Infiniti Variable Compression Turbo Breaks Cover

by Lawana Perkins | Posted on Sunday, October 2nd, 2016

Back in August Infiniti tantalized us with a bit of info on a radical new 2.0-liter turbocharged gasoline engine that promises V-6 gas-engine performance with four-cylinder diesel fuel economy and four-cylinder gas engine emissions, mass, and packaging benefits. The engine is slated for production in 2018. Everything we learned and surmised in August has been confirmed by press releases issued in advance of the engine’s Paris debut, along with considerably more information.

Infiniti Variable

Perhaps the biggest revelation was official output, which Infiniti pegs at 268 hp and 288 lb-ft of torque (rpm levels have yet to be disclosed). The target improvement in fuel efficiency is established at 27 percent relative to a V-6 of equivalent output, so think miles per gallon, not liters per 100 km when you do that math. Infiniti claims to have built and tested more than 100 engine prototypes, subjecting them to almost 2 million miles of equivalent road testing during 30,000 hours of test-bed development. The engine is currently undergoing real-world testing. The 20-year development program has resulted in more than 300 patents, including one for the multilink system and its electric motor actuator, which incorporates a Harmonic Drive reduction gear. Renault Sport Formula 1 even assisted with the development testing in the later stages of the program and is credited with helping resolve a high-speed bearing vibration problem.

Other details: The turbocharger is a single-scroll unit that bolts directly to a cylinder headintegrated exhaust manifold. The bore is listed as 84.0mm, and the official stroke is published at 94.1, but that appears to be a total stroke distance from top dead center during 14:1 operation to bottom dead center at 8:1 operation, as the displacement is listed at 1,997cc during 8:1 compression and 1,970cc at 14:1. Yes, the peculiar geometry of this multilink system actually alters the piston stroke infinitesimally between 90.1mm and 88.9mm.

That sprayed-in liner negates the need for iron liners and contributes to an overall weight savings of 55 pounds relative to the reference VQ V-6. A two-stage variable displacement oil pump enables lower pressures at engine speeds below 3,000 rpm and higher oil-flow pressure as speeds or loads increase. Similarly, a multiway flow-control valve manages engine thermal loads, routing coolant as warranted between the radiator, cabin heater, and oil cooler depending on conditions.

After decades of following numerousattempts to crack the variable compression code, we eagerly await our first drive of this world-first technology. Oh, and we hear there’s yet another variable-compression story brewing in Paris from another source, so stay tuned.

Questions we’ll be asking after the press conference:

  • How does the cost compare with the reference VQ engine?
  • Variable compression has been identified as an enabling technology for homogeneous-charge compression ignition. Do studies suggest any further efficiency improvements could be wrought from incorporating HCCI here?
  • Variable compression can also unlock the performance potential of gasoline/alcohol flex-fuel vehicles. Might there be global applications in places such as Brazil for this technology?
  • What does that Harmonic Drive reduction gear do to improve the customer experience over a chain or normal gear drive?
  • Does your integrated exhaust manifold include any volumetric efficiency tricks such as those we’ve seen from Mazda (twinning cylinder outputs to leverage exhaust pulse energy scavenging benefits) or lag-reducing measures such as small and large passages to accelerate exhaust flow onto the turbine wheel?

If you have further questions, send them my way, @MT_Markus on Twitter.

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