JP4793871B2 - 4-cycle engine - Google Patents

Description

  The present invention relates to a four-cycle engine in which a structure of intake and exhaust passages formed in a cylinder head and a structure of a squish area formed between a piston and a cylinder head are related to each other.

  Conventionally, there are those shown in FIGS. According to this publication, in the plan view of the cylinder with the cylinder axis in the vertical direction, when the one horizontal direction is the front, the downstream end of the intake passage that communicates the atmosphere side with the combustion chamber of the cylinder The intake passage is formed in the cylinder head so that is located on the rear side of the combustion chamber. The downstream end of the intake passage is formed to be a plurality of intake openings in the left-right direction. On the other hand, the exhaust passage is formed in the cylinder head so that the upstream end of the exhaust passage that communicates the combustion chamber to the atmosphere side is located on the front side of the combustion chamber. The upstream end of the exhaust passage is formed to have a plurality of exhaust openings in the left-right direction. In addition, a squish area having a small gap between the upper and lower surfaces is formed between the upper surface of the piston at the top dead center and the lower surface of the cylinder head.

  In the intake stroke during operation of the engine, the intake openings are opened, and air on the atmosphere side is drawn into the combustion chamber through the intake passage. After the air-fuel mixture generated by the air thus sucked and the separately supplied fuel passes through the compression stroke, it is used for combustion in the combustion chamber in the explosion stroke. And the heat energy by this combustion is converted into motive power and outputted. Next, in the exhaust stroke, the exhaust openings are opened, and the combustion gas generated by the combustion passes through the exhaust passage and is discharged to the atmosphere outside the cylinder as exhaust.

  In the compression stroke, when the piston reaches top dead center, a squish flow that vigorously flows is generated by the air-fuel mixture compressed and pushed out in the squish area. The squish flow mixes the air-fuel mixture in the combustion chamber to make the concentration more uniform, thereby improving engine performance.

  Incidentally, as described above, the downstream end of the intake passage is formed on the rear side (intake side) of the combustion chamber. For this reason, the air-fuel mixture on the rear side of the combustion chamber shortly after being drawn into the combustion chamber through the intake passage is lower in temperature than the air-fuel mixture warmed on the front side (exhaust side) of the combustion chamber. Tend to. Thus, when the air-fuel mixture at the rear side of the combustion chamber is low in temperature, flame propagation during combustion of the air-fuel mixture during the subsequent explosion stroke tends to be delayed. As a result, there is a risk of knocking occurring on the rear side of the combustion chamber.

  Here, in the conventional technique, the first gap dimension at the rear part of the squish area is larger than the second gap dimension at the front part of the squish area. For this reason, it is thought that the following effect | action arises in the said prior art.

That is, in the compression stroke, when the piston reaches top dead center, the squish that is generated at the front of the squish area and flows backward rather than the squish flow that is generated at the rear of the squish area and flows forward. The flow is more powerful. As a result, the high-temperature air-fuel mixture on the front side of the combustion chamber is supplied to the low-temperature air-fuel mixture on the rear side of the combustion chamber and mixed with the air-fuel mixture. Accordingly, it is considered that the temperature of the air-fuel mixture in the combustion chamber is made more uniform, the flame propagation during combustion is partially delayed, and the occurrence of knocking is further prevented.
JP 2002-115549 A

  By the way, in the above-described conventional technique, the squish flow generated in the left and right portions of the front portion of the squish area tends to simply flow backward. For this reason, the mixture of the air-fuel mixture in the combustion chamber becomes insufficient, and it may not be possible to make the concentration and temperature of the air-fuel mixture more uniform. Therefore, at the time of combustion of the air-fuel mixture in the subsequent explosion stroke, there is a risk that a flame propagation may be delayed in a part of this air-fuel mixture. That is, there is room for improvement in the conventional technique in order to prevent the occurrence of knocking.

  The present invention has been made paying attention to the above-described circumstances, and the object of the present invention is to delay the flame propagation in each part of the air-fuel mixture during combustion of the air-fuel mixture in the combustion chamber during the explosion stroke of the engine. Is to prevent the occurrence of knocking more reliably.

In the first aspect of the present invention, when the axial center 3 of the cylinder 2 is vertically oriented and the cylinder 2 is viewed in plan (FIGS. 1, 2, and 8), when one horizontal direction is the front (Fr), the atmosphere side The intake passage 12 is formed in the cylinder head 6 so that the downstream end of the intake passage 12 communicating with the combustion chamber 11 of the cylinder 2 is located on the rear side of the combustion chamber 11, and the downstream end of the intake passage 12 is The exhaust passage 13 is formed to have a plurality of intake openings 20-22 in the direction, and the upstream end of the exhaust passage 13 that communicates the combustion chamber 11 with the atmosphere side is located on the front side of the combustion chamber 11. Is formed in the cylinder head 6, and the upstream end of the exhaust passage 13 is formed into a plurality of exhaust openings 28 in the left-right direction, and the upper surface of the outer edge portion of the piston 8 at the top dead center and the lower surface of the cylinder head 6. Between These on, Oite the four-stroke engine gap dimension between the lower surface to form a small squish area 62,
The upper end of the piston 8 is the axis of the cylinder 2 in a side view (FIG. 3) in appearance of the piston 8 by a line of sight along a direction orthogonal to the axis 3 of the cylinder 2 and the one direction (Fr). The first gap dimension T1 at the rear end 62a of the squish area 62 is set to be linearly orthogonal to the center 3, and is larger than the second gap dimension T2 at the front end 62b of the squish area 62. the third gap dimension T3 of the first in the longitudinal direction of the intermediate portion 62c of the one in which was Itasa case to one of the gap size of the second clearance dimension T1, T2.

