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A hit-and-miss engine is a type of four-stroke internal combustion engine that was conceived in the late 19th century and was produced by various companies from the 1890s through approximately the 1940s. The name comes from the method of speed control that is implemented on these engines (as opposed to the "throttle governed" method of speed control). The sound made when the engine is running without a load is a distinctive "POP whoosh whoosh whoosh whoosh POP" as the engine fires and then coasts until the speed decreases and it needs to fire again to maintain its average speed. Hit-and-miss engines were made by a multitude of engine manufacturers during their peak usage which was from approximately 1910 through the early 1930s when they began to be replaced by more modern designs. Some of the largest engine manufacturers were Stover, Hercules, International Harvester (McCormick Deering), John Deere and Fairbanks Morse. == Construction == A hit-and-miss engine is a type of flywheel engine.〔http://www.osagcd.com/FeaturedEngine.html〕 A flywheel engine is an engine that has a large flywheel or set of flywheels connected to the crankshaft. The flywheels maintain engine speed during engine cycles that do not produce driving mechanical forces. The flywheels store energy on the combustion stroke and supply the stored energy to the mechanical load on the other three strokes of the piston. When these engines were designed technology was not nearly as advanced as today and all parts were made very large. A typical engine weighs approximately 1000 pounds (454 kg). Typically, the engine material was mainly cast iron and all significant engine parts cast from it. Small functional pieces are made of steel and machined to perform their function.〔 The fuel system of a hit-and-miss engine consists of a fuel tank, fuel line, check valve and fuel mixer. The fuel tank most typically holds gasoline but many users would start the engines with gasoline and then switch over to a cheaper fuel such as kerosene or diesel. The fuel line connects the fuel tank to the mixer. Along the fuel line is a check valve which keeps the fuel from running back to the tank between combustion strokes. The mixer creates the correct fuel/air mixture by means of a needle valve attached to a weighted or spring-loaded piston usually in conjunction with an oil-damped dashpot. Mixer operation is simple, it contains only one moving part, that being the needle valve. While there are exceptions, a mixer doesn't store fuel in a bowl of any kind. Fuel is simply fed to the mixer, where due to the effect of Bernoulli's principle, it is self-metered in the venturi created below the weighted piston by the action of the attached needle valve, the method used to this day in the SU carburetor. Sparks to ignite the fuel mixture are created by either a spark plug or a device called an ignitor. When a spark plug is used, the spark was generated by either a magneto or else a trembler (or 'buzz') coil. A buzz coil uses battery power to generate a continuous series of high voltage pulses which are fed to the spark plug. For igniter ignition, either a battery and coil is used or a "low tension" magneto is used. With battery and coil ignition, a battery is wired in series with a wire coil and the igniter contacts. When the contacts of the ignitor are closed (the contacts reside inside the combustion chamber), electricity flows through the circuit. When the contacts are opened by the timing mechanism, a spark is generated across the contacts which ignite the mixture. When a low tension magneto (really a low-voltage high-current generator) is used, the output of the magneto is fed directly to the igniter points and the spark is generated as with a battery and coil. Except for very large examples, lubrication was almost always manual. Main crankshaft bearings and the connecting rod bearing on the crankshaft generally has a grease cup which was a small container (cup) filled with grease and a cover which screws down on the cup. When the cover is screwed down tighter, grease is forced out of the bottom of the cup and into the bearing. On very early engines there may be just a hole in the casting of the bearing cap where lubricating oil is to be squirted while the engine is running. The piston is lubricated by a drip oiler that continuously feeds drips of oil onto the piston. The excess oil from the piston runs out of the cylinder onto the engine and eventually onto the ground. The drip oiler can be adjusted to drip faster or slower depending on the need for lubrication, dictated by how hard the engine is working. The rest of the moving engine components were all lubricated by oil that the engine operator would have to apply from time to time while the engine was running. Virtually all hit-and-miss engines are of the "open crank" style, that is, there is no enclosed crankcase. The crankshaft, connecting rod, camshaft, gears, governor, etc. are all completely exposed and can be viewed in operation when the engine is running. This makes for a messy environment as oil and sometimes grease are thrown from the engine as well as oil running onto the ground. Another disadvantage is that dirt and dust can get on all moving engine parts, causing excessive wear and engine malfunctions. Frequent cleaning of the engine is therefore required to keep it in proper operating condition. Cooling of the majority of hit-and-miss engines is by hopper cooling, with water in an open reservoir. There were a small portion of small and fractional horsepower engines that were air-cooled with the aid of an incorporated fan. The water-cooled engine has a built in reservoir (larger engines usually don't have a reservoir and require connection to a large external tank for cooling water via pipe connections on the cylinder). The water reservoir includes the area around the cylinder as well as the cylinder head (most cases) and a tank mounted or cast above the cylinder. When the engine runs it heats the water. Cooling is accomplished by the water steaming off and removing heat from the engine. When an engine runs under load for a period of time, it is common for the water in the reservoir to boil. Replacement of lost water is needed from time to time. A danger of the water-cooled design is freezing in cold weather. Many engines were ruined by the forgetful operator neglecting to drain the water when the engine was not in use and the water freezing and breaking the cast iron engine pieces. However, New Holland patented a v-shaped reservoir, so that expanding ice pushed itself up and into a larger space, so that the ice wouldn't break the reservoir. Water jacket repairs are common on many of the engines that exist today. 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「Hit-and-miss engine」の詳細全文を読む スポンサード リンク
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