Patent Application
20080173171
The present application relates to internal combustion engines, and, in particular, to cylinder crankcase assemblies.
Two-stroke, internal combustion engines usually are small (as opposed to 4-stroke engines) and therefore they are commonly used for lightweight vehicles such as motorcycles, mopeds or and motorized garden appliances such as trimmers, blowers, and chainsaws. Generally, it is desirable for these engines to be of a light weight.
The two-stroke engine generally is composed of a crankcase, cylinder block, and cylinder head, collectively referred to as a “cylinder crankcase short block.” Typically, a cylinder crankcase short block is made from separate components that need to be machined and fastened together, thus requiring mounting holes to be carefully machined within certain tolerances. Moreover, the fasteners add additional weight to the cylinder crankcase short block.
Cylinder crankcase short blocks also require seals between the components to avoid the leakage of air and/or fuel. The use of seals exposes the cylinder crankcase to failures such as the deterioration of a seal or leaking.
U.S. Pat. No. 2,489,150 to McCoy discloses an integrally cast cylinder crankcase and block. The cylinder head is a separate piece that must be mounted to the cylinder block so that a sleeve may be pressed into the cylinder block prior to the cylinder block being covered with the cylinder head. Similarly, U.S. Pat. No. 3,983,852 to Chatourel teaches a one-piece cylinder and crankcase with an integral cylinder head. The cylinder and crankcase casting of Chatourel, however, requires a separate cover that attaches to the casting. This cover “seals” the casting and acts as a support, or bearing surface, for a camshaft.
A cylinder-crankcase is disclosed herein that includes a cylinder block having a cylinder head for receiving a spark plug. The cylinder-crankcase also includes a crankcase, and a crank arm for supporting a crankshaft. The cylinder block, cylinder head, crankcase, and crank arm are a single, monolithic piece.
The present disclosure also includes a method for forming a cylinder-crankcase. The method includes forming a cylinder block, cylinder head, crankcase, and crank arm as a single, monolithic piece so that the cylinder-crankcase is formed without any fasteners and gaskets.
Turning now to
The cylinder-crankcase 2 includes a crankcase 4, a cylinder block 6, and a cylinder head 8. The crankcase 4 includes a frame 10. The center of the frame 10 has a crank arm 12 for supporting a crank shaft 14. The crank arm 12 also supports a counterweight 15 (
The crankcase includes a plurality of fingers 22 that surround the crank arm 12. Lower fingers 24 act as fins to facilitate the entry of cooling air into the cylinder block in order to cool the cylinder-crankcase 2. Referring to
The cylinder block 6 also includes several portions for the attachment of various engine components. For example, the cylinder block includes at least one boss 38 that receives a mounting screw in order to mount a spark plug initiator such as an ignition module. As shown in
The cylinder block 6 also includes an exhaust mounting 40 and a carburetor mounting 42 for the attachment of an exhaust and carburetor, respectively. Although the exhaust and carburetor mountings 40, 42 may be configured in a variety of ways with respect to each other (i.e., side by side, etc.), those skilled in the art will recognize that it is preferable to locate the exhaust and carburetor mountings 40, 42 on opposite sides of the cylinder block 6 so that the heat the carburetor may experience from the exhaust is reduced.
The cylinder block includes a chamber 32 for housing a reciprocating piston assembly that moves within the chamber and that is connected to the connecting rod 18 described above. As explained further below, the chamber also receives a gaseous mixture of fuel and air from the crankcase. A lower face 46 of the cylinder block includes an opening 48 that allows the piston assembly to be placed within the chamber 32. Referring to
The cylinder head 8 is located atop the cylinder block 6, and as explained above, is cast monolithically with the cylinder block 6 and crankcase 4. While the cylinder head 8 may have numerous configurations, in a preferred embodiment, the cylinder head 8 is comprised of at least one fin 50 similar to the plurality of fins 34 associated with the cylinder block 6. The fin 50 includes an opening 52 that opens into the chamber 32 of the cylinder block. The opening 52 is for the reception of a spark plug 54 that is threaded through the cylinder head 8 and partially into the chamber 32.
The operation of the engine is as follows: as the piston assembly moves upwardly within the chamber, a vacuum will be created that draws the gaseous mixture of fuel and air from the carburetor and into the crankcase. At the same time, during the upward stroke of the piston, any gaseous mixture already in the chamber will be compressed and ignited by the sparkplug, producing a high-pressure charge. This charge, in turn, will drive the piston in a downwardly direction, allowing any gases remaining in the chamber to be expelled through the exhaust, and allowing the gaseous mixture in the crankcase to enter into the chamber by passing through the passages. The upward and downward movement of the piston, in turn, will drive the connecting rod and crankshaft.
As explained above, the entire cylinder-crankcase (i.e., the crankcase, including the crank arm and cylinder bores, cylinder block and cylinder head) is cast as one monolithic piece. The present cylinder-crankcase therefore eliminates the need for additional fasteners and parts to assemble the cylinder-crankcase. This provides several benefits: 1) the parts forming the cylinder-crankcase do not need to be machined to “mate” or have aligning holes for fasteners 2) the weight of the cylinder-crankcase will be reduced due to the lack of fasteners; and 3) joint weakness and fracture, which is most likely to occur in areas where parts are fastened together, will be greatly reduced since the cylinder-crankcase is monolithic. Moreover, unlike prior-art cylinder crankcases, the present cylinder-crankcase can support bearings, via the integral bearing bores, without requiring additional, separate supporting components.
Similarly, the monolithic cylinder-crankcase also eliminates the need for gaskets and other seals that typically are required for cylinder-crankcases that are fastened together. This in turn, provides the advantage of further reducing the weight of the cylinder-crankcase and eliminating failures often associated with seals such as deterioration and leakage, which can lead to the loss of compression.
Advantageously, the cylinder-crankcase also may be made through other processes and still retain the benefits enumerated above. The cylinder-crankcase may be formed through injection molding. A metal cylinder sleeve, made of a material such as cast-iron, may then be inserted into the cylinder block via the opening 48 in the cylinder block. Not only are the above benefits still realized, but the addition of the sleeve will reduce noise generated by the engine. In alternate embodiments, the cylinder-crankcase may be molded over the sleeve when the cylinder-crankcase is being formed.
It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention. For example, although the cylinder-crankcase 2 has been described in conjunction for use with a two-stroke cylinder engine, those skilled in the art will appreciate that the monolithic cylinder-crankcase may be used in conjunction with a four-stroke cylinder engine.
