阅读说明：本技术 倒吹燃料的吸回构造 (Suck-back structure of reverse blowing fuel ) 是由 宫崎秀史 竹本和彦 于 2018-06-19 设计创作，主要内容包括：在发动机(E)的燃料供给装置(6)的上游侧配置有与燃料供给装置(6)的进气通路(24)相连的第一燃料存储部(46)。在空气滤清器(8)的过滤元件(40)与第一燃料存储部(46)之间,配置有抑制从进气通路(24)的倒吹的倒吹抑制板(66)。形成有将积存于空气滤清器(8)内的燃料滞留部(52)的燃料吸回至进气通路(24)的吸回通路(54)。吸回通路(54)使空气滤清器(8)内的燃料滞留部(52)与形成于第一燃料存储部(46)的下游端的吸回孔(56)连通。(A first fuel storage unit (46) connected to an intake passage (24) of a fuel supply device (6) is disposed upstream of the fuel supply device (6) of an engine (E). A reverse blow-down suppressing plate (66) that suppresses reverse blow-down from the intake passage (24) is disposed between the filter element (40) of the air cleaner (8) and the first fuel storage section (46). An intake passage (54) is formed for sucking back fuel accumulated in a fuel retention section (52) in the air cleaner (8) to the intake passage (24). The suction/return passage (54) communicates a fuel retention section (52) in the air cleaner (8) with a suction/return hole (56) formed at the downstream end of the first fuel storage section (46).)

1. A suck-back structure for blowback fuel, comprising:

a first fuel storage unit disposed upstream of a fuel supply device of an engine and connected to an intake passage of the fuel supply device;

a suction passage that sucks back fuel accumulated in the air cleaner to the intake passage; and

a blowback suppression plate that is disposed between the filter element of the air cleaner and the first fuel storage portion and suppresses blowback from the intake passage,

the suck-back passage communicates a fuel retention portion in the air cleaner with a suck-back hole formed in the first fuel storage portion.

2. The suck-back configuration of blow-back fuel of claim 1, wherein,

a blowback prevention piece that faces the inlet of the intake passage and prevents blowback from the intake passage is formed at an upstream end of the first fuel storage portion.

3. The suck-back configuration of reverse-blown fuel according to claim 1 or 2, wherein,

the air cleaner includes a filter case connected to the fuel supply device and a filter cover covering the filter case and the filter element,

the suction passage is surrounded by the filter case, a pair of protruding walls formed integrally with the filter case, and a closing member abutting on the front ends of the pair of protruding walls.

4. The suck-back configuration of blow-back fuel of claim 3,

the closing member is formed by the blowback suppression plate mounted to the filter case.

5. The suck-back configuration of reverse-blown fuel according to claim 3 or 4, wherein,

the opening area of the suck-back hole is set sufficiently smaller than the passage area of the suck-back passage so that the suction action by the intake air flowing in the intake passage is exerted.

6. The suck-back configuration of reverse-blowing fuel as set forth in any one of claims 1 to 5,

the blowback prevention plate has a blowback prevention portion for preventing blowback and an intake air passage portion for passing intake air, covers an inlet of the intake passage, and is detachably fastened to the filter case.

7. The suck-back configuration of reverse-blowing fuel as claimed in any one of claims 1 to 6,

the fuel retention portion is formed between the reverse blow suppression plate and the lower portion in the filter case,

an inlet of the suction passage is disposed in the fuel retention section.

8. The suck-back configuration of reverse-blowing fuel as claimed in any one of claims 1 to 7,

the first fuel storage portion protrudes upstream from an inlet of an intake passage of the filter case,

a second fuel storage portion extending along a part of a periphery of the inlet is formed at the filter case,

the second fuel storage portion is connected to a side edge in the intake air flow direction in the first fuel storage portion.

9. The suck-back configuration of reverse-blowing fuel as claimed in any one of claims 1 to 8, wherein,

the fuel supply device is a carburetor having an air passage and a mixture passage,

the suck-back hole is communicated with the mixture passage.

Technical Field

The present invention relates to a blow-back structure for a reverse blow fuel of a small engine used in a small power machine such as a lawn mower or a chain saw.

