Powertrain
The gasoline-powered portion of the HS 250h powertrain is the 2.4L 2AZ-FXE inline-four engine. The 2AZ-FXE produces 147 hp (110 kW) and 105 ft·lbf (142 N·m) of torque at 4000 revolutions per minute. This is assisted by an electric motor for a combined output of 187 hp (139 kW). The HS 250h uses a similar hybrid drivetrain as the Toyota Camry Hybrid.
The HS 250h's EPA fuel economy is estimated at 35 miles per US gallon (6.7 L/100 km; 42 mpg) in the city and 34 miles per US gallon (6.9 L/100 km; 41 mpg) on the highway. The HS 250h engine runs on the Atkinson cycle, and the powertrain uses a continuously variable transmission. A 90 pounds (41 kg) nickel metal hydride battery situated between the trunk and rear seats serves to power the electric motor. An additional system included on the HS 250h's Lexus Hybrid Drive powertrain is an exhaust-heat recovery system to reduce engine warm-up periods (optimizing engine start-stop times). The Atkinson cycle configuration and exhaust-heat recovery system is also used on the 2010 Lexus RX 450h.
The HS 250h can be operated in either driver-selectable EV, Eco, or Power modes. The EV mode is suited for short-distance pure electric driving at speeds of up to 20 miles per hour (32 km/h), the Eco mode can be selected for the greatest fuel efficiency in mixed gas-electric driving, and the Power mode offers more performance in contrast to the Eco mode. The 0–60 time is listed at 8.4 seconds and the top speed is 112 miles per hour (180 km/h).
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