Suction tube unit of stratified scavenging engine

A suction tube unit connected between a cylinder block and a carburetor in a stratified scavenging engine has a suction tube for mixture made of an elastic material; and a suction tube for stratified scavenging air made of an elastic material. The suction tube for mixture and the suction tube for air have, at respective inlet ends connected to the carburetor, respective wall portions which face each other and have complementary shapes. A clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air.

REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Japanese Patent Application No. 2014-241907, filed Nov. 28, 2014, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a stratified scavenging engine, and specifically to a suction tube unit connected between a cylinder block and a carburetor of a stratified scavenging engine.

BACKGROUND ART

A stratified scavenging engine is used in, for example, a chain saw, a brush cutter and an edge trimmer. In the stratified scavenging engine, mixture consisting of fuel and air, and stratified scavenging air are supplied to a cylinder block through respective suction tubes. Generally, the mixture produced in a carburetor is supplied to the cylinder block through a suction tube for mixture, while the stratified scavenging air is supplied to the cylinder block through a suction tube for air, which does not pass through the carburetor (refer to, for example, the Patent Publication 1).

On the other hand, another kind of stratified scavenging engine in which both of mixture and stratified scavenging air are supplied through a carburetor is known (refer to, for example, Patent Publication 2). In this carburetor of the stratified scavenging engine, one bore is formed, and a butterfly-type choke valve and a butterfly-type throttle valve are disposed in the one bore so that two passages are defined in the one bore when both of the valves are full-opened. Then, the mixture flows through the passage on one side of the full-opened valves (or the passage provided with a fuel injection aperture), while the stratified scavenging air flows through the passage on the other side.

In this kind of the stratified scavenging engine, a suction tube disposed between the cylinder block and the carburetor is a one suction tube into which a passage for mixture and a passage for air are integrated. Concretely, as shown inFIG. 5, an entire inlet cross-sectional profile of the suction tube102of the stratified scavenging engine100corresponds to a cross-sectional profile of a bore (not shown) of the carburetor (not shown), and the passage for mixture106and the passage for air108are defined by a common partition104in a thin plate form which aligns with the throttle valve in the fully-opened position. In this way, by integrating the passage for mixture106and the passage for air108into the one suction tube102, the stratified scavenging engine100can be made compact.

Further, the suction tube is made of a rubber or a resin in order to prevent vibration and heat of the engine100from being transmitted to the carburetor. In a chain saw, the suction tube is typically made of a rubber.

SUMMARY OF THE INVENTION

When fuel, such as gasoline, passes through the passage for mixture106, the partition104in the form of a thin plate made of a rubber is swelled. Since the partition104is fixed to a cylindrical material forming the one suction tube102, the partition104is deformed so as to curve in an S-shape, as indicated by two-dot chain lines104′ inFIG. 5.

Further, since a negative pressure caused in the passage for mixture106becomes larger than a negative pressure caused in the passage for air108when a piston (not shown) in the engine100is lowered, the partition104made of an elastic material, such as a rubber, is entirely deformed so as to be pulled toward a side of the passage for mixture106.

If such deformation of the partition104is caused, misalignment of the passage for mixture106and the passage for air108in the suction tube102with the passage for mixture and the passage for air in the carburetor would be caused so that when the mixture and the stratified scavenging air flow from the carburetor to the suction tube102, they may be mixed with each other to form a mixed flow.

Further, since the cross-sectional profile of the passage for air102is changed due to such deformation of the partition104so as to influence the flow of the stratified scavenging air, a stratified scavenging operation may not be achieved as designed. Especially, a flow rate of the stratified scavenging air when the piston of the engine100is lowered may be shifted from a designed value.

It is therefore an object of the present invention to provide a suction tube unit which is compact, prevents the mixed-flow of the mixture and the stratified scavenging air, and restricts a change in the cross-sectional profile of the passage for air, and also to provide a stratified scavenging engine having the suction tube unit.

In order to achieve the above-stated object, a suction tube unit according to the present invention, which is connected between a cylinder block and a carburetor in a stratified scavenging engine, has a suction tube for mixture made of an elastic material; and a suction tube for stratified scavenging air made of an elastic material; wherein the suction tube for mixture and the suction tube for air have, at respective inlet ends connected to the carburetor, respective wall portions which face each other and have complementary shapes, and wherein a clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air.

In this suction tube unit, since the suction tube for mixture and the suction tube for air have respective wall portions facing each other and having complementary shapes, the suction tube for mixture and the suction tube for air are entirely configured to be unitary although they are separated from each other, so that the suction tube unit and the stratified scavenging engine can be arranged to be compact. Further, since the clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air, a deformation of the wall portion of the suction tube for mixture due to a swelling operation and/or a negative pressure is separated from a deformation of the wall portion of the suction tube for air. As a result, a mixed flow of the mixture and the stratified scavenging air can be prevented, and a change in the cross-sectional profile of the passage for air can be restricted.