Background

In a small engine (gasoline engine) used in a small power machine such as a lawn mower, an air cleaner is connected to an upstream side of a fuel supply device such as a carburetor, and air is introduced through the air cleaner by an intake negative pressure generated during a stroke of a piston. When air (intake air) passes through the fuel supply device, fuel is sprayed to form an air-fuel mixture, and the air-fuel mixture is supplied to the combustion chamber (for example, patent document 1).

Disclosure of Invention

Problems to be solved by the invention

Since the intake air is accompanied by pulsation due to pressure fluctuation at the intake port of the cylinder, the intake air may blow back into the air cleaner through the intake passage during high-speed operation or the like. If this amount increases, the elements of the air cleaner may be clogged by the fuel and the lubricating oil in the intake air.

In patent document 1, a blowback prevention plate is provided integrally with a filter case to prevent blowback from an intake passage. The reverse blow fuel blocked by the reverse blow prevention plate is drawn back to the intake passage by the intake negative pressure. However, since the blowback fuel is in the form of a mist, it is difficult to block the entire blowback fuel in the structure of patent document 1. Therefore, a part of the blowback fuel scatters into the filter case and adheres to the wall of the filter case. The fuel adhering to the wall of the filter case liquefies and remains in the case.

In patent documents 2 and 3, liquefied fuel is accumulated in the bottom of a filter case and sucked back to an intake passage using a pipe. However, in the structures of patent documents 2 and 3, since the suction passage is formed by a pipe, the passage becomes long. Therefore, the passage resistance increases and the suck-back force becomes weak. In addition, a pipe, a connector, a holder, and the like are required, and the number of parts increases.

In patent document 4, a blowback guide member that guides blowback fuel toward the bottom of the filter case while blocking the blowback fuel is provided, and the blowback fuel guided by the blowback guide member is accumulated in a fuel accumulation portion at the bottom of the filter case. The fuel in the fuel reservoir is returned to the intake passage through a return passage formed integrally with the filter case. The return passage has a slit shape with one side wall open, and the fuel in the fuel reservoir is returned to the intake passage through the return passage by surface tension and suction negative pressure of the return passage. However, in the structure of patent document 4, since all of the blowback fuel is blocked by the blowback guide member and accumulated in the fuel pool, the fuel in the fuel pool increases, and it is difficult to return all of the blowback fuel from the return passage to the intake passage.

An object of the present invention is to provide a reverse blow fuel suction structure capable of effectively sucking reverse blow fuel into an intake passage while suppressing reverse blow from the intake passage.

Means for solving the problems

In order to achieve the above object, a blow-back fuel suction structure according to the present invention includes: a first fuel storage unit disposed upstream of a fuel supply device of an engine and connected to an intake passage of the fuel supply device; a suction passage that sucks back fuel accumulated in the air cleaner to the intake passage; and a blowback suppression plate that is disposed between the filter element of the air cleaner and the first fuel storage unit and suppresses blowback from the intake passage. The suck-back passage communicates a fuel retention portion in the air cleaner with a suck-back hole formed in the first fuel storage portion.

According to this configuration, the reverse blow fuel from the intake passage is blocked by the reverse blow suppression plate. This can suppress the blowback of fuel from the intake passage. Part of the blowback fuel blocked by the blowback suppression plate is accumulated in the first fuel storage portion. The fuel accumulated in the first fuel storage portion is directly returned to the intake passage connected thereto by the suction negative pressure. The remaining portion of the blowback fuel liquefies in the air cleaner and remains at the bottom of the air cleaner. The fuel remaining at the bottom of the air cleaner is sucked back into the intake passage from the suck-back hole by the suction action of the intake air flow. In particular, if the suction hole is formed in the downstream portion of the first fuel storage portion, the suction effect becomes large. In this way, according to the above configuration, the blowback of fuel from the intake passage can be suppressed by the blowback suppression plate, and the fuel can be efficiently sucked back into the intake passage from the first fuel storage portion and the suck-back hole by the suction action of the intake air flow.

