Lexus' Flagship SUV Goes Green
We just returned from a day in northern California testdriving the new Lexus RX 450h, and as you might expect, it's a rolling encyclopedia of new-car tech. We'll do our best to explain it all in thumbnails, but suffice to say, it's a capable and civilized alternative to your run-of-the-mill crossover rigs.
The heart of the RX is the time-proven Toyota 2GR 3.5L V-6 (a variant of which Lotus will be using next year on its GT4 Supersport race cars), which has been refined for this application with the addition of an EGR system for improved emissions and cooling, and an exhaust heat recovery system to aid in quicker heat-up times (i.e., cold-start conditions). The motor also runs an Atkinson-style combustion cycle (the power stroke is longer than the compression stroke), which helps to achieve greater fuel economy and thermal efficiencies at the expense of horsepower. How to remedy? In the RX's case, two ways.
First, the gas engine works in concert with Lexus Hybrid Drive, a battery-actuated hybrid system similar to Toyota's (Prius) Hybrid Synergy Drive. The Lexus system can be run for brief periods at high speeds as well as at idle (and during braking) to provide an extra power boost as needed, such as on steep inclines or for passing. In the new RX application, the battery can provide an extra 50 horses to the V-6's 245, resulting in 295 peak hp at 6,200 rpm. Second, the engine is mated to an electronic CVT transmission. We're not too keen on these "pointless" gearboxes, but we do know that they have fewer internals to break, are less expensive than a conventional slushbox, and can keep an engine revving in its "sweet spot" longer than fixed-gear transmissions. Add everything up and you arrive at an EPA-estimated 26 mpg on the highway, 28 city, from a V-6 powertrain that is amply powerful, frugal, and super-clean (SULEV-rated) in operation.
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The heart of the RX's all-wheel-drive system is "Active Torque Control," which utilizes a pair of electric motors--one to power the front wheels, the other the rears, each housed in a gear-driven transaxle--to provide front-to-rear torque bias. The RX operates under normal conditions as a conventional front-drive. When wheel slippage is detected, the system activates an electromagnetic clutch-drive coupling device bolted to the rear differential to transfer power, front to rear, at splits of up to 55/45. (A third electric motor under the hood acts as a starter to power the batteries, and can recharge the other motors as needed.) An onboard power inverter boosts battery voltage to 600-plus, and converts the juice from DC to AC to drive the electric motors. Have we lost you yet?
The RX's suspension is independent at both ends--the rear double-wishbone configuration a new feature for 2010--with two-mode onboard shock tuning for sport/touring functions, and standard wheels are 18-inch alloys, with 19s optional. Ground clearance, at under 7 inches, is less than optimal, and our tester's 55-series Michelins, while sure-footed on pavement, don't lend much sidewall for dirt duties. Thankfully, the Lexus' interior is what you'd expect from this marque, with its trademark wooden steering wheel and leather everywhere. Shucks, this thing's nicer inside than my house! (It's probably worth more than my house is by now, too, but that's another story.)
Fuel-efficient powertrain, high-lux interior, great as-advertised mileage.
Ground clearance? What ground clearance? We're still getting used to CVT trannies.
A civilized and capable alternative to your run-of-the-mill crossovers. Just stay away from the rock trails.
Vehicle/model: 2010 Lexus RX 450h
Base price: N/A
Engine: 2GR-FE 3.5L DOHC V-6
Max hp & torque (lb-ft): 295 (engine + electric)/234 (engine only)
Transmission(s): P313 electronic CVT
Transfer case(s): Nope
Low-range ratio: Don't ask
Frame type: Steel unitbody
Suspension, f/r: MacPherson strut, coil springs/double wishbone, coil springs
Max crawl ratio: N/A
Steering: Electric power rack-and-pinion
Brakes, f/r: 12.9x1.1 vented disc/12.2x0.4 solid disc
Wheels (tested): 19x7.5 alloy
Tires (tested): 235/55R19
Wheelbase (in): 107.9
Length (in): 187.8
Height (in): 66.5
Base curb weight (lb): 4,810
Max approach/departure angles (deg): 29/25
Minimum ground clearance (in): 6.9
GVWR (lb): 5,980
Max cargo volume (cu. ft.): N/A
Max towing capacity (lb): 3,500
EPA mileage figures, city/hwy (mpg): 28/26
Fuel capacity (gal): 19.2