Driven Dog

In a unit carrier system in which a plurality of cars are driven over a track way by means of the frictional interaction of reaction surfaces and propulsion wheels, apparatus for transmitting relatively large amounts of power to the cars. The apparatus comprises a dog pivotally mounted on the bottom of each car and a motor-driven endless chain carrying a plurality of cooperating pawls in the track way. The car preferably enters the system at a speed in excess of the chain speed, and the dog is pivoted out of the way by the back of one or more of the pawls, but the car gradually loses speed until the front of one of the pawls overtakes the dog, forces it against a stop, and thereafter pushes the car along.