The propeller shaft: what it is, how it works and what its parts are

the transmission shaft

El transmission shaft It is in charge of bringing the rotation of the engine to the wheels that are on a different axis. That is, you will find it in a car with a front engine, but with rear or total traction. It is therefore a bar or bars, that together with other elements, have to withstand torque without deteriorating or causing vibrations.

When the vehicle is front-wheel drive or all-wheel drive with a rear engine, instead of a propeller shaft, it is usually called shift secondary shaft. Although its function is essentially the same and its basic elements as well.

The function of the transmission shaft

Specifically, its job is to communicate gearbox and differential. To understand what role inside transmission, we are going to review its main elements: the flywheel transmit the turn to clutch, this one at gearbox and from there it goes to transmission shaft when the engine is on a different axle than the drive wheels. From this, go to differential and from there it divides to two bearings, one for each wheel.

Audi S4 Avant drift

Transmission shaft parts

the transmission shaft it is rarely a simple bar. At least, in cars and similar vehicles whose wheels have to have some mobility due to the suspension. For this reason, they usually have other components that allow the rotation to be transmitted, even if the angle of the bar changes at certain times. The parts of a transmission shaft are:

Tree

Is the bar itself that will transmit the twist. That's why you must have a very strong construction made of steel or other metals of equal or greater strength that can withstand the torque without twisting. The problem comes when the engine is very powerful or the distance that the transmission shaft has to travel is very large.

Transmission shaft warning sign

The longer the bar has to be, the easier it will be for it to twist and lose some of the torque that is coming to it from the engine. Therefore, in these cases it is usually split into two bars or more, joined by cardans or elastic joints. In this case they are usually called for example rear axle y previous tree, to which can also be added another center tree if it is that it has been divided in three.

gimbals

They are the ones that allow rotation can be transmitted between two axes even if they are not aligned. Therefore, they have to withstand the same torque as the tree or trees themselves. They are also often called cardan joints or cardan joints.

Transmission shaft coupling

If there is only one undivided shaft, it will carry at most one gimbal at each end. That is, at the junction with the gearbox and at the junction with the differential. If the tree has been divided into several, for the aforementioned reasons, will also take care of join them together.

They must be permanently lubricated, because if not, the friction of metal against metal would wear them out very quickly. To keep them that way, they are usually encapsulated in bellows that retain fat inside. In essence, it is the same as the CV joint, because being rigorous, a cardan joint is actually a type of CV joint.

Related article:
In what state is the drive shaft bellows?

They are designed to be able to transmit rotation effectively with angle changes up to 25º depending on the construction they have and the needs of the car. For example, in a sports car that is so rigid that there are only going to be slight angle changes, gimbals with much less rotational change capacity will be required or even resort to elastic joints in some of its parts.

elastic joints

When the angle change what will there be is minimal, it is not necessary to use gimbals. It will be enough to use the calls elastic joints. Which is nothing more than placing one or more discs of an elastic material between the pieces to be joined. They will be screwed, but these screws will allow some movement in and out to accompany the deformation of the elastic joints.

These parts usually support a angle change between the components that bind up to 8th. So they are usually used, for example, in central shafts that are fixed to the vehicle and therefore will not move much. In addition, if it has an elastic joint on each side to join the front and rear shafts, it means that the difference in angle that will be supported between these two shafts will finally be 16º. In other words, 8º from the front shaft to the central shaft and another 8º from the latter to the rear shaft.

Related article:
All-wheel drive types

Supports

With the transmission shaft, the connection between the gearbox and the differential is made, but many times you have to fix it to the car chassis. Especially if it is articulated with several trees. This is taken care of by the transmission shaft supports, which can be completely fixed or allow some mobility of it.

sliding sleeve

As it is a mechanical component that has to assume certain mobility and angle changes, it also requires a sliding sleeve. It's about a segment that varies its length as necessary. This is because the distance from the gearbox to the differential is not always the same when the axle components are moved.

A few centimeters would be enough for the entire transmission shaft and other parts to deteriorate in a short time. That is why the shaft that has the sliding sleeve can also be called telescopic shaft. Because it extends like a telescope as required.

Images – Nathanael Burton, Filippo Giunchedi, fasteddy760


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