In a general-purpose engine including a cylinder block extending obliquely from one side of a crank case, and a cylinder head connected to an end surface of the cylinder block via a gasket, a unidirectional valve for allowing a flow of a fluid from a crank chamber to a valve operating chamber and blocking a reverse flow of the fluid is installed in an upper oil passage. In a case where lubricant oil reserved in the crank chamber flows into the valve operating chamber via a lower oil passage when the engine inclines such that the inclined cylinder block further slants, positive pressures transmitted from the crank chamber to the valve operating chamber push the oil, which once flows into the valve operating chamber, back to the crank chamber via the lower oil passage.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an improvement of a general-purpose engine used for power of various work machines such as a lawn mower and the like, particularly, a general-purpose engine comprising: a crank case having a mounting flange in a bottom portion of the crank case; a cylinder block extending obliquely from one side of the crank case; and a cylinder head connected to an end surface of the cylinder block via a gasket, in which a crank chamber in the crank case includes oil spray generating means for generating oil spray for lubricating engine parts by scattering lubricant oil reserved in the crank chamber, and upper and lower side portions of the cylinder block and the cylinder head are provided respectively with an upper oil passage and a lower oil passage which communicate the crank chamber and a valve operating chamber in the cylinder head with each other.

Description of the Related Art

Such a general-purpose engine is known as disclosed in, for example, Japanese Utility Model Publication No. 62-15451.

In a general-purpose engine of this type, depending on a use condition of a work machine, an inclined cylinder block may be further inclined. In this case, it is likely that: a large amount of oil reserved in a crank chamber flows into a valve operating chamber via a lower oil passage; thereby, the amount of oil reserved in the crank chamber decreases to a large extent, and oil spray generating means insufficiently generates oil spray; and lubrication of engine parts is hindered.

SUMMARY OF THE INVENTION

The present invention has been made with the foregoing situation taken into consideration. An object of the present invention is to provide a general-purpose engine in which even though oil reserved in a crank chamber flows into a valve operating chamber via a lower oil passage when an inclined cylinder block is further inclined, the oil once flowing into the valve operating chamber is quickly pushed back to the crank chamber to secure the amount of oil reserved in the crank chamber, and to keep engine parts lubricated without hindrance.

In order to achieve the object, according to a first aspect of the present invention, there is provided a general-purpose engine comprising: a crank case having a mounting flange in a bottom portion of the crank case; a cylinder block extending obliquely from one side of the crank case; and a cylinder head connected to an end surface of the cylinder block via a gasket, in which a crank chamber in the crank case includes oil spray generating means for generating oil spray for lubricating engine parts by scattering lubricant oil reserved in the crank chamber, and upper and lower side portions of the cylinder block and the cylinder head are provided respectively with an upper oil passage and a lower oil passage which communicate the crank chamber and a valve operating chamber in the cylinder head with each other, wherein a unidirectional valve for allowing a flow of a fluid from the crank chamber to the valve operating chamber and blocking a reverse flow of the fluid is installed in the upper oil passage, and in a case where the lubricant oil reserved in the crank chamber flows into the valve operating chamber via the lower oil passage when the engine inclines such that the obliquely extending cylinder block further slants, positive pressures transmitted from the crank chamber to the valve operating chamber via the unidirectional valve push the oil, which once flows into the valve operating chamber, back to the crank chamber via the lower oil passage. Note that the oil spray generating means corresponds to an oil dipper24of an embodiment of the present invention, described later.

According to the first aspect, even though a large amount of oil flows from the crank chamber into the valve operating chamber via the lower oil passage when, depending on a use condition of a work machine, the engine is forced to be oriented such that the obliquely extending cylinder block is further slanted, operation of the unidirectional valve in the upper oil passage, based on operation of the engine, causes positive pressures out of pulsating pressures generated in the crank chamber to be transmitted to the valve operating chamber via the upper oil passage. For this reason, pressure inside the valve operating chamber becomes higher, and the oil once flowing into the valve operating chamber can be pushed back to the crank chamber via the lower oil passage. This prevents a decrease in the amount of oil reserved in the crank chamber, and enables the oil spray generating means to always generate the oil spray, accordingly making it possible to keep the engine parts lubricated satisfactorily.

