McLaren MP4/4 'racks' operated front suspension

[Giando]

Hello!
During the weekend I’ve been watching this incredible video about the technical details of the mytical McLaren MP4/4 Honda, hosted by some key people who actually worked on the car, Steve Nichols, Matthew Jeffreys and Neil Trundle.

I strongly recommend to watch it in its entirety if you guys haven’t yet.



At 1:50:42 Jeffreys describes the front suspension system: it’s a pull rod, but since they didn’t have much room to mount an actual rocker, they used instead what they refer to as ‘racks’.



There’s also a brief still image of the original drawing.



And also Nichols shows the components of the dampers starting at 1:58:46.

I’m struggling to understand how that system works: could someone kindly explain it to me? I’m not familiar with ‘racks’. I would love to understand correctly and in detail what happens when the pull-rod… pulls up, for example, and so how the movement of the arm is transferred to the damper, how the spring is operated etc.

Thank you very much!

[jjn9128]

he literally explains in the video - no space for a rocker, so a track which describes the arc of travel.

[Giando]

he literally explains in the video - no space for a rocker, so a track which describes the arc of travel.

Thank you. I've listened to that part, of course.

But english is not my mother-tongue and also I probably have a limited knowledge of how a 'rack' works, mechanically, so I came here for help.

I know how a rack works in a steering mechanism, for example, i just don't get how the rack could transfer the movement to the damper in this peculiar case... I see in the drawing the connector of the pull-rod to the rack at the base of the damper unit, i see the arc of travel also but i cannot understand how that works.

[Farnborough]

Your English is very good, but fine technical detail is often difficult to translate effectively.

He is speaking of "track" (instead of Rack) as used in English for race~TRACK which I believe is "pista da corsa" in Italian.

There's more discussion and a view of the rollers on the base end of spring damper at 1:59 time in video.

The pullrod is connected to the damper with one pivot that includes the two rollers sitting one each side of damper body.
If the pullrod is put under tension without any location, then it will try to pull the spring damper sideways towards the wheel assembly.
Those two rollers are given a TRACK to force the direction the pivot now takes.

Pull the rod and the track now will allow the rollers only to travel along that track. Track being vertical will make the pull force bring the base of damper upwards only to compress the spring and damper, making the suspension work.

By changing that TRACK into a curve, the path made by the spring damper will be altered relative to the amount of movement the pullrod made. Using different TRACK curves will change how that characteristic can be altered to give different response within the system, without changing the spring.

[SiLo]

This is really interesting, but I'm trying to make sense of the diagram. It seems like the damper is still there? Is it now just pivoting about it's top point and the bottom follows a small arc?

[Farnborough]

This is really interesting, but I'm trying to make sense of the diagram. It seems like the damper is still there? Is it now just pivoting about it's top point and the bottom follows a small arc?

Yes, as he notes in explaining, it mimics a " conventional" rocker in this respect.

If that track moved the roller toward the wheel,assembly, then would deliver a declining rate. Whereas arcing away from wheel assembly would deliver rising.

[Giando]

Your English is very good, but fine technical detail is often difficult to translate effectively.

He is speaking of "track" (instead of Rack) as used in English for race~TRACK which I believe is "pista da corsa" in Italian.

There's more discussion and a view of the rollers on the base end of spring damper at 1:59 time in video.

The pullrod is connected to the damper with one pivot that includes the two rollers sitting one each side of damper body.
If the pullrod is put under tension without any location, then it will try to pull the spring damper sideways towards the wheel assembly.
Those two rollers are given a TRACK to force the direction the pivot now takes.

Pull the rod and the track now will allow the rollers only to travel along that track. Track being vertical will make the pull force bring the base of damper upwards only to compress the spring and damper, making the suspension work.

By changing that TRACK into a curve, the path made by the spring damper will be altered relative to the amount of movement the pullrod made. Using different TRACK curves will change how that characteristic can be altered to give different response within the system, without changing the spring.

Oh thanks so much... i didn't get the 'rack' word correctly, first thing.

Then i can see how it works... it makes sense. It's quite simple, put the way you did.
So the pull-rod is actually just 'pushing' (or lifting) the damper bottom-up by let's say travelling toward the centerline of the car. Quite unusual, but actually very effective given the performance of the car.

Thanks