SNCF Electric Locomotive Drive

I recently visited the French railway museum Cité du Train in Mulhouse, Alsace which is very highly recommended if you happen to be in east France or well worth a special trip over.

One exhibit, the drive on an SNCF electric locomotive, really puzzled me. I spent a considerable amount of time examining the display but failed to explain to myself how the direct drive from the traction motor to the rail wheel worked or why it was so arranged. Unfortunately there was no information, either in French or English, accompanying the display and I doubt that my elementary language skills could have elicited much from a member of the museum staff, so I moved on to other exhibits remaining baffled.

The drive seemed be direct from a gear on the traction motor shaft to a larger gear that appeared to be coupled to the rail wheel by two opposing levers with short meshed arcs. I couldn't discern any suspension from the wheels to the locomotive chassis, not to say it didn't exist somewhere, but just that I couldn't see any flexibility. The arrangement was quadruplicated and appeared on each end of the four traction motors' shafts so power was transmitted to eight wheels in total.

I am posing this question from a position of complete ignorance, so if I have missed something obvious I apologise, but could someone explain this arrangement or point me in the direction where some further information may be available. Absentmindedly, I failed to make a note of the type or manufacturer of the locomotive, sadly.

Edited By Chris Crew on 15/05/2023 00:12:40

Edited By Chris Crew on 15/05/2023 00:14:06

Hi Chris,

The loco appears to be a type 2D2, and the mechanism a "Buchli drive":

Wikipedia article: https://en.wikipedia.org/wiki/Buchli_drive - it appears to be a method of decoupling the drive motor and gears from the traction wheel, reducing unsprung weight.

Cheers,

Jez.

Edited By Jez on 15/05/2023 07:17:17

Jez,

Thank you for putting me out of my misery, all is now explained!

I must admit that, having never seen this mechanism before, I was completely baffled by its operation but the animation in the wiki article makes everything clear.

Chris c.

Fascinating concept Jez! The wiki article and superb animation really clarify it's operation.

As it says though, a lot of moving parts that would require frequent lubrication and maintenance

It is also called a 'Link' drive and examples were developed by Brown Boveri and also by Oerlikon for large electric passenger locomotives. It allows the motor to be rigidly mounted in the chassis along with the gear drive to preserve correct alignment, but allows the driven axle to move on its suspension. It also reduces unsprung weight in comparison with a nose-suspended axle-hung motor which makes for less damage to trackwork.

There is a detailed explanation of it in a textbook I have (Electric Traction by A.T.Dover) along with some diagrams and pictures. Even after reading this I still can't understand how it works .

I'll have to look at the Wiki article I think.

Perko7

It got me puzzled too and I had all the time in the world to examine the real thing in the museum. I am flattering myself that I may have got there eventually if the rail wheel and suspension hadn't been hidden by the locomotive chassis, but the animation on wiki explains everything in less than a minute. A very clever and basically simple mechanism once you see it in operation although I would think that the design engineering is highly involved. 

Edited By Chris Crew on 15/05/2023 13:02:34

I think the LMS steam turbine loco had a similar arrangement to isolate the reduction box from the drive axle.

There is a diagram here

**LINK**

See 8th diagram/picture.

Martin