Propulsion Noise. Then and now.
Martin Murray, CTO, Mahindra Electric
Read about the how the “knocking” sound came to be associated with good fuel efficiency and how that perception has changed to accepting silence as a better standard for understanding performance.

CTO Electric Blog June 7, 2020 - About Propulsion Noise

During the industry's drive to improve ICE efficiency 40 years ago, propulsion engineers focused on optimizing gasoline engine-fuel and spark control. It was well-known that operating gasoline engines near the “knock limit” was good for fuel efficiency. “Knock” is another word for pre-ignition which is a phenomenon where two or more combustion kernels occur during the ignition phase. This audible noise sounds similar to marbles rattling about in a metal can. Some engineers argue that this knocking sound was “the sound of efficiency” and customers would embrace it knowing that their engine was operating efficiently.

Likewise, at the birth of automotive electrification more than 20 years ago, some engineers argued that the high-pitch whirling sound of the electric drive was “high tech” and “space-age” and that the customer would embrace this noise as evidence of goodness.

Of course, we know now that customers don’t like engine knock or whirling sounds. They associate silence with quality and high performance. After customers enjoy their first experience in the smooth, strong, quiet, liquid-like acceleration with electric drive, they become aware of the awesome potential of this technology and hold these expectations for every future product.

At Mahindra Electric, our challenge is to apply our scientific knowledge about motors, electronics, and gear trains to aim for a quiet drive. We know that power density, material cost, packaging space, and other design factors offer many trade-offs, so we will aim for customer solutions with the correct balance of design factors. We will continually enhance our NVH measurement capabilities to track our progress through development, and we will work in close partnership with our plants and suppliers to ensure that all the products we produce maintain the NVH character we design.

About the author:

Martin J Murray is Chief Technology Officer for Mahindra Electric Mobility Limited based in Bangalore, India, responsible for overall engineering activities and information technology for vehicles, propulsion systems, and propulsion components.

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