Toyota is the undisputed leader in the hybrid vehicle market, accounting for some 75% of all hybrid vehicles sold on the planet, and is constantly improving its technology.
One example of this, reflected in the Toyota Prius alone, is the improvement in fuel economy over the years. Toyota hybrid vehicles have exhibited steady improvement in fuel economy. Toyota Prius, for example, started at 41 mpg in 1997, and is expected to hit 55 mpg for the 2015 model year. Improvements in body construction, such as lightweight materials and aerodynamics, as well as in the internal combustion engine, have helped to improve fuel economy, but that’s not all.
Additionally, advancing technology in electric motors, nickel-metal hydride (NiMH) batteries, and controls, have also made gains for Toyota’s hybrid vehicle lineup. Focusing on the power control unit (PCU), Toyota has made some very promising developments in semiconductor performance. The PCU controls power flow between the NiMH battery pack and the electric motor-generators, including voltage regulating and power inversion. The silicon semiconductors, essentially a bank of high-power transistors and diodes, take up a lot of space in the vehicle. The PCU also generates a lot of heat and, according to Toyota engineer Kimimori Hamada, could be made more efficient.
The new PCU, developed jointly between Toyota and Denso, uses silicon carbide (SiC), instead of silicon (Si), semiconductors. The new SiC PCU is just 20% the size of the original Si PCU, 4 kg compared to 18 kg, which could make it more adaptable to different vehicles. Lighter weight makes for better fuel economy, it’s true, but the SiC semiconductors are also more efficient, reducing cooling requirements and improving motor-generator efficiency, making for even better fuel economy gains. The only caveat is that SiC components are about ten times more expensive. A new hybrid vehicle inverter assembly, the current Si PCU, sells for about $7,000. Would that make a comparable SiC PCU worth about $70,000? Ouch!