I know mine are older and I have been frank with them because of it. But, it is a mistake not to be age appropriately open with your child. No, your child doesn't need to ever think they did something wrong, they need to know that dads behavior has nothing to do with them. And, since the child is young, they need to be reminded of that fact often. Your husband is only fooling himself that he thinks his child isn't wise enough to know what's going on. Kids are smarter than we give them credit for.
On another note, until your husband is sober at least for a year, don't allow your young one to ride in a car with him. I have had this very same issue in the past with my children. It's not easy and will be an inconvenience to say the least, but drunk driving scares the heck out of the kids and puts their lives in danger. I didn't tell my husband at first that he wasn't allowed to drive our boys anymore, instead I started it by telling my kids not to ride with him and they were relieved. I eventually told my AH, he didn't like it of course, but that's tough. I didn't want a dead kid that I would never stop feeling guilty for allowing to ride with him knowing the possibility that he could be driving my kids drunk. Its just not worth the risk.
You have to put your child first, not your husbands feelings in this respect. Your childs mental, emotional, and physical safety come first.
Big hugs...it's hard, so hard. That is what helped me become stronger was to put my sons first and not the selfish, misguided, drunken thoughts and wishes of my husband.