Infiniti variable-compression engine: more complexity, incremental gains


Infiniti VC-Turbo engine

Infiniti VC-Turbo engine

Enlarge Photo

To meet stricter global emissions standards, carmakers are trying to squeeze every last bit of efficiency out of internal-combustion engines.

That has led Infiniti to turn to a technology engineers have toyed with for some time, one that so far hasn't been used in production cars.

General Motors, Mercedes-Benz, and Saab have all experimented with variable-compression engines, but Infiniti hopes to be the first to put the technology into production.

DON'T MISS: Infiniti plans VC-T engine with variable compression ratio

Such engines have the ability to alter their compression ratios.

That's the volume of the combustion chamber when a piston is at the bottom of its stroke, compared to when a piston is at the top of its stroke after compressing the volume inside the cylinder—a ratio that is fixed in conventional engines.

Infiniti announced its engine—called the VC-T (Variable Compression - Turbo)—in August, and gave more details at the recent 2016 Paris Motor Show.

Infiniti VC-Turbo engine

Infiniti VC-Turbo engine

Enlarge Photo

Set to go into production in 2018, the Infiniti VC-T is a 2.0-liter turbocharged 4-cylinder engine, producing 268 horsepower and 288 pound-feet of torque.

It can switch its compression ratio from a performance-oriented 8:1 to a 14:1 ratio for maximum fuel efficiency.

The engine's actual capacity ranges from 1,970 to 1,997 cubic centimeters, depending on the compression ratio used.

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The compression ratio is changed by a device Infiniti calls the Harmonic Drive, which uses an electric motor and mechanical linkages to adjust the connection between a piston and the crankshaft.

It controls the maximum height a piston can reach within the cylinder, and consequently the compression ratio.

Ratios are adjusted automatically depending on driving conditions, without any involvement from the driver.

Infiniti VC-Turbo engine

Infiniti VC-Turbo engine

Enlarge Photo

Infiniti has previously said the VC-T engine will use a more efficiency-focused setting under light loads, and switch its configuration to offer more power when needed.

As well as the promised efficiency benefits, Infiniti claims the VC-T will have lower levels of noise and vibrations than other inline-4 engines.

But it is also rather more complex than conventional gasoline engines, for gains that seem likely to be measured in single percentage points or low double digits.

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And no internal-combustion engine can match the overall energy efficiency of an electric powertrain.

While its parent Nissan offers the Leaf, the best-selling electric car in history, Infiniti has no electric cars in its current lineup.

It sells multiple hybrid models, but has repeatedly pushed back plans for an all-electric car, which seems to be a fairly low priority for the carmaker.

2012 Infiniti LE Concept

2012 Infiniti LE Concept

Enlarge Photo

Which leads to an interesting question: will there be a point at which the cost and complexity of wringing out another percent or two of efficiency from conventional drivetrains no longer be worth it?

That day hasn't come yet, and may not for many years. But it's at least conceivable now—which it probably wasn't just a decade ago.

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