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[Question] About AMX 10 RC transmission


Monochromelody
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As we know, AMX 10 RC is a very special wheeled AFV for it's skid steering system. 

It can perform neutral steer, a.k.a. pivot steer or steer in place. 

150932rcvcthxt82cvv99v.bmp

 

The transmission case is similar to some tank transmission. 

114737ell0f58nfn0np0y2.jpg

 

The driver uses steering levers instead of a steerig wheel, and it's almost identical with those on AMX 10P tracked AFV. 

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↑wheeled AMX 10 RC

↓tracked AMX 10 P

114750yoiqxxjv4lbzvopj.jpg

 

It even had a variant running on tracks: 

110142uzqo7pgy2o0pzgn0.jpg

 

As for steering principle, there are different descriptions. 

 

Some info says AMX 10 RC use a triple-differential system, like some British tanks and AFVs. A similar skid-steering wheeled vehicle, TV1000 "Rhino" also use steering levers instead of steering wheel, and it have triple-differential system. 

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When I looked for historical information, I found that French invented the first double-differential steering system for wheeled vehicle since 1898. And French tanks used double differential system since 1920s:

 

Renault NC: "Cletrac" type double differential, or controlled differential. First tank using Cletrac system. Single radius. 

Char B1: "Naëder" type double differential, steering control via steering wheel connected to appareil Naëder(Naëder device). First production tank with hydrostatic steering mechanism. Step-less steering. Pivot steer. 

Somua S35: "Somua" type double differential, steering control via steering wheel connected to mechanical steering clutch. Single radius. Pivot steer. 

 

ARL 44: "ZF" type double differential, steering control via steering wheel. According to the document Notice du Char de transition, it can perform double radius steering and pivot steer. 

Char Lorraine 40t: "ZF" type double differential. Detail unknown. Double radius. Pivot steer. 

Char AMX 50: "ZF" type double differential. Detail unknown. Double radius. Pivot steer. 

AMX 13: "Cletrac" type double differential, or controlled differential. A more compact design, steering mechanism integrated with gearbox. Single radius. 

 

AMX 30: "Cletrac" type (1961 prototype or before), single radius; 

                "Somua" type variant (early version AMX 30B, 5SD-200D), single radius, pivot steer; 

                 hydrostatic double-differential (AMX 30B2 upgrade, ENC-200), step-less steering, pivot steer. 

 

There's no clear evidence that French could gave up their experience on double-differential mechanism and turned to British triple-differential. 

 

I tried to look for AMX 10RC operator's handbook, but only gunnery handbook found on the internet. 

 

Any further detail information about AMX 10RC transmission would be appreciated. 

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2 hours ago, Collimatrix said:

Double differential and triple differential steering systems aren't that different.

As far as I know, double-differential system split and transfer steering power flow by engaging different clutch(direction clutch, sometimes radius clutch), or brake certain steering planetary gear, or simply by a hydraulic pump-motor unit. 

Triple-differential system split steering power flow by braking either side steering planetary gear(usually sun gear), transfer steering power flow to the other side via a differential. 

 

It's much easier for a double-differential system to achieve different steering radius. For example, 

Single radius: Somua steering system(Somua S35), 5SD-200D(AMX 30B), CD-500(M41 Walker Bulldog), MT75(Japan Type 74)

Double radius: Maybach Argus(Tiger I), ZF 4HP250(Leopard 1)

Triple radius: ZF LSG3000(K1 MBT, C1 Ariete, EE-T1 Osório)

Step-less steering: Naëder system(Char B1), FBTV-2B(Strv 103), SLM system(Panzer 68), HSWL 123(KJPz 4-5), HSWL 194(Marder IFV), HSWL 354(Leopard 2), S6-80(SK105), X1100(M1), TN54(Challenger 1)

All these are double-differential system. 

 

Triple-differential system usually have single radius, like CD-850 series(M46 to M60), TN12(Chieftain)

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Triple differential systems have a single steering radius per gear ratio of the transmission.  Chieftains, for instance, have six forward gears, which means that they have six turning radii when moving forward.  If the tank is in high gear it will turn a very wide radius.  If it is in low gear it will turn a much tighter radius.  If it is in neutral it will spin one track forward and one track backwards.

Older steering systems like the Cletrac steering system in the Sherman had one turn radius regardless of what gear the tank was in.

It is true that triple differential systems are not generally amenable to having multiple turn radii per gear ratio.  This is because the steering drive is engaged when the tank is driving straight forward.  However, triple differential systems are generally easier to maintain, and they give most of the flexibility of a double differential system.

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37 minutes ago, Collimatrix said:

Triple differential systems have a single steering radius per gear ratio of the transmission.  Chieftains, for instance, have six forward gears, which means that they have six turning radii when moving forward.  If the tank is in high gear it will turn a very wide radius.  If it is in low gear it will turn a much tighter radius.  If it is in neutral it will spin one track forward and one track backwards.

Yes, Chieftain tank has a single steering radius for every gear, while Leopard 1 would have two steering radius for every gear, 4×2=8. And Ariete tank have 4×3=12 steering radius in total. 

 

The British prefer triple differential system for it's easier to produce and maintain, and a braking drum could probably be cheaper than a multidisc clutch. 

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014532b5mpm1zz5xaw545s.png

According to the gear train schematic, AMX 10RC have a triple-differential steering mechanism. This is more common on British after-war period armoured vehicle but quite rare on a French AFV. It differs from a Merritt-Brown gearbox, for the ring gear and sun gear of the steering planetary both driven in the same direction. 
 

Designed in the 1970s, the transmission of AMX 10RC shares some similarity with the TN15 gearbox of Alvis Scorpion light tank(FV101). Both of them combine the forward-reverse selector with the input bevel gears. 
 

The gear shifting part use a set of constant mesh gears with synchronizer and planet gears to have different gear reduction ratio. In total it can provide 4 forward ranges, as well as 4 reverse ranges, having the same gear ratios. 

 

When the range set to 'neutral' position, a pivot steer would be made. A pair of hydraulic-actuated disc brake is used for steering, controlled by a pair of steering levers. 

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