Hetzer preselect gearbox compared to Ferret

[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

[Tobias Weibel]

Hi at all

I'm happy to help.
Unfortunately, my technical English is not so good. That's why I can't argue with you.

The two items were on the drive end of the engine are an flywheel and the safety sliding clutch

safety sliding clutch:


Are the Brake Bands new?
It is very important that the brake bands are adapted (grinding)

[Tobias Weibel]

Here is the description of the steering from the manual.
I think it's better if I write this in German.
I don't know which translation program is good.

****************
Fahrt in gerader Richtung

Kein Lenkhebel wird betätigt.
Alle Bremsbänder sind Lose.
Radius- und Ortslenktrommel sind über die Lamellenkupplung (10) miteinander verbunden.
Da beide Trommeln (8/9) fest über die Kupplung (10) miteinander verbunden sind, sind auch die beiden Sonnenräder (12 und 14) über die Ritzelwelle (2) kraftschlüssig.
Beim Antrieb der Kegelradwelle dreht sich der Satellitenkasten (15) mit der gleichen Drehzahl wie die Welle. Da die Planetenräder (13) verschiedene Zähnezahlen aufweisen, können sich diese Räder nicht um ihre eigene Achse drehen..
Folglich dreht sich die Radius- und Ortslenktrommel wie auch die Ritzelwelle drehzahlgleich mit dem Satellitenkasten.

Radiuslenkung

Der Radiuslenkhebel wird zurückgezogen. Dadurch wird:
1. Die Lamellenkupplung (10) ausgekuppelt.
Das heisst die Radius- (9) von der Ortslenktrommel (8) getrennt.

2 Die Radiuslenktrommel (8) durch das Bremsband abgebremst.
Das heisst die Radiuslenktrommel (9) und das kleine Sonnenrad (12) stehen still.

Wenn sich der Satellitenkasten dreht müssen sich nun die grossen Planetenräder (13) auf dem stillstehenden Sonnenrad (12) der Radiuslenktrommel abwälzen. Die kleinen Planetenräder drehen sich drehzahlgleich mit dem grossen. Die Drehrichtung dieser Räder ist dieselbe wie diejenige des Satellitenkasten. Die kleinen Planetenräder (13) wälzen sich nun auf dem Sonnenrad (14) der Ritzelwelle ab. Infolge der Zähnedifferenz des kleinen Planetenräder (13) zum grossen Sonnenrad (14) muss sich dieses Sonnenrad in der Drehrichtung des Satellitenträgers zu drehen beginnen. Bei einer Umdrehung des Satellitenkastens (15) erhalten wir eine Reduktion der Antriebsdrehzahl der Ritzelwelle von etwa einem Viertel. Durch den Drehzahlunterschied der beiden Antriebsräder fährt der Panzerjäger eine Kurve.

Bei gleichzeitiger Betätigung beider Lenkhebel erhalten wir eine Reduktion der Geschwindigkeit. Das Fahrzeug fährt gerade aus.

Ortslenkung

Hebel wird mit eingedrücktem Druckknopf zurückgezogen.
Dadurch wird:
1. Die Lamellenkupplung (10) ausgekuppelt.
2. Die Ortslenktrommel (8) duch das Bremsband (6) abgebremst.
Die Ritzelwelle (2), die Ortslenktrommel ((8) und das grosse Sonnenrad (14) stehen still.

Bei sich drehendem Satellitenkasten (15)wälzen sich die kleinen Planetenräder (13) auf dem grossen, stillstehenden Sonnenrad (14) ab, die grossen Planetenräder drehen sich drehzahlgleich mit den kleinen, in der gleichen Drehrichtung wie der Satellitenkasten.
Durch die Zähnezahlen bedigt, erhalten wir eine Übersetzung auf die Radiuslenktrommeln (9) in entgegengesetzter Drehrichtung des Satellitenkasten. Die Radiuslenktrommel dreht sich mit etwa 4 - 5-facher Drehzahl des Satellitenkasten. Da das Antriebsrad blockiert ist dreht sich das Fahrzeug um die Mitte auf der Auflagefläche der Raupe.

