Roll center height for active suspension leaning INTO corner

[g-force_addict]

What would be the optimal roll center height for a car with active suspension making it lean INTO corners?

My guess is the lower the better.
Roll center below ground so it shifts center of gravity slightly into the corner.
Or course it shouldn't be so low that the left side scrapes the ground.

[Lycoming]

what do you mean making it lean into corners? low roll center heights are popular because they lower the jacking force.

[Jersey Tom]

It's my sincere hope that some day more people will realize jacking forces aren't inherently good, bad, or evil. They're just there. Sometimes you want LOTS of jacking force. Sometimes you don't.

[Raptor22]

indeed, what you want is dependant on the tyre load at that point in time. Over loading a tyre does not make it last long even if the strategy is ultimate performance and not longevity

[Jersey Tom]

Not sure I follow your line of reasoning with "overloading" tires. Jacking forces don't change the steady state load transfer (as a primary effect anyway), they just try to change the orientation of the body.

[olefud]

indeed, what you want is dependant on the tyre load at that point in time. Over loading a tyre does not make it last long even if the strategy is ultimate performance and not longevity

The roll center won't change the total weight transfer though it can increase the weight transfer at one end while decreasing it at the other end. Max tire traction is usually with equal tire loading at all four corners. However, to balance a car for under/oversteer by changing the roll center at one end, max traction may be compromised yet provide better performance.

Jacking is another question.

[Tommy Cookers]

Am I the only one who finds the original question ambiguous and contradictory ?

With Active why would one want to lean into corners ?

With Active surely the suspension geometry is quite unimportant ?

[Jersey Tom]

With Active why would one want to lean into corners ?

Think the intent there is active camber control / positive camber on the inside wheels while cornering. Depending on the vehicle and tires, may be a monstrous lot of work for little gain.

[Tim.Wright]

Am I the only one who finds the original question ambiguous and contradictory ?

With Active why would one want to lean into corners ?

With Active surely the suspension geometry is quite unimportant ?

It depends what is actually active. If its only active ride, then the roll centres still affect the amount of load going throug the ride actuator so they are important.

If you have active ride and active kinematics, perhaps they are not so important.

I'd say there are more gains to be made using active ride by controlling the things you cant see (forces) compared to what you do see (body roll ). After all, the primary purpose of roll centre analyses are for load transfer calcs not just roll angle calcs.

Tim

[olefud]

From a wealth of ignorance, it would seem that active ride control would be useful with a road vehicle in allowing a boulevard ride while reacting to demanding cornering with a bit more resistance. For competition ride height control for aero purposes makes sense. What other benefits are there?

[GSpeedR]

From a wealth of ignorance, it would seem that active ride control would be useful with a road vehicle in allowing a boulevard ride while reacting to demanding cornering with a bit more resistance. For competition ride height control for aero purposes makes sense. What other benefits are there?

The ability to actively change lateral balance based on feedback from chassis sensors is certainly a benefit. Algorithms to assist the driver, to prevent loss of control (stability), and to control dynamic cross-weight and chassis platform can be used. It is quite a challenge to have many algorithms acting at once, particularly with 'only' 4 corner actuators to work with. Coherence will suffer when control bandwidths overlap so there should be a hierarchy present for competing systems. For example, a system set up to control ride (body motion, tire load variation) may compete with a system controlling aero platform, especially if vehicle modes creep into the lower frequency ranges. The aerodynamicist would obviously prioritize chassis platform.

[DaveW]

Aerodynamicists do what aerodynamicists do...

The "challenge" you described is helped by implementing a "modal" suspension, allowing spring & dampers to be set-up independently, and position error control loops to be set for each mode. The error control loops can be set quite fast if no motion is expected - one reason for demanding no roll. The other reason is that both roll out & roll in requires transient roll response, neither of which is actually a virtue...(it is fair to say that we worried about that before the event, mistakingly thinking that a driver might need roll for control purposes).

[GSpeedR]

Very true, DaveW. However I would imagine that the unsprung degrees of freedom still pose problems even with a modal scheme, especially if stiffness ratios (effective suspension stiffness/tire stiffness) become large and high downforce levels are required. I realize that you wrote 'helped' rather than 'solved', and I don't want to appear argumentative as my experiences in this field are limited.