JPH09324639A - Crankcase reed type two cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a sealing property of a reed valve without reducing a compression ratio, and to improve a trapping efficiency by reducing a passage resistance. SOLUTION: In the case where a reed valve installation seat surface 67 connected to a crank chamber is formed on a crankcase 2 to which an upstream cylinder block 7 is connected, the crankcase 2 is partitioned into a front case 3 to which a cylinder block 7 is connected and a rear case 4 along a shaft center of a crankshaft 5. Then, the installation seat surface 67 is formed on the rear case 4, and at the same time, a reed valve 66 is installed on the installation seat surface 67 astride the partition surface A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crankcase lead type two-cycle engine used in, for example, a motorcycle.

[0002]

2. Description of the Related Art As a crankcase reed valve type engine, there is a conventional engine described in Japanese Patent Application No. 1-263974. This engine is a front opening V type 2 cylinder 2
It is a cycle engine, and a crankcase is divided into a front case and a rear case by a dividing surface including an axis of a crankshaft, and an upper cylinder and a lower cylinder are formed on a front wall of the front case to have a V-shape when viewed in the crankshaft direction. It is configured to be connected. The lower cylinder reed valve mounting seat surface is bridged to the inside of the V bank of the front wall of the front case, and the upper cylinder reed valve mounting seat surface is crossed at a substantially right angle to the front and rear case split surfaces. It is a structure formed by.

[0003]

However, in the above-mentioned conventional engine, since the mounting seat surface is formed so as to straddle the front and rear cases, there is a problem that the sealing performance is low when the reed valve is mounted. is there.

In the above conventional structure, the mounting seat surface is
Since it is formed across the rear case, it has a structure in which the intake passage is bent backward for reasons such as securing a space for the carburetor, and the passage resistance is large. Since it is oriented in the direction, there is also a problem that the intake efficiency is low.

The present invention has been made in view of the above-mentioned conventional situation. The sealability of the reed valve can be ensured without lowering the compression ratio, the passage resistance can be reduced, and the intake direction can be located near the bottom dead center. It is an object of the present invention to provide a crankcase lead type two-cycle engine that can improve intake efficiency by directing it toward a piston.

[0006]

According to a first aspect of the present invention, there is provided a crankcase reed type 2 in which an intake port communicating with a crank chamber is formed in a crankcase, and a reed valve mounting seat surface is formed at an external opening of the intake port. In the cycle engine,
The crankcase is divided into a front case and a rear case in which a cylinder block is provided by a dividing surface including the axis of the crankshaft, the mounting seat surface is formed on the rear case, and the reed valve is formed on the mounting seat surface. Is attached, and the reed valve is extended to the crank chamber side beyond the dividing surface.

According to a second aspect of the present invention, in the first aspect, a balancer shaft is disposed in an upper portion of the rear case in parallel with the crankshaft, and the mounting seat surface is provided at a central portion in the axial direction of the balancer shaft of the rear case. Is formed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 5 are views for explaining a crankcase lead type two-cycle engine according to an embodiment of the present invention, and FIGS. 1 to 4 are a left side view, a plan view, and a rear view of the engine of the present embodiment, respectively. FIG. 5, right side view, and FIG. 5 are configuration diagrams showing an oil passage of a lubricating system. The front, rear, left, right, top, and bottom in the present embodiment are as shown in each drawing.

In the drawings, reference numeral 1 denotes a water-cooled V-type two-cylinder two-cycle engine, and the engine 1 is suspended and supported by a body frame of a motorcycle (not shown). A crankcase 2 of the engine 1 is divided into a front case 3 and a rear case 4 along an axis of a crankshaft 5, and the crankshaft 5 is a bearing by a mating surface A portion of the front and rear cases 3 and 4. It is supported via 6.

