Home / Tech News / A shift to thrift as Infiniti reinvents engine’s internals

A shift to thrift as Infiniti reinvents engine’s internals



Has the internal combustion engine just earned a stay of execution against the rallying electrification army?

Despite improvements such as fuel injection, turbocharging and variable valve timing, the engine as we know it has barely changed over the past century.

Now, just as we’re about to farewell the petrol burner and switch to electricity, Infiniti — Nissan’s prestige arm — has fitted a re-imagined engine to its new QX50 premium mid-size SUV.

The result of two decades of development and covered by 300 patents, the 2.0-litre VC-Turbo turbo (200kW/380Nm) features a revolutionary variable compression ratio to optimise power, torque and economy at the same time.

Due for an Australian launch late this year, the QX50 slots between the QX30 and the QX70 to take on the Audi Q5, BMW X3 and Mercedes-Benz GLC.



Its engine is reckoned to match the power of the 3.5-litre V6 fitted to the previous QX50 sold in the US, but with more torque and nearly 30 per cent better fuel economy. The company also claims it is 10 to 15 per cent thriftier than rivals.

The QX50’s constant variable transmission feels underwhelming, a trait of its kind, even with eight preset “ratios” to take the power to all four wheels. It claims 6.7 seconds for the
0-100km/h sprint and a top speed of 230km/h.

Infiniti fits its semi-autonomous ProPilot Assist — the emphasis is firmly on “assist”, as it can partially steer along on a well-marked highway. In stop-start traffic, it maintains a set distance to cars ahead, stopping completely if necessary.

Several of the functions require electric rather than mechanical steering but this comes at the price of numb, game console-like feedback.

With V6 levels of power, diesel-like torque figures and the uncommon fuel economy for an SUV (10.4L/100km), the QX50’s engine represents arguably the biggest advance in internal combustion technology since Honda’s VTEC variable valve timing breakthrough on the NSX nearly 30 years ago.

It might just buy the tried and proved petrol powertrain another decade before we make the mainstream jump to electric or hydrogen platforms.

GIVE IT THE ELBOW

A high compression engine squashes the air-fuel mixture inside a cylinder to create a bigger explosion and more power, also creating a lot of heat. So it needs fuel sprayed to cool the cylinders, meaning that it delivers more power but wastes fuel to stop valuable internals from warping.

In Infiniti’s VC-Turbo, an elbow in the conrod shortens the piston’s stroke and increases the volume of the combustion chamber on the run.

The regular high compression ratio (14:1) generates a lot of power. When the elbow rocks the conrod sideways to expand the swept volume, the lower ratio (8:1) delivers maximum economy, torque and engine longevity.

The QX50 starts at the highest ratio with a light throttle to get the most from every drop of fuel, then drops the ratio as it accelerates to cruising speed.

It takes just over a second and if it wasn’t for a small light on the dash, you’d never know something special was happening under the bonnet.



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