Thursday, April 16, 2015

Torsion Bar Explanation

The torsion bar at the end opposite the swing arm is fixed (no need for lubrication). It ONLY reacts the torsional load from the bar. This torsional load is not very high, so the fitting does not need to be very large. Yes, if you drew a stripe on the outside of the bar you would see it twist as the roadwheel moves up and down. At the fixed end the stripe would not move, at the swing arm end you would see a lot of twisting motion (matching that of the swing arm).

The side with the swing arm has a large bushing (or bearing) that reacts ALL the loads EXCEPT torsion. This means it must support the weight of the tank plus any dynamic loads imposed by the roadwheel as it goes about its gyrations, side loads, impacts, etc. This is the part that requires lubrication. Since this fitting takes the majority of the load, it is physically larger.

 If you have access to an old Volkswagen Beetle, take a look at the torsion bar front suspension. It is identical in principle.

One end of the bar is set into a fixed splined holder, that's welded to the hull. The other end splines into the pivot that holds the wheel. The bar is under stress, at REST. This is what gives the suspension spring--so that there is controlled arc motion, both up and down.

The rows of bars are staggered so that each adjacent bar operated the opposite side road wheels. Two shock absorbers is all that is normally needed per side. One on the front wheel, one on the back. These help control pitching and dampened bumps.

Both ends need lubrication because the bar actually twists when force is applied to it (wheel moves up and down). Therefore, the entire bar undergoes torsional motion.

The Panzer III chassis and the Panzer IV chassis were designed around the same time. The torsion bar suspension was chosen for the Pz III and the leaf springs, for the IV. It ends up that the torsion bar suspension (for the weight it's supporting) had better off road handling, than the leaf spring suspension.

Torsion bar suspension allows for simpler interleaved road wheel design. This improved the off-road handling, up to a point. Also, eliminated the need for return rollers (and all their inherent problems).

Longitudinal torsion bars, like the Porsche Tiger I style, are quite complicated, fragile, and subject to failure. So many of the vehicles carrying this type of suspension (Tiger I, Ferdinand, etc)---were reverted back to the Henschel traverse torsion bars, in later models.

The bar end that is housed into and across the hull fits into a pug which has splines machined in it this pug is commonly referred to as an anchor or anchor pug as in not moveable…anchored, normally the pug is bolted in a mounting point in the hull (it’s nice to be able to remove a damaged pug without using a welding torch)The roadwheel arm spindle also has splines machined in it to secure the bar to it, both the pug and the spindle end of the bar have a "blind-spline" that matches a "blind-spline in the anchor pug and roadwheel spindle, this is used to align the roadwheel arm at the proper angle to the ground...oh ya torsion bars are marked to show the direction of twist, the spindle end twists and the anchored end is held fast...why you don't see it used in the early tank models I would guess is because the machine tool manufactures had not yet developed a multi-spindle boring machine needed for accurate finish spindle holes boring of the hulls, these came later.

Panzer III

Tiger I

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