Breathing system in combustion engine

A breathing system in a combustion engine includes an air cleaner (3) for purifying air to be supplied to the engine. The air cleaner (3) includes a cleaner casing (30) having a blow-by gas inlet port (33) and an intake air discharge port (34). The breathing system also includes a breather passage (8) having first and second breather passage portions. The first breather passage portion is fluidly connected with the inlet port (33) for communicating a crank chamber (1a) to a portion of an interior of the air cleaner (3) downstream of the cleaner element (50). The second breather passage portion fluidly connects the blow-by gas inlet port (33) and the intake air discharge port (34) and has a drain hole (95) for draining into the cleaner casing (30) a water component, separated from a blow-by gas (G) flowing through the breather passage (8).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a breathing system in a four-cycle combustion engine that is used as a drive source for a working machine, for example, a small-size snowplow.

2. Description of the Prior Art

The conventional breather passage employed in the four-cycle combustion engine is formed with a breather chamber into which a blow-by gas leaking from the combustion chamber into a crank chamber through around an outer periphery of a reciprocating piston is introduced. Within this breather chamber, an oil component such as oil mists contained in the blow-by gas is separated from the blow-by gas. The separated oil component is returned to the crank chamber. On the other hand, the blow-by gas, from which the oil component has been removed, is supplied to the combustion chamber through an intake system of the combustion engine so that reburning of the blow-by gas can be carried out within the combustion chamber. See, for example, the Japanese Utility Model Registration No. 2556039.

As is well known to those skilled in the art, the blow-by gas leaking from the combustion chamber contains a substantial amount of water component. For this reason, it is desirable to remove the water component from the blow-by gas prior to the blow-by gas being supplied to the fuel intake system of the combustion engine. It has, however, been found that the prior art breather passage cannot sufficiently separate and remove the water component contained in the blow-by gas.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention is intended to provide a breathing system in a combustion engine, which is effective to separate and remove a water component contained in a blow-by gas.

In order to accomplish the foregoing object of the present invention, there is in accordance with the present invention provided a breathing system in a combustion engine, which includes an air cleaner having a replaceable cleaner element and operable to purify air to be supplied to the combustion engine as the air flows through the cleaner element. This air cleaner includes a cleaner casing having a blow-by gas inlet port and an intake air discharge port both defined therein. The breathing system also includes a breather passage having a first breather passage portion and a second breather passage portion. The first breather passage portion is fluidly connected with the blow-by gas inlet port of the cleaner casing for communicating a crank chamber to a portion of an interior of the air cleaner downstream of the cleaner element. The second breather passage portion fluidly connects the blow-by gas inlet port and the intake air discharge port and has a drain hole defined therein for draining into the cleaner casing a water component, separated from a blow-by gas flowing through the breather passage.

According to the present invention, the oil component such as oil mist contained in the blow-by gas can be separated and removed from the blow-by gas as the latter from the crank chamber flows through the breather passage. Also, as the blow-by gas flows through the second breather passage portion formed in the breather passage, the water component contained in the blow-by gas and having a high specific gravity collides against an inner surface of the second breather passage portion under the influence of a centrifugal force and is therefore separated and removed from the blow-by gas then flowing through the second breather passage portion. The blow-by gas, from which the water component has been removed, is subsequently supplied to the intake system of the combustion engine through the intake air discharge port together with the air purified by the cleaner element of the air cleaner. On the other hand, the water component separated and removed from the blow-by gas is drained into the air cleaner casing through the drain hole formed in the second breather passage portion.

In a preferred embodiment of the present invention, a baffling projection may be formed in the blow-by gas inlet port. This baffling projection may have a baffling face lying perpendicular to the direction of flow of the blow-by gas. The blow-by gas collides against the baffling face as it flows into the curved passage portion through the blow-by gas inlet port. This collision facilitates separation and removal of the water component from the blow-by gas.

In another preferred embodiment of the present invention, the blow-by gas inlet port may be positioned below the intake air discharge port and the curved passage portion may be formed with a zigzag flow path for flowing the blow-by gas in a zigzag fashion. In this case, the drain hole is defined in a lowermost portion of the curved passage portion.

