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INFINITI unveils new QX50 with variable compression ratio engine; 35% improvement in fuel economy over prior FWD V6

At the Los Angeles Auto Show, INFINITI revealed the all-new QX50—a premium mid-size SUV featuring the first production application of the VC-Turbo variable compression ratio engine, transforming on demand. (Earlier post.)

An innovative combustion engine design, the 2.0-liter VC-Turbo engine adjusts its compression ratio to optimize power and efficiency. It combines the power of a 2.0-liter turbocharged gasoline engine with the torque and efficiency of a four-cylinder diesel engine.

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The QX50 is the most important vehicle we have ever launched, and it embodies everything the brand stands for: beautiful design, advanced technology and empowering performance. As a premium, mid-size SUV, it’s the right vehicle at the right time in one of the world’s fastest growing segments.

—Christian Meunier, INFINITI Global Division Vice President

The VC-Turbo changes its compression ratio seamlessly with an advanced multi-link system, continuously raising or lowering the pistons’ reach to transform compression ratio—offering both power and efficiency, on demand.

The multi-link system uses an electric motor with a unique Harmonic Drive reduction gear to transform its compression ratio. The electric motor is connected to the Harmonic Drive with a control arm; as the Harmonic Drive rotates, the control shaft at the base of the engine rotates, moving the multi-link system within the engine.

As the angle of the multi-link arms changes, it adjusts the top-dead-center position of the pistons—and the compression ratio with them. An eccentric control shaft changes the compression ratio of all the cylinders at the same time. As a result, the engine capacity varies between 1,997 cc (for a low 8:1 ratio) and 1,970 cc (high 14:1 ratio).

INFINITI_VC-Turbo_Infographic_03
  1. When a change in compression ratio is needed, the Harmonic Drive turns and moves the actuator arm.

  2. The actuator arm rotates the control shaft.

  3. As the control shaft rotates, it acts upon the lower link, which changes the angle of the multi-link.

  4. The multi-link adjusts the height the piston can reach within the cylinder, thus changing the compression ratio.

Click to enlarge.

A high compression ratio gives greater efficiency, but in certain applications poses the risk of premature combustion (knocking). A low compression ratio allows for greater power and torque, and avoids knocking. In operation, the QX50’s VC-Turbo engine offers any compression ratio between 8:1 (for high performance) and 14:1 (for high efficiency).

The engine delivers 268 hp (200 kW) @ 5,600 rpm and 280 lb-ft (380 N·m) @ 4,400 rpm. The VC-Turbo’s specific power output is higher than many competing turbocharged gasoline engines, and comes close to the performance of some V6 gasoline engines. The unit’s single-scroll turbo ensures immediate accelerator responses, on demand.

Equipped with the VC-Turbo engine, the QX50 delivers gasoline fuel economy of 27 mpg (US combined, front-wheel drive; 26 mpg all-wheel drive). In front-wheel drive specification, this offers a 35% improvement in fuel efficiency over the V6 gasoline engine in the previous QX50, while the new all-wheel drive model’s 26 mpg represents a 30% improvement.

The engine block and cylinder head are cast in lightweight aluminum alloy, while the multi-link components are manufactured in high-carbon steel alloy. Compared to INFINITI’s 3.5-liter VQ V6 engine, the 2.0-liter VC-Turbo weighs 18kg less and requires less space in the engine bay.

The VC-Turbo can switch between both Atkinson and regular combustion cycles without interruption, enabling greater efficiency and performance as it transforms.

Under the Atkinson cycle, air and fuel intakes overlap, allowing the fuel in the combustion chamber to expand to larger volumes for greater efficiency. The INFINITI engine operates the Atkinson cycle under higher compression ratios, with longer piston strokes allowing the intake valves to open for a short time as the compression stroke starts. The Atkinson cycle is commonly used in hybrid engines to maximize efficiency.

As the compression ratio drops, the engine reverts to a regular combustion cycle—intake, compression, combustion, exhaust—in separate phases to enable greater performance.

The VC-Turbo engine combines a number of existing INFINITI technologies to realize its variable nature. The engine employs both MPI (multi-point injection) and GDI (gasoline direct injection) to balance efficiency and power in all conditions:

  • GDI improves combustion efficiency and performance, and enables the engine to avoid knocking at higher compression ratios

  • MPI mixes fuel and air earlier, enabling complete combustion in the chamber for greater efficiency at low engine loads

The engine switches between both at regular engine speeds, with both sets of injectors able to work in conjunction under higher loads.

A single-scroll turbocharger maximizes performance and efficiency, enabling immediate throttle responses at any speed or compression ratio. The turbocharger ensures equivalent performance to a naturally aspirated six-cylinder unit. Small enough to aid the compact overall dimensions, a single-scroll system also reduces the loss of thermal energy and exhaust pressure.