An upper cylinder block 7 is bolted and fixed to the upper portion of the front wall of the front case 3, and an upper cylinder head 8 is bolted and fixed to the upper surface of the cylinder block 7. A lower cylinder block 9 and a lower cylinder head 10 are laminated and fixed to a lower portion of the front case 3, and the upper and lower cylinder blocks 7,
The cylinder shaft 9 has a so-called V shape, which is V-shaped when viewed in the crankshaft direction.
The V banks are arranged so as to form 90 banks.
It is open toward the front of the vehicle.

Pistons 11, 11 are slidably inserted in the cylinder bores 7a, 9a of the cylinder blocks 7, 9 respectively, and each piston 11 is connected to a connecting rod 12a.
To the crankshaft 5. A plurality of scavenging ports 15 communicating with the crank chamber and the inside of the cylinder bores 7a, 9a are formed in the cylinder blocks 7, 9 at intervals in the circumferential direction.

Exhaust ports 16 and 16 are formed on the lower walls of the cylinder blocks 7 and 9, and exhaust pipes 17 and 17 are connected to the exhaust ports 16. A variable exhaust valve 18 is inserted into each of the exhaust ports 16. The variable exhaust valve 18 has a fully closed position where the valve portion 18a advances to retard the exhaust timing, and retreats to advance the exhaust timing. It is configured to move forward and backward between the fully open position to be angled. The exhaust variable valve 18 is controlled according to the operating state such as the engine speed. For example, the exhaust variable valve 18 is driven to the fully closed position in the low speed rotation range to delay the exhaust timing, and is fully opened in the high speed rotation range to accelerate the exhaust timing. To be done.

A balancer shaft 20 is arranged in parallel with the crankshaft 5 in the upper rear part of the crankshaft 5 of the rear case 4. A weight 20 is provided at the left end of the balancer shaft 20.
a, a balancer gear 20b integrated with a balancer weight is mounted at the right end thereof.
Ob meshes with a balancer drive gear 21 mounted on the right end of the crankshaft 5.

A cassette type speed change mechanism 25 is arranged at the rear portion of the rear case 4. The transmission mechanism 25 has a main shaft 27 having a transmission gear group 26 mounted on a lower rear portion of the crankshaft 5, and a counter gear group 28 meshing with the transmission gear group 26 mounted on an upper rear portion of the main shaft 27. Drive shafts 29 are arranged in parallel with the crankshaft 5, and the right ends of the main shaft 27 and the drive shaft 29 are supported by a cassette base 30 separate from the crankcase 2.
4a, and the other end is supported by a boss of the rear case 4 via a bearing 34b. The cassette base 30 is a boss (not shown) formed in the rear case 4. It is bolted and fixed detachably. The speed change mechanism 25 is configured to switch between the lowest speed stage and the highest speed stage by rotating the change shaft 31.

The left end of the drive shaft 29 is the rear case 4
The drive sprocket 32 is mounted on the protrusion, and the sprocket 32 is connected to the rear wheel sprocket via a chain (not shown).

Here, the drive shaft 29 is arranged so as to be located below the bisector B of the bank angle formed by the cylinder axes C of the upper and lower cylinder blocks 7 and 9 in a vehicle mounted state. . As a result, the height of the upper wall of the crankcase can be lowered and the position of the carburetor 70 can be lowered, as compared with the conventional drive shaft arranged on the bisector or above the bisector. Is obtained.

The right end of the main shaft 27 projects outward from the case cover 33, and a dry clutch 35 is mounted on the projecting portion. This clutch 35 has a large number of clutch plates 35 between an outer drum 35a connected to the crankshaft 5 via a crank gear 36 and a reduction gear 37, and an inner drum 35b connected to the main shaft 27.
c. A push rod 40 connected to the inner drum 35b is inserted into the axis of the main shaft 27 so as to be able to advance and retreat.
The cam portion 41a of the push lever 41 is engaged with the left end of the “0”. By rotating the push lever 41, the engine power is disconnected.