According to a second aspect of the present invention, in addition to the first aspect, the gasket interposed between the cylinder block and the cylinder head divides the upper oil passage into an upstream passage on the crank chamber side and a downstream passage on the valve operating chamber side, the gasket includes a valve attachment hole, and a plurality of through-holes disposed surrounding the valve attachment hole, and communicating the upstream passage and the downstream passage with each other, and the unidirectional valve includes a valve body having an elastic umbrella portion seated on an upper surface of the gasket facing the downstream passage, and covering a group of the through-holes, and a stem portion projecting from a boss portion of the elastic umbrella portion, and penetrating through the valve attachment hole, and a retaining member fitted and fixed to the stem portion, and thereby clamping the gasket in cooperation with the boss portion.

According to the second aspect, it is possible to easily attach the unidirectional valve by use of the gasket, and to use the unidirectional valve without making major alterations to a conventional engine, as well as to minimize improvement costs.

According to a third aspect of the present invention, in addition to the second aspect, the stem portion is formed smaller in diameter than the valve attachment hole such that an outer peripheral surface of the stem portion is prevented from touching an inner peripheral surface of the valve attachment hole, and the retaining member includes a plurality of positioning claws respectively engaging with the plurality of through-holes to thereby hold the stem portion at a position concentric with the valve attachment hole.

According to the third aspect, the stem portion of the valve body does not touch the inner peripheral surface of the valve attachment hole with a certain distance kept between an overall periphery of the stem portion and the inner peripheral surface of the valve attachment hole. Accordingly, the stem portion can be prevented from damage due to its contact with a sharp inner peripheral edge of the valve attachment hole in the thin gasket, and to maintain durability of the stem portion. Furthermore, since the through-holes for allowing passage of the positive pressures double as the holes with which the positioning claws engage, it is unnecessary to provide dedicated positioning holes in the gasket. This contributes to simplifying the structure.

According to a fourth aspect of the present invention, in addition to the second or third aspect, the stem portion includes a first shaft portion extending from the boss portion, and fitted into a fitting hole in the retaining member, and a second shaft portion coaxially continuing to the first shaft portion via an expanded portion, and being smaller in diameter than the first shaft portion, and the expanded portion is formed larger in diameter than the first shaft portion to hold the retaining member on the first shaft portion by engaging with a rear surface of the retaining member.

According to the fourth aspect, ease of installation of the unidirectional valve can be enhanced.

The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiment which will be provided below while referring to the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Descriptions will be hereinbelow provided for an embodiment of the present invention on the basis of the accompanying drawings.

InFIGS. 1 and 2, a general-purpose engine E includes: a crank case2having a mounting flange1in its bottom portion; a cylinder block3extending obliquely from one side of the crank case2; and a cylinder head5connected to an end surface of the cylinder block3via a gasket4. A fuel tank T and an air cleaner A are attached to upper portions of the crank case2and the cylinder block3, respectively. The mounting flange1is mounted on a work machine which uses the general-purpose engine E as a driving source.

A crank shaft7is disposed in a crank chamber13inside the crank case2. The crank shaft7is linked, via a connecting rod9, to a piston8which is fitted in a cylinder bore3aof the cylinder block3. In addition, a combustion chamber10continuing to the cylinder bore3a,as well as an intake port11iand an exhaust port (not illustrated) both opened to the combustion chamber10are formed in the cylinder head5. The cylinder head5is provided with: an intake valve12ifor opening and closing the intake port11i;and an exhaust valve (not illustrated) for opening and closing the exhaust port. An intake rocker arm18iof a valve operating device15for driving the intake valve12ito open and close, and an exhaust rocker arm (not illustrated) of the valve operating device15for driving the exhaust valve to open and close are disposed in a valve operating chamber14inside the cylinder head5. The intake rocker arm18iand the exhaust rocker arm are swung by a cam shaft17, which is disposed in the crank chamber13and driven at a reduced speed by the crank shaft7, via an intake push rod19iand an exhaust push rod (not illustrated), respectively. Thereby, the intake rocker arm18iand the exhaust rocker arm open and close the intake valve12iand the exhaust valve, respectively. The intake push rod19iand the exhaust push rod are disposed extending in a lower side portion of the cylinder block3.

In the crank chamber13, lubricant oil23is reserved at a certain level which does not reach a lower oil passage21. An oil dipper24for generating oil spray by scattering the oil23is annexed to a larger end portion of the connecting rod9.

