SEAT Ibiza - rwd turbo
Discussion
Currently there is a E46 M3 diff across the back axle. It's the GKN preloaded speed proportional item (has a light no slip preload and then applies cross axle locking in proportion to cross axle speed difference) and is entirely mechanical (uses internal oil pump driven by difference in speed between output shafts to apply pressure to a clutch pack across the diff.
This is a good diff as it is very "driveable" because the locking force is nice and linearly applied with slip. But it does mean you end up with a lot of cross axle speed difference and so it isn't as "tight" as say a conventional heavily preloaded plate type diff etc.
Ultimately, i'm going to use my prototype ABS system to attempt to add "Brake steer" to the diff at some point, although i'm not sure if i will have to take the existing plates/pump out to get that to work. I think not because the std locking gain is quite low. Another option is to fit the later "active" type internals to the diff, as used in the current M5 (and Jag XFR) that adds an external 'lecy oil pump to modify the cross axle locking ratio.
This is a good diff as it is very "driveable" because the locking force is nice and linearly applied with slip. But it does mean you end up with a lot of cross axle speed difference and so it isn't as "tight" as say a conventional heavily preloaded plate type diff etc.
Ultimately, i'm going to use my prototype ABS system to attempt to add "Brake steer" to the diff at some point, although i'm not sure if i will have to take the existing plates/pump out to get that to work. I think not because the std locking gain is quite low. Another option is to fit the later "active" type internals to the diff, as used in the current M5 (and Jag XFR) that adds an external 'lecy oil pump to modify the cross axle locking ratio.
Max_Torque said:
Currently there is a E46 M3 diff across the back axle. It's the GKN preloaded speed proportional item (has a light no slip preload and then applies cross axle locking in proportion to cross axle speed difference) and is entirely mechanical (uses internal oil pump driven by difference in speed between output shafts to apply pressure to a clutch pack across the diff.
This is a good diff as it is very "driveable" because the locking force is nice and linearly applied with slip. But it does mean you end up with a lot of cross axle speed difference and so it isn't as "tight" as say a conventional heavily preloaded plate type diff etc.
Ultimately, i'm going to use my prototype ABS system to attempt to add "Brake steer" to the diff at some point, although i'm not sure if i will have to take the existing plates/pump out to get that to work. I think not because the std locking gain is quite low. Another option is to fit the later "active" type internals to the diff, as used in the current M5 (and Jag XFR) that adds an external 'lecy oil pump to modify the cross axle locking ratio.
Interesting. Two glasses of wine in so stuggling to envisage how active braking would work on an E46 diff. Isn't the delta S between the two wheels what drives the pump and thus the clutch pack - reduce the delta and you reduce oil pressure. This is a good diff as it is very "driveable" because the locking force is nice and linearly applied with slip. But it does mean you end up with a lot of cross axle speed difference and so it isn't as "tight" as say a conventional heavily preloaded plate type diff etc.
Ultimately, i'm going to use my prototype ABS system to attempt to add "Brake steer" to the diff at some point, although i'm not sure if i will have to take the existing plates/pump out to get that to work. I think not because the std locking gain is quite low. Another option is to fit the later "active" type internals to the diff, as used in the current M5 (and Jag XFR) that adds an external 'lecy oil pump to modify the cross axle locking ratio.
As an Evo owner do mount the 'external' oil pump within the car. Or at least environmentally seal it better than Mitsubishi ever did
rhinochopig said:
Interesting. Two glasses of wine in so stuggling to envisage how active braking would work on an E46 diff. Isn't the delta S between the two wheels what drives the pump and thus the clutch pack - reduce the delta and you reduce oil pressure.
As an Evo owner do mount the 'external' oil pump within the car. Or at least environmentally seal it better than Mitsubishi ever did
The answer is, It depends! Not much of an answer i know, but the reason i've added the cross axle speed sensors so i can log the actual speed differential of the "M" diff.As an Evo owner do mount the 'external' oil pump within the car. Or at least environmentally seal it better than Mitsubishi ever did
To act as an LSD, a system that applies the rear brakes must prevent the (more lightly loaded) inside wheel from overspeeding excessively, but if the system has enough control authority, it can underspeed that wheel, and add a positive yaw moment. Because of the tyre slip characteristic, fairly significant yaw moment can be created with as little as 15% slip. The question i don't know, is how does "15% slip" relate to what the M diff is setup to do. My suspicion, having driven a few M3s is that the diff is actually pretty loose, and doesn't really start to work until there is a large cross axle speed difference (ultimately, the M3 is a road car, not a track car, and so the diff is set up to be pretty benign)
On a 'wing and a prayer' part 2!
