The present invention relates to a portable 4-cycle engine used for driving a portable machine such as a back pack blower or a bush cutter, and to the portable machine equipped with the 4-cycle engine.
The present application claims priority from Japanese Patent Application Nos. 2006-012876 and 2006-012877, the disclosures of which are incorporated herein by reference.
Combustion chamber shapes for ideal 4-cycle engine performance have been studied in order to improve the output of the engine, or to reduce harmful exhaust-gas emissions. For example, the wedge-shaped combustion chamber and the bathtub combustion chamber are known (see Japanese Examined Patent Publication No. Sho 60-5774). Some large 4-cycle engines for use in vehicles or the like have a separate cylinder and cylinder head to achieve a more appropriate combustion chamber shape.
On the other hand, portable 4-cycle engines for use in back pack blowers, bush cutters and the like conventionally have a cylinder head integral with the cylinder because their top-priority requirements are small size and light weight (see, for example, Japanese Patent No. 3159296).
One problem with the engine having a separate cylinder and cylinder head, however, is that the cylinder head must be firmly and air tightly fastened to the cylinder, because otherwise the combustion gas will leak through the interface, resulting in a power loss. Sometimes combustion gas may leak through the interface resulting from thermal expansion of the cylinder head due to a sharp temperature gradient which occurs in the cylinder head where the combustion chamber is formed. Such gas leak causes an engine power loss, and contamination or damage of the engine. Accordingly, improvements in the cooling performance and rigidity of the cylinder head are the crucial issues in designing engines with a separate cylinder and cylinder head.
One of the portable machines, for example, back pack blowers may be operated at length at a high speed of 8,000 rpm, and also bush cutters may be operated in an rpm range of 7,000 to 10,000 rpm. The cylinder and the cylinder head are subjected to high-frequency impact during the operation, and also the cylinder head is subjected to direct impact from the valve train components in the valve train area inside the cylinder head. Therefore, the cylinder head in particular needs to have high rigidity in order to prevent deformation or damage of the cylinder head and to maintain the seal between the cylinder and the cylinder head. Increasing the thickness of the cylinder head or the height of the bosses provided for bolt-tightening with the cylinder leads to an increase in the size and weight of the engine, which is incompatible with the top-priority requirements that the portable machine should be small and light.
For these reasons, portable machines are usually not equipped with 4-cycle engines with a separate cylinder and cylinder head. On the other hand, conventional 4-cycle engines with a one-piece cylinder and cylinder head assembly have reached their limitations in enhancing the engine power output, and portable machines equipped with such engines have a problem of poor operability due to the low engine power output.
The present invention was devised in view of the above problems in the conventional techniques and its object is to provide a portable 4-cycle engine with a small, lightweight, high-power, and high-durability cylinder head for use in portable machines such as back pack blowers, bush cutters and the like which are required to be small, light, and powerful.
Another object of the invention is to provide a portable machine equipped with a 4-cycle engine with improved engine cooling performance, operation efficiency, and maintenance accessibility.
The portable 4-cycle engine of the present invention is of the type which allows cooling air to flow to the cylinder head on top of the cylinder in the direction of the crankshaft, the cylinder head being separable from the cylinder. To achieve the above object, in one embodiment of the present invention, the 4-cycle engine comprises a cylinder, a cylinder head separately disposed on top of the cylinder and including a combustion chamber at a side of the cylinder, a cooling fan for introducing the cooling air to the cylinder head in which the cooling fan is connected to an end of the crankshaft, a valve train area formed on the cylinder head at the downwind side of the cooling air in the cylinder head, and a plurality of vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft. In addition, the valve train area and the vertical fins are integrally formed with the cylinder head.
With the configuration in which the valve train area is formed in the cylinder head at the downwind side of the cooling air, and in which the vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft are integrally formed with the cylinder head, the 4-cycle engine can maintain high rigidity and good cooling performance even though heat and combustion pressure become higher with the increase of the power output of the engine. Thus the 4-cycle engine is small, light, and powerful, and can work to its full potential as the power source of a portable machine.
