The Structure of $W_4$-Immersion-Free Graphs
  We study the structure of graphs that do not contain the wheel on 5 vertices W4 as an immersion, and show that these graphs can be constructed via 1, 2, and 3-edge-sums from subcubic graphs and graphs of bounded treewidth. 
R\'emy Belmonte and Archontia Giannopoulou and Daniel Lokshtanov and   Dimitrios M. Thilikos
math.CO