Upfitters can save time, improve quality, and ultimately increase customer satisfaction by taking advantage of the multiplexed electrical systems that chassis manufacturers are making accessible to the truck equipment industry.

A Work Truck Show session provided an overview from the perspective of a manufacturer and a truck equipment distributor who has learned to use these systems to provide power for a wide range of truck equipment.

Speaking at the workshop were Guy Chollet, engineering manager for Auto Truck Group, and Bryan Howard, vocational sales manager for Freightliner Trucks.

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Providing an upfitter's perspective, Chollet said this technology has been in the industry, our homes and appliances for years, but what's new is the opportunity to use the processes to make our systems more efficient and reliable.

“Multiplexing significantly reduces the number of electrical components we have to install,” he said. “Connections are lessened markedly and devices reduced. As a result, we become more efficient as we're going to make installations more quickly, more reliably, and we're able to get more work through our facilities. There are shortened production intervals, enhancing output without increases in facilities or labor forces. Lastly, we become competitive. We need to be able to explain to our customers that they can use multiplexing.

“Failure to understand and utilize these systems lessens the ability to compete with other potentially smaller rivals. An inability to explain and rationalize this technology detracts from the perceived knowledge and credibility of the supplier.

Guy Chollet, Auto Truck Group

“It requires planning. As in most systems, the opportunity to get ahead of situations and set up trucks to be able to dictate features and to be able to structure the conditions a truck is built in is going to be critical. Multiplexing is very flexible. In the perhaps not-so-distant past, we have all worked with trucks that were not right, but were available. We need to determine what features the circuits are going to require. It may be as easy as the type of switches. Switches could be SPST or SPDT, latched or momentary.”

Things to consider

Chollet offered distributors a series of things to keep in mind when integrating the power needs of truck equipment into a truck's multiplexed electrical system.

  • Will one switch operate one output? More than one?

  • Will current demands exceed 7A? 20A? Are sufficient outputs available? Is another processor receiving an output, providing an input?

  • Ten 7A outputs and 12 20A outputs are available.

  • Are added relays, diodes or solenoids needed? Do concerns with high amperage or polarity exist? Is it a requirement to switch digital signals?

  • Inputs stemming from other circuits often have to trigger a relay, crossing ground as the input.

  • Less than 7A requires a fuse protection, greater than 20A may need an added relay triggered or a second output.

“Freightliner provides thousands of parameters,” Chollet said. “New trucks arrive without software installed. It's a requirement for the TEM to download the appropriate codes. These codes are specific. There are thousands of them. Search features exist to sort them. Vocational truck managers can do this and some dealers will do it. These are available through Access Freightliner.

“Because codes are so prolific, they may be able to find existing ones that will work for your applications. Freightliner will see to your programming requirements. The earlier in this process a need is recognized, the better their ability to react in time will be realized.

“The ordering dealer should receive the initial request. He can more ably check procedures that are already written. Procedures can be downloaded to a truck at any time during its life. Chassis delivery need not be delayed for these features.

“A number of cables are available. Cables already used for engine interfaces (Cummins and Detroit Diesel) are suitable. Due to conditions, a laptop is just handier. Bad Internet connections are troublesome. Notably, if the connection is lost during a download, the larger truck program could be corrupted. Then you'd have to reload that and it will take extra time and could be a complication. The program for making downloads is available on the Access Freightliner website.”

He said installation processes should be reviewed.

“You're working with processors that are voltage-sensitive,” he said. “They operate at voltage levels significantly below what your system is, so they can be damaged by 12 and 14 volts. That's usually their maximum threshold. Any of your magnetic coils could create a transient voltage. It's not evident on a meter. It's certainly not evident on an analog meter. You have to pick it up on an oscilloscope because it operates on thousandths of a second. What do you do about that? There are external circuits you can implement that are quick to do and will save you a great deal of pain and expense.”

The view of a chassis manufacturer

All truck manufacturers utilize multiplexing, Freightliner's Bryan Howard explained. The difference is how they're using multiplexing.

Bryan Howard - mug right Bryan Howard, Freightliner Trucks “Some OEMs only multiplex what you would refer to as powertrain controllers — electronic control modules, transmission control modules, things like that,” said Bryan Howard, vocational sales manager for Freightliner Trucks. “Some OEMs multiplex chassis and powertrain controllers. So we've moved from a more fuse- and relay-based control system to a solid-state control system with a processor.”

He said multiplexing is “the sending of multiple signals or streams of information on a signal path at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end. The aim is to share an expensive resource and simplify the connection inputs and outputs.”

Multiplexing can be compared to a computer network, he said. Multiple control modules communicate with each other to coordinate truck functions. The various control modules are communicating truck functions with each other. Signals are transmitted via the J1939 data link (the twisted pair).

“We're sending messages, and they're all based on a protocol,” he said. “With SAE, it's just like any SAE definition. There is a certain set of messages SAE has identified that only OEMs utilize. There are specific messages for specific signals. Because we're following SAE standards, there is a common language.”