According to this preferred embodiment, since the blow-by gas can flow from the blow-by gas inlet port towards the intake air discharge port upwardly through the zigzag flow path, the blow-by gas collides against a wall of the zigzag flow path as it flows upwardly through the zigzag flow path, so that the water component of a relatively high specific gravity can be separated and removed from the blow-by gas. Also, the water component removed from the blow-by gas can be drained into the cleaner casing through the drain hole defined in the lowermost portion of the curved passage portion.

Preferably, the zigzag flow path may be made up of a generally U-shaped wall formed integrally formed with a side wall of the cleaner casing, a baffling plate so formed integrally with the U-shaped wall as to protrude inwardly of the zigzag flow path, and a passage cover for closing an opening of the U-shaped wall opposite to the side wall of the cleaner casing.

In a further preferred embodiment of the present invention, the blow-by gas inlet port may be positioned adjacent the intake air discharge port and the curved passage portion may include a generally U-shaped duct having a downstream duct portion inserted into an upstream portion of the air discharge port. In such case, the downstream duct portion of the duct may preferably have a cross-sectional area (passage area) smaller than those of other duct portions of the duct to define a small diameter duct portion, so that the blow-by gas can be smoothly discharged from the duct by the ejector effect brought about by the air flowing out of the intake air discharge port.

In a still further preferred embodiment of the present invention, the cleaner casing may be made up of first and second casing halves, which are separable from each other in a horizontal direction. The first casing half is positioned adjacent a carburetor and is provided with the blow-by gas inlet port for receiving the blow-by gas, the intake air discharge port and the curved passage portion, while the second casing half accommodates the cleaner element for purifying the air. The provision of the blow-by gas inlet port, the intake air discharge port and the curved passage portion in the first casing half allows the space available in the second casing half to be used to accommodate the cleaner element.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1illustrates a plan view, with a portion cut out, of an important portion of a general-purpose four-cycle, two-cylinder internal combustion engine to which a breathing system according to a first preferred embodiment of the present invention is applied, andFIG. 2illustrates a cross-sectional view taken along the line II—II inFIG. 1. The illustrated combustion engine is of a type being mounted on a working machine, for example, a small-sized snowplow, and provides a drive source for such working machine.

Referring toFIGS. 1 and 2, the combustion engine includes an engine block20having a crankcase1and two cylinders integrally formed with the crankcase1. The two cylinders2are arranged to represent a V-shaped arrangement. A cylinder head21is fixed to each of those cylinders2. Each of the cylinders2has a cylinder bore2adefined therein. An oil pan10for accommodating lubricant oil is secured to a bottom region of the crankcase1, and an air cleaner3and a carburetor4, forming respective parts of an intake system of the combustion engine are disposed between the cylinders2of the V-shaped arrangement. A crankshaft5, which serves as a drive output shaft, is rotatably supported by the crankcase1while extending vertically through the crankcase1. A reciprocating piston6movable in a direction of the longitudinal axis of the cylinder bore2ais movably accommodated within each of the cylinder bores2aand is drivingly connected with the crankshaft5through a respective connecting rod55.

A camshaft7is accommodated within the crank chamber la at a location laterally of the crankshaft5so as to extend parallel to the crankshaft5. This camshaft7is formed with intake and exhaust cams71and72, which when the camshaft7is driven about its longitudinal axis, drive intake and exhaust valves (not shown) through tappets73and then through rocker arms74. The camshaft7is formed with a gear7aadjacent a lower end portion thereof. This gear7ameshes with a crank gear5afixedly mounted on the crankshaft5so that rotary motion of the crankshaft5can be transmitted to the camshaft7.

FIG. 3illustrates the air cleaner3on an enlarged scale. The air cleaner3includes an air cleaner casing30made up of first and second casing halves31and32. The first and second casing halves31and32represent generally cup-like and cap-like configurations and are, therefore, separable in a horizontal direction. The first casing half31is positioned adjacent the carburetor4and has a side wall31a. A blow-by gas inlet port33, through which a blow-by gas G in the crank chamber la enters the air cleaner3, is formed in an intermediate portion of the side wall31awith respect to the height of the first casing half31. This blow-by gas inlet port33forms a part of a breather passage8as will be described in detail later. Also, an intake air discharge port34is formed in an upper portion of the side wall31a.

