The difference from a conventional engine is that the engine stroke is increased or decreased automatically. The stroke is the distance the piston travels up and down in order to turn the crankshaft. A shorter distance that is closer to the combustion chamber increases the compression ratio because there is less space for the fuel/air mixture. When the system is operating in low compression mode the piston travels more and does not reach as high. The combustion chamber then ends up being farther away and a lower compression ratio is achieved.
What is novel about this approach is how the combustion chamber was left in the same place. Past efforts by SAAB had the engine head moving the combustion chamber away from the pistons. This drastically changes the characteristics of the combustion process. Something that makes emissions control challenging. Any power loss due to a dynamic combustion chamber is removed by pressurising it with a turbocharger, just like Nissan did.
Possible issues with this design could be:
- Uneven wear of the cylinder bore due to the piston travel being dynamic.
- An overboost condition during a high compression cycle could damage the mechanism and even crack the engine block.
- Increased NHV due to regular wear and tear making its way into the valvetrain and transmission input shaft.
This is a good effort and I hope Nissan is able to pull it off. Make sure to wait two years before you buy a vehicle with this technology. Dont be the guinea pig. :)
> A shorter distance that is closer to the combustion chamber increases the compression ratio because there is less space for the fuel/air mixture. When the system is operating in low compression mode the piston travels more and does not reach as high.
I think this is partly inaccurate. The images show the piston at the top of the stroke; when the compression ratio is high the piston is higher at the top of the stroke. But the bottom of the stroke is the same in both cases. That means the actual length of the stroke--the distance the piston travels--is greater in high compression mode. This is consistent with the definition of compression ratio, which is the ratio of cylinder volume at bottom of stroke vs. top of stroke; a larger compression ratio means a larger difference between these volumes, i.e., a longer piston stroke to get the piston higher (closer to the top of the cylinder) at the top of the stroke.
Yes, you are correct. It was a mistake on my end. Thanks for pointing it out. I cannot update the post to fix the mistake. Hope people upvote your post to make sure it stays visible.
Erm, I'm not sure I get it. I think I'd need to see an animation. If the crankshaft is fixed I don't see how that linkage can change the stroke length because all it shows in that diagram is the piston further along the stroke, which is what all piston engines do when the crankshaft rotates.
So yeah, I probably need to see an animation to grok it.
The crankshaft is in the middle part it doesn't move in relation to the head.
The image explains is pretty well, the piston is connected to the "multi-link" which changes the angle make the piston head move further into the cylinder.
Haha, this reminded me of a friend who did a summer engineering internship with a U.S. automaker. He came back and related one of the most important things he learned: "never, ever buy a first-run car." I remember hearing him tell about tolerances still being adjusted after all these cars had shipped, cringing to think of all the problems that could cause.
Engine control computers are even more fun. A friend of mine works for Audi's/VW's supplier, and honestly my biggest surprise about the emission scandal was that the code actually worked.
(They had to write their own linter, because they need to ship slightly broken code written by code generators, and last I heard Windows XP is still part of the compilation chain…)
Yep, your friend is absolutely correct: always buy a model during the mid or end cycle, when most of the bugs have been diagnosed, worked out, and the designs revised.
Let's also recognize that shortblock costs will be much, much higher with this design when you need a rebuild. Many engine builders won't touch this, and I'd suspect the Nissan OEMs will say that these engine shortblocks are "factory replaceable only". Who is going to make aftermarket bearings for the multilink setup? How does the engine operate under actuator failure?
I figure these engines won't be rebuilt. Its simpler to swap one in since its a four cylinder.
The engine should operate OK in case the actuator stops adjust the stroke. There really isn't anything new in terms of parts. They simply took proven implementations of each part and applied them in a new configuration. The biggest issue might be cylinder bore degradation due to the variable stroke. I need to learn more about its lubrication system before I can pass judgement. It probably has some additional jets in the middle shaft that sprays the piston and the bore on different angles. Nissan already uses jets on their turbocharged engines. I just sondas how they might pull it of here. The oil galleries shouldn't be so different from a conventional engine.
Realistically, how often is a petrol I4 engine rebuilt in consumer cars? I've seen 1980's Volvo redblock engines with 300k miles on them run as smooth as butter. Short of neglecting timing belt changes, running without oil, or incompetent modifications, nothing much kills a petrol engine before the rest of the car is scrap.
The sub 200hp 80s turd can leak out all it's coolant and overheat. Chances are it will be just fine after the leak is fixed and the system is refilled. The same can't be said for most more modern things. When one part of the system craps out there's likely to be more carnage elsewhere, it's just part of the nature of a more refined system.
