Krauss-Helmholtz bogie

A Krauss-Helmholtz bogie (Krauss-Helmholtz-Lenkgestell) is a mechanism used on steam locomotives and some electric locomotives to improve curve running.

The bogie comprises a carrying axle connected to a coupled axle via a shaft or lever. In straight running, any radial movement of the carrying axle results in a sideways movement of the coupled axle in the opposite direction. However, the carrying axle is centred by means of two heavy duty springs just behind it. In addition the pivot pin may be allowed to move sideways, but again is held centrally by heavy springs. When travelling round a curve, the carrying axle swings to one side causing the coupled axle to move sideways in the opposite direction. In this way radial forces during curve running are more or less evened out on both axles, so that riding qualities similar to those of a normal bogie are achieved and wear and tear reduced on wheel flanges and rails.

The bogie is a type of pony truck and was named after the locomotive firm of Krauss and the engineer, Richard von Helmholtz. By contrast a Bissel bogie is independently installed in the frame, and sideways guidance of the locomotive is achieved by elastic forces. The distribution of these forces is not tightly defined and, in addition, they are dependent on the curve radius.

Because the advantages of a pony truck come into play particularly on tight curves, the Krauss-Helmholtz bogie initially appeared on branch line, Lokalbahn and narrow gauge locomotives. One of the first locomotives of this type was the Bavarian D VIII. On this tank locomotive the bogie was located at the rear; however in the majority of cases it was at the front or - if the locomotive had to have equally good riding qualities in both directions - at both ends.

Later this pony truck arrangement was also adopted by the DRG standard locomotives (Einheitslokomotive) of the Deutsche Reichsbahn, e.g. on the ten-coupled classes: 44, 45, 50 and 85. An exception was the Class 84, that was fitted with Schwartzkopff-Eckhardt II bogies or Luttermöller axle drives.

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