In the present invention, a blow-back prevention piece that faces an inlet of the intake passage and prevents blow-back from the intake passage may be formed at an upstream end of the first fuel storage portion. According to this configuration, the blowback prevention piece can further suppress blowback of fuel from the intake passage.

In the present invention, the air cleaner may include a filter case connected to the fuel supply device, and a filter cover covering the filter case and the filter element, and a periphery of the suction passage may be covered with the filter case, a pair of protruding walls integrally formed therewith, and a closing member abutting on front ends of the pair of protruding walls. According to this configuration, the suction passage formed of the passage whose outer periphery is closed can be easily formed by the filter case, the pair of projecting walls, and the closing member. By making the suction circuit a circuit whose outer periphery is closed, the suction force generated by the intake negative pressure can be effectively utilized. In this case, the closing member may be formed by the blowback suppression plate attached to the filter case. According to this configuration, it is not necessary to separately prepare a closing member, and an increase in the number of components can be prevented.

In the case where the periphery of the suck-back passage is covered with the filter case, the pair of projecting walls, and the blowback prevention plate, the opening area of the suck-back hole may be set to be sufficiently smaller than the passage area of the suck-back passage so that the suction action by the intake air flowing through the intake passage is exerted. According to this configuration, since the outlet of the suck-back passage is throttled by the suck-back hole, the suction action by the intake negative pressure can be effectively utilized.

In the present invention, the blowback prevention plate may have a blowback prevention portion that prevents blowback and an intake air passage portion that allows intake air to pass therethrough, and the blowback prevention plate may be detachably fastened to the filter case so as to cover an inlet of the intake air passage. According to this configuration, the air cleaner can be easily cleaned by removing the blow-down suppressing plate.

In the present invention, the fuel retention portion may be formed between the filter case and the blowback prevention plate at a lower portion in the filter case, and an inlet of the suction passage may be disposed in the fuel retention portion. According to this configuration, since the fuel retention portion is formed in the narrow space, the fuel in the fuel retention portion can be smoothly sucked back into the intake passage.

In the present invention, the first fuel storage portion may protrude upstream from an inlet of the intake passage of the filter case, a second fuel storage portion extending along a part of a peripheral edge of the inlet may be formed in the filter case, and the second fuel storage portion may be connected to a side edge of the first fuel storage portion in an intake air flow direction. According to this configuration, the second fuel storage unit is provided, so that the blowback fuel can be stored even if the posture of the engine changes. The thus-stored blowback fuel can be sucked back to the intake passage by the suction action produced by the intake air.

In the present invention, the fuel supply device may be a carburetor having an air passage and an air-fuel mixture passage, and the suction hole may communicate with the air-fuel mixture passage. Thus, the blowback fuel suction structure of the present invention can be applied to a two-cycle engine having an air-pilot type scavenging structure.

Any combination of at least two of the configurations disclosed in the claims and/or the description and/or the drawings is also comprised in the present invention. In particular, any combination of two or more of the claims is also included in the present invention.

Drawings

The invention will be more clearly understood from the following description of a preferred embodiment with reference to the attached drawings. However, the embodiments and the drawings are only for illustration and description and should not be used to determine the scope of the present invention. The scope of the invention is to be determined by the claims appended hereto. In the accompanying drawings, like reference numerals designate identical or corresponding parts throughout the several views.

Fig. 1 is a front view showing an engine having a blow-back fuel suction structure according to a first embodiment of the present invention.

Fig. 2 is a vertical cross-sectional view showing an intake system of the engine.

Fig. 3 is a side view of a filter case of the engine as viewed from an upstream side in an intake air flow direction.

Fig. 4 is a side view showing a state where the blowback suppression plate is detached from fig. 3.

Fig. 5 is a perspective view of the filter case.

Fig. 6 is a vertical cross-sectional view showing the suck-back structure.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the present specification, the "front-rear direction" refers to the axial direction of a crankshaft of an engine, the "up-down direction" refers to the axial direction of a cylinder bore, and the "left-right direction" refers to a direction orthogonal to both the front-rear direction and the up-down direction. The terms "upstream" and "downstream" refer to upstream and downstream in the flow direction of intake air. In the following embodiments, a small two-cycle engine used in a lawn mower is exemplified, but the present invention can also be applied to other small power machines such as a chain saw.

