Lexus recently debuted the all-new 2013 GS350 at the Pebble Beach Concours d’Elegance, but waited until the Frankfurt auto show to reveal the new GS450h hybrid variant. As we found out driving a prototype of the new GS350, Lexus’s new GS platform is sportier than the last one, and the new hybrid version should be no different. But more central to the GS450h’s fuel-sipping mission, Lexus made several tweaks to its hybrid system to extract a significant efficiency boost over the outgoing car.
The original GS450h was quicker than its non-hybrid GS350 counterpart, but didn’t quite deliver when it came to the expected bump in fuel economy. This must have rubbed Lexus the wrong way, because this time around, the company is claiming a fuel-efficiency improvement of more than 30 percent versus the old car—with similar performance. Engineers took Lexus’s corporate 3.5-liter, port- and direct-injected V-6 engine, increased the compression ratio from 10.5:1 to 13.0:1, and adapted it to run on the Atkinson combustion cycle. In an engine running the Atkinson cycle, the intake valves stay open longer to reduce energy losses and convert combustion to engine power more effectively. For extra green points, Lexus is going after a Super-Ultra Low Emissions Vehicle II classification for the GS. The updated engine teams up with an electric motor and a generator, and sends power to the 450h’s rear wheels through a continuously variable transmission, same the previous generation.
The electric side of the new GS450h’s propulsion equation also received some attention. The 2013 450h features an upgraded power control unit that limits the voltage sent to the drive motor when the driver selects Eco mode and boosts it when one of the two Sport modes is engaged. Drivers tailor their drive by choosing from among Eco, EV, Sport S, and Sport S+ modes. Lexus reduced the electric motor’s friction, and the generator was made more effective by expanding the regenerative-braking operating window.
Despite the improvements to the GS450h’s engine and electronics, the 2013 model produces a combined 338 hp—2 fewer than before. Nevertheless, Lexus thinks the GS450h will be able to run from 0-to-60 mph in 5.6 seconds. The last GS450h we tested made it to 60 mph in 5.5 seconds, so that’s probably a good guess. Finally, the hybrid’s rear-mounted nickel-metal hydride battery pack was repackaged to reduce trunk intrusion.
Thanks to: Car and Driver
