Shoichi Sasaki

Power control system for hybrid automobile

Non-European countries
Technical field
Until the mid 1990s, lack of battery performance stalled the commercial use of hybrid cars. Things changed with the introduction of a new breed of power-management system, developed by Japanese engineer Shoichi Sasaki for Toyota's hybrid automobiles in 1997. Millions of hybrid vehicles have been sold today.

An environment-friendly technology, hybrid automobiles combine "regular" combustion engines with electrical drives. Today, their owners enjoy tax benefits and low fuel consumption. But for a long time, the technology suffered from a crucial fault. The rechargeable batteries lost their ability to charge fully after periods of extended use.

In 1994, a development team led by engineer Shoichi Sasaki at Toyota in Japan received the assignment to perfect the technology. They reviewed over 100 designs for hybrid vehicles and researched battery technology extensively.

Sasaki's discovery: Batteries reach their optimal life span when kept at a constant state of charge (SOC) between 40 and 60% of their full capacity. Overcharging the battery leads to "aging" effects similar to those common in laptop computers.

Based on this finding, Sasaki created a new power management system that constantly monitors battery charge in a hybrid vehicle. It controls power supply to the battery and levels discharge to maintain the optimal state of charge. 

The battery is charged by motor generators while driving, or by energy released during braking. Discharge happens when the car's electric drive takes over, mainly in city traffic - a driving environment featuring (fuel-intensive) stop-and-go patterns. 

The new power-control system developed by Japanese inventor Shoichi Sasaki ensures a long life for batteries in hybrid cars. The invention paved the way for the next generation of hybrid vehicles based on the step-up voltage concept. The concept allows for compact battery size with improved driving performance.

Numerous other brands have also introduced hybrid vehicles, and many companies and governments offer benefits for purchasing hybrids. By 2008, Toyota had already sold more than 1 million "Prius" automobiles worldwide.


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