The invention of claim 2 is a plan view (FIGS. 1, 2 and 8) of the cylinder 2 in which the axial center 3 of the cylinder 2 is vertical, and when one horizontal direction is the front (Fr), the atmosphere side The intake passage 12 is formed in the cylinder head 6 so that the downstream end of the intake passage 12 communicating with the combustion chamber 11 of the cylinder 2 is located on the rear side of the combustion chamber 11, and the downstream end of the intake passage 12 is The exhaust passage 13 is formed to have a plurality of intake openings 20-22 in the direction, and the upstream end of the exhaust passage 13 that communicates the combustion chamber 11 with the atmosphere side is located on the front side of the combustion chamber 11. Is formed in the cylinder head 6, and the upstream end of the exhaust passage 13 is formed into a plurality of exhaust openings 28 in the left-right direction, and the upper surface of the outer edge portion of the piston 8 at the top dead center and the lower surface of the cylinder head 6. Between These on, Oite the four-stroke engine gap dimension between the lower surface to form a small squish area 62,
The upper end of the piston 8 is the axis of the cylinder 2 in a side view (FIG. 3) in appearance of the piston 8 by a line of sight along a direction orthogonal to the axis 3 of the cylinder 2 and the one direction (Fr). The first gap dimension T1 at the rear end 62a of the squish area 62 is set to be linearly orthogonal to the center 3, and is larger than the second gap dimension T2 at the front end 62b of the squish area 62. The third gap dimension T3 in the front-rear direction midway portion 62c is smaller than the first gap dimension T1 and larger than the second gap dimension T2.

  In the invention of claim 3, in addition to the invention of claim 1 or 2, the clearance dimension T1-T3 of the squish area 62 becomes larger toward the axis 3 of the cylinder 2 in the radial direction of the cylinder 2. It is what I did.

In the invention of claim 4, in particular, as illustrated in FIG. 8, in a plan view (FIG. 8) of the cylinder 2 in which the axial center 3 of the cylinder 2 is vertically oriented, a certain horizontal direction is forward (Fr). The intake passage 12 is formed in the cylinder head 6 so that the downstream end of the intake passage 12 that communicates the atmosphere side with the combustion chamber 11 of the cylinder 2 is located on the rear side of the combustion chamber 11, and the intake passage 12 is formed so as to be a plurality of intake openings 20-22 in the left-right direction, while the upstream end of the exhaust passage 13 for communicating the combustion chamber 11 to the atmosphere side is located on the front side of the combustion chamber 11 The exhaust passage 13 is formed in the cylinder head 6 so that the upstream end of the exhaust passage 13 forms a plurality of exhaust openings 28 in the left-right direction, and the upper surface of the outer edge portion of the piston 8 at the top dead center Above cylinder head Between the lower surface 6, on these, to form a squish area 62 gap dimension is small between the lower surface, the intake passage 12 so as to extend toward the combustion chamber 11 from the rear area of the cylinder 2, the cylinder When an imaginary line 53 extending in the front-rear direction through the second axis 3 is set, the intake passage 12 is further away from the imaginary line 53 toward one side of the imaginary line 53 as it goes rearward. In the four-cycle engine
The upper end of the piston 8 is the axis of the cylinder 2 in a side view (FIG. 3) in appearance of the piston 8 by a line of sight along a direction orthogonal to the axis 3 of the cylinder 2 and the one direction (Fr). The first gap dimension T1 at the rear end 62a of the squish area 62 is set to be linearly orthogonal to the center 3, and is larger than the second gap dimension T2 at the front end 62b of the squish area 62. it is obtained by mutually different third gap dimension T3 of the right and left in the front-rear direction of the intermediate portion 62c of.

According to a fifth aspect of the invention, in addition to any one of the first to fourth aspects of the invention, the intake passage 12 includes a single main passage 16 forming an upstream side thereof, and a downstream side of the intake passage 12. And the first to third branch passages 17-19 branched from the downstream end of the main passage 16 toward the combustion chamber 11, and the first passage opening toward the combustion chamber 11 is provided. -In a four-cycle engine provided with first to third intake valves 23-25 that can open and close the first to third intake openings 20-22 of the third branch passages 17-19,
Among the first to third branch passages 17-19, the start timing of the opening operation of the intake valve corresponding to the branch passage having a longer length is made earlier than that of the other intake valves.

  In this section, the reference numerals appended to the above terms are not to be construed as limiting the technical scope of the present invention to the section “Example” described later or the contents of the drawings.

  The effects of the present invention are as follows.

