'H' for performance: Lexus 400h combines the latest generation Hybrid Synergy Drive with its top-selling SUV and finds improvements in both performance and fuel economy. Maybe you can have your cake and eat it too

Automotive Industries, Feb, 2005 by John Peter

Are you happy with your Lexus RX330, but you'd like a little more power--maybe enough to dust off the guy down the street in the Mercedes ML 500.

How about a luxury Lexus SUV that goes from 0 to 60 in 7.3 seconds? That's about three-tenths of a second faster than your 330 and puts you on par with your neighbor's ML 500, or 3.4 seconds 30 to 50 mph, a second quicker than competitive vehicles. What if it had 650 lb.ft. of torque at launch, and on top of all that performance, it got about 28 to 30 mpg. No, it's not some kind of super diesel, it's a hybrid-electric SUV. Hybrid isn't just for fuel economy anymore.

In fact, Denny Clements, group vice president and general manager, Lexus division, says that the RX400h won't be sold on fuel economy at all.

"We're going to market it on the basis of performance, package and quality," says Clements, "and exceed the buyer's expectations on fuel economy."

Clements says that research shows the fuel economy is not even on the list when buying luxury SUVs, though it does show up as a post purchase complaint.

With an expected average of 28 miles per gallon, fuel mileage should no longer be a factor.

Hybrid Changes

At first glance the 400h doesn't look much different from its sister 330. There are three principle differences in the front of the vehicle. The grille was redesigned and an extra cooling inlet was added for the hybrid components, which required a redesign of the front fascia. Round fog lamps replace the rectangular fog lamps of the 330.

The changes to the rear of the vehicle are even more subtle. The tail lamps now have horizontal trim pieces and the bulbs have been replaced with LEDs. LEDs use less energy while giving off a brighter light and are also a lot more durable than incandescent bulbs, requiring less maintenance.

The extra cooling inlet in front caused an addition in drag that needed to be offset. Fairings were installed behind the front and rear wheels to split up the airflow coming off the tires. Some new underbody shields were also added to the vehicle. These tweaks brought the coefficient of drag back in line with the RX330.

Interior differences consist of brushed-aluminum inserts replacing the wood inserts on the 330 and a modified IP cluster that replaces the tachometer with a power meter.

This RX400h rides on specific 18-in. by 7-in. aluminum wheels fitted with P235/55R 18-in. tires. Lexus chose not to go with rolling resistance tires. Because of the vehicle's power and performance characteristics, it was felt that the vehicle needed sufficient rubber underneath it and a rolling resistant tire would have been too much of a compromise.

The 400h has front struts with internal rebound springs and linear control valves, tuned for sportier handling.

Safety First

In the active safety area, the 400h's Electronically Controlled Braking (ECB) system combines the regenerative braking of a hybrid vehicle with the cooperative hydraulic braking system into what is essentially a brake-by-wire system. ECB becomes an integral component of both the powertrain system and the handling system.

The RX400h is equipped with Vehicle Dynamics Integrated Management (VDIM).

VDIM is a proactive stability control system that anticipates vehicle instability in virtually any direction. The system integrates a yaw rate sensor, deceleration sensor, speed sensor and steering sensor that send data to the Electronically Controlled Braking system (ECB). The ECB system translates brake stroke speed and pressure and generates the precise amount of combined electric regeneration and hydraulic pressure needed for virtually any driving condition. VDIM interfaces with the ABS, brake assist, vehicle stability control and traction control, allowing more precise control of these systems. It also uses a new electronic power steering system to optimize steering assist. The system uses a 42 VDC electric motor, wrapped around the rack Power is supplied by a DC/DC converter.

An additional sensor has been added to the vehicle that senses both side collision and rollover due to side collision, and triggers the front and rear side curtain airbags. Modifications have also been made to the body reinforcements and structural geometry to account for the additional 300 pounds of mass in the event of a collision.

Quiet Please

Several NVH improvements were made to the 400h. The extra weight, extra torque and improved handling characteristics required additional torsional rigidity. Several gussets and reinforcements were added to stiffen up the body.

The windshield is made of an acoustic damping laminated glass to keep out unwanted noise when the engine is shut off at rest. The cooling fan blade tips and shroud were redesigned to reduce the noise signature and keep it from being transmitted into the cabin. The 400h also uses direct gear drive on the front transaxle, which further reduces noise.

Powertrain

The 400h uses the same 3MZ-FE 3.3L 24-valve, V-6 engine that's found in the RX330. It puts out 208 hp, about 10 percent less than the 330 due primarily to changes in the intake and exhaust systems for hybridization.