2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Tommy Cookers.

You write:

• (afaik the 1924 Mercedes functionality was later emulated by Alfa Romeo in their Tipo B/'P3' and 'Bimotore' cars)
  http://www.grandprixhistory.org/alfa-romeo-bimotore.htm

Quote from https://www.forza-mag.com/issues/154/ar ... ity-clause

Alfa Romeo Bimotore 1935



Some more details:



All this "complexity" was necessary in order to utilize two long engines: an in-line 8-cylinder engine in front of the driver and another in-line 8-cylinder engine behind the driver, with a common gearbox / differential at the middle of the car (the drive wheels were the rear wheels).

I can't see how this architecture affects the inertia torque on the engine casing.



You also write:

• the point of the Mercedes axle is that each wheel/road contact load is unaffected by the engine power being used

Sorry but, again, I can’t get how the Mercedes axle eliminates the inertia torque on the engine casing and on the frame of the car.

A drawing / plot / photo would help.

Thanks
Manolis Pattakos

[Zynerji]

Hi Manolis,

See below a similar concept where the kinematics can be adjusted on the fly to reduce any order. Probably not much use in flatplane l4 where the 2nd order appears to dominate in most practical situations but more appropriate for engine configurations where the dominating excitation changes between inertia torques and gas pressure torques with engine speed.

https://www.google.com/url?sa=t&source= ... 27jRhp3VoZ

Doesn't the MGU-K do this in F1 now? I always thought the K would go into "recovery" mode at certain parts of rotation to counteract these harmonics...

[Tommy Cookers]

Hi Manolis,
See below a similar concept where the kinematics can be adjusted on the fly to reduce any order. Probably not much use in flatplane l4 where the 2nd order appears to dominate in most practical situations but more appropriate for engine configurations where the dominating excitation changes between inertia torques and gas pressure torques with engine speed.
https://www.google.com/url?sa=t&source= ... 27jRhp3VoZ

Doesn't the MGU-K do this in F1 now? I always thought the K would go into "recovery" mode at certain parts of rotation to counteract these harmonics...🤔

it could do something at 1200 crankshaft rpm but seemingly little or nothing at 12000 crankshaft rpm

the K frequency response (wrt self and external load) limit will be about 5 Hz
but the K could be used as an active damper (of an externally-forced cycle)
because the K torque can always respond quicker if the K's not accelerating or decelerating itself


the recovery of the existing passive mechanical (isolation) effects under the conditions of interest is maybe 99.7%

are people thinking of an inline-4 F1 engine ?

NOTE to self - a '3 Hz' system I remember had its 1st order pole designed to 5 Hz (and a '2 Hz' was designed to 3 Hz)

[Zynerji]

Honda said theirs switched 40Hz. Is that really too slow to have this effect? Maybe I'm remembering the MGUH numbers...

[Mudflap]

The switching frequency is not the same as the torque control frequency.
PMSMs can and are sometimes used for active torsional vibration control at low frequencies (100s of hz)

[Tommy Cookers]

K generation equivalent to 40 Hz works as the rate of change of rpm applied by the ICE to the K is acceptable to the K
(ie the electric 'time constant' is small enough to allow 40 Hz - but the electromechanical 'time constant' wouldn't be)

the K won't do the job under discussion if the rate of change of rpm applied by the ICE to the K is unacceptable to the K
ie the K hasn't enough load rejection capability

a K-style electromagnetic 'inertial force absorber' is 95% efficient - a mechanical 'absorber' is eg 99.7% efficient
there's little or no 'inertial force' available to be absorbed in eg an F1 90 deg V6


regarding the Mercedes-style axle (eg in the Bimotore) ....
the axle is unrelated to the twin engines - it was used earlier (as I said) in the Tipo B cars
the twin CWPs appeared in 1914 in what was the first Mercedes GP propshaft-driven axle (1913 M GPs used chain drive)
the twin CWPs were (then) apparently to allow (positive) camber to match perfectly the road camber
we can still wonder what (the honorary Dr and onetime Merc TD) Porsche did for the Mercedes axle design pre 1924
my view (on the axle's USP) came iirc (via sources eg Pomeroy, Clutton ?, and Karslake) from the Posthumous book
eg Pomeroy's book has only the 1914 car
btw Mercedes and Benz nominally had some co-operation from 1924 but actually merged in 1926

[manolis]

Hello Zynerji

You write:

• "Doesn't the MGU-K do this in F1 now? I always thought the K would go into "recovery" mode at certain parts of rotation to counteract these harmonics..."
  and
  "Honda said theirs switched 40Hz. Is that really too slow to have this effect? Maybe I'm remembering the MGUH numbers..."

The plot at the top of the last page:



explains the case.

The gas torque (cyan curve), i.e. the (per crank rotation) mechanical energy provided to the set of the four pistons by the working gas, is seven times (or so) smaller than the inertia torque (white curve), i.e. seven times smaller than the (idling) mechanical energy oscillating between the set of the four pistons and the crankshaft / flywheel / transmission / drive wheels.

Subtracting the gas torque from the inertia torque, it results the combined torque (green curve). The green and white curves are similar in size and shape (i.e. the "counteraction" from the gas is too small).

As for the mechanical energy that can be "milked" from the exhaust gas, it is smaller than the mechanical energy provided by the gas to the pistons.


Regarding the frequency:

At 9,000rpm (i.e. at 9,000/60=150 crank rotations per second, i.e. at 150Hz) where the 1600cc four-cylinder engine operates in the video, the frequency of the inertia torque is 2*150Hz=300Hz.


So, it is not only that the energy contained in the gas (and in the exhaust gas) is too small to seriously counteract (somehow) the inertia torque, but it is also that the required frequency of the "counteraction" is too high to be impemented by some kind of "MGU-K".

Thanks
Manolis Pattakos