Ford Focus RS Forum banner

1 - 20 of 378 Posts

·
Registered
Joined
·
387 Posts
Discussion Starter #1 (Edited)
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
 

·
Registered
Joined
·
182 Posts
@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 :)
 

·
Registered
Joined
·
716 Posts
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.
 

·
Registered
Joined
·
2,182 Posts
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.
 

·
Registered
Joined
·
466 Posts
Oh now I am excited!
 

·
Registered
Joined
·
2,541 Posts
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.


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
2,441 Posts
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
 

·
Registered
Joined
·
387 Posts
Discussion Starter #9
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.

Sent from my iPad using Tapatalk
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
 

·
Registered
Joined
·
716 Posts
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!
 

·
Registered
Joined
·
387 Posts
Discussion Starter #11

·
Registered
Joined
·
722 Posts
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
I was under the impression it was also an inferred reading and that the PTU is what needed to be cooled.
 

·
Registered
Joined
·
387 Posts
Discussion Starter #15
@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 :)
Sure thing, our engineers have the subframe back in the RS for testing but I do have some closer shots of the RDU.

-Sara

 

·
Registered
Joined
·
387 Posts
Discussion Starter #18 (Edited)
I was under the impression it was also an inferred reading and that the PTU is what needed to be cooled.
+1, that was my understanding
Great point! We are starting the development with the source of the problem (the differential). If testing reveals that treating the overheating symptoms at the diff is not a solution to the shutdown, we will look to other options (and the PTU is certainly on our radar).

Threads like this excite me. Thanks for taking the plunge @Mishimoto !
Fully agree. Glad someone is finally looking into this. Hopefully it will be ready by next season!
They're making it harder and harder to nitpick those small issues in the RS. Good job @Mishimoto
Thanks for the excitement guys!

-Sara
 

·
Premium Member
Joined
·
1,072 Posts
I was under the impression it was also an inferred reading and that the PTU is what needed to be cooled.
Funny thing is, the video in other threads re leaks in the PTU seals on a range of Ford cars suggests that overheated PTUs are what cause lubrication breakdown and seal failures = leaking. Maybe that is why the PTU temp/stress level ends up controlling all of this stuff?
 

·
Registered
Joined
·
1,653 Posts
Funny thing is, the video in other threads re leaks in the PTU seals on a range of Ford cars suggests that overheated PTUs are what cause lubrication breakdown and seal failures = leaking. Maybe that is why the PTU temp/stress level ends up controlling all of this stuff?
Not saying overheating and oil degredation isnt causing seal issues but most of the cars with PTU seal leaks are from memory street driven and very new cars. Unlikely they have had any overheat issues.

Ciao
 
1 - 20 of 378 Posts
About this Discussion
377 Replies
83 Participants
ControlNode
Ford Focus RS Forum
FocusRS.org is the largest forum community to discuss the 2016+ Focus RS. Join to talk about performance, specs, reviews and more!
Full Forum Listing
Top