This invention relates to internal combustion engines, and more particularly to engines having an integral cylinder head.
Many types of internal combustion engine designs are known for use in lawnmowers, generators, snowblowers and the like as well as for motor vehicles. I n a typical prior art engine design, the engine housing is made of at least three distinct engine housings. Typically, there is a separate housing for the cylinder head that encloses the cylinder bore and the valves, and at least two additional housings for enclosing the other engine components. A cam shaft cover is also used to enclose the cam shaft in overhead cam (OHC) engines. The need for these engine housings requires additional die casting and assembly steps in the engine manufacturing process. These additional steps increase the cost of the engine.
Conventional engine designs require that the cam shaft be mounted in bosses affixed to the inside of the engine housing. These designs require additional or more complex assembly steps to insert the cam shaft into the engine housing. Separate cam shaft bearing components must also be manufactured and inserted about the cam shaft, resulting in additional manufacturing and assembly cost.
The crankshaft in conventional engine designs is typically disposed within opposite apertures machined in the engine housing side walls. These designs also increase the assembly time and require that separate crankshaft bearings be manufactured and placed around the crankshaft, further increasing the manufacturing and assembly cost.
The difficulty in assembling the conventional crankshaft and connecting rod components require that a two piece connecting rod be used to connect one end of the rod to the crankshaft throw. The two pieces of the connecting rod are typically bolted together by a pair of bolt assemblies. The need for a multi-piece connecting rod and the bolt assemblies also results in increased manufacturing and assembly costs.
In conventional overhead cam engines, the cam shaft is driven by a timing belt or chain assembly. Prior art timing belt drives have several disadvantages. First, the idler pulley must be adjusted so that the belt has the correct amount of tension. If the tension is too low, there is a risk that the belt will jump a tooth on the sprocket, causing improper engine timing. If the tension in the timing belt is too high, the belt and the bearings tend to wear prematurely.
A second disadvantage of prior art timing belts is that they typically require a belt guard or cover to keep debris off of the belt. A third disadvantage is that they typically require an oil seal on the cam shaft.
Chain assemblies used to drive cam shafts also have several disadvantages. First, chain drives, like belt drives, require an idler sprocket to adjust the tension. Second, chains require lubrication and are difficult to assemble. Third, chain drives require a rub rail on the outer side of the chain to keep the chain from slipping.
One obsolete method for driving the cam shaft used bevel gears. However, such bevel gears typically required very small center line and axial alignment tolerances, on the order of about .+-.0.001 inches. These small, critical tolerances require precision machining of the bevel gears at increased expense.
Typical small internal combustion engines require one or more additional shafts mounted to the inside of the engine housing to operate the oil slinger for engine lubrication and the engine governor for controlling engine speed. These additional shafts also require extra manufacturing and assembly steps, thereby further increasing the cost of the engine.
Therefore, it is desirable to reduce the number of engine housings, bearings, shafts and other component parts to decrease the manufacturing and assembly costs of an internal combustion engine.