The story behind the “Mercury” suspension – Part A

Posted: February 3, 2012 in Formula 1, Technology
Tags: , , , , , ,

Again, thanks to my friend for this article below…:

There has been a lot of discussion going on in various websites and forums about our proposed system, over the last couple of days. Sadly, most of this discussion has revolved around its legality and/or the impact of Mercury on the environment, rather than its merits and the technical reasons behind it.

We will leave it to the self-proclaimed “experts” on the different forums to argue about its legality, as we trust that finally the real experts (i.e. the FIA) will decide if it’s legal or not. Just an interesting observation. ScarbsF1′s report on the new McLaren MP4-27 mentions that he asked Paddy Lowe regarding the Lotus anti-dive brake system and he said that the team looked into it but dismissed it immediately because the engineers felt that it was illegal. However, when ScarbsF1 inquired with regards to interlinked systems, the team refused to comment…

Enough with that. In the meantime, we will try to explain over the next couple of days, to the few fans with an interest in the technical aspects of the sport, the idea behind the system, and more specifically:

1. Why it is not just another” interconnected /hydro-elastic suspension” – as some like to claim,

2. Why it is not “enough” to just “lock out” the front suspension under braking, and

3. Which specific characteristics of an F1 car, have been  leading  to the development of the Lotus –Renault “reactive ride height” system [now banned by the FIA] and our proposed system.

In order to do so, let´s first take a look at a “generic” F1 car according to the 2011 rules.

First, we will define, which loads we have in a hard braking manoeuver at top speed [5G deceleration] and we will later show what this means to the front ride height [front wing height over the ground] of the car.

We will show all the maths [no panic – it´s simple], and we will make some assumptions along the way. Now as is the case with every assumption, we can make some “wrong” assumptions, but this will not take away from the general principle or overall concept, nor will it render the final conclusion void. So, if you feel we have made some wrong (or inaccurate) assumptions in terms of overall downforce levels, centre of gravity [CoG] height, % of front downforce or tyre stiffness, we encourage you to do the calculations based on your own numbers, and to see what the end result looks like. We are confident, that it will not be night and day different from our final values.

So let´s look at some numbers:

To comply with the 2011 rules, a Formula 1 car must have a minimum weight of 640 kg including the driver.  To complete a race distance of approximately 300 km without refueling, the car will need an estimated 160 kg of fuel. The weight distribution between the front and the rear axle is set by the rules to 45.5-46.7% front and 53.3-54.5% rear and we assume a maximum downforce value of 15000 N [1523 kgf] and a distribution of 43% at the front axle [feel free to use your own values here].

Therefore the fuel load changes the total weight of the car by approximately 25% between Qualifying and the start of the race. This in itself is already a great challenge when it comes to choosing the appropriate setup for the car. On top of this, the amount of downforce generated by current Formula 1 cars will change the load at the wheels by about 300% at the front and about 322% at the rear. For the suspension and the tyres, the car appears to be three times as heavy at high speeds, than it is at low speeds. Combine this 300% increase in vertical load with the very low ground clearance of a Formula 1 car, and you start to see, where the challenge for the race engineers lies. The lower the car can run to the ground, the more downforce it will produce, as long as a minimum clearance is maintained, and the skid block/plank does not get excessively worn.

During braking, load will be transferred from the rear axle to the front axle; the underlying calculation for the load transfer is:

Total load transfer = (total weight of the car x longitudinal acceleration x CoG height) / wheelbase

We use a car with a ½ full tank as basis for our calculations. Please see the graphics below for the results.

Load @ the wheels (no braking)

Load @ the wheels - braking & decelerating with 5Gs

5G Braking values

As you can see, from the calculations above, the weight on the front axle increases by +267 kg and decreases by -267 kg at the rear axles during the 5G braking maneuver in our example. What this means to our front ride height and front wing and splitter (tea-tray) height, we will explain in the next blog entry.

Stay tuned…..

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Comments
  1. Excellent post.
    It does reveal the potential usefulness of cross-interlinked type suspension, something that Mercedes may be cooking.
    Honestly, I’ve read reports about that approximately one year ago, but I haven’t seen much evidence about it, as well as the supposed passive F-Duct in the nose.

    So, if that turn out to be true, it will explain the late appearance of Merc AMG team in the testing schedule. Time will tell.

    • abu says:

      Thanks mate! :)

      The front F-duct (which was passive, like you say) was used during the last races of 2011, and the drivers didn’t like the car handling, so it will not be used in 2012.

  2. I was actually wrong – my article about Merc F-Duct and interconnected suspension originates at the end of October – http://f1framework.blogspot.com/2011/10/why-2012-development-began-in-mid.html.
    Still, an exciting concept if made real, let’s hope that MGP-AMG will surprise us.

  3. John Evans says:

    Would it not be better to have a system that would hydraulically link the front and rear with cylinders that would force the rear to compress when the front does and V-V. A spring could be added anywhere to adjust. It would behave like a front to rear swaybar. Right side and left side of car would not be connected. This would allow for easy adjustment and be much lighter than a mercury system – which F1 would probably ban due to toxicity.

