The idea was originally intended for F1 and the author was interviewed by some designers with mixed luck.
We now commonly see "third damper" or "third bump stop element" systems in F1. French-Canadian Luc Pellerin has some interesting ideas that take the concept one step further. In his own words:
Conventional Two Spring System:
IN ONE WHEEL BUMP: When one wheel is being raised sharply in relation to the chassis, the contact patch load is increased due to the stiffness of the springs and anti-roll bar. The load and movements are transmitted via the push-pull to the rocker on the left side. This in turn will compress the spring and damper assembly and the load is transmitted to the chassis which induces a roll moment. To make things worst, the rocker rotation on the left tends to rotate the rocker on the right proportionally to the stiffness of the Torsion bar which in turn remove load from the contact patch on the opposite side. This increases the lateral load differential which causes an even higher induced roll moment to the chassis and corner weight differential.
Three Springs & Dampers Conventional Suspension
ONE WHEEL BUMP & LATERAL LOAD TRANSFER
*If the third spring is fully loaded, some of the added contact patch load will be transmitted to the laterally opposed contact patch which is a desirable thing.
Depending on loading of the third spring: the contact patch load will increase or decrease.
**If the third spring is not fully loaded and if a stiff Torsion Bar is used, it is more likely that the load will not be transmitted to the other side. In fact, it could unload the right side same as two springs and dampers suspension as shown in Fig 1.3
Therefore, the behavior of the system will vary according to down force witch makes things more unpredictable.
Generally, roll stiffness will be set to resist the highest expected lateral G’s which occur when high down force is present causing the following problem:
WHEN THE DOWN FORCE IS REDUCED,
THE SYSTEM IS OFTEN TOO STIFF !
CONVENTIONAL SUSPENSIONS 1) When race cars using down force hit a bump with one wheel such as when passing curbs, at times when the down force is minimal we will notice that as one of the front wheels is lifted, it is common to see the laterally opposed wheel coming off the ground. A fraction of a second later, the same will occur when the back wheel is riding the bump.
I will call this the pogo effect! Drivers often have to do all the turning before or after the bump since the rest of the time, they are airborne.
2) The same is true to a lesser degree when we have sudden track camber changes. The front wheels are on a slope that is different from the back wheels. At times when the down force is low, it is common to see wheel lock under braking.
REACTIVE SUSPENSION.
As will be shown after, the proposed REACTIVE SUSPENSION will alleviate these problems greatly since 1) the roll stiffness is proportional to the down force 2) the load generated by a one wheel bump is transmitted to the laterally opposed wheel which results in more even corner weights.
Reactive Suspension By Luc Pellerin
IN HEAVE : Left & right rockers rotate in the same direction causing the Roll Lever (RL) to slide in the slotted guide causing the center spring to be compressed.
Rising wheel rates can be achieved in a number of ways such as with rising-rate springs, bump rubbers and by design of the rockers in the same way that is done with conventional suspensions.
The purpose of adding a third spring in modern day race cars is to de-couple roll rate from heave rate. This system offers the same possibilities. It only does it better. The use of a third damper is optional but it could allow to dampen heave more than roll as is often desired.
IN ROLL, as one wheel goes up relative to the chassis, the laterally opposed wheel goes down causing the rockers to rotate in opposite direction. Therefore, the Roll Lever (RL) will rotate as shown.
Note that the total load on the central spring remains the same. (Unlike conventional suspension where one spring will want to uncoil while the other is being compressed.)
HOW DOES THE SYSTEM GENERATE ANTI-ROLL?
The rotation of the RL will cause the offset of the line that is formed by the base of the spring & damper assembly and the end of the Roll Lever. As we know, a torque or Moment is equal to the Force * Effective lever which is the perpendicular distance between the force and the pivot of the RL. Therefore, we obtain a Moment around the pivot of RF which is proportional to down force. This moment is now available to oppose the contact patch differential from left to right. Plots of the wheel loads and wheel rates in roll and heave can be made to match current race car heave and roll chararteristics.
For example : We could design the system to generate half a degree of chassis roll when 1G Lateral and 1 G of down force are applied.
The same set up would still generate half degree of chassis roll when 3 G lateral and 3G down force are applied.
WHAT YOU GET IS WHAT YOU NEED LEADING TO BETTER TRACK COMPLIANCE
REACTIVE SUSPENSION & ONE WHEEL BUMP
IN A ONE WHEEL BUMP SITUATION
The Roll Lever (RL) is simultaneously rotated around the pivot point (P) and is sliding to compress the spring. "The spring will not be compressed if there is no support from both sides. This characteristic is inherent to this system at all vertical loads unlike conventional suspensions.
Therefore, part of the added load at the contact patch is transmitted to the opposite side. (The difference in load from side to side is the energy absorbed by the dampers + Roll Lever Reactive Moment.) (RLRM)
Obviously, when the RLRM becomes too great, no more load is reaching the other side. Anything in between is a net gain from conventional suspensions!!!
Adding this feature to the Reactive to down force feature, we end up with a better compliance when the car is slowing down.
More REACTIVE vs CONVENTIONAL….
A lot of people usually think that the Reactive Suspension will induce more vertical acceleration to the chassis in one wheel bump situations. WRONG!
I will respond by saying that since the two systems are equivalent in roll and heave rates, the vertical acceleration of the chassis will be the same.
This can be explained by the fact that conventional suspensions will resist the bump with both springs since the torsion bar is linking one rocker to the other.
However, there is an important disadvantage due to the fact that since the torsion bar is biasing the opposite wheel upward, and since the wheel has a relative low inertia, it will be easily lifted off the ground losing contact patch load. So much for performance!
In the case of the Reactive Suspension, the added contact patch load when one wheel is passing a bump is transmitted directly to the chassis in two distinct path.
-via the spring that is being compressed
-via the roll lever as energy is being stored by the moment generated around the pivot of the Roll Lever (RL).
Note that nothing is biasing the laterally opposed wheel upward other than if the elevation of the chassis is changed. Since the inertial of the chassis is high, chances are the laterally opposed wheel will remain on the ground.
In how many more ways do I have to say this suspension system is better?!
PACKAGING :
There are now many options for packaging the system. It can be put as commonly seen on top of the car or vertically in front of the driver’s feet. In fact, I proposed this vertical arrangement to various racing teams between the two seasons. In fact, it would be possible to have all the heavy stuff such as the dampers, vertically mounted near the bottom of the car.
If passive hydraulics were more popular, it could be remotely installed under the driver’s legs. If that was done, I would go as far as proposing to link the front and back in the same way that the system is linking the left to the right. Let’s walk before we run!
