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Discussion Starter #1 (Edited)
I'll start with mine.

I figure the front wheel will be handled much like the ST, they have already mentioned the front will use brake torque bias.

I think the rear does not have a diff connected to the ring gear, but instead has a spool. If the clutches on the rear are normally open the wheels in the back are not locked so cornering is not adversely affected like a spool directly connected to both wheels normally would. They have already stated the car is normally drives like a FWD, only sending power to the rear when needed, so clutches normally in the open position make sense to me. Closing one of the two clutches also gives the 100% to one side as advertised.

Not sure if there is any front/rear diff or if it is more like the way Honda did the 4WD on their 80s Civics ("ring gear on front diff to pinion gear" to shaft to pinion gear to ring gear with some disconnect or viscus coupler along the shaft). The RS would not need anything but the shaft between the pinions if the rear clutches are normally open though. I'm really leaning to it being like the Honda Civic/CR-V RT4WD system, just instead of a single mechanical activated clutching device on the shaft connected to a diff there is a spool with two (one on each axle) electronically controlled clutching devices.

If the front wheel is spinning but the ring gear always turns at the rate based on [engine rpm * selected gear * final drive] the gripping front wheel rpm can be less than that of the diff, so more power to the rear since the spinning wheel is causing a loss of power up front... I don't know if I've explained my mind right on this or not, maybe if someone thinks they under stand me and can word it better I'll confirm if that was what I was saying, well trying to say, or not.

So, anyone else want to take a crack at it and later find out who guessed it.
 

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Discussion Starter #2 (Edited)
Well, let me add another thought. If the rear clutch packs use hydraulics to actuate them, unless there are electric pumps in RDU (or hydraulic pressure is provided from a pump on the engine) there is only FWD in the first moments of a launch. I know in the CR-V system that was also a hydraulic activated clutch pack the main pump was driving with the driveshaft. In the CR-V system though there was a second pump behind the clutch pack, if the pumps were turning about the same speed no pressure was made to activate the clutch pack since the second pump pulled the fluid from the chamber the front pump put it.

In the ford it is likely that there are solenoid valves that are normally open to prevent pressure from building and actuating the clutches. When the electric control closes a valve for a clutch pack the pressure builds and the clutch closes. The normally open pressure relief valves would also make it so there is less resistance to the drive shaft turning, but with the fluid already being pumped through the system if the valve snaps shut the clutches can close very quick.

No differing theories?
 

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Discussion Starter #4
That thought came to me over night also.

How to store the pressure:
  • Use a piston and spring to have fixed pressure there are more parts to maintain.
  • Using air that is compressed when the fluid is pushed in to maintain the pressure, that pressure can vary based on temp changes.
Then how to control the pressure in the storage:
  • Controlling the flow in/out could be done with addition electronic valve, which [are|is an] additional point of failure as is the pressure sensor that would be needed to accurately control the valve.
    [*]Have the pump always pump into the accumulator and a over pressure bleed off valve when max pressure is reached. But this adds a constant increased resistance to the drive shaft turning and hurts the efficiency of the system.
 

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I would say it really depends on operating pressure, all those are possibilities. The first step though is to find out how it is making pressure first. I tried doing some research on the GKN system but fell up short. There is almost no information on a system brake down on how it actually controls clutch pressure, sadly there are a few videos for the Haldex system :(
 

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Where did Focus RS get its AWD From? - Ford Focus RS Forum

What's interesting is that Car and Driver discovered that the Focus's 'Rear-Drive Unit' shares remarkable similarities to Land Rovers 'Active Driveline' they debuted on hot versions of the Evoque.

Quote:
The official details of what Ford calls the Focus's Rear-Drive Unit are almost identical to those of the rear axle "Active Driveline" that Land Rover recently introduced on higher-performance versions of the Range Rover Evoque. Both use twin electronically controlled clutches on the rear axle to send torque to the back wheels, and both are claimed to be capable of the same neat side-to-side torque-vectoring trick.
:rolleyes:
 

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Focus RS AWD System Explained

Here's a good article that goes into the technical aspects of the Focus RS AWD system. Here's the part i didn't like. Thoughts anyone???

