6 ms·

Here is a simple explanation gathered from this image http://o.aolcdn.com/hss/storage/midas/de3e84cf46030cd7b3ea39900a1fa7ba/204201576/image1+%281%29.JPG http:/

Here is a simple explanation gathered from this image http://o.aolcdn.com/hss/storage/midas/de3e84cf46030cd7b3ea39900a1fa7ba/204201576/image1+%281%29.JPG http://o.aolcdn.com/hss/storage/midas/de3e84cf46030cd7b3ea39... : 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. :)

themodelplumber 10y ago
> Make sure to wait two years 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.
- creshal 10y ago
  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…)
  - Johan-bjareholt 10y ago
    I'm guessing you refer to AutoSARL when you talk about the code generation. Its insane that its an industry standard.
    - Pica_soO 10y ago
      Less insane then binding yourself for all eternity to one supplier?
- Annatar 10y ago
  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.
micaksica 10y ago
> Possible issues with this design could be: 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?
- asimuvPR 10y ago
  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.
  - semi-extrinsic 10y ago
    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.
    - asimuvPR 10y ago
      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.
pdonis 10y ago
> 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.
- asimuvPR 10y ago
  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.
- TheSpiceIsLife 10y ago
  I don't follow how the stroke length changes. The conrod (upper-link in the image) is a fixed length, therefore the stroke length is fixed. The compression ratio changes because the mechanism changes where TDC (Top Dead Centre) is. Or have I misunderstood something? Edited to add: If TDC moves then the bottom of the stroke moves with it because the conrod is a fixed length, right?
  - TheSpiceIsLife 10y ago
    Never mind, I see now how the mechanism changes the stroke length.
    - zglennie 10y ago
      Can you elaborate? I'm trying to figure it out. I'm also confused about where the crankshaft is supposed to be in this picture.
larrydag 10y ago
Clever design but that looks like a lot of moving parts. I wonder about longevity of the engine.
- dsfyu404ed 10y ago
  Figuring out longevity will probably wait until they've been shipping for a few years.
  - HeyLaughingBoy 10y ago
    Or... maybe, just maybe, after they've done longevity testing!
drzaiusapelord 10y ago
- A lot more moving parts and complexity - The added maintenance of turbos - Added cost might not be worth it compared to a hybrid or electric, especially used
nwmcsween 10y ago
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.

themodelplumber 10y ago

> Make sure to wait two years 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.

creshal 10y ago
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…)
- Johan-bjareholt 10y ago
  I'm guessing you refer to AutoSARL when you talk about the code generation. Its insane that its an industry standard.
  - Pica_soO 10y ago
    Less insane then binding yourself for all eternity to one supplier?
Annatar 10y ago
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.

micaksica 10y ago

> Possible issues with this design could be: 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?

asimuvPR 10y ago
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.
- semi-extrinsic 10y ago
  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.
  - asimuvPR 10y ago
    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.

pdonis 10y ago

> 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.

asimuvPR 10y ago
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.
TheSpiceIsLife 10y ago
I don't follow how the stroke length changes. The conrod (upper-link in the image) is a fixed length, therefore the stroke length is fixed. The compression ratio changes because the mechanism changes where TDC (Top Dead Centre) is. Or have I misunderstood something? Edited to add: If TDC moves then the bottom of the stroke moves with it because the conrod is a fixed length, right?
- TheSpiceIsLife 10y ago
  Never mind, I see now how the mechanism changes the stroke length.
  - zglennie 10y ago
    Can you elaborate? I'm trying to figure it out. I'm also confused about where the crankshaft is supposed to be in this picture.

larrydag 10y ago

Clever design but that looks like a lot of moving parts. I wonder about longevity of the engine.

dsfyu404ed 10y ago
Figuring out longevity will probably wait until they've been shipping for a few years.
- HeyLaughingBoy 10y ago
  Or... maybe, just maybe, after they've done longevity testing!

drzaiusapelord 10y ago

- A lot more moving parts and complexity - The added maintenance of turbos - Added cost might not be worth it compared to a hybrid or electric, especially used

nwmcsween 10y ago

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.