Fig. 1 is a front view of a small engine having a blow-back fuel suction structure according to an embodiment of the present invention. In fig. 1, the two-cycle engine E includes a crankcase 2 rotatably supporting a crankshaft 1, and a cylinder 4 connected to an upper portion of the crankcase 2. A cylinder head is integrally formed in the cylinder 4. A crank chamber 2a (fig. 2) is formed inside the crankcase 2, and a combustion chamber 4a (fig. 2) is formed inside the cylinder 4.

A fuel supply device 6 and an air cleaner 8 constituting an intake system are connected to one of left and right side portions (left side in fig. 1) of the cylinder 4. A muffler 10 constituting an exhaust system is connected to the other of the left and right side portions (right side in fig. 1) of the cylinder 4. In the present embodiment, a carburetor is used as the fuel supply device 6. However, the fuel supply device 6 is not limited to this, and may be constituted by a fuel injector (fuel injector) and a throttle valve upstream thereof, for example. The structure of the air cleaner 8 will be described later. A fuel tank 12 is mounted on a lower portion of the crankcase 2. The cylinder 4 and the muffler 10 are covered by a shroud 14.

As shown in fig. 2, a cylinder hole 4b is formed inside the cylinder 4. A piston 16 reciprocating in an axial direction C1 (vertical direction) is inserted into the cylinder hole 4 b. The combustion chamber 4a is formed by the upper surface of the piston 16 and the cylinder bore 4 b. An insulator 18 is provided between the cylinder 4 and the fuel supply device 6. The insulator 18 is made of a heat insulating material such as resin, and is provided for the purpose of insulating heat from the high-temperature cylinder 4.

An air intake system is provided with an air passage 20 and a mixture passage 22 that communicate with the cylinders 4. The air passage 20 and the air-fuel mixture passage 22 are arranged in parallel with each other, and the air passage 20 is formed on the upper side and the air-fuel mixture passage 22 is formed on the lower side. These air passage 20 and air-fuel mixture passage 22 form an intake passage 24. The air passage 20 and the mixture passage 22 are formed in the carburetor (fuel supply device) 6 at a part of the upstream side thereof, and in the insulator 18 at the downstream side thereof. The air passage 20 and the air-fuel mixture passage 22 are introduced into the air a purified by the air cleaner 8. In the air-fuel mixture passage 22 in the fuel supply device 6, the fuel F is sprayed to the air a to generate the air-fuel mixture M.

The fuel supply device 6 has a cylindrical body 9 that rotates about an upper and lower axial center within a main body 90. The cylinder 9 is formed with a mixture passage 22. A throttle valve 6a having a needle that moves up and down is provided in the air-fuel mixture passage 22, and the supply amount of the air-fuel mixture M is adjusted.

The mixture passage 22 has an intake port 22a that opens on the inner peripheral surface of the cylinder 4. A scavenging port 26a for introducing the air-fuel mixture M from the scavenging passage 26 into the crank chamber 2a is formed in the peripheral wall of the cylinder 4. An exhaust port 28a of an exhaust passage 28 opens on the inner circumferential surface of the cylinder 4. The exhaust port 28a is formed on the opposite side of the intake port 22a in the cylinder bore 4b in the circumferential wall of the cylinder 4 with the axial center direction C1 therebetween. The exhaust gas (combustion gas) from the exhaust passage 28 is discharged to the outside through the muffler 10 (fig. 1).

A reed valve 30 is mounted at the downstream side outlet of the air passage 20 in the insulator 18. When the pressure of the communication passage 32 connected to the air passage 20 rises to a predetermined value or more, the reed valve 30 closes the air passage 20. That is, the air a from the air passage 20 is introduced into the upper portion of the scavenging passage 26 through the communication passage 32 by opening the reed valve 30.

