Breather device for engine

In a breather device for engine, in which an inlet of a breather chamber communicates with a crank chamber through a reed valve, the reed valve being formed of: a fixed stopper plate arranged so as to be opposed to a valve seat formed on an end face of the inlet facing the breather chamber; and an elastic valve plate fixed at one end thereof to the stopper plate and capable of bending elastically to change its position from a closed position in which the elastic valve plate closes the inlet by seating on the valve seat to an opening limit position in which the elastic valve plate opens the inlet and abuts against the stopper plate, the stopper plate is provided at a center part thereof with an oil discharge hole through which oil present between the elastic valve plate and the stopper plate is pushed out when the elastic valve plate is pushed toward the opening limit position in which the elastic valve plate abuts against the stopper plate by pressure in the crank chamber. Accordingly, it is possible to prevent the elastic valve plate from sticking to the stopper plate even if oil mist adheres to the elastic valve plate or the stopper plate of the reed valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 USC §119 based on Japanese patent application No. 2008-147722 filed Jun. 5, 2008. The subject matter of this priority document is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improvement of a breather device for engine, in which an inlet of a breather chamber communicates with a crank chamber of an engine through a reed valve that allows gas to flow only in one direction from the crank chamber side to the breather chamber side, the reed valve being formed of: a valve seat formed on an end face of the inlet facing the breather chamber; a fixed stopper plate arranged so as to be opposed to and distanced form the valve seat; and an elastic valve plate fixed at one end thereof to the stopper plate and capable of bending elastically to change its position from a closed position to an opening limit position, the closed position being a position in which the elastic valve plate closes the inlet by seating on the valve seat, the opening limit position being a position in which the elastic valve plate opens the inlet and abuts against the stopper plate.

2. Description of the Related Art

Such a breather device for engine is known from Japanese Patent Application Laid-open No. 64-4812, for example.

In the conventional breather device for engine, gas sent under pressure from a crank chamber to a breather chamber includes lubricant oil mist, and the oil mist might adhere to an elastic valve plate or a stopper plate of a reed valve. Such oil mist adherence possibly causes the elastic valve plate to stick to the stopper plate when the elastic valve plate is brought to an opening limit position in which the elastic valve plate abuts against the stopper plate. This might inhibit the closing operation of the elastic valve plate, which is to be performed when the crank chamber is decompressed. As a result, the crank chamber cannot be kept under negative pressure.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of such circumstances, and has an objective to provide a breather device for engine in which an elastic valve plate can be prevented from sticking to a stopper plate even if oil mist adheres to the elastic valve plate or the stopper plate of a reed valve.

In order to achieve the above object, according to a first feature of the present invention, there is provided a breather device for engine, in which an inlet of a breather chamber communicates with a crank chamber of an engine through a reed valve that allows gas to flow only in one direction from the crank chamber side to the breather chamber side, the reed valve being formed of: a valve seat formed on an end face of the inlet facing the breather chamber; a fixed stopper plate arranged so as to be opposed to and distanced form the valve seat; and an elastic valve plate fixed at one end thereof to the stopper plate and capable of bending elastically to change its position from a closed position to an opening limit position, the closed position being a position in which the elastic valve plate closes the inlet by seating on the valve seat, the opening limit position being a position in which the elastic valve plate opens the inlet and abuts against the stopper plate, wherein the stopper plate is provided at a center part thereof with an oil discharge hole through which oil present between the elastic valve plate and the stopper plate is pushed out when the elastic valve plate is pushed toward the opening limit position in which the elastic valve plate abuts against the stopper plate by pressure in the crank chamber.

According to the first feature of the present invention, when the elastic valve plate is pushed up against the stopper plate by positive pressure generated in the crank chamber, oil present between the elastic valve plate and the stopper plate is pushed out toward not only the peripheral edge part of the stopper, but also the oil discharge hole. Accordingly, the oil present between the elastic valve plate and the stopper plate can be reduced speedily and drastically. In addition, the presence of the oil discharge hole allows a small contact area between the elastic valve plate and the stopper plate. Accordingly, the elastic valve plate can be surely prevented from sticking to the stopper plate. Thereby, the elastic valve plate can have improved valve-closing responsiveness to speedily perform the closing-valve operation, and can close the inlet speedily and surely when the crank chamber is decompressed.

Moreover, the oil discharge hole plays another function of applying the pressure in the breather chamber to the elastic valve plate abutting against the stopper plate. Accordingly, when the crank chamber is decompressed, the elastic valve plate is biased toward the valve-closing side by the difference between the pressure in the crank chamber and the pressure in the breather chamber. The elastic valve plate can thus have valve-closing responsiveness improved further.

Further, according to a second feature of the present invention, in addition to the first feature, the stopper plate is provided at a peripheral edge part thereof with paired oil discharge cutouts which are formed side by side with the oil discharge hole between the cutouts.