Take some random engine, now engineer a oiling system that depends on having three different jets at each cylinder to ensure reasonable longevity. Now make the operation of those jets highly dependent on a maximum oil viscosity (small jet, low volume, thick oil would just dribble) and spec'ing the rest of the system for thicker oil (using bigger jets and so on) would be a needless waste of fuel (pumping around lots of thick oil takes more energy than the same amount of thin oil). Now tack on a heat exchanger so you can use the coolant system to bring the oil up to temp ASAP. Wash rinse repeat until the entire system is designed to have every part working together. Now you've got really long chain where any screw up by any supplier results in the whole system breaking down and a bunch of crap engines (or whatever major system you're designing) that wind up getting replaced under warranty at 75k (costing money, damaging reputation, etc., etc.).
The Nissan engine in the article is very much subject to this. Unless they want to leave a lot of performance on the table they've basically got two rotating assemblies they have to get right. That should be easy but for awhile every Hyundai dealership had pallets stacked up with v6 short blocks indicating that it's not that easy.
> The sub 200hp 80s turd can leak out all it's coolant and overheat. Chances are it will be just fine after the leak is fixed and the system is refilled.
Oh, most definitely this. My first car, '86 Volvo 240 with the B230E engine, had a coolant leak about two years before we scrapped it (in 2012). When the engine started overheating, you'd turn the coupe heater to max (and open windows all the way), since that tapped into the lowest part of the cooling system, so you got the temp down and could keep going for ~10 miles before refilling with water. Then as winter approached I bought a bottle of radiator fixer (about $20) which fixed the leak, did a full coolant change to get proper antifreeze, no problems afterwards.
Depends on the brand. Nissan engine quality has gone down in the last 15 years. Their flagship engine the VQ3XDETT has been good but the rest of the lineup has suffered. Its not yet as cas as a chrysler9 engine, but its not what it was during the 80s and 90s.
I seriously doubt their actual levels of quality have gone downhill. Automotive quality has been on an enormous upswing - the WORST cars of today are better than the BEST cars of 25 years ago.
No worries - where there is management, especially middle management, there's always trouble.
And at PSA concern, there is a lllooottt of management! NISSAN is nowhere near the ingenuity and quality they were back in the '80's and the '90's, after all, most of the engineering comes from Renault now, and not Japan. And the Japanese get all the low end engineering designs from Renault, while Renault, Peugeot, and Citroen get all the good engineering in the European models. Ah the "benefits" of being part of the PSA concern!
I remember studying a NISSAN Cherry back in 1988 and my jaw was on the ground with how much cutting edge technology that little car was loaded with (and it was just a city car!), and I look at all the garbage cars NISSAN has been pumping out today... it's an atrocity. Even if I compare the 280 ZX turbo and today's offerings... the 280 ZX is impressive, while today's assortment is something I would be ashamed to be seen in.
Oh, Renault cheap car engineering. I'm still wondering who in their right mind designed the oil filter on the K4J engine that's installed upside down, such that (short of flipping the entire car 90° on its front end) there is no way to change oil without spilling half a pint all over the engine block and the floor below.
This is just nonsense. Compare, for a start, what would happen to your 280ZX in, say, a 40mph crash. Now see how the modern 370z would fare.
Things that would have been considered exotic in the late 80s - like turbochargers or 6 speed gearboxes are now commonplace. Features that are now standard weren't even options.
Crash ratings, equipment, and drivetrain configuration do not have to do with quality. WHen they joined Renault they inherited their mediocre management and engineering.
You know how much I care about crash ratings?!? I couldn't care less! I'm comparing performance and design first and foremost.
Compare the iconic NISSAN Skyline GT with a Qashqai NISMO edition, the epitome of garbage NISSAN is pumping out today, and things come into perspective pretty clearly.
One look at 1990's NISSAN Primera and one can see what it meant to be at the cutting edge of aesthetics. One look at any of the NISSAN's today, and one can see what it means to design cars by committee.
Try to find a good looking NISSAN with a diesel engine and a manual transmission today. I dare you!
The VQ3XDETTs are used in the GT-R, no? That's a sweet engine for sure, I'm not surprised that a lot more engineering has gone into it compared to something like the MR16DE.
Yes, it is the one from the GT-R. Nissan used to over-engineer their smaller engines. The SR20 engine family was built to handle boost across all models. It made them very durable.
That depends on how popular rebuilds are. If this design proves out many engines will go to this and then a rebuilder who refuses to touch this design won't be in the business anymore.
