I found this topic
Is it possible to have a grouped bar chart with 2 dimensions without it forcing stacked bars?
It looks like this in not possible.
Anyone found a solution or extension that can provide this feature?
Basically I got 3 dimension and one expression and when adding 3 dimension QV starts to stack the values.
I don't think that this is possible with one chart but if you used more then one chart which are laying over eachother or you used the grid-option for charts you might get a (nearly) suitable solution.