Automotive

Turbo power meets extreme efficiency: Infiniti unveils world's first production engine with variable compression ratios

Turbo power meets extreme effi...
Infiniti's 2.0-liter, 4-cylinder, four cylinder VC-T engine can vary its cylinder compression ratios between 8:1 (allowing high turbo boost for maximum performance) and 14:1 (giving you maximum efficiency when you're cruising)
Infiniti's 2.0-liter, 4-cylinder, four cylinder VC-T engine can vary its cylinder compression ratios between 8:1 (allowing high turbo boost for maximum performance) and 14:1 (giving you maximum efficiency when you're cruising)
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The compression ratio change is achieved by tilting the multi-link using a harmonic drive linked to an actuator arm
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The compression ratio change is achieved by tilting the multi-link using a harmonic drive linked to an actuator arm
Infiniti's 2.0-liter, 4-cylinder, four cylinder VC-T engine can vary its cylinder compression ratios between 8:1 (allowing high turbo boost for maximum performance) and 14:1 (giving you maximum efficiency when you're cruising)
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Infiniti's 2.0-liter, 4-cylinder, four cylinder VC-T engine can vary its cylinder compression ratios between 8:1 (allowing high turbo boost for maximum performance) and 14:1 (giving you maximum efficiency when you're cruising)
Infiniti's VC-T engine: the first production-ready engine with variable compression ratios
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Infiniti's VC-T engine: the first production-ready engine with variable compression ratios
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Forget variable length intakes and variable valve timing, Infiniti is going all the way and introducing variable cylinder compression ratios. The new VC-T turbo engine automatically adjusts between a high-powered 8:1 and a hugely efficient 14:1 ratio as you drive.

As environmental protection measures continue to tighten the screws, combustion engine manufacturers are getting more and more creative in their efforts to squeeze more out of gasoline.

Here's a fascinating example: Infiniti is about to unveil the world's first production-ready variable compression ratio engine at this year's Paris Motor Show.

The Infiniti VC-T is a 2.0-liter 4-cylinder turbocharged petrol engine with the ability to raise and lower the stroke of its pistons, giving it a range of available compression ratios from 8:1 all the way up to 14:1.

Infiniti's VC-T engine: the first production-ready engine with variable compression ratios
Infiniti's VC-T engine: the first production-ready engine with variable compression ratios

The engine changes compression ratios depending on how you're driving; when you put your foot down and the turbo starts working hard, forcing a heap of air into the cylinder, the air-fuel mix becomes more likely to pre-detonate. That's why high-performance turbo engines need to run lower compression ratios – the Subaru WRX, for example, runs the same 8:1 ratio that the VC-T can at peak performance.

But when you're cruising, that's unnecessary and inefficient – you get significantly better fuel economy from a higher compression engine.

The VC-T engine constantly changes its ratio to give you high performance when you ask for it, and excellent economy when you don't. It does this using an actuator arm that changes the angle of a multi-link that sits around the crankshaft, raising and lowering the top and bottom points of the piston stroke without moving the crankshaft or the cylinder head.

The compression ratio change is achieved by tilting the multi-link using a harmonic drive linked to an actuator arm
The compression ratio change is achieved by tilting the multi-link using a harmonic drive linked to an actuator arm

There have been other variable compression ratio engines built, just none for production. Peugeot, for example, used a system that changed the length of the conrods to achieve a similar result. Porsche has recently patented a design that puts the small end bearing in an eccentric adjuster to make the same kinds of adjustments.

Infiniti won't be releasing solid figures on the VC-T engine's performance until Paris at the end of September. But it should deliver more than the current QX60 3.5-liter V6, which makes some 265 horsepower and 248 foot-pounds, with about a 27 percent boost in fuel efficiency. And the company claims the weight penalty won't kill the idea, as the engine will only be around 22 lbs heavier than a typical inline four of the same capacity.

