ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

however, that inspired Kimes to invent the rocker clutch, a passive one-way clutch that would become key later on. Further inspiration came in 2013 after Kimes reviewed the dual-motor arrangement of Tesla’s S and X models, and determined that there had to be ways to improve their efficiency. “Other early projects indicated to us that the larger the vehicle, the greater the need for a multi-ratio gearbox,” Kimes says. “Although the industry wasn’t quite there yet, it was obvious to us that it would get there eventually, so we formed Sigma to develop the powertrains that these future commercial EVs would need.” EMAX development “We started developing the EMAX’s power flow concept in earnest in 2013, to squeeze more efficiency out of electric powertrains already incorporating multiple traction motors,” Kimes says. “Early modelling suggested that by adding a summing gearset with the ability to change ratio, we could provide significant efficiency gains to larger classes of vehicles.” The concept design evolved over the subsequent five years, while Kimes and his team pursued development of the electric clutch technology required to make their concept a reality. In 2015, during a three- speed gearbox project for Mahindra’s North American division, sufficient lessons and supply chains were established to start developing and commercialising SPT’s all-electric powertrain concept. Numerous iterations were performed during the early concept stages, and there was a strong focus on developing the technology around the components, so that when the EMAX’s design was being finalised, much of the work was a simple matter of putting the pieces together. Kimes explains, “Early on, we relied heavily on drive cycle simulation using the Advisor program to decide our general direction. Then we developed our own internal powertrain simulation tools to integrate motor efficiency data and provide optimisation knobs for improving the powertrain’s performance and efficiency.” In 2019, feeling confident that the (now patented) clutch technology was sufficiently mature, SPT began building the first EMAX prototypes. It then engaged a full-time staff of software engineers to develop the controls, interfaces and simulations necessary for operating and testing the transmission. Prototypes were then tested on SPT’s custom-built electric powertrain dynamometer. This is a test stand featuring battery emulation and with an input port on one side (where one or two motors can be mounted axially, one after the other) and an output shaft on the other. With its flexibility regarding e-motors, the powertrain can be modularly adapted to any size and weight of EV, but SPT sees Class 6-8 vehicles as gaining the highest improvements, with potentially 15% higher energy efficiency across their drive cycles compared with the next best powertrains, and with shifting times of 250-500 ms with minimal torque interruptions. Background Sigma Powertrain was formed in 2016 to explore applications for an electrically controllable EV powertrain clutch technology invented and patented by John Kimes (founder and CEO of Sigma) and his team. Kimes had been mulling over the concept for an all-electric transmission during his days at the Ford Motor Company, after seeing the DPS6 dual- clutch automatic transmission from Getrag (now Magna PT) and the 10% fuel economy gains it produced in Ford vehicles such as the Fiesta and Transit. “Automatic hydraulic transmissions like those are great for smooth and power-dense gearshifts, but they nonetheless pay a tremendous price in parasitic losses in power across their torque converters, friction clutches, high-pressure oil pumps and so on,” Kimes explains. “Getrag answered the question of how to turn a manual transmission into an automatic to improve fuel economy – parasitic losses – so I determined that the key to making an automatic architecture with the much lower parasitic losses typical of a manual was to get rid of the hydraulics.” The resulting concept was a step- ratio transmission with no hydraulics, but the missing piece of the puzzle was electrically controllable clutches, which had not yet been invented. In the meantime, Sigma’s patented technology can be modularly adapted for two-motor and single-motor solutions in E=s of eɈecti]ely any size, with some key embodiments pictured here Winter 2021 | E-Mobility Engineering 21 Dossier | Sigma Powertrain EMAX transmission