J1939 is a high-speed vehicle communications network using the Controller Area Network (CAN) protocol that permits any device to transmit a message on the network when the data link is idle. Each message includes an identifier that defines the message priority, who sent it, and what data is contained within it. Collisions are avoided due to the arbitration process that occurs while the identifier is transmitted, permitting high-priority messages to get through with minimal delay.

He said it's critical to understand the difference between how traditional high-current, hard-wired switches and low-current Smart Switches operate. Low-current switches send signals to the bulkhead module without being hard-wired to it.

He said an input is a device that feeds a signal into the system, or a signal that feeds a message into the system. It's anywhere a signal is being sent into the control.

There are two types of inputs:

  • Body (hard-wired) input. This is a physical input into the system, usually through a park-brake, service-brake, or door switch.

  • Signal input. This is a J1939-based message broadcast from a control module, such as range indication (neutral, reverse) or park-brake status. “So that message now can be read by anything actually connected into the backbone, so now the instrument cluster can turn on that park-brake light. I didn't have to run a direct wire to the instrument wire. It was all available information on the J1939 network.”

An output is the signal or message that comes out of a system component or device. “Our outputs are going to be solid-state outputs,” Howard said. “We have specific outputs on our modules that provide power — 20 amps, five amps, whatever the amps might be.”

A body (hard-wired) output is a physical output from the system, usually a 12V power source, for headlights, the service-brake switch, or door switch.

A parameter is a computer code (programming) used to customize the configuration of the system.

“In the Freightliner world, they're basically little chunks of programming,” he said. “I have a program that says when the park-brake switch is closed, and I see this ground input, broadcast the message under 1939, and turn on that park-brake switch instrument light.”

A high-current switch is a switch in which the power to operate a piece of equipment flows through the switch (traditional hard-wired switch).

“I have a 12-volt battery source. I send power to the switch. The switch is a physical toggle. It connects two conductors together.”

A low-current switch is a switch that only signals the system to activate a feature (multiplexed switch).

“The reason for that is, I really don't have the battery power for the output going directly to the switch,” he said. “My switch is an input device to my programmable controller. The programming for one OEM is written so that the program is looking at that specific location in this module and saying, ‘If that location is in the on position, do X/Y/Z. Turn on an output to do something with that.’ With Freightliner, our switches have a unique ID, so when the controller sees the switch is in the on position, it will do what it's supposed to do based on the program of the parameter.”

An impact on profits

Howard said multiplexing is important moving forward because it has an impact on a company's bottom line from the standpoint of the time it potentially takes to do upfits and also, in the long term, in the ability to diagnostically troubleshoot some of these systems in the field.

“The electrical interface has the opportunity to be the biggest strength or most glaring weakness,” he said. “Multiplexing can simplify body installations by reducing wiring, centralizing connections, and allowing programming flexibility. Multiplexing is important because it has a direct impact on a body builder's ability to build on a chassis platform. A vocational truck has no value until a body is installed. But multiplexed electrical interfaces are one of the least well understood aspects of the body and chassis connection.”

He said that some are experts already, but for others, multiplexing might be a totally foreign concept, so he tried to give a detailed background in layman's terms.

He said PTO switches based on multiplexing have the ability to control multiple operations with no additional wiring. The control module has output to power PTO solenoid, and programming for PTO output can include safety interlocks with no additional wiring for the park brake, neutral interlock, RPM thresholds, and vehicle-speed thresholds. Programming for the PTO switch can send J1939 remote set speed messages to the engine ECM with no additional wiring.

“So there's a lot of manipulation I can do without changing any wiring on the chassis,” he said. “My wiring remains fairly simplistic because I really only have an outgoing circuit and ingoing circuit coming back. In the bulkhead module, we can also broadcast a message to, for instance, the Cummins ECM, and as soon as it sees the message, it elevates the RPM.

“There's increased flexibility. I can give you an additional piece of hardware that has inputs and outputs that are not for truck features but for body features. With Freightliner, as part of the truck, I can give you an extra item that has, for example, 12 20-amp outputs. Those outputs don't do anything until you decide what to use them for. So you can associate those switches with those outputs.”

In explaining the most basic comparison between a traditional hard-wired and a multiplexed electrical system, he said the multiplex system does away with fused switches wired directly to the battery. Instead, low-current Smart Switches send signals to the bulkhead module and to its slave, the chassis module via the J1939 backbone.

Building safer trucks

Safety features are important: There's a horn warning when the driver door is opened with the park brake not set. There's also one that automatically engages the headlights when the driver turns on the windshield wipers, which increases driver visibility and makes the truck more visible to oncoming traffic.

Howard said accessible programmability is going to vary by OEM. Training is available and there's ease of integration.

“If you are going to use multiplexing, think about, ‘Do I need to spec the truck with Smartplex modules? How many outputs am I going to use? What types of amperages? Quantities of inputs? Two position, three position? Indicator lights? Interface connectors? When you get the truck, it's really a blank canvas.

“We're going to give you a programmable controller. We're giving you the expansion capabilities. You've got switches and inputs and outputs, and you're going to design features you need to add to the truck. As you start to interface with your OEM, we'll start to help you build and understand how to spec the truck.”

Find the NTEA Work Truck Show Report archive with articles from 2012 to present