Working with system integrator DynoTec, the world-renowned German auto company leveraged ELM-series EtherCAT measurement terminals and PC-based automation to tune up its vehicle development capabilities
A vehicle’s chassis is much more than a basic consideration. That foundational structure impacts how a car looks, performs and represents the carmaker’s brand. That’s why Mercedes-Benz leaves nothing to chance.
At the Mercedes Technology Center (MTC) plant in Sindelfingen, Germany, car axles are examined with the highest precision on four test benches – in parallel with road tests and simulations. The aim is to validate processes, analyze any vehicle anomalies and identify the components causing them.
To do so, the Mercedes-Benz developers use a signal processing component called the Hydromat. Developed by Daimler AG, this modular control system for sophisticated test benches supplies setpoint input, measured value processing, output stages and monitoring functions. The data acquisition (DAQ) tool helps developers measure the reactions of the vehicles while applying forces/displacements and torques in a high-precision and reproducible manner. So the suspension, kinematics and elastokinematics of the chassis can be recorded quickly and reliably.
This data can be visualized as characteristic diagrams, characteristic curves and characteristic data sets. Approximately 90 parameters are then compared with the digital twins of the vehicles. This protects both the development vehicles/prototypes as well as the digital development process in that important area known as the Mercedes-Benz driving characteristics.
“That’s why the test benches are an integral part of the Mercedes-Benz vehicle development process, where we ensure that parameters such as the component design, simulations, test benches and the road work together in harmony,” says Uwe Lochner from the chassis analysis team at Mercedes-Benz in Sindelfingen.
A look under the hood of the Mercedes-Benz test bench
To examine a chassis, the team at Mercedes-Benz sets the vehicle up on the test bench using the front axle jacks. Next, it’s positioned and fixed over the four hydraulic jacks. Finally, the vehicle axles are loaded and measured very precisely.
“When we talk about precision, we mean measuring distances with 0.1 mm and angles at 0.1 degrees and less than 2 Hz with high sampling rates,” explains Walter Selg, Managing Director of DynoTec Prüfstandstechnik GmbH, a system integrator focused on test bench applications.
During the excitation process, numerous sensors register the displacements, angles, forces and torques. All data is acquired using standard PC-based control technology from Beckhoff, displayed live on a monitor at the test bench for the operator, and forwarded in parallel to a database system. “After the test run, all measured values are automatically processed and any limit violations are displayed in the results,” Selg says.
Using these results, Lochner and his colleagues determine whether they will release the vehicle for further testing or whether the vehicle requires further analyses or mechanical modifications.
Back in the early 2000s, the control functionality for the test benches was outsourced to an RCP (rapid control prototyping) system from dSpace. Mercedes-Benz discontinued internal development for the remaining Hydromat functions, and it soon became difficult to procure spare parts for the legacy controllers in use.
So Mercedes-Benz commissioned DynoTec to design and implement an integrated automation solution for the test benches. The main goal in this modernization project was to retain the modular concept of the test benches.
“Our first approach was to find a series product on the market that featured as many Hydromat functions as possible,” Lochner says. “In the end, we didn’t find a series product that could 1-to-1 replace Hydromat. But we did find a promising open automation platform and ecosystem consisting of EtherCAT Terminals, controls and a development environment at Beckhoff.”
DynoTec gives test benches a tuneup
Just like a pit crew in a race, the experts at DynoTec were well prepared for a rapid tuneup of the Hydromat. And New Automation Technology from Beckhoff helped them accelerate this transformation. EtherCAT proved to be a key differentiator due to its high speed, flexibility and openness. It would provide an ideal replacement for several 30-meter analog signal lines. And it could readily connect new controls to the RCP system via an existing EtherCAT interface.
The industrial Ethernet protocol also allowed the engineering teams to explore different architecture options, explains Rainer Fischer, Managing Director of DynoTec: “This gave us the opportunity to implement a test bench concept providing decentralized data logging and digital measurement signal transmission – with all possible advantages in terms of wiring and signal quality.”
When it came to verifying and validating the decentralized control concept, DynoTec examined many issues:
What is the ideal coupling method to integrate the RCP system (synchronous/asynchronous, MainDevice to SubDevice, SubDevice to SubDevice, or distributed clocks)?