A lower portion of the side wall31aof the first casing half31is formed with an air intake port35for introducing an air A into the air cleaner3. The air A introduced into the air cleaner3through this air intake port35is supplied towards a cleaner element50, accommodated within an element chamber32adefined in the second casing half32, through an introducing passage36formed within a lower region of the second casing half32, so that the air A can be purified as it flows through the cleaner element50. The purified air A is discharged from the air cleaner3through the intake air discharge port34and is then supplied to the carburetor4before introduced into the combustion engine.

Referring again toFIGS. 1 and 2, the breather passage8has a first breather passage portion establishing a fluid connection between the crank chamber la in the crankcase1and the air cleaner3. In the illustrated embodiment, the first breather passage portion of the breather passage8includes a breather chamber80defined at a location laterally of the camshaft7within the crank chamber1aand delimited between an outer wall portion1band a partition wall portion1c, both forming respective parts of the wall of the crankcase1. The first breather passage portion of the breather passage8also includes an upstream passage portion8A extending between the breather chamber80and the crank chamber1a, and a part of a downstream passage portion9A extending between the breather chamber80and the air cleaner3.

The breather passage8is partly shown on an enlarged longitudinal sectional representation inFIG. 4. The upstream passage portion8A of this breather passage8is made up of an elongated hollow85and first to third transverse hole81to83. The elongated hollow85is defined within the camshaft7so as to extend in an axial direction of the camshaft7(or in a vertical direction as viewed fromFIG. 4). The first transverse hole81is formed in a portion of the camshaft7adjacent the upper intake cam71so as to extend in a radial direction of the camshaft7for communication with the elongated hollow85. The second transverse hole82is formed above the first transverse port81and in an upper end portion of the camshaft7, which portion is rotatably supported by a bearing portion1dintegrally formed with the crankcase1, so as to extend in the radial direction of the camshaft7for communication with the elongated hollow85. The third transverse hole83is formed in the bearing portion1drotatably supporting that upper end portion of the camshaft7so as to align with the second transverse hole82and to open into the breather chamber81.

During the intake stroke of the combustion engine in which the piston6shown inFIG. 1descends with the pressure inside the crank chamber1aincreasing, when the second transverse hole82of the upper end portion of the camshaft7aligns with the third transverse hole83of the bearing portion1dof the crankcase1, the upstream passage portion8A allows the blow-by gas G within the crank chamber1ato flow into the elongated hollow80through the first transverse hole81and subsequently into the breather chamber80through the second and third transverse holes82and83. During the strokes other than the intake stroke, the second transverse hole82is held out of alignment with the third transverse hole83and, therefore, the blow-by gas G does not flow into the breather chamber80. An oil component separated from the blow-by gas G within the breather chamber80is returned to the crank chamber1athrough a recovery passage84.

As shown inFIG. 1, the downstream passage portion9A of the breather passage8is made up of a cylinder passage91, so formed as to extend from the breather chamber80through the cylinder2and the corresponding cylinder head21, and a breather tube92made of a synthetic resin and disposed to connect a discharge end91aof the cylinder passage91and the blow-by gas inlet port33of the air cleaner3. The blow-by gas G flowing into the breather chamber80flows towards the air cleaner3through the cylinder passage91and then through the breather tube92, as shown by the arrow.

FIG. 5illustrates a side view showing the interior of the first casing half31of the air cleaner casing30andFIG. 6illustrates the first casing half31in a perspective representation. As hereinbefore described briefly, the intake air discharge port34, through which the air purified by the cleaner element50is supplied from the air cleaner3to the carburetor4shown inFIG. 3, is defined in an upper center portion of the side wall31aof the first casing half31. The blow-by gas inlet port33for receiving the blow-by gas G from the breather chamber80is defined laterally of and below the intake air discharge port34. The air intake port35is defined at a lower end portion of the side wall31a. Also, the first casing half31is formed with a curved passage portion (a second breather passage portion)93curved from the blow-by gas inlet port33towards the intake air discharge port34and forming a part of the downstream passage portion9A of the breather passage8.