According to the first aspect of the present invention, the downstream end of the intake passage that communicates the atmosphere side with the combustion chamber of the cylinder when a certain horizontal direction is the front in a plan view of the cylinder with the cylinder axis in the vertical direction. The intake passage is formed in the cylinder head so as to be positioned on the rear side of the combustion chamber, and the downstream end of the intake passage is formed with a plurality of intake openings in the left-right direction, while the combustion chamber is disposed on the atmosphere side. The exhaust passage is formed in the cylinder head so that the upstream end of the exhaust passage to be communicated is located on the front side of the combustion chamber, and the upstream end of the exhaust passage is formed with a plurality of exhaust openings in the left-right direction. , between the upper and lower surfaces of the cylinder head of the outer edge portion of the piston at the top dead center, these on, Oite the four-stroke engine gap dimension between the lower surface to form a small squish area,
The squish is made so that the upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston by a line of sight along a direction orthogonal to the axis of the cylinder and the one direction. The first gap size at the rear end portion of the area is made larger than the second gap size at the front end portion of the squish area, and the third gap size at the midway portion in the front-rear direction of the squish area is set as the first and second gap sizes. It is caused Itasa case to one of the gap dimension of.

  For this reason, in the compression stroke of the engine, when the piston reaches top dead center, it is generated at the front end of the squish area and rearward than the squish flow generated at the rear end of the squish area and flowing forward. The squish flow that flows in the direction is stronger. As a result, the high-temperature air-fuel mixture on the front side of the combustion chamber is supplied to the low-temperature air-fuel mixture on the rear side of the combustion chamber and mixed with the air-fuel mixture. As a result, the temperature of the air-fuel mixture in the combustion chamber is made more uniform, and it is prevented that the flame propagation during the combustion of the air-fuel mixture in the subsequent explosion stroke is partially delayed, and the occurrence of knocking is further prevented. The

Moreover, as described above, and a third gap dimension at the intermediate portion in the front-rear direction of the squish area was Itasa case to one of the gap dimension of the first, second gap dimension.

  For this reason, when the piston reaches top dead center, each squish flow generated at each midway portion of the squish area is substantially orthogonal to the squish flow generated at the rear end portion and the front end portion of the squish area. And flow so as to face each other. Therefore, each squish flow generated in each part of the squish area is sufficiently mixed with each other. As a result, the concentration and temperature of the air-fuel mixture are made more uniform, and knocking can be prevented more reliably.

According to the second aspect of the present invention, the downstream end of the intake passage that communicates the atmosphere side with the combustion chamber of the cylinder when a certain one horizontal direction is the front in a plan view of the cylinder in which the axial center of the cylinder is vertical. The intake passage is formed in the cylinder head so as to be positioned on the rear side of the combustion chamber, and the downstream end of the intake passage is formed with a plurality of intake openings in the left-right direction, while the combustion chamber is disposed on the atmosphere side. The exhaust passage is formed in the cylinder head so that the upstream end of the exhaust passage to be communicated is located on the front side of the combustion chamber, and the upstream end of the exhaust passage is formed with a plurality of exhaust openings in the left-right direction. , between the upper and lower surfaces of the cylinder head of the outer edge portion of the piston at the top dead center, these on, Oite the four-stroke engine gap dimension between the lower surface to form a small squish area,
The squish is made so that the upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston by a line of sight along a direction orthogonal to the axis of the cylinder and the one direction. The first gap size at the rear end portion of the area is made larger than the second gap size at the front end portion of the squish area, and the third gap size at the midway portion in the front-rear direction of the squish area is smaller than the first gap size. It is larger than the second gap dimension.

  For this reason, the same effect as the first aspect is produced.

  According to a third aspect of the present invention, the gap size of the squish area is increased in the radial direction of the cylinder toward the axial center of the cylinder.

  For this reason, the squish flow generated in each part of the squish area tends to be directed toward the axial center of the cylinder, and is opposed to each other, so that the air-fuel mixture is more reliably mixed. Therefore, the occurrence of knocking is further reliably prevented.

The fourth aspect of the present invention is that the downstream end of the intake passage that communicates the atmosphere side with the combustion chamber of the cylinder when a certain one horizontal direction is the front in a plan view of the cylinder in which the axial center of the cylinder is vertically oriented. The intake passage is formed in the cylinder head so as to be positioned on the rear side of the combustion chamber, and the downstream end of the intake passage is formed with a plurality of intake openings in the left-right direction, while the combustion chamber is disposed on the atmosphere side. The exhaust passage is formed in the cylinder head so that the upstream end of the exhaust passage to be communicated is located on the front side of the combustion chamber, and the upstream end of the exhaust passage is formed with a plurality of exhaust openings in the left-right direction. , corresponding to the lower surface and the cylinder head of the outer edge portion of the piston at the top dead center, on these, the gap size to form a small squish area between the lower surface, the intake passage rearward region of the cylinder Extending toward the combustion chamber and setting a virtual line extending in the front-rear direction through the axis of the cylinder, the intake passage is directed toward one side of the virtual line toward the rear, In a 4-cycle engine that is farther away from this imaginary line,
The squish is made so that the upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston by a line of sight along a direction orthogonal to the axis of the cylinder and the one direction. a first gap dimension at the rear portion of the area is larger than the second gap dimension at the front end portion of the squish area, and are differentiated from each other a third gap dimension of the left and right in the middle portion of the longitudinal direction of the squish area.

  Here, as described above, in the case where the intake passage is separated toward one side of the imaginary line, out of the intake air that is sucked into the combustion chamber through the intake passage, The flow rate of the intake air flowing through the intake opening tends to be different from that flowing through the other side intake opening. The air-fuel mixture tends to be low in temperature at the side of the combustion chamber on the side where the intake air flow rate is large.

