GREEN MACHINE The new Lexus RX 450h is cleaner and more fuel efficient than the RX 400h

INNER WORKINGS See how hybrids work with a cutaway display of the GS 450h

By Justin Lee

SPORTS UTILITY VEHICLES aren’t the most beloved class of vehicles, especially to environmentalists, with their fuel-guzzling nature and higher emissions due to big engines and high kerb weights.

But Lexus turned that image on its head with its RX 400h hybrid SUV. Launched in 2006, it was local distributor Borneo Motors’ most popular hybrid vehicle with around 400 examples on the roads.

The second-generation model has recently been launched and is now called the RX 450h. It gets an updated Lexus Hybrid Drive system and has a larger 3.5-litre V6 in place of the 3.3-litre V6 in the old car. Drive is transmitted through a continuously variable transmission.

Combined power output has increased by 27bhp to 295bhp and this has not come at the expense of fuel economy, which has improved from 12.4km/L (quoted, for the combined cycle) to 15.9km/L.

As before the vehicle can operate on its electric motors or petrol engine alone, or with a combination of both. It’s innovative four-wheel drive system uses an electric motor in the rear, rather than a mechanical differential of conventional 4WD machines.

The RX 450h’s fuel efficiency has been attributed to three new features: Atkinson cycle combustion, cooled exhaust gas recirculation and exhaust heat recovery.

In an Atkinson cycle engine the valves close late, delaying compression. This creates a high expansion ratio for less compression, reducing intake and exhaust energy losses and converting combustion energy into engine power more effectively. As a result the exhaust temperature is lower than in conventional engines.

Exhaust gas recirculation reintroduces cooled exhaust gas into the combustion chamber, further reducing the engine’s operating temperatures. Together these technologies minimise the need for any fuel enrichment to provide a cooling effect and protect the catalytic converter from overheating damage, thereby improving fuel economy and reducing emissions.

The exhaust heat recovery system uses exhaust gas heat to warm the engine coolant at start-up. This reduces the time the engine needs to warm up, allowing it to be shut off earlier for longer electric motor-only operation.

A bonus for greenies - Lexus also claims that the RX 450h has the lowest CO2 figure of any premium SUV at 148g/km.

The car comes only in ‘Luxury’ trim and has non-moonroof, moonroof and wide-moonroof options costing $188,000, $192,000 and $195,000 respectively, all with COE.

A Hybrid Story

Want to find out the inner workings of a hybrid car? From now till June 29, head down to the Lexus showroom located at 33 Leng Kee Road to view a cutaway exhibit of the GS 450h.

This technological display demonstrates how the Lexus Hybrid Drive system transfers power through the vehicle when in operation from regeneration to driving. It has strategically placed neon tubes to highlight the flow of energy.