Patent Application
20130228152
The present invention relates to an air supply device of a stratified scavenging two-cycle engine. In particular, the present invention relates to an air supply engine provided with a carburetor and an insulator.
A carburetor applicable to a stratified scavenging two-cycle engine is provided with separate passages, i.e., a mixture passage for generating air-fuel mixture and supplying the air-fuel mixture to an engine body, and an air passage for supplying air for stratified scavenging (e.g., Patent Literature 1).
According to Patent Literature 1, a butterfly valve that is moved in conjunction with a throttle operation is provided in a bore forming each passage so as to control the flow rate of the air passing through the bore. Such a carburetor is attached to a cylinder block or the like of the engine body via an insulating member with heat insulation. Accordingly, the insulator is also necessarily provided with a mixture passage through which the air-fuel mixture passes, and an air passage through which air for stratified scavenging passes.
A carburetor for a conventional two-cycle engine, which is not stratified scavenging type, is originally configured as a single-bore carburetor provided with only one bore for air to flow in, which defines an inner space functioning as a mixture passage for air-fuel mixture. In order to apply such a single-bore carburetor to a stratified scavenging two-cycle engine, there has been typically known a technique of dividing the single mixture passage into two parts, i.e., one part as a mixture passage and the other part as an air passage (e.g., Patent Literature 1). Since being originally provided as a single-bore carburetor, such a carburetor is provided with one butterfly valve that is moved in conjunction with a throttle operation.
The single-bore carburetor of the above type, being applicable to a stratified scavenging two-cycle engine, is the same as a carburetor for a conventional two-cycle engine in terms of size and an operation mechanism of a butterfly valve and has a considerably small size and a simplified structure as compared with a carburetor provided with separate mixture passage and air passage. Thus, applying the single-bore carburetor to a stratified scavenging two-cycle engine allows reduction in the size of the engine and significantly contributes to weight reduction. Further, in the carburetor provided with the separate mixture passage and air passage, a throttle operation needs to be performed against return springs in butterfly valves respectively provided in these passages, so that the load during the operation is relatively large. However, the single-bore carburetor described the above has only one return spring. Using the single-bore carburetor leads to not only reduction in size and weight but also reduction of fatigue during operation.
PTL 1: US 2006/0219217 A1
PTL 2: WO 08/033062 A1
In the carburetor provided with the separate mixture passage and air passage, a timing at which the valve in the air passage is opened is usually delayed as compared with a timing at which the valve in the mixture passage is opened. In order to delay the timing, the valves are moved in conjunction with each other using a specific link mechanism. As a result, when the engine is driven in a speed range from an idling speed range to a low-middle speed range, supply of air for stratified scavenging to the engine body is stopped, thereby suppressing unstable combustion during idling.
In contrast, a single-bore carburetor is provided with only one butterfly valve moved in conjunction with a throttle. When the valve is moved by operating the throttle during idling, not only the part as a mixture passage but also the part as an air passage is undesirably opened at the same time, so that air for stratified scavenging is supplied to the engine body even in the above speed range. As a result, the uniformity of fuel concentration becomes impaired in a cylinder, which often causes unstable combustion.
An object of the invention is to provide an air supply device with a single bore applicable to a stratified scavenging two-cycle engine, the air supply device which is capable of improvement in combustion stability at a low-middle speed or lower.
According to an aspect of the invention, an air supply device of a stratified scavenging two-cycle engine, including: a carburetor provided with a single bore for air to flow in, the bore having therein a throttle valve provided by a butterfly valve that rotates in conjunction with a throttle operation so that, when the throttle valve is opened, a carburetor-side mixture passage for generated air-fuel mixture to flow in and a carburetor-side air passage for the air to directly flow in are substantially defined on a downstream side of the throttle valve in the bore; and an insulator provided on a downstream side of the carburetor, the insulator provided with an insulator-side mixture passage that is in communication with the carburetor-side mixture passage and an insulator-side air passage that is in communication with the carburetor-side air passage, the air supply device includes: a mixture passage defined by the carburetor-side mixture passage and the insulator-side mixture passage; an air passage defined by the carburetor-side air passage and the insulator-side air passage; and a flow-rate regulator provided inside the air passage, the flow-rate regulator bulging inward in the air passage, in which at least a part of a periphery of a valve body of the throttle valve is close to the flow-rate regulator until the valve body is rotated by a predetermined rotation angle from an initial position corresponding to an idling speed.