"Because there is always sliding friction between the input and output friction plates of the clutches, to prevent overheating and premature wear, the clutches can only be “slightly” engaged in most of the time, which means the rear wheels will get meaningful amount of power only in some special circumstances, such as: hard acceleration, cornering etc., so it can be considered as an “on-demand” type AWD system."


Link:

Exclusive: 2016 Ford Focus RS AWD System Analysis - YouWheel.com - Car News and Review
 

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Here's a good article that goes into the technical aspects of the Focus RS AWD system. Here's the part i didn't like. Thoughts anyone???

"Because there is always sliding friction between the input and output friction plates of the clutches, to prevent overheating and premature wear, the clutches can only be “slightly” engaged in most of the time, which means the rear wheels will get meaningful amount of power only in some special circumstances, such as: hard acceleration, cornering etc., so it can be considered as an “on-demand” type AWD system."


Link:

Exclusive: 2016 Ford Focus RS AWD System Analysis - YouWheel.com - Car News and Review
This article is dated 03-06-2015. There are others thread already that has this and newer information : http://www.focusrs.org/forum/9-focus-rs-discussions/884-rs-transmission.html and http://www.focusrs.org/forum/31-focus-rs-suspension/862-focus-rs-awd-system.html and http://www.focusrs.org/forum/9-focus-rs-discussions/1021-transmission-strength-talk.html

Maybe this should be incorporated in the existing RS Transmission , Focus RS AWD System , and Transmission Strength threads.

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Here's a good article that goes into the technical aspects of the Focus RS AWD system. Here's the part i didn't like. Thoughts anyone???

"Because there is always sliding friction between the input and output friction plates of the clutches, to prevent overheating and premature wear, the clutches can only be “slightly” engaged in most of the time, which means the rear wheels will get meaningful amount of power only in some special circumstances, such as: hard acceleration, cornering etc., so it can be considered as an “on-demand” type AWD system."


Link:

Exclusive: 2016 Ford Focus RS AWD System Analysis - YouWheel.com - Car News and Review

hmm... I have difficulty believing the rear clutches slip whenever they are engaged. that certainly would make the (70%) 100% to one wheel factor difficult to achieve.
I imagine slipping is part of the design at times, but if they never are able to fully lock (like a trans clutch) we have a problem.
 

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They do not fully lock, it is a slip based design. This is why if you add power to the engine, the rear will not receive more. The clutches only engage enough to transfer the amount of TQ requested up to a certain limit. It is also not hard at all to have 100% of the 70% to the rear, just keep one side open and apply as much TQ allowed to the correct side only. We should have more info soon (hopefully) but the rear is using an overdrive design. We do not know the ratio yet but it seems substantial and kind of has to be to achieve TQ vectoring but at the same time if the clutches were to lock then you would have the rear spinning a lot faster then the fronts which is impossible unless they are slipping.


hmm... I have difficulty believing the rear clutches slip whenever they are engaged. that certainly would make the (70%) 100% to one wheel factor difficult to achieve.
I imagine slipping is part of the design at times, but if they never are able to fully lock (like a trans clutch) we have a problem.
 

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We do not know the ratio yet but it seems substantial and kind of has to be to achieve TQ vectoring but at the same time if the clutches were to lock then you would have the rear spinning a lot faster then the fronts which is impossible unless they are slipping.
Sounds like a good way to kill some tires.

Must explain the Michelin and Ford tire collaboration ;)
 

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They do not fully lock, it is a slip based design. This is why if you add power to the engine, the rear will not receive more. The clutches only engage enough to transfer the amount of TQ requested up to a certain limit. It is also not hard at all to have 100% of the 70% to the rear, just keep one side open and apply as much TQ allowed to the correct side only. We should have more info soon (hopefully) but the rear is using an overdrive design. We do not know the ratio yet but it seems substantial and kind of has to be to achieve TQ vectoring but at the same time if the clutches were to lock then you would have the rear spinning a lot faster then the fronts which is impossible unless they are slipping.
Sounds like a good way to kill some tires.

