TRAVERSE CITY, MI – It may sound counter intuitive, but the gasoline-engine part of the Toyota Prius hybrid-electric propulsion system has played a major role in increasing the hybrid’s efficiency since it was introduced in 1997.

Most industry talk around hybrids seems to center on battery technology and electric motors.

However, improvements such as reducing mechanical friction within the engine and replacing the belt-driven water pump with an electric version have yielded double-digit fuel-economy improvements, says Justin Ward, program manager-advanced technology vehicles at the Toyota Technical Center in Ann Arbor, MI.

Moving from the first- to the second-generation Prius, Toyota saw a good fuel-efficiency bump simply by reducing piston-ring friction and other sources of internal engine friction, Ward tells attendees at the Center for Automotive Research’s Management Briefing Seminars here.

The auto maker also substantially reduced emissions by storing warm engine coolant in a thermos-like canister that is released during cold starts for faster warm ups.

This concept was enhanced on the latest-generation Prius by using exhaust gas to warm up coolant quickly for cold starts. A heat-recirculation system, powered by an electric water pump, increases the Prius’ fuel economy as much as 10% in winter, Ward says.

Toyota has built 4 million hybrid-electric vehicles since 1997 and is looking forward to continued growth in the HEV market, Ward says.