Reducing noise seems to be the theme from the movers and shakers shaping the future of electric vehicles in the most recent meeting of the Gear and Power Transmission Research Lab (GEARLAB).

This consortium currently has 75 members and the sponsor feedback section of the meeting was focussed on noise reduction according to the article in Gear Solutions magazine by Lane Winkleman.
Without the cover of noise created by an internal combustion engine, the drivetrain becomes the largest contributor of noise inside the cabin.

So what are the main causes of drivetrain noise in EVs?

There are usually two main contributors to drivetrain noise – transmission error and frictional vibration.

Transmission error – can be targeted by designers who can make changes to the micro geometry of the gear to meet the lower noise requirements.

The next main contributor to noise is frictional vibration, mostly vibro-acoustic noise, whereby the friction generated by intermeshing gears is transmitted through the shafts and amplified in the housing.

The most common methods of reducing this are lubrication and reducing surface roughness of the tooth flank. However, this method can be fine-tuned if lessons are to be learnt from the aerospace industry.

The article below describes how the causes of frictional noise were put to the test in both a research environment and later the theories gained were tested in the real world in a Sikorsky S-76C+ main transmission. The cabin noise issues are the same for the plane as they are for an electric vehicle. The test was without and then with isotropic superfinishing.

The results were clear and the conclusion was that the increased demand for quiet electric vehicles may lead to the industry considering isotropic superfinishing as they do in the aerospace industry. Please go through to the article for more detail and analysis of the initial research and real-world testing results here.