Ok, I'll try to look for more.
I found several contemporary sources (at least 3 magazines of the 30s) reporting Cheret's presence at the Bol d'Or race of 1931 and the car was called 'Sphinx' or 'Sphinx-Staub'.
Fortunately there is a lot of material about Cheret and Bol d'Or races.
Is that a Bol d'Or race? Mine should be the '31 edition, is the car in your picture younger?