According to the second feature of the present invention, oil present between the elastic valve plate and the stopper plate can be reduced further speedily and drastically by pushing out the oil present between the elastic valve plate and the stopper plate toward the oil discharge hole and toward the paired oil discharge cutouts. Consequently, the elastic valve plate can be more surely prevented from sticking to the stopper plate.

Further, according to a third feature of the present invention, in addition to the second feature, in the oil discharge hole, a part sandwiched by the paired oil discharge cutouts has a smaller width than other parts.

According to the third feature of the present invention, the stopper plate can be prevented from having less rigidity because of the presence of the paired oil discharge cutouts. Thereby, the stopper plate can rigidly limit the position of the elastic valve plate at the opening limit position.

Here, the inlet and the outlet correspond respectively to an inlet hole20and an exhaust pipe21of an embodiment of the present invention, which will be described below.

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

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be explained below with reference toFIG. 1 to 3.

InFIG. 1, reference numeral E denotes a general-purpose engine. An engine body1of the general-purpose engine E is formed of a crankcase2supporting a crankshaft (not shown), a cylinder block3provided to one side of the crankshaft2in a continuous manner and placed substantially horizontally, and a cylinder head4joined to an end face of the cylinder block3. The cylinder block3has a cylinder bore3ainto which a piston6is slidably fitted. The piston6is connected to the crankshaft via a connecting rod5. A combustion chamber7and intake and exhaust ports8and8′ are formed in the cylinder head4. The combustion chamber7is in communication with the cylinder bore3a, and the intake and exhaust ports8and8′ are open to the combustion chamber7. Moreover, intake and exhaust valves11and11′ are attached to the cylinder head4to open and close the intake and exhaust ports8and8′, respectively.

A head cover10is joined to the cylinder head4, and the head cover10and the cylinder head4define a valve operation chamber9in between. Intake and exhaust rocker arms12and12′ are pivotally supported by the cylinder head4in a swingable manner. In the valve operation chamber9, one ends of the respective intake and exhaust rocker arms12and12′ are connected to valve heads of the respective intake and exhaust valves11and11′. A camshaft, which is not shown, is connected to the other ends of the intake and exhaust rocker arms12and12′ via intake and exhaust push rods13and13′, respectively.

The intake and exhaust push rods13and13′ are placed in a continuous pass hole14. The pass hole14is provided in a top wall part of the cylinder block3and the cylinder head4to allow the inside of the crankcase2, namely, a crank chamber2a, to be communicated with the valve operation chamber9. The pass hole14inclines downward toward the crank chamber2a. This design allows oil mist adhered to the inner peripheral surface of the pass hole14to return toward the crank chamber2a.

A breather chamber15having an open top face and a boss16protruding into the breather chamber15are integrally formed on a top wall of the cylinder block3. The open top face of the breather chamber15is closed by a lid plate18fixed to the breather chamber15by a bolt17. The boss16is provided with an inlet hole20which communicates the pass hole14to the inside of the breather chamber15. Moreover, an exhaust pipe21is provided to one side wall of the breather chamber15at a position as distanced from the inlet hole20as possible. The exhaust pipe21is open to the outside, and preferably, is open to the intake path of an inlet system (not shown) of the engine E—for example, an air cleaner or a carburetor—through a breather hose22.

A reed valve25is provided on the inlet hole20to allow gas flow only in one direction—from the pass hole14side, namely, the crank chamber2aside, to the breather chamber15side.

The boss16and the inlet hole20are both of elliptical shape in cross section. A flat valve seat26and paired positioning walls27and27are formed in an end face of the boss16on the breather chamber15side. The positioning walls27and27are arranged side by side with a longitudinal end part of the valve seat26in between. An elastic valve plate28and a stopper plate29are overlapped at their one end parts and are fitted between the positioning walls27and27. The elastic valve plate28is capable of closing the inlet hole20by sitting on the valve seat26, and the stopper plate29limits the opening of the elastic valve plate28. The elastic valve plate28and the stopper plate29are fastened to the boss16by a single bolt30.

The stopper plate29has a flat base part29aand a curved part29b. The base part29ais formed at one end part of the stopper plate29and fixed to the boss16by the bolt30. The curved part29bextends from the base part29atoward the other end part while curving away from the valve seat26. The stopper plate29is rigid enough to maintain an opening limit position B of the elastic valve plate28, which will be described below.

AsFIG. 1shows, the elastic valve plate28is capable of bending elastically to change its position between a closed position A and the opening limit position B. In the closed position A, the elastic valve plate28sits on the valve seat26and thereby closes the inlet hole20. In the opening limit position B, the elastic valve plate28abuts against the stopper plate29and thereby opens the inlet hole20.

An oil discharge hole31is provided at a center part of the curved part29bof the stopper plate29. The oil discharge hole31has one half part31aon the bolt30side and the other half part31b, and is formed such that the lateral width of the one half part31ais smaller than that of the other half part31b. Paired oil discharge cutouts32and32are formed in a peripheral edge of the curved part29bin such a manner as to be located side by side with the narrow one half part31abetween the cutouts.

