Explaination of McLaren J-Damper = Inerter

[ReubenG]

IMO one of the most interesting features of the inerter is that it can increase the effective inertia of the suspension system, without adding significantly to the mass. Also as it applies force proportional to relative acceleration of two nodes, it decouples suspension roll and bounce nicely.

[mep]

There are several references to the electrical R C I network,
but which role plays the inerter at this system.

I think the damper must be R.

So spring is I and inerter is C.
Is this true?
Or can the inerter also be I,
and it does not matter what is C and I.

I searched for a patent where it's explained how it is mechanically working:
http://www.patentgenius.com/patent/7316303.html

[Carlos]

Here's a quote explaining how it works from the Cambridge University release ben_watkins supplied:
http://www.admin.cam.ac.uk/news/dp/2008081906
"The inerter looks superficially like a conventional shock absorber, with an attachment point at each end. For example, one end may be attached to the car body and the other to the wheel assembly. A plunger slides in and out of the main body of the inerter as the car moves up and down. This causes the rotation of a flywheel inside the device in proportion to the relative displacement between the attachment points.

The result is that the flywheel stores rotational energy as it spins. In combination with the springs and dampers, the inerter reduces the effect of the oscillations and thus helps the car to retain a better grip on the road.

Though they remain the preserve of F1 for now, inerters have many other potential applications. In time, they could extend far beyond the realm of motorsport and be incorporated into conventional road vehicles and motorcycle steering systems, to name just two areas."

You may remember checkered kindly supplied links - which document the development of the inerter all the way back to 2002 - see his post from May 20th 2008:
viewtopic.php?f=6&t=5426&p=74928&#p74928
The titles of the papers are quite specific:
Synthesis of Mechanical Networks: The Inerter
The Inerter Concept and Its Application
Performance Benefits in Passive Vehicle Suspensions Employing Inerters
Positive Real Synthesis Using Matrix Inequalities for Mechanical Networks: Application to Vehicle Suspension

[pgj]

This a terrific discussion with some fascinating information.

Does anyone have a handle on the size of these units? I assume that the the amount of liquid in each unit is quite small, but it is just a guess.

[Ian P.]

I doubt the unit has much liquid in it at all. Just enough to lubricate the moving parts.
As for size....yes it does matter. The indications are that they have got it down to the size of a conventional damper (shock absorber for us NA types).
What I would like someone to clarify, this device absorbs energy from the movement of the suspension and rather than translating it directly into fluid movement and heat as a conventional damper, it converts it into potential energy in the form of a spinning mass. Absolutely brilliant. But how is this energy disipated?? There must be an adjustable means of adding friction to the spinning element (slow it down and dissipate the energy) or it would simply reach a peak spinning velocity and become none functional. This just screams for interractive electronic control....npi (no pun intended). Maybe the addition of a suitable liquid could achieve this.
When Renault got trounced for the hydraulic Mass Damper, they were using it as an isolated chasis damper mounted in the nose of the car. It was not connected to the suspension. I was surprised this got as far as it did because the rules prevent the addition of ballast in the nose and it is only a minor leap to infer this is part of the sprung part of the car that can move. Interesting that this is still a viable and accepted device so long as it rotates rather than just translates. The J Damper may well have some application in chasis mass dampers as well as suspension movement control.
One wonders if the F1 cars were not able to get under the weight minimum (ie. utilize balast) would there be as much interest in devices such as this that can effectively be added to the car without any weight penalty. KERS may shed some light in this area next season.

[bazanaius]

another example fro mrace-car engineering

http://www.racecar-engineering.com/alla ... -work.html

[repaf1]

What I would like someone to clarify, this device absorbs energy from the movement of the suspension and rather than translating it directly into fluid movement and heat as a conventional damper, it converts it into potential energy in the form of a spinning mass. Absolutely brilliant. But how is this energy disipated??.

To add to this question, how is the rack coupled to the flywheel. When Terminal 2 (Node2) moves due to road input, it moves the rack, which in turn, spins the flywheel. But doesn't Terminal 2 (Node2) have to return back to it's original position, like other suspension components do??? When it does return, what does the rack do to the flywheel, will it spin in reverse?

I can see how the inerter absorbs energy and places it in a flywheel, but how does the rack return to its original position without reversing the rotation of the flyhweel?

