What age did your toddler just Crash out and sleep by him/herself?

I usually go out every day, and DS sleeps as I am driving about...Sometimes he will fall asleep in my arms with his bottle...then i put him down....However this is slowly diminishing, and I am in a bit of a pickle now, since I cant get him to have a nap when he is tired, by just putting him into his cot.....I hate the controlled crying thing, and I just wont do it...Has anyone got any gentle suggestions to get my son to have a nap when he is tired and not fight it?? He doesnt like being held or rocked when he is tired, he is such a hard one to calm and get to nap!!!!

Any thoughts or suggestions would be much appreciated.