  Therefore, in the above case, the left and right third gap sizes may be made different from each other as described above so that more squish flow flows toward the side of the combustion chamber where the air-fuel mixture tends to be low in temperature. In this way, a higher temperature air-fuel mixture is mixed with the air-fuel mixture that tends to be low. Thereby, the temperature of the air-fuel mixture in the combustion chamber is made more uniform, and the occurrence of knocking is more reliably prevented.

According to a fifth aspect of the present invention, the intake passage forms a single main passage that forms the upstream side of the intake passage, and a downstream side of the intake passage, and branches from the downstream end of the main passage toward the combustion chamber. First to third intake passages each having three first to third branch passages, each opening and closing the first to third intake openings of the first to third branch passages opening toward the combustion chamber. In a 4-cycle engine with a valve,
Among the first to third branch passages, the start timing of the opening operation of the intake valve corresponding to the branch passage having a longer length is made earlier than that of the other intake valves.

  Here, the pressure loss of the intake air flowing through the branch passage having a longer length tends to be larger. For this reason, the intake timing of the intake air into the combustion chamber tends to be delayed compared to the intake air flowing through the other branch passages. Therefore, the start timing of the valve opening operation of the intake valve corresponding to the branch passage having a longer length as described above is made earlier. The combustion chamber can be sucked into the combustion chamber without much delay with respect to the other intake air flowing through the other branch passages.

  Therefore, each intake air flowing through each branch passage can be sucked into the combustion chamber almost simultaneously. As a result, compared to the case where there is a difference in the intake timing of each intake air into the combustion chamber, a so-called “strong tumble flow” air-fuel mixture in which the flow direction is clearer and the flow velocity is faster is burned. “Effect” that it can be obtained in the chamber and overall high filling efficiency can be obtained.

  That is, according to the above-described invention, a mixture of “strong tumble flow” can be obtained in the intake stroke of the engine, and a mixture having a more uniform concentration and temperature can be obtained in the subsequent compression stroke. This is extremely beneficial for engine performance.

  Regarding the four-cycle engine of the present invention, in the explosion stroke of the engine, at the time of combustion of the air-fuel mixture in the combustion chamber, the occurrence of knocking can be prevented more reliably by preventing delay in flame propagation in each part of the air-fuel mixture. In order to realize the purpose of doing so, the best mode for carrying out the present invention is as follows.

  That is, in the plan view of this cylinder with the cylinder axis in the vertical direction, when the one horizontal direction is the front, the downstream end of the intake passage that communicates the atmosphere side with the combustion chamber of the cylinder is the rear portion of the combustion chamber. The intake passage is formed in the cylinder head so as to be located on the side. The downstream end of the intake passage is formed to be a plurality of intake openings in the left-right direction. On the other hand, the exhaust passage is formed in the cylinder head so that the upstream end of the exhaust passage that communicates the combustion chamber to the atmosphere side is located on the front side of the combustion chamber. The upstream end of the exhaust passage is formed to have a plurality of exhaust openings in the left-right direction. Between the upper surface of the outer edge of the piston at the top dead center and the lower surface of the cylinder head, a squish area having a small gap between the upper and lower surfaces is formed.

The upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston as viewed along a direction perpendicular to the axis of the cylinder and the one direction. The first gap size at the rear end of the squish area is larger than the second gap size at the front end of the squish area. The third gap dimension in the longitudinal direction of the intermediate portion of the squish area is allowed Itasa case to one of the gap dimension of the first, second gap dimension.

  In order to describe the present invention in more detail, the first embodiment will be described with reference to the attached FIGS. 1-7.

  In FIG. 1-5, reference numeral 1 denotes a four-cycle single cylinder engine used in a vehicle such as a motorcycle. For convenience of explanation, the direction of the arrow Fr will be described below as the front.

  The engine 1 includes a cylinder 2 that protrudes upward from a crankcase that supports a crankshaft (not shown). The cylinder 2 projects upward from the crankcase and has a cylinder body 5 in which a cylinder hole 4 having a longitudinal axis 3 is formed, and an upper end opening of the cylinder hole 4 attached to the upper end surface of the cylinder body 5. A cylinder head 6 that closes the cylinder head 6, a cylinder head cover 7 that is attached to the cylinder head 6 so as to close the upper surface of the cylinder head 6, and a cylinder hole 4 that is slidably fitted in the axial direction and is connected to a cylinder head (not shown). A piston 8 is provided that is linked to the crankshaft by a rod. The axis 3 of the cylinder hole 4 corresponds to the axis of the cylinder 2.

  A space surrounded by the upper portion of the cylinder body 5, the cylinder head 6, and the piston 8 located in the vicinity of the top dead center is defined as a combustion chamber 11. The lower surface of the cylinder head 6 corresponding to the combustion chamber 11 has a truncated conical shape and is a so-called pent roof. An intake passage 12 is formed in the rear portion of the cylinder head 6 to communicate the atmosphere side with the combustion chamber 11. The intake passage 12 extends from the rear upper area of the cylinder 2 toward the combustion chamber 11. In addition, an exhaust passage 13 is formed in the front portion of the cylinder head 6 to connect the combustion chamber 11 to the atmosphere side. The exhaust passage 13 extends from the combustion chamber 11 toward the front upper area of the cylinder 2.

