Nissan are rumoured to be introducing a variable compression ratio petrol engine soon, using the system described in this patent. Perhaps that long dreamed-of development will turn into reality at last. If it does the advantages could be very substantial, which implies that other manufacturers would follow suit later.
Apparently the way it works is that the eccentric shaft at 8 can be turned (slowly, not at engine speed) through 180 degrees, thus raising or lowering the small conrod at 7 and pivoting the triangular piece at 4. In this diagram conrod 7 is shown at its low point, with the result that the compression ratio is at maximum (14:1 or so) - suitable for startup and slow running with no pressure from the turbocharger. If the eccentric shaft 8 is turned, small conrod 7 is raised higher and triangular piece 4 is turned anti-clockwise so that the piston 9 and the main conrod 3 are in a lower position throughout their stroke. This reduces the compression ratio to say 8:1 - suitable for high speed running with a high turbocharger pressure. The stroke of the piston and the swept volume of the engine remain the same; it is only the volume of the combustion chamber (and hence the compression ratio) which changes. It is suggested that Nissan will introduce this engine first in one of their Infiniti models, with others to follow later.
It's just a patent at this stage, companies file hundreds of these a year covering/protecting whatever they think may make it to production one day... Until a prototype is released to the public I wouldn't get your hopes up too much
The patent in question was public knowledge over thirteen years ago. The interesting news is that Nissan are (apparently) going to announce next month that a production car using a version of this system is due for release in 18 months or so.
Set to be unveiled at Paris Motor Show in early September. Nissan develops 'major breakthrough' in engine technology | Stuff.co.nz
interesting stuff. wonder if nissan dont have much faith in electric yet to invest so much in a new engine?. obviously no expert but with the likes of variable vane turbos, variable valve timing and lift available thees days it looks rather a cumbersome way of achieving it too. hmm. :smileys:
you would think. some sort of solenoid controlled extra chamber. less moving metal the better. think i will get the crayons out. :smileys:
With an extra chamber you would run into gas flow problems presumably, with the drawing above you still retain the same combustion chamber characteristics although with many extra moving parts. Can't see other manufacturers following suit in a hurry. Steve
It strikes me that bearing at B, at the top of the conrod (7) would be subject to a lot of stress from a heavy loading and a high speed reciprocating motion. I saw a similar idea a few years back but I can't remember from which manufacturer although I think they were bike related. In it though, the whole cylinder block was moved up or down.
It looks like an elegant and simple solution to me. Reminds me of the counterbalance in the Rotax built BMW 800 engine.
being able to change the length of the con rod would be ideal. could a hydraulic ram activated by oil pressure handle it like the twin air valve system used by fiat. hmm. wheres me crayons
The Nissan engine will certainly have variable valve timing as well as the variable compression ratio system.
There have been several ideas over the years, since there are many ways of doing it. This Nissan concept looks like the simplest so far. But if you can find a simpler one, I would love to hear about it.
Well yes, bearing B would indeed be subject to a lot of stress. But all conrods, big-ends, and little-ends in all i/c engines are subject to a lot of such stresses, yet manufacturers seem to have mastered ways of making components which can withstand those stresses reliably. I do not see that the components in this system would be stressed more than usual.
This has been looked at by many people very much cleverer than I am. I'm just surprised that such an apparently simple problem as varying the volume of a combustion chamber requires such a seemingly complex solution. It clearly is a much more complex problem than one might think.