In an embodiment of the suction tube unit according to the present invention, preferably, it further has an adapter disposed between the carburetor and the suction tube for mixture and between the carburetor and the suction tube for air, the adapter having a bore; wherein a single partition aligning with the wall portions of the suction tube for mixture and the suction tube for air is provided in the one bore, and the partition has a recess fitted to the wall portions of the suction tube for mixture and the suction tube for air.

In this suction tube unit, since the wall portions of the suction tube for mixture and the suction tube for air are positioned in the recess of the partition of the adapter, an effect of preventing the mixed-flow is enhanced, and the change in the cross-sectional profile of the passage for air can be further restricted.

In this embodiment of the suction tube unit according to the present invention, preferably, the adapter has a recess which receives the inlet end of the suction tube for mixture and the inlet end of the suction tube for air.

In this suction tube unit, the sealing performance between the suction tube unit and the carburetor can be enhanced.

In another embodiment of the suction tube unit according to the present invention, preferably, the wall portion of the suction tube for mixture has a reinforcing rib. In another embodiment, preferably, the suction tube for mixture and the suction tube for air are made of different materials. In another embodiment, preferably, the wall portion of the suction tube for mixture and the wall portion of the suction tube for air are planar.

In addition, in order to achieve the above-stated object, a stratified scavenging engine according to the present invention has the above-stated suction tube unit and a carburetor.

In an embodiment of the stratified scavenging engine according to the present invention, preferably, the carburetor has one bore connected to the suction tube for mixture and the suction tube for air, and the carburetor has a choke valve and a throttle valve disposed in the one bore.

According to the present invention, a suction tube unit which is compact, prevents a mixed-flow of mixture and stratified scavenging air, and restricts a change in a cross-sectional profile of a passage for air can be provided, and a stratified scavenging engine having the suction tube unit can be also provided.

DESCRIPTION OF EMBODIMENTS

Referring to the drawings, an embodiment of a suction tube unit according to the present invention will be explained. As shown inFIG. 1, a stratified scavenging engine10has a cylinder block12, a carburetor14and a suction tube unit16connected between the cylinder block12and the carburetor14.

As shown inFIGS. 2 and 3, the carburetor14has one through bore18, a choke valve20and a throttle valve22, the choke valve20and the throttle valve22being disposed in the one through bore18. The one through bore18is connected to a suction tube for mixture30and a suction tube for air32, which will be described later. The choke valve20and the throttle valve22are butterfly valves which rotate around respective axes20a,22a. The one through bore18has, for example, a circular cross section, and has a partition24between the choke valve20and the throttle valve22, the partition24being aligned with the choke valve20and the throttle valve22when these valves2022are in respective fully-opened positions. Thus, when the choke valve20and the throttle valve22are in the respective fully-opened positions, a passage for mixture26and a passage for air28are defined. Although the partition24is provided in the present embodiment, the partition24may be omitted when the choke valve20and the throttle valve22are arranged so as to form the passage for mixture26and the passage for air28.

The suction tube unit16has a suction tube for mixture30connected to the passage for mixture26of the carburetor14, a suction tube for air, namely, stratified scavenging air,32connected to the passage for air28of the carburetor14, and an adapter34connecting the suction tube for mixture30and the suction tube for air32to the carburetor14.

The suction tube for mixture30and the suction tube for air32are made of rubber, and as shown inFIG. 4, they do not have any common walls. Concretely, the suction tube for mixture30and the suction tube for air32have respective wall portions36,38at respective inlet ends30a,32aconnected to the carburetor14, and the wall portions36,38face each other and have complementary shapes, so that a clearance space40is provided between these wall portions36,38. In the present embodiment, both of the wall portion36of the suction tube for mixture30and the wall portion38of the suction tube for air32have planar-plate shapes. Reinforcing ribs36a,38afor preventing deformations of the wall portions36,38may be provided on respective surfaces of the wall portions36,38(in the present embodiment, around the suction tube for mixture30and the suction tube for air32), the respective surfaces facing each other.

In the present embodiment, a cross-sectional profile of the inlet end30aof a bore30cof the suction tube for mixture30and a cross-sectional profile of the inlet end32aof a bore32cof the suction tube for air32are substantially semicircular. When the suction tube for mixture30and the suction tube for air32are incorporated into the stratified scavenging engine10as the suction tube unit16, the suction tube for mixture30and the suction tube for air32are arranged so that the bores30c,32ctotally (or collectively) define a substantially circular cross-sectional profile. This substantially circular cross-sectional profile substantially corresponds to the cross-sectional profile of the one through bore18of the carburetor14.

A cross-sectional profile of an outlet end30bof the bore30cof the suction tube for mixture30and a cross-sectional profile of an outlet end32bof the bore32cof the suction tube for air32are arbitrarily determined. The suction tube for air32has a flange42at the outlet end32bof the suction tube for air32, the flange42being attached to the cylinder block12. The outlet end30bof the suction tube for mixture30is attached to the flange42.

