Buchli drive

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Buchli drive

What it is
The Buchli drive is a transmission system once used on electric locomotives. Named after Swiss engineer Jakob Buchli, it is a spring-loaded design where each floating axle has its own motor housed in a spring-mounted part of the locomotive frame. The weight of the motors does not rest on the driving wheels, which helps reduce what the wheels transmit to the rails.

How it works
- A gear wheel is fixed to the locomotive frame. Inside this gear wheel are two levers connected to gear segments that mesh with each other.
- The other end of the levers connects through universal joints to tension bars, which again connect through more universal joints to the driving wheel.
- When the driving wheel moves, the internal parts shift the gear segments so the wheel can move in a horizontal or vertical direction while still transferring momentum to the wheel.
- Each wheel can be powered by its own traction motor, or, in variants, two motors may work on one axis and drive a common gear wheel.

Why it mattered
- The system allowed bigger and faster locomotives by placing heavy traction motors in a way that kept their weight off the wheels.
- It reduced the amount of unsprung weight on the rails, which helps track wear and ride quality.
- It was most popular in the early to mid-20th century, especially for high-speed express trains.

Disadvantages and decline
- The Buchli drive has many moving parts, requiring frequent lubrication and careful maintenance.
- At higher speeds the components can become imbalanced, causing issues above about 140 km/h. As a result, it fell out of favor and was largely replaced by simpler, smaller drive systems.

Design variations
- Standard design: one-sided, separate traction-motor drives with the motor framework inside the locomotive body and the gear wheel in an outside frame.
- Outside-frame design: engine framework sits outside the wheel disks; gear wheels are on one side and covered by a casing.
- Group drive: motors arranged between floating axles, driving neighboring gears.
- Bilateral drive: drive wheels paired with two gear wheels and motors on both sides to balance forces.
- Two motors per axis: two driving motors share one gear and axle.

Where it was used
- The Buchli drive powered about 240 Swiss locomotives for many decades, including the SBB Ae 3/6 I class (1921–1994).
- It saw use in France, Germany, Italy, Indonesia, Japan, and the United States among other places, especially on express locomotives.
- Today it’s mostly a historical technology, replaced by more compact and reliable drives.

See also
- Quill drive
- Tschanz drive
- Winterthur universal drive