Another Parallel Leaf Question.

[scrimshaw]

Hope someone can explain to a 'non auto engineer' the basics to this problem.

I was recently informed that occasionaly parallel springs on a rear axle are not always exactly parallel and have some angle in them due to mounting requirements on the rails (toe-in).
I always thought that the shackles could only move fore and aft to accomodate the lengthening and shortening of the spring and were ridgid enough laterally to exclude any other kind of linkage on the axle (e.g. Panhard rod).

How is it possible then, for the shackle to tolerate this misalignment and still give lateral support? Won't the shackles bind, or at best wear very quickly on the inside if they are forced to move exactly fore and aft along the cars centreline when they could possibly be at a 3 or 4 degree angle to each other (I estimated the angle based on angle of chassis rails)?

What am I missing? Thanks for your time.

 

[NormPeterson]

Bushing compliance? (3 places)
Shackles not infinitely rigid in the lateral direction?
Shackle pins intentionally not parallel to the vehicle Y-axis?


Norm

 

[GregLocock]

"Toe in" on leaf springs has been around since the year dot, or at least the 1930s, deliberately.

And I think that a Panhard rod is an excellent idea for a Hotchkiss.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[scrimshaw]

Gentlemen, thanks for your replies. Please keep in mind these comments are from a non auto engineer just interested in how these things work.

OK I can see that the bushings would be capable of this if soft enough but it can't do anything for precise handling. I assume that's what Greg meant about the Panhard rod.
I know the shackle linkage is not that solid but forcing it to twist when it is not designed too just doesn't seem 'proper'.
Angling the shackle pins seem like a much better idea.

Do you think shackles fore and aft would improve things or be unnecesary? (Assuming suitable linkage for axle alignment of course).

Thanks again for your time.

 

[NormPeterson]

Somehow I doubt that precise handling has ever been of much priority during the design of most Hotchkiss arrangements. Load carrying capability, simplicity, and ease of installation perhaps.

By the time you've added a longitudinal link to each axle end and a PHB for lateral control, you're 3/4 of the way toward a 3-link.

Not that some rather complex arrangements involving longitudinally-oriented leaf springs have never been tried, or have never had any success in competition - I happen to have handy a brief description of a real oddball. Leaf springs with a swivel arrangement in each pad, upper and lower links each side, and a Watts link for lateral location.


Norm

 

[GregLocock]

FWIW I'd be very keen to try shackle at the front, eye at the back, one day. That would need a very stiff body to make sense, not a typical truck chassis.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.