What the 'Fric' is it?

[gt6racer]

Riderate is correct in that these systems can be set up for different purposes. You can go for increased roll/pitch stiffness at similar wheel rates to the base car, or go for similar roll/pitch rates as the base car and then achieve significantly reduced wheel rates.
The WRC application by Citroen was for sure both axles, and used interlinked mechanical roll bars. (It had no pitch contribution - that wasn't so important in this arena). As riderate correctly noted, it's the low wheel rate, and resultant more even wheel loading, that offered the benefit, resulting in a chassis less upset by the terrain under the car. In Loeb's words in 2005 "One of the Xsara’s strong points is its polyvalence – its ability to adapt quickly from one terrain to another… Its balance is simply remarkable.”

[DaveW]

... at similar wheel rates to the base car

Forgive me, but what precisely does this mean. I'm afraid to me it implies similar vertical spring rates - if so, and thinking only of one axle for the moment, in what way does the response differ from the same low vertical spring rate coupled with a stiff (mechanical) bar?

If I'm correct, then the major difference between the Kinetic system & stiff bars is that the former tries to minimize warp load. This may not be an issue for a rally driver (see above), but it might be for a circuit driver if the vehicle lacks lateral balance.

On the other hand, if the vehicle does have a natural balance, then the Kinetic system should be able manage changes in single wheel road inputs far better than a stiff bar solution....assuming it is working as intended.

[gt6racer]

Hi Dave,
I'm sorry that my terms are confusing - this is often a point of discussion. I hope this helps....
Let's assume for now we decide not to reduce the heave spring rate. ( If roll stiffness is the dominant factor, we could elect to soften the springs and put more on the roll system.)
We can look at the situation in two ways.
First we can look at body fixed. The corner spring is not impacted, with or without the system, so its contribution stays the same with or without the system. For the WRC type system, the front and rear bars are effectively now in series, and so the effect at the corner being measured will be to show a lower rate than the base car. There will now also be a load change at the other wheels, ( Vs only the one opposite the moving one for a base car) but of course no displacement since body is fixed. So in this case, there is no warp - but there is an impact to the wheel rate.
The second case is that the car body will move when a wheel is moved upwards -ie body free. Now you'll see more benefit as the front bar will drive opposite motion in the rear bar, balancing out the wheel loads, reducing the pressure in the bar system, and hence reducing the effective stiffness of the lifted wheel.
Which case is most applicable to reality changes by the situation. Rock crawlers will see the second case. A high speed racecar might not see much body movement, but there's benefit either way.

[Smokes]

Spring return side of fail close hydraulic actuators of used in subsea equipment, a majority of the the fluid is taken up in the pipework.It is used to keep the pipework and actuators at hyperbaric pressure subsea and prevent hydraulic locking.Trapped air will cause more issues than entrained air.

http://www.perar.it/?page_id=934 click for a idea about what they look like.

[DaveW]

Thanks, gt6racer. Your post explains it well....

[DaveW]

So your point is that someone once put this concept together in a poorly designed fashion? How shocking.

Just noticed the "calibrated flow restrictor" in this diagram. Perhaps it is the cause of the high rear friction/stiction - it does have the characteristic of a blind preloaded shim valve.

[gt6racer]

Dave, the damping valve can be of any type - so depending upon the speed you measured at, you could possibly have been seeing some damping.
High stiction/friction is not inherent to this type of technology (no more than a mono tube). The WRX is a strut suspension and is not ideal for the technology implementation - similar to the challenge of building a mono tube based strut. It requires a dry (greased) bearing which is subject to the strut side loads, and perhaps that challenge wasn't well addressed on the car you saw.

[DaveW]

The WRX is a strut suspension and is not ideal for the technology implementation - similar to the challenge of building a mono tube based strut. It requires a dry (greased) bearing which is subject to the strut side loads, and perhaps that challenge wasn't well addressed on the car you saw.

Agreed. But the standard WRX isn't a disaster (I guess the springs would be offset to minimize bending moments). The vehicle wasn't any old vehicle, it was built as a demonstrator for the technology. I think the system was similar to the one you described.

