The Lexus RX 350 grew in all dimensions and adds a double wishbone suspension for the first time, which engineers describe as the biggest challenge—and among the biggest weight contributors.
Believe it or not, the Lexus RX 450h is the first Toyota hybrid to sport a simple “Eco Mode” light (other Toyota hybrids display it in a multi-colored compass-like gauge), to indicate when drivers are achieving maximum mpg.
Problem? The RX, which launched the luxury crossover SUV market 10 years ago, the RX, which is the mainstay of overall Lexus sales, the RX, of which there are nearly 783,000 on the road, the RX, which is the best-selling vehicle in its class, the RX...a problem? Well, in a sense, at least as the designers and engineers went to work on what is now the 2010 RX 350 and its hybrid companion, the RX 450h. After all, they wanted to develop a vehicle that would go beyond what the previous two generations (RX 300 in '98; RX 330 in '03, with the first hybrid derivative, the 400h, appearing in '05) and attract a new demographic without alienating those who were already partisans. That was the problem.
The new demo-graphic? The folks with XY chromosomes. "We had many men tell us sort of sheepishly, 'Yeah, this is the car my wife drives,'" says Mark Templin, Lexus Group vp and general manager. So the designers and engineers went to work. When they did the research clinics for the new RX, Templin says, the guys said, "This is a vehicle I'm driving."
Lexus RX chief engineer Takayuki Katsuda says the mantra of the RX engineering team was confidence, control and comfort. And all three were in play with the team's big-gest challenge: designing the new double-wishbone independent rear suspension from the ground up. "This is the first time for the double wishbone, and it is a much more complex design than Macpherson. But it has many advantages in stability." The more compact design, which includes a wider arm span, a rigid trailing arm, and carrier joints, not only adds steadiness, but it also takes away the strut tower covers on either side of the cargo flooring, freeing up about 4.5% more cargo space. The integration also meant the design team had to design new air-funneling underbody covers for both the front and rear, which was a plus as they contribute to a lower co-efficient drag (0.33 from 0.35).
In February 2006, the RX 330 became the RX 350, as a 3.5-liter engine was put under the hood. The 2010 has the same 3.5-liter, but as it is paired with a new six-speed (up from five) Multi-Mode Automatic Transmission, it provides 275 hp, up 5 hp, and better overall fuel efficiency, at 18/25 mpg in FWD and 18/24 AWD. The RX 450h brings the sixth-generation of the Synergy Hybrid System and with it, the first application of the Atkinson Cycle instead of the Otto Cycle in the SUV. The compression ratio in the 3.5-liter (12:5 with the Atkinson and 10:5 in Otto), increases efficiency but is offset with less power-a potentially troublesome issue for an SUV. "With the Atkinson you don't get a good performance at low RPM," says Bob Allan, manager-Lexus College. "But matching it up with a hybrid transaxle makes it much more efficient. And that's why this has plenty of low-end torque." Inside the transaxle, the magnet configuration was redesigned and lower friction roller bearings added to help increase power output by another 3 to 4%. A new power inverter, which translates the DC power from the battery to AC for the electric motor, also shows incremental gains in weight vs. output. At 48.5 lb., the new inverter is about 17.6 lb. (8 kg) lighter than its predecessor, while volume is decreased by half. What's more, power density is increased by some 40%. A new exhaust heat recovery system warms the engine up to five times faster than the previous version, decreasing the time for the engine to switch to the EV mode. The recovery system detects when the engine coolant is ice cold and shuts the exhaust flow control valve, routing the gas through the coolant chamber and the heat with it. At normal operating temperatures, the exhaust flow valve is open, letting the exhaust gas to bypass the chamber. For instance, at 0° the engine is warm enough for shutdown within 1.5 to 2 minutes, compared with up to 10 minutes in the previous HEV system.
All Quiet on the LX Line
What was the biggest contributor to production errors on the RX line at Toyota Motor Manufacturing Canada, one of just two places where the vehicle is built? No, it wasn’t materials or logistics or tolerances or machinery or any of the usual factory suspects. Rather, it was noise. While some workers can block it out, Toyota manufacturing engineers found others are more distracted by regular old production din. So engineers sought to block it by adding more hushed electric trolleys, outfitted carts with rubber rollers, and increasingly equipped line workers with electric tools instead of air-compressed ones. The combination of efforts lowered sound levels on the line to 60 decibels (dB), according to Lexus RX chief engineer Takayuki Katsuda. For comparison, 66-dB sound intensity is about equal to the ambient noise of typical background conversation in a restaurant.
Where silence is especially golden is in the final inspection area, which is now known as the “sound dome.” There, sound levels are reduced down to 50 dB for the final quality inspections. The benefit here is obvious, as inspectors in the dome listen closely for any inconsistencies in up to 500 different vehicle sounds to catch any production or material problems.
Apparently, the sound reductions were not aimed at remedying any ongoing production errors. Rather, the strategy was to improve overall worker concentration and decrease the number of times a single task is repeated because of distraction. “It may sound insignificant, but taking two or three seconds to return a part or a bolt adds up over time,” says Bob Allan of Lexus College. Toyota first instituted sound deadening processes at the Toyota Motor Kyushu (TAK) plant in Japan where the RX is also built (it is the sole source of the RX 450h), and exported it in stages to Cambridge in early 2008. It was fully implemented there for the RX 350 when production began in late December.