If this design takes 1/10th of a second off lap times rebuilders will quickly not work on anything else, even if for every other application this engine is junk. (in most other applications the engine will outlast the car without a rebuild)
The piston wear shouldn't be an issue as Nissan will have to cycle (high/low compression) the pistons anyways otherwise the split ring will catch on a the lip that normally occurs, it would be nice if they used sleeves in case there is an issue but I doubt they will. How would the turbo over boost? The ECM controls what the turbo does and if the waste gate is open or not. It would be interesting to see if and how they control compression to each cylinder, maybe a waste gate at each cylinder on the manifold.
The issues I see:
* Regular gasoline explodes from too much compression, if this engine requires premium gasoline it's sort of dead out the door.
* NOX emissions increase with efficiency and in general efficiency increases with compression, there are two prevailing ways to fix this: cheat and inject urea.
* It greatly complicates where all the force is being generated which will probably lead to more failures.
> The higher the ratio, the more efficiently the engine works, producing better fuel economy and, with the addition of a turbo-charger, more power.
> Traditionally, design engineers had to fix a gasoline engine's combustion compression ratio, essentially deciding whether to go for power or economy.
Everything gets better with higher compression ratio, so where's the compromise? As I understand it, the only reason engine makers don't crank the ratio as high as possible is to avoid knocking.
Higher compression ratio = better combustion = more power with less fuel, regardless of turbo.
Higher compression will always mean better fuel efficiency. My moms Mazda CX-5 runs a 13.5 compression ratio and gets 27mpg. The power/efficiency trade off appears when you're talking about turbocharged engines.
Turbos compress air into the combustion chamber, so when you compress compressed air, you get exponentially compressed air. If you don't adjust the compression ratio for the turbo, you're going to get knock. An engine with a 13.5 compression ratio can run perfectly fine on regular gas, but an engine that runs the same ratio and 20 psi of boost with melt itself even on premium gas.
This is a problem for any kind of work vehicle. They almost always have turbos to give them the power to haul their loads with reasonable ease. But this forces the engineers to design the engine with a lower compression ratio, which means at light engine loads, when the turbo isn't doing anything, the engine isn't fulfilling its full potential. It's still compressing air at a low ratio, even though it's not taking in already compressed air. This is where Nissans innovation comes in. The compression ratio will change according to the degree with which the turbo is compressing air. Allowing the engine to run at peak efficiency through the entire range of engine load.
So this only reduces inefficiency while the the engine revs too low for the turbo to kick in? Then it is competing with electrically assisted turbocharging (spin the turbo electrically when there is not enough exhaust pressure, basically a super/turbo hybrid using electric transmission), as both are addressing the same inefficiency.
I know where I would put my bets in terms of price, reliability and ease of development.
At lower revs the turbo is more likely to boost the engine if you demand power, of course depending on the dimensions of the turbo, but it doesn't make sense to put a performance turbo that works in the upper rpm range, in a regular car.
In any case, an electrically assisted turbo is not a replacement for this. This is a way to have high compression at low loads, such as highway crusing, and ability to lower compression when boost is needed for performance.
>> while the the engine revs too low for the turbo to kick in?
This is a common misconception of 'turbo lag'. A modern turbo is actually operating at the low revs too. The boost is there. But a modern turbo engine, especially a diesel, has a very narrow powerband, giving the impression that the turbo isn't active until higher rpms. This isn't real 'turbo lag'. Real 'turbo lag' is the delay caused by the fact that the turbo depends on exhaust pressures, which rise only momentarily after throttle increases. But this problem has largely been solved via mutli-stage turbos, lighter turbo parts, waste gates and the like. Real turbo lag, where it is noticeable, occurs at all rpm ranges.
Audi SQ7 is coming up with an electrical supercharger and two sequential turbochargers to deliver lagless and variable boost for high performance in all of the rev range.
High compression ratios produces high combustion temperatures. This leads to the formation of nitrous oxide (NOx).
We have a lot of techniques to improve mpg that increase NOx. If you can figure out how to easily inhibit NOx formation inside the combustion chamber you could be a rich man.
Incedentally this is one way direct gasoline injection can improve economy. The injector sprays directly into the cylinder, and can do so in a way that forms a little donut of air/fuel mix that is insulated from the walls by a layer of air. It is then ignited. The air barrier helps keep combustion temperatures down.
One last thing, really high compression tends to result in a chamber that is very flat and narrow, which can counterproductively cause hotspots and incomplete combustion because the flame front is restricted. This can be fixed with undersquare pistons with longer travel, but that leads to big, low-power, slow-revving engines, like diesels!
Under certain conditions (high load, warm day), you'll start hearing a 'pinging' sound on high-compression engines; that's the air/fuel mixture pre-igniting before it is supposed to (before the spark fires) essentially turning the engine into a wannabe diesel and ruining performance/efficiency.
