Lexus equips NX entry-level SUV with new turbo gasoline engine

  • 19-Sep-2014 12:01 EDT
2015_Lexus_NX_200t_002.jpg

While the Lexus NX and its engine will be produced at a Toyota Motor Kyushu plant in Japan, the vehicle will be sold in 80 global markets.

Development of the concept that became the newest and fourth entry into Lexus’s line of SUVs, the compact NX, began in 2009, though the design was finished relatively recently, according to Takeaki Kato, Chief Engineer of the NX. The Lexus LF-NX concept debuted at the 2013 Frankfurt Motor Show, and the production NX goes on sale in November or December of this year, despite the program coming of age during an overall difficult economic environment, the aftermath of what Kato refers to as the “Lehman shock.”

Kato says that during the development period his team of 2000 engineers kept focused on the program’s goals, which boiled down to the identified need to develop “innovative solutions for key core technical issues such as the engine and the platform,” he said, with the ultimate aim of being competitive in the segment.

To convince management to give the go ahead to the program, “revised product concepts [were presented] over and over” by the design, engineering, and manufacturing teams, eventually arriving “via a new level of collaboration” at the final concept and eventual production vehicle.

While often described as all-new, the Lexus NX is actually based on (or “loosely connected to,” as Lexus sees it) the Toyota RAV4. That said, the loosely connected reference can be justified in that 90% of the NX consists of newly engineered parts and systems.

The most obvious indicator of its newness is its “racier” exterior that Lexus hopes will provide enough design edginess to appeal to its target of “young users,” though that demographic term may be somewhat relative in regards to the standard Lexus audience as the company estimates its targeted “young users” have a $130,000 household income.

Besides the aesthetics of the exterior (Lexus claims the NX design team used a die of the signature spindle grille as a base over which molten steel was poured to see how the shape would naturally form), the lightweight body structure consists of different grades of hot stamped and high-tensile-strength sheet steel, with enough aluminum to contribute lighter weight while also contributing to the NX’s highly rigid body.

Borrowing from some non-SUV Lexus (sedan) models, the NX takes advantage of body adhesive, laser screw welding, and additional spot welds to increase panel joint strength throughout the body. Body adhesive applied at places such as between the front pillar and dash panel and between the wheel housing inner and outer panels allowed for the joining of panel surfaces over a greater area, contributing to rigidity and handling stability. Laser screw welding spots were added between existing spot welds at the front and rear door openings and rear quarter panel opening to suppress cross-sectional deformation.

In terms of firsts underneath the NX body, Lexus created an all-new gasoline engine architecture in the 2.0-L four-cylinder turbocharged port and direct-injection engine. Injection is split between the direct injectors and the port injectors according to driving conditions. The engine features an air-to-liquid intercooler that is mounted on the engine to minimize the intake volume downstream of the twin-scroll turbocharger, developed completely from scratch by Lexus engineers.

Combining the cylinder head, exhaust manifold, and intercooler with variable control of the wastegate valve minimizes the amount of components in the engine compartment while adding to low speed torque fuel economy. Active wastegate control minimizes pumping losses by reducing backpressure during low engine load. A dual exhaust system reduces backpressure and noise.

To minimize turbo lag, the four-into-two exhaust manifold system pairs cylinders according to their expansion or compression stroke to reduce pumping losses and eliminate exhaust gas interference. The turbo engine produces 235 hp (175 kW) at 5600 rpm with 258 lb·ft (350 N·m) of torque from 1650-4000 rpm and up to 17 psi (1.2 bar) of boost at wide open throttle.

The dual variable valve timing with intelligence (VVT-iW) system optimizes torque throughout the engine speed range and provides the capability to advance and retard intake cam timing to switch between engine cycles. Specifically, VVT-iW allows the engine to start in the Otto cycle and then switch between it and the more fuel efficient Atkinson cycle as needed, with the late intake valve closing of the Atkinson cycle reducing pumping losses and boosting fuel economy.

Manufacture of the engine and vehicle will be at the Toyota Motor Kyushu plant in Japan, while the vehicle itself will be sold in 80 global markets. Lexus initially anticipated global yearly sales of about 16,000, though after feedback from dealers, etc., the company doubled its yearly output to about 32,000 units. (Estimates are that sales of the NX will include just under half being the 200t with the new engine, and just over half being the 300h with the hybrid drive system.)

Although Lexus has not announced any other applications for the NX’s turbo engine, the engine was bench-tested for more than 10,000 hours before extensive on-road testing, covering more than 600,000 mi (970,000 km). In fact, the company has so embraced the new turbocharger that it developed new manufacturing and material technologies to ensure a high-quality, and environmentally sound, production line for the entire assembly process. Low-distortion electron beam welding is used on the turbine wheel, while the turbine housing uses new heat-resistant cast steel with reduced nickel content.

It would be hard to imagine that such an investment in time, energy, and money would be kept unique to an entry-level SUV, albeit a Lexus. It is quite certain the turbocharger will appear in other Lexus applications, it is the what and the when that are unknown.

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