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Banish driveline oscillations with inerter technology
  [vote for,

The inerter <link> is an interesting component in automotive engineering. It was introduced to motorsport by McLaren where it was used to counteract the bouncy- oscillations in the suspension that are a big problem in F1 cars with big bouncy tires and aerodynamics that amplify bouncy behavior*. When an inerter is used within the suspension system, upward movement of the wheels is used to generate inertia - for example by spinning up a flywheel. If the suspension is to oscillate it must first slow, stop and then re-accelerate the flywheel in the opposite direction. In this way, it inhibits rate of change not velocity, like a conventional oil damper.

Oscillations also exist in the driveline, an educational example of this is to take a reasonably powerful front wheel drive car, stomp on the loud pedal and dump the clutch. In the absence of fancy electronics etc, what often happens is that the steering wheel will wobble accompanied by some telltale chirruping noises from the tires as you safely pull away**. This is because torque can oscillate between the two wheels dependent on the varying traction and type of differential fitted.

So, fit the differential with an inerter. To do this, each drive shaft drives an idler in the differential rotating cage assembly which in turn drives a flywheel that is essentially coaxial with the drive shaft/cage. With significant up- gearing, this would lead to the flywheel spinning up whenever there was relative movement between the drive shaft and rotating cage, i.e. one wheel is slipping.

This will be particularly good at damping driveline oscillations with the added benefit that it isn't just throwing energy away like viscous diffs, it's all there still in the flywheels. It would be interesting to know how it drives, I imagine it would cause initial turn-in understeer and very stable mid-corner handling on constant-radius corners***. Probably very suitable to a center differential, or something limousiney.

*If the car rises up slightly, the undertray develops less downforce. Conversely if the car squats down slightly, the aero package generates more force pushing it down further. Add in springy tires, energy and any form of initial disturbance and you have an expensive space hopper.

**That was confident, hesitation-free acceleration to the speed of traffic flow officer. I can assure you, any momentary loss of traction was well controlled and almost certainly attributable to the damp road surface at that particular junction, and the 6 previous junctions. The council really should do something.

*** Possibly some strange straightening-out induced oversteer behavior - send lots of budget, and a specced- out S-class, I'll find out.

bs0u0155, Sep 22 2020

Inerter https://www.racecar...nding-the-j-damper/
[bs0u0155, Sep 22 2020]

Differential https://en.wikipedi...(mechanical_device)
[bs0u0155, Oct 01 2020]


       Will the increase in weight and the component on component wear and servicing requirements be worth the amount of bounced torque recovered?* Not to mention the space needed for the design.   

       *The fundumental knock/question of any new mechanical add on.
wjt, Sep 26 2020

       Aren't there any existing components of a car that could be made to do dual duty as flywheel masses? For instance, what if a disk were carved out of, say, a spoiler and made to spin in place, in the existing plane of the spoiler?
pertinax, Sep 26 2020

       Spoiler alert!   

       This will add some significant wear on the clutch.
RayfordSteele, Sep 26 2020

       //This will add some significant wear on the clutch//   

       Thinking about this, I think I need to clarify. Take a look at the first image of the spur-gear differential in <link>, it's a lot easier to imagine than with the complications of bevel gears. We have the gear attached to the drive shaft driving the first smaller gear. Those connect over as a 1:1 gearbox to the other drive shaft.   

       Imagine that first idler shaft penetrates the casing. On the outside it has a larger spur gear connected to the shaft. Mounted on the driveshaft, co-axially with a bearing is a small gear driven by the larger external spur. This is connected to the flywheel. A ballpark mass for this would be 5kg or so.   

       So accelerating straight, you would have to spin that 5kg up to wheel RPM, since it's connected to the differential carrier and in a straight line is geared to it 1:1. I disagree that this will add any significant load to the clutch, there's a lot more than 5kg rotating mass already in the system, and the clutch already has to cope with the forces associated with accelerating the whole car.   

       Where significant forces do come in, is when the wheels have mismatched speeds. In a one wheel slipping situation, assuming the flywheel drive gear ratios are 100:1 (2x10:1) then one wheel being stationary and the other accelerating up to the equivalent of 20mph (340rpm/5.6rps) in 0.5s then the flywheel will be accelerated up to 34,000 rpm delivering about 360 Nm (265 ft/lb) torque to the system/other wheel. That's ball park stuff, but actually better than I thought.   

       *you only need to have an effect on one side of a differential since they're mechanically linked, but having identical sides might be worth it for packaging & symmetry.
bs0u0155, Oct 01 2020


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