial networks that have one master with the capacity to monitor a large number of slave modules, are low in cost.
An eighth LIN is in the architecture for future electronic upgrades, and a ninth LIN appears on vehicles with diesel engines, with alternator and glow-plug modules as slaves to the engine computer. The previous architecture had a total of four LINs.
A key PowerNet objective was to reduce data transmission loading on the individual buses so there is no more than 30% of the bandwidth capacity in use at any one time. The greater bandwidth for the interior bus and addition of a 125-kb/s telematics bus help provide that and also permit increased functionality. Today’s microcontrollers, Yagley said, can easily operate at the higher speed.
The 125-kb/s telematics bus, which has modules to cover audio and radio, also includes a new hands-free module (HFM) for voice recognition from Magneti Marelli. An HFM previously had been on the 83.3-kb/s bus, so the new location also takes load off the faster new interior bus.
Along with the simplification of key modules, the new architecture permits use of a lower cost design (twisted two-wire, nonfault tolerant) for the data buses. The 83.3-kb/s data bus previously used was the twisted two-wire fault tolerant type, Yagley said.
Chrysler also has a new PC-based diagnostic system called Wi-tech. Within PowerNet, the familiar SAE J1962 diagnostic link connector is wired directly into the 500- and 125-kb/s interior CANs vs. the previous system in which the connector was wired to the instrument cluster/body computer gateway. Putting most diagnostics—and reflashing of modules—directly through to the 500- and 125-kb/s interior buses also permits simplification within the new body computer.
Wi-tech includes a pod that connects to the J1962 link, and the pod can provide wireless connectivity to an access gateway wired to a PC. The PC can display a PowerNet topography diagram showing all active installed modules, and with color coding to indicate any modules with trouble codes or modules for which a reflash is available. A few simple mouse clicks display codes, clears them, and reflashes with new software if necessary.