Flexicoil suspension

Flexicoil suspension is a wear-resistant low-maintenance suspension system for railway vehicles. It is a type of secondary suspension between the bogie truck and chassis|frames of railway Passenger stock, Goods or Freight wagons, and Locomotives. Steel spring suspension is more common than air suspension as it is less expensive to build and maintain.


As early as the 1930s, flexicoil suspensions (though not known by this term) were fitted to locomotives in Spain, the Soviet Union and Africa.[1]

Flexicoil suspensions under high speed DB standard electric locomotives were first used in Germany in the 1950s and 1960s, notably the DB Class 103.[2]

Between 1969 and 1971, British Rail conducted trials of new flexicoil bogie trucks under Class 86 locomotive, no E 3173,[3][4] which was affectionately nicknamed "Zebedee", after the jack-in-the-box character on the BBC television series The Magic Roundabout.[4] The trails were successful and led to refitting all Class 86 units with flexicoil bogie trucks, making them Class 86/2.[2] [3]

Clyde#Flexicoil-A1A and EMD#Flexicoil-C

The term "Flexicoil" originated with Frank Shea of Clyde Engineering in Australia and Dick Dilworth of EMD in North America, during their 1947~1951 colaborated development of a new 3axle bogie truck for pending new 6axle locomotives, the Clyde#ML1 (first sold in 1951) and EMD#SD7 (first sold in 1952). The resulting Clyde#Flexicoil-A1A and EMD#Flexicoil-C provided significant rail loading and traction advantages relative to prior bogie truck designs, and were standard on EMD 6axle locomotives until superceded in 1972 by the EMD#HT-C; as of this 2019 writing, the Flexicoil-C remains a common bogie truck on operating locomotives in North America.

Technical details

The springs in a flexicoil suspension are made of steel. Protruding from above and below, and into, each spring is a spherical rubber dome that can absorb some of the horizontal forces. These domes are connected firmly to either the vehicle body (above) or the bogie frame (below). Under this arrangement, each flexicoil spring is twisted and moved from its vertical axis when the vehicle is cornering. This helps the two bogies to align themselves equally underneath the vehicle body. The vertical forces are absorbed entirely by the steel springs.

As the springs have relatively soft characteristics, hydraulic vertical dampers must also be installed for vibration damping at higher speeds than 160 km/h (99 mph), along with longitudinal dampers. Lateral damping is not normally required.

In railway passenger cars fitted with flexicoil suspension, the springs are the only mechanical connection between the bogie and the car body. In heavier types of flexicoil suspension rolling stock, a bogie pivot fitted with rubber-metal bearings is used to hold a cross anchor yoke, which transfers the forces to the bogie frame via two cross anchor link pins. Some, such as the Italian D.445 class, have additional traction rods.[5]

Locomotive bogies are usually also provided with a weight transfer linkage, or with a different tension transmission.

See also

  • Glossary of rail terminology


  1. "Voith Maxima – Das Vorbild" [Voith Maxima – the Prototype]. Saechsische Waggonfabrik Stollberg (in German). Sven Heydecke. p. 3. Retrieved 15 August 2010.
  2. Duffy, Michael C (2003). Electric railways 1880-1990. London: Institution of Electrical Engineers. pp. 335–336. ISBN 978-0-85296-805-5.
  3. "Class History - AL6 / 86". The AC Locomotive Group's website. The AC Locomotive Group. Retrieved 13 August 2010.
  4. "High speed testing on WCML in the 70's". Testing Times. Retrieved 13 August 2010.
  5. Mattia Centeleghe (2007). "Analisi della locomotiva gruppo D445" [Analysis of the D445 group locomotive] (PDF) (in Italian). p. 8.

This article is based upon a translation of the German language version as at August 2010. The original authors can be seen here.

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