Suction tube unit of stratified scavenging engine

Abstract

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.

Claims

1. A suction tube unit for a carburetor having one bore including a mixture-flow passage and a scavenging-air-flow passage, the passages being defined on opposite sides of a full-opened butterfly-type valve, the suction tube unit comprising: a suction tube for mixture, the suction tube for mixture being made of an elastic material; a suction tube for stratified scavenging air, the suction tube for air being made of an elastic material, and an adapter disposed between the carburetor and the suction tube for mixture and between the carburetor and the suction tube for air, wherein the suction tube for mixture and the suction tube for air have, at respective inlet ends connected to the adapter, respective wall portions which face each other and have complementary shapes, wherein a clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air, wherein the adapter has one bore, and 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.

2. The suction tube unit according to claim 1, wherein 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.

3. The suction tube unit according to claim 1, wherein the wall portion of the suction tube for mixture has a reinforcing rib.

4. The suction tube unit according to claim 1, wherein the suction tube for mixture and the suction tube for air are made of different materials.

5. The suction tube unit according to claim 1, wherein the wall portion of the suction tube for mixture and the wall portion of the suction tube for air are planar.

6. A stratified scavenging engine comprising: a suction tube unit, comprising: a suction tube for mixture, the suction tube for mixture being made of an elastic material; a suction tube for stratified scavenging air, the suction tube for air being made of an elastic material, a carburetor having one bore including a mixture-flow passage and a scavenging-air-flow passage, the passages being defined on opposite sides of a full-opened butterfly-type valve, and an adapter disposed between the carburetor and the suction tube for mixture and between the carburetor and the suction tube for air, wherein the suction tube for mixture and the suction tube for air have, at respective inlet ends connected to the adapter, respective wall portions which face each other and have complementary shapes, wherein a clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air; wherein the adapter has one bore; and 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.

7. The stratified scavenging engine according to claim 6, wherein the carburetor butterfly-type valve comprises a choke valve and a throttle valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a stratified scavenging engine according to the present invention.

(2) FIG. 2 is a cross-sectional view of the stratified scavenging engine according to the present invention.

(3) FIG. 3 is a cross-sectional view of a suction tube unit according to the present invention taking along a line 3-3 shown in FIG. 1.

(4) FIG. 4 is a cross-sectional view of the suction tube unit according to the present invention taking along a line 4-4 shown in FIG. 1.

(5) FIG. 5 is a cross-sectional view of a suction tube in prior art.

DESCRIPTION OF EMBODIMENTS

(6) Referring to the drawings, an embodiment of a suction tube unit according to the present invention will be explained. As shown in FIG. 1, a stratified scavenging engine 10 has a cylinder block 12, a carburetor 14 and a suction tube unit 16 connected between the cylinder block 12 and the carburetor 14.

(7) As shown in FIGS. 2 and 3, the carburetor 14 has one through bore 18, a choke valve 20 and a throttle valve 22, the choke valve 20 and the throttle valve 22 being disposed in the one through bore 18. The one through bore 18 is connected to a suction tube for mixture 30 and a suction tube for air 32, which will be described later. The choke valve 20 and the throttle valve 22 are butterfly valves which rotate around respective axes 20a, 22a. The one through bore 18 has, for example, a circular cross section, and has a partition 24 between the choke valve 20 and the throttle valve 22, the partition 24 being aligned with the choke valve 20 and the throttle valve 22 when these valves 20 22 are in respective fully-opened positions. Thus, when the choke valve 20 and the throttle valve 22 are in the respective fully-opened positions, a passage for mixture 26 and a passage for air 28 are defined. Although the partition 24 is provided in the present embodiment, the partition 24 may be omitted when the choke valve 20 and the throttle valve 22 are arranged so as to form the passage for mixture 26 and the passage for air 28.

