Your father is at a particularly difficult stage of the disease. He's aware of his mental shortcomings but also knows that he's unable to do anything about it. His frustration
and subsequent aggression are totally understandable. He's striking out at your mother probably because she's the easiest target. This kind of rage is usually a cry for help. The best way to help both him and your mother is to shift the "bad-guy" roles to others so you and your mother can be his best allies. Let others be the bearers of bad news. If your mom can get accustomed to empathizing with him rather than correcting or criticizing, his violent outburst will likely lessen. Your mom is probably right in her criticism, however, it becomes counterproductive with a person with dementia.
The car situation seems to be the over-riding issue for your father. As you say you've tried everything that we normally suggest: hiding the keys, hiding the car, pretending the car doesn't run, all to no avail. The consequence is that he blames your mother for the car problems and unfortunately he's correct, so you want to shift the responsibility to an authority figure and let your mother play the role of sympathetic spouse.
Request a "formal" order from his doctor that he has to stop driving and sell the car. Many state motor vehicle department will test a person whose judgment is in question. Talk to them. You may also talk to your local police department for advice. This is a search for a figure of authority for whom your father has respect. It may help you get him to understand that the car is no longer an option and he may even accept the car being sold. Go to search on Caring.com: "Driving" this will give you more tips and a list of state laws relating to these issues.
In order to help your father with his resentment over your mother's work, collaborate with his companion on something purposeful to do during the day. It doesn't matter what it is or if he's able to actually achieve anything as long as he feels accomplished and enriched. (Suggestions: lectures, musical performances, library visits, picnics, movies, or café lunches "“ or home bound projects: gardening, cooking, art projects, simple wood work, like bird feeders, or housework)
A couple of suggestions to maintaining harmony with a person with dementia:
This is not the same person you knew before. He looks the same and sounds the same, but his reality is constantly shifting and he can no longer relate to your reality. He easily succumbs to depression from feeling lonely, lost, and confused. Those of us in his life need to become his strongest supporters even if it means ignoring hurtful outbursts and rantings.
You'll never win an argument with a demented person. All you'll manage to do is aggravate the situation. No matter how outrageous his behavior, try to ignore it and if you feel you can't, step outside for a deep breath and remind yourself that it's the disease, not him.