According to the above aspect of the invention, the flow-rate regulator that is close to the valve body of the throttle valve is provided in the air passage. Thus, by keeping the valve body close to the flow-rate regulator while the valve body is at a predetermined rotation angle from the idling speed range to a low-middle speed range, the air passage can be closed in such a speed range while opening only the mixture passage, so that the supply of air for stratified scavenging can be restrained. Accordingly, the uniformity of air-fuel mixture concentration in a cylinder is maintained in or below the low-middle speed range, so that a stable combustion can be achieved even when a single-bore carburetor is applied to a stratified scavenging two-stroke engine.
In the air supply device according to the above aspect of the invention, an extended portion that extends toward the carburetor to be fitted into the carburetor-side air passage of the carburetor may be provided near an upstream end of the insulator-side air passage of the insulator, and the flow-rate regulator may be provided on the extended portion as a part of the insulator. Alternatively, the insulator may include an insulator body provided on an engine body of the stratified scavenging two-cycle engine and an intermediate member interposed between the insulator body and the carburetor, an extended portion that extends toward the carburetor to be fitted into the carburetor-side air passage of the carburetor may be provided near an upstream end of a part of the intermediate member forming the insulator-side air passage, and the flow-rate regulator may be provided on the extended portion as a part of the intermediate member. Alternatively, the flow-rate regulator may be provided as a part of the carburetor near a downstream end of the carburetor-side air passage of the carburetor.
In the air supply device, it is preferable that the valve body of the throttle valve be close to the flow-rate regulator until the valve body is rotated from the initial position by a rotation angle of 20 to 40 degrees.
When the close state is released at a rotation angle of less than 20 degrees, the supply of the air for stratified scavenging in the low-middle speed range increases according to the shape of the flow-rate regulator, so that the combustion performance may not be sufficiently improved. In contrast, when the close state is kept at a rotation angle of over 40 degrees, the air for stratified scavenging may not be sufficiently supplied beyond the middle speed range, so that the emission may not be sufficiently reduced.
In the air supply device, it is preferable that an opposing surface of the flow-rate regulator that comes close to the valve body be a spherical surface extending along a rotation path of the valve body. With the above arrangement, while the valve body and the flow-rate regulator are close to each other, the clearance therebetween is constant, so that the supply of the air for stratified scavenging can be securely restrained.
In the air supply device, it is preferable that the flow-rate regulator be configured so that the close state relative to the valve body is gradually released as the valve body is rotated.
According to the above arrangement, since the close state between the valve body and the flow-rate regulator is not immediately released, the flow rate can be smoothly and evenly controlled in accordance with the rotation angle, thereby further stabilizing the combustion state.
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An exemplary embodiment of the invention will be described below with reference to the attached drawings.
As shown in
An air cleaner (not shown) is attached on the upstream side of the carburetor 2. The insulator 3 is fixed to a cylinder block of an engine body (not shown) with bolts or the like. Likewise, the carburetor 2 is fixed to the insulator 3 with bolts or the like. The insulator 3 is made of synthetic resin to have heat insulation. Thus, the insulator 3 prevents heat transfer from the engine body to the carburetor 2.
A detailed description will be made on the carburetor 2.
The carburetor 2 has a single-bore structure in which a single bore 4 through which air passes is provided. The contour, outer structure, size and the like of the carburetor 2 are identical to those of a single-bore carburetor for a conventional two-cycle engine, which is not stratified scavenging type. Incidentally, the carburetor 2 of this exemplary embodiment is applied to a stratified scavenging type engine and the inner space of the bore 4 is divided by a plate-shaped separator 5 into two passages.
One of the two passages is a carburetor-side mixture passage 8 in which a main jet 7 for ejecting fuel is provided to a venturi 6. The other passage is a carburetor-side air passage 9 through which only air for stratified scavenging passes. Air is introduced into both the passages 8 and 9 through a circular inflow opening 10 of the bore 4. In the carburetor-side mixture passage 8, fuel is ejected from the main jet 7 to the introduced air to generate air-fuel mixture. The air-fuel mixture is supplied to the insulator 3 through a circular outflow opening 11 of the bore 4. The air introduced into the carburetor-side air passage 9 is directly supplied to the insulator 3 through the outflow opening 11.
