Hello everyone and welcome in this video we're gonna be learning about the world's first variable compression
turbocharged engine which is going to be used in a production vehicle
i'm super happy to say that this video is made in partnership with
Infiniti who flew me out to the Detroit Auto Show to see the engine in person and talk with infinity
engineers to learn all the details about how this engine works
and there's a lot of innovation going on aside from the obvious of changing compression ratio
we'll also chat about the cylinder liner balancing characteristics efficiency characteristics as well as some of the testing to ensure
reliability so the initial question is what's a compression ratio?
and why create a car with a variable compression ratio in the first place well the compression ratio,
or the ratio of the maximum cylinder volume to the minimum cylinder volume can be used to create
efficiency and power characteristics of an engine now Infiniti wanted to design an engine that could match the power of a naturally aspirated
6-cylinder engine while still achieving the efficiency and torque
characteristics of smaller diesel engines all with improved emissions
so how exactly does it work?
well the engine operates on the same basic four strokes as any other engine intake compression power and exhaust
that said it can completely alter the compression ratio to target increased horsepower or increased fuel economy
there are four basic steps for changing the compression ratio in this engine
first a harmonic drive essentially an electric motor rotates an actuator arm
second the actuator arm rotates a control shaft similar in principle to a camshaft
which forces a lower linkage to move up or down based on the orientation of the cam lobe,
third the lower link changes the angle of the multi-link which is connected by an upper link to the piston
finally the upper link moves from the multi links rotation, which causes the piston to move up or down
changing the compression ratio so for example if the engine was operating in its power mode
but wanted to switch to an efficiency mode the harmonic drive as shown would rotate to the left
this would then rotate the control shaft
which would pull the lower link slightly down this would rotate the multi-link slightly to the right
which would then force the upper link slightly upward,
decreasing the space between the piston and the cylinder head thus increasing the compression ratio, okay, so now that we understand how it works
why would you want to switch between compression ratios?
Starting with the scenario of creating maximum horsepower a low compression ratio of just 8:1 is used
this is because the engine is
turbocharged so when you pull in significantly more air and fuel with the turbocharger you can make significantly more power
however the likelihood of engine knock
increases engine knock can be destructive to an engine however by using lower compression ratios
you can reduce the likelihood of it occurring so when the engine is creating its peak power of 268 horsepower
or its peak torque of 287 pound-feet. It's doing so by lowering the compression ratio and
maximizing boost with the turbocharger switching between the two extremes from a compression ratio of 8:1 to 14:1 or vice versa
can happen in 1.2 seconds so what about when the engine operates at peak efficiency at a ratio of 14:1?
Well generally speaking the higher a
compression ratio used the greater the thermal efficiency of an engine is in other words high compression ratios mean better fuel economy
so when the engine is operating at low loads for example when you're idling or when you're cruising down the highway
it will switch to higher compression ratios to maximize fuel economy now
not only does it change the compression ratio,
but it also switches from a traditional engine cycle to the atkinson cycle by altering valve timing
the atkinson cycle leaves the intake valve open for a short duration of the compression stroke
which means some of the air fuel mixture is pushed out of the cylinder what this does is effectively cause the expansion ratio,
the piston moving down to be greater than the compression ratio
the piston moving up which allows the engine to get the maximum amount of useful work out of combustion now so far
i've made it seem like the engine operates in two distinct modes, but in reality
it's fully variable and can operate it any unique compression ratio between 8:1 and 14:1
ultimately the engine will choose the ideal compression ratio for the situation depending on the drivers throttle input if the driver is not
asking for power it will adjust the compression ratio to operate as efficiently as possible
for the given gas pedal position and the innovation with this engine doesn't end with a change in compression ratio
there are a lot of unique features
for example
inline 4-cylinder engines are inherently
unbalanced that means that the engines vibrate and so to compensate
four-cylinder engines often use balancing shafts which add complexity and consume power
but eliminate the vibration the reason 4-cylinder engines are unbalanced is because of the crankshaft design
which creates a secondary force that is not balanced out based on the movement of the piston,
you'll notice however that this engine doesn't have balancing shafts
and that's because the geometry of the crankshaft assembly does not cause the piston to create a secondary
imbalance to my knowledge there's no other inline 4-cylinder engine out there that won't have secondary balancing issues without the use of
balancing shafts, so not only can it change compression ratio
but it's beautifully smooth and balanced at any compression ratio it chooses another unique
characteristic of this crankshaft linkage is that it nearly?
eliminates side forces from the piston on the cylinder walls in a typical engine a piston will have a large
opposing side force on the cylinder wall as it also pushes downward rotating the crankshaft
this is because with normal engines the connecting rod is at a significant angle when rotating the crankshaft
this engine however maintains a nearly vertical
connecting rod for the combustion stroke as the piston is moving downward
which eliminates the side force from combustion against the cylinder wall with less force against the cylinder wall there's less friction and as the
force is all in the desired direction. This is more efficient now looking at the cylinder liner. You'll notice. It's very shiny and reflective
this so-called mirror coating is the result of the same plasma sprayed cylinder liner
that's used on the Nissan GTR after the plasma spray is applied
there's a very fine cylinder bore honing
which ultimately leaves behind a very strong durable and highly reflective cylinder liner the engine also uses both direct injection and
port injection it was found that the most efficient combustion at low loads occurred with both port and direct injection
active and this also helps to keep the valves clean at
higher loads only direct injection is used which meets the power demands and allows for precise fuel injection timing
now looking at all of the linkages below the piston it can seem a bit complex and
complexity can lead to reliability concerns, so I asked Infinity's engineers about their testing protocols
which were used to develop this engine and what made them confident in the engines
reliability the testing for this engine as you might imagine was quite extensive
the final product is the result of the engine going through over a hundred different
prototype iterations from there the engine has been through over three million kilometres of equivalent road testing and
30,000 hours in test beds most impressively
600 development cars were driven around the United States and scattered across the globe testing the engine in every imaginable
climate and weather condition I asked Infiniti how many cars would be used in testing a more generic?
engine design to which they replied about 50, so with 600 test vehicles nearly 12 times the real-world
testing was done on this engine to ensure reliability and durability
targets were met a few other interesting facts about the engine it has an integrated exhaust
manifold so the distance the exhaust travels to the turbo is extremely short
helping to spool the turbo quickly and also warming up the catalytic converter
quickly
the total height of the engine is actually the exact same as other four cylinders rather than taller from the added linkage
It uses premium octane fuel and it will be first sold in the Infiniti
QX50 though it has also debuted in the Q inspiration a concept car highlighting infinities future design language so a huge
thank you to Infinity for bringing me out to the Detroit Auto Show
giving me an inside look at how this engine works and of course for sponsoring this video
and thank you all for watching if you have any questions or comments, please feel free to leave them below.