Below the main shaft 27 of the cassette base 30, the drive shaft 4 of the oil pump 42 constituting a lubricating system is provided.
2a is pivotally supported. Further, a rotation shaft 43a of a cooling water pump 43 constituting a cooling system is coaxially connected to the drive shaft 42a, and the cooling water pump 43 is disposed on the left side wall of the rear case 4.

A rotor 44 is connected to the inside of the cassette base 30 of the drive shaft 42a, and a driven gear 45 driven by the main shaft 27 is connected to the outside thereof.
A strainer housing 30a communicating with a suction port of the oil pump 42 is provided at a lower edge of the cassette base 30.
Are integrally formed, and a mesh 46 is bolted and fixed to the lower surface opening of the housing 30a.

The strainer housing 30a is formed so as to bulge toward the outside of the cassette base 30, and an oil sump portion 4c is formed in a portion of the rear case 4 located below the strainer housing 30a. As described above, in the present embodiment, since the strainer housing 30a is formed outside the cassette base 30, the oil reservoir 4c can be arranged on the right edge of the rear case 4, and the lower exhaust pipe 17 passing below the rear case 4 can be arranged. Can be avoided.

That is, the exhaust pipe 17 from the lower cylinder block 9 is arranged below the rear case in a rearwardly lowered state. Therefore, when the strainer housing is formed inside the cassette base as in the conventional case, the oil sump portion is positioned as shown by the chain double-dashed line in FIG.
In order to avoid the interference between the oil sump and the exhaust pipe 17, the exhaust pipe 17 must be arranged so as to pass further downward, which causes a problem that the minimum ground clearance cannot be secured.

When the strainer housing is formed inside the cassette base, the clutch, the case cover, and the cassette mission must be removed when the suction port is serviced and inspected. On the other hand, in the present embodiment, workability can be improved because it is only necessary to remove the clutch 35 and the case cover 33.

A first oil passage 50 communicating with the discharge port of the oil pump 42 is formed in the cassette base 30 in the front-rear direction (see FIG. 4). Case 4 after the above
The second oil passage 5 communicating with the downstream end of the first passage 50.
1 is formed in the crankshaft direction, and the downstream end of the second oil passage 51 extends close to the cooling water discharge passage 48 of the cooling water pump 43 (see FIG. 1).

The rear case 4 has a second oil passage 5
A third oil passage 52 extending upward from the downstream end of the first case 1 is formed. The third oil passage 52 is formed obliquely inward from the upper wall of the rear case 4 toward the front and inside.
The downstream end of the third oil passage 52 is connected to a passage (not shown) communicating with the axis of the main shaft 27 through the cam portion 41a of the push lever 41 from here. Lubricating oil is supplied from the second oil passage 51 to the drive shaft 29 through the oil passages 53 and 54. An oil pipe 55 is installed above the main shaft 27 in parallel therewith, and an oil passage 52 communicates with the oil pipe 55.

In the lubricating system of this engine, the oil sump portion 4c
The lubricating oil sucked up from the first to third oil passages 50 to 5
2 through the main shaft 27 to the transmission gear group 26, the drive shaft 29 to the counter gear group 28, and the oil pipe 55 to the gear groups 26 and 28 in an oil shower state.

In the present embodiment, since the third oil passage 52 is formed obliquely inward from the upper wall of the rear case 4, as shown in FIG. 5, it is below the second oil passage 51 and the third oil passage 52. It is possible to dispose the cooling water discharge passage 48 on the outside. As a result, the cooling water pump 43 can be disposed on the front side of the main shaft 27, the cassette base 30 can be reduced in size, the transmission mechanism can be made compact accordingly, and the engine as a whole can be reduced in size. This can improve the degree of freedom in layout when mounted on the vehicle body. In addition,
Conventionally, since the third oil passage was formed vertically in the vertical direction, a cooling water pump was arranged behind the main shaft to avoid interference with the oil passage, and the cassette base was large. There was a problem of becoming.