With each new generation, combustion engines are forced to become ever more complex Rube Goldberg machines, with more sophisticated electronics and even more moving parts.

On the other end of the scale sit electric motors, which are simple, massively powerful and quiet. They don't need valves or injectors or clutches. They're so flexible they don't even need gearboxes much of the time. They deliver full torque from a standstill, with nothing like the bizarre power curves you need to deal with on a combustion engine. And of course they're incredibly efficient, generating far less waste heat and converting a vastly higher percentage of your fuel energy into motion.

But until batteries can offer all-day driving range or quick enough charging to make recharge stops practical (and do it all at a competitive price) we'll be stuck here marveling at the ingenuity of combustion engineers trying to wring every last drop out of last century's technology.

Source: Infiniti

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14 comments
JoeSalas
i'm baffled by this conclusion. need more input.
Steve Jones
If memory serves, Saab also had a design for a variable-compression engine which did so by somehow tilting the whole engine block away from the crank. Interesting stuff. I was under the impression there is also a use for it in non-turbo engines, by varying the compression ratio through the rev range, but that's just a vague recollection.
Mel Tisdale
Surely a lighter solution is to have a fly-by-wire throttle on the inlet manifold to the combustion chambers and on the exhaust feed to the turbo charger. All that is then required is monitor the resultant cylinder pressure at t.d.c. and adjust the pressure of the charge to suit the performance required at any particular moment.
Bob
Since there is more energy in a gallon of diesel than a gallon of gasoline, I wouldn't count the diesel out yet. I would imagine a diesel-electric hybrid being the car of the future.
DaveWesely
Yes, ICE is on the way out, but the lack of battery technology is sort of a red herring. The vast majority of trips are less than 30 miles and batteries could be swapped out on long road trips with proper battery standardization. That simple small step would eliminate most, if not all of the technological hurdles.
Expanded Viewpoint
It looks to me like way more complexity being built into a system than is needed to accomplish the goal. Just look at all of that extra machine work to make those parts alone!! And then when you factor in the original assembly time of each engine, the cost of the additional parts when they break and wear out and such, who would really want one of these things except the tech junkies who are always looking for their next "fix"? Just how much more will be added to the bottom line of the cost of the car when all is said and done? And right now, as gasoline prices are plummeting (2.19 a gallon yesterday at ARCO) how can this boondoggle be justified? Yes, Diesel fuel has more BTU in it than gasoline, but what is the most efficient way to extract it? Is external or internal combustion better?
habakak
Bob....dieselgate. Wow. It is almost a shame that the age of the ICE is coming to an end. They are truly powerful and amazing works of engineering today. And efficient and clean compared to just a decade ago even. But they are peaking so it's time to roll in the next better technology. We won't marvel over these engines for too long. In 10 years hardly any automobile manufacturer will be making ICEs anymore.
sidmehta
"But until batteries can offer all-day driving range or quick enough charging to make recharge stops practical..."
If you are willing to pay, you can swap batteries in the same time as it takes to fill gas - at least that's what Elon's video claims.
Better yet, on all-day drives plan your charging with lunch / snack time. Teslas take between 20 - 40 minutes. It's free.
Just don't use the auto-pilot!
PeterOsborne
The internal combustion engine was developed in the late 19th century. By the end of the 1st. World most on the mechanical developments has been made. Then after WW2 , the final configuration we use even today were finished. After that, electronics have been the drivers of advances. Electric cars have been around since the first decade of the 20th Century , and range + recharging time was the big problem. One hundred six years the same problems exist. The exotic metal batteries of today suffer from losing recharge capacity loss, expense to manufacture , environmental damage from mining, making them difficult to be competitive in the open market. Hopefully we'll see a solution to the problems soon, it would be exciting to see success and the resulting competition between electric and internal combustion engines.
Martin Hone
I'm with Mel. Who needs the extra complication. And how much better is the fuel efficiency at the higher compression ratio anyway ?