Left: PCU with silicon power semiconductors (current production model). Right: PCU with SiC power semiconductors (future Toyota's target). (CreditL Toyota Motor Corporation)Toyota Motor Corporation, in collaboration with Denso Corporation (Denso) and Toyota Central R&D Labs., Inc. (Toyota CRDL), has developed a silicon carbide power semiconductor for use in automotive power control units (PCUs). According to the company’s press-release, this development can improve hybrid vehicle (HV) fuel efficiency by as much at 10%.
Through use of silicon carbide power semiconductors, Toyota aims to improve HV fuel efficiency by 10% under the Japanese Ministry of Land, Infrastructure, Transport and Tourism’s (MLIT) JC08 test cycle and reduce PCU size by 80% compared to current PCUs with silicon-only power semiconductors. Silicon carbide power semiconductors have low power loss when switching on and off, allowing for efficient current flow even at higher frequencies. This enables the coil and capacitor, which account for approximately 40% of the size of the PCU, to be reduced in size.
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PCUs play an important role in hybrids and other vehicles with an electrified powertrain: they supply electrical power from the battery to the motor to control vehicle speed, and also send electricity generated during deceleration to the battery for storage. However, PCUs account for approximately 25% of the total electrical power loss in HVs, with an estimated 20% of the total loss associated with the power semiconductors alone. Therefore, a key way to improve fuel efficiency is to improve power semiconductor efficiency, specifically by reducing resistance experienced by the passing current. Since launching the “Prius” gasoline-electric HV in 1997, Toyota has been working on in-house development of power semiconductors and on improving HV fuel efficiency.
As silicon carbide enables higher efficiency than silicon alone, Toyota CRDL and Denso began basic research in the 1980s, with Toyota participating from 2007 to jointly develop silicon carbide semiconductors for practical use. Toyota has installed the jointly developed silicon carbide power semiconductors in PCUs for prototype HVs, and test driving on test courses has confirmed a fuel efficiency increase exceeding 5% under the JC08 test cycle.
In December last year, Toyota established a clean room for dedicated development of silicon carbide semiconductors at its Hirose Plant, which is a facility for research, development and production of devices such as electronic controllers and semiconductors.
Toyota will exhibit the technology at the 2014 Automotive Engineering Exposition, to be held from May 21 to May 23 at the Pacifico Yokohama convention center in Yokohama. The automaker will begin test driving vehicles fitted with the new PCUs on public roads in Japan within a year and aims to commercialize the technology by 2020.