There are a few other undesirable things about high-compression.
And I just read your message about knocking. same thing. Nevermind.
Modern engines (as in, post 1989) will sense an engine knock (or a misfire) and go into open cycle ECU mode, ignoring the lambda sensor inputs. It'll run really rough and rich in order to avoid any more knocking, which could seriously damage the engine.
Higher compression ratios mean higher temperatures. Higher temperatures means more NOX in the output. As it is cars _already_ have to run richer than stoichiometric in order to keep from melting the catalytic converter. I would expect this will require some extraordinary pollution control measures as well.
There's plenty of ways to get temperatures down. Bigger intercooler, even refrigerated intercooling, water or water-methanol injection in various forms, going to high alcohol content fuels, etc. Even putting a waste heat recovery unit (WHRU) between the manifold and the catalytic converter is doable.
If you want to get really crazy, imagine a WHRU on the manifold in the form of a Rankine cycle where the expander drives a compressor for the air inlet. Like a thermal turbo, if you will, giving you more charge air than NA but with much smaller parasitic power losses than a mechanical turbo.
The drawback is that higher compression ratios require higher octane fuels. Nissan claims to have solved this by some kind of intelligent feedback system that allows them to control compression ratios on the fly. Presumably the compromise there is that it will require more moving parts, be expensive, and may come with issues of its own.
Variability in something like a combustion chamber is a cool idea, so is variability in the angle of turbo vanes. The issue is how you do it, affordably, and in a way that lasts the way that consumers expect from their cars.
The obvious precedent for variable-pitch blades are variable-pitch propellers on aircraft and helicopters. I don't want to say it's a solved problem for turbos, but there is almost a century's worth of prior art on the topic. That's one of those things that (in hindsight) really makes you wonder what took so long to think up.
Because it has to be cheap and reliable at 1000*C for 200,000 miles over 10 years while constantly accelerating to 280,000RPM and decelerating with no oil or cooling air circulating when the car is stopped. https://garrett.honeywell.com/products/how-a-turbo-works/
Variable geometry turbos are a thing, and have been for some time. The larger trucks and semis use this technology. Typically they are hydraulically controlled.
That's a challenge, but the thing is a turbo deals with blazing hot exhaust gasses just out of the manifold. A prop is still a marvel of engineering, but it doesn't need to be made of boron carbide to not melt.
A better comparison would be variable pitch vanes on jet turbines.
Right, I figured this must actually be an anti-knocking technology. My point was just that the quote implied power and economy are optimized by taking the compression ratio in different directions, which is wrong.
1) lets the engine have high compression AND a turbo. Typically a turbo is run with lower compression, because even today nobody can make an engine run 14:1 with a turbo. Speculating, when you floor it the compression might drop to 8:1 and the turbo kicks in; then when you highway cruise, it runs 14:1 for efficiency.
2) lets the little engine still hit big torque numbers at low speeds. This is most likely if the engine is variable stroke, as longer strokes improve low speed torque.
Ahhhh, those both make a lot of sense. This could be a nice feature on higher-end cars that try to use smaller engines, with more turbos, for the sake of fuel and emissions then?
Maybe the trick would be to have two crank shafts, with two pistons per "cylinder" (or combustion space), and run them slightly out of phase with each other to vary the compression....
Despite claiming they could replace diesels, I don't see any real numbers other than comparisons with their own gasoline engines. For internal combustion engines, the most efficent are still two-stroke diesels, which can have thermal efficiencies of over 50%:
Seeing as this design includes several more moving parts than conventional ones, it's an open question how much reliability and longevity are affected; I remember reading in a book that over the years many have tried to make more efficient engines and succeeded in achieving that goal, only to be let down because of real-world reliability issues.
Variable compression? So logical next step is variable octane, right? One tank of 87 and one tank of 93, dynamically mixed in response to changing compression ratio. :)
A common way to run lots of boost on turbocharged cars is to use 87-93 normally, and E85 under high boost. You get the high octane when you need it, without the 30% hit to fuel economy when you don't.
I've seen this done before, but I wouldn't consider it common. In my experience, the two most common approaches for mitigating knock on high boost street cars involve either running E85 all the time (or a reduced mixture like E30), or using a water/methanol injection system. A secondary fuel system with race gas is more common on nitrous cars though.
Anecdote: I'm running a water/alcohol injection system on my 335i (tuned on higher than stock boost). It really helps on the hotter days. Currently, I'm running a mixture of ethanol (everclear) and distilled water. Most people use methanol, but it's not really compatible with the viton gaskets inside of my pump.
