Tank steering systems

Tank steering systems allow a tank, or other continuous track vehicle, to turn. Because the tracks cannot be angled relative to the hull (in any operational design), steering must be accomplished by speeding one track up, slowing the other down (or reversing it), or a combination of both. The half-track avoids this by combining steerable wheels and fixed-speed tracks.

Early steering systems were adopted from tracked work vehicles, generally using a clutch to reduce power to one track, causing it to slow down. These designs have numerous problems, notably when climbing hills or running at high speed, as the reduction in power causes the overall speed to slow. Delivering power to both tracks while turning them at different speeds is a difficult design problem.

A series of more advanced designs were introduced, especially through World War II, that maintained power to both tracks during steering, a concept known as regenerative steering. Some also allowed one track to move forward while the other reversed, allowing the tank to spin in place, a concept known as neutral steering. The first really successful system was the British double differential design of 1924, which was copied by both the US and Germans.

Most modern western designs use a variation of the double differential, while Soviet designs preferred to use two separate transmissions in a single housing. Systems using electric motors with variable speed controls have been tried on a number of occasions, but have not entered widespread service.

One solution to the steering problem is to use two separate drivetrains, each driving one track. Steering is accomplished by changing gears on one and not the other. This maintains power to both tracks while steering, produces a wide range of turning circles, and even allows one track to be reversed while the other moves forward, allowing the tank to turn in place. This may be combined with brakes to further control the steering radius.

The obvious disadvantage to this design is the cost and complexity of two drive trains, and the increased maintenance load that implies. Another is that if one engine fails, the other cannot be used to drive both tracks. Both of these problems were greatly reduced in the case of steam power, where the majority of the engine in terms of size and weight is the boiler, and the cylinders that extract that power are much smaller in comparison. It can also provide variable output by controlling the amount of steam sent to each cylinder. It is much more complex when used with internal combustion engines.

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Wikipedia