In the illustrated embodiment, a zigzag flow path94is formed in the curved passage portion93so as to allow the blow-by gas G to flow in a zigzag fashion so that a water component contained in the blow-by gas G can be separated and removed from the blow-by gas G by the effect of an inertia force. More specifically, the side wall31aof the first casing half31is, as best shown inFIG. 6, formed integrally with a generally U-shaped wall93a. This U-shaped wall93aopens in a lateral direction of the first casing half31or opens into the interior of the air cleaner casing30and is curved from the blow-by gas inlet port33towards the intake air discharge port34. Opposite wall portions of the U-shaped wall93aare formed integrally with a plurality of baffling plates93bthat protrude from the respective wall portions into the zigzag flow path94. The baffling plates93bprotruding from one wall portion of the U-shaped wall93aand the baffling plates93bprotruding from the other wall portion alternately extend in the zigzag flow path94in directions different from each other. The zigzag flow path94is delimited by the U-shaped wall93a, the baffling plates93bintegral with the U-shaped wall93aand a passage cover96for closing the opening of the U-shaped wall93aopposite to the side wall31aas will be described later.

At the upstream end portion of the zigzag flow path94where the blow-by gas G flows into the curved passage portion93through the blow-by gas inlet port33, a drain hole95, through which the water component separated from the blow-by gas G can be drained into the air cleaner casing30, is formed in a lowermost portion of the upright wall93aby removing such lowest portion of the U-shaped wall93a.

FIG. 7is a side view, showing a condition in which the curved passage portion93is formed by closing the opening of the U-shaped wall93awith the passage cover96, andFIG. 8is a perspective view of the passage cover96as viewed from a rear side thereof. The passage cover96is curved to follow the curvature of the U-shaped wall93a(FIG. 5) and is made up of a first flat plate member96afor covering the opening of the U-shaped wall93a, a second flat plate member96bfor covering the opening outwardly of the intake air discharge port34(FIG. 5), and a substantially rectangular connecting tube96cdisposed between the first and second flat plate members96aand96band having one end connected with a gas discharge port93c(FIG. 5) which is a generally U-shaped open free end of the U-shaped wall93a. The other end of this connecting tube96cadjacent the second flat plate member96bis formed with a bushing96dthat is partly inserted into the intake air discharge port34.

FIG. 9is a side view showing an outer appearance of the first casing half31of the air cleaner casing3andFIG. 10is a cross-sectional view taken along the line X—X inFIG. 5. The breather tube92is fluidly connected with the blow-by gas inlet port33. One end of the breather tube92has a sealing member92ain the form of, for example, an O-ring mounted thereon so that a gap between the blow-by gas inlet port33and the breather tube92can be sealed off. In a region deep into the blow-by gas inlet port33or in an axially intermediate region of the blow-by gas inlet port33, the first casing half31is formed integrally with a baffling projection37that extends from an upper area of the blow-by gas inlet port33to a position substantially intermediate of the height of the blow-by gas inlet port. The drain hole95is located below the baffling projection37. As best shown inFIG. 10, the baffling projection37has a baffling face37alying perpendicular to the direction of flow of the blow-by gas G so that the water component can be separated and removed from the blow-by gas G when the latter collides against the baffling face37a.

FIG. 11is a longitudinal sectional view of the second casing half32that is mounted on the first casing half31and closes the opening of the latter. This second casing half32has a lower end portion formed with engagements39adapted to be inserted into and, hence, engaged in respective retainers38(FIG. 5) provided in a lower end of the first casing half31. The second casing half32also has an upper end portion formed with engagement pawls41adapted to be inserted into respective insertion holes40adefined in corresponding catch members40(FIG. 5) provided in an upper end of the first casing half31. An engagement41ais formed integrally with each of the engagement pawls41and, on the other hand, a stopper40bfor engagement with the respective engagement41ais formed integrally with the first casing half31at an upper area of the insertion hole40afor receiving therein the corresponding engagement pawl41.