I think the point of the person you replied to is that any variation in octane is handled by the fuel injection system. This renders having two tanks unnecessary (unless you require more distance between fill ups).
It can adapt to lower octane fuel by adjusting the timing, it's far from optimal, and at high enough boost level you need higher octane regardless. At non boost levels, you need less octane rating to prevent knock, but under boost you need higher octane rating. So you run the higher octane fuel all the time, and that is less efficient.
Correct. This involves relying on feedback from knock sensors which literally "listen" for the specific tone that a detonation event produces (usually somewhere in the 6-7 kHz range depending on cylinder geometry). You will sometimes hear this phenomenon referred to as "pinging", and it’s actually audible to the driver if severe enough. There is also another method of knock detection which involves using the spark plugs to detect the resistance of the air inside the combustion chamber immediately after an ignition event, which I believe is an indirect way of measuring cylinder pressure. I’m not positive on this, but I think the idea is that you want peak cylinder pressure at the moment of time where the piston is like 20 degrees after top dead center. Earlier than that, and the majority of the force is wasted pressing directly down on the crank shaft. This is more advanced and is used only in specific cars such as the E90 BMW M3.
If the ECU detects knock, it will retard timing. This works to an extent, but you’re ultimately worse off than if you just ran premium fuel in the first place. The other issue is that (on systems with conventional knock sensors) this causes you to basically “bounce” off of the knock threshold. Knocking is terrible for the bearings inside of the engine and should generally be avoided, but running regular fuel in a car that calls for premium results in the ECU constantly trying to creep up timing (or switch to the high octane map), only to be confronted with knock again.
absolutely every company has one of those. I'm familiar with the bmw one: VANOS something. from the 90s.
variable compression is nothing new, just very prone to failure. the other downside was it was much harder to work on the engine, but nobody cares about that anymore.
Interesting news, The Reuters article[1] they cite has more content than the current article[2], but even the Reuters article looks very PR-like.
The TLDR appears to be:
The new engine uses variable compression technology, which [allows] at any given moment to choose an optimal compression ratio for combustion.
> The [new VC-T engine] averages 27 percent better fuel economy than the 3.5-liter V6 engine it replaces, with comparable power and torque. Nissan says the new engine matches the diesel engine in torque.
It will be officially unveiled at next month's Paris motor show
So if this engine changes the compression ratio (the amount the mixture is compressed) how is all this complexity better than a supercharger which changes the amount the air is compressed? Surely increasing the compression of the mixture and compressing the air before it goes in is pretty much the same thing? Except...that all that variable stroke length mechanism is a lot more complicated, and patentable?
I am far from an expert, but there are two ways I know of to do something like variable compression, one is that Saab technique already mentioned, where the cylinder head is displaced to change the size of the combustion chamber.
The wiki page shows a complicated mechanical arrangement for having a smaller intake volume vs. expansion volume, but the "poor man's" way to do this is to just keep the intake valve open for the first part of the compression stroke. The upside is that you can then adjust the effective compression ratio with valve timing. The downside is that it reduces the intake manifold vacuum by blowing back some of the intake air, not sure how that's handled.
The way that makes most sense to think about this to me is in terms of dynamic compression.
At full throttle the turbo is shoving a large mass of air into the cylinder for every firing. The compression ratio has to be fixed lower to control detonation under these circumstances.
At light throttle / cruise there is now hardly any mass of air in the cylinder, so although mecanically nothing has changed (same / fixed compression ratio) we are hardly compressing the air at all and we're giving away a load of efficiency for that reason.
The ability to up the compression ratio at cruise / light throttle claims some of that basic efficiency back.
> "Increasing the fuel efficiency of internal combustion engines is critical to automakers. Not all consumers will accept a battery electric vehicle solution.
This is still using ignition timing and spark plugs. Additionally, the connecting shim and the timing advancer/retarder introduce not one, but two points of failure.
Thanks, but no thanks: I'll just stick to my simple (by comparison) direct injected turbo diesel cars.
When there is a gasoline engine which can ignite the fuel without spark plugs and ignition timing, that'll be the right solution. mazda experimented with this (see "VCCI"), but it never made it into production, because it's not a trivial problem to solve. This Nissan patent is a mechanical engineer's equivalent of a duct tape hack.
Or we could just ditch this entire nonsense with pistons and optimize the Chrysler's super simple turbine car engine until it matches today's exhaust emission regulations. This was a tough problem to solve in 1978, but should be doable now with a particulate filter. And that engine isn't picky: since it's a turbine, it'll run on anything that's combustible, from filtered cooking oil to cologne.
