Push rod connected to upright instead of LCA

[Fomaliot]

Hi all,

Question: What is the main advantage for a road race car suspension, to have the push rod directly connected to the upright instead of connecting it to the lower control arm? is it just for packaging requirement or is there a real geometric advantage to it? i wonder because the ferari F1 have the push rod connected to the upright.

Thanks in advance.

 

[CoryPad]

You reduce/eliminate bending stresses in the lower control arm (due to vertical forces at the contact patch) when you connect the push rod directly to the upright.

Regards,

Cory

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

 

[BrianPetersen]

If the point where the pushrod connects on the upright is directly in line with the line joining the upper and lower ball-joints, the forces imposed by the pushrod won't affect the steering. If it isn't aligned in that manner, the suspension designers had better be a lot smarter than I am, because there will be a torque component that will influence the steering!

It does eliminate a bending load on the arm that it would otherwise be attached to.

 

[GregLocock]

Also it'll have a better motion ratio which makes it easier to design the rest of the system.

Cheers

Greg Locock

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

 

[formula94lt1]

In "Racecar Engineering" there is an article that says teams are adopting this setup, mounting on the upright, to reduce understeer..... that one threw me. How could that effect understeer?

 

[GregLocock]

You can use the force in the link to tune the bump/roll steer.

Almost all stabiliser bars that link to the spindle have some roll-steering effects.






Cheers

Greg Locock

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

 

[murpia]

Clever positioning of the pushrod on the upright can add or subtract cornerweight with steer. There are reasons for doing either that will depend on the rest of the geometry, and the car.

I don't believe that bump inputs need affect the steering any more than they already can do with 'standard' geometry. But I have not analysed such a geometry personally.

Regards, Ian

 

[GregLocock]

In bump you get a fight across the rack - ie both tie rods go into tension or compression, which can give a symmetrical change in toe due to compliances. This is not unique to pushrod on strut designs of course.



Cheers

Greg Locock

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

 

[hemipanter]

On my site I have a few pictures of pushrod to upprights applications.

http://www.hemipanter.se/

klick
"Corvette Nordic Supercar"
If you look at the spherical bearing for the lower A-arm you will find that such unit can be used without suffering from vertical loadings which is not what they are designed for. In this case the loading will only take place in the bearing designed directions. It will also to some extent balance the side load of components during corenring.
Also, whatch that the forceline over all A-arm legs is focused in the centre of all spherical bearings.
Goran

 

[Fomaliot]

Thanks all for the comments. It is greatly appreciate.

I am working on the design of a suspension for a prototype car (personal project), and having that push rod connected to the upright was interesting. But after playing around with the 3d model (and getting more gray hair then i can afford ) I decided to attach the push rod to the LCA. There is just, not enough room to get that push rod attach point in line with the king pin axes. And since suspension is not my field, better keep it simple. Here a picture of the assembly.

[

http://files.engineering.com/getfil...-a1bb-954673ddfe52&file=Suspension_ass-01.jpg

]

Regards,
Fom

 

[Diggdog]

The longitudinal offset from the kingpin of the PR outboard point will have the effect of reducing the load differential between the inside and outside PR. This pro-roll effect with larger steer angles is very useful for bringing the inside tyre back into play in tight corners (e.g. hairpins. In fact, the effect on understeer in practice is very similar to increasing the caster. It is particularly useful for reducing inside front wheel lift however it can 'mask' the feel of the tyre aligning moment and this non-linear tyre cue has to be 'driven through'.

I think you have made the right decision to avoid it though as unless low speed understeer is costing you lap time it's best avoided as can make subsequent diagnosis of general handling issues more tricky.

Cheers,

Digger