Patent Classifications can be complicated and much of the time one can find patents by keyword searching and clicking on patent classes assigned to a particular patent. This page is for those who wish to pursue a deeper understanding of classifications and need a more thorough search. The image below shows the hierarchy of the patent classification system.. A class with the alphanumeric characters “F02D 41/02” is described by the nested structure below. The USPTO has patent classification searching as does Espacent and the Lens. Purdue library has a good libguide on the different patent classification systems.
Picture from https://link.springer.com/article/10.1007/s11192-018-2905-5