Disesl engines have very fine control of ignition timing via injection timing which is now very complex. There are tiny pilot injections and multiple short injections over a carefully controlled length of time so I don't agree that needing to time a spark makes spark ignition a more complex and by implication worse solution.
First of all, timing by injection is still simpler than timing by spark: in gasoline engines, the computer must time both the injection and the ignition.
Second, timing by spark means that spark plugs are necessary, so that is more parts, and more parts means higher probability of failure.
Third, spark plugs are needed to start a chain reaction of igniting fuel, because gasoline fuel is volatile enough as not to be combustible. Gasoline fuel is not flammable, but the vapor is, did you know that? That's what makes it volatile as far as combustibility, otherwise we would have self igniting gasoline engines by now.
I'd say that modern disel injector problems were more common than spark plug problems, so I guess we'll have to agree disagree :) I could also draw your attention to the cost and ease of replacement of a spark plug vs a diesel injector, or all the extra emissions treatment equipment that modern diesels need that petrol doesn't, but I don't think we're going to convince each other here :)
How long have you worked on diesels in order to be able to claim that?
How many cases of diesel engines with injector problems have you had during your career as a mechanic?
How much does, on the average, a diesel injector cost?
How often do they have to be replaced?
I've worked on diesel engines since I was a little kid, and have yet to work on one with injector problems.
The following are ultramodern mazda injectors, for instance; if you look at the spray pattern and the capability of these programmable injectors, it's pretty obvious it's going to be tough for them to experience problems:
modern piezoelectric technology is wonderful, isn't it? And wouldn't you know it, all modern diesel engines sport piezoelectric injectors.
But let's suppose for a moment that you are correct, and that I'm wrong. Your logic has one flaw, and that is that in a diesel engine, I will (and have) get three times the kilometrage that you will get with a gasoline engine. Even if I had to replace all of the injectors, I will still have come out ahead. How?
Assuming that you are running the simplest, ultramodern gasoline V8 (I picked V8 in particular because that is the most reliable of the gasoline engines), if you maintain it according to the extreme maintenance schedule, you might get about 460,000 km out of it before requiring a rebuild. By that time, I will have gotten almost 1,300,000 km on the diesel and maybe need an engine rebuild, and that engine rebuild might not even need new injectors, if I changed my fuel filter every 15,000 km (which I do), and every 30,000 km added one liter of biodiesel to my tank!
In economics, the Jevons paradox occurs when technological progress increases the efficiency with which a resource is used (reducing the amount necessary for any one use), but the rate of consumption of that resource rises because of increasing demand.
Oh, so that's how it works. See Fig. 2 of the patent. It's a lot like the Peugeot MCE-5, an earlier variable-displacement engine. The Nissan mechanism looks simpler and seems to take up less space inside the engine. Maybe that will make this workable. Variable-displacement isn't new, but previous attempts were mechanically clunky. It adds extra moving parts to the highest-load path in an engine - the piston to crankshaft connection. It has to deliver large benefits to justify the costs and problems that implies.
Most engines already have knock sensors. They're used to adjust fuel/air ratio and spark timing to just above/after where the engine starts to knock. A few engines adjust valve timing while running, which is also complex mechanically, but not as difficult as adjusting compression. Now there's another variable to tweak.
It may take a machine learning system to tune such an engine. All those interdependent variables to adjust make that a hard problem. Different values required based on engine speed, load, temperature, fuel consumption, and emissions outputs. All this is usually expressed as precomputed tables which are interpolated within the engine controller. Those tables have to be developed somehow.
This looks cool, but complicated.
The problem addressed seems to be that turbocharged (and supercharged) engines are sub-optimal at lower powers.
IMHO mild electric hybrids, or full serial electric hybrids would be a more elegant solution - only run the combustion engine when full power is needed, and use the electric motor otherwise. "full power" could be used to top the battery if it's not all required for motion.
That's exactly what the Koenigsegg Regera does, it has three total electric motors in addition to the engine. The one in front of the engine is used as energy conversion and as a starter for the motor. There are two more electric motors on each axle for supplying the initial grunt, while the engine builds horsepower, supplementing the electric motor. The motors also aid in regenerative braking and torque vectoring. There is no transmission between the engine, electric motors and the wheels, relying only on a torque converter, using the entire rpm range of the engine from zed to 250 mph. In addition, the engine has no camshafts, relying on electronics and pneumatics for the intake and exhaust valves. And of course, it has two turbo chargers as well.
Turbocharging and supercharging grew up in aviation , where there is much more variable air pressure due to altitude. They were more a "hack" to get more envelope out of an engine system. Started seeing them on consumer ground vehicles in the '80s, when everything had to have a "turbo"
button because PCs had one.
