Moog and Element Materials Technology have fabricated a unique high-frequency multi-axis shaker table
In the world of automotive R&D, hydraulic simulation tables are a workhorse for performing tests on everything from what’s under a vehicle (for example, transmissions and suspensions) to inside the cabin (for example, seats and headrests). As OEMs increasingly develop EVs, engineers face new design challenges that experts say standard test and simulation equipment can’t handle.
“Auto industry simulation tables can typically reach 50Hz; but EV testing requires much higher frequencies, up to 150Hz,” says Kevin Oliverio, department manager for hydraulics at Warren, Michigan-based Element Materials Technology.
According to Oliverio, most of the vibration testing on, say, automotive suspensions and components starts to roll off around 50Hz. But EV battery components require a much higher threshold. With frequencies from 50 to 150Hz, a test lab can simulate a capacitor’s ability to deal with vibration as well as how well soldering bonds stand up. Higher frequency testing, up to 150Hz, also enables automakers and battery designers to accurately see the rate of charge and discharge under all conditions. This level of testing, says Oliverio, enables feedback equivalent to what a vehicle’s battery would experience while a car is moving versus parked.
Testing battery components was something, Olivero says, Element began undertaking seven years ago on a traditional simulation table for a large automotive OEM. The Element team saw where the auto industry was heading and increased its testing capability by bringing another simulation table online. With the use of battery cyclers, Element was able to measure a battery cell’s response over time. This also led Element’s team to enclose its table in an environmental chamber, including fire suppression and venting. As the auto industry kept pushing the boundaries of EVs, Element looked to stay a step ahead and add high-frequency testing.
The design and benefits of high-frequency test and simulation
Element approached Moog with its need for high frequency battery testing. Element’s request was to upgrade its existing Moog multi-axis shaker table, or MAST, which the motion-control company had installed several years ago at Element’s Warren facility. Moog set about solving Element’s challenge by quickly developing a dual servo valve manifold upgrade, allowing the Moog MAST to achieve the higher frequency required to perform EV battery testing. Element disassembled the hydraulic actuators on the table and shipped them to Moog for re-engineering. Moog quickly modified the design, performed the upgrade, and reassembled and tested the actuators. In a few weeks, the team reinstalled the upgraded high-frequency table at Element for use on a large, incoming OEM order.
“We looked at our existing system at Element in terms of acceleration and displacement and worked with them to beat the performance specifications,” Larry Rogers, associate key account manager for automotive testing at Moog. “All six actuators have to be controlled exactly in terms of speed and time, and that’s a significant challenge when the table has to vibrate at up to 150Hz.”
The upgraded, high-frequency Moog MAST can test vehicle components, including batteries and electronics, for vibration, durability, and reproduce data collected on proving grounds. Underpinning Moog’s high-frequency shaker table is a six-leg hexapod (or Stewart platform), which the company originally developed for flight simulators. The hexapod has two equilateral triangular frames set one above the other, offset at 30°. Each apex of the top triangle is connected to the two apexes below it on the lower triangle via Moog actuators. Moog’s engineers designed the new table to reach frequencies up to 200Hz. The battery packs going into some of the EVs on the market include as many as 2,500 batteries, which can weigh 450kg or more. The high-frequency Moog MAST includes a table measuring 2,300 by 2,000mm and an actuator peak force of 53kN, which will handle a system payload of up to 600kg. Like traditional systems, the Moog MAST at Element has six degrees-of-freedom, moving the table in the x, y and z axes, with rotational movements over all three (i.e., pitch, roll and yaw). Without simulation technology like the kind in place at Element, OEMs lack real-time data about battery testing, Oliverio says, so they pull from generic specifications.
“If a car or battery maker wants to know what happens to a vehicle’s battery cell when the driver goes from 0 to 60 in 3 seconds, we use the new Moog MAST to replicate that,” Oliverio adds. “The table is resonance free up to 150Hz with a full payload.”
Oliverio says Element has combined the high-frequency table from Moog with the motion-control company’s test software and the Moog Test Controller to test EV battery packs in ways not possible until now. With the test controller and a power spectral density profile, Oliverio and his team can run a vibration test on a large battery pack before the OEM puts the vehicle on the road to see what shakes loose. This enables Element to get involved in the vehicle maker’s design and development process much earlier. Insight gained early in the process can then be applied to automobile specifications and use cases. Oliverio says customers are now coming to Element to take their testing a step further and replicate data they have collected from a proving ground or verify an EPA model with the new high-frequency shaker table.
“Real-time replication with 6DOF, especially for battery packs, is the next, big wave of testing,” Oliverio adds. “Other EV makers, like Tesla, are focused on the in-cabin gadgetry, so testing how that holds up is a priority, too.”
Oliverio says one advantage of working with Moog to upgrade the table versus buying a completely new system was the cost, another was the engineering know-how. A new table would have been an order of magnitude more expensive than the engineering Moog provided in three weeks, Oliverio notes.
“We’re now running live battery-pack charging and discharging in an environmental system at 150Hz; there may be less than ten other locations in the world that can offer that,” remarks Oliverio. “We’re running headfirst into the battery game, and high-frequency testing is getting us return customers and a line-up of new ones.”