Does divorce take place if I swore to my wife, "You are divorced if we ride in the car with him," and then she rode in a car with him that he had borrowed from his friend?

The reference point for an oath is the intention of the one swearing it. If there is no intention, then the reference point is the reason for the oath. If you intended only to prevent your wife from riding in your relative's car, and did not intend to prevent her from riding with him in someone else's car, or if you do not recall your intention and the reason for the oath implied this, then you have not broken your oath. However, if the intention or the reason implied preventing her from riding with this relative in general, then you have broken your oath. The fatwa adopted by us is that divorce occurs in the event of breaking the oath, and this is the view of the majority of scholars. Whereas some scholars, like Ibn Taymiyyah, are of the opinion that a conditional divorce not intended to cause divorce, but rather as a threat, takes the ruling of an oath, thus requiring an expiation for an oath and not resulting in divorce. We advise presenting the matter to trustworthy scholars in your country.