  The intake passage 12 is divided into a main passage 16 that forms the upstream side of the intake passage 12 and a downstream side of the intake passage 12 that branches from the downstream end of the main passage 16 toward the rear portion of the combustion chamber 11. Three first to third branch passages 17-19 are provided. The downstream ends of the first to third branch passages 17-19 are first to third intake openings 20-22 that open toward the rear part of the combustion chamber 11, and the first to third intake openings 20-. 22 are juxtaposed in the left-right direction. There are provided first to third intake valves 23-25 for closing the first to third intake openings 20-22 from the combustion chamber 11 side so as to be opened and closed. In addition, a spring 26 is provided to urge the intake valves 23-25 to perform a closing operation.

  The exhaust passage 13 includes a pair of left and right branch passages 27 that form the upstream side of the exhaust passage 13 and extend forward from the front portion of the combustion chamber 11. The upstream end of each branch passage 27 is a pair of left and right exhaust openings 28 that open toward the front of the combustion chamber 11. Two exhaust valves 29 are provided to close the exhaust openings 28 from the combustion chamber 11 side so as to be opened and closed. Further, a spring 30 is provided to urge the exhaust valves 29 so as to close them.

  A valve operating device 33 is provided for opening and closing the intake valves 23-25 and the exhaust valves 29 as appropriate. The valve gear 33 includes an intake cam shaft 35 and an exhaust cam shaft 36 provided in a cam chamber 34 formed between the cylinder head 6 and the cylinder head cover 7. The intake cam shaft 35 and the exhaust cam shaft 36 are supported by the cylinder head 6 so as to be rotatable around axial centers 38 and 39 extending in the left and right directions, respectively. The intake camshaft 35 and the exhaust camshaft 36 are linked to the crankshaft by a chain winding device 40 having a timing chain.

  The intake camshaft 35 is rotatable integrally with the shaft main body 42 around the shaft center 38, and protrudes integrally with the shaft main body 42. The intake camshaft 35 is connected to the first to third intake valves 23-25 via a lifter 43, respectively. Three first to third cam noses 44 to 46 that engage with the cam are provided. On the other hand, the exhaust camshaft 36 is also cam-engaged with the exhaust valves 29 via lifters 47, respectively.

  A carburetor 48 as a fuel supply device is provided on the upstream end side of the intake passage 12. A spark plug 49 is attached to the cylinder head 6 substantially on the axis 3 of the cylinder 2. The discharge portion 50 of the spark plug 49 is disposed in the vicinity of the shaft center 3 and at the upper end portion of the combustion chamber 11.

  The engine 1 will be described more specifically.

  In a plan view of the cylinder 2 (FIG. 1), the first to third intake openings 20-22 are formed on the rear side of the combustion chamber 11, and the exhaust openings 28 are on the front side of the combustion chamber 11. Is formed. The first intake opening 20 is formed on one side R of an imaginary line 53 extending in the front-rear direction through the axis 3 of the cylinder 2. On the other hand, the third intake opening 22 is formed on the other side L of the virtual line 53. Further, the first intake opening 20 and the third intake opening 22 are located at substantially the same position in the front-rear direction, and are behind the first and third intake openings 20 and 22 and on the virtual line 53. The second intake opening 21, the main passage 16, and the second branch passage 18 are formed. The first and third branch passages 17 and 19 are inclined so as to approach the virtual line 53 toward the downstream end of the main passage 16 toward the rear.

  In FIG. 1-4, the upper surface 60 of the piston 8 is a flat surface that is almost entirely orthogonal to the axis 3 of the cylinder 2. Between the upper surface 60 of the outer edge portion of the piston 8 at the top dead center and the lower surface 61 of the cylinder head 6, a squish area 62 having a small clearance T1-T3 between the upper and lower surfaces 60, 61 is formed. Yes. In each part of the squish area 62, the upper and lower surfaces 60, 61 extend substantially parallel to each other. Further, each gap size of the squish area 62 is about 0.3 mm-0.9 mm.

The first gap dimension T1 at the rear end portion 62a of the squish area 62 is larger than the second gap dimension T2 at the front end portion 62b of the squish area 62. Further, each of the third gap dimension T3 in the front-rear direction of the right and left intermediate portions 62c of the squish area 62 is substantially the same as each other, and the first, if either one of the second gap dimension T1, T2致It has been made. The third gap dimension T3 may be smaller than the first gap dimension T1 and larger than the second gap dimension T2.

  In FIG. 2, on the upper surface of the piston 8 closer to the axial center 3 of the cylinder 2 than the squish area 62, the piston 8 reaches top dead center, and the intake valve 23-25 and the exhaust valve 29 are respectively When the valve is opened, a fitting hole 65 is formed in which the lower ends of the valves 23-25 and 29 are detachably fitted. This prevents the upper surface of the piston 8 reaching the top dead center from interfering with the opened valves 23-25 and 29, and further reduces the minimum volume of the combustion chamber 11. Thus, the compression ratio of the air-fuel mixture 55 is improved.

  1-6, during operation of the engine 1, the valve gear 33 is interlocked with the crankshaft. The intake cam shaft 35 and the exhaust cam shaft 36 of the valve gear 33 are cam-engaged with the intake valves 23-25 and the exhaust valves 29, so that the intake valves 23-25 and the exhaust valves 23-25 are exhausted. The valve 29 is appropriately opened and closed.