Um eine Beschädigung der Zahnräder des Umlaufgetriebes und denjenigen des Seitenantrieb vorzubeugen, darf die Ortslenkung nur im 1. Vorwärts- und im Rückwärtsgang betätigt werden.

Press the button on the steering lever only in 1st gear or reverse gear.

***************************************

[Niels V]

Possibly you could also reach out to the https://www.facebook.com/thegraebecollection/ they have some experience with that type of gearbox, in their Swedish based Marder replica.

[James P]

Originally Posted by Niels V

Possibly you could also reach out to the https://www.facebook.com/thegraebecollection/ they have some experience with that type of gearbox, in their Swedish based Marder replica.

Bob and his son are great guys, I would also suggest the Ontario museum people contact David C in Michigan, another Hetzer/G13 owner.

[David Herbert]

Tobias,
Once again thank you for your help here. Your technical English is much better than my German or French so I am working just from the drawings and the important instruction not to press the button in any gear other than R or 1.

Malcolm,
As you say the "safety" clutch is only a torque limiter, though I am puzzled why they didn't use a fluid flywheel which was well established technology by then and would have been much nicer to drive.

To re-write my previous post in the light of the video and more from Tobias:

If no levers are pulled the drive goes to both tracks at exactly the same speed so the vehicle moves in a straight line.

If one lever is pulled all the way without pressing the button, the clutch inside the brake drum is released and the brake band nearest the centre of the vehicle tightened giving a lower ratio drive to that track. That side track then turns slower than the other which remains in high and the vehicle turns with apparently quite a large radius.

If one lever is pulled while pressing the button, the clutch is released as above but the middle brake band is applied which, if the lever is pulled hard, completely stops that track causing a pivot turn. It seems that doing this does not change the other track which therefore remains in high. This type of turn requires a lot of power and also tends to promote a skid on a hard surface rather than a turn, hence the instruction to only do it in 1 or R.

In both of these types of turn there must be a brief neutral (clutch released) before the brakes are applied or there will be excessive brake wear. However, in that neutral position the vehicle will turn the wrong way on a downhill slope as that track is no longer holding it back. This can be very dangerous and is a major reason why clutch and brake steering (which this is a form of) stopped being used as tanks became faster. Also the tendency to just skid in a straight line without actually turning can be quite exciting as I found out with a Valentine once. Adjustment is key here.

In theory, if you pulled one lever while pressing its button and the other without pressing its button, you would get a pivot turn towards the button pressed side, with the other track in low. This would be a bit more relaxed than having the driving track in high but would require a lot more training to get right in a tight spot so I suspect was discouraged.

Controlled differentials are SOoooo much easier !

David

[Malcolm Towrie]

Thanks, David. Good summary.

I also notice from the German instructions that pulling both tillers back with the thumb buttons not depressed results in a straight line gear reduction to whatever gear you are in.

The instructions say the reduction of the drive speed is "of about a quarter" which I assume means to 75% of what the other track is driving at, rather then to 25%.

Our T-54 does this too which is quite handy when your ground guide is looking a bit stressed.

Malcolm

[Malcolm Towrie]

Originally Posted by Tobias Weibel

Hi at all

I'm happy to help.
Unfortunately, my technical English is not so good. That's why I can't argue with you.

The two items were on the drive end of the engine are an flywheel and the safety sliding clutch

safety sliding clutch:


Are the Brake Bands new?
It is very important that the brake bands are adapted (grinding)

Tobias, thanks again for the new schematics.
I find it quite humbling that so many Europeans, like yourself, are quite fluent in
English, yet we British and North Americans are hopeless at European languages. Thank God for Google Translate.

I don't know the condition of the brake bands but they do look new. And if you are referring to grinding of the brake drums, no, I dont think they have been ground, they look a bit scored.

Malcolm