[DaveKillens]

The rack end is fixed to the movement of the suspension, and it would be continually moving in and out, and spinning the flywheel to and fro. The rotation and direction of the flywheel is directly proportional to the movement of the suspension.
My question is whether there is an inerter fixed to each corner of the car, or located where the third spring is, and basically moves relative to the pitching of the car. But then again, and a third option, maybe there are six inerters for the suspension...? Two, four, or six inerters per car?

[RacingManiac]

I am under the impression that the device moves as the suspension moves, in the same direction as the suspension. The idea is that the movement loads up the device, spins the flywheel as the vehicle takes a set going into a corner, or diving underbraking, or squating under acceleration. That energy stored by the inerter is dissipated when other inputs are added to disturb the chassis movement from its intended direction(bumps, curbing, washboarding near the braking zone...etc) will have to overcome the stored energy(or inertia is more appropreate) before it can upset the chassis. Its like adding inertia to the suspension system without adding actual mass. Kinda like adding downforce to the car to get more grip but not actually adding mass. And since you can tune your inerter to react to certain frequency of input, you can isolate the wanted movement of the vehicle rolling, and pitching(generally lower frequency and slower speed), from the extraneous, higher frequency(and speed) input of bumps and road profile. So that the vehicle can change direction in a S-curve or a chicane, but won't be affected by the sharp bump and curbing as is negotiating those turns....You can probably attach the 2 terminals, one to each corner of the chassis like the existing 3rd damber, and it should react to roll, pitch, and also single wheel bump. I'd imagine F1 teams runs 2, one at each axle. And If Peugeot's Le Mans car have it as well, they only have it upfront hidden in the monocoque, since nothing of the sort was seen at the rear...

[timbo]

There are several references to the electrical R C I network,
but which role plays the inerter at this system.

I think the damper must be R.

So spring is I and inerter is C.
Is this true?
Or can the inerter also be I,
and it does not matter what is C and I.

I searched for a patent where it's explained how it is mechanically working:
http://www.patentgenius.com/patent/7316303.html

From the .pdf version inerter (mass) is C. One thing that makes me wonder is why current is chosen as analog to force. Ain't it more logical that it is voltage that is force?

[pipex]

From the .pdf version inerter (mass) is C. One thing that makes me wonder is why current is chosen as analog to force. Ain't it more logical that it is voltage that is force?

I think that the use of the Force-Current analogy instead of the Force-Voltage one is because the former maintains a direct equivalence of the mechanical elements to the electrical ones (resistor-damper, capacitor-mass, inductor-spring), including connections (wires) => electric circuit == mechanical circuit. The latter is a bit more involved. This way it makes the compensation admittance easier to obtain and mechanically realizable, providing the correct grounding of the masses. Then the problem of the mechanical ground is presented and the inerter is proposed as the solution. Then you can design a complete realizable mechanical compensator based in electrical circuit theory. That is what i understand.
Maybe the same is applicable in the other analogy, but not as direct or clear, or it could be not realizable. This is the same as in electrical circuits, the voltage is the dual of the current. This could lead to a (non realizable?) dual of the inerter with other applications?

[riff_raff]

J is the symbol typically used to denote polar moment of inertia. Since McLaren's dampener employs a flywheel, calling it a "J dampener" seems quite logical.

Of course, flywheel dampener devices are nothing new. I worked on the design of the docking base used for the US Space Shuttle and Russian Mir rendezvous. That docking base mechanism employed several flywheel dampeners to absorb and dissipate the momentum forces caused by the Shuttle bumping into the Mir during docking.

[Powerslide]

The main advantage of it (the mass dampener) on the Renault system was in controlling the wheel oscillations riding over the curbs and I think the purpose of the inerter is the same. As timbo suggested it deals with frequency, the quick spike of movement going over curbing. The movement of the wheel accelerates the flywheel (via a screw) and the inertia of the flywheel consumes the added energy of the quick movement of the wheel over the abrupt change. That's my story and I'm sticking to it.

See if these don't help:
http://en.wikipedia.org/wiki/Moment_of_inertia
http://en.wikipedia.org/wiki/Rotation_a ... fixed_axis

i believe this is its main aim as well

[Just_a_fan]

Holy thread revival, Batman!

[Cold Fussion]

While we are here, how come we don't tend too see (as far as I'm aware) Inerters on road cars (even super cars). Is it purely a cost thing, or is it something like the inertier coefficient is too sensitive to be used on the very varied conditions on a road as opposed to a race track?