Table name for Security Audit Log SM20


I want to make a report to calculate total SAP Used(logon) hours for a specified period (week/year/month) for User(s). In this regard I used SM20 transaction code and calculate time using Logon Successful time and User Log off time data. This Audit Log data saves into files. Now I want to know the table name for Users, Login time and Log out times so as to make a report which I could fire periodically.

Or is there any function module for this?

thanks in advance.