Quarter-elliptic rear leaf springs.

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pdq67
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Quarter-elliptic rear leaf springs.

Post by pdq67 » Mon Nov 28, 2016 11:02 am

What are everybody's thought's on installing, "quarter-elliptic", springs on my 1st Gen. Camaro by making my sub-frame connectors strong enough to mount them solid up front.

Then attach them to my rear end so that they pivot and that's it. By probably use something like, "Johnny-Joints"... No shackles is all.

I would probably need a watts or a panhard bar to hold side to side sway tight.

Just trying to think outside the loop.

Might be able to use a stiff F/G mono leaf spring to save a lot of weight, imho??

Heck, I might take two Astro Van F/G springs and cut them in half and stack them to try this on the CHEAP?

pdq67

PS., I know now that I am retired, I have way too much spare time on my hands!!

Brian P
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Re: Quarter-elliptic rear leaf springs.

Post by Brian P » Mon Nov 28, 2016 12:29 pm

Quarter-elliptic springs have been used in the past. A google photo search for "quarter elliptical suspension" returns quite a number of examples.

The connection at the fixed end of the springs needs to be a very strong moment connection (it has to resist twisting). A rigid end mount will also make the spring resist side-to-side motion (cornering forces). If you use it in conjunction with a panhard rod, the geometry will have to be carefully chosen to avoid binding. Probably the axle (pivot) end of the spring would need to allow side-to-side "give".

I'm not sure how this would be "better" than a traditional Hotchkiss layout given that you already have the space to use full-length leaf springs. The photos that I see on Google appear to be for suspension designs where the axle is very close to the end of the vehicle, or even beyond the end of the frame of the vehicle in the case of solid-axle front suspensions. In those situations there is nowhere to put the other end of the spring, so there is a legitimate excuse for using this design.

I know the Cord automobile of the 1930s used upper and lower quarter-elliptic springs to locate its rigid front axle.

If the intent is to control axle wrap-up, I think one of the proven solutions, e.g. a supplementary upper locating link, will work better.

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Re: Quarter-elliptic rear leaf springs.

Post by pdq67 » Tue Nov 29, 2016 6:42 pm

Brian,

I very much thank you for posting back on this.

I post stuff and usually don't get squat back for helpful info.

I only brought this up because of the possibility of saving a bunch of rear end weight is all if I used junkyard Astro Van F/G rear leaf springs cut in two and stacked.

I would probably use a rear, "track locator", bar, that would be located at the bottom of my rear end, "pumpkin", if you will, so that my rear end roll center would be as low as I can make it.

Add this to my now front end roll center that is about 2.5" above ground and I should HOPEFULLY corner like a, SK-8 Board!!

pdq67

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Re: Quarter-elliptic rear leaf springs.

Post by Brian P » Tue Nov 29, 2016 8:15 pm

I doubt if it would end up lighter than a normal Hotchkiss leaf spring arrangement by the time all is said and done - including whatever you have to do at the fixed end of the springs to absorb that moment load. If you are stuck with a live rear axle it's hard to get lighter than Hotchkiss leaf springs because the same elements do the springing and the axle-locating, and they do a decent job of spreading applied loads out around the chassis instead of applying them in concentrated locations that then have to be beefed up. Of course, there are side effects, e.g. axle wrap-up, and imprecise side-to-side location.

Among the production live-rear-axle setups that I know of, the one that has the best geometry is that used in the S197 Mustang - 3-link with panhard rod, coil springs. The roll center is not too high, they can have decent anti-squat, bump-steer and roll-steer behaviour is not bad, axle wrap is well controlled, there's no binding within reason.

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Re: Quarter-elliptic rear leaf springs.

Post by barnym17 » Sun Jan 29, 2017 9:20 am

the half leaf setup is used a lot in dirt track modified racing,make the front mounts wide enough the spring can move side to side with approx 1/4 to half inch clearance then use either a full length panhard bar to control lateral location and roll center height. This setup requires a coil spring on top of the housing for the actual spring of the chassis, the half leaf is acting merely as a control arm to resist axle wrap and provide the thrust to the chassis. The entire reason for doing this on dirt is to allow spring wrap to cushion the contact patch of the tire upon throttle application. It has pretty much been phased out by the 3 link system using control rods at the bottom locations with heim joints and a torque absorbing upper link using either a spring or rubber bushing to cushion the the hit at the tires.

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Re: Quarter-elliptic rear leaf springs.

Post by pdq67 » Sun Jan 29, 2017 5:54 pm

What about this??

Take, "sheets", of really thin banding type steel, say .015" thick and cut it many times so that you come up with a stack of them shaped like upper and lower A-Arms.

These are then installed above and below the frame-fixed pumpkin and they are continuous mounted above and below the pumpkin side to side.

They will have rear drive spindles mounted both upper and lower to them. And the spindles have through holes for the drive axles...

No nothing except tempered sheet metal a-arms. Match the spring rate of the stacked sheet metal a-arms so you won't need real springs, but only shocks.

pdq67

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Re: Quarter-elliptic rear leaf springs.

Post by Brian P » Sun Jan 29, 2017 7:02 pm

I have some inspiration for you.

Let's start with this.

Image

Transverse leaf spring that doubles as a lower control arm, in conjunction with a "normal" upper arm. Since the knuckle connection to a leaf spring can only be a pin connection (not a ball joint), this uses king-pins for steering. The shocks connect to the knuckle. This is from the 1955 Fiat 600; Fiat used similar designs for first front suspensions and then rear suspensions for a few decades. But, they only used this design on the non-driven end. In this case it was for the front suspension of a rear-engine car.

Note that the leaf spring is attached to the chassis at two points. Imagine what happens in two-wheel bump - the center of the leaf spring will go up and down a little. Now compare to what happens in body roll - the center of the leaf spring (roughly) stays put, which forces each end to move more, i.e. it's stiffer in roll than it is in two-wheel bump. So the leaf spring also acts as an antiroll bar. The Chevrolet Corvette, which uses transverse leaf springs to this day, uses this effect to this day.

Now look at this ...

Image

The lower A-arm goes to a ball joint and the transverse leaf spring also acts as the upper control arm. I haven't found a photo of what this looks like with the powertrain not in place but obviously the transverse leaf spring (and the steering rack) are routed above the final drive of the transmission (which is a transverse transaxle in this case). This is from the Autobianchi Primula from 1964.

The successor to *that* car was the Fiat 128, which set the pattern for front-drive cars to this day: Transverse engine, end-on transaxle, MacPherson front suspension with coil springs. Notably, they went away from the transverse leaf spring - although that car still used one in the rear suspension, but it didn't serve to guide the hub, it was just a spring (and an antiroll bar).

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Re: Quarter-elliptic rear leaf springs.

Post by Brian P » Sun Jan 29, 2017 7:30 pm

I know of no high-performance vehicles that use the leaf springs to also guide the path of the hubs ... outside of the traditional Hotchkiss live rear axle drive, and even that has gone out of favour.

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