Offset front susp push/pull rod mounting

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hardingfv32
30
Joined: Sun Apr 03, 2011 6:42 pm

Offset front susp push/pull rod mounting

Post by hardingfv32 » Tue Dec 26, 2017 5:56 pm

Regarding the mounting of the push/pull rods to the front uprights at high offsets to develop ride height changes in turns:

Would this greatly increase the loads on the steering system?

Would this effect the self centering feature (if still used) that is usually a feature of the steering system?

This whole idea is very impressive... what team developed it first?

Brian

roon
311
Joined: Sat Dec 17, 2016 6:04 pm

Re: Offset front susp push/pull rod mounting

Post by roon » Tue Dec 26, 2017 11:03 pm

It seems logical to me. The steering is the only powered, active element in the suspension systems... So why not make use of it as such?

It's the power steering system which is lowering and raising the front of the car, in this sense.

dans79
149
Joined: Sun Mar 03, 2013 6:33 pm
Location: USA

Re: Offset front susp push/pull rod mounting

Post by dans79 » Wed Dec 27, 2017 12:13 am

Off all the things the FIA could be adding rules for this fairly ridiculous.

Greg Locock
159
Joined: Fri Jun 29, 2012 11:48 pm

Re: Offset front susp push/pull rod mounting

Post by Greg Locock » Wed Dec 27, 2017 4:35 am

On production cars we use the antiroll bar to spindle droplink geometry to do useful things with the steering wheel torque. The useful geometrical construction is true view down the steering axis.

bill shoe
216
Joined: Wed Nov 19, 2008 7:18 am
Location: Dallas, Texas, USA

Re: Offset front susp push/pull rod mounting

Post by bill shoe » Wed Dec 27, 2017 7:18 pm

Castor and trail already create large loads in the steering, so the highly-inset pushrod-pickups may not change the steering forces. Difference is the inset pushrod-pickups move the front corners up and down in-phase as opposed to castor/trail which typically moves the front corners anti-phase.

Two obvious ways to comply with new 5mm limit-
1). Reduce the amount of pushrod-pickup inset so you have less ride-height change for a given amount of steering travel.
2). Reduce the steering travel.

Number 2 is interesting, if not good! During a clean fast lap only a small fraction of steering travel is used, even on an F1 car with limited travel (compared to road car). The rest of the travel is for the occasional extreme countersteer, and for turning into pit stalls during stops, etc. So the FIA has created an incentive for teams to reduce the "extra" steering lock that is useful for unplanned vehicle-dynamics outliers and pitstops.

How to get around the obvious options? WWAND (what would Adrian Newey do)?

hardingfv32
30
Joined: Sun Apr 03, 2011 6:42 pm

Re: Offset front susp push/pull rod mounting

Post by hardingfv32 » Thu Dec 28, 2017 5:33 pm

My thought was that castor/trail produce what I think is a centering force for the steering system. With this offset mounting system it would seem that any time the push mounting is off center there is a force causing the steering to move off the center position. Do the latest power steering systems prevent the driver form feeling this?

Brian

roon
311
Joined: Sat Dec 17, 2016 6:04 pm

Re: Offset front susp push/pull rod mounting

Post by roon » Fri Dec 29, 2017 2:20 am

I think Merc, STR and RB are the main teams experimenting with this. I'm not sure what what the other teams have or have not developed.

With Merc & STR there is the obvious detail of the exposed outboard upper control arm pivots. While this may have been aero-related, it may also have also have been kinematics related.

Red Bull's approach I believe to be different, and maintains all the pivot points within the wheel. Consider the following photo of the RB13's front suspension, taken late in the season. Pay special attention to the pushrod mount, a shiny metallic arm sprouting off the center of the wheel upright.

Morteza wrote:
Thu Oct 19, 2017 6:00 pm
Image
Via AMuS
Sevach wrote:
Tue Oct 31, 2017 12:32 pm
Image

New front suspension.
Note how the pushrod mounts to an arm which places the pivot point well outside of the kingpin axis. I've never noticed such a mounted method before. It struck me as unique when I first saw it. Essentially they are steering the outboard end of the pushrod through a wider arc orbiting the kingpin axis.

Steering would therefore alter the distance and angle between the pushod outer pivot and the bellcrank. Which is probably always the case unless the pushrod out pivot intersects the kingpin axis; but in this application, more exaggerated.

Depending on the exact location of the outboard pushrod pivot relative to the kingpin axis, it would be possible to have steering angle compress and unload the front suspension, thus altering ride height, and powered by the steering rack.


Image

There's plenty of room within the A-arms for the pushrod to displace fore-to-aft as its outer end orbits the kingpin axis. It looks as though, in the photo above, the pushrod mounts aft of said axis, which would cause the inside steered wheel to compress the inside corner suspension, while the outside wheel would relieve the outside corner suspension. Said another way: when turning left, the front left suspension would compress, while the front right suspension would extend. This would roll the car slightly into the turn, which seems ideal, as well as place the inside corner of the front wing lower to the ground.

All this being said, we're still talking about only a few millimeters of alteration for these suspension pivot points. But this gets magnified by the distance between those points and the road surface, and the shape of the tire.
Last edited by roon on Fri Dec 29, 2017 2:40 am, edited 2 times in total.

bill shoe
216
Joined: Wed Nov 19, 2008 7:18 am
Location: Dallas, Texas, USA

Re: Offset front susp push/pull rod mounting

Post by bill shoe » Fri Dec 29, 2017 2:37 am

hardingfv32 wrote:
Thu Dec 28, 2017 5:33 pm
My thought was that castor/trail produce what I think is a centering force for the steering system. With this offset mounting system it would seem that any time the push mounting is off center there is a force causing the steering to move off the center position. Do the latest power steering systems prevent the driver form feeling this?

Brian
My guesses --
* No, the power steer systems do not prevent this. However the castor and trail overwhelm the anti-centering force of the pushrod-offset once the car is going a significant speed. So the steering weight builds up in a strong/intuitive manner off-center at the speeds that matter.
* It would be really useful to have a nit-picky technical driver like Kimi Raikkonen to give feedback on the steering feel.
* You could get some of the self-centering feel back with really massive amounts of kingpin inclination, but probably not worth it. Brings to mind the chain of negative events in "There was an old lady who swallowed a fly...". On the other hand, the unusual Mercedes and Toro Rosso front corners (with upper-joints inboard of the wheels) do lend themselves to more kingpin inclination. :?