In an intake stroke in which the piston 16 rises as indicated by a two-dot chain line in fig. 2, the air-fuel mixture M from the air-fuel mixture passage 22 receives a negative pressure in the crank chamber 2a and is directly introduced from the intake port 22a into the crank chamber 2 a. On the other hand, the air a from the air passage 20 is subjected to the negative pressure of the crank chamber 2a during the intake stroke, and is temporarily introduced from the communication passage 32 into the upper portion of the scavenging passage 26.

In a scavenging stroke in which the piston 16 is lowered, indicated by a solid line in fig. 2, the air-fuel mixture M introduced into the crank chamber 2a is discharged from the scavenging port 26a into the combustion chamber 4a via the scavenging passage 26. At this time, the air a stored in the upper portion of the scavenging passage 26 is ejected into the combustion chamber 4a ahead of the air-fuel mixture M. As described above, the engine E of the present embodiment has an air-pilot type scavenging structure.

Next, the structure of the air cleaner 8 will be described. The air cleaner 8 includes a cleaner case 36 connected to a main body 90 of the fuel supply device 6, and a cleaner cover 38 attached to the cleaner case 36. The air cleaner 8 is attached to the insulator 18 together with the fuel supply device 6 by a common fastening member (not shown) such as a bolt.

The filter case 36 and the filter cover 38 of the present embodiment are molded products made of resin. The filter case 36 is substantially rectangular when viewed from the left-right direction. The filter cover 38 is bowl-shaped with the filter case 36 side open. However, the material and shape of the filter case 36 and the filter cover 38 are not limited to these. An air cleaner chamber 39 is formed in the filter case 36 and the filter cover 38.

A filter element 40 is disposed in the air cleaner compartment 39. The filter element 40 is made of paper, for example, and filters and purifies air. That is, air introduced from an air intake port (not shown) formed in a gap between the filter case 36 and the filter cover 38 passes through the filter element 40 and is then supplied to the fuel supply device 6. In the present embodiment, the filter cover 38 covers the filter case 36 and the filter element 40.

In the filter case 36, the first filter outlet 42 and the second filter outlet 44 are arranged in parallel in the vertical direction. Specifically, the second filter outlet 44 is provided above the first filter outlet 42. The first filter outlet 42 communicates with the mixture passage 22. The second filter outlet 44 communicates with the air passage 20. That is, the first and second filter outlets 42, 44 constitute inlets of the intake passage 24.

A first fuel storage portion 46 connected to the mixture passage 22 is formed in the filter case 36. That is, the first fuel storage portion 46 is disposed on the upstream side of the fuel supply device 6 and is connected to the mixture passage 22 of the fuel supply device 6. Specifically, the first fuel storage 46 protrudes upstream from the first filter outlet 42 of the filter case 36. In the present embodiment, the first fuel storage portion 46 is integrally formed to the filter case 36 by mold molding.

As shown in fig. 5, the first fuel storage 46 has a semicircular shape with an upper part opened. The semicircular recess stores a portion of the blowback fuel. A blowback prevention piece 48 is formed continuously with the upstream end of the first fuel storage portion 46. The blowback prevention piece 48 prevents blowback of fuel from the mixture passage 22. The blowback prevention sheet 48 is formed to face the first filter outlet 42 so as to be substantially orthogonal to the passage direction of the first filter outlet 42. The blowback prevention sheet 48 is also integrally formed with the filter case 36 by die molding. A positioning projection 48a is formed on the upstream end surface of the blowback prevention sheet 48.

A second fuel storage portion 50 is formed in the filter case 36. A part of the blowback fuel from the intake passage 24 is also stored in the second fuel storage portion 50. The second fuel storage portion 50 extends along a portion of the periphery of the first filter outlet 42. In the present embodiment, the second fuel storage 50 extends along a front portion (a front-side portion in fig. 1) of the peripheral edge of the first filter outlet 42. Therefore, when the engine changes its posture and the front side in fig. 5 is the lower side, the blowback fuel is stored. The second fuel storage portion 50 is connected to a side edge 46a in the intake air flow direction in the first fuel storage portion 46.