In the bore 4 of the carburetor 2, a choke valve 12 is disposed on the upstream side and a throttle valve 13 is disposed on the downstream side. The valves 12 and 13 are respectively rotated by rotation shafts 14 and 15 that extend along a depthwise direction of the figure. The valves 12 and 13 of this exemplary embodiment respectively include plate-shaped and substantially-circular valve bodies 16 and 17. The valve bodies 16 and 17 are respectively fixed to the rotation shafts 14 and 15 with screws 18 and 19. The choke valve 12 is rotated by operating a choke lever (not shown). The throttle valve 13 is rotated in conjunction with the operation of a throttle lever (not shown).
In
The separator 5 is disposed between the valves 12 and 13 as described above. When both the valves 12 and 13 are rotated to the fully-opened positions (see
Incidentally, though the separator 5 is provided in the bore 4 according to this exemplary embodiment, the separator 5 may only be provided as necessary (i.e., the separator 5 is omissible). Even when the separator 5 is omitted, by opening the throttle valve 13, the carburetor-side mixture passage 8 and the carburetor-side air passage 9 are substantially defined not only at an area divided by the throttle valve 13 but also on the downstream side of the throttle valve 13.
A detailed description will be made on the insulator 3.
The insulator 3 is provided with an insulator-side mixture passage 21 that is in communication with the carburetor-side mixture passage 8 of the carburetor 2, and an insulator-side air passage 22 that is in communication with the carburetor-side air passage 9. The carburetor-side mixture passage 8 and the insulator-side mixture passage 21 in combination form a mixture passage 40 according to the exemplary embodiment that penetrates the carburetor 2 and the insulator 3. The carburetor-side air passage 9 and the insulator-side air passage 22 in combination form an air passage 41 according to the exemplary embodiment that penetrates the carburetor 2 and the insulator 3.
The downstream end of the insulator-side mixture passage 21 is in communication with the inner space of a crankcase via an intake port provided on the cylinder block (not shown). The downstream end of the insulator-side air passage 22 is in communication with the vicinity of a scavenging port of a scavenging passage via an air port (not shown).
The intake port and the air port are opened and closed as a piston reciprocates to function as a piston valve (piston-valve type), or, alternatively, as a lead valve moves in response to pressure pulsation in the inner space of the crankcase (lead-valve type). When the piston moves upward to generate negative pressure in the inner space of the crankcase, the air-fuel mixture generated in the carburetor-side mixture passage 8 passes through the insulator-side mixture passage 21 and the intake port to be supplied to the inner space of the crankcase.
At the almost same time, the air for stratified scavenging introduced into the carburetor-side air passage 9 passes through the insulator-side air passage 22 and the air port to be stored in the scavenging passage near the scavenging port. The air stored in the scavenging passage is utilized in a scavenging process to scavenge combustion gas in a combustion chamber before the air-fuel mixture comes from the crankcase. Thus, in the stratified scavenging two-cycle engine, scavenging is initially performed by the air for stratified scavenging, so that discharge of unburned fuel contained in the air-fuel mixture in the scavenging process is restrained to improve emission.
The passages 21 and 22 of the insulator 3 are separated from each other by a centrally-disposed separate portion 23. An upstream opening 24 of the insulator-side mixture passage 21 and an upstream opening 25 of the insulator-side air passage 22 are formed in a semicircular shape. The upstream opening 25 of the insulator-side air passage 22 is provided with an extended portion 26 over the entire periphery of the opening that extends toward the carburetor 2. In molding the entire insulator 3, the extended portion 26 is also integrally formed. When the carburetor 2 is attached to the insulator 3, the extended portion 26 fits in the carburetor-side air passage 9.