How does the signal quality of AD/DA converters from different manufacturers compare to the current system?
Which RCP system task runtimes result from the configurations?
DynoTec replaced the centralized, legacy PLC technology with decentralized control cabinets and EtherCAT Terminals mounted on the four jacks. The control cabinets contain the components for DAQ and servo valve control for adjusting the jacks in the x, y and z directions and for rotating them around the z axis.
The PLC task and the associated HMI run on a CX5140 Embedded PC from Beckhoff. The high-performance hardware allows the system status and error history to be visualized in detail on a CP2219 multi-touch built-in Panel PC. A C5240 19-inch slide-in Industrial PC handles the measurements and corresponding visualization.
TwinCAT 3 HMI Server (TF2000) software supports the visualization functions. All computers in the test benches are linked to a higher-level operating computer via TwinCAT ADS. In the overall architecture, the Beckhoff control system acts as the MainDevice and triggers the RCP system via UDP communication to achieve incredible synchronization and control quality.
Full-throttle resolution and sampling rates
The decisive factors for DynoTec and Mercedes-Benz were the high sampling rates offered by the ELM3xxx measurement terminals, the high speed of data transmission via EtherCAT, and the simple, compact and modular data logging directly on the four hydraulic jacks. “All in all, our standardized system, which integrates classic PLC tasks and sophisticated measurement technology, ensures significant cost advantages,” summarizes Rainer Fischer.
Based at Beckhoff’s office in Balingen, Germany, Dieter Völkle saw these advantages firsthand while collaborating with DynoTec and Mercedes-Benz on the project. “This is true even when dealing with the high bandwidth and resolution requirements that test benches place on the measurement technology,” Völkle says.
During a test run, the system synchronously records up to 136 measurement channels at 5 ksps each (10 ksps optional). This corresponds to a total sampling rate of 680 ksps. In addition, there are 36 setpoint or output channels with 5 ksps each and around 300 channels with post-mortem diagnostic data, which are recorded at 100 sps.
There is also a measuring box for external signals on each test bench. Each box has 16 analog inputs for special measurement technology and 16 analog outputs. These outputs can provide any measurement channel to synchronously record the outputs with the DAQ technology installed in the vehicle, for example.
EtherCAT and PC Control eliminate gridlock on the test bench
The compact EtherCAT Terminals not only make it easier to log signals but also to reduce footprint requirements. “We were able to remove one out of five computer control cabinets on the test bench,” adds Uwe Lochner. Because the control cabinets are less cramped, engineers can troubleshoot and fix faults faster, while retaining space to add functionality in the future.
In addition to space, the time savings are just as important for vehicle testing. The modular system structure of PC-based control offers a distinctive advantage here, too. The process of converting the other test benches was much more repeatable and way faster.
“Compared to the first test bench, we were able to reduce downtime by more than 30% when converting the last test bench,” says DynoTec’s Fischer.
In the same way that automakers never stop pushing the limits on their vehicle designs, test bench equipment will continue to evolve as well. For DynoTec, the next phase of the project will entail implementing the TwinCAT Analytics Logger. This real-time data logger is easy to configure and streams all measurement data to a central storage location. This simplifies post-processing across all test benches. With TwinCAT Analytics, it is possible to analyze both the historicized data and the live measurement data online.
After solving its demanding measurement and automation requirements, the Mercedes-Benz project proved to the test bench experts at DynoTec that EtherCAT measurement terminals and PC-based control can meet the highest demands of the automotive industry. And they have continued to implement those Beckhoff technologies in new projects. In one application, for example, DynoTec used the ELM3602 EtherCAT Terminals to implement one-third octave band analysis of triaxial IEPE vibration sensors with a sampling rate of 50 ksps.
“The scalable Beckhoff platform offers us entirely new opportunities,” Selg says. “Now, we can handle projects of any size with a fully standardized system.”
How can expandable measurement and DAQ technology enhance your test-bench applications? Contact your local Beckhoff sales engineer today.
Philip Ehlers is the Automotive Industry Manager at Beckhoff Automation LLC.
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