Next, the intake system of the engine 1 will be described. A lower intake passage 60 communicating with the crank chamber of the lower cylinder block 9 is provided at a front wall in the V bank of the front case 3.
The lower reed valve 61 is inserted and arranged in the intake passage 60. The reed valve 61 has a mounting seat surface 62 formed on the opening edge of the intake passage 60.
The mounting seat surface 62 is formed so as to be substantially parallel to the split surface A of the crankcase 2.

The reed valve 61 has a structure in which a vent hole 61b is formed in a slope portion of a valve body 61a having a triangular cross section, and the vent hole 61b is opened and closed by a valve plate 61c. The reed valve 61 automatically opens and introduces air into the crank chamber when the pressure in the crank chamber becomes negative due to the rise of the piston 11, and closes when the pressure becomes positive to prevent the air from returning when the piston descends. In addition, 61d is a stopper for regulating the opening of the valve plate 61c.

An upper intake passage 65 communicating with the crank chamber of the upper cylinder block 7 is formed in the upper wall 4a of the rear case 4, and an upper reed valve 66 having the same structure as that described above is formed in the intake passage 65. It is inserted and arranged so as to extend to the crank chamber side beyond the dividing surface A. An upper mounting seat surface 67 is formed at the opening edge of the intake passage 65, and the upper reed valve 6 is attached to the mounting seat surface 67.
The carburetor 70 and the cab joint 70a are bolted and fixed using the bolt holes 67a, and the carburetor 70 is bolted and fixed via the cab joint 70a. The mounting seat surface 67 is formed rearward so as to be substantially parallel to the division surface A, and is provided with the balancer shaft 20.
Is formed near the center in the axial direction (see FIG. 3) and forward of the balancer shaft 20.

Here, since the mounting seat surface 67 projects upward from the upper wall surface of the crankcase 2, the split surface A
In order to ensure the sealing performance of the front portion of the mounting seat surface 67 of the mounting surface 67, the front portion of the mounting seat surface 67 of the divided surface A is fastened and fixed by three bolts 67b and 67c. In this case, the upper one bolt 67b is screwed from the front case 3 side to the rear case 4 side, whereas the lower two bolts 67c are screwed from the rear case 4 side to the front case 3 side. Has been inserted. This facilitates bolting work in a narrow place.

According to the present embodiment, the mounting seat surface 67 is formed only by the upper wall 4a of the rear case 4, and the upper reed valve 66 is mounted on the mounting seat surface 67.
As compared with the case where the reed valve 66 is formed so as to straddle the front and rear cases, it is possible to secure the sealing property when the reed valve 66 is mounted.

Further, since the mounting seat surface 67 is constituted only by the upper wall 4a of the rear case 4, the seat surface 67 can be formed so as to be substantially parallel to the dividing surface A, and the intake passage can be made substantially linear. The angle θ between the axis D and the cylinder axis C can be made obtuse, which reduces passage resistance and allows the intake flow to be directed near the skirt of the piston 11 located near bottom dead center, thereby increasing intake efficiency. Can be improved.

By the way, in order to improve the intake efficiency, the intake passage resistance is reduced and the intake negative pressure source is
That is, it is effective to direct the axis D of the intake passage near the skirt portion of the piston located near the bottom dead center. In the present embodiment, since the mounting seat surface 67 is constituted only by the rear case 4 as described above, linearization of the intake passage and directing to the intake negative pressure generation source can be realized. Further, in the present embodiment, the drive shaft 29 is positioned below the bank bisector B, so that the upper wall 4a of the rear case 4 can be lowered and the position of the carburetor 70 can be lowered accordingly. This contributes to straightening the intake passage and directing the negative pressure source.

Further, since the reed valve 66 is inserted and arranged so as to extend to the crank chamber side beyond the dividing surface A, the length of the intake passage 65 communicating with the crank chamber can be shortened and the volume of the crank chamber can be made small. The compression ratio can be increased.