That is, the second fuel storage portion 50 extends from the front edge of the first filter outlet 42 toward the upstream side in the intake air flow direction, and extends upward from the side edge 46a of the first fuel storage portion 46. The second fuel storage 50 is folded back at its upper end rearward, and is connected to a contamination prevention sheet 51 covering the lower half of the second filter outlet 44. The anti-mixing sheet 51 prevents the blowback fuel from the first filter outlet 42 from entering the air passage 20 (fig. 2) through the second filter outlet 44. In the present embodiment, the second fuel storage portion 50 is formed integrally with the filter case 36 by die molding. However, the second fuel storage portion 50 may be omitted.

In the air cleaner 8, a fuel retention portion 52 is formed at the bottom of the cleaner case 36. The remaining portion of the blowback fuel from the intake passage 24 remains in the fuel retention portion 52. In the present embodiment, a horizontally extending stepped surface provided at the bottom of the filter case 36 constitutes the fuel retention section 52.

A suck-back passage 54 is formed in the filter case 36. The suction passage 54 sucks back the fuel accumulated in the fuel retention portion 52 in the air cleaner 8 to the air-fuel mixture passage 22 (intake passage 24) in fig. 2. In the present embodiment, the suction passage 54 communicates the fuel retention portion 52 with the first fuel storage portion 50. Specifically, a suction hole 56 is formed in a downstream portion of the first fuel storage portion 46, and the suction passage 54 communicates the fuel retention portion 52 with the suction hole 56. That is, the inlet 54a of the suction passage 54 is disposed in the fuel retention portion 52, and the outlet 54b of the suction passage 54, i.e., the suction hole 56, is disposed in the first fuel storage portion 46.

However, the suck-back hole 56 is not limited to the downstream portion of the first fuel storage portion 46 as long as it is formed in the first fuel storage portion 46. In the case where the second fuel storage portion 50 is provided as in the present embodiment, the suck-back hole 56 may be formed in the side edge 46a of the first fuel storage portion 46 connected to the second fuel storage portion 50. The configuration of the suck-back passage 54 will be described in detail later.

As shown in fig. 4, two screw insertion holes 58, 58 and two cylindrical bosses 60, 60 are formed on the inner surface (the surface facing the upstream side) of the filter case 36. Two screw insertion holes 58 are provided on both sides of the first filter outlet 42. In the present embodiment, the filter case 36 is attached to the insulator 18 together with the fuel supply device 6 of fig. 2 by a fastening member (not shown) such as a bolt inserted through the bolt insertion hole 58.

The two protrusions 60 are provided obliquely above and obliquely below the first filter outlet 42 with the first filter outlet 42 interposed therebetween. That is, one projection 60 is provided above one screw insertion hole 58, and the other projection 60 is provided below the other screw insertion hole 58. Each boss 60 is formed with a threaded hole 60 a. In the present embodiment, the projection 60 is formed integrally with the filter case 36 by die forming.

A mounting piece 62 is formed at the upper end of the filter case 36. A screw hole 62a is formed in the attachment piece 62. On the other hand, a locking piece 64 is formed at the lower end of the filter case 36. Two locking pieces 64 are provided side by side at the lower end of the filter case 36. The locking piece 64 is engaged with a locked portion (not shown) of the filter cover 38 shown in fig. 2, and the filter cover 38 is attached to the filter case 36 by the attachment screw 41 using the screw hole 62a of the attachment piece 62. However, the attachment structure of the filter case 36 and the filter cover 38 is not limited to this.

A blowback suppression plate 66 shown in fig. 3 is provided in the air cleaner chamber 39 of the air cleaner 8. Specifically, the blowback suppression plate 66 is disposed between the filter element 40 and the first fuel storage portion 46 shown in fig. 2. The blowback suppression plate 66 suppresses blowback of fuel from the intake passage 24. The blowback suppression plate 66 abuts against the upstream end surface of the blowback prevention sheet 48 of the first fuel storage portion 46. On the other hand, a gap is formed between the blowback suppression plate 66 and the filter element 40.

