IIT Guwahati team recommends drivetrain and battery sizing for e-2W in India • EVreporter

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IIT Guwahati team recommends drivetrain and battery sizing for e-2W in India • EVreporter


Need for India specific drive cycle

The primary purpose of any drive cycle is the performance assessment of a vehicle in terms of emissions, fuel consumption, and mileage. Drive cycle patterns are different for different countries. It depends on traffic intensity, road profile, driving skill, and geographical location. India is home to diverse climatic conditions ranging from tropical to monsoon. Moreover, the acceleration and deceleration profiles for standard drive cycles available in the country are soft, which is far from reality as traffic congestion is one of the significant issues in India.

For an efficient and economical design of drive train, heat exchanger, and even for research purposes, there is a dire need for an India-specific drive cycle for different regions based on diverse factors such as rural, urban, tropical, and monsoon conditions.

Key findings of the report

Assuming EV powertrain in place of Internal combustion engines, the performance needs of electric two-wheelers have been studied by the E-Mobility Lab, IIT Guwahati. The team analyzed different kinds of motors, ways of mounting motors, battery ratings, etc., that our EVs would demand to achieve parity with original vehicles on their respective drive cycles. Also, parameters such as the presence and absence of a pillion, motor optimization for acceleration figures or everyday driving, etc., were kept in mind. Battery ratings thus obtained were also extrapolated to decent range targets.

The key findings in different aspects such as drive cycle metrics, energy regeneration, fuel consumptions, emissions, Continuous Variable Transmission (CVT), battery ratings, motor ratings, and torque ratings for diverse conditions are as follows.

Drive cycle metrics

Kinetic Intensity (KI) – For Electric Vehicles, higher values of Kinetic Intensity usually indicate more stop-and-go driving and, therefore, more opportunities for regenerative braking.

The results show that the Renukoot drive cycle has the higher Kinetic Intensity, followed by Hyderabad Drive Cycle. Hence, a higher regeneration efficiency can be observed in Renukoot and Hyderabad Drive cycles.

Relative Positive Acceleration (RPA) – Relative positive acceleration can be used to distinguish between soft driving and harsh driving. Higher values of RPA generally indicate a harsher driving pattern.

The Hyderabad drive cycle is dynamic, and the metropolitan characteristics are inferred with a higher RPA value.

Fuel Consumption and Emissions

Lesser Emissions – Driving Optimized Motor – For any payload (150 kg/ 70kg), a motor optimized for driving would decrease fuel consumption as peak torque requirement would be lower than a motor optimized for acceleration case. This results in lower fuel consumption and lower emissions.

Better Acceleration – Acceleration Optimized Motor – For any payload (150 kg/ 70kg), an acceleration-optimized motor can deliver higher torques to achieve better acceleration performance. However, it will result in higher fuel consumption and higher emissions.

Regenerative Braking

The possibility for good regenerative braking is higher among the drive cycles with more stop-and-go durations. An efficient regenerative braking system can produce considerable regeneration (around 10-20%) in two-wheelers.

  • Renukoot and Hyderabad Cycles have higher KI (0.0048 1/m and 0.0046 1/m) with higher regeneration efficiencies (73.4% and 69.1%).
  • Around 18-20% improvement in fuel consumption is observed in Hyderabad and Renukoot drive cycles.

CVT Analysis

Improved Efficiency – CVT allows seamless change of gear ratios over a continuous range. In contrast with the traditional gear shifting technique used in two-wheelers, CVT enables the engine/motor to operate at better efficient points. An Optimized CVT ratio would result in higher operating efficiency for the motor’s same Power and Torque ratings. 10-15% improvement is observed in operating efficiencies for the proposed rule-based CVT mode.

Mileage Improvement – With improved efficiency, the fuel consumption would be comparatively lower, resulting in better mileage.

  • Guwahati drive cycle experiences the maximum reduction in Fuel Consumption of around 17-25 % in acceleration optimized case and about 11-18 % in driving optimized case for proposed rule-based CVT mode.
  • Hyderabad drive cycle has a minimum reduction in Fuel consumption of around 2-8 % in acceleration optimized case and about 1-7 % in driving optimized case for proposed rule-based CVT mode.

Regeneration with CVT

An intelligently controlled CVT ratio has a higher regenerative braking efficiency than a vehicle with a constant gear ratio. Hyderabad and Renukoot provide the maximum regeneration opportunities with 0.015 kWh/km and 0.009 kWh/km, respectively. Over 27% improvement in fuel consumption is observed in Hyderabad and Renukoot drive cycles for CVT with Regeneration compared to CVT without Regeneration.

Drivetrain and Battery Ratings

Torque requirement for economy mode with reduced acceleration requires a lower peak torque than sports mode acceleration, so the motor’s efficiency also increases. Further, lower torque ratings can highly benefit electric bikes to have relatively small motors, which will improve the driving range of the bikes.

For the exact range requirements, the kW ratings of the battery would change based on the type of motor being used. The choice of motors for an optimal battery size for different kinds of two-wheelers considered in this study follows the following order:

PMSM > Sync Rel > IM,

And for hub motors, the order is PMSM Hub > SyncRel Hub > IM Hub

Recommendations on Drivetrain and Battery Sizing

The optimal drive train parameters can be decided depending on vehicle type, expected range, and driving profile. For the analysis purpose, a PMSM motor is chosen. An efficiency of 0.8 at peak torque operating point, converter efficiency of 0.9, and battery utilization factor of 0.8 is considered for the 150 km range requirement.

Commute Scooter Category
Sports Bike Category
Mid-Range Bike Category
Retro Bike Category

Leading Electric 2Ws closest to recommended sizing

As per this analysis, we found that TVS iQube, Ather 450X, and Bajaj Chetak electric 2-wheelers are the vehicles in the current Indian market which are closest to recommended sizing for their respective categories.

This article was first published in EVreporter June 2022 Magazine that can be accessed here.

About the Author(s)

We would like to thank Dr.ing. Praveen Kumar (Professor – IIT Guwahati) (L) and Mr Mulpuri L N Sai Krishna(Research Scholar at EML – IIT Guwahati) (R) for sharing their research findings with our readers. The full report is available with the E-mobility Lab, IIT Guwahati.

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