Split ring changes the direction of current after every half rotation. So it is also called commutator.

Electric motor is a device which converts the electrical energy into mechanical energy.In an electric motor the split ring commutator is used to reverse the direction of current in the coil. During the working of an electric motor whenever the coil passes from the vertical position, the direction of current through the coil has to be reversed, so that the coil continues to rotate in the same direction.Hence it reverses the direction of current in the coil after evry half rotation of the coil and thus the direction of couple rotating the coil remains unchanged and the coil continues to rotate in the same direction.