NB steering wheel structure?

785 Views 19 Replies 2 Participants Last post by Giniw, 4 mo ago

Giniw

Discussion Starter · 6 mo ago (Edited)

Hello Everyone,

I have a NB steering wheel and I am drawing it in a CAD system but I was wondering if anyone knows how its internal branch structure is made under the leather and plastic?
It starts as an aluminium branch but I gather it has to end up with some steel to join the steering wheel rim? (which I assume is steel?)

I suspect the aluminium branch near the center has actually an internal steel spoke underneath but it would be very interesting to see how it's really done?

Has anyone ever had a look at that and took a few photos?

Thanks in advance!

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Giniw

Discussion Starter · #2 · 6 mo ago (Edited)

PS: I don't actually own an mx5 (just the steering wheel ^^) so I guess the introduction could be short:
I live in France, and I own two Lotus (Elan M100 & Esprit) and often work on old Jaguar too (from the 50-60'). And my daily is a good old Micra K11 lol
The NB steering wheel is to replace the ugly airbag steering wheel of the Esprit (I like my cars stock, but this will be an exception as the OEM one is horrendous! It was mandatory in the USA and an option for everyone else, but it's seriously ugly — it comes from a 90-92 Pontiac Firebird and really doesn't fit the Esprit interior x_x)

Garffey

· #3 · 6 mo ago

Hi Giniw... 👋

Can't say I have personal experience of the Nardi steering wheels although they are highly thought of...and sought after!
Usually the frame is steel construction with the outer padding bonded to it...at the point you show on the picture maybe there is a similar clamping arrangement at the joint as there is to connect the wheel to the centre, as I'm not aware that you can weld aluminium to steel!

And the bottom 'spoke' is quite clearly steel...

Good luck with the modification!

Giniw

Discussion Starter · #4 · 6 mo ago (Edited)

Garffey said:
although they are highly thought of...and sought after!

Indeed, it really transform the look of the interior!

Garffey said:
as I'm not aware that you can weld aluminium to steel!

The splined steel centre is embedded in the cast alloy, I assume it's the only(?) way to bond steel and aluminium? I suspect the the left and right spokes might be the same, as there is no steel spoke connected to the splined centre for sure — I drilled and removed the steel centre to replace it with another hub and there were no steel spokes connected to it.
A guy on another forum (miata.net) reckon it could be fully cast in one piece since the MPV was an all magnesium steering wheel (apparently)
To be honest it doesn't matter that much to know for sure how the spokes are built since what really matters is only the centre near the new hub I want to add and secure. It's just that now I am there I would have liked to draw a fully accurate steering wheel.

Garffey said:
Good luck with the modification!

Thank you very much!

By the way here is the CAD I made (mostly done, but there are still a few details missing — bottom steel spoke for instance, obviously!)

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Garffey

· #5 · 6 mo ago (Edited)

Good job that Giniw....

When I left engineering back in 1987 CAD-CAM was just beginning to become a 'thing'....sadly I knew very little about computers/software other than you had to plug one in!...😂😂
But yes, it looks a good job there!

It would be great to see this progress!
Having looked at your photo the bottom steel spoke doesn't look anything like as substantial as the other two, but I'm no designer!...And the rest of the structure is so it could almost have been a two spoke affair!
It's interesting to see the structure for something that just taken for granted every time you get in the car.

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Giniw

Discussion Starter · #6 · 5 mo ago (Edited)

Hi (and happy new year!)

So, it's a slow progress but a progress nonetheless!

Since the bottom spoke (6h) is a steel rod of a diameter of 5mm I looked for further steel elsewhere with a magnet.
It appears the three spokes have an internal structure made of some magnetic material (=so, steel), and I first thought it would make sense that the bare 5mm steel rod is a good example of the whole thing, and so I made a 5mm internal structure for the three branches and the rim too.
But a 5mm steel rod would probably be too flimsy for the whole rim so I thought it would probably be encased in a aluminium casting like the visible parts of the horizontal spokes (so ~14mm aluminium over a 5mm steel rod).

Then I realized there were two holes for each horizontal spoke and the steel rod could actually be seen at the bottom of the holes, so I measured a 10mm rod for the steel internals of the horizontal spokes. That makes more sense than a mere 5mm one but that leaves us wondering whether some aluminium is actually covering the whole rim under the leather since I guess it's less necessary ... I guess at most it would be a 14mm aluminium cast over the 10mm steel rod, and so I drew it like that since I can't know for sure without destroying it(?) anyway.