Furthermore, an upper oil passage20and the lower oil passage21, which communicate the crank chamber13and the valve operating chamber14with each other while penetrating through the gasket4between the cylinder block3and the cylinder head5, are provided to upper and lower side portions of the cylinder block3and the cylinder head5, respectively. The lower oil passage21is disposed between the intake push rod19iand the exhaust push rod.

A unidirectional valve V for allowing a flow of a fluid from the crank chamber13to the valve operating chamber14and blocking a reverse flow of the fluid is installed in the upper oil passage20. The unidirectional valve V is attached to the gasket4, as follows.

As shown inFIGS. 3 and 4, the gasket4divides the upper oil passage20into an upstream passage20aon the crank chamber13side and a downstream passage20bon the valve operating chamber14side. The gasket4is provided with: a valve attachment hole25; and multiple (three in the illustrated example) through-holes26disposed surrounding the valve attachment hole25, and communicating the upstream passage20aand the downstream passage20bwith each other.

The unidirectional valve V includes: a valve body28made from an elastic material such as rubber or the like; and a retaining member29made from a synthetic resin. The valve body28includes: an elastic umbrella portion30; a boss portion31formed at a center of the elastic umbrella portion30, and projecting toward the gasket4; and a stem portion32extending from the boss portion31. Furthermore, the stem portion32includes: a first shaft portion32aextending from the boss portion31, and being fully smaller in diameter than the valve attachment hole25; and a second shaft portion32bcoaxially continuing to the first shaft portion32avia an expanded portion32c,and being smaller in diameter than the first shaft portion32a. The valve body28is disposed with the stem portion32inserted in the valve attachment hole25, and with the umbrella portion30seated on an upper surface4aof the gasket4facing the downstream passage20b.

The retaining member29has a fitting hole34in a central portion, and further has, in an outer periphery, positioning claws35which are as many as the through-holes26, and which project in an axial direction.

Connecting of the retaining member29to the valve body28is achieved by: inserting the second shaft portion32bof the valve body28into the fitting hole34; and thereafter pressing the retaining member29toward the first shaft portion32awhile pulling the thus-inserted second shaft portion32b. Thereby, the expanded portion32cstretches, and reduces its diameter. This makes it possible for the fitting hole34of the retaining member29to pass through the expanded portion32c, and to become fitted to the first shaft portion32a.Thereafter, once the second shaft portion32bis released from the pulling, the expanded portion32creturns to its original shape with a larger diameter, and engages with a rear surface of the retaining member29. Thereby, the expanded portion32cholds the retaining member29at a position where the retaining member29is fitted to the first shaft portion32a. Once fitted to the first shaft portion32a, the retaining member29clamps the gasket4in cooperation with the boss portion31of the valve body28.

At this time, the multiple positioning claws35of the retaining member29engage with the multiple through-holes26in the gasket4to thereby hold the stem portion32at a position concentric with the valve attachment hole25. Thereby, the first shaft portion32a, which is fully smaller in diameter than the valve attachment hole25, is prevented from touching an inner peripheral surface of the valve attachment hole25, since a certain distance is kept between an overall periphery of the first shaft portion32aand the inner peripheral surface of the valve attachment hole25.

It should be noted that albeit not illustrated, a breather pipe for discharging a blowby gas into an intake system is connected to an upper portion of the valve operating chamber14.

Next, descriptions will be provided for an operation of this the embodiment.

While the general-purpose engine E is in operation with a normal orientation in which the mounting flange1is set horizontally, the oil23reserved in the crank chamber13does not reach the lower oil passage21, and the oil dipper24swinging in response to rotation of the crank shaft7is hitting and scattering the reserved oil23, thereby generating the oil spray. Peripheries of the piston8and the connecting rod9are lubricated with the oil spray. Furthermore, the oil spray passes the upper oil passage20and the lower oil passage21, and reaches the valve operating chamber14, where the oil spray also lubricates the valve operating device15.

Particularly since the unidirectional valve V for allowing the flow of the fluid from the crank chamber13to the valve operating chamber14and blocking the reverse flow is installed in the upper oil passage20, only positive pressures out of pulsating pressures generated in the crank chamber13in response to reciprocating motion of the piston8can pass through the upper oil passage20, and the positive pressures carry the oil spray to the valve operating chamber14.