  In particular, in FIG. 6, TDC indicates the top dead center of the piston 8, IN indicates the valve operation of the intake valve 23-25, and EX indicates the valve operation of the exhaust valve 29. According to FIG. 6, as the crank angle (time) progresses, the lift amounts of the intake and exhaust valves 23-25 and 29 are increased and opened, and the lift amount is decreased to close the valve. It is made to work.

  In the intake stroke of the engine 1, the air on the atmosphere side and the fuel supplied by the carburetor 48 are drawn into the combustion chamber 11 through the intake passage 12 by opening the intake valves 23-25. . In the explosion stroke after the compression stroke following the intake stroke, the air-fuel mixture 55 generated by the air and fuel sucked as described above is used for combustion in the combustion chamber 11. The combustion gas resulting from this combustion passes through the exhaust passage 13 and is discharged to the atmosphere as exhaust 56 in the exhaust stroke. In the above case, the intake passage 12 is formed so that the air-fuel mixture 55 becomes a tumble flow by the inertial force of the air-fuel mixture 55 due to air or fuel sucked into the combustion chamber 11 through the intake passage 12.

  Among the first to third branch passages 17-19, the start timing of the opening operation of the intake valve corresponding to the branch passage having a longer length is made earlier than that of the other intake valves. Specifically, the period during which each of the intake valves 23-25 is open (about 300 °) and the lift amount are the same, but the first and third intake valves 23, 25 are opened. The valve operation (solid line in FIG. 6) is advanced by a short period (5-10 °) overall from the valve opening operation of the second intake valve 24 (two-dot chain line in FIG. 6).

  As described above, the start timing of the valve opening operation of each intake valve 23-25 is made earlier or later is caused by the first to third cam noses 44-46 in the circumferential direction of the intake cam shaft 35. It is obtained by properly setting the relative position.

  According to the above configuration, the start timing of the opening operation of the intake valve corresponding to the branch passage having a longer length among the first to third branch passages 17-19 is made earlier than that of the other intake valves. ing.

  Here, the pressure loss of the intake air 57 flowing in the branch passage having a longer length tends to be larger. For this reason, the intake timing of the intake air 57 into the combustion chamber 11 tends to be delayed as compared to the intake air 57 flowing in the other branch passages. Therefore, the start timing of the opening operation of the intake valve corresponding to the branch passage having a longer length as described above is advanced, and for this reason, the intake air 57 flowing in the branch passage having the longer length is used. Can be sucked into the combustion chamber 11 without much delay with respect to the other intake air 57 flowing in the other branch passages.

  Therefore, the intake air 57 flowing through the branch passages can be sucked into the combustion chamber 11 almost simultaneously. As a result, the so-called “strong tumble flow” mixture in which the flow direction is clearer and the flow velocity is faster than in the case where the intake timing of the intake air 57 into the combustion chamber 11 is different. 55 can be obtained in the combustion chamber 11, so that an overall high charging efficiency can be obtained, that is, an “effect” that the fuel consumption of the engine 1 can be further improved is produced.

  More specifically, as described above, the second intake opening 21 and the main passage 16 are formed behind the first and third intake openings 20 and 22. Therefore, the first and third branch passages 17 and 19 corresponding to the first and third intake openings 20 and 22 tend to be longer than the second branch passage 18 corresponding to the second intake opening 21. Thus, the pressure loss of the intake air 57 flowing through the first and third branch passages 17 and 19 tends to be larger.

  Therefore, as described above, the start timing of the opening operation of the first and third intake valves 23 and 25 for opening and closing the first and third intake openings 20 and 22 is earlier than that of the second intake valve 24. is doing. Therefore, as described above, even if the pressure loss of the intake air 57 flowing through the first and third branch passages 17 and 19 is larger, the intake air 57 is caused to flow to the intake air 57 flowing through the second branch passage 18. It can be sucked into the combustion chamber 11 without much delay. Therefore, in the specific configuration described above, the same effect as the “effect” is produced.

  Note that the start timings of the opening operations of the first intake valve 23 and the third intake valve 25 may be substantially the same, or any of them may be slightly earlier.

Further, as described above, the first gap dimension T1 at the rear end 62a of the squish area 62 is made larger than the second gap dimension T2 at the front end 62b of the squish area 62, so 3 the first clearance dimension T3 in section 62c, is caused Itasa case to one of the gap size of the second clearance dimension T1, T2.

  For this reason, in the compression stroke of the engine 1, when the piston 8 reaches top dead center, the front end of the squish area 62 is generated rather than the squish flow S generated at the rear end 62a of the squish area 62 and flowing forward. The squish flow S generated in the part 62b and flowing backward is stronger. As a result, the high-temperature mixture 55 on the front side of the combustion chamber 11 is supplied to the low-temperature mixture 55 on the rear side of the combustion chamber 11 and mixed with the mixture 55. Thereby, the temperature of the air-fuel mixture 55 in the combustion chamber 11 is made more uniform, and it is prevented that the flame propagation during the combustion of the air-fuel mixture 55 in the subsequent explosion stroke is partially delayed, and the occurrence of knocking is prevented. More prevented.

Moreover, as described above, and a third gap dimension T3 in the front-rear direction of the intermediate portion 62c of the squish area 62 of the first, was Itasa case to one of the gap size of the second clearance dimension T1, T2.

