tågväxellådor

A tågväxellåda is the gearbox used in railway locomotives, translating literally to "train gearbox". It is a mechanical transmission that couples the power source (typically a diesel engine or electric traction motor) to the driving wheels. By varying the gear ratio, the valve box allows a locomotive to accelerate from low speeds, maintain efficient cruising speed, and climb gradients.

In diesel‑electric locomotives the diesel engine drives a generator or alternator that supplies electricity to traction motors. The tågväxellåda is located between the prime mover and the generator, converting the high‑rpm engine output to a more manageable shaft speed. In pure electric locomotives, a gearbox may be omitted altogether, but many early electric and steam‑powered units still employed a traditional crankshaft gearbox to drive the axles.

Typical gearboxes in classic steam locomotives were simple two‑ or three‑speed units mounted just behind the driving wheels. The operator could change through two, three, or four gear ratios (e.g., 1‑to‑1, 2‑to‑1) to handle different track conditions. The shift was usually done by hand, often with the aid of a clutches or a lever inside the cab. In modern diesel locomotives, most gearboxes are automated and integrated into the traction control system. Automatic gearboxes use epicyclic or planetary gear sets that allow smooth shifting without interrupting power flow.

Electric and hybrid locomotives typically use a jackshaft gearbox when a mechanical coupling to the wheels is needed, such as in early 20th‑century electric units that used traction motors directly on the axles. In contemporary designs most electric locomotives drive the wheels via axle‑hung motors, eliminating the need for a conventional tågväxellåda.

Maintenance of a tågväxellåda focuses on oil lubrication, bearing inspection, and gear tooth wear. Regular checks of gear lubrication and shrinkage of gear tooth plates are essential for preventing failure under high load. The durability of a gearbox directly impacts a locomotive’s operational reliability and fuel economy.

Modern high‑speed trains have largely moved to all‑electric drive systems, but the concept of the tågväxellåda remains fundamental to understanding locomotive technology and the evolution of railway traction systems.