Sample data used in defining vibration test regime

Accelerated stress testing facility for drive trains

Batteries for automotive use are being subjected to accelerated stress screening using vibration systems based on data collected on field accelerometers.

Automotive engineering consultancy, Drive System Design (DSD), has overcome one of the biggest challenges facing companies developing new products for completely new applications; devising a realistic test programme to validate a product early in its development, in order to avoid costly revisions later. Taking accelerometer data from prototype field trials, DSD configured a comprehensive vibration test programme to provide accelerated life testing for a custom-designed battery system.

DSD’s client, Hyperdrive Innovation, develops powertrain systems for electric, hybrid and conventionally powered vehicles, including robotics, off-highway and automotive applications. Hyperdrive’s Engineering Director, Robin Shaw explains the reasoning for the test:

“Accelerated testing undertaken independently was attractive to us as it meant we could run a programme in a short time frame to give both ourselves and our customer added confidence that our battery system was robust and ready for series production,” he says. “We appreciate the professionalism and expertise demonstrated by DSD in designing an optimum test regime using real-life data and then running this test in its independent facility for one of our custom-designed battery packs.”

Unlike derivations of previous products or revisions to existing applications, which can use historically proven tests, the new product required DSD to devise the test specification from scratch. The key objective was to have a representative regime for testing both the complete battery system and Hyperdrive’s own Battery Management System (on a PCB) to a short as timescale as possible.

“Any all-new product or application creates a validation challenge; early confirmation of the design is vital to minimise development risk, but established test regimes are often inappropriate,” explains DSD’s managing director, Mark Findlay. “The methods developed by our engineers to overcome this barrier have the potential to help clients across a wide range of industries, products and applications, where no relevant baseline data exists.”

The raw data was collected from two accelerometers sampling at different frequencies, with DSD’s first task being to convert the data into a meaningful format. Appropriate vibration amplitudes, frequencies and durations were taken from the field data to create a duty cycle with the required Factor of Safety, using Labview and Matlab software.

A test profile based on the frequency content of the data was defined to represent an average of many repeated tests. DSD rejected simply replicating the field data on a shaker rig as this would only have simulated the previous test, not provided an accelerated test capability.

DSD designed the fixtures and frames for the test rig to ensure loading was applied through the standard system mounting points. Testing was carried out in three perpendicular axes, under ambient conditions, and was completed within five days. Hyperdrive then took back the battery pack to test the integrity of all systems and electronic parts.

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