Game Changer: Infiniti's VC-T Variable Compression Engine

World's first production continuously variable compression setup, coming to Infiniti QX50 in 2018, promises performance and efficiency

Infiniti will launch the world's first production continuously variable compression ratio engine in 2018. The engine, a 2.0-liter turbocharged inline four called VC-T, will debut in the new QX50 crossover in 2018. The Infiniti QX50 is the brand's Audi Q5, BMW X3 and Mercedes-Benz GLC competitor which will be built in Mexico in a new plant jointly constructed with Daimler.

Nissan engineers have reportedly been working on the engine concept for more than 20 years, and the company claims to have filed more than 300 patents protecting the design and associated technologies.

In simple terms the engine features two connecting rods attached to opposite sides of a metal plate that rotates around a journal on the crankshaft, which is mounted mid-way up the block. The top end of the upper connecting rod is connected to the piston in the conventional manner, and the lower end connected to one side of the plate. The upper end of the lower connecting rod is attached to the opposite side of the plate, and the lower end is attached to an eccentric shaft mounted below the crank.

An actuator link rotates the eccentric shaft, moving the lower connecting rod up or down, which in turn rotates the plate around its axis on the crankshaft. The corresponding motion on the other side of the plate lowers or raises the lower connection point of the upper connecting rod, and therefore lowers or raises the top dead center position of the piston, effectively changing the compression ratio.

Engineers say the system allows the compression ratio of the Infiniti VC-T engine to be seamlessly and continuously varied between 8:1 and 14:1. The engine will adopt a lower compression ratio under hard acceleration or heavy loads to allow the turbocharger to deliver maximum boost, and move to a higher compression ratio on light throttle to allow for fuel-efficient lean-burn running. The engine, which uses both port and direct injection, will switch between Atkinson and regular combustion cycles without interruption. Inlet valve timing is controlled electronically.

Though it's not yet quoting exact numbers, Infiniti claims the 2.0-liter VC-T engine will deliver more than the 265 hp and 248 lb-ft of torque developed by the 3.5-liter V-6 currently available in the QX60 crossover, with a 27 percent boost in fuel efficiency. Infiniti says the variable combustion ratio mechanisms and related hardware increases VC-T engine's weight by about 22 lb compared with a regular inline 4, and that friction losses are similar to those in a four-cylinder engine with a balance shaft.

Variable compression ratio engines have existing in engineering labs for decades, but Infiniti will be the first to have a production version with a continuously variable compression ratio. The VC-T engine will be used in other Infiniti models, and also in future Nissans.

Allowing its premium Infiniti brand to debut the engine suggests Nissan is preparing to bet big on variable compression ratio technology, especially in Europe. Engineers say the engine is cheaper to build than a Euro 6 compliant diesel, and it won't be subject to the growing backlash against diesels in Europe because of increased concerns over particulate emissions.

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