Citroen Variable Compression Petrol Engine
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  1. #1
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    Default Citroen Variable Compression Petrol Engine

    Hi Folks,

    came across a rumour on the French forums of PSA having purchased rights to some technology involving variable compression on a petrol engine....

    Apparently providing improved smoothness, power, and economy similar to diesel...

    Anyone come across this before?

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    David Laloum

  2. #2
    Moderator Alan S's Avatar
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    I was going to be a smart arse and say I discovered this years ago when I ballsed up setting the tappets on an Austin, but seriously, you have to give credit where it's due, where would the motor Industry be today if these guys hadn't punted on innovative ideas over the years?
    When you think about it, compression on a need basis would make for some unbelieveable smoothness and fuel consumption improvements based on a need basis is logical when you think about it.
    No doubts, a varience on the technology they learnt a few years back when they tried to make a 100 MPG car but "failed" by 6 MPG might also come into play even though the previous effort was diesel.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  3. #3
    1000+ Posts Uga Boga's Avatar
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    Citroen only sell a small amount of petrol engined cars... was it 100,000 out of 3million? or something similar.

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    To be honest, I consider this a SAAB innovation.

    SAAB released a variable compression ratio engine a good few years ago - hasn't made it into production. From what I can understand, reliability of the technology has been a major sticking point.

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  5. #5
    1000+ Posts brenno's Avatar
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    SAAB were dabbling with the concept a few years back;

    http://www.autospeed.com/cms/A_0458/article.html

    ...and an article detailing various other approaches;

    http://www.autospeed.com/cms/A_1903/article.html

  6. #6
    1000+ Posts Ken W's Avatar
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    I guess I will have to join autospeed to read the full articles - Ho Hum

    Ken W

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    1000+ Posts brenno's Avatar
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    Sorry Ken, I thought they were freely available articles. I didn't realise I was logged in.

    If you want to see the contents of the article, I can email you a copy.

  8. #8
    Moderator Alan S's Avatar
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    I don't think it's all that uncommon for various car makers to "dabble" with ideas, it happens all the time.
    Citroen apparently played around with active suspensions back in the '50s before deciding to finish it off when Vlovlov started trying to develop a system in the late 80s and brought it in on the XMs. Anyone who's ever seen the demo on Citroenet of the BX and the D both using early versions would be aware of this.
    By the same token, it takes an innovative manufacturer to take the plunge and buy the rights and then develop the idea for mass production whilst a more mainstream will keep dabbling and possibly only take it up after the other has improved the idea and brought it to reality; we only have to look at the C-matic transmission to see that and compare that system to similar ones who tried to match them but who never made the grade or a more recent case we were made aware of when GM developed an auto to suit an ATF and that idea has since been adapted to many of it's competitors car, so it happens right across the spectrum of car makers.


    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  9. #9
    Fellow Frogger! tlampre's Avatar
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    Variable compression has been in prototype form at least since the mid eighties when an Australian company built a prototype of a 5 cylinder 'wobble plate' engine. The cylinders were in a ring pattern around the drive shaft. It showed promise and got some impressive backing but like so many ideas vanished quietly. I can put some pics up tonight if anyone is interested.

    Other companies have also dabbled, SAAB's engine was a conventional inline 4 with the added feature of a tiltable head to change the size of the combustion chambers, if memory serves. There have been other inline designs where the crankshaft could move up and down.

    All have had problems with sealing, either oil or gases, but the advantages of such an engine are enough to keep them interested.

    Trevor

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