The 2011 Lexus RX 450h is identical to the 2011 Lexus RX 350, except where it isn’t, and the differences are not great…or yes it is and yes they are.
Confused as we are? Let’s get past the fundamentals. Lexus RX models—mostly unchanged from the all-new 2010 RX’s—are mid-size crossover-styled SUVs. the RX 350 having a conventional drivetrain with a 3.5-liter V-6 engine and front or all-wheel drive.
The 2010 Lexus RX 450h, however, was a full hybrid similar to (yet again different from) the Toyota hybrid drive system. The RX 450h updated the first-generation RX hybrid, the Lexus RX 400h, with a new engine and a variously enhanced drivetrain. It’s still capable, as are all Toyota/Lexus hybrids, of operating under electric-only, gasoline-engine-only or combined modes.
Engine The new engine is a 3.5-liter Atkinson-cycle V-6. An Atkinson-cycle engine is a conventional four-stroke gasoline engine except for valve timing. The intake valves close later than a conventional engine and without going into technical details, it reduces energy losses in the engine for more efficient combustion and better fuel mileage. The RX 450h’s engine is rated at 245 horsepower, up from 208 in the previous RX 400h.
The RX 450h stores its 288-volt nickel metal hydride (Ni-MH) battery pack under the rear seat. It’s more compact and lighter than that of its predecessors. The power control unit that houses the power converter, inverter and condenser—we’ll just have to learn this new electrical jargon in this new era of hybrids and electric cars—is also smaller and lighter.
AWD or FWD Like the RX 350, the RX 450h is available in front or all-wheel drive versions. A bit of gearhead info (the rest of you can step out for coffee): The front-drive version has two motors. The first is called MG—for motor-generator one—which is the starter for the gas engine and it’s an engine-driven generator that can charge the battery pack or power other electric motors (power-steering pump, water pump and air-conditioning compressor drive motors) as needed. The electric motor that actually drives the front wheels is MG2 and the power from it and the V-6 engine goes to the drive wheels via a planetary gear-type continuously variable transmission. MG1 controls the output speed of the transaxles through the planetary gear set, without clutches or viscous coupling.
(OK, everyone back in): This new arrangement of hybrid components allows greater range of performance from the electric motor and that, along with a more powerful gas engine, makes a stronger performer overall. Full throttle put paid to the reputation of hybrids being poor performers.
The 2010 Lexus RX 450h is also available with all-wheel drive, as we tested it, and rather than a driveshaft-type arrangement of a conventional all-wheel drive system, the RX 450h just throws on another engine out back (MGR), like the 2009 Toyota Highlander Hybrid. The hybrid system varies front and rear torque distribution electronically, depending on traction availability.
Normally the rear motor is just along for the ride, but nail the throttle from a stop on slippery pavement and the front wheels can be felt to slip momentarily before traction control takes over. But while it does, the rear motor pushes the RX 450x ahead.
All three of the RX 450h’s motors can function as generators for recovering energy, of course. There’s a setting to that allow the driver to use engine braking and an “AI-SHIFT” that keeps the transmission in the best range for driving downhill was new with 2010 RX 450h.