A Lexus Like No Other But Like The Rest

Gary S. Vasilash

Introducing The RX 400h: Luxury, Not Economy

While the Lexus RX 400h provides better fuel economy than the RX 330 on which it is based (~25%), and although this is a full gas-electric hybrid, the vehicle is all about luxury and performance, not frugality and thrift. After all: This is a Lexus.

The Challenge.

The expectations of Toyota owners must always be met. The high expectations of Lexus owners must always be exceeded.—Masaki (Frank) Sanayama, assistant chief engineer, Lexus RX 400h.

What may be forgotten is that the original crossover luxury SUV in the market was the Lexus RX 300, which went on sale in March 1998. Five years later, in March '03, the RX 330 went on sale; it is 6.1-in. longer than its predecessor, and a 3.3-liter engine was put under its hood. There are slight differences between the RX 300 and its successor. But the continuity is evident in many ways. In its first year out, the RX 300 was named "Most Appealing Luxury SUV" in the 1998 J.D. Power & Associates Automotive Performance Execution and Layout (APEAL study). In its first year out, the RX 330 scored first in the Luxury SUV segment of the J.D. Power & Associates APEAL study. See what he means about exceeding expectations? If there is a vehicle that does that consistently, it is the RX. The vehicle was initially, and continues to be, built in a Toyota facility in Kyushu, Japan. Since late 2003, the RX 330 is also being produced in Cambridge, Ontario, Canada. And the expectations continue to be exceeded. The vehicle keeps gaining accolades and racking up sales. It also happens to the best-selling luxury SUV on the market. 

So you have to imagine that it was with some trepidation that the Lexus RX 400h program was commenced. It is one thing to produce a Toyota Prius, a gas-electric hybrid. After all, that vehicle, now in its second generation (see AD&P, October 2003 or http://www.autofieldguide.com/articles/100302.html), although exceptional, is the sort of vehicle that people who are environmentally oriented are drawn to (of course, the increase in gas prices since that car was introduced has resulted in a tremendous increase in people who are interested in the Prius's comfortable frugality, such that in August 2004, Toyota Motor Corp. announced that production for the vehicle would be boosted from 10,000 units per month to 15,000 to meet worldwide demand). The Prius is a vehicle that causes expectations in the fuel-efficiency arena to be heightened. But with Lexus, this is a whole different proposition. This is a successor to the RX 300 and the RX 330. Which means a lot. Get it right, and there's another big win for Lexus. Get it wrong, and, well . . .

Denny Clements, group vice president and general manager, Lexus Div., acknowledges that so far as the kind of consumers who buy or consider the brand are concerned, "We found that it is not necessarily about being green or more fuel-efficient, or even about a higher level of performance. Rather, it is all about delivering a better total package." Which means green (although that isn't the key motivator: apparently research has shown that while the Lexus 400h intender believes that is a good thing, they don't want to be particularly vocal about it), providing fuel efficiency (which means deploying a new variant of the Hybrid Synergy Drive introduced in the '04 Prius), and providing a bit of head-snapping performance when you put your foot into it (as a result of the combination of the 208-hp 3.3-liter V6 and the high-torque electric drive motor-generator, which boosts it to 268 hp—but let's face it, this is a sport utility vehicle that has a curb weight of 4,365 lb., not a sports car. Speaking of the mass: the vehicle is 300 lb. heavier than the RX 330).


Stealth Mode.

One of the things that you'll notice about the RX 400h is that when put in visual comparison with the RX 330, it is hard to sort the two out. However, one of the issues of high-efficiency vehicles—as in a gas-electric hybrid—is aero drag. After all, the slipperier the body, the better the fuel efficiency. By and large, SUVs are giant rectangles. Not exactly the most conducive to sliding through the air. While the RX 330 does have smooth, sharp surfaces, and isn't some sort of giant shoebox, engineers looked at the ways they could improve it without changing its essential character. Which they have done. In fact, unless someone is an RX 330 specialist, they would probably be challenged trying to spot the differences. The overall size change is miniscule, with an inch added to the overall length and 0.3 in. to the height of the RX 400h: try to discern that when the overall length is 187.2 in. and the overall width is 66.3 in. According to Sanayama, the length change is essentially predicated on a new front fascia, one that includes an additional air inlet in the bumper for cooling the hybrid system. Yes, there are new fog lamps in the new bumper. And if you crawl under the vehicle you'll spot underbody covers. There are fairings for both the front and rear tires (which, incidentally, are P235/55R 18s on 18 x 7-in. aluminum wheels: the sizeable setup one would expect on an SUV, not some comparatively diminutive hard low-rolling resistance rubber). A consequence of all this is that the coefficient of drag for the RX 400h is 0.35, the same as for the RX 330, despite the fact that that additional cooling opening in the front increases drag. Another item that you may spot that differentiates the RX 400h (without looking under the hood, which is a dead giveaway) are LED tail lamps (which are not only long-lived, but which require less power, and when you're working a hybrid system, you are concerned about power). When you climb inside, the differences are similarly subtle. Whereas the RX 330 has wood trim bits on places like the center stack and on the arm rest where the window switches are located, the RX 400h has brushed aluminum, a more technical look for what is a more technical vehicle.


