Hetzer preselect gearbox compared to Ferret

[David Herbert]

Ok,
From the above it can be seen that each side functions separately. Slowing one side does not speed up the other so there is no regeneration unlike a controlled differential (Sherman / Stuart) or Merit Brown (Centurion / Cromwell etc).

The two outer bands are simply brakes to stop that track.
Each side has a clutch which is spring engaged like a car clutch. If engaged with no brakes applied that track is in high gear (normal for straight running).

Clutch disengaged with no brakes gives neutral which if the other side is still in high, will result in a gentle turn towards the side in neutral depending on road conditions. However on a down slope the vehicle will turn the other way which can be exciting.

Clutch disengaged and the inner brake band applied will give low gear to that track resulting in a geared turn (if the other track is in high) of a radius depending on the gear ratios.

It is possible to design the controls so that it is possible to have one track in neutral with the brake applied and the other in low, resulting in a pivot turn with one track locked but it seems from Malcolm's earlier post that that has not been done here. On Crusader it was relatively easy as the brake bands were air operated so all that was needed was a rather ingenious valve block.

The Praga-Wilson main transmission I think is a five forward one reverse unit, very similar to those used in cars and buses in the UK.

I do not know what the units are on the front of the engine.

David

[Richard Farrant]

Originally Posted by David Herbert

I do not know what the units are on the front of the engine.

David

Hi David,
I was intrigued to know what the two items were on the drive end of the engine. Using a german to english translation on Google, it seems one is flywheel (logical) and the other means 'sliding clutch'. No doubt some else knows more on this.

[David Herbert]

Centrifugal clutch possibly ?

Sorry, I could have googled it too but was too lazy !

If it is a centrifugal clutch it might be stuck from lack of use which might explain why it is necessary to engage neutral to avoid stalling.

Also I should have thanked Tobias for joining in.

David

[Richard Farrant]

Originally Posted by David Herbert

Centrifugal clutch possibly ?

Sorry, I could have googled it too but was too lazy !

If it is a centrifugal clutch it might be stuck from lack of use which might explain why it is necessary to engage neutral to avoid stalling.

Also I should have thanked Tobias for joining in.

David

David,
There is another word before before 'sliding clutch', which is Sicherheilts, which translates as Safety, so safety sliding clutch. I think centrifugal is most likely as it does not need a separate control.

Yes, thanks to Tobias for the interesting diagrams and welcome to the forum.

[leo tomaiolo]

this is in response to the question about turning in the 'Hetzer'. i have had the pleasure of driving both the Hetzer and Shermans. i don't have much on the technical information of the wilson gear box but i appears as though it's being covered. the Hetzer in question is owned by the American Heritage Museum. it's quite a good runner and very nimble. i my opinion it's as maneuverable as the Sherman all day. the Hetzer has a 2 stage steering. trying to remember how it goes but i believe as the steering controls are set to high speed turning normally and when engaged the steering has a much tighter 'feel' and turns much more responsive. the Hetzer was originaly from the Littlefield collection. it started life as a G13 and was converted back to war time configuration. it has the 6 cylinder petrol engine and 5 speed gear box. i've included some pictures. if you look at the steering controls you will see a button that gets pressed with your thumb to engage the hi/low steering. a side shot of the transmission and drivers postion. last up, me driving and a shot of my truck with my ford.

[Malcolm Towrie]

Fantastic information, Tobias. Thank you very much.

Here's a video I took of the operation of the steering and brakes before I got this info. I'm sure the above will answer my questions.
Malcolm

https://youtu.be/E8c9TRP9nSA

[Malcolm Towrie]

My interpretation of googles interpretation of the first schematic is the flywheel has an integral safety torque limiter, in other words a slipping clutch to protect the drivetrain, rather than a centrifugal clutch. Quite unusual. Maybe because the Wilson gearbox will engage with a helluva bang if some effort is not made to rev-match to the selected gear.

The thing to the right of the flywheel translates to be a step-up or step-down gearbox.

The clutch operation that puzzled me in the video seems to have the effect of disconnecting the steering drum from the drive shaft during gear steering operation to allow gear reduction, and the combined effect of braking the track and disconnecting the track from the drive shaft during brake steering operation.

Malcolm