The RX is the best-selling Lexus
, and one in five sold is the hybrid version. It's no surprise, then, that with the new third-generation RX - the second to have a hybrid powertrain - Lexus is treading very carefully.
The design is a careful evolution, both inside and out. The car is slightly longer and wider but manages to look sleeker than before. The interior retains the traditional Lexus virtues of comfort (on even bigger, cushier seats) and refinement (with available semi-aniline leather for a still more luxurious feel). Lexus has joined the Germans by adopting an iDrive-style controller instead of a touch screen for its optional navigation system. But rather than a knob you twist and push, the Lexus control (called Remote Touch) works more like a joystick that you move from side to side or forward and back, and then make a selection by pressing buttons on the side of the unit. It takes some getting used to.
Other new options don't require a learning curve, such as the head-up display and the curb-view camera; the latter is located in the right-side mirror, and at low speeds it shows an image of what's alongside the car. The hybrid model supplements its previous ECO indicator, which lights up when you're driving efficiently, with a selectable ECO mode, which changes the responsiveness of the throttle and instructs the climate control to use the A/C compressor more judiciously. There's also an EV mode, which extends the threshold before the engine starts, up to a still-modest 8 to 10 mph.
The changes aren't dramatic, but Lexus has given its cushy suburban hybrid a slightly greener tinge. Lexus engineers identify four elements that underpin the brand's hybrids: performance, quiet refinement, low emissions, and fuel economy. In this redesign, the latter received the most emphasis.
Whereas the standard RX350's 3.5-liter V-6 is little changed (adding 5 hp for a total of 275 hp), the RX450h got a whole new gasoline engine. Replacing the old 3.3-liter is a new 3.5-liter V-6 that runs on the more efficient Atkinson cycle. EPA numbers for the front-wheel-drive RX hybrid are up by 1 mpg city and 3 mpg highway, to 28/27 mpg. The all-wheel-drive version adds 2 mpg all around and is now rated at 28/26 mpg.
Despite the increased fuel economy, the RX pecking order has been preserved, with the hybrid again outmuscling the standard RX350. The hybrid's total power output is up by 27 hp, to 295 hp, and both the gasoline engine and the electric motors make more torque. Against that, however, is the car's weight gain of more than 400 pounds. Still, the RX hybrid accelerates quickly and smoothly. Once again, the all-wheel-drive model adds a third motor/generator, which is the sole source of propulsion for the rear wheels. In either version, the start-up and shutdown of the gasoline V-6 is seamless, but in steady-state cruising on level ground, there is the faintest surging as the batteries switch between charging and assisting. In the chassis department, the new RX is treated to a wider track and a new rear suspension - control arms replace struts and intrude less into the cargo hold. There's also an optional sport suspension, but it's not likely to keep BMW X5 engineers up nights. The electric power steering, now on both RX models, is better than most, linear and not overboosted.
2010 Lexus RX450h
Base Price: $45,000 (est.)
ENGINE: DOHC 24-valve V-6
DISPLACEMENT: 3.5 liters (211 cu in)
HORSEPOWER: 245 hp @ 6000 rpm
TORQUE: 234 lb-ft @ 4800 rpm
Batteries: Nickel-metal-hydride, 288v
Motor/generators: Two permanent magnet AC, 165 hp (fwd); three permanent magnet AC, 232 hp (awd)
total horsePower: 295 hp
total Torque: 257 lb-ft
Continuously variable automatic
STEERING: Power-assisted rack-and-pinion
SUSPENSION, FRONT: Strut-type, coil springs
SUSPENSION, REAR: Control arms, coil springs
BRAKES F/R: Vented discs/discs, ABS
TIRE SIZE: 235/60SR-18
L x W x H: 187.8 x 74.2 x 66.3 in
WHEELBASE: 107.9 in
TRACK F/R: 64.2/63.8 in
WEIGHT: 4650 lb (fwd), 4810 lb (awd)
EPA FUEL MILEAGE: 28/27 mpg (fwd), 28/26 mpg (awd)
Connoisseur's Guide to Hybrid Systems
In spite of currently cheap fuel prices, hybrid vehicles are hot. Here's a closer look at how the four key collaborative hybrid powertrains that are currently in production actually work.
HONDA INTEGRATED MOTOR ASSIST
In 1999, Honda introduced the original two-seat Insight hybrid, powered by a tidy Integrated Motor Assist (IMA) system. The 2009 five-passenger Insight is powered by a fifth-generation IMA consisting of a 1.3-liter dual-spark-plug gasoline engine, a 13.4-hp DC motor/generator, and a continuously variable automatic transmission. The DC machine sandwiched between the engine and the transmission aids acceleration, converts kinetic energy to electrical energy (used to charge the batteries), serves as a flywheel, and cranks the engine following its shutdown at stoplights. The electric motor is also capable of propelling the Insight unassisted at speeds as high as 30 mph. A lighter and more compact Intelligent Power Unit located under the trunk floor houses electronic circuits and 84 D-size nickel-metal-hydride batteries capable of storing 0.58 kilowatt-hours of energy.
Originally conceived for city bus use, GM's Two-Mode hybrid system teams a gasoline engine with an automatic transmission loaded with two electric motor/generators, two or three planetary gear sets, and four or five multiplate clutches. Following development by a consortium including BMW, Chrysler, and Daimler engineers, GM introduced Two-Mode on 2008 Chevrolet Tahoe and GMC Yukon SUVs. The 2009 Saturn Vue is the first model to use the Two-Mode system in a transverse front-wheel-drive application. A 262-hp, 3.6-liter V-6 with direct injection and variable valve timing collaborates with two 74-hp electric motors to provide two continuously variable and four fixed gear ratios. The nickel-metal-hydride battery pack located below the cargo floor contains 22 modules providing a 1.8 kilowatt-hour energy capacity.
LEXUS HYBRID DRIVE
In contrast with hybrid systems aimed mainly at improved mileage, the powertrain Toyota engineered for use in the 2006 RX400h emphasizes power and performance. The evolved system in the 2010 RX450h combines a 245-hp, 3.5-liter V-6 with two electric motor/generators and two planetary gear sets to drive the front wheels. An optional on-demand all-wheel-drive system adds a third electric motor/generator for the rear axle. As in the Toyota Prius, one planetary gear set provides continuously variable drive ratios. The second one reduces the electric motor's speed. The larger V-6 has late intake-valve closing (Atkinson cycle) and extra exhaust-gas recirculation for improved efficiency. Waste heat captured from the catalytic converter warms the coolant and allows the engine to be shut down more frequently.
TOYOTA HYBRID SYNERGY DRIVE
The original Toyota Prius introduced in Japan in 1997 was the fruit of four years of R&D work in Japan aimed at doubling small-car mileage. Using a clever drive system invented by TRW in 1970, the Prius combined a small four-cylinder engine with two electric motor/generators and a planetary gear set to power the front wheels. The smaller electric machine starts the gas engine on cue, regulates the engine-to-wheels drive ratio through the planetary gears, and provides electricity to charge the batteries and energize the larger electric machine. During deceleration, that machine also serves as a generator to convert unwanted kinetic energy to electrical energy used to charge the batteries. The fourth-generation Prius, the Camry, the Highlander, the Nissan Altima, and all Ford and Mercury hybrids use this system with subtle variations.