Must explain the Michelin and Ford tire collaboration ;)
And this very scary, because rears going faster is EXACTLY what this Ford video says:

http://www.focusrs.org/forum/31-focus-rs-suspension/436-interview-gkn-focus-rs-awd-designer-14.html


Hopefully, it only happens going into turns. :)

YMMV,

MidCow3



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I'm no rocket surgeon, but last time I checked, you want all 4 wheels going the same speed in a straight line.


In all seriousness, it will be interesting to find out when that sort of conditions need to occur to engage the "overdrive". You've got to assume that drift mode has a lot to do with when it engages, but it just seems semi counter-intuitive to have AWD that functions that way. In the end though, FOE/GKN know a hell of a lot more than most of us do about this AWD, and by initial reviews, it looks promising.
 

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I'm no rocket surgeon, but last time I checked, you want all 4 wheels going the same speed in a straight line.


In all seriousness, it will be interesting to find out when that sort of conditions need to occur to engage the "overdrive". You've got to assume that drift mode has a lot to do with when it engages, but it just seems semi counter-intuitive to have AWD that functions that way. In the end though, FOE/GKN know a hell of a lot more than most of us do about this AWD, and by initial reviews, it looks promising.
I'm going to try to explain this as best as I can. Anytime the system engages the RDU clutches you are going to have an overdrive situation, it would be like starting out in second gear instead of first and you feather the clutch to make it slip more so the engine doesn't stall. The clutches will engage very slightly if it only needs to transfer minimal power. To achieve TQ Vectoring the outside clutch will apply a lot of pressure and transfer a lot of TQ due to the ratio offset and overdriving that wheel. The wheels will always be going the same speed unless you induce slip. The clutches take the abuse, the tires don't, unless you provoke it, and I bet especially going of the first Ride reviews, that provoking slip will not be to difficult because of the design of the system.
 

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That's sort of what I figured, considering the ring gear is obviously a fixed ratio, so you can't change that.

I'm more curious as to what situations would engage the clutch packs to their fullest extent. I should have worded that better the first time.
 

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That's sort of what I figured, considering the ring gear is obviously a fixed ratio, so you can't change that.

I'm more curious as to what situations would engage the clutch packs to their fullest extent. I should have worded that better the first time.
I would say in Drift mode is the only mode where it may apply TQ to it's fullest potential when trying to induce a slide and break the traction of the outside wheel. I'm sure you would get an aggressive transfer during a launch as well. The problem is the system is always changing and shuffling TQ around depending on what the driver wants or what the car is doing. The other thing to remember it is using a spool in the rear so the only time there will be an even split across both clutches is when the vehicle is going straight. I'm not too sure what situation would absolutely cause the clutches to be at their fullest extent, it sounds like the way the system is engineered it will do whatever is needed to drive the car where the driver wants it, up to its limitations. Extreme yaw and launching would be the two things I think would put the most strain on the system.
 

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I would say in Drift mode is the only mode where it may apply TQ to it's fullest potential when trying to induce a slide and break the traction of the outside wheel. I'm sure you would get an aggressive transfer during a launch as well. The problem is the system is always changing and shuffling TQ around depending on what the driver wants or what the car is doing. The other thing to remember it is using a spool in the rear so the only time there will be an even split across both clutches is when the vehicle is going straight. I'm not too sure what situation would absolutely cause the clutches to be at their fullest extent, it sounds like the way the system is engineered it will do whatever is needed to drive the car where the driver wants it, up to its limitations. Extreme yaw and launching would be the two things I think would put the most strain on the system.
You mean donuts and burnouts? Hehe
 

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Discussion Starter #20
That's sort of what I figured, considering the ring gear is obviously a fixed ratio, so you can't change that.

I'm more curious as to what situations would engage the clutch packs to their fullest extent. I should have worded that better the first time.
I know there are CVP devices that could be put inline between the PTU and the RDU gears that could change the ratio on the fly and while under load. But, not seen any mention from Ford or GKN of such a device in this drive line. I think a good CVP and controller would be awesome as it could do 1:1 while straight, then under drive the back in turns in slippery conditions for best traction and even overdrive it some too for "drift mode". It could be the smartest "center diff" ever. Fallbrook + Ford + GKN and we could have the smartest AWD.
 
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