How I can add my own midi patterns for use with SI-Drum Kit 1? 

Drag/drop the MIDI patterns to the pattern grid. To trigger the patterns use MIDI notes 8,9,10 and 11. MIDI note 7 stops the pattern.

The other way is copy the MIDI files into  "C:\ProgramData\Cakewalk\Studio Instruments\SI-Drum Kit\Patterns" or a folder under it and rename the "C:\ProgramData\Cakewalk\Studio Instruments\SI-Drum Kit\Pattern\patterns.lst"
 
The next time SI Drums starts it will create a new patterns.lst with the new MIDI files.

Thank you very much for your answer. I copied the MIDI files to the folder "C:\ProgramData\Cakewalk\Studio Instruments\SI-Drum Kit\Patterns" and did not work. And the strange thing is that I can't find the file "patterns.lst". I don't notice where the default patterns are stored...

For the version of Studio Instruments NOT included with Sonar, the location is
C:\ProgramData\Cakewalk\Studio Instruments\SI_Patterns\Drums
 
 
 

I have a patterns.lst in the folder in the patterns folder. The file is rebuilt automatically by SI-Drums when it is not found. This is how SI-Drums knows what patterns are in the folder. I thought it was always this way. I have the Studio Instruments package installed with SONAR Platinum. There may be older versions with a different layout.
 
 
Edit: confirmed, there are at least two directory layouts for Studio Instruments

Steve - it appears the directory structure is different between the SI package purchased stand-alone and the version bundled with Sonar.
 
The other difference I'm aware of is the lack of stand-alones in the bundled version.

BobF
Steve - it appears the directory structure is different between the SI package purchased stand-alone and the version bundled with Sonar.
 
The other difference I'm aware of is the lack of stand-alones in the bundled version.

That makes sense. Like I said, I have the plug-ins by way of SONAR. I suspect the differences explain the name change from Studio Instruments to the SI series. Now that you mention it, I remember the question about the missing stand alone versions. IIRC, the stand alone synths that SONAR ships are based on Minihost from Tobybear. Tobybear is no more. Here is a similar product SAVIHost. I prefer to use VSTHost from the same source when I work outside of the DAW or need to test a plug-in in a different host.

BobF
C:\ProgramData\Cakewalk\Studio Instruments\SI_Patterns\Drums

This is the old Studio Instruments path, the SONAR path is in msg #3.
 
 
edit: corrected to confirm multiple file layouts.

I've had both versions installed.  I have both paths after uninstalling the unbundled version.
 
I'll do some testing and report back