The extended portion 26 defines a flattened portion 27 at a portion continuous with the separate portion 23. When the throttle valve 13 is rotated to the fully-opened position, the valve body 17 of the throttle valve 13 is brought into contact with the flattened portion 27. The valve body 17 and the flattened portion 27 are thus overlaid on each other. The flattened portion 27 extends in parallel with a rotation axis 15A of the throttle valve 13 (see
Being observed on the downstream side of the insulator-side air passage 22, as shown in
The flow-rate regulator 28 is kept close to the end of the valve body 17 for a while after the throttle valve 13 begins to rotate from the idling position. As a result, the carburetor-side mixture passage 8 begins to open simultaneously when the throttle valve 13 begins to rotate, so that the carburetor-side mixture passage 8 is promptly brought into communication with the insulator-side mixture passage 21. In contrast, the carburetor-side air passage 9 is brought into communication with the insulator-side air passage 22 with delay. In this exemplary embodiment, as shown in
When the rotation angle of the throttle valve 13 exceeds 40 degrees as shown in
Further, as shown in
Incidentally, since the air-fuel mixture side and the air side are separated by the separator 5, the valve body 17, the protruding flattened portion 27 and the like, the air-fuel mixture hardly comes into the insulator-side air passage 22 irrespective of the rotation angle of the throttle valve 13.
As described above, in the air supply device 1 according to this exemplary embodiment, the flow-rate regulator 28 is provided on the upstream end of the insulator-side air passage 22 at a position close to the valve body 17 of the throttle valve 13. Thus, when the throttle valve 13 is rotated by an angle corresponding to a range from the idling speed range to the low-middle speed range, the carburetor-side mixture passage 8 is opened while the carburetor-side air passage 9 is closed. As a result, in the above rotation range, the air for stratified scavenging is prevented from being supplied, thereby preventing impairment of the uniformity of air-fuel mixture concentration in a cylinder. Even when the carburetor 2 (the single-bore carburetor) is used in a stratified scavenging two-cycle engine, the combustion state can be stabilized.
It should be understood that the scope of the invention is not limited to the above-described exemplary embodiment, but includes any modifications as long as the object of the invention is achieved.
For instance,
As a result, the carburetor-side air passage 9 is opened slightly earlier than that of the above exemplary embodiment (alternatively, may be opened upon the rotation of the valve body 17). However, the close state between the flow-rate regulator 28 and the valve body 17 is not immediately released over the entire area of the flow-rate regulator 28 upon exceeding a predetermined rotation angle, but is gradually released from a part of a periphery of the valve body 17 to open the carburetor-side air passage 9. Accordingly, the flow rate of the air for stratified scavenging at the start of opening the carburetor-side air passage 9 is sufficiently small and does not cause serious influence on the combustion state. Rather, by gradually opening the carburetor-side air passage 9 as in the first modification, a smooth and even flow rate control in accordance with the rotation angle can be achieved, thereby further stabilizing the combustion state.
Further, when the throttle valve 13 is fully opened, the opening area of the carburetor-side air passage 9 in the first modification is the same as that in the above exemplary embodiment. Accordingly, a sufficient amount of the air for stratified scavenging can be supplied in a high rotation range, so that emission can be securely improved.
Incidentally, the shape and the like of the flow-rate regulator 28 may be determined in any manner considering an engine displacement or required combustion characteristics and is not limited to those shown in the above exemplary embodiment and the first modification.
Further, the extended portion 26 having the flattened portion 27 and the flow-rate regulator 28 may be provided by a semicircular ring independent of the insulator 3 that is detachably fitted to the insulator 3 and the carburetor 2. At this time, a plurality of the extended portions 26 having differently shaped flow-rate regulators 28 may be prepared, an appropriate one of which may be selected to be used in accordance with required performance.
The second modification provides the same advantages as the above exemplary embodiment in spite of the difference in the structure thereof, so that the object of the invention can be achieved.
The third modification provides the same advantages as the above exemplary embodiment in spite of the difference in the structure thereof, so that the object of the invention can be achieved.
The invention is applicable to an air supply device of a stratified scavenging two-cycle engine installed in a portable work machine such as a brushcutter, a chain saw, an engine blower or a hedge trimmer.
1 . . . air supply device
2 . . . carburetor
3 . . . insulator
4 . . . bore
8 . . . carburetor-side mixture passage
9 . . . carburetor-side air passage
13 . . . throttle valve
17 . . . valve body
21 . . . insulator-side mixture passage
22 . . . insulator-side air passage
26 . . . extended portion
28 . . . flow-rate regulator
29 . . . spherical surface
30 . . . insulator body
31 . . . intermediate member
40 . . . mixture passage
41 . . . air passage
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/006542 | 11/8/2010 | WO | 00 | 5/8/2013 |
