Researchers Test High-speed Flywheels For Regenerative Braking Systems

A research group has developed a way to test high-speed flywheels which are being touted as potentially cost-effective means to reduce fuel consumption and emissions.

By storing mechanical energy and reusing it, such as in regenerative braking systems, the UK effort is working toward what is hoped could be an elegant alternative to present systems.

The researchers are testing in a new purpose-built container to better understand the performance of the rapidly turning flywheels in order to design a safer housing. Led by engineering firm Ricardo, the “FlySafe” project is a collaboration that also includes the University of Brighton and two other flywheel developers.

“The test environment which has now been completed – developed by the FlySafe project and installed at the Centre for Automotive Engineering – is believed to be the first and most advanced of its type in the world and is capable of testing flywheels spinning at up to 60,000 revolutions/minute in a vacuum,” said a statement from Ricardo.

“In addition to providing for non-destructive testing, it incorporates advanced imaging and sensor technology to investigate the behavior of flywheels when they are caused to fail at high-speed through the incorporation of a range of engineered defects.”

Video is acquired with a high-speed system recording at 20,000 images per second with the flywheel illuminated by a high-intensity pulsed laser synchronised to the camera. At this high frame rate the camera can record approximately just two seconds of video, so accurate synchronisation of the recording with the failure event is critical. The University of Brighton has developed a custom data acquisition system monitoring a number of sensors to enable this. These include accelerometers, strain, pressure, distance and temperature measurements within the flywheel enclosure and allowing to trigger the camera on the occurrence of specific conditions which might be expected to lead to failure. Such failure conditions might include, for example, a sudden expansion of the flywheel due to the onset of delamination or fragmentation, loss of vacuum pressure, or loss of speed.

High speed image of forced failure through delamination.

High speed image of forced failure through delamination.

In passenger vehicles today, regenerative brakes more commonly use a motor-generator to generate current upon deceleration and this electrical energy is in turn stored in the traction battery.

In certain systems however, a flywheel module is an integral part. It collects energy as the vehicle slows, which later sends to the drive shaft during acceleration. Electromagnetic flywheels generate energy in a similar fashion, but the energy storage acts more like a battery. Both setups save fuel and increase efficiency, though they also add extra weight to the car.

Other applications for the technology include electric trains and construction equipment. In Formula One racing, flywheels have been used for several season in the car’s kinetic energy recovery system, providing a vital power boost when needed.

David Rollafson, Ricardo’s vice president of innovation, explained how this new test environment can lead to better flywheels in these already-established applications, and may even lead to the adoption of flywheel regenerative systems in other fields.

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“A major challenge in designing compact and lightweight high-speed flywheel systems … is in the provision of safety containment systems,” he said. “In the absence of detailed data on potential failure mechanisms, these previously have had to be very conservatively engineered.

“The meticulous and detailed research being carried out on the FlySafe project and the existence of the test facility at the University of Brighton, will enable the partners to propose a BSI flywheel safety standard to promote a higher level of design optimization while retaining the full required safety level. I believe that these achievements of FlySafe will accelerate the commercialization of this very promising environmentally friendly technology across a range of industry sectors.”