In the breather chamber15, a maze19(seeFIG. 2) is formed between the inlet hole20and the exhaust pipe21. This design allows oil mist mixed in gas traveling from the inlet hole20to the exhaust pipe21to be separated from the gas. A small hole33(seeFIGS. 1 and 2) is provided in a lowermost part of the breather chamber15to allow the separated oil to return toward the pass hole14.

Next, operations of this embodiment will be explained.

While the engine E is in operation, pressure in the crank chamber2apulsates along with the reciprocating motion of the piston6. When the crank chamber2ais positively pressurized, the positive-pressure gas pushes up the elastic valve plate28of the reed valve25from the valve seat26to open the inlet hole20and then travels to the breather chamber15being under atmospheric pressure. When, on the other hand, the crank chamber2ais negatively pressurized, the negative-pressured gas pulls the elastic valve plate28toward the valve seat26. The inlet hole20is thus closed to block inflow of outside air to the crank chamber2a. In this way, while the engine E is in operation, the crank chamber2ais kept under negative pressure averagely.

When the positive pressure is released to the breather chamber15through the inlet hole20opened by the elastic valve plate28, blowby gas generated in the crank chamber2atravels to the breather chamber15through the inlet hole20at the same time. Then, the blowby gas is taken into the inlet system of the engine E from the exhaust pipe21through the breather hose22, and is then subjected to a combustion process in the combustion chamber7of the engine E along with the air-fuel mixture.

Now, usually, lubricant oil mist drifting in the crank chamber2aand the like is mixed in gas including the blowby gas, which is sent under pressure from the crank chamber2aside to the breather chamber15. The oil mist is separated from the gas in the course in which the gas travels in the breather chamber15from the inlet hole20to the exhaust pipe21. Oil thus separated then flows along the bottom face of the breather chamber15down to the small hole33to return to the pass hole14and then to the crank chamber2a.

Meanwhile, the oil mist carried to the breather chamber15along with the gas may adhere to the parts of the reed valve25. In particular, when the elastic valve plate28is pushed by the positive pressure to abut against the curved part29bof the stopper29and is thus in the opening limit position B, with the oil mist adhering to the faces of the elastic valve plate28and the stopper plate29facing each other, a phenomenon tends to occur in which the elastic valve plate28sticks to the stopper plate29. To this regard, in the present invention, since the oil discharge hole31is provided at the center part of the curved part29bof the stopper plate29, when the elastic valve plate28is pushed up against the curved part29b, the oil present between the elastic valve plate28and the curved part29bcan be pushed out toward not only the peripheral edge part of the curved part29b, but also the oil discharge hole31. Accordingly, the oil present between the elastic valve plate28and the stopper plate29can be reduced speedily and drastically. In addition, the presence of the oil discharge hole31allows a small contact area between the elastic valve plate28and the stopper plate29. Accordingly, the elastic valve plate28can be surely prevented from sticking to the stopper plate29. Thereby, the elastic valve plate28can have improved valve-closing responsiveness to speedily perform the closing-valve operation, and can close the inlet hole20speedily and surely when the crank chamber2ais decompressed.

Moreover, the oil discharge hole31also plays a function of applying the pressure in the breather chamber15to the elastic valve plate28abutting against the stopper plate29. Accordingly, when the crank chamber2ais decompressed, the elastic valve plate28is biased toward the valve-closing side by the difference between the pressure in the crank chamber2aand the pressure in the breather chamber15. The elastic valve plate28can thus have a valve-closing responsiveness improved further.

In addition, the paired oil discharge cutouts32and32are formed in the peripheral edge of the curved part29bin such a manner as to be located side by side with the oil discharge hole31between the cutouts. Accordingly, the oil present between the elastic valve plate28and the stopper plate29can be reduced further speedily and drastically by pushing out the oil present between the elastic valve plate28and the curved part29btoward the oil discharge hole31and toward the paired oil discharge cutouts32and32. Consequently, the elastic valve plate28can be more surely prevented from sticking to the stopper plate29.

Further, the oil discharge hole31is formed such that the lateral width of the one half part31aon the bolt30side is smaller than that of the other half part31b, and the paired oil discharge cutouts32and32are formed with the narrow one half part31abetween the cutouts. Accordingly, the stopper plate29can be prevented from having less rigidity because of the presence of the paired oil discharge cutouts32and32. Thereby, the stopper plate29can rigidly limit the position of the elastic valve plate28at the opening limit position B.

The present invention is not limited to the above-mentioned embodiment and may be modified in a variety of ways as long as the modifications do not depart from its gist. For example, the breather chamber15can be provided to any part as long as the part is in communication with the crank chamber2a, and therefore can be provided to the valve operation chamber9.