As others have said it has nothing to do with you. He drinks because he drinks. He will take care of his problem when he is ready to. You are doing the right thing for you and your child by going to Alanon and letting you child know his rights when it comes to determining being in the car with your husband. My AH was doing the exact same thing as your husband. Hiding booze. Lying about it. Risking his child's life. Risking his job. Risking our marriage. It came to a head late summer and he agreed to go into a 30 day inhouse program. This was after I used my Alanon skills and "got out of his way". He almost died with BAC so high when I had the ambulance take him to the hospital they almost had to intubate him because they were afraid he would stop breathing. I convinced the ER doctors to put him in the psych ward for three days to detox and found him a bed at the Rehab. His choices were to either go there or find a new place to live so I could amke a new life for me and my kids. He came out end of Sept and he has been faithfully going to his outpatient program and AA. One of the biggest lessons I learned was not doing it alone. I was so afraid of family and friends realizing that he wasn't just a hard drinker but a drunk. I reached out to my husbands family, mine, friends, etc. I don't know what I would have done without them. The helped me financially and emotionally. I live in a small town and when I called the ambulance I knew them all. The secret was out. And that was ok. Secrets can kill. I felt so much better not keeping this secret all to myself.
Get the support you need. That is the most important. And get out of the way.