When the first casing half31and the second casing half32are assembled to form the cleaner casing30, while the engagements39of the second casing half32are engaged in the corresponding retainers38of the first casing half31, the engagement pawls41of the second casing half32have to be inserted into the corresponding insertion holes40ain the catch members40provided in the first casing half31so that the engagements41aof the engagement pawls41can be engaged in the stoppers40bin the insertion holes40a.

The operation of the breathing system of the structure described above will now be described.

As a result of change in pressure inside the crank chamber1a, which is brought about by the reciprocating motion of the piston6(FIG. 1), the blow-by gas G flowing from the combustion chamber22into the crank chamber1athrough a gap between the piston6and a liner23in each of the cylinders2is introduced into the breather chamber80through the upstream passage portion8A of the breather passage8(FIG. 4).

The blow-by gas G so introduced into the breather chamber80is reduced in flow velocity and pressure within the breather chamber80to allow an oil component such as oil mist to be separated and, hence, removed from the blow-by gas G. The removed oil component is subsequently returned to the crank chamber1athrough the recovery passage84. The blow-by gas G within the breather chamber80flows through the downstream passage portion9A (FIG. 1) of the breather passage8and then towards a downstream area of the cleaner element50within the air cleaner3, that is, towards the intake air discharge port34.

When the blow-by gas G is supplied to the intake air discharge port34through the downstream passage portion9A of the breather passage8, since the downstream passage portion9A is provided with the curved passage portion93curved within the first casing half31from the blow-by gas inlet port33towards the intake air discharge port34, a water component contained in the blow-by gas G and having a high specific gravity collides against an inner surface of the curved passage portion93under the influence of a centrifugal force developed as the blow-by gas G flows along the curved path of the curved passage portion93and is therefore separated and removed from the blow-by gas G. In particular, since the zigzag flow path94is defined in the curved passage portion93so as to extend from the blow-by gas inlet port33to the intake air discharge port34, the blow-by gas G collides against the baffling plates93bprovided within this zigzag flow path94and, therefore, the water component contained in the blow-by gas G can be efficiently separated and removed from the blow-by gas G.

Also, as shown inFIG. 10, since the baffling projection37is formed in the deep region of the blow-by gas inlet port33to which the breather tube92is connected, the blow-by gas G from the breather tube92collides against the baffling projection37so that the water component contained in the blow-by gas G can be further separated and removed.

The water component so removed from the blow-by gas G can be discharged into the first casing half31through the drain hole95defined in the lowermost portion (the most downstream portion) of the curved passage portion93. Also, the blow-by gas G, from which the water component has been separated and removed, is supplied to the carburetor4though the intake air discharge port34together with the air purified by the cleaner element50, so that reburning of the blow-by gas G can be carried out within the combustion chamber22(FIG. 1).

The breathing system according to a second preferred embodiment of the present invention will now be described.FIG. 12illustrates, in a side view, the interior of the first casing half31formed with the breather passage according to the second embodiment of the present invention andFIG. 13is a perspective view thereof. The first casing half31is formed with an element chamber31bfor accommodating the cleaner element50. This first casing half31is also formed with the blow-by gas inlet port33that is positioned above the element chamber31band generally intermediate of the width of the first casing half31and protrudes outwardly from the side wall31aof the first casing half31. The first casing half31is further formed with the intake air discharge port34below and adjacent the blow-by gas inlet port33. The air intake port35is formed in the first casing half31at a location laterally of the blow-by gas inlet port33and above the element chamber31b. The air A entering the air intake port35is introduced into the element chamber31b. As the air A flows through the cleaner element50within the element chamber31b, the air A can be purified and is then introduced into a delivery chamber31dby way of a plurality of passages46defined among a plurality of projecting plates45arranged between the intake air discharge port34and the element chamber31b. The purified air A so introduced into the delivery chamber31dsubsequently flows through the intake air discharge port34towards the carburetor4(FIG. 3).

