HBK Helps Daimler Trucks Ensure Structural Integrity

Daimler Trucks North America (DTNA) is the leading heavy-duty truck manufacturer in North America. Headquartered in Portland, Oregon, DTNA produces commercial vehicles under the Freightliner, Western Star, and Thomas Built Buses nameplates.

Customers rely on Daimler trucks, such as the new Western Star 49X, to get the job done and keep their businesses running smoothly. They need reliable vehicles that can withstand hundreds of thousands of miles on the road.

To meet the needs of these demanding customers, and deliver long-term durability, maximum uptime, operator comfort and safety, DTNA tests their trucks in the lab, on the test track, and on the road.

Problem

To ensure the reliability of their products, Daimler Trucks North America needed to develop a solution that ties together field test data and lab test data, ensuring that lab tests simulate real-world conditions. Additionally, test setup time had to be dramatically reduced, while simultaneously producing highly reliable and repeatable test results.

Solution

Sensor, hardware and software were selected from Hottinger Brüel & Kjær (HBK), including nCode automation for data management and collaboration, GlyphWorks for data analytics and SomatXR data acquisition with catman software.

Results

With the new equipment, the group could reduce test setup time by 60%, from 12 hours to 5 hours. The sensors are connected to an on-board SomatXR data acquisition system, which then connects to the controller via EtherCAT. This not only reduces cabling time, but eliminates time spent troubleshooting analog noise problems and finding and eliminating ground loops in the analog cabling.

The Data Acquisition Challenge

This comprehensive approach to testing posed a particular problem for Joe Griffin, a test engineer in the Product Validation Engineering (PVE) Shaker Lab in Portland. As a test engineer in the structural durability test lab, his job was to develop a solution that ties together field test data and lab test data to ensure that lab tests simulate real-world conditions, thereby ensuring the reliability of DTNA products. To accomplish this, Griffin selected sensor, hardware and software from Hottinger Brüel & Kjær (HBK), including:

  • Automation for data management and collaboration
  • GlyphWorks for data analytics
  • SomatXR data acquisition with catman software

In addition to making sure that lab tests accurately simulate real-world road conditions, Griffin was also tasked with streamlining the way that DTNA runs tests in the structural durability test lab. He needed to find a way to dramatically reduce test setup time, while simultaneously producing highly reliable and repeatable test results.

In 2016, DTNA upgraded its lab by purchasing Instron Labtronic 8800ML shaker controllers. One of the reasons the team chose the Instron controller was because it enabled them to connect the data acquisition hardware to the controller via a real-time, Ethernet-based bus called EtherCAT™.

EtherCAT

EtherCAT (Ethernet Control Automation Technology) offers a high bandwidth connection between devices (clients) and the master or controller application using "distributed clock" technology that integrates and synchronizes all data. EtherCAT extends the IEEE 802.3 Ethernet standard and enables data transmission with predictable timing and precise synchronization. Ethernet packets are no longer first received, interpreted, processed, and copied on to each device in each connection. The EtherCAT protocol continues to transmit data directly in a standard Ethernet frame, without changing the basic structure.

The EtherCAT client devices take the data intended for them as the frame passes through the device. Similarly, input data is inserted as it passes through with an offset of only a few nanoseconds. Because EtherCAT frames contain data from many devices operating in both transmit and receive modes, the usable data rate increases to over 90%. This allows the full duplex characteristics of 100BASE-TX to be fully exploited and effective data rates of over 100 Mbit/s to be achieved.

 

 

In the past, all inputs to the shaker controller were purely analog voltage lines coming from the eDAQ bridge layer DAC connection. The sensors, such as strain gage used in bridge type configurations, were digitalized by ADC and again normalized to ± 10 V and wired to the controller in parallel, sensor for sensor. This consumed a lot of time and was error prone. Using analog inputs and outputs also limited the number of channels that could be used for correlation and cable length.

To reduce setup times—and setup errors—DTNA needed data acquisition equipment that supported Instron’s EtherCAT master integration via single cable.

ComparisonAnalog old pathDigital new path
190 channels

190 x ADC

Configure 190 x ADC

190 X ADC

190 X Cables voltage (BNC)

Configure 190 x DAC

Configure 190 x ADC

190 x ADC

Configure 190 ADC (TEDS)

1 X Cable (Ethernet 4 x 2 pair)

Auto update EC master

 

# EtherCAT is a registered trademark of Beckhoff

HBK: Experienced, Well-known and Trusted Partner

After some evaluation, the test engineers decided to go with HBK. One of the reasons they choose HBK is that HBK has extensive experience in the field of structural integrity. A second reason is that they were already HBK users. DTNA has been using Somat eDAQ data acquisition systems for more than 15 years and as a result trusted its measurement technology and its ruggedness in tough testing conditions.