    • abu says:

      Yes, in theory you can have a hydraulically linked system that compresses both suspensions but this would take away from the performance. What we are trying to do here is not raise the car, but actually allow the car to be designed and operated with smaller ride heights. The limitation on front ride height comes from the fact that the wing touches the ground under braking, due to the diving effect. Our system negates that, so the car can be ran lower. A system which compresses both sides (rear and front) limits your initial ride height, so it makes the car inefficient around corners.
      Also, the mercury solution is extremely light. May I suggest reading our previous posts about it – you’ll see that the amount of mercury and oil required is actually very small (200-300ml) and the piping can be arranged to travel close to the bottom of the car so as not to affect the CoG. It takes advantage of the heave cylinders which are already part of the suspension – all in all, it’s a very lightweight solution.

      • John Evans says:

        “Yes, in theory you can have a hydraulically linked system that compresses both suspensions but this would take away from the performance.”

        No, it does not compress anything with outside work. It forces one end to compress only when the other end does (or V-V). This is what a swaybar does from side to side. You could actually use a pair of typically configured swaybars mounted on the sides of the tub for that matter and connected front to rear. The rise in the rear would balance the dive in the front if the system was stiff enough, for 0 dive, just as an infinitely stiff swaybar would result in 0 roll (excluding tire compliance).

        Note that the McLaren mp4-12c uses a hydraulic swaybar system, and what we are talking about is nothing but a longitudinal, rather than a lateral swaybar system.

      • abu says:

        Oh, I understand what you are saying completely and I agree about the swaybar action and that it’s “passive”, i.e. it does not require outside work. That’s fine. Basically, what you are saying, is have anti-roll bars installed along the longitudinal axis of the car. If we are referring to mechanical anti-sway bars there are significant drawbacks with such a design: First you must consider the weight. Sway bars (or anti roll bars) are usually steel bars in U-shape, which connect to torsion springs and mechanical linkages – this is a significantly heavier proposition than a hydraulically linked “mercury” suspension which uses 200-300 ml of mercury. Also, since we have independent suspensions in a F1 car, you’d need 2 such anti-sway bars linking front left to rear left, and front right to rear right, further increasing the weight. Another significant drawback is that the forces will be transmitted from the rear wheel bumps to the front. Together with the very increased stiffness that will be required to make the system cope with the excessive forces under braking (as we have explained in the region of 7000N), this would create so many problems when the car is running over the kerbs or uneven surfaces, causing significant jarring between back and front. These issues can be dealt with in a hydraulic system, with acceleration-sensitive and position-sensitive bleed valves. Also, I am concerned that this configuration would have to be so stiff, that you could even risk lifting the rear wheels under braking, just like in a bike, and it would certainly create an extra load that the front tyres and brakes will have to deal with.
        Now, if we are talking about hydraulic anti-sway bars, I guess in theory they could work. I am really interested in finding out more about it – do you have any drawings / ideas you can share with us? I am not aware of the MP4-12 hydraulic sway-bar system.

  4. John Evans says:

    Hi Abu,
    Sorry, but I have seen only photos and passing references to the MP4-12 system.

    Anyway if Mark Ortiz (writes the suspension piece in Race Car Engineering) is correct, and he is pretty sharp, we are both wrong. Here is what he wrote in his Chassis Newsletter Feb 2012 :
    The device uses a small hydraulic system, actuated by brake torque, to raise the front end a little bit, compensating for compression under braking. Rather than being attached to the upright in a completely rigid manner, the caliper is mounted to the upright on a bracket that can rotate with respect to the upright – somewhat like a brake floater on a beam axle. The caliper bears against a piston, or pushrod acting on a piston, in a small master cylinder attached to, or built in unit with, the upright. Under braking, the master cylinder sends fluid under pressure through a short hose to a slave cylinder built into the lower end of the suspension pushrod. With sufficient hydraulic pressure, the pushrod extends, raising the front ride height.

    An anti-dive effect is thus achieved, without any wheelbase or caster change in heave. If such a system is tested on a K&C rig, Equation (1) will not apply. There can be a positive jacking coefficient without having a locked wheel contact patch moving forward when the suspension is compressed. In fact, if the suspension geometry provides zero anti-dive as conventionally analyzed, the system will show slight rearward motion at the contact patch as the hydraulics work, when rearward force is applied to the contact patch. The system will create a compliance. However, this particular compliance will be accompanied by an increase in wheel load if the sprung mass is not allowed to rise, or a ride height increase compared to behavior without the system if the sprung mass is not constrained vertically.

    The FIA banned the system under the rule prohibiting movable aerodynamic devices. Some have suggested that they should have used another rule that prohibits suspension devices primarily intended to influence aerodynamics. ………

    • abu says:

      Hi mate – yeah, I know all about the Lotus anti-dive system, but it’s completely different to what we are discussing here. As you said, it’s a hydraulic piston activated by brake torque off a floating brake caliper that pushes the pushrod. It’s a completely different concept and I had already written about it back in early January about it – here: , here and here

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