As shown in fig. 3, the blowback suppression plate 66 of the present embodiment is made of a rectangular metal plate. However, the material and shape of the blowback suppression plate 66 are not limited to these. The blowback suppression plate 66 is formed with one pin insertion hole 66a and two screw insertion holes 66b, 66 b. In a state where the positioning projection 48a of the filter case 36 of fig. 5 is inserted into the pin insertion hole 66a, the screw 68 of fig. 3 is inserted into the screw insertion hole 66b and fastened to the screw hole 60a (fig. 4) of the filter case 36. Thus, the blowback prevention plate 66 is detachably fastened to the filter case 36.

The blowback suppression plate 66 has a holeless blowback suppression portion 69 and an intake air passage portion 70 through which intake air passes. The blowback suppression portion 69 faces the first filter outlet 42 in the flow direction of the intake air. That is, the blowback suppression portion 69 covers the inlet of the intake passage 24, and suppresses blowback of fuel from the intake passage 24.

The intake air passage portion 70 communicates the upstream side and the downstream side of the blowback suppression plate 66 to pass the intake air. In the present embodiment, the air cleaner chamber 39 (fig. 2) is divided into an upstream side and a downstream side by the blowback suppression plate 66, and the upstream side and the downstream side communicate with each other through the intake air passage portion 70. In the present embodiment, the intake air passage portion 70 is formed by a plurality of punched holes. However, the intake air passage portion 70 is not limited to the punched hole. As shown in fig. 2, the fuel retention portion 52 is formed between the filter tank 36 and the blowback suppression plate 66 at a lower portion in the filter tank 36.

Next, the details of the suction passage 54 will be described. As shown in fig. 4, the filter case 36 is formed with a pair of protruding walls 72, 72 protruding from the filter case 36. The protruding wall 72 is integrally formed with the filter case 36 by die forming. The protruding height of the protruding wall 72 is the same as the amount of protrusion of the first fuel storage portion 46 from the filter case 36. That is, the blowback suppression plate 66 abuts against the projecting ends 72a of the projecting walls 72, 72 in a state of being attached to the filter case 36. In other words, the lower portion of the blowback suppression plate 66 constitutes a closing member that abuts the projecting ends 72a of the projecting walls 72, 72. However, a closing member may be provided in place of the blowback suppression plate 66.

The suction passage 54 is covered with the filter case 36, the pair of projecting walls 72 and 72, and the lower portion of the blowback prevention plate 66, and the outer periphery is closed. That is, the drawback passage 54 is formed by a rectangular passage whose outer periphery is closed. In the present embodiment, the opening area S1 of the return hole 56 shown in fig. 2 is set smaller than the passage area S2 of the suction passage 54. The ratio of the opening area S1 to the passage area S2 (S1/S2) is preferably 0.1 to 0.5, and in the present embodiment is about 0.2.

Next, the operation of the blow-back fuel suction structure according to the present embodiment will be described with reference to fig. 6. Particularly, during high-speed engine operation, fuel may blow back from the fuel supply device 6 to the air cleaner 8 as indicated by arrow F due to pulsation caused by the action of the intake port 22a of the cylinder 4 and the throttle valve 6 a. The blowback fuel collides with the blowback prevention piece 48 and the blowback suppression portion 69 of the blowback suppression plate 66 and is blocked. A part F1 of the blowback fuel blocked by the blowback prevention piece 48 and the blowback suppression plate 66 accumulates in the first fuel storage portion 46. The blowback fuel F1 accumulated in the first fuel storage portion 46 is sucked back into the intake passage 24 connected thereto by the suction force SF generated by the intake air flowing in the intake passage 24.

The remaining portion F2 of the blowback fuel that is caught by the blowback prevention piece 48 and the blowback suppression plate 66 remains in the fuel retention portion 52. The blowback fuel F2 accumulated in the fuel retention portion 52 is sucked back into the intake passage 24 from the suction passage 54 via the suction hole 56 by the suction force SF of the intake air flow.

According to the above configuration, the reverse blow-down fuel is blocked by the reverse blow-down prevention plate 66 and the reverse blow-down prevention sheet 48, and therefore adhesion of the reverse blow-down fuel to the inner surface of the filter cover 38 and the filter element 40 can be suppressed. Further, the fuel F1 accumulated in the first fuel storage 46 is sucked back into the intake passage 24. The blowback fuel F2 scattered from the first fuel storage portion 46 and accumulated in the fuel retention portion 52 at the bottom of the filter case 36 is sucked back into the intake passage 24 from the suction passage 54 and the suction hole 56. Therefore, the blowback fuel F2 can be suppressed from remaining in the filter case 36.

