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Thread: Dangerous cylinder deactivation trouble on 2018 CX-5 and 6 models

  1. #571
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    I looked through this document and the cd system looks damn complicated.
    In my opinion the game is not worth the candle. I am rather pessimistic about the durability of such solutions.
    I would prefer a classic engine without such inventions.

  2. #572
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    2019 CX-5 Reserve Eternal Blue

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    Aug 2018
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    Central Virginia, USA...the winding rural part
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    Quote Originally Posted by Mulligan View Post
    I found Mazda*s patent (US20150377151A1) that describes the cylinder deactivation mechanism. Like any patent, it*s not light reading, and there*s an extra layer of difficulty because it*s been translated from the original Japanese. However, if you*re willing to slog through it, you*ll get a very good understanding of how CD is implemented. Interestingly, the patent isn*t limited to cylinder deactivation. Discussion of the variable valve timing system is interwoven through the document. The unifying theme is that both systems are controlled by a variable capacity oil pump.

    I won*t try to summarize it beyond noting that it confirms the default condition is for all four cylinders to be operative. The pin that locks the HLA in its extended position is engaged by a spring. To deactivate the cylinder, the pin is driven inward (disengaged) with oil pressure, allowing the HLA to be compressed (shortened) by the cam, thereby stopping the open/shut movement of the intake and exhaust valves.

    After studying the patent*s drawings and descriptions, I*m more convinced than ever that the reason the rocker falls off is that the HLA is somehow inhibited from springing back to its extended length, which creates a gap between the top of the HLA and the rocker. Unfortunately, there isn*t enough detail in the patent to figure out what is responsible for inhibiting the HLA from extending. I hope the cause is entirely a function of the oil pressures that are being tweaked by Mazda*s reprogramming of the PCM in the recall.
    Interesting that the car has a variable capacity oil pump. Is that a common thing in cars? I had assumed that the pressure managing the HLA on #1 and #4 would have been a mechanism located specifically at those two points (directed nozzles), and not management of the engine-wide pressure.

    I wonder what the range of the operating pressure is (are we talking a swing in a few psi, or is it a 10+ psi variation), and how the changes in pressure during engine operation might affect global lubricating performance. Any car I have ever had with an oil pressure gauge has always operated at a steady pressure, other issues (like being down a quart) notwithstanding. This also raises other weak points in the system, like having one's oil always topped off so as to maintain peak pressure in the system rather than introducing risk of low-pressure failure.

    Or do I misunderstand, and that variable capacity pump is dedicated to this function, and there is a separate pump for the engine in general?
    Last edited by Avoidin Deer; Yesterday at 09:04 AM.

  3. #573
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    2018 CX-5 GT

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    May 2018
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    Washington
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    Quote Originally Posted by Avoidin Deer View Post
    ... I had assumed that the pressure managing the HLA on #1 and #4 would have been a mechanism located specifically at those two points (directed nozzles), and not management of the engine-wide pressure...
    Although the engine-wide oil pressure is regulated in response to a lot of engine parameters, the oil pressure change seen by the HLAs that turns CD on/off is controlled by a couple direction switching valves (number 46 and 47 in the schematic at figure 4).



    Here's a picture of those valves. I assume the holes of different sizes at the two locations control both the direction of oil flow and the oil volume/pressure.


  4. #574
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    2019 CX-5 Reserve Eternal Blue

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    Quote Originally Posted by Mulligan View Post
    Although the engine-wide oil pressure is regulated in response to a lot of engine parameters, the oil pressure change seen by the HLAs that turns CD on/off is controlled by a couple direction switching valves (number 46 and 47 in the schematic at figure 4).



    Here's a picture of those valves. I assume the holes of different sizes at the two locations control both the direction of oil flow and the oil volume/pressure.

    Thanks for that.

    That's a lot of precision in an environment where so many violent actions occur.

    Fascinating stuff. (Interesting that those valves are made in Germany).

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