HBK was able to provide exactly what they were looking for. The system that DTNA specified included the following units from the new ruggedized SomatXR Series with the following module configuration:

This system allows them to acquire data from all different sensor types used in their testing and has proven to be ideal for gathering data in harsh environments, such as the test track and durability lab.

In the lab, the data acquisition system connects to EtherCAT to provide data to the Instron controller in real-time with minimum latency and in parallel via Ethernet and without any bandwidth limitations to a PC running catman. The only difference between the data acquisition system used on the test track and the data acquisition system used in the durability lab is the single module that connects the system to the network, making it a very simple process that ensures data integrity and comparability between the lab and test track configurations.

Although there were some challenges in the beginning, such as how to use the new data acquisition and shaker controller hardware and software, HBK proved to be the perfect partner. HBK is one of only a few companies offering a mobile recorder that can operate just as easily in the lab.

QuantumX, the non-ruggedized brother of SomatXR, introduced real-time EtherCAT integration in 2008. Like QuantumX, SomatXR offers Twin Signal Path. All inputs creates 2 digital signal paths, because of the bandwidth limitations of EtherCAT and to allow users to keep on working with catman software for data acquisition and analyzing the structural integrity of the test specimen:

-        1st signal real-time low latency output oriented with 1 ms loop time

-        2nd signal high-speed time stamped PC based data acquisition and analysis with up to 100 kS/s per signal depending on module type

From Test Track to Test Lab

To perform realistic durability tests in the lab, DTNA relies on data gathered from the real world, namely its High Desert Proving Grounds in Madras, Oregon. Completed in 2017, the High Desert Proving Ground stretches across 87 acres and includes a 3.5-mile test track with highly engineered surfaces that allow DTNA engineers to simulate nearly any type of conditions of their vehicles will encounter nearly anywhere in the world. The track is a 3D topography of the road conditions that come from a sample of Daimler driving across European roads to create a real life road profile to apply to both providing grounds in Germany and Oregon.

At the proving ground, a test vehicle is instrumented with a variety of sensors, including:

  • Accelerometers (DC MEMS type: 50g, 0 … 2000 Hz)
  • Bridge / strain gauges (350 Ohm, in ¼ bridge configuration, ½ and full bridge own load cells)
  • Wheel force transducers (6 x WFT from MTS SWIFT analog voltage or Kistler RoaDyn on CAN)
  • Displacement sensors (LVDT, string pots)
  • Voltage (hall effect displacement, home brew …)

Although the number of channels varies depending on the type of vehicle, the minimum number of sensors that DTNA attaches to a vehicle is seven; to drive a shaker, you need as many recorded channels as the number of actuators used in the lab durability test. For this application, there are four vertical actuators, two longitudinal actuators, and one fore/aft actuator.

Typically, DTNA gathers data from 48 different sensors during the road test. The more data they collect, the more realistic will be the simulation in the shaker lab. The SomatXR data acquisition equipment gathers data from these channels while a test driver pilots the vehicle on the test track. This phase takes about two weeks to complete.

Using GlyphWorks and nCode Automation for Data Analysis, Storage and Report

Once the test data has been collected, Griffin and his team use GlyphWorks to analyze the data. GlyphWorks is a data processing system offered by HBK that contains a comprehensive set of standard and specialized tools performing durability analysis. Designed to handle huge amounts of data, GlyphWorks provides a graphical user interface designed to allow users to visualize, analyze, and manipulate test data, saving users both time and money.

One of the things DTNA does with GlyphWorks is find the most significant parts of the road test data and edit out the data collected when the test vehicle was rolling over smooth road. Analysts also parts of the track data that can’t be simulated on the shaker. By concentrating on only the most applicable data, the lab tests can be run in much shorter time than durability tests on the test track.

Once the road test data has been “trimmed,” engineers use GlyphWorks to calculate the system transfer function and calculate initial drive file. The drive file contains the data supplied to the Instron controller, which controls the shakers in the lab.

The next step is to refine the drive file. To do this, they instrument an assembly, such as a truck cab, with sensors in the same positions as the test vehicle at the test track. Then, they feed the drive file to the Instron controller, run it, and measure the response data at each sensor location.

