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A screw-propelled vehicle is a land or amphibious vehicle designed to cope with difficult snow and ice or mud and swamp. Such vehicles are distinguished by being moved by the rotation of one or more auger-like cylinders fitted with a helical flange that engages with the medium through or over which the vehicle is moving. Modern vehicles called ''Amphirols'' and other similar vehicles have specialised uses. The weight of the vehicle is typically borne by one or more pairs of large flanged cylinders; sometimes a single flanged cylinder is used with additional stabilising skis. These cylinders each have a helical spiral flange like the thread of a screw. On each matched pair of cylinders, one will have its flange running clockwise and the other counter-clockwise. The flange engages with the surface on which the vehicle rests. Ideally this should be slightly soft material such as snow, sand or mud so that the flange can get a good bite. An engine is used to counter-rotate the cylinders—one cylinder turns clockwise and the other counter-clockwise. The counter-rotations cancel out so that the vehicle moves forwards (or backwards) along the axis of rotation. The principle of the operation is the inverse of the screw conveyor. A screw conveyor uses a helical screw to move semi-solid materials horizontally or at a slight incline; in a screw propelled vehicle, the semi-solid substrate remains stationary and the machine itself moves. == Early developments == One of the earliest examples of a screw-propelled vehicle was designed by Jacob Morath, a native of Switzerland who settled in St. Louis, Missouri in the United States in 1868.〔 〕 Morath's machine was designed for agricultural work such as hauling a plough. The augers were designed with cutting edges so that they would break up roots in the ground as the machine moved.〔 An early patent for an auger driven farm tractor.〕 One of the first screw-propelled vehicles that was actually built was designed by James and Ira Peavey of Maine. It was patented by Ira Peavey in 1907; the Peavey family has been famous for its contributions to the lumber industry ever since blacksmith Joseph Peavey of Stillwater, Maine, invented the tool known to this day as a Peavy. The Peavey Manufacturing Co. is still located in Maine.〔 〕 The Peaveys' machine had two pairs of cylinders with an articulation between the pairs to effect steering. At least two prototype vehicles were constructed: one was steam powered the other used a gasoline engine.〔 〕 The prototypes worked well on hard packed snow but failed in soft powder because the flanges had nothing to grip into. The machine was designed to haul logs, but its length and rigid construction meant that it had difficulty with the uneven winter roads for which it was intended. Peavey's invention could not compete with the Lombard Steam Log Hauler built by Alvin Lombard and it was not produced commercially. (The Lombard vehicle was an early example of a half-track vehicle, it resembled a railway locomotive with a sled or wheels in front for steering and caterpillar tracks for traction.) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Screw-propelled vehicle」の詳細全文を読む スポンサード リンク
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