The adapter34is made of resign and has a bore44. A cross-sectional profile of the bore44substantially corresponds to the cross-sectional profile of the one through bore18of the carburetor14. A single partition46is provided in the bore44, the partition46being aligned with both of the wall portion36of the suction tube for mixture30and the wall portion38of the suction tube for air32, so that in the bore44, a passage for mixture and a passage for stratified scavenging air are separated from each other. In the present embodiment, since the throttle valve22protrudes from the carburetor14, the partition46is provided only at a downstream portion (on an engine side) of the bore44so that the throttle valve22abuts the partition46. Further, the passage for mixture26and the passage for air28of the carburetor14are connected to the bore30c(the passage) of the suction tube for mixture30and the bore32c(the passage) of the suction tube for air32, respectively.

The adapter34has a recess50which receives and fits to the inlet end30aof the suction tube for mixture30and the inlet end32aof the suction tube for air32. Especially, both of the wall portions36,38are fitted to a recess50aof the partition46. Due to this fitting, sealing at the inlet end30aof the suction tube for mixture30and hermetically sealing at the inlet end32aof the suction tube for air32are achieved. Further, communication between the suction tube for mixture30and the suction tube for air32is prevented.

Next, an operation of the embodiment of the suction tube unit according to the present invention will be explained.

When the choke valve20and the throttle valve22are in the respective fully-opened positions, a mixture flowing in the passage for mixture26of the carburetor14flows via the adapter34into the bore30cof the suction tube for mixture30, while an air flowing in the passage for air28of the carburetor14flows via the adapter34into the bore32cof the suction tube for air32.

A fuel component flowing in the suction tube for mixture30swells the wall portion36of the suction tube for mixture30made of rubber so that the cross-sectional profile of the inlet end30aof the suction tube for mixture30is deformed. However, since the clearance space40is provided between the wall portion36of the suction tube for mixture30and the wall portion38of the suction tube for air32, the cross-sectional profile of the bore32cof the suction tube for air32is not influenced by the deformation of the cross-sectional profile of the suction tube for mixture30.

Further, when a piston (not shown) of the engine10is lowered, the wall portion36of the suction tube for mixture30made of the rubber is deformed due to a negative pressure caused in the suction tube for mixture30. However, since the clearance space40is provided between the wall portion36of the suction tube for mixture30and the wall portion38of the suction tube for air32, the cross-sectional profile of the bore32cof the suction tube for air32is not influenced by the deformation of the cross-sectional profile of the suction tube for mixture30.

Thus, the flow in the suction tube for air32is that as designed, so that a predetermined stratified scavenging effect is surely achieved to enhance the rotation stability. Further, due to the clearance space40, a heat dissipation performance of the suction tube unit16is enhanced so that transmitting heat of the engine10to the carburetor14is restricted.

The suction tube for mixture30and the suction tube for air32are positioned by fitting the inlet end30aof the suction tube for mixture30and the inlet end32aof the suction tube for air32to the recess50of the adapter. At the same time, hermetically sealing between the adapter34and the inlet ends30a,32aof the suction tube for mixture30and the suction tube for air32are surely achieved. Further, since the wall portion36of the suction tube for mixture30is fitted to the recess50aof the adapter34, the deformation of the wall portion36of the suction tube for mixture30is restricted. Even if the wall portion36is deformed, the sealing effect of the inlet end30aof the suction tube for mixture30is maintained.

Since the reinforcing ribs36a,38afor preventing deformation of the wall portions36,38are provided on the respective surfaces of the wall portions36,38, the respective surfaces facing each other, deformation of the entire cross-sectional profiles of the suction tube for mixture30and the suction tube for air32are restricted so that cross-sectional areas of the suction tube for mixture30and the suction tube for air32remain constant. Thus, variations of amounts of supplying mixture and air can be restricted.

Although the embodiment of the present invention has been explained, the present invention is not limited to the embodiment, and various modifications can be performed within the scope of the present invention recited in the claims. It goes without saying that such modified embodiments fall within the scope of the present invention.

Although the suction tube for mixture30and the suction tube for air32are made of rubber in the above-stated embodiment, they may be made of any elastic material. Further, a material of the suction tube for mixture30and a material of the suction tube for air32may be different from each other. For example, the suction tube for mixture30is made of a deformation-resistant material restricting deformation, while the suction tube for air32may be made of a material which is cheaper than that of the suction tube for mixture30. Then, each of the passages of these tubes can be provided with a desirable function different from that of the other.

Although the suction tube for mixture30and the suction tube for air32are attached to the carburetor14via the adapter34in the above-stated embodiment, they may be attached to the carburetor14without using the adapter34. In this case, for example, the carburetor14may be provided with recesses which receive the inlet end30aof the suction tube for mixture30and the inlet end32aof the suction tube for air32.

Although the cross-sectional profile of the bore30cof the inlet end30aof the suction tube for mixture30and the cross-sectional profile of the inlet end32aof the suction tube for air32are substantially semicircular in the above-stated embodiment, other cross-sectional profiles may be employed. Further, although the wall portion36of the suction tube for mixture30and the wall portion38of the suction tube for air32are substantially planar, they may be curved as long as they have complementary shapes.

The carburetor14may be a butterfly-valve type carburetor14as in the above-stated embodiment, or a rotary-valve type carburetor.