Using GlyphWorks again, they compare the data they just acquired with the data acquired on the test track. If there is a significant difference between the test track data and the test lab data, they calculate a new drive file, using the amount of the error between the two sets of data. They repeat this process until error between the test lab data and the test track data has converted to a reasonable value. Typically, this takes between eight and twelve iterations before the engineers are satisfied that the drive file will ensure a rigorous test.

Reasonable value is based on a judgment call from Daimler durability test engineers based on understanding the differences between the full vehicle and chassis. It relies on the Intron TWR software to blend RMS error and pseudo damage calculations on the transducers with a fixed intercept and slope. Engineers also use level crossing comparisons to judge if the right number of zero crossings occurred during the test, and what amplitude levels are captured. This varies based on the test intent – a simple hood test is treated differently than a test on the chassis frame.

At this point, they’re ready to do durability testing using the final drive file. Once a test has been run, they’ll use GlyphWorks again to analyze the test data. And, when the data is ready to be archived, they use nCode Automation, a web-based environment for automatically storing and reporting engineering data. nCode Automation, also part of the HBK product family: it not only eases test data storage and retrieval, it makes it easier to share test data with design engineers.

"I Love This Job"

Some engineers are just naturally “truck guys.” Joe Griffin is one of those guys. His father was an engineer for Daimler Trucks, and his mother worked there, too, in several different positions. So, as a kid, he heard stories about the company and the work there.

After high school, Joe attended the University of Portland to pursue a degree in Mechanical Engineering. In 2014, he was an intern in the shaker lab, and in 2015, he earned his bachelor’s degree and joined Daimler full-time. One of his first assignments was to drive trucks around the country, gathering data that would help Daimler build a better test track.

When the durability test lab was upgraded in 2016, he was in the right place at the right time. As a recent graduate, he embraced the new technology, and his bosses relied on him to help bring the new systems online.

When you talk to Joe, you get the feeling that he’s the right guy for the job. He has a passion for trucks and for making them the best they can be. “I love this job!” he exclaims.

EtherCAT Synchronizes Connections and Cuts Costs

SomatXR EtherCAT integration allowed DTNA

  • save cost by using one solution only in field, lab and bench.
  • to get high quality analog data and a reliable freely scalable solution
  • to save cost and space by going fully digital with less material and parts in use (simplicity)
  • to save time and cost by dramatically reducing complexity and setup time by min. 60% with a plug and play auto integration into INSTRON without any intermediate file generation and reading (ESI)

More about EtherCAT

Conclusion

The test lab upgrade has really paid off for Daimler, and Griffin attributes much of their success to their decision to “go digital.” By that they mean their choice of EtherCAT—short for Ethernet for Control Automation Technology—to connect their data acquisition systems to the test stands in the lab and to their IT infrastructure. EtherCAT is a technology that provides users with short cycle times and time -stamped synchronization between nodes on an EtherCAT network.

Despite some early challenges, going digital has proven to be the right thing to do. The SomatXR data acquisition system works very well with the Instron test stands. “It’s basically plug and play,” said Griffin.

With the new equipment, Griffin’s group has reduced test setup time by 60 percent, from 12 hours to 5 hours. Instead of running long, analog sensor cables from the test piece to the controller, the sensors are connected to an on-board SomatXR data acquisition system, which then connects to the controller via EtherCAT. This not only reduces cabling time, but eliminates time spent troubleshooting analog noise problems and finding and eliminating ground loops in the analog cabling. Note that the digital signal is noise-immune, since it moves through a built-in analog filter that then digitizes the data immediately in the amplifier.

Griffin also credits SomatXR’s catman software for saving setup time and improving data quality. Griffin says:

“catman guides us through the setup in a user-friendly way. We love that it checks channels for sensor or cable failure, and the raw data acquisition, data analysis and preparation helps us to be quicker from idea to result.”

Another benefit is that the measurement data has a far higher quality than what they were able to obtain before. Says Griffin:

 “Improved data gives our internal customer—Mechanical Engineering—better insights on how to improve and optimize their designs.”

The end result: more reliable trucks with lower test costs and a shorter time-to-market.

About DTNA

Daimler Trucks North America is the leading commercial vehicle manufacturer in North America. Headquartered in Portland, Oregon, DTNA produces commercial vehicles under the Freightliner, Western Star, and Thomas Built Buses nameplates. DTNA portfolio of distinctive brands serves a multitude of industries and commercial vehicle applications. The company also is a leading provider of heavy- and medium-duty diesel engines and components.

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