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AssigneeMTD Southwest, Inc.
InventorsShiro Kawamoto, Harry Gene Rickard, John Sheldon, Yoichi Imgawa
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A portable, operator-carried power tool having an implement supported on an operator-carried frame, and a lightweight, four-stroke, internal combustion engine drivably connected to the implement and supported by the frame. The engine has a crankshaft situated in a crankshaft housing and a cylinder block secured to the crankshaft housing, the crankshaft being provided with a crankcase ventilation passage extending between the crankcase and an outlet end in communication with an air/fuel induction passage. A passage establishes communication between the interior of the crankcase and the valve chamber through a cam and cam gear region of the cylinder block. An oil mist generator is connected drivably to the crankshaft for agitating liquid oil in the crankcase to establish a lubricating oil mist. The crankcase, the cam region and the valve chamber form a closed oil mist containment whereby lubricating oil mist is distributed throughout the engine during operation regardless of angular orientation of the engine. The crankshaft ventilation passage establishes lean crankcase gas distribution to the engine air/fuel intake. The crankcase is designed to avoid flow of liquid oil through the crankshaft passage when the engine is not running. meet the 2000 CARB emissions regulations. In addition, they operate quieter compared to two-stroke engines. Unlike two-stroke engines which simultaneously admit a fresh charge of fuel and air mixed with lubrication oil while exhausting combustion products, including unburned fuel, a four-stroke internal combustion engine maintains the lubricating oil relatively isolated from the combustion chamber. The intake and exhaust valve region and the camshaft and cam drive portions of a four-stroke internal combustion engine are lubricated with oil supplied from the crankcase. The combustion chamber remains relatively isolated from the crankcase. Lubricating oil is not introduced into the air/fuel mixture as in the case of a two-stroke engine. Lubrication of the cylinder wall occurs as a film of crankcase oil develops on the cylinder wall. The piston rings seal the variable volume combustion chamber and effectively prevent mixing of the lubrication oil with the combustion gases. One disadvantage of using four-stroke internal combustion engines for outdoor power tools, aside from a weight disadvantage, traditionally has been the inability to operate the engine upside down or at the extreme tilt angles that would be required by the operator. Oil in the crankcase in those instances would tend to be drained through the engine block to the intake and exhaust valve region of the engine and would enter the air/fuel mixture intake flow path as well, thereby upsetting otherwise efficient fuel combustion during operation. Continuous operation of the engine, even for relatively short periods, may result in piston seizure because of an interruption of lubrication oil flow to the cylinder wall. Many of the shortcomings associated with the use of four-stroke engines with outdoor power tools have been solved by the teachings of U.S. Pat. Nos. 5,241,932 and 5,421,292, which are incorporated in the present disclosure by reference. Those patents, which are assigned to the assignee of the present invention, disclose engines which avoid the weight disadvantage of using a four-stroke internal combustion engine in an outdoor power tool. Further, they make provision for efficient engine operation throughout a wide range of angular dispositions or orientations. Copending U.S. patent application Ser. No. 08/614,835, filed Mar. 8, 1996, which also is assigned to the assignee of the present invention, describes a further improvement in the earlier prior art teachings. That improvement makes it possible to maintain distribution of lubrication oil mist throughout the engine while maintaining the liquid lubrication oil isolated from the valve chamber and the cam and cam drive system. The engine of the copending application, which is incorporated in the present disclosure by reference, includes a lubricating oil mist passage that is formed in the crankshaft and in the crankshaft counterweight. The crankshaft passage facilitates distribution of lubricating oil in the form of an oil mist through the region of the camshaft and the camshaft drive of the engine and through oil mist flow passages to an overhead valve chamber. A lubricating oil mist generator driven by the crankshaft agitates liquid oil in the crankshaft and develops a lubricating oil mist which is transferred through the engine in a flow path defined in part by the crankshaft passage. Large oil droplets in the oil mist and liquid oil in the crankcase are prevented from entering the crankshaft passage by the effect of centrifugal force due to the rotation of the crankshaft and the crankshaft counterweight during engine operation. A fine oil mist, however, may pass through the crankshaft passage and through the engine lubrication system since the mist is relatively unaffected by the centrifugal forces created by the rotating crankshaft.
An operator-carried, lightweight power tool comprising a frame with an implement mounted thereon, a four-stroke internal combustion engine with a crankshaft drivably connected to said implement, said engine being supported by said frame;
An operator-carried, lightweight power tool comprising a frame with an implement mounted thereon, a four-stroke internal combustion engine with a crankshaft drivably connected to said implement, said engine being supported by said frame;
An operator-carried, lightweight power tool comprising a frame with an implement mounted thereon, a four-stroke internal combustion engine with a crankshaft drivably connected to said implement, said engine being supported by said frame;
An operator-carried, lightweight power tool comprising a frame with an implement mounted thereon, a four-stroke internal combustion engine with a crankshaft drivably connected to said implement, said engine being supported by said frame;
An internal combustion engine having a four-stroke cycle comprising a crankcase with a lubrication oil chamber, a cylinder block secured to said crankcase and having a cylinder bore and a cam chamber;
An internal-combustion engine comprising a crankcase with a lubrication oil chamber, a cylinder block secured to said crankcase and having a cylinder bore and a cam chamber;
An internal combustion engine having a four-stroke cycle comprising a cylinder block, a crankcase below said cylinder block;
A four-stroke internal combustion engine comprising a crankcase with a lubrication oil chamber, a cylinder block secured to said crankcase and having a cylinder bore and a cam chamber;
Dependencies are inferred from the claim text.