1、例句 he fills with joy when feeling his wife‘s belly 这里的when词性是介词嘛 ,它的作用也是引导时间状语从句。
2、由 when 等引导的状语从句,如果主语与主句的主语一致或是 it ,谓语动词又含 be 动词时,主语和 be 动词常常被省略,就变成“ when + V-ing/ V-ed/ adj/ 介词词组”的结构.,那么he fills with joy when feeling his wife‘s belly的原句就是he fills with joy when he was feeling his wife‘s belly省略而来,此时when的作用是连词引导的时间状语从句
那么像这样原句省略后,when的词性感觉发生了改变,这样理解对嘛