An integrated exhaust manifold is built into the aluminum cylinder head to further enhance packaging and efficiency. This enables INFINITI engineers to position the catalytic converter next to the turbo, creating a shorter flow path for hot exhaust gases. This means the emissions control process can start sooner, as the catalytic converter heats up more quickly.

Closely controlling the flow of exhaust gases through the turbocharger, an electronically-controlled wastegate actuator maintains turbocharger boost pressure. This ensures high fuel efficiency and performance under all conditions while minimizing emissions.

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The uncommonly smooth VC-Turbo does away with the two balance shafts required in conventional four-cylinder engines, due to the layout of its multi-link system.

The VC-Turbo is smoother than conventional in-line engines, and has the low noise and vibration levels expected of a traditional V6. This is, in part, a result of its multi-link design, where the piston connecting rods are almost vertical during the combustion cycle (rather than moving wider laterally, as they would in a traditional crankshaft rotation). This represents the ideal reciprocating motion, and entirely negates the need for balance shafts. Despite the addition of a multi-link layout, the engine is therefore as compact as a conventional 2.0-liter four-cylinder engine.

The result is uncommonly low levels of vibration. During internal tests, INFINITI benchmarked the engine against four-cylinder engines from rival manufacturers. The VC-Turbo produces reduced engine noise—almost as refined as a V6.

INFINITI’s low-friction ‘mirror bore coating’ contributes to a 44% reduction in cylinder friction, allowing the engine to rotate more smoothly. The coating is applied to the cylinder walls by a plasma jet, then hardened and honed to create ultra-smooth cylinder walls.

The QX50’s 2.0-liter VC-Turbo engine employs an active engine mount vibration damping system, called an Active Torque Rod (ATR), to reduce engine noise even further. The QX50 is the only car in its class to offer this kind of technology. Integrated into the upper engine mount, where the most high-torque noise and engine vibration is generated, the ATR has a G-sensor that detects vibrations. It then creates opposite, reciprocating vibrations, enabling the four-cylinder engine to be as smooth and quiet as a V6, reducing engine noise by 9dB (compared to the current QX50). This helps to make VC-Turbo one of the quietest and smoothest engines in the premium SUV segment.

XTRONIC CVT. The VC-Turbo engine is paired with INFINITI’s new XTRONIC continuously-variable transmission (CVT), a ‘shift-by-wire’ system which eliminates the need for traditional gears. The XTRONIC CVT reacts instantly to driver inputs, with an infinite number of gears matched to the transformation of the engine through different compression ratios.

The transmission adjusts immediately under hard acceleration as the engine transforms to a lower compression ratio. A higher gearing ratio for cruising speeds matches the higher compression ratio of the engine, enhancing fuel efficiency. A high final gear ratio (5.846) creates an instantaneous and decisive acceleration character.

The final drive ratio works seamlessly with the wide-range single-scroll turbocharger, allowing the engine to operate at lower compression ratios, and deliver the immediate acceleration to match the transforming, variable performance delivered by the VC-Turbo engine. Pre-programmed gears allow drivers to change engine speeds on demand, in line with their driving style.

The new XTRONIC CVT adopts the latest transmission technologies to enhance efficiency and acceleration. A torque converter ensures a direct connection between the accelerator pedal inputs and the engine response. An electric oil pump system works in-tune with the Idle Stop system, distributing oil throughout the transmission to enable immediate restarts and enhance fuel efficiency.

This ‘shift-by-wire’ transmission enhances the QX50’s powertrain packaging, with the fully-electronic system replacing the mechanical transmission linkage. This means the XTRONIC CVT takes up less space, eliminating the need for a large transmission case or tunnel mount. This enhances cabin space in the process, and results in a larger central armrest and center console area for maximum elbow room.

The shift-by-wire configuration also empowers the driver with quicker gear shifts, with more immediate and instantaneous shifts in manual mode. Driver inputs are transmitted directly to the CVT by wire, while a short stroke for the shifter itself delivers a high quality, silent gear change feel.

Comments

And Bri

As i said in an earlier post at autobloggreen, im interested to buy this engine but smaller in a low cost small car. Im here to save gas to the utmost degree but journalists car manufacturers and bloggers all try to coax us to spend more than the least physical amount of money to drive our cars. This is dictated by the stock market financial mob. I confronted the laws of physics and i am sure that we can sell a brand new car for less than 8 000$ that do over 120 mpg on regular gas without costly maintenance. Also notice that my article is way more interesting than the usual car blog articles for no money at all. The entire economy and cultural space is plague by inneficient money makers and i despise them.

