Penske 8780 shock

[hardingfv32]

The new Penske 8780 shock is five way adjustable. What would the five adjustments be?

Brian

[WilO]

HS bump/rebound
LS bump/rebound
gas preload

[ubrben]

LSC/HSC/LSR/HSR/Inerter?

http://www.racecar-engineering.com/arti ... uspension/

Ben

[hardingfv32]

I thought I would start with an easy question before moving on the what a 'hybrid inerter, (8780-H)' might be.

Brian

[WilO]

apologies, Ben is of course, correct. I should have known that....I saw that article recently.

[DaveW]

I would have expected that a Penske person might have replied to Brian's post. Sadly, not.

Penske's literature suggests that the 8780 can be configured to be all things to all men, but perhaps not all at the same time.

I am reasonably sure that the configuration shown in Ben's reference is a relatively conventional "shimmed" damper with no inerter. Fundamentally, that would have 2 compression & 1 rebound adjustment, perhaps with an add on "regression" adjustment in compression (&, perhaps, rebound). In the examples I have seen, adding an integral inerter replaces the rebound adjuster (perhaps that would be the H variant?).

[hardingfv32]

adding an integral inerter replaces the rebound adjuster (perhaps that would be the H variant?).

1) This is the same mechanical style inerter that we have discussed before? It is now compact enough to be added to the internals of a large body shock.

2) Have you actually worked on a system with an inerter? Is the user friendly for an suspension expert?

Brian

[DaveW]

This is the same mechanical style inerter that we have discussed before? It is now compact enough to be added to the internals of a large body shock.

Yes & yes. To be fair, with an unknown vehicle, I would choose a rebound adjuster over an inerter, but perhaps one of the configurations of the 8780 overcomes that limitation.

Have you actually worked on a system with an inerter? Is the user friendly for an suspension expert?

Yes, several & kind of. It is two seasons since one team used them to win a series championship - don't ask...

[JACKHOLE]

Got anymore information on these? Sound interesting. Are there teams using these or still using a j-damper?

[DaveW]

Damper design, build & support is a fairly specialist skill. Packaging is another fairly demanding activity, especially in the F1 world. For those reasons, several teams design their own dampers using internals provided by damper manufacturers.

There are companies that bridge the two activities, designing & manufacturing bespoke dampers supplied in packages agreed with each the team. Multimatic is probably the most active. Others, e.g. Penske, Ohlins, Koni, & Sachs are also players. I would guess that the Penske 8780 is an attempt to provide the hardware for "bespoke" designs, but I have been unable to unearth details.

Both Multimatic & Penske (perhaps others as well) supply internal inerter (j-damper) options.

[hardingfv32]

Is the internal j-damper (mechanical) a Penske produced item?

Brian

[DaveW]

The all important ball screw of a mechanical inerter is a specialised supplier item. The rest is fairly straight straightforward. Inerters have been designed and manufactured several "damper" suppliers and race teams (including a junior race team). Incorporating an inerter inside a damper is a packaging exercise that was first accomplished by Multimatic, I believe.

[GSpeedR]

Dave, do you have idea of how the in-damper inerter is configured? I wonder if the resultant inerter forces are in series with the 'normal' damper forces or with the gas spring force(?).

[Pierce89]

I thought the only reason for these, was the Indycar rule allowing inerterters, but only if contained in the shock body. If this setup was better I don't imagine the F1 teams would be using their 3rd member style inerters.

[DaveW]

Dave, do you have idea of how the in-damper inerter is configured? I wonder if the resultant inerter forces are in series with the 'normal' damper forces or with the gas spring force(?).

In a good damper (with a correctly sized & loaded reservoir) the gas spring force of a non-through rod damper should constant, and equal to the charge pressure multiplied by the rod area. It acts exactly like preloading a spring, and has (or should have) no impact on the dynamic behaviour on the suspension.

An inerter acts (normally) directly across the damper. It generates a force proportional to its "equivalent mass" times the acceleration on one end of the damper relative to the other. In a similar way, a (coil over) spring generates a change in force proportional to the displacement of one end of the damper relative to the other, and an ideal damper generates a change in force proportional to the velocity of one end of the damper relative to the other.

Hence a suspension transfer function, comprising spring stiffness K, inerter equivalent mass M, and a damper strength C, can be written

,

where is the frequency, and is the square root of -1.

This demonstrates that an inerter acts to reduce the dynamic spring rate at low frequencies. It has a number of other characteristics, useful or otherwise, & interesting things start to happen when the dynamic spring stiffness becomes less than zero...

I hope this helps.