Around the element chamber31b, the blow-by gas inlet port33and the intake air discharge port34, a sealing wall31cis formed so as to protrude from the side wall31aof the first casing half31and is cooperable with a second casing half (not shown) to seal the inside of the first casing half31from the outside. The second casing half32is mounted on the first casing half31by a plurality of mounting elements31eso that the sealing wall31ccan seal the element chamber31band the delivery chamber31dfrom the outside.

FIG. 14is a cross-sectional view taken along the line XIV-XIV inFIG. 12. The breather tube92extending from the cylinder2is connected to an outer portion of the blow-by gas inlet port33. This breather tube92extends upwardly from the discharge end91aof the cylinder head21and is then curved at an introducing passage portion92aon an upstream side of the blow-by gas inlet port33so as to extend substantially horizontally, representing a generally L-shaped configuration. A generally U-shaped duct98forming a curved passage portion is provided between an inner portion of the blow-by gas inlet port33and the intake air discharge port34. A drain hole95for discharging into the first casing half31a water component, separated and removed from the blow-by gas G, is formed in a lower portion of the connection between the duct98and the blow-by gas inlet port33. Even in this second embodiment, the baffling projection37for separating and removing the water component contained in the blow-by gas G when the blow-by gas G collides against the baffling face37of the baffling projection37is formed in a region deep into the blow-by gas inlet port33with which the breather tube92is fluidly connected. The drain hole95is positioned below the baffling projection37.

The duct98has a large diameter duct portion98a, a duct body98band a small diameter duct portion98c. The large diameter duct portion98adefines an upstream duct portion of the duct98and is fitted to the connection with the blow-by gas inlet port33. The duct body98bhas a cross-sectional area (passage area) progressively decreasing from the large diameter duct portion98awhile curved in a generally U-shaped configuration from the large diameter duct portion98a. The small diameter duct portion98c, defining a downstream duct portion of the duct98, is formed at a downstream end of the duct body96band inserted into an upstream portion of the intake air discharge port34. The small diameter duct portion98chas a cross-sectional area (passage area) smaller than those of the large diameter duct portion98aand the duct body98band, therefore, has an outer diameter smaller than those of the large diameter duct portion98aand the duct body98b. Also, this duct98is made up of two split tube members, which are connected together by a plurality of connecting elements96d.

As shown inFIG. 15in an enlarged side view, the side wall31aof the first casing half31has a portion, corresponding to the connection between the blow-by gas inlet port33and the duct98, formed with inner and outer tubes47and48in a coaxial relation. A groove49is formed between the inner and outer tubes47and48to receive and fix the large diameter duct portion98a(FIG. 14) of the duct98. A lower portion of each of the inner and outer tubes47and48is depleted to define the drain hole95.

According to the second embodiment of the present invention, when the blow-by gas G flows into the air cleaner3through the breather tube92by way of the blow-by gas inlet port33, the blow-by gas G collides against the baffling face37aof the baffling projection37, disposed in the deep region of the blow-by gas inlet port33, resulting in removal of the water component contained in the blow-by gas G. Also, since the generally U-shaped duct98is disposed between the blow-by gas inlet port33and the intake air discharge port34, the water component contained in the blow-by gas G and having a high specific gravity collides against the inner surface of the duct98under the influence of a centrifugal force developed as the blow-by gas G flows along the curved path of the duct98and is therefore separated and removed from the blow-by gas G. In addition, since the introducing passage portion92aof the breather tube92is curved, the water component contained in the blow-by gas G can also be separated and removed as the blow-by gas g flows through the introducing passage portion92a.

The water component removed from the blow-by gas G can be discharged into the first casing half31through the drain hole95defined in the lower portion of the connection between the duct98and the blow-by gas inlet port33. Also, the blow-by gas G, from which the water component has been separated and removed, is supplied to the carburetor4through the intake air discharge port34together with the air purified by the cleaner element50, so that reburning of the blow-by gas G can be carried out within the combustion chamber22. At this time, since the downstream duct portion of the duct98is constituted by the small diameter duct portion98chaving the diameter smaller than the upstream duct portion98a, the ejector effect brought about by the air flowing out of the intake air discharge port34effectively acts on the exit of the small diameter duct portion98c, resulting in the smooth discharge of the blow-by gas G from the duct98.