I've been having another stab at making some rear wing end plates / mounts that don't look totally gash ;-) tbh, it's a job i've been putting off as it a real PITA to do nicely. I've mocked up some end plates in MDF to get an idea how they look:
Not totally hideous, but hardly lovely either ;-(
It seems its really rather difficult to get a big wing on the back of a steep "hatchback" shaped car without that wing looking like it's fallen off a passing jumbo and just been nailed on where it fell....... Hmmm, think this needs a few more days looking at / rumination ......
I've been having another stab at making some rear wing end plates / mounts that don't look totally gash ;-) tbh, it's a job i've been putting off as it a real PITA to do nicely. I've mocked up some end plates in MDF to get an idea how they look:
Not totally hideous, but hardly lovely either ;-(
It seems its really rather difficult to get a big wing on the back of a steep "hatchback" shaped car without that wing looking like it's fallen off a passing jumbo and just been nailed on where it fell....... Hmmm, think this needs a few more days looking at / rumination ......
For what it's worth, I think you've almost nailed that, second time of asking.
I like the profile shape, and the angled piece part way up to accommodate 'over-width'.
Does the profile need to be that wide (I'm sure you've done a calc to show that it needs to be, probably to do with air resistance when sideways! )?
I'm only wondering what it would look like with a more narrow section in profile?
I like the profile shape, and the angled piece part way up to accommodate 'over-width'.
Does the profile need to be that wide (I'm sure you've done a calc to show that it needs to be, probably to do with air resistance when sideways! )?
I'm only wondering what it would look like with a more narrow section in profile?
Max_Torque said:
rhinochopig said:
Interesting. Two glasses of wine in so stuggling to envisage how active braking would work on an E46 diff. Isn't the delta S between the two wheels what drives the pump and thus the clutch pack - reduce the delta and you reduce oil pressure.
As an Evo owner do mount the 'external' oil pump within the car. Or at least environmentally seal it better than Mitsubishi ever did
The answer is, It depends! Not much of an answer i know, but the reason i've added the cross axle speed sensors so i can log the actual speed differential of the "M" diff.As an Evo owner do mount the 'external' oil pump within the car. Or at least environmentally seal it better than Mitsubishi ever did
To act as an LSD, a system that applies the rear brakes must prevent the (more lightly loaded) inside wheel from overspeeding excessively, but if the system has enough control authority, it can underspeed that wheel, and add a positive yaw moment. Because of the tyre slip characteristic, fairly significant yaw moment can be created with as little as 15% slip. The question i don't know, is how does "15% slip" relate to what the M diff is setup to do. My suspicion, having driven a few M3s is that the diff is actually pretty loose, and doesn't really start to work until there is a large cross axle speed difference (ultimately, the M3 is a road car, not a track car, and so the diff is set up to be pretty benign)
Re the wing: Think big: get rid of the wing and go for a BT46B-esque concept
Max_Torque said:
Thing is, i want to leave enough room for a lower element, mounted below the current one, that could be active if necessary to act as an air brake / wing staller during high speed heavy braking etc........
You see that's what I love about this car/thread - the fact that you are applying so many 'modern' super/race car technologies to something you are building in your garage. Love it and can't wait to see videos of this immense car in action Max_Torque said:
Thing is, i want to leave enough room for a lower element, mounted below the current one, that could be active if necessary to act as an air brake / wing staller during high speed heavy braking etc........
Ah, yes, that does make things harder. It should look less harsh when moulded without the sharp edges.I used foam sheeting for quite a few of the more complex multi-curved carbon parts, like the roof scoop and dash inserts! These MDF plates are just a mock up to try to get an idea of what looks "nice" in terms of shape, bulk, and form on the back of the car. Without putting the whole car into CAD, it's the closest and quickest technique i've found to do that.
As you say, they will need to have more "form" added so they look less slabby, but don't worry, i have a plan for that..... ;-)
As you say, they will need to have more "form" added so they look less slabby, but don't worry, i have a plan for that..... ;-)
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