I still have to add a few details and then I should be able to begin the finite element analysis optimisation

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Garffey

· #7 · 5 mo ago

Hi Giniw.....Happy new year to you too!

The detail there is fantastic and nice to see what goes on in a naked steering wheel!..

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Giniw

Discussion Starter · #8 · 5 mo ago (Edited)

Thanks!

I just finished adding the springs plastic sleeves and upper cups to the assembly. Just an approximation from a few photos I have with me on my phone since I don't have the steering wheel with me, so that will have to be adjusted (I reckon their diameter could be a bit too large)

He are two new renderings since you seem to enjoy them as much as I do! (totally pointless and a waste of time for my little project, but I do like them

)

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Giniw

Discussion Starter · #9 · 5 mo ago (Edited)

... and I just added the four springs:

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Giniw

Discussion Starter · #10 · 5 mo ago (Edited)

Still a couple of adjustments to do to the screws & so on (proper screw lengths and springs parametrisation for instance), but it's starting to look quite neat in my opinion!

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Giniw

Discussion Starter · #11 · 5 mo ago (Edited)

Et voilà, as they say in english! (I may add the airbag steel bottom as it clearly contributes to the horn/airbag bracket rigiditiy — not too sure if it's of any significance for the bottom part though ...)

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Giniw

Discussion Starter · #12 · 5 mo ago (Edited)

(strangely the webp conversion of the images I paste on the forum are a tad darker than my original pngs — maybe I should have sent jpgs so hopefully the forum won't recompress it? Anyway, it's doesn't really matter ^^')

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Giniw

Discussion Starter · #13 · 5 mo ago (Edited)

Fixed the plastic clip aka spring cup aka isolator.
Added the rubber washer under the head of the screw.
Fixed the spring geometry to look like the real one (dead coils at the beginning and end of the spring)

This steering wheel is really neatly designed, especially when I compare it to the GM 90-92 Pontiac Firebird one (basically a steel hub welded to two steel rods and a rear metal sheet, and plastic bits for the horn). Congratulations to Mazda (Nardi?) for this lovely contraption!

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Giniw

Discussion Starter · #14 · 5 mo ago (Edited)

Now, I may add the rear metal casing of the airbag in the future but I consider the steering wheel CAD somehow finished.

I just started experimenting with meshing for the finite element analysis/optimisation. Here it's the steel hub part with an added steering column to avoid meshing the hub splines (unnecessary and would add much complexity to the mesh)

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Giniw

Discussion Starter · #15 · 5 mo ago (Edited)

(oh, I just noticed one could do a 3D rendering with all the parts automatically exploded too ^^)

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Giniw

Discussion Starter · #16 · 5 mo ago (Edited)

Not much done lately, I am still experimenting with the meshing. I have to learn how to make it work properly.

So, just a sectional plan rendering of the aluminium casting I made a couple of days ago to better show how I think is the steel internal structure (one has to remember the hub shown here is a custom one: it is not the original one from the NB):

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Giniw

Discussion Starter · #17 · 4 mo ago (Edited)

Hi guys,

Giniw said:
Now, I may add the rear metal casing of the airbag in the future but I consider the steering wheel CAD somehow finished.

Et voilà! (that last part was harder to draw than I imagined, but it's now pretty accurate, except the stiffener near the "ears", which are not round in the real thing. And the ears themselves which I don't know how they are under the plastic cover — same for the big hole in the center, but I won't tamper the airbag, that's for sure!)

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Giniw

Discussion Starter · #18 · 4 mo ago (Edited)

I am also still experimenting with the meshing and analysis.
Here is an automatic meshing with the alloy part alone (and I applied a torque to it, with a clamping located at the puller holes near the hub)

/!\ The internal steel structure is NOT present in the analysis, so the alloy spokes are basically thin tubes (2mm thickness), hence why the spokes stresses look a bit high.
Still some work to eventually make a proper analysis (refine that mesh, add the steel mesh, add a few other parts and link them together properly for the analysis and it should be good). But, in the meantime, a few iso colours are still nice to look at

)

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Garffey

· #19 · 4 mo ago

Interesting.....
Back in my engineering days, some of the technical drawings we worked with looked....Err...Technical! 😜
But this is worlds apart, would have loved to be more involved with hindsight.

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Giniw

Discussion Starter · #20 · 4 mo ago (Edited)

Hehe, these are just ray-tracing renderings but the actual view you get when you design the thing is nowhere near as nice.
It looks like that in the real-time rendering:

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