The configuration with a separate cylinder and cylinder head allows ease in forming an ideal wedge-shaped combustion chamber to enhance the compression ratio and to improve the engine output.
Another embodiment of the portable 4-cycle engine of the present invention, which is of the type which allows cooling air to flow to the cylinder head on top of the cylinder in the direction of the crankshaft, comprises a cylinder, a cylinder head disposed on top of the cylinder including a combustion chamber at a side of the cylinder, and an intake port and an exhaust port, in which both the ports are oppositely formed with each other in the cylinder head in a direction orthogonal to the crankshaft. The engine further comprises a cooling fan connected to an end of the crankshaft for introducing the cooling air to the cylinder head, a valve train area formed above the intake port and the exhaust port, and a plurality of vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft. In addition, the intake port, the exhaust port, the valve train area and a plurality of the vertical fins are all integrally formed with the cylinder head.
With the configuration in which all of the intake port, the exhaust port, the combustion chamber, the valve train area, and the vertical fins are all integrally formed with the cylinder head, the cylinder head has high rigidity and can be made thinner and lighter. The vertical fins conduct heat from the combustion chamber and the exhaust port to the low-temperature valve train area, and also the vertical fins themselves are cooled by cooling air. Thus, the portable 4-cycle engine is small, light, and powerful, being equipped with the cylinder head with high cooling performance.
One embodiment of the portable machine of the invention is equipped with a 4-cycle engine which is of the type which allows cooling air to flow to the cylinder head on top of the cylinder in the direction of the crankshaft. The 4-cycle engine comprises a cylinder, a cylinder head separately disposed on the cylinder and including a combustion chamber at a side of the cylinder. The engine further comprises a valve train area formed at the downwind side of the cooling air in the cylinder head, and a plurality of vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft. Additionally, the valve train area and the vertical fins are integrally formed with the cylinder head.
With the configuration of the 4-cycle engine in which the valve train area is formed in the cylinder head at the downwind side of the cooling air, and in which the vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft are integrally formed with the cylinder head, the 4-cycle engine can maintain high rigidity and good cooling performance even though heat and combustion pressure become higher with the increase of the power output of the engine. Thus the 4-cycle engine can work to its full potential as the power source of the portable machine, and the portable machine is small, light, powerful, and highly operable.
Another embodiment of the portable machine of the invention is equipped with a 4-cycle engine which is of the type which allows cooling air to flow to the cylinder head on top of the cylinder in the direction of the crankshaft, and which includes an intake port and an exhaust port facing each other along a direction orthogonal to the crankshaft, a combustion chamber, provided in the cylinder head, communicating with the intake port and the exhaust port, a valve train area formed above the intake port and the exhaust port, and a plurality of vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft. The intake port, the exhaust port, the valve train area, and the vertical fins are all integrally formed with the cylinder head.
With the configuration of the 4-cycle engine in which the intake port and the exhaust port facing each other along a direction orthogonal to the crankshaft, the combustion chamber communicating with the intake port and the exhaust port, the valve train area formed above the intake port and the exhaust port, and the vertical fins protruding upward from the cylinder head and extending in the direction of the crankshaft are all integrally formed with the cylinder head, the cylinder head has high rigidity and can be made thinner and lighter. The vertical fins conduct heat from the combustion chamber and the exhaust port to the low-temperature valve train area, and also the vertical fins themselves are cooled by cooling air. Thus, with the 4-cycle engine with high cooling performance, the portable machine is small, light, powerful, and highly operable.
These and other objects and advantages of the present invention will become clear from the following description with reference to the accompanying drawings, wherein:
Preferred embodiments of the portable 4-cycle engine and the portable machine equipped with the engine of the present invention will be hereinafter described with reference to the drawings.
