Abbrevs

[Super-User]

Hello,
I have the following problem with Abbrevs:
"GNU Emacs 20.7.1 (sparc-sun-solaris2.8, X toolkit)\n of Tue Oct 16 2001 on 
jupiter"
............................................................
a. ELISP> (abbrev-expansion "XSAR_1" shell-mode-abbrev-table)
   "/export/home/JUPITER_XSAR_1/"
b. ELISP> (expand-abbrev)
   nil

Question: Why does (expand-abbrev) not the same work as
          `abbrev-expansion' obviously does?  
Do I need any setup of variables such that Abbrevs accepts uppercase
abbrevs? 

Thank you very much in advance for any hint.

Regards Willi.Rattei@dlr.de