Consumers Know Best.

As committed as we were to creating the world's most advanced hybrid vehicle, we were ever-mindful of the need to create a product that was consumer-driven. Engineers can easily get suckered into the notion that because they are the inventors, they necessarily know what's best. That what they like is necessarily what everyone should like. One of my jobs was to keep our focus on the customer—and not on our own priorities.—Sanayama

One of the things that the Lexus customer is looking for, as Clements observes, is performance. So the hybrid power system was engineered with that in mind. As this is a "full" hybrid system, it can operate under electric power only, with power from the internal combustion engine only, or with the two combined. The engine used for the RX 400h is a revised version of the V6 that's used in the RX 330 (which is (1) not surprising given that there are so many other similarities between the two vehicles; (2) rather surprising, given that it might seem as though the engineers would want to create something significantly different for the first hybrid luxury SUV; and (3) par for the course, taking both into account, as this is the nothing-if-not-pragmatic Toyota at work.) Not only are there calibration adjustments for the Variable Valve Timing with intelligence and electronic throttle control systems, but because the engine shuts off at times, and fairly regularly when one is in stop-and-go traffic, there had to be some nontrivial reworks. For example, the power steering pump, water pump and AC compressor for the system are all electrically powered—the belt-driven versions wouldn't work. The alternator is replaced by motor generators. Which brings us to the three motor-generators: MG1, MG2, MGR. MG1 doesn't provide motive force, as do MG2 (a permanent magnet machine located in the front of the vehicle that is rated at 123 kW @ 4,500 rpm) and MGR (a rear transaxle permanent magnet machine that provides 50 kW @ 4,610-5,120 rpm). MG1works as a starter, generator, and variable ratio control for the hybrid transaxle. This last-named function means that MG1, which is connected to the sun gear in the power split planetary gear set, controls the output speed of the transaxle by regulating the amount of electrical power it generates, as that varies its rpm. In addition to the power-split gear set, there is a motor speed reduction unit. MG2 is connected to its sun gear. Not only does MG2 provide power to the drive wheels, but the motor speed reduction unit can reduce the speed of MG2 so that the motor's torque is increased; when this kicks in, there's extra oomph added to the performance of the V6. And as for MGR: it is the means to an all-wheel-drive capability; it provides an additional 650 ft.-lb. of torque (there is electronic distribution between the front and rear as required). Oh, yes. The battery pack: a 288-volt DC NiMH unit that's fitted under the rear seat in three groups for more efficient packaging (there are 30 modules, each consisting of eight cells). There is a converter that raises the voltage to 650-V DC, then an inverter that turns it to 650-V AC. Because of the under-the-seat packaging, the total interior volume of the RX 400h is 140-ft3, as compared with 140.8-ft3 for the RX 330.


Exceeding Expectations.

So with all of that trickiness going on—seamlessly so far as the driver is concerned, unless she happens to be gazing at the power meter placed where the tach would otherwise be or monitoring the power distribution graphics on the display screen—one might think that that's enough. That's certainly something that exceeds expectations. But no, that's not enough. The RX 400h is equipped with a new stability control system that's designated VDIM: Vehicle Dynamics Integrated Management. This is an über controller that's in charge of the electronic braking control (including regenerative braking), anti-lock brakes, electronic brake force distribution, brake assist, traction control, vehicle stability control, and interactive steering boost. Essentially, the VDIM system senses the driving conditions and makes corrections and adjustments (to the brakes, throttle, steering) as required, but in such a way that it is more anticipative rather than reactive. As Dave Hermance, executive engineer, Environmental Engineering, Toyota Technical Center (Ann Arbor), puts it, "The feeling is that you suddenly became more skillful. It's smooth. You just think that you're very good." You may not be. But the RX 400h is.