It's never been clear to me that they are really all the great of a fit with terrestrial engines. Part count goes up, heat goes way up in spots and there is of course lag.
Much better low rpm power, and a more or less flat torque curve is possible. You can have a smaller engine, resulting in increased efficiency, while still having the power equal to a larger engine.
Not to mention that diesel engines are pretty much useless without a turbo.
Audi is working on a type of electric turbocharger that spools the turbo ahead of the exhaust gas pressure, to eliminate lag . VW is working on one that uses an air compressor to pre-spool the turbo charger. And Eaton has an electric assisted supercharger that helps the supercharger spool, it can also can start the engine, and recover energy from engine braking.
I'm wondering if something like stored kinetic energy like that on the Audi e-tron (a carbon vacuum sealed flywheel) could also be used to ram air into the intake, and how much resistance the air would have against the stored energy.
Well, somewhat, if you mean an electric only compressor. Turbos actually increase efficiency because besides intake compression, they extract energy from the exhaust with the turbine.
Formula 1 cars have a mixture: there's an electric motor / generator in the turbo, so that the turbo can be spun up when there's not enough exhaust yet, but the engine needs a lot of air (when you start accelerating). Or the opposite: when there's excess exhaust energy that you don't need for intake charge anymore (when you've stopped accelerating), you can run the motor as generator providing electricity for batteries. Since the turbo rotation speed is so high and torque small, a relatively small motor-generator will suffice.
Not at all. Problem is that ir has been an uphill battle to develop such technology. The energy required to move a turbo compressor fast enough ti generate boost is very high. A hydraulic approach has also been under works but proved challenging. Although Garret has promoted turbochargers with embedded motors to speed up the compressor speed and reduce lag.
The electric motor to be used would have to be a pretty unusual motor. IMO, supercharging is "better" because the PTO side of an engine is less ... trouble than the exhaust side. Superchargers are generally heavier.
Super chargers generally result in a fairly large parasitic loss to power it. Turbo more or less harvest free energy with only a minimal loss due to increased back pressure.
Some superchargers provide linear boost, others behave much like a turbo. In any casem FI is used to increase efficiency, so it doesn't make sense to use a super charger with a must larger parasitic loss. Modern turbo can provide boost from 1500 rpm, and result in a flat torque curve - the only negative thing is the lag.
I'm curious as to what, if anything, would preclude variable displacement from being used in diesels as well as petrol engines. Diesels also have performance/economy tradeoffs like this gasoline engines, so it stands to reason that tweaking compression should give similar benefit. I've got a feeling that rumors of diesel's impending demise are greatly exaggerated.
Difficult, yes, but doable: mazda's SKY-D diesel features 14:1 compression and Tier II Bin 5 / Euro VI compliant emissions without Urea. The lower emissions were achieved by lowering the compression ratio and lengthening the exhaust manifold, so that the exhaust gasses can cool. As the result, mazda is the only manufacturer selling diesel passenger cars in Japan.
They work well enough on new vehicles coming out of the factory.
The real problem is 5-10 years later when these systems need repair or replacement. For many the economic temptation to have them "nulled" is too great (fuel efficiency is improved by removing the DPF) - and that once-clean diesel is now a toxic, polluting nightmare.
This is a huge problem in the UK - and why we need to phase out diesel in private/light motor vehicles.
In the UK, there is no emissions test for particulate or NOx emissions, other than the subjective "does it emit visible smoke?".
A visual inspection for the presence of the DPF is required, but this is easily defeated by installing a look-alike "null" filter.
The people doing the MOT testing can be pretty shady anyway. Since any mechanic can operate as a testing facility, it's often the same people who remove DPFs that will then pass them in the MOT inspection.
I agree with you. A strict emissions test regime would be a good first step. But politicians have known about this for years and little has been done - apparently it's a too hard (or too expensive) problem to fix.
The thing is, even brand-new "clean" diesels are still worse polluters, for toxic particulates and NOx, compared to petrol and petrol-electric hybrid vehicles.
London already has a disincentive on diesels coming into effect by 2019, when pre-Euro 6 (i.e. older than September 2015) diesel vehicles will be subject to a £12.50/day charge to drive in London.
There are calls to extend this to cover all diesel vehicles, eventually leading to a total ban:
Licensing of new diesel taxis will also soon be prohibited in London, and all single-deck busses will be zero-emission by 2020 (and double-deck busses will, at minimum, be hybrids).
This is an excellent implementation of variable valve gear timing that external combustion steam locomotives have had for about a century and a half. Impressive to see it put into an internal combustion engine.