And Bri

Hey folks, The world can do like me and pollute 2x less by consuming less. Take the car radios and speakers for exemple. These devises are working for a lifetime and just me bought a good car sound system till more than 30 years and when i put my car to garbage i keep the radio for the next car. 99% of tesla owners buy costly electronics installed in the car which are useless and keep the car for 2 to 3 years before selling their garbage to another one and we have to constantly to maintain a big polluting electronic infrastructure that only give some wet dreams to stupid gadgets maniacs that harass us thereafter and accuse all the poors of polluting their world.

mpgJuan

It would be informative to know from Nissan more about the thermal efficiency gain for this engine over similar engines - for the city and highway cycles. The % gain in mpg almost certainly is dominated by downsizing from a 3.7 liter engine to a 2.0 liter turbocharged engine.

It would be nice if commenters kept on topic, but I will note that in the US, the OEMs design to a lot of safety standards and the high expectations of the purchasers. If practical vehicle mpgs of 120 were actually attainable, they would appear in select markets somewhere in the world.

Arnold

Nissan are correct to say that this is unquestionably the most important single 'advance to I.C.E. since the early 1900's. Hybrid designs that allow engines to run in sweet spot have the same ability to challenge the inherent efficiency compromises of ICE engines by going to the root of the problem. In this case fuel quality variations.

This concept - now a realised in mass production, targets the problem by providing the ability to exponentially increase the engine operating parameters especially fuel.

Using feedback from conventional sensors means the engine can adapt in 'real time' or so close as to be described and generally accepted as instantly.

Here lies the only risk area flaw as I see it.
It can only adapt after the fact so reactive rather than preemptive (aside that its control strategy program -is)

The next level improvement would be to input the fuel quality with accurate next gen fuel analysis.

That would assist the ECU to find and stay in the ballpark more and stray less into the fuzzy logic area that looks for a 'kick from the knock sensor feedback' to set it's limits. That conventional strategy means the engine is always drifting from 'ideal' to sub optimum running in order to set the upper limits. So I'm saying that means the engine can only really find it's best place by bumping into limits. (ugly)

Modern engines originally used this method to limit engine damage but it became incorporated into the engines fuel and ignition management strategy and is associated with a high rate of engine failure.
This V.C. ICE should be more capable but to achieve the best possible outcomes will depend on a lot of very sophisticated code and computing power.

As an interesting solution to engine design it seems really well executed. Cost will be a concern.

To build 120 mpg vehicles you need to specify the intended use. Adjusting KW outputs and engine sizing, vehicle weight and c.d. (light weighting).
65 mpg will be the next milestone.


Lad

Disappointed that Nissan hasn't produced an upscale BEV in their premium brand. All they have is a Leaf; not what I call "all in" on electric mobility...they are still selling obsolete, tricked out ICEVs as fast as they can.

Arnold

Fuel quality sensors or analysis is an important area for development in many industrial applications.
I'm told for instance that spirit alcohol for human consumption rely on guesswork to remove the unavoidable highly toxic methanol components. The practice is to take the first flush from the 'barrel and use that for widow cleaner or put it in the car's fuel tank. There is no test only guesswork.

The problem with using knock sensors to find the limits of detonation as a way to set compression ratio's could also be alleviated by either refining the piezo sensors and placement.
Inevitably AFAIK. piezo's need to be impacted on to generate a signal.

Some alternative method that recognises detonation tendencies earlier- well before they they go out of range and propagate through the engine block.

One area pressure aberration sensing could be be sited may be directly or indirectly from the piston/ rod/ big end or possibly via the actuator arm / 'harmonic drive on this motor.


CheeseEater88

You could always place more knock sensors on a car. Have more or less a three dimensional ping map. Sound takes time to travel, and if the data rate is fast enough, perhaps in a separate module, you could see which one signalled first(that and see the intensity), but the crank sensor should be enough to know which cylinder.


As they are now, they are extremely accurate, and engines can pinpoint on thier own which cylinder or bank has a problem. They are used in conjunction with wideb and O2s for leaner burns.

Ford uses knock sensors as more or less its go to for fuel trim. It advances timing till it knocks then backs off. That's why ecoboosts love water/methanol injection and still can take otherwise crappy fuels with very little problems.

I was putting in 85/86octane in my car, the $0.80 jump to 87 was a bit steep. I also felt like when i spent the money on the 87, it wasn't really fresh, in a town of 800 people, i probably was they only one buying.

CheeseEater88

I should add, cars run lean/rich mix all the time, like alternating, it's never ever optimal.

If we didn't have catalytic converter, we could run as close to stoichometric 100% of the time, but we don't.

