Modal Analysis Of Motor And Mount As A Stress Member

The concept of integrating powertrain components into a vehicle's structural framework has been a key engineering approach in motorsports and high-performance vehicles, writes Raunak Dhoot.

- Raunak Dhoot.

Ducati's trellis frame motorcycles have long employed the engine as a stressed member, eliminating the need for a conventional frame. Similarly, Formula 1 and hybrid endurance racing prototypes use their internal combustion engines as primary load-bearing structures, reducing weight while improving torsional rigidity. With the shift towards Electric Vehicles (EVs), this principle is being re-evaluated, particularly in the context of electric motors and their mounts. This article explores the modal analysis of an electric motor and its mounting structure when used as a stressed member, assessing vibrational characteristics, chassis integration challenges, and how topological optimisation can mitigate NVH (Noise, Vibration, and Harshness) concerns and strengthen the chassis torsionally.

The Role Of The Motor As A Stress Member

Traditional EV architectures rely on a subframe or a dedicated cradle to isolate the motor from the chassis. However, by treating the motor mount as an integral structural component, allowing chassis loads to pass through the motor itself, the vehicle benefits from:

I. Enhanced Torsional Stiffness:

The integration of the motor into the chassis reduces flex, leading to improved handling precision. Porsche's 919 Hybrid LMP1 car exemplifies this approach, where the hybrid power unit was an essential load-bearing structure i.n the rear bulkhead

II. Reduced Weight:

Eliminating an independent mounting cradle or subframe lowers overall mass. Tesla's structural battery pack follows a similar philosophy by integrating battery cells into the monocoque for added rigidity.

III. Improved Packaging and Aerodynamics: