For a vehicle, its mass distribution combined with overall weight determines its ride dynamics. In this write-up, Dinkar Agrawal answers the FAQs around light weighting in the case of electric two-wheelers.
What is the importance of light-weighting in case of electric vehicles and how are the vehicle dynamics different than an ICE vehicle?
Light-weighting is important in every type of automobile. Especially in EVs, the main performance parameters i.e. top speed, acceleration and range are directly linked to the weight of the vehicle. Higher the weight, more is the power needed to get to the target speed. Higher the weight, more is the battery capacity required to get to the target range.
Also, the starting torque in EVs is very high as compared to ICE vehicles. The instant throttle at the start of the ride can literally get your front wheel lifted if there is not sufficient weight on the tyre. So, there is a fine balance that should be considered at the time of deciding the light-weighting strategy.
Speaking of dynamics, Mass distribution of the vehicle is the chief contributor to ride dynamics. In case of an EV, this is highly tuneable. We can relocate motor, battery, MCU, Onboard charger and other components as per our convenience to get the target weight distribution. Whereas in ICE vehicles, the main lumped mass i.e engine cannot be relocated with ease to change mass distribution. The option of tweaking mass distribution aids a lot in improving the ride dynamics of the vehicle.
Which all parts of the electric vehicle and powertrain can/should be modified to ensure a lower weight?
Major contributor to the weight of an electric vehicle is the battery pack, but reducing battery weight is subject to cellular chemistry level R&D. As a light weighting strategy, each and every part in the EV should be designed for minimum weight and max factor of safety. Due to less amount of parts in an EV, weight of frame can be reduced. Apart from that, rotating parts such as rims, tyre, brake rotor etc contribute to weight and rotational inertia of the vehicle. High attention should be given to such parts, so to increase the overall acceleration performance of the vehicle.
What are the ways to achieve light-weighting in EVs?
Lightweight structure and parts can be designed using topology optimization process and light weight construction materials. Different steel grades with varying properties can be used after topology optimization to provide best strength to weight performance.
Apart from that, designing parts to serve multiple purpose can also result into weight reduction. For an example, accommodating battery pack into the floor board adds structural rigidity to frame, less material is required in encasing battery pack and lowers the Centre of Gravity of the vehicle. Another example would be designing motor casing with upper pick up points of monoshock and swing arm pivot in case of mid mount motor.
Current trends in light weighting of electric 2Ws are limited to use of Al alloy, Al-Mg alloys and Topology Optimization of parts. Other new age tech such as Carbon Fiber Reinforced Polymer (CFRP) composite parts and frame are at very nascent stage due to its production limitation. Also, the use of noble metals like Titanium(Ti) and its Alloy is at a nascent stage due to cost factor.
We are likely to observe rise of CFRP, Ti and Ti-alloy with widespread availability of additive manufacturing technology. Also to get max benefits of topology optimization, additive manufacturing is the best manufacturing technology.
What are the trade-offs with respect to costs and performance? What are your recommendations to achieve the optimal tradeoff for an electric 2W?
As mentioned in above answer, Al alloy and Al-mg alloy are available in market which can aide decrease in weight of vehicle but it comes with comparatively higher cost. Plus, Al alloys has low fatigue performance when compared to Steel. Due to low fatigue performance of Al alloy, parts are prone to catastrophic failure under fatigue. So, special care should be taken while designing such parts.
Our recommendation is to use steel in majority of cases. As steel is predominantly used in the automobile industry, the production techniques for steel parts are at matured stage in India. Also, steel is considered one the best material for fatigue performance.
Can you talk about mass decompounding effects?
Mass decompounding is a very effective strategy for light-weighting of EVs. For E2W, systems such as Handle bar assembly, body panels, rims and tyres can be used to apply mass decompounding and get best suitable results of it. As E2W have less number of parts, mass decompounding and light weighting strategy are aligned to part level optimization process.
Is it possible to use the body for energy storage?
Using body as energy storage system is possible in 4W applications. But in case of 2Ws, doing so will compromise the possibility of swapping.
How is Oben EV approaching this concept in their product development?
At Oben, we are highly focused on light-weighting the vehicle by using prevailing materials. Use of new age technology such as topology optimization with available grades of steel, which results in best cost to performance ratio. Once the new age technologies and materials would be common place, we will start adopting it. Apart from that, we are using high density cells available in market at present stage to get best cost to weight and cost to performance ratio.
About the author
We would like to thank Dinkar Agrawal for sharing his experience and knowledge in the EV domain to write this explainer for EVreporter.
Dinkar is the founder of Oben EV – an upcoming EV start-up currently developing an electric scooter and charging infrastructure in India and abroad.
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