.

It's all reactionary, but cars are really good at mapping and learning trends.

We gain efficiencies from the precision we are adding. Smaller injections via direct injection, faster and more power computers, more sensors, better sensors like wideband o2, hotter sparks.

Look to diesels, typically in America, diesels trend most advancements, turbo chargers, direct injection, and a slew of other technologies. These much bigger, and much more expensive engines have been the proving grounds for lots of new tech. It think the truck i was reading had over 20 injections per stroke for fuel.

Well probably see particulate filters, and higher pressure fuel rails in the near future on gasoline cars where emissions restrictions make it so.

Paroway

This sounds impressive, but the 2017 QX50 combined mileage was a pathetic 20 MPG, so a 35% improvement is still only 27 mpg.

CheeseEater88

Yeah, 27mpg isn't good. My brother can manage 26 mpg (highway cruise) in his F150, just by obeying posted speed limits.

It plummets above 65mph I'm told.

I used to drive 63miles one way to work, so i bought a 1.0l fiesta, and i did ~70mph, the whole way, i got nearly 40mpg, others doing similar commutes at lower speeds(55-60) were cracking into the 50mpgs.

DJ_D

European manufacturers will add gasoline particulate filters within the next 1-2 years. Some premium brands have already started for their upcoming engines.

dursun

Manufacturers are not going to let the ICE die anytime soon

CheeseEater88

It'll die a lot faster with gasoline particulate filters. People can barely manage owning diesel trucks with dpf and scr here in the states. semis and smaller pickups all have some issue with driver not knowing how to drive to clear the filter off. You have to get on the throttle hard, for an extended amount of time.

Putting that in the hands of an uninformed populous, not just professional drivers, will be a PR disaster. Warranty replacements will be costly. Cost to own will skyrocket, and people will hold on to thier aging cars longer than ever to avoid a particulate system.

We are on the cusp of BEVs becoming mainstream, 5-10years we'll probably start seeing exponential growth.

Bringing a BEV to market should be an easier affair than an ICE, parts are drop in, cells are known, it's more or less packaging concerns, like weight size and cost.


The cost is dropping, we'll see a decent push in the midsize car market.

Engineer-Poet
That conventional strategy means the engine is always drifting from 'ideal' to sub optimum running in order to set the upper limits. So I'm saying that means the engine can only really find it's best place by bumping into limits. (ugly)

You only get significant changes in fuel composition after refueling.  This typically happens only after many miles of travel.  Also, those limits are soft; subtle knock is detectable before it becomes an NVH issue, and is even desirable as it indicates eg. that spark advance is optimized.

It can only adapt after the fact so reactive rather than preemptive (aside that its control strategy program -is)

Even 20 years ago, engine control algorithms took notice of leading inputs like throttle plate angle which precede changes in manifold pressure and air charge.  All of this can be modeled quite accurately, and in the case of Atkinson cycle operation air charge is controlled by the engine.  You are way behind the times.

The problem with using knock sensors to find the limits of detonation as a way to set compression ratio's could also be alleviated by either refining the piezo sensors and placement.

They were already fairly well-refined by 1980.  I was there.  Knock "rings" the engine block at characteristic frequences which are easy to detect.

I was putting in 85/86octane in my car

Obviously a high-altitude dweller.  85 octane is not available near sea level.

fsdriver

Thanks E-P for your quick discussion on Knock Sensors. I always assumed that they kept you very close to the peak....fringe knocking for maximum performance and economy. Never heard a tech discussion that included the "leading edge" stuff like throttle plate changes. My 1994 Lumina must have been a little slower, you could get a good rattle when cracking the throttle from an idle but then be unable to get another for a long time.

Octane 85 Fuel: My last "totally mechanical" ignition advance car was a 1978 Zephyr. Borderline ping at sea level (Iowa) on Octane 87, not ping at all on 85 in Colorado (9,000 feet, Summit county) on our annual Ski Trip Once found some 83 octane near Aspen, still could not get a ping out of it.

Ya just gotta be careful to run it down and refill with something better as you leave the mountains, that stuff would begin pinging dangerously in Nebraska!! Hopefully the knock sensors have eliminated much of that danger.

Fasteddie

Wow....another adder to engine technology. Like all modern engines, I am sure this HCCI engine will be reliable, BUT the complexity that is going into such engine designs points to a tipping point in propulsion for personal vehicles:

https://uploads.disquscdn.com/images/b38ebc1a186a135702db4e343ebfd23b5547c35d55d66d8f0d786f2da7fd4baf.jpg

Engineer-Poet

Fasteddie, watch the trends of technology sometime.  The existing paradigm can advance, but a superior one WILL overcome... eventually.

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