SEAT Ibiza - rwd turbo

SEAT Ibiza - rwd turbo

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anonymous-user

Original Poster:

53 months

Thursday 25th September 2014
quotequote all
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.

rhinochopig

17,932 posts

197 months

Thursday 25th September 2014
quotequote all
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.

As an Evo owner do mount the 'external' oil pump within the car. Or at least environmentally seal it better than Mitsubishi ever did biggrin

wessy

29 posts

204 months

Friday 26th September 2014
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Absolutely amazing, just incredible what you have achieved, the engineering and technical information is out of this world, thank you for sharing all your expertise.

anonymous-user

Original Poster:

53 months

Friday 26th September 2014
quotequote all
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 biggrin
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.

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)


anonymous-user

Original Poster:

53 months

Saturday 27th September 2014
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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 ......

cravir

57 posts

186 months

Saturday 27th September 2014
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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! laugh)?

I'm only wondering what it would look like with a more narrow section in profile?

confucuis

1,303 posts

123 months

Saturday 27th September 2014
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If those supporting metal structures on the middle of the wing are to stay you could paint them black. It might hide them and make the whole thing look a bit more neat?

anonymous-user

Original Poster:

53 months

Saturday 27th September 2014
quotequote all
Metal supports are temporary, just to hold the wing element in the right place and at the right attitude.

Thickness, profile, and final shape of end plate supports tbc ;-)

rhinochopig

17,932 posts

197 months

Saturday 27th September 2014
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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 biggrin
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.

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)
Sounds like a headache in the making. It's a good job you enjoy the journey biggrin

Re the wing: Think big: get rid of the wing and go for a BT46B-esque concept hehe

anonymous-user

Original Poster:

53 months

Sunday 28th September 2014
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Attempt No: 3





Revised the angles of the, er, angled bits, copied for both sides, now needs the glue to set and the car to be taken outside where i can stand far enough away from it to get an idea of the side profile that looks the best when cut into those end plates!

Megaflow

9,347 posts

224 months

Sunday 28th September 2014
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Getting there. IMO the angle between the two vertical planes needs to be shallower.

anonymous-user

Original Poster:

53 months

Sunday 28th September 2014
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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........

rasto

2,188 posts

236 months

Sunday 28th September 2014
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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 thumbup

Megaflow

9,347 posts

224 months

Sunday 28th September 2014
quotequote all
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.

chuntington101

5,733 posts

235 months

Monday 29th September 2014
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Just do it already and stop messing about trying to make it look pretty! its a wide arch RWD rally SEAT Ibiza for F sake. People will either LOVE it or HATE it.

And if they hate it then they are idiots. smile

AER

1,142 posts

269 months

Monday 29th September 2014
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put your MDF away Max and get some Depron sheet out. Laminate a few 2-3mm sheets together after the appropriate bending and then get some proper flowing curves going. The air will love you for it and it'll be ready to slap some carbon, kevlar and epoxy on straight away!

anonymous-user

Original Poster:

53 months

Monday 29th September 2014
quotequote all
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..... ;-)

CamMoreRon

1,237 posts

124 months

Monday 29th September 2014
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Crikey that wing is a bit steep, isn't it? What is it from?

anonymous-user

Original Poster:

53 months

Monday 29th September 2014
quotequote all
CamMoreRon said:
Crikey that wing is a bit steep, isn't it? What is it from?



Podie

46,630 posts

274 months

Monday 29th September 2014
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Max_Torque said:
CamMoreRon said:
Crikey that wing is a bit steep, isn't it? What is it from?
Do they know it's missing yet? hehe