United-Kingdom engineering specialist Ricardo recently revealed extensive development details of its latest automotive 48-V 25-kW e-motor and associated inverter, which it claims can deliver up to a 50% increase in power density compared with current production electric machines. The project is of potential significance to automotive OEMs moving towards high-volume electric-vehicle (EV) production models requiring enhanced motor power density without cost and complexity drawbacks.  

Emphasis during the new e-motor’s development was placed on thermal management—chiefly, gaining efficiency via reduction of thermal resistance, particularly concerning the inverter’s metal oxide semiconductor field-effect transistor (MOSFET). Ricardo revealed its solution is based on the use of direct oil cooling of the heat sink, using the same automatic transmission fluid used to cool the e-motor itself. 

The project was the subject of a paper read by Ricardo’s Dr. Lawrence Alger, Technical Business Manager, at the recent CTI (Car Training Institute) Berlin Symposium. Ricardo’s electric powertrain sees the compact silicon inverter driving a frameless 6-phase, 8-pole interior permanent-magnet motor with ATF (automatic transmission fluid) cooling and “novel” windings. Both oil- and water-cooled inverter variants were explored, but from the outset, a salient development aim was cooling of motor, inverter and the associated dual-clutch transmission (DCT) from the same oil supply, reducing thermal resistance of the inverter via jet cooling. 

Neville Jackson, Ricardo’s Chief Technology and Innovation Officer, told Automotive Engineering: “48-V mild hybrid solutions are very likely to be the key enabler to meet medium-term fleet average CO₂ targets as cost-effectively as possible. Whilst the first generation of 48-V systems are largely standalone components added to existing powertrains, cost and weight reduction will increasingly demand more integrated solutions. 

He added that the company’s 25-kW motor, inverter and dual-clutch transmission “are focused on the requirement for even more cost-effective integrated designs. They offer not only cost-efficiency but can deliver improvements in vehicle drivability through the additional instantaneous torque delivered to the vehicle during pull-away and transient maneuvers.” 
 
25kW “sensible” for mild hybrid 
At the Berlin event, Alger stated that the conclusions drawn from extensive test results and simulation data showed a 25-kW peak rating to be a “sensible” upper limit for a 48-V mild hybrid and that a motor close to that rating could be fitted into a current eDCT (electronic dual-clutch transmission) and thermally controlled via existing oil cooling, demonstrating that a “relatively small” oil-cooled inverter could be created for the application. 

An added plus was that the inverter demonstrated the feasibility of cooling electrically live surfaces under powerboard components with an electrically insulating fluid in an automotive application. “Conventional PCB construction methods are used to reduce manufacturing costs, utilizing mass produced off-the-shelf devices,” said Alger, “whilst still breaking down thermal barriers using impingement cooling.” 

Ricardo also showed its new transverse eDCT concept at the Berlin Symposium.  \Based on the company’s experience in supercar transmission design, it is described as being some 37% shorter than its target/reference products, aiding better weight distribution and reduced vehicle polar moment of inertia.  Continue reading »