The mounting seat surface 67 is attached to the balancer shaft 20.
Since it is formed closer to the center in the axial direction, it is possible to avoid the intake passage and the carburetor from interfering with the weight 20a and the balancer gear 20b, and it is possible to bring the balancer shaft 20 close to the crankshaft 5 and also from these points. The passage 65 can be shortened and the compression ratio can be further improved.

That is, in the couple balancer having a larger balancer effect as the balancer weight interval is wider, the weight 2
0a and the balancer gear 20b are arranged far left and right, so that the weight 20a and the balancer 20b can be made small in diameter when the required balancer effect is the same, and therefore the balancer shaft 20 can be brought close to the crankshaft 5. It was made.

Incidentally, in the prior art, in order to avoid the interference of the balancer shaft with the balancer weight, it is necessary to dispose the carburetor, and thus the mounting seat surface, away from the balancer shaft in the direction perpendicular to the axis, and to balance the shaft with the crankshaft. There was a problem that the intake passage became long after all.

Further, in this embodiment, the carburetor 70 can be connected to the intake passage 65 so that the intake passage axis D is substantially straight, the passage resistance can be reduced, and the air flow can be directed to the negative pressure generating source. Yes, the intake efficiency can be improved.

In the above embodiment, the case where the invention is applied to the V-type 2-cylinder 2-cycle engine has been described. However, the present invention is not limited to this, and can be applied to single-cylinder and parallel multi-cylinder engines.

[0040]

As described above, according to the crankcase reed type two-cycle engine according to the invention of claim 1, the crankcase is divided into a front case and a rear case, and the reed valve mounting seat surface is provided in the rear case. Since the reed valve is formed on the mounting seat surface so as to extend to the crank chamber side beyond the split surface, the reed valve can be sealed and the intake passage can be shortened to improve the compression ratio. There is an effect, and there is an effect that the passage resistance is reduced and the intake efficiency can be improved by directing the intake flow toward the negative pressure generation source.

According to the second aspect of the present invention, the mounting seat surface is formed at the axial center of the balancer shaft of the rear case. Therefore, even when the balancer shaft is arranged in the upper part of the rear case, the mounting seat surface is It can be arranged in front of the balancer shaft and close to the crankshaft without interfering with the balancer, the weight, and the balancer gear, and the intake passage length can be shortened, the crank chamber volume can be reduced, and its compression ratio can be improved.

[Brief description of drawings]

FIG. 1 is a left side view for explaining a crankcase reed two-cycle engine according to an embodiment of the present invention.

FIG. 2 is a plan view of the engine.

FIG. 3 is a rear view of the engine.

FIG. 4 is a right side view of the engine.

FIG. 5 is a configuration diagram showing an oil passage of the engine.

[Explanation of symbols]

1 Crankcase reed 2-cycle engine 2 Crankcase 3 Front case 4 Rear case 5 Crankshaft 7 Upper cylinder block 66 Upper reed valve 67 Upper mounting seat A Split surface

Claims (2)

[Claims] 1. A crankcase reed two-cycle engine in which an intake port communicating with a crank chamber is formed in a crankcase, and a reed valve mounting seat surface is formed in an external opening of the intake port, wherein the crankcase is connected to a crankshaft. A front surface and a rear surface, each of which is provided with a cylinder block, is divided into a front surface and a rear surface by a dividing surface including an axis, and the mounting seat surface is formed on the rear case, and a reed valve is mounted on the mounting seat surface. A crankcase lead type two-cycle engine, characterized in that the crankcase lead type is extended beyond the dividing surface toward the crank chamber. 2. The balancer shaft according to claim 1, wherein the balancer shaft is arranged in parallel with the crankshaft on the upper portion of the rear case, and the mounting seat surface is formed at an axially central portion of the balancer shaft of the rear case. A crankcase reed 2-cycle engine characterized by the following.