(8) The suction tube unit 16 has a suction tube for mixture 30 connected to the passage for mixture 26 of the carburetor 14, a suction tube for air, namely, stratified scavenging air, 32 connected to the passage for air 28 of the carburetor 14, and an adapter 34 connecting the suction tube for mixture 30 and the suction tube for air 32 to the carburetor 14.

(9) The suction tube for mixture 30 and the suction tube for air 32 are made of rubber, and as shown in FIG. 4, they do not have any common walls. Concretely, the suction tube for mixture 30 and the suction tube for air 32 have respective wall portions 36, 38 at respective inlet ends 30a, 32a connected to the carburetor 14, and the wall portions 36, 38 face each other and have complementary shapes, so that a clearance space 40 is provided between these wall portions 36, 38. In the present embodiment, both of the wall portion 36 of the suction tube for mixture 30 and the wall portion 38 of the suction tube for air 32 have planar-plate shapes. Reinforcing ribs 36a, 38a for preventing deformations of the wall portions 36, 38 may be provided on respective surfaces of the wall portions 36, 38 (in the present embodiment, around the suction tube for mixture 30 and the suction tube for air 32), the respective surfaces facing each other.

(10) In the present embodiment, a cross-sectional profile of the inlet end 30a of a bore 30c of the suction tube for mixture 30 and a cross-sectional profile of the inlet end 32a of a bore 32c of the suction tube for air 32 are substantially semicircular. When the suction tube for mixture 30 and the suction tube for air 32 are incorporated into the stratified scavenging engine 10 as the suction tube unit 16, the suction tube for mixture 30 and the suction tube for air 32 are arranged so that the bores 30c, 32c totally (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 bore 18 of the carburetor 14.

(11) A cross-sectional profile of an outlet end 30b of the bore 30c of the suction tube for mixture 30 and a cross-sectional profile of an outlet end 32b of the bore 32c of the suction tube for air 32 are arbitrarily determined. The suction tube for air 32 has a flange 42 at the outlet end 32b of the suction tube for air 32, the flange 42 being attached to the cylinder block 12. The outlet end 30b of the suction tube for mixture 30 is attached to the flange 42.

(12) The adapter 34 is made of resign and has a bore 44. A cross-sectional profile of the bore 44 substantially corresponds to the cross-sectional profile of the one through bore 18 of the carburetor 14. A single partition 46 is provided in the bore 44, the partition 46 being aligned with both of the wall portion 36 of the suction tube for mixture 30 and the wall portion 38 of the suction tube for air 32, so that in the bore 44, a passage for mixture and a passage for stratified scavenging air are separated from each other. In the present embodiment, since the throttle valve 22 protrudes from the carburetor 14, the partition 46 is provided only at a downstream portion (on an engine side) of the bore 44 so that the throttle valve 22 abuts the partition 46. Further, the passage for mixture 26 and the passage for air 28 of the carburetor 14 are connected to the bore 30c (the passage) of the suction tube for mixture 30 and the bore 32c (the passage) of the suction tube for air 32, respectively.

(13) The adapter 34 has a recess 50 which receives and fits to the inlet end 30a of the suction tube for mixture 30 and the inlet end 32a of the suction tube for air 32. Especially, both of the wall portions 36, 38 are fitted to a recess 50a of the partition 46. Due to this fitting, sealing at the inlet end 30a of the suction tube for mixture 30 and hermetically sealing at the inlet end 32a of the suction tube for air 32 are achieved. Further, communication between the suction tube for mixture 30 and the suction tube for air 32 is prevented.

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

(15) When the choke valve 20 and the throttle valve 22 are in the respective fully-opened positions, a mixture flowing in the passage for mixture 26 of the carburetor 14 flows via the adapter 34 into the bore 30c of the suction tube for mixture 30, while an air flowing in the passage for air 28 of the carburetor 14 flows via the adapter 34 into the bore 32c of the suction tube for air 32.