To put it concretely, when a positive pressure out of the pulsating pressures generated in the crank chamber13acts on the elastic umbrella portion30of the unidirectional valve V via the through-holes26in the gasket4, the elastic umbrella portion30is pushed open, and allows the positive pressure to pass through the upper oil passage20. On the other hand, when a negative pressure acts on the elastic umbrella portion30via the through-holes26, the elastic umbrella portion30is pulled to the gasket4, becomes seated on the upper surface4a, and closes the through-holes26, thereby blocking the negative pressure from passing through the upper oil passage20. In this manner, only the positive pressures pass through the upper oil passage20.

In a case where, depending on a use condition of the work machine, the general-purpose engine E is forced to be oriented such that the obliquely extending cylinder block3is further slanted, a large amount of oil23flows from the crank chamber13into the valve operating chamber14via the lower oil passage21. However, when the general-purpose engine E is operated, operation of the unidirectional valve V, in the upper oil passage20as described above, causes the positive pressures out of the pulsating pressures generated in the crank chamber13to be transmitted to the valve operating chamber14via the upper oil passage20. For this reason, pressure inside the valve operating chamber14becomes higher, and the oil23once flowing into the valve operating chamber14can be accordingly pushed back to the crank chamber13via the lower oil passage21. This prevents a decrease in the amount of oil23reserved in the crank chamber13, and enables the oil dipper24to always generate the oil spray, accordingly making it possible to keep the engine parts lubricated satisfactorily.

Meanwhile, the gasket4interposed between the cylinder block3and the cylinder head5is provided with: the valve attachment hole25; and the multiple through-holes26disposed surrounding the valve attachment hole25, and communicating with the upper oil passage20. The unidirectional valve V includes: the valve body28which includes the elastic umbrella portion30for covering the group of the through-holes26while seated on the upper surface4aof the gasket4facing the downstream passage20bof the upper oil passage20, and the stem portion32projecting from the boss portion31of the elastic umbrella portion30, and penetrating through the valve attachment hole25; and the retaining member29fitted and fixed to the stem portion32so as to clamp the gasket4in cooperation with the boss portion31. For these reasons, it is possible to easily attach the unidirectional valve V by use of the gasket4, and to use the unidirectional valve V without making major alterations to a conventional general-purpose engine, as well as to minimize improvement costs.

Furthermore, the stem portion32of the valve body28is formed smaller in diameter than the valve attachment hole25such that the outer peripheral surface of the stem portion32does not touch the inner peripheral surface of the valve attachment hole25. Meanwhile, the multiple positioning claws35of the retaining member29engage with the respective through-holes26in the gasket4to thereby hold the stem portion32at the position concentric with the valve attachment hole25. For these reasons, the stem portion32does not touch the inner peripheral surface of the valve attachment hole25with the certain distance kept between the overall periphery of the stem portion32and the inner peripheral surface of the valve attachment hole25. Accordingly, the stem portion32can be prevented from damage due to its contact with a sharp inner peripheral edge of the valve attachment hole25in the thin gasket4, and to maintain durability of the stem portion32. Furthermore, since the through-holes26for allowing the passage of the positive pressures double as the holes with which the positioning claws35engage, it is unnecessary to provide dedicated positioning holes in the gasket4. This contributes to simplifying the structure.

Moreover, the stem portion32includes: the first shaft portion32aextending from the boss portion31of the umbrella portion30, and fitted into the fitting hole34in the retaining member29; and the second shaft portion32bcoaxially continuing to the first shaft portion32avia the expanded portion32c,and being smaller in diameter than the first shaft portion32a. The expanded portion32cis formed larger in diameter than the first shaft portion32ato hold the retaining member29on the first shaft portion32aby engaging with the rear surface of the retaining member29. For these reasons, when the fitting hole34of the retaining member29is fitted to the first shaft portion32a, the fitting hole34can easily pass through the expanded portion32cwith the diameter of the expanded portion32cdecreased by pulling the second shaft portion32b.Accordingly, ease of installation of the unidirectional valve V can be enhanced.

The present invention is not limited to the foregoing embodiment. Various design changes can be made to the present invention within the scope not departing from the gist of the present invention. For example, instead of the oil dipper24, an oil slinger to be rotationally driven by the crank shaft7may be used to generate the oil spray.