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POWERTRAINS


A new approach to optimising EV powertrains


UK-based engineering specialist, Drive System Design (DSD), details its plan for optimisation of next- generation commercial and autonomous vehicle electric powertrains.


released two technical papers that detailed the benefits of using the approach. The research presented identifies opportunities for lowering the drivetrain cost to reduce the battery requirements of commercial vehicles. Meanwhile, DSD also details the development of a process to optimise EV powertrains for the passenger car market, using an autonomous vehicle as an application example, introducing unique drive cycle conditions.


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COMMERCIAL VEHICLE EFFICIENCY “Enhancing the efficiency of the electrified powertrains utilised in commercial vehicles has two-fold benefits: reducing energy consumption and lowering the total cost of ownership, which in turn makes greener, cleaner vehicles a more viable fleet option,” Simon Shepherd, Head of Electrification tells us. “A systems engineering approach enables development teams to take a step back and assess where in the powertrain tangible gains can best be made. For example, increasing the unit cost of, say, the motor in favour of a more efficient alternative can actually lower the total vehicle cost.” The principle is detailed in DSD’s technical paper, ‘Commercial EVs: applying a systems engineering approach to optimise the powertrain to tackle the total cost of ownership challenge’. DSD evaluated over 4,000 different powertrain permutations of inverter, motor and transmission to find the optimal configuration, utilising a variety of optimisation techniques, processes and tools to quantify the impact of sub- system’s characteristics on overall powertrain performance and cost. “There are a number of complex powertrain sub-system


interactions that require appropriately informed design decisions,” explains Shepherd. “To go back to the example of increasing the unit cost of a motor, a more efficient electric power unit consumes less energy and can enable a significant reduction in battery capacity. We found that further powertrain energy and cost savings were possible by downsizing the motor


❱ ❱ Simon Shepherd of DSD believes a total


systems approach is required to find the optimum choice of


powertrain specification


systems engineering approach to electric vehicle (EV) powertrain optimisation could provide significant development time and cost benefits, according to DSD. The UK-based drivetrain engineering consultancy recently


❱ ❱ EV powertrain


optimisation can lead to more efficient commercial vehicles and a “comfort profile” suitable for autonomous cars


and using a multi-speed transmission to deliver the necessary wheel torque to meet performance targets. The additional complexity of the transmission is more than offset by the cost reduction in the motor and reduced battery size. Weight reduction of the overall system, particularly of the battery as the required cycle kWh reduces, is a further benefit of this approach, which offers increased maximum payload capacity, reduced overall vehicle weight and greater vehicle range – key issues for future EVs.”


AUTONOMOUS VEHICLES The company’s second paper, ‘Electric drivetrain architecture optimisation for autonomous vehicles based on representative cycles’ evaluates the cost of EV technology adoption versus performance benefits, where subjective feedback comes from a passenger and not the driver. Again, DSD is an advocate of utilising a systems approach to analyse each possible sub- system to enable complete powertrain concept generation. “The characterisation of sub-system and component


level behaviour permits the accurate prediction of system performance and cost. This enables mapping of the potential design space and investigation of a wide range of complex powertrain interactions and trade-offs at a system level,” says Shepherd.


Autonomous vehicles’ elimination of the human driver


subjects the vehicle powertrain to a significantly narrower range of operating conditions. Gone is the requirement for a ‘performance feel’ driving style, replaced by a need to maximise occupant comfort This may not sound like a big change, but is manifested through a smoother velocity profile and fewer torque peaks, which as an added bonus is also likely to result in extended total mileage in the duty cycle. “This combination of factors enables the use of a smaller motor and a lighter, lower cost system, ensuring the drivetrain package is minimised while performance and range targets are met, and that cabin space is maximised,” concludes Shepherd. As regulations become more stringent and the race to bring


electrified powertrains and autonomous functions to market intensifies, innovative approaches such as those shown by DSD could prove to offer a vital competitive advantage to vehicle manufacturers and tier 1 suppliers.


Automotive Test & Validation Vol 2 No. 1 /// 9


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