In an engine belt drive system, the idler pulley (also known as a guide pulley or jockey wheel) plays an important auxiliary role. The main functions of the idler pulley in the engine belt drive are as follows:

1. Changing the direction of the belt

Adjusting the belt path: The idler pulley can change the direction of the belt, allowing it to connect more effectively to various components on the engine (such as the alternator, water pump, air conditioning compressor, etc.). This adjustment enables the belt to achieve a complex transmission path within a limited space, ensuring that all components can work properly.

Optimizing spatial layout: By changing the direction of the belt, the idler pulley can help to optimize the spatial layout in the engine compartment, making the arrangement of the engine and its components more compact and rational.

2. Increasing the belt wrap angle

Improving transmission efficiency: The idler pulley can increase the wrap angle of the belt with the drive or driven pulley (i.e., the angle of contact between the belt and the pulley). A larger wrap angle means that the contact area between the belt and the pulley increases, thereby increasing the friction between the belt and the pulley, reducing the possibility of slippage, and improving transmission efficiency.

Reducing belt tension: With the same friction requirements, a larger wrap angle can reduce the required belt tension, thereby reducing the load on the belt and bearings, and extending the service life of the belt and bearings.

3. Assisting in belt tensioning

Maintaining tension: In some engine belt drive systems, the idler pulley can assist the tensioner pulley in maintaining the belt tension. By adjusting the position of the idler pulley, the belt tension can be finely adjusted to ensure that the belt maintains the proper tension during operation.