iTECH: Data Capacity Expansion

Truck makers and technology companies are working to expand onboard vehicle electronics’ capacity to handle the many sensors, components and computers pushing current infrastructure to its limit.

Technology experts agree that the J1939 data bus — a length of twisted copper wire that runs from the engine control module to the back of the tractor and carries electronic communications for everything from engine diagnostics to tire-pressure monitoring — must double its capacity to handle the increasing demands of intravehicle communications found on more and more trucks.

“With brake and body controllers, telematics, instrument clusters, data logging, radios, [heating, ventilation and air-conditioning] controllers, automated transmissions and so on, the demands for capacity are skyrocketing,” Kenneth DeGrant, an engineering manager for Dearborn Group Technologies, said in February during the annual meeting of the Technology & Maintenance Council of American Trucking Associations in Tampa, Fla.

While current technology allows the J1939 bus to process communications at a rate of 250,000 bits per second, or 250 kilobauds, DeGrant said that within two or three years that will double to 500 kBd. The higher the rate, the more data the system can carry. The question for truck makers — and ultimately fleets — is how best to manage all the data that will be flowing along that spine.

It may sound like down-in-the-weeds technobabble, but the data capacity of the J1939 bus affects how effectively electronic systems on a truck can function. While industry experts agree the move to 500 kBd is inevitable, opinions are divided on the how truck makers, and motor carriers, best can bridge the transition while ensuring all systems on the truck keep doing what they need to do.

“Bus loads on the J1939 250 kBd backbone for a fully featured truck are approaching a critical state,” said Chinpai Jong, senior manager in mechatronics for Daimler Trucks North America, Portland, Ore., which manufactures Freightliner and Western Star trucks. “In order to integrate more features to meet market demands, J1939 will have to increase its speed to 500 kBd in the coming years.”

The rise of onboard diagnostics related to emissions controls is a major cause of increased demand for communications capacity on trucks, DeGrant said. The U.S. Environmental Protection Agency and the California Air Resources Board insist that trucks be equipped with sensors to monitor diesel emissions so the vehicles are in compliance with antipollution rules. Those sensors must then deliver their findings — via J1939 — either to an in-cab computer or the engine control module. With the proper electrical hookups for communications it can run the length of one or two trailers, for a maximum length of 40 meters, or about 133 feet, he said.

It is these systems, plus fleets’ increased use of telematics, that are pushing the industry to the shift to the higher capacity data bus, said Dan Fuglewicz, director of automotive and embedded technology for Xata Inc., Eden Prairie, Minn., which develops software for the trucking industry.

“Users want all types of real-time data from their truck — operational data, fault data, safety system data, driver data,” he said. “They use this data to better manage and control their operations and costs, and they require as much data, as fast as they can get it. It’s actually the telematics users — fleet managers, maintenance managers, technicians, and even drivers — who are driving data capacity.”

A key question for manufacturers is how to equip trucks to handle all that data.

Navistar Inc., Lisle, Ill., which makes International trucks, has been involved in research being done by SAE International, formerly the Society of Automotive Engineers, on advancements to the J1939 bus, said Eric Swenson, the truck maker’s manager of vehicle requirements. He said SAE has published “data bus topology,” or guidance, on the move to 500 kBd.

DeGrant has been following the SAE’s work, and believes truck makers have two options: doubling the capacity of a single wire or running two 250 kBd wires in parallel. DeGrant said he prefers the twin option, one data bus dedicated to critical communication, such as braking, and the other set aside for more ordinary data.

Jong says that while a dual 250 kBd bus strategy can work in the short-term, it won’t take long for the industry to outgrow the 250 kBd standard.

“At the rate new, sophisticated features are being added to the powertrain and active safety systems, the ‘mission critical’ J1939 250 kBd bus for ABS and powertrain will still reach its critical state in the near future,” he said. “The long-term strategy for meeting increased customer demands on energy efficiency and safety . . . is to increase the ‘mission critical’ J1939 bus to 500 kBd. In the long run, this, combined with a separate J1939 250 kBd ‘nonmission-critical’ bus, will allow room for future growth while ensuring reliability.”

Fuglewicz agreed that the industry should tread cautiously before completely abandoning the 250 kBd bus. “Having one 500 kBd J1939 does lend itself to the risk that an aftermarket system may not be compatible with the bus and may result in the vehicle not operating correctly,” he said. Importantly, plug-in receptacles on the systems are different.

Selecting a strategy may ultimately come down to what users want to accomplish, Swenson said.

“There can be arguments for either approach,” he said. “The design choice . . . is not unlike selecting single semi-trailers or double trailers for a logistics operation. What makes the most sense depends on the cargo — or in this case, data — to be conveyed. Insisting there must be a nexus of all data traffic can be impractical.”

But understanding how far a single bus can be pushed, in either a single or double-bus network, is critical. Based on current usage, DeGrant said, J1939 usually operates at 35% to 40% of capacity and sometimes spikes as high as 50%. A decade ago the rate was 20% to 25% of capacity, he said.

“Above 65% of the data bus capacity is considered undesirable,” Jong said. “On an average-featured truck today, there is still considerable data bus capacity, [but] once the data bus reaches the critical state, message drop-out starts to occur. The driver will begin to experience occasional loss of function.” He added, “Some safety systems have a malfunction warning light. The light will turn on, and a fault code may show up.”

Jong also noted that, should a truck have both 250 kBd and 500 kBd systems, there can be no crossover between the two. “On one J1939 bus, controllers of two different speeds, 250 kBd and 500 kBd, do not mix,” he said. “All participating third-party manufacturers need to move their controllers to 500 kBd together in order for them to be connected to the J1939 500 kBd bus.”

Xata, for one, is preparing for the change.

“We are actively engaged in engineering development work with 500 kBd J1939 and testing our devices on production vehicles,” Fuglewicz said. “We know several truck [original equipment manufacturers] have already adopted 500 kBd J1939, and more are sure to follow.”

Daimler also is bracing for the change.

“DTNA has been laying down the groundwork to be ready for moving to 500 kBd J1939 backbone for some time,” Jong said. “Our work includes a strategy for maintaining the integrity of the data bus, increasing the vehicle’s overall reliability and enhancing ease of service.” He added that Daimler’s Freightliner M2 medium-duty hybrid trucks already are utilizing a 500 kBd bus for “sophisticated energy management functions.” Like Navistar, DTNA is also participating in the SAE study group.

“Overall, this is a positive change to the industry,” DeGrant said. “It will buy us another 10 years without having to totally redesign the vehicle network architecture.”

Fuglewicz added, “As more and more ‘smart’ devices are built into the vehicle — or are added aftermarket — with fleets wanting to know the status of these devices in real-time, the existing 250 kBd J1939 will eventually reach its limit.”

In-cab equipment maker Qualcomm Inc., San Diego, and software provider TMW Systems Inc., Beachwood, Ohio, declined to comment for this story. Truck makers Kenworth Truck Company, Kirkland, Wash.; Peterbilt Motors, Denton, Texas; and Volvo Trucks North America and Mack Trucks Inc., both located in Greensboro, N.C., also did not comment.