Electrification: Innovative Approaches to the Propulsion System

In a future of full vehicle electrification, OEMs and suppliers alike face the challenge of reinventing their platforms, manufacturing processes and product lines. At the same time, they confront growing but variable regional regulations and myriad infrastructure requirements. 

There’s room for both incremental innovation and novel approaches—but deep changes must be made. 

“The scope of current drivelines will not be able to meet the requirements of systems of the future,” says Tim Lawler, product manager, Robert Bosch. Creating a sustainable business model and product plan in a shifting global market is a significant challenge, he notes. 

Higher voltage for next-gen vehicles 

Lawler details some of the many requirements for the advancement of electrification in all vehicle segments, whether fully electric or plug in hybrids: a wide bandgap semiconductor to boost system efficiency; high-power charging to bring time at the charger more in line with time at the fuel pump; and a high-power DC-to-DC converter to support comfort and convenience features.  

The entire system must be optimized to increase efficiency while reducing weight and cost—a difficult balance to achieve. Not to be overlooked in the optimization is simplified installation into the vehicle, Lawler notes.  

Bosch is developing systems from 48 to 800 volts for nextgeneration vehicles. Lawler says higher-voltage systems will support advanced features such as electric all-wheel drive, roll stabilization and cooperative braking. 

Moving to higher-volt systems requires changes to transistors and other elements of electrical systems. For example, wide band-gap silicon carbide (SiCpower transistors could replace silicon IGBTs in electric drivetrain applications, says Christian Pronovost, senior product manager with Dana IncSiC resists high temperatures, allowing for higher electrical conductivity than traditional semiconductors.  

Replacing conventional silicon power transistors with SiC power transistors allows faster switching, resulting in lower power losses and increased efficiency, according to Pronovost. It’s possible to build a more efficient, lighter and smaller electric traction system with greater vehicle range and performance. 

For the past five years, TM4, acquired this year by Dana, has participated in an electric-vehicle racing series, employing a variety of power transistor technologies. This experience has both proven the benefits of SiC devices and shown some challenges with using it in a traction system.  

According to Pronovost, SiC devices enable not only higher density on the powertrain inverter itself but also on the motor. On the other hand, a drawback to its high switching speed is some highfrequency electromagnetic interference.  

H2020 ECOCHAMPS sparks innovation 

While regulation to reduce emissions pushes electrification forward, governmental support to industry can play a valuable role. A case in point is the EU-funded H2020 ECOCHAMPS project that aims to boost the development of hybrid powertrains for passenger cars and commercial vehicles.  

As part of the initiative, Ricardo collaborated with Daimler and Renault to demonstrate a 25kW 48-volt electric motor and inverter as a modular hybrid (MHT) for a dual-clutch transmission.  

When developing novel technologies, modeling and simulation in advance of prototyping saves time and money. Ricardo uses simulations to test proposed designs, according to Cedric Rouaud, global technical expert, thermal, engineering consulting and quality, for Ricardo UK 

In the case of the motor and inverter, simulation showed that a 25kW rating would be optimum for a Csegment vehicle. And, throughout the design process, simulation was used to measure thermal resistance of the inverter to ensure it was on par with a water-cooled design 

The final design is a novel frameless IPM motor with windings, designed to fit into the same space as an existing 15kW induction design. Not only the inverter, but also the motor and gearbox are cooled by the same dielectric oil.   

Ricard found that with an electrified drivetrain of 15kW rating, 70 to 90 percent of the available energy can be regenerated. Increasing the rating to 25kW makes 80 to 97 percent of the energy available for regenerating. 

Rethinking the basics 

Some companies take a less incremental approach, rethinking entire structures. EXEDY proposes a redesigned stator and rotor to solve some of the complexities of electric vehicle development. The company’s newly developed variable flux technology motor concept is more efficient, according to Taichi Kitamura of EXEDY Corporation Japan. 

In a permanent-magnet synchronous motor there’s a trade-off between maximum torque and maximum speed, Kitamura says. But variable flux technology allows the torque and speed to be varied widely and continuously. 

The key to this technology is a new motor structure that has a field winding and a non-laminated rotor core. The field winding is in axial opposition to the rotor, which is assembled from a concave-convex shaped core, a claw shaped core, and permanent magnets. If direct current is supplied to the field winding, magnetic flux is generated around the winding and then the non-contact flux supplies the rotor. 

EXEDY has a few concepts for how variable flux technology can be used. For example, the company prototyped an entry-level electric direct drive. Integrating a starter and generator into a single electric motor reduces the number of parts and lowers mechanical loss.  

In a battery-electric vehicle, variable flux technology can take the place of a specialized EV transmission. Kitamura says, “One of the benefits of this e-shifting motor is that there is no torque interruption with the shifting characteristic.  

The motor does use electric energy to activate the field winding, but this is typically done at higher speeds, so it’s similar to a turbo-charged internal combustion engine. 

There are both advantages and disadvantages to this approach that are dependent on factors including vehicle size, purpose and use. 

Most approaches to electric-vehicle design take the conventional vehicle as a starting point, replacing the central gas-fueled motor with an electric one and modifying the drivetrain technologies. Protean Electric takes an entirely different approach, placing electric motors in each wheel.  

The system, dubbed ProteanDrive, combines an electric motor with power and digital controls; its designed to integrate with existing systems including brakes, suspension and steering.  

According to Chris Hilton, Protean CTO, benefits are improved torque response, enhanced handling and faster acceleration, reduced stopping time and improved traction control—with less time spent charging and greater range. It also simplifies the assembly or conversion process. 

The directdrive, in-wheel motor system enables modular vehicle architecture, with high efficiency and more freedom in the design, Hilton says. To prove this, Protean created a concept for a vehicle platform with an unlimited steering angle suitable for city driving where maneuvering through tight spaces is important. 

At the CTI Symposium, our experts promise to illuminate the latest thinking in solving today’s challenges. 

Lectures in the track on electrification enablers: 

  • Evaluation of voltage increase in electric automotive powertrains and fast charging infrastructure (P3 North America Inc.) 
  • Bosch development in electromobility, including 48 – 800 V systems for next generation vehicles (Robert Bosch LLC) 
  • Advances in electric power control: silicon carbide for electric traction drives (Dana Incorporated) 
  • Death of the disconnect? A holistic view of EV drive-line efficiency (Drive System Design Inc.) 
  • Development of a high power 48 V e-machine (Ricardo Ltd) 
  • An in-wheel motor system in comparison to electric axles (Protean Electric) 
  • Variable flux technology can open the door of e-motor performance design (Exedy Corporation) 

 Welcome to CTI SYMPOSIUM USA!

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