Referring to
Fuel such as gasoline supplied from a fuel tank (not shown) is mixed with air in the carburetor 16 and fed to the combustion chamber 15 (see
The intake port 10e and the exhaust port 10f are opposite each other and integrally formed at the top of the cylinder head 10. One end of the intake port 10e communicates with the combustion chamber 15 (see
Above the intake port 10e and the exhaust port 10f is a valve train area 10g accommodating the valve train components including an intake valve 20, an exhaust valve 12, push rods 11, and others which will be described later. The valve train area 10g is integrally formed with the intake port 10e and the exhaust port 10f being connected to them by using a pair of valve guide bosses 10f2. The valve train area 10g is located in the cylinder head 10 at the downwind side. The upper part of the valve train area 10g is closed by a rocker cover 9.
As shown in
A plurality of vertical fins 10d1, 10d2, 10d3, and 10d4 are integrally formed with the upper part of the cylinder head 10 on the side of the fan 6, i.e., on the upwind side of the cooling air. These fins 10d1, 10d2, 10d3, and 10d4 not only guide the cooling air efficiently and enhance the cooling effect for the cylinder head 10, but also increase the rigidity of the cylinder head 10 and the intake port 10e, exhaust port 10f, valve guide bosses 10f2, and valve train area 10g that are integrally formed with the cylinder head 10.
This configuration of the portable 4-cycle engine 2 with a separable cylinder 8 and cylinder head 10 allows ease in forming an ideal combustion shape in the cylinder head 10 to enhance the compression ratio and to improve the engine output. The increase in the engine output increases the heat and combustion pressure but this can be dealt with by the enhanced rigidity and cooling performance of the engine 2 due to the configuration in which the valve train area 10g is located on the cylinder head 10 at the downwind side of the cooling air and in which a plurality of vertical fins 10d1 to 10d4 protruding upwards from the cylinder head 10 and extending along the direction of the crankshaft 5 are integrally formed with the cylinder head 10. Therefore, the 4-cycle engine 2 is small, light, and powerful, and can work to its full potential as the power source of a portable machine.
In this embodiment, the ignition plug 14 is located near the opening 10g2 on the upwind side, and interposed between the vertical fins 10d2 and 10d3. The vertical fin 10d3 is joined to the valve guide boss 10f2 and the valve train area 10g. The joint between the vertical fin 10d3, and the valve guide boss 10f2 is connected to the outer end of the valve guide boss 10f2 away from its center in a direction orthogonal to the crankshaft direction. The cooling air flowing from the upwind side bifurcates at the ignition plug 14, but because of this configuration, it is not dissipated by the vertical fins 10d2 and 10d3 and effectively cools the outer circumference of the valve guide boss 10f2, and the air currents meet at the opening 10g2 and cool the outer circumference of the intake port 10e and the exhaust port 10f.
The opening 10g2 which is wider on the upwind side readily takes in cooling air, and its tapering shape in the downwind side increases speed of the airflow towards the downwind side, improving cooling efficiency for the surrounding of the valve guide bosses 10f2. Particularly, temperature around the valve guide 12b of the exhaust port 10f (see
Reference numeral 10h denotes a phantom line orthogonal to the crankshaft 5 drawn at the position where it intersects the centerline 8a of the cylinder 8 (see
Referring to
The engine drive system is lubricated by known techniques such as the one disclosed in Japanese Unexamined Patent Application Publication No. Hei 10-288019: Oil is fed from an oil tank (not shown) into the crankcase 4 using the change in the crankcase internal pressure, where the oil is nebulized and fed to the push rod guide 10g3 to lubricate the intake valve 20, exhaust valve 12 and others in the valve train area 10g, after which it is returned to the oil tank. The oil is thus circulated to ensure smooth movement among working parts.
