I thought that mass damper and inerter were the same thing.
Thank you. It's true that you never stop learning.henry wrote: ↑Fri Sep 11, 2020 12:25 pmThey’re not the same thing. The inerter is attached to the suspension and is driven actively by it. A mass damper is connected to the chassis and moves passively.
They are both intended to control,indirectly, the relatively undamped vibrations of the tyres.
Mass dampers are banned now,inerters will be banned in 2022 when, in theory, the 18” tyres will be stuffer and more intrinsically damped.
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 Omega is the frequency, and I 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...
There is no natural frequency for an inerter, but there is also no natural frequency for a spring until it's connected to a mass.Mudflap wrote: ↑Sat Sep 12, 2020 2:06 amIs the implication that with an inerter there is no fixed natural frequency ?
So whenever the system would resonate, the acceleration across the inerter would increase the load adding to the effective (apparent) mass and decreasing the natural frequency ?
On a second thought no it won't, it would just increase the apparent mass of the wheel by a fixed amount and lower it's natural frequency a bit.
Is that the whole point of inerters?
I wonder if the 2022 cars will lose a lot of the ability to ride the kerbs that is such a feature of current cars?10.2.6 On each axle, the state of its suspension system must be uniquely defined by the rotation, and angular velocity of its two rockers. Inertial and hysteresis effects are acceptable provided they are incidental.
In addition, the following systems or configurations are not permitted:
a. Any response of the suspension elements to body accelerations and/or angular acceleration of the rockers (e.g. any inerters, mass dampers, acceleration-sensitive valves in the dampers).
Same.thisisatest wrote: ↑Sun Sep 13, 2020 4:14 amMy understanding is that the use of inerters is driven mainly by the tires with tall, soft sidewalls. Their lower natural frequency (for a tire) approaches the relatively high frequency (for a car) of the suspension, kind of meeting in the middle.
With the introduction of 18in wheels and tires, the need for inerters should be greatly reduced anyway.
How does increasing the effective unsprung mass effect the whole system, what benefit does it bring? And is this a secondary effect to what DaveW mentioned, where the effective spring rate changes with frequency?Tim.Wright wrote: ↑Sat Sep 12, 2020 11:24 amThere is no natural frequency for an inerter, but there is also no natural frequency for a spring until it's connected to a mass.
Correct that it simply increases the effective unsprung mass. It's a reflected inertia type problem where the additional unsprung mass is equal to the rotational inertia of the inerter rotor multiplied by the square of it's motion ratio.