What novel had a time travel car and dinosaurs?

I am trying to remember the title of a science fiction novel about a man who has a car that can travel back in time, and he can park it about 10 seconds ahead, so no one but him can see it. He travels to the time of the dinosaurs and likes it there, so he goes to the middle ages to find a pretty woman who has no relatives and takes her with him to live among the dinosaurs. I read this book about 20 years ago, and the library no longer has it. Anyone know this novel?