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Old 03-11-19, 06:07
Malcolm Towrie Malcolm Towrie is offline
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Join Date: Aug 2015
Location: Whitby, Ontario, Canada
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Quote:
Originally Posted by David Herbert View Post
Hi Malcolm,
If there was a fluid flywheel or clutch, it would be between the engine and the Wilson gearbox, not between the gearbox and the steering system.

Also the selection and engagement of gears in any Wilson box is done by engaging the band brake for that gear. Thus the selection and the clutch is combined into one action as there is effectively one clutch (the band brake) for each gear. When you press the pedal down fully, any brake band that was engaged is released (which is why you need to press it all the way down) and on raising the pedal the next selected gear is engaged. Only one new gear can be selected at a time as there is a hinged sprag for each brake band that only engages if pushed out by a cam. All the cams are on a shaft that is turned by the gear selection lever and only one sprag is pushed out at a time. So the CHOICE of gear is controlled by the gear selector lever and the disengagement / engagement by the gear change pedal.

I have no experience of Pz38t but I thought that the steering was similar to the system on British Crusader, ie a bevel box (no differential) to turn the drive 90 degrees and then epicyclic / band brake steering units inboard of each final drive to give: High, low and stop separately for each track ( or at least drive and stop). There must be brakes that work together for stopping the vehicle and on a small tracked vehicle designed in the 30s it would be very unusual for it not to be possible to engage them separately to give a pivot steer.

I expect to be corrected about the steering system so if anyone has a nice drawing of the system used in a Hetzer it would be great to see it.

David
David, I messed up, didn't I. I can only attribute it to the lateness of the hour.

Yes, I'm familiar with how a Wilson preselect works (and a brilliant design it is), I just didn't word that second paragraph very well. I meant the Ferret doesn't need to use the bands as a clutch, in fact the manual warns against it, IIRC. So the gear selected for pulling away is selected, the gear change pedal is pushed down, the selected gear engages, the pedal is let up quickly so the band bites quickly, avoiding slippage, and the fluid coupling prevents the engine from stalling.

But the Hetzer appears to use the band as a clutch when pulling away from a stop. As I said, you have to select neutral (actually "0" on the plate) before letting up the gear change pedal at a standstill or the engine will stall.

Your description of the Crusader steering is interesting. That may be the design used in the Hetzer as the "differential" casing is surprisingly compact. It being a simple bevel box would explain that.

The Hetzer has brake drums outboard of the steering drums but as far as I can see, there is no way to brake individual drums to allow pivot steering. I'll double check.

Malcolm
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