(16) A fuel component flowing in the suction tube for mixture 30 swells the wall portion 36 of the suction tube for mixture 30 made of rubber so that the cross-sectional profile of the inlet end 30a of the suction tube for mixture 30 is deformed. However, since the clearance space 40 is provided between the wall portion 36 of the suction tube for mixture 30 and the wall portion 38 of the suction tube for air 32, the cross-sectional profile of the bore 32c of the suction tube for air 32 is not influenced by the deformation of the cross-sectional profile of the suction tube for mixture 30.

(17) Further, when a piston (not shown) of the engine 10 is lowered, the wall portion 36 of the suction tube for mixture 30 made of the rubber is deformed due to a negative pressure caused in the suction tube for mixture 30. However, since the clearance space 40 is provided between the wall portion 36 of the suction tube for mixture 30 and the wall portion 38 of the suction tube for air 32, the cross-sectional profile of the bore 32c of the suction tube for air 32 is not influenced by the deformation of the cross-sectional profile of the suction tube for mixture 30.

(18) Thus, the flow in the suction tube for air 32 is that as designed, so that a predetermined stratified scavenging effect is surely achieved to enhance the rotation stability. Further, due to the clearance space 40, a heat dissipation performance of the suction tube unit 16 is enhanced so that transmitting heat of the engine 10 to the carburetor 14 is restricted.

(19) The suction tube for mixture 30 and the suction tube for air 32 are positioned by fitting the inlet end 30a of the suction tube for mixture 30 and the inlet end 32a of the suction tube for air 32 to the recess 50 of the adapter. At the same time, hermetically sealing between the adapter 34 and the inlet ends 30a, 32a of the suction tube for mixture 30 and the suction tube for air 32 are surely achieved. Further, since the wall portion 36 of the suction tube for mixture 30 is fitted to the recess 50a of the adapter 34, the deformation of the wall portion 36 of the suction tube for mixture 30 is restricted. Even if the wall portion 36 is deformed, the sealing effect of the inlet end 30a of the suction tube for mixture 30 is maintained.

(20) Since the reinforcing ribs 36a, 38a for preventing deformation of the wall portions 36, 38 are provided on the respective surfaces of the wall portions 36, 38, the respective surfaces facing each other, deformation of the entire cross-sectional profiles of the suction tube for mixture 30 and the suction tube for air 32 are restricted so that cross-sectional areas of the suction tube for mixture 30 and the suction tube for air 32 remain constant. Thus, variations of amounts of supplying mixture and air can be restricted.

(21) 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.

(22) Although the suction tube for mixture 30 and the suction tube for air 32 are made of rubber in the above-stated embodiment, they may be made of any elastic material. Further, a material of the suction tube for mixture 30 and a material of the suction tube for air 32 may be different from each other. For example, the suction tube for mixture 30 is made of a deformation-resistant material restricting deformation, while the suction tube for air 32 may be made of a material which is cheaper than that of the suction tube for mixture 30. Then, each of the passages of these tubes can be provided with a desirable function different from that of the other.

(23) Although the suction tube for mixture 30 and the suction tube for air 32 are attached to the carburetor 14 via the adapter 34 in the above-stated embodiment, they may be attached to the carburetor 14 without using the adapter 34. In this case, for example, the carburetor 14 may be provided with recesses which receive the inlet end 30a of the suction tube for mixture 30 and the inlet end 32a of the suction tube for air 32.

(24) Although the cross-sectional profile of the bore 30c of the inlet end 30a of the suction tube for mixture 30 and the cross-sectional profile of the inlet end 32a of the suction tube for air 32 are substantially semicircular in the above-stated embodiment, other cross-sectional profiles may be employed. Further, although the wall portion 36 of the suction tube for mixture 30 and the wall portion 38 of the suction tube for air 32 are substantially planar, they may be curved as long as they have complementary shapes.

(25) The carburetor 14 may be a butterfly-valve type carburetor 14 as in the above-stated embodiment, or a rotary-valve type carburetor.