A method of producing a polymer-clay nanocomposite comprises providing a supply of polymer-clay mixture, exfoliating the mixture through solid-state shear pulverization in the presence of cooling sufficient to maintain the extruded mixture in the solid state during the pulverization, and discharging the resulting exfoliated mixture. The invention provides improved consumer convenience at steering andor speed control. When the current detecting unit detects an abnormal increase of the load current and the counter electromotive force detecting unit detects that an occurrence of the counter electromotive force which exceeds a predetermined threshold value, the semiconductor switch corresponding to the load circuit is cut off. Thus, the invention provides a method for easily synchronizing an address signal, i. The third back-volume portion enables the effective diameter of the membrane to be formed more accurately.