In this embodiment, the bottom 10g1 of the valve train area 10g is inclined downwards from the upwind side where the ignition plug 14 is located to the downwind side. At the downwind side of the valve train area 10g is integrally formed a push rod guide 10g3 having bores for accommodating the push rods 11 and extending downward. With this configuration, the lubricating oil which has condensed inside the valve train area 10g flows down along the bottom 10g1 of the valve train area 10g and collects in the push rod guide 10g3, and an excess of lubricating oil is prevented from remaining inside the valve train area 10g. Although not shown, the valve train area 10g includes a breather system so as to return the blow-by gas to the intake system. If a surplus of oil remains in the valve train area 10g, the oil is discharged to the outside, and such wasteful consumption may lead to lubrication deficiency of the engine drive system. With the configuration of this embodiment, unnecessary oil consumption is prevented.
Further, with the bottom 10g1 of the outer circumference of the valve train area 10g forming part of the structure which introduces cooling air into the opening 10g2, the cooling effect for the valve train area 10g and its vicinity is further enhanced. Since the exhaust valve 12 and its surroundings which tend to be hot are efficiently cooled as mentioned above, troubles such as loosening of the valve guide boss 10f2 and the valve guide 12b due to high temperature or malfunction of the sliding valve stem 12a caused by deformation of the valve guide 12b are prevented.
Furthermore, as shown in
The combustion chamber 15 of this embodiment is wedge-shaped for achieving high output. Such shape can be formed ideally by the design which has a separate cylinder 8 and cylinder head 10. The ignition plug 14 being located on the deeper side of the combustion chamber 15 further increases the compression ratio and contributes to formation of an ideal combustion chamber shape which results in higher engine output.
In this embodiment, as shown in
In the present embodiment, the valve train area 10g is formed in the cylinder head 10 at the downwind side of the cooling air, with the push rod guide 10g3 communicating with the valve train area 10g, and therefore the valve train components (not shown) is mounted on the crankshaft 5 at the downwind side. This means that the engine can be connected to the machine body including the crankshaft 5 and the fan 6 on the opposite side from the push rod guide 10g3, as with this embodiment, with a shorter connection shaft length. A shorter length of connection shaft between the crankshaft 5 and the fan 6 means less shaft wobbling and less vibration of the machine 1. In the case of the back pack blower 1 shown in
The intake port 10e, the exhaust port 10f, and some of the vertical fins 10d1 etc., are located around the bolt head shoulders 10c where the joint condition between the cylinder 8 and the cylinder head 10 is ideal. With this configuration, the cylinder head 10 has high rigidity around the bolt head shoulders 10c, making it less likely that deformation occurs at the joint interface. That is, the cylinder 8 and the cylinder head 10 of this portable 4-cycle engine 2 have high surface pressure on their joint surfaces 10b.
As such machines 1 and 30 are carried by the operator during operation, the power source engine 2 is desired to be small, light, and powerful. The portable 4-cycle engine of the present invention is capable of high power output and has excellent maintenance accessibility, as described above, without increasing the size or weight as compared to the conventional engines. Also, the portable machine equipped with this engine as the power source is small, light, and powerful, and has good operation efficiency and maintenance accessibility.
While there has been described what are at present considered to be preferred embodiments of the present invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.
Number | Date | Country | Kind |
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2006-012876 | Jan 2006 | JP | national |
2006-012877 | Jan 2006 | JP | national |
Number | Name | Date | Kind |
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2725045 | Flatz et al. | Nov 1955 | A |
2753853 | Hands | Jul 1956 | A |
2985155 | Hockel | May 1961 | A |
4216746 | Freyn | Aug 1980 | A |
5564374 | Hoffman et al. | Oct 1996 | A |
5588408 | Kurihara | Dec 1996 | A |
5606944 | Kurihara | Mar 1997 | A |
6039020 | Kawamoto et al. | Mar 2000 | A |
Number | Date | Country |
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60-5774 | Feb 1985 | JP |
3159296 | Feb 2001 | JP |
Number | Date | Country | |
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20070169726 A1 | Jul 2007 | US |