Since the suck-back hole 56 is formed in the downstream portion of the first fuel storage portion 46, the suction effect by the flow of intake air in the mixture passage 22 is large. Therefore, the blowback fuel F2 remaining in the fuel retention portion 52 can be efficiently sucked back into the intake passage 24. Thus, according to the above configuration, the blowback fuel F1 can be prevented from flying apart by the blowback prevention plate 66 and the blowback prevention piece 48, and the blowback fuel F1 can be efficiently sucked back into the intake passage 24 from the first fuel storage portion 46 and the suck-back hole 56 by the suction action of the intake air flow.

The suck-back passage 54 is a passage whose outer periphery is closed by the filter case 36, the pair of projecting walls 72, and the blowback suppression plate 66. By making the suck-back passage 54a passage whose outer periphery is closed, the suction force SF generated by the intake negative pressure can be effectively utilized. Further, the blowback prevention plate 66 is used as a part of the wall of the suck-back passage 54. This eliminates the need for additional components, and reduces the number of components.

The opening area S1 of the suck-back hole 56 is set smaller than the passage area S2 of the suck-back passage 54. This makes it easy for the suction action by the intake air to act in the suck-back passage 54. As a result, the blowback fuel F2 accumulated in the fuel retention portion 52 can be efficiently sucked back into the intake passage 24 by the suction force SF of the intake air flow.

The blowback suppression plate 66 is detachably fastened to the filter case 36. This makes it possible to easily remove the blowback suppression plate 66 from the filter case 36, and thus to easily clean the inside of the air cleaner 8.

The fuel retention portion 52 is formed between the filter case 36 and the blowback suppression plate 66 at a lower portion in the filter case 36. An inlet 54a of the suction passage 54 is disposed in the fuel retention portion 52. By forming the fuel retention portion 52 in such a narrow space, the blowback fuel F2 in the fuel retention portion 52 can be smoothly sucked back into the intake passage 24.

As shown in fig. 5, the filter case 36 is provided with a second fuel storage portion 50. Thus, even if the posture of the engine changes, the blowback fuel F1 can be stored in the second fuel storage portion 50. In the present embodiment, when the work tool (the cutter blade in the case of a lawnmower) is directed upward and the work is performed, the blowback fuel F1 is accumulated in the second fuel storage unit 50. The blowback fuel F1 stored in the second fuel storage portion 50 is drawn back to the intake passage 24 by the suction action. In the case where the second fuel storage portion 50 is provided, the suck-back hole 56 is preferably provided in the vicinity of the boundary portion between the first and second fuel storage portions 46 and 50.

As shown in fig. 2, the fuel supply device 6 of the present embodiment is a carburetor, and a suction hole 56 communicates with the mixture passage 22 on the lower side of the carburetor. Thus, the blowback fuel suction structure of the present invention can be applied to an air-pilot type scavenging structure.

The present invention is not limited to the above embodiments, and various additions, modifications, and deletions can be made within the scope not departing from the gist of the present invention. In the above embodiment, the intake passage 24 includes the air passage 20 and the mixture passage 22, but may not include an air passage. Further, the blowback prevention sheet 48 may not be provided. In this case, the upstream end surface of the first fuel storage 46 abuts against the blowback suppression plate 66. Therefore, such a mode is also included in the scope of the present invention.

Description of the reference numerals

6 Fuel supply device (carburetor)

8 air filter

20 air passage

22 passage for mixed gas

24 air intake passage

36 filter box

38 filter cover

40 Filter element

42 first Filter outlet (inlet of intake passage)

46 first fuel storage portion

48 back-blowing prevention sheet

50 second fuel storage

52 fuel retention portion

54 suck-back passage

54a suction back passage

56 suck-back hole

66 blowback suppressing plate (closing member)

69 reverse blowing suppressing part

70 air intake passage part

72 protruding wall