A picture is worth a thousand words.... Here is a plot of the estimated damper load/velocity trajectories, green front & red rear. The input was a swept sine heave, starting at 0.5 Hz and sweeping upwards. Load is in Newtons, velocity is mm/sec. Load variations with no damper movement is a good indication of friction.

The front is typical for a strut suspension, although the friction is quite high compared with a standard WRX.

The rear is locked initially. When it finally starts to move the apparent friction falls, suggested that once the friction is overcome, it takes time for it to reset. The characteristic is reminiscent of a pre-loaded shim valve (which requires time for the fluid boundary layer to be ejected after the valve closes, during which time it still leaks fluid).

The corresponding frequency response functions show that the rear response is affected at frequencies below 2 Hz (which would be expected include both heave & pitch vehicle modes). It follows, it think, that both modes are effectively controlled by the front dampers only.

Arguably, the devil is in the detail...

p.s. Here is a plot of the roll & warp response functions. They show that warp is well controlled, presumably without help from the rear suspension (Note: the displacements are measured between the body & wheel at both axles). It is impossible, I think, to estimate the effective roll stiffness, however.

[DaveW]

Here, if you have the patience to wait, is a contribution to the FRIC debate.

I have some difficulty reconciling these ideas with those of mep, or RideRate. Any thoughts?

[JACKHOLE]

The rear is locked initially. When it finally starts to move the apparent friction falls, suggested that once the friction is overcome, it takes time for it to reset. The characteristic is reminiscent of a pre-loaded shim valve (which requires time for the fluid boundary layer to be ejected after the valve closes, during which time it still leaks fluid).

Dave, I am Having a hard time wrapping my head around this wondering if you could explain a little more or an example. I haven't heard of this before.

I know its a little off topic.

Thanks, JACKHOLE

[DaveW]

You might like to look here.

[RideRate]

Here, if you have the patience to wait, is a contribution to the FRIC debate.

I have some difficulty reconciling these ideas with those of mep, or RideRate. Any thoughts?

Could we get that vid embedded somewhere to make it easy to watch?

[DrewP]

All through this topic there's talk of load being helped by FRIC's actions. From what I know of load transfer, it's not impacted by suspension per se (it'd have the same value on a rigid and a softly damped chassis), which can only impact the speed at which it happens.
With that in mind mind doesn't FRIC only minimise susp. movement (roll/pitch), thus helping aero and suspension geometry, but not changing load transfer, thus not affecting the amount of grip each wheel has (other than said positive effect on geometry))?

Please correct my way of thinking as it's a similar conundrum that's bothered me with road cars, such as Porsche's PDCC, which many motoring hacks cite as a way of reducing load transfer, rather than roll/pitch.

[DaveW]

Could we get that vid embedded somewhere to make it easy to watch?

You could download it & then watch it at your leisure - VLC should play it.

All through this topic there's talk of load being helped by FRIC's actions.

Not load transfer, but down force (aero) control by controlling ride height & rake (also roll, possibly).

[RideRate]

All through this topic there's talk of load being helped by FRIC's actions. From what I know of load transfer, it's not impacted by suspension per se (it'd have the same value on a rigid and a softly damped chassis), which can only impact the speed at which it happens.
With that in mind mind doesn't FRIC only minimise susp. movement (roll/pitch), thus helping aero and suspension geometry, but not changing load transfer, thus not affecting the amount of grip each wheel has (other than said positive effect on geometry))?

Please correct my way of thinking as it's a similar conundrum that's bothered me with road cars, such as Porsche's PDCC, which many motoring hacks cite as a way of reducing load transfer, rather than roll/pitch.

You are right, the main benefit of the system is to control suspension movement and thus has little to no significant bearing on steady state load transfer and the resulting wheel loads. When we say grip we are speaking of the dynamic load variation (at the contact patch) from road inputs and irregularities. This is 'grip' that can be improved via shock and spring tuning since it is a vibrations problem.