Patent search by keywords:
1) On uspto.gov, click on "search for patents" in the top right corner over the search box.
2) In the column on the left, underneath Search for Patents, click on Patent Full-Text Databases
3) In the Patents column click on Advanced Search
4) You will see a list of field codes to use in your search. I recommend either TTL or ABST. Follow the format in the example. As a unique example, try searching internal combustion by entering in the following (don't forget the quotation marks if you're searching a phrase) and hitting search: abst/("internal combustion")
5) Click on one of the results to examine
Patent by classification:
1) Same as above
2) In the left column click on Patent Classification
3) There are multiple options here, but your best bet is to select Browse Index to USPC
4) If you select the "I" index, you'll be able to scroll through the document (use HTML to take advantage of the hyperlinks) to a term. You will find that "Internal Combustion Engines" is in the list. Examine the classification.
5) As an example, click on the "597+" next to "Waste heatdriven motor" under "Fluid pressure motor combined"
6) In the results list, clicking on the [A] next to a definition will bring up a list of applications. Clicking on the [P] will bring up a list of actual patents with numbers.
Patents at MIT – MIT Libraries, Massachusetts Institute of Technology. This research guide has four patent video tutorials, including a comparison of free online patent databases and searching the Free Patents Online database.
UTexas Patent Searching – McKinney Engineering Library, The University of Texas at Austin. This tutorial is guide on how to search the USPTO site.
Penn State's Physical and Mathematical Sciences Library Tutorial – University Libraries, Penn State University. This tutorial provides general information on patents, searching techniques, and resources.