Edit: looking at the posted image, they change the stroke depth of the power linkage. That plus valve timings let them customize the entire combustion cycle.
How are they preventing engine knock ? At 14:1 compression you'd have to be running premium gas, which would pretty much cancel the efficiency saving, in a $$ perspective.
Direct injection makes a significant difference by delivering cooler fuel at the correct timing point. The fuel is also delivered at a higher pressure and with better atomization.
I think direct injection allows engines to run higher compression ratios without knocking. I'm not sure exactly why, but I assume it's because the fuel sprays directly on top of the piston which could allow it to cool any hot spots which would have normally caused detonation.
The fuel probably has to fully vaporize before it can ignite. This happens in the manifold for a normal EFI, or in the carburetor for an older engine. There's some short period of time that this is happening, and so if you time the injection to happen with enough time to vaporize the fuel before ignition it probably doesn't have enough time to pre-ignite before spark.
Not sure, but would assume a gas engine can run with a higher compression ratio when under partial load than full load. If you can increase the compression ratio on the fly then you can keep the compression ratio at optimum over the whole power band. Goes double if you have a turbo since the boost provide by the turbo goes from nil to lots at the high end of the power band.
I think there isn't much improvements to be had for engines at full power. But lots of room for improvement at partial power. Interesting bit, hybrid cars have really low emissions. Which says to me they're avoiding running their engines at power/rpm ranges that create high emissions.
I have a lot of respect for Nissan's engineers, but somewhat less respect for their lawyers, who hounded Uzi Nissan for a decade trying to get him to turn over his domain.
Cybersquatting is obnoxious, but once they found out it was the guy's actual name, and that he was using it to run his own business, they should have just accepted he had a right to the site and worked to buy it from him or moved on.
Lawyers are tools. (Being one, I feel I can say so, with a humble degree of confidence.)
Certainly there's a give-and-take between lawyers giving advice and clients taking it, but by the "big X" their lawyers essentially do what they are told - lest the big client move elsewhere.
All to say: Lawyers doing a bad thing are often a symptom of an internal disease or conflict.
Which is to summarize a whole host of conflicting emotions: I'm slightly defensive about the profession, wholly sympathetic to the outcomes of wielding lawyers to achieve evil ends, and biased by personal experience – but nevertheless appreciative of comments, like this, that highlight the responsibility that lawyers bear to not only advise and act but to represent the reputations of institutions.
Fellow attorney, I know how it feels to be defensive about the profession.
So I should have said I'm less than enthused with their legal strategy, rather than placing blame on a specific group of people.
GC definitely has an obligation to provide guidance on legal strategy before following the board's demands, and maybe they did so. Impossible to say where things broke down in this case.
I had to chuckle at your first sentence. Over here (UK) 'tool' is often used in slang as a derogatory term for a person, effectively likening them to an obvious part of the male anatomy...
Well, people defending themselves about doing bad things by stating that they are just doing what they are told are rightfully criticized. Even more so when they are in a high end profession.
This is all moot. Battery technology and charging infrastructure for EVs will improve so much over the next 5 to 10 years that engines running on dinosaur juice will no longer be worth the hassle for mainstream vehicles.
Downvoted, so I owe you an explanation. This comment didn't add to the conversation, it diverts away from it. And to the degree that it's a related topic, all you've done is to assert your own opinions, without any substance behind it.
So all companies related to gas technology should just close up shop? Something that may or may not work is on the horizon, so all the engineers that have been researching gas technology for years should throw in the towel and quit? There is no chance that electric overtakes gas in 5 years.
The difference from a conventional engine is that the engine stroke is increased or decreased automatically. The stroke is the distance the piston travels up and down in order to turn the crankshaft. A shorter distance that is closer to the combustion chamber increases the compression ratio because there is less space for the fuel/air mixture. When the system is operating in low compression mode the piston travels more and does not reach as high. The combustion chamber then ends up being farther away and a lower compression ratio is achieved.
What is novel about this approach is how the combustion chamber was left in the same place. Past efforts by SAAB had the engine head moving the combustion chamber away from the pistons. This drastically changes the characteristics of the combustion process. Something that makes emissions control challenging. Any power loss due to a dynamic combustion chamber is removed by pressurising it with a turbocharger, just like Nissan did.
Possible issues with this design could be:
- Uneven wear of the cylinder bore due to the piston travel being dynamic.
- An overboost condition during a high compression cycle could damage the mechanism and even crack the engine block.
- Increased NHV due to regular wear and tear making its way into the valvetrain and transmission input shaft.
This is a good effort and I hope Nissan is able to pull it off. Make sure to wait two years before you buy a vehicle with this technology. Dont be the guinea pig. :)