  For this reason, when the piston 8 reaches top dead center, each squish flow S generated in each midway portion 62c of the squish area 62 is generated by the rear end portion 62a and the front end portion 62b of the squish area 62. The squish flow S flows so as to be substantially orthogonal to and opposed to each other. Therefore, each squish flow S generated in each part 62a-62c of the squish area 62 is sufficiently mixed with each other. As a result, the concentration and temperature of the air-fuel mixture 55 are made more uniform, and knocking can be prevented more reliably.

  FIG. 7 shows the experimental results for the engine 1. That is, when the result of the engine 1 (solid line in the figure) is compared with the result of the conventional five-valve engine (dashed line in the figure), the output is approximately at each throttle opening (%) of the carburetor 48. It can be seen that (kw) is improved.

  4, the gap dimension T1-T3 of the squish area 62 may be increased in the radial direction of the cylinder 2 toward the axial center 3 of the cylinder 2.

  In this way, the squish flow S generated in each part of the squish area 62 tends to be directed toward the axial center 3 of the cylinder 2 and is opposed to each other, so that the mixture 55 is more reliably mixed. Done. Therefore, the occurrence of knocking is further reliably prevented.

  That is, according to the above-described configuration, it is possible to obtain the “strong tumble flow” air-fuel mixture 55 in the intake stroke of the engine 1 and to obtain the air-fuel mixture 55 having a more uniform concentration and temperature in the subsequent compression stroke. This is extremely beneficial in terms of engine performance.

  Although the above is based on the illustrated example, the left and right intake openings may be only a pair of left and right, and the engine 1 may be four valves. The fuel supply device may be a fuel injection valve.

  FIG. 8 below shows the second embodiment. The second embodiment is common in many respects to the configuration and operational effects of the first embodiment. Therefore, regarding these common items, common reference numerals are attached to the drawings, and redundant description thereof is omitted, and different points are mainly described. In addition, the configuration of each part in these embodiments may be variously combined in light of the object and operational effects of the present invention.

  In order to describe the present invention in more detail, the second embodiment will be described with reference to FIG.

  In FIG. 8, the main passage 16 is bent so as to be farther away from the virtual line 53 toward the other side L that is one side of the virtual line 53 as it goes rearward. The start timing of the opening operation of the first intake valve 23 is made earlier than that of the third intake valve 25.

  Here, as described above, the main passage 16 is further away from the virtual line 53 toward the other side L of the virtual line 53 as it goes rearward. For this reason, the first branch passage 17 corresponding to the first intake opening 20 tends to be longer than the third branch passage 19 corresponding to the third intake opening 22. The pressure loss of the intake air 57 flowing through the passage 17 tends to be larger.

  Therefore, as described above, the start timing of the opening operation of the first intake valve 23 that opens and closes the first intake opening 20 is made earlier than that of the third intake valve 25. Therefore, as described above, even if the pressure loss of the intake air 57 flowing through the first branch passage 17 is larger, the intake air 57 is not greatly delayed from the intake air 57 flowing through the third branch passage 19. The combustion chamber 11 can be inhaled. Therefore, in the specific configuration described above, the same effect as the “effect” is produced.

  The start timings of the valve opening operations of the second intake valve 24 and the third intake valve 25 may be substantially the same, but in the illustrated example, the third branch passage 19 is more than the second branch passage 18. Therefore, it is preferable that the start timing of the opening operation of the third intake valve 25 is slightly earlier than that of the second intake valve 24.

  The left and right third gap dimensions T3 corresponding to the upper surfaces 60 of the left and right outer edge portions of the piston 8 are different from each other.

  Here, as described above, when the intake passage 12 is separated toward one side (the other side L) of the imaginary line 53, the intake passage 12 is sucked into the combustion chamber 11 through the intake passage 12. Of the air-fuel mixture 55 (intake air 57), the flow rate of the air-fuel mixture 55 (intake air 57) flowing through the first intake opening 20 on one side R and the flow rate of the third air intake opening 22 on the other side L are: Tend to be different from each other. The air-fuel mixture 55 tends to be low in temperature at the side of the combustion chamber 11 on the side where the flow rate of the air-fuel mixture 55 (intake air 57) is large.

  Therefore, in the above case, the left and right third gap dimensions T3 are made different from each other as described above so that more squish flow S flows toward the side of the combustion chamber 11 where the air-fuel mixture 55 tends to be low in temperature. Just do it. In this way, the higher temperature air-fuel mixture 55 is mixed with the air-fuel mixture 55 that tends to be low in temperature. Thereby, the temperature of the air-fuel mixture 55 in the combustion chamber 11 is made more uniform, and the occurrence of knocking is more reliably prevented.

1 is a partial plan view of an engine according to a first embodiment. FIG. 1 is a partial plan view of an engine including a piston according to a first embodiment. FIG. 1 is a partial side cross-sectional view of an engine, showing Embodiment 1. FIG. FIG. 4 is a partial enlarged cross-sectional partial cutaway view of FIG. 3 showing the first embodiment, and is a view when the piston reaches top dead center. 1 is a partial front sectional view of an engine according to a first embodiment. FIG. FIG. 5 is a graph illustrating the suction and exhaust valve opening and closing operations according to the first embodiment. It is a graph which shows Example 1 and shows an experimental result regarding the throttle opening of a carburetor, an engine speed, and an output. FIG. 2 shows a second embodiment and corresponds to FIG.

