Diff's Hot, Take it Easy - Mishimoto's Focus RS Rear Diff Cooler R&D
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Diff's Hot, Take it Easy - Mishimoto's Focus RS Rear Diff Cooler R&D

This is a discussion on Diff's Hot, Take it Easy - Mishimoto's Focus RS Rear Diff Cooler R&D within the Focus RS Performance forums, part of the Focus RS Garage category; Part 1: The Rear Differential At Mishimoto we are big fans of our little blue car. Over the past few months you could say we ...

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Thread: Diff's Hot, Take it Easy - Mishimoto's Focus RS Rear Diff Cooler R&D

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    Diff's Hot, Take it Easy - Mishimoto's Focus RS Rear Diff Cooler R&D

    Part 1: The Rear Differential

    At Mishimoto we are big fans of our little blue car. Over the past few months you could say we have formed a bond that only burnouts and track days can build. In testing various Focus RS parts (and maybe doing a few donuts, for science) we noticed that it is very easy to make the rear differential in the RS angry, and you won’t like it when its angry. The rear diff makes the rules. Overheat it, and you’re likely to end up parked for the day. When the rear diff heats up, the ECU in the RS pulls power in an attempt to cool it down. Therein lies the problem: We have a car that begs to be driven to the absolute limits and rear diff that is programmed to shut down when it reaches a certain temperature. Don’t get us wrong, the problem doesn’t seem to be with the diff itself, but rather with its inability to dissipate heat fast enough to keep up with this blue bat out of hell.


    Focus RS rear differential


    Focus RS rear differential


    Focus RS rear differential

    As a peace offering, we decided to kick off R&D of a rear diff cooler and we hope it pleases this beast.

    The Rear Differential

    Given our cooling theory, we did what any other gearheads would do with access to a development facility such as ours: We took the entire subframe out to get a better look at the angry little ball of metal. The first step is often the hardest, and in this case it is no different. Dropping the rear subframe was no easy undertaking given that the driveshaft had to be disconnected in a very specific way to keep from damaging it. It’s safe to say that there is nothing straightforward about the design of this car, but that is what makes it interesting.


    Mishimoto engineer scanning the Focus RS rear differential

    Before we removed any part of the RS, we used our 3D scanner to get a better idea of the space we had to work with in the rear of this car. By collecting measurements this way, it saves a substantial amount of design time and often results in more accurate prototypes.


    Focus RS with the rear subframe removed

    With the subframe finally out, we could take a look at the design of the differential and how we could incorporate the cooler. Check out some shots of the subframe after we removed it from the RS!


    Focus RS rear subframe


    Focus RS rear subframe


    Focus RS rear differential

    Coming Up!

    Now that we have a better look at the rear of the Focus RS, we can begin to create some prototype coolers. Stay tuned for more on our prototype designs, and in the meantime let us know what you think about this project in the comments below.

    Thanks for reading!

    -Sara
    Last edited by Mishimoto; 12-13-2016 at 08:17 AM.
    412focusrs, Bugasu, MN_RS and 21 others like this.

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    @Mishimoto

    Any chances you could get pictures of the RDU control module up close and personal? It'd save me some time considering its location is not very accessible, but it appears you guys have it out
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    I thought there was talk before that there is no temp sensor in the RDU, and that based off other parameters (engine oil temp, ptu temp, or something else) it calculates the temp of the RDU. In other words, cooling the RDU with its own cooler wont keep it from shutting down as the car will never know its back there. Not sure if more information has come out since I last read up on the topic, but worth noting.
    Last edited by Cheapo911; 12-12-2016 at 04:03 PM.
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    Nobody's going to be able to say you guys were cutting corners! Love the scan arm. It will be interesting to see if you find it necessary to get into the ECU or RDU control module code. Looking forward to what you cone up with. Props.

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    Oh now I am excited!

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    Quote Originally Posted by Cheapo911 View Post
    I thought there was talk before that there is no temp sensor in the RDU, and that based off other parameters (engine oil temp, ptu temp, or something else) it calculates the temp of the RDU. In other words, cooling the RDU with its own cooler wont keep it from shutting down as the car will never know its back there. Not sure if more information has come out since I last read up on the topic, but worth noting.
    I think this is still accurate.


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    Very cool. Can't wait to see how this turns out.

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    Quote Originally Posted by Cheapo911 View Post
    I thought there was talk before that there is no temp sensor in the RDU, and that based off other parameters (engine oil temp, ptu temp, or something else) it calculates the temp of the RDU. In other words, cooling the RDU with its own cooler wont keep it from shutting down as the car will never know its back there. Not sure if more information has come out since I last read up on the topic, but worth noting.
    I'm interested but concerned about the info Cheapo911 is quoting. It would suck to have everything nice and cool back there yet have an extrapolated state shut the AWD down.

    Jim
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    Quote Originally Posted by Cheapo911 View Post
    I thought there was talk before that there is no temp sensor in the RDU, and that based off other parameters (engine oil temp, ptu temp, or something else) it calculates the temp of the RDU. In other words, cooling the RDU with its own cooler wont keep it from shutting down as the car will never know its back there. Not sure if more information has come out since I last read up on the topic, but worth noting.
    Quote Originally Posted by Grimlock View Post
    I think this is still accurate.

    Sent from my iPad using Tapatalk
    Quote Originally Posted by DeltaT View Post
    I'm interested but concerned about the info Cheapo911 is quoting. It would suck to have everything nice and cool back there yet have an extrapolated state shut the AWD down.

    Jim
    Great point guys, and what Delta brought up is exactly what we are trying to avoid. We want to be sure that any cooling system we come up with not only functions to cool the differential, but treats the underlying problem of the computer pulling power from the rear.

    There are several sensors that run into the front of the diff, but without taking the actual differential apart, it is hard to tell what they read. It is very possible that the rear differential operates off of a calculated temperature as Cheapo suggested, similar to what we ran into with the oil cooler. Still this is all part of the process and we will certainly share what we find during R&D with you all.

    -Sara
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    Quote Originally Posted by Mishimoto View Post
    Great point guys, and what Delta brought up is exactly what we are trying to avoid. We want to be sure that any cooling system we come up with not only functions to cool the differential, but treats the underlying problem of the computer pulling power from the rear.

    There are several sensors that run into the front of the diff, but without taking the actual differential apart, it is hard to tell what they read. It is very possible that the rear differential operates off of a calculated temperature as Cheapo suggested, similar to what we ran into with the oil cooler. Still this is all part of the process and we will certainly share what we find during R&D with you all.

    -Sara
    Glad to hear you're aware of the possibility and hope you guys can find a solution!
    DeltaT likes this.
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