You have what is called a Civil War US M1840 Heavy Cavalry Saber. This Saber was made by Sheble & Fisher of Philadelphia. These sabers were used by the Union Cavalry. Your sabre is easily recognized as a M1840 sabre because of a distinct hilt with a three bar brass guard, and a leather covered wooden grip bound with roped brass wire, with a brass pommel. Your sabre also has it's original steel scabbard with two suspension rings. From what I can see in the photos, it appears to be in very nice condition with the leather all intact.
Here is a little history of the Sheble & Fisher company I was able to find:
Samuel Sheble and John Stevenson were listed as fork manufacturers, and by 1862 they were listed as a supplier for military goods in the Philadelphia business directory. John Fisher at about this time was listed as, among other things, a hardware, cutlery, and instrument maker. It is believed that Samuel Sheble and John Fisher started manufacturing at around 1859, when it was first noted that their firm 'Sheble and Fisher' were listed in the business directory. It is unclear as to how many swords Sheble and Fisher made of the M1840 & M1860 Cavalry Sabers, M1840 Artillery Saber, or NCO swords. This is primarily due to the fact that no known evidence of a wide spread government contract exist, only a small amount of M1840 Artillery Swords & 1,000 NCO swords are known to have been furnished to the government; this is further complicated by the fact that none of the swords in existence are known to have government inspector's stamps.
The retail value of your sabre on todays market would be in the $950-$1,300 range.
This is really a great piece of history that you don't see every day. Thank you for letting me take a look at it. Please remember to rate this answer using the stars. If you have any other question, just let me know.