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder 3 Axis 4 Cylinder hole 5 Cylinder body 6 Cylinder head 8 Piston 11 Combustion chamber 12 Intake passage 13 Exhaust passage 16 Main passage 17 First branch passage 18 Second branch passage 19 Third branch passage 20 First intake opening 21 Second Intake Opening 22 Third Intake Opening 23 First Intake Valve 24 Second Intake Valve 25 Third Intake Valve 28 Exhaust Opening 33 Valve Operating Device 35 Intake Cam Shaft 38 Axis Center 42 Shaft Body 43 Lifter 44 First Cam Nose 45 First 2 cam nose 46 3rd cam nose 48 carburetor 49 spark plug 50 discharge part 53 virtual line 55 mixture 56 exhaust 57 intake 60 upper surface 61 lower surface 62 squish area 62a rear end 62b front end 62c midway R one side L other side T1 First gap size T2 Second gap size T3 Third gap size S Squish flow

Claims (5)

In a plan view of this cylinder with the cylinder axis in the vertical direction, when the one horizontal direction is the front, the downstream end of the intake passage that connects the atmosphere side to the combustion chamber of the cylinder is at the rear side of the combustion chamber. The intake passage is formed in the cylinder head so as to be positioned, and the downstream end of the intake passage is formed to be a plurality of intake openings in the left-right direction, while the upstream end of the exhaust passage communicating the combustion chamber to the atmosphere side The exhaust passage is formed in the cylinder head so as to be positioned on the front side of the combustion chamber, and the upstream end of the exhaust passage is formed with a plurality of exhaust openings in the left-right direction so that the piston at the top dead center between the upper surface and the lower surface of the cylinder head of the outer edge, these on, Oite the four-stroke engine gap dimension between the lower surface to form a small squish area,
The squish is made so that the upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston by a line of sight along a direction orthogonal to the axis of the cylinder and the one direction. The first gap size at the rear end portion of the area is made larger than the second gap size at the front end portion of the squish area, and the third gap size at the midway portion in the front-rear direction of the squish area is set as the first and second gap sizes. 4-cycle engine, characterized in that was Itasa case to one of the gap dimensions. In a plan view of this cylinder with the cylinder axis in the vertical direction, when the one horizontal direction is the front, the downstream end of the intake passage that connects the atmosphere side to the combustion chamber of the cylinder is at the rear side of the combustion chamber. The intake passage is formed in the cylinder head so as to be positioned, and the downstream end of the intake passage is formed to be a plurality of intake openings in the left-right direction, while the upstream end of the exhaust passage communicating the combustion chamber to the atmosphere side The exhaust passage is formed in the cylinder head so as to be positioned on the front side of the combustion chamber, and the upstream end of the exhaust passage is formed with a plurality of exhaust openings in the left-right direction so that the piston at the top dead center between the upper surface and the lower surface of the cylinder head of the outer edge, these on, Oite the four-stroke engine gap dimension between the lower surface to form a small squish area,
The squish is made so that the upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston by a line of sight along a direction orthogonal to the axis of the cylinder and the one direction. The first gap size at the rear end portion of the area is made larger than the second gap size at the front end portion of the squish area, and the third gap size at the midway portion in the front-rear direction of the squish area is smaller than the first gap size. A four-cycle engine characterized by being larger than the second gap dimension.   The four-stroke engine according to claim 1 or 2, wherein the gap size of the squish area is increased in the radial direction of the cylinder toward the axial center of the cylinder. In a plan view of this cylinder with the cylinder axis in the vertical direction, when the one horizontal direction is the front, the downstream end of the intake passage that connects the atmosphere side to the combustion chamber of the cylinder is at the rear side of the combustion chamber. The intake passage is formed in the cylinder head so as to be positioned, and the downstream end of the intake passage is formed to be a plurality of intake openings in the left-right direction, while the upstream end of the exhaust passage communicating the combustion chamber to the atmosphere side The exhaust passage is formed in the cylinder head so as to be positioned on the front side of the combustion chamber, and the upstream end of the exhaust passage is formed with a plurality of exhaust openings in the left-right direction so that the piston at the top dead center between the upper surface and the lower surface of the cylinder head of the outer edge portion, on these, the gap dimension between the lower surface forms a small squish area, the intake passage is directed to the combustion chamber from the rear area of the cylinder When the imaginary line extending in the front-rear direction through the axial center of the cylinder is set, the intake passage extends from the imaginary line toward one side of the imaginary line toward the rear. In a four-cycle engine that is greatly separated,
The squish is made so that the upper end of the piston is linearly orthogonal to the axis of the cylinder in a side view on the appearance of the piston by a line of sight along a direction orthogonal to the axis of the cylinder and the one direction. a first gap dimension at the rear portion of the area is larger than the second gap dimension at the front end portion of the squish area, that is different from each other a third gap dimension of the left and right in the longitudinal direction of the intermediate portion of the squish area 4-cycle engine shall be the feature. The intake passage forms one main passage that forms the upstream side of the intake passage, and three first to second branches that form the downstream side of the intake passage and branch from the downstream end of the main passage toward the combustion chamber. A four-cycle engine provided with first to third intake valves, each of which has a three-branch passage and is capable of opening and closing the first to third intake openings of the first to third branch passages that open toward the combustion chamber. In
2. The start timing of the opening operation of the intake valve corresponding to the branch passage having a longer length among the first to third branch passages is made earlier than that of the other intake valves. 4 cycle engine according to any one of 4 to 4.

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