US Patent 7398862 Car door lock

A door locking system for a freight or passenger elevator or goods lift installation having vertically spaced landings served by a vertically movable car, the landings and car each being protected by associated horizontal slide doors, a mechanical interlock device at each landing that prevents a landing door from opening without the presence of the car in registration with the landing, a door lock on the car for normally preventing the car door from opening when the car is out of registration with any landing, the interlock device being arranged to mechanically enable the door lock to release the car door to open when the car is in registration with a landing.