*wheeeee* — Behind the sound of an EV

A friend of mine, who has an NVH CAE background (basically he’s an engineer who works on simulation of noise and vibration) told me 5–6 years back, “Electric Vehicle is the future.” “So what?” I asked. A very thoughtful reply came my way, “So there will be NO Vibration, NO Noise issue and a good time for me to switch my domain expertise from NVH.”

He was pretty much on point — Electric is the present. However, we completely misunderstood the notion of NVH from the Electric Vehicle perspective. And that remains true for most of us — unless one has designed, developed and delivered them to run on the roads — like we have, at Ather Energy.

Conventional Internal-Combustion engines when present on a machine, have their own characteristics of sound and vibrations and we as users, whether it’s a 2-wheeled Motorbike or 12-wheeled Cargo mover, are accustomed to those characteristics owing to prolonged User Exposure (not the User Experience). No doubt, when an EV comes into the picture, we as users, expect it to be quieter, lesser in vibrations and smoother while running. But an Electric Vehicle in itself is an assembly of major sources of noise and vibrations as compared to IC engine Vehicles. How then do we tackle this challenge?

The Problem Statement

”If you have one hour to save the world, better spend fifty-five minutes defining the problem and only five minutes finding the solution.” says a popular quote. Precise understanding of the problem and correctly defining it is more challenging than finding the solution itself.

NVH issue in EV is twofold -

1. Different characteristics of the vibration sources in EV

2. Our “Used To” part for IC Engines NVH characteristics

Let’s try to understand the second part quickly. Imagine yourself riding an IC Engine motorbike, let’s say at a good high speed and then you turn off the engine with gears in neutral. Will you still be comfortable in coasting down the road in such circumstances- the answer is NO. Road-tire, chain drives, gear drives and any loose peripheral due to missing screw or loose bolt will cause a lot more irritation if not a louder noise in such conditions. The problem thus unearthed by making powertrain silent goes as a subset of EVs — especially 2-Wheeled motorbikes, where we don’t have the luxury to enclose such systems as we can do in cars. Deterioration of all such components in service life further aggravates the issue.

Now coming to the first part — Different characteristics of vibration sources in EV’s. Motor induced vibrations are present in EVs similar to its counterpart IC engine induced vibrations — the difference however being the electromagnetic forces which come from motor pack. It’s far easier to understand combustion induced vibrations in IC engines than electromagnetic forces. The frequency range of interest increases 5–6 folds easily with electromagnetic forces than it would in IC engines. NVH engineers are not used to working on this higher side of the frequency zone. Usually energy content dwindles in this HF zone but here we have dominating forces and complexity of current and magnets to add as toppings.

Deep Dive

To understand the phenomena better we did tests, lots of tests — in different use case scenarios, running up and down slopes, coast-up and coast-down, different loads and payloads etc. This deep dive with test data led us to understand the major sources and issues. Same Accelerometers, Microphones, Operational Deflection shapes, Modal Analysis, Torsional Vibration Analysis etc… will still do the job for you, just that the players are different, and the signatures are different and hence new unexplored avenues open up for you as an NVH Engineer.

The true solution for Product Cycle

Discover the problems through physical testing, learn more and more with test data but testing helps in the later part of the product development. It’s more of a reaction than action in case of test driven designs, which is against our philosophy at Ather Energy.

CAE simulation is the obvious answer to this but in such a scenario, it comes with own challenges. We are now trying to couple the two streams of Physics viz. Electromagnetics with Vibrations and Acoustics. Of course, we need three different solvers for the same simulation model — in such cases where output of first is fed as input to the second and then to the third one. Trying out with the various available options, we simulated the Electro-Magnetic Force coupled NVH Simulation. Real challenge for simulation engineers doesn’t end with just simulating the real life virtually but by the degree of correlation you achieve with test data and your virtual models. The attempt to replicate the observations from test in a virtual domain is by far more challenging and can’t be done if we don’t have a deep understanding of the test data and the governing physics laws for the system. Developing high fidelity simulation models also helped us to visualize and understand the physical phenomena in detail by powerful Results Processing Tools.

Up the ladder

Engineering the sound which comes out of vehicles from component interactions and different paths has huge impact at customers’ end. One would like to ride a vehicle where the sound resonates with and responds to the rider’s nudge to the throttle. Sound Engineering with Psychoacoustics is the focus on next steps — produce Signature sound from our vehicles, which impacts users and makes us stand out in the crowd. Here we are not only talking about removing any unwanted irritating noise early in the design cycle but also how to produce a signature sound with the same parts and acoustics engineering (not by putting a digital speaker). Investing our efforts and resources in NVH have resulted in a vision of converting the NVH characteristics (which are usually mistaken) as granted for EVs to become prime attributes of our products. If my NVH friends in Simulation, Testing or Design are reading this article — The future of Intelligent EVs is bright and so is yours. You don’t have to switch from your NVH work domain, just expand it to accept the new challenges of EV-NVH.