JPH0374651A - Balancer device for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce the number of parts of a balancer device and to decrease the size and the weight of an internal combustion engine by a method wherein primary and secondary first balancer weights are rotatably supported to main and auxiliary shafts, respectively. CONSTITUTION:Primary and secondary first balancers 8 and 10 are supported to main and auxiliary shafts 4 and 6, respectively. This constitution eliminates the need for mounting a balancer shaft for an exclusive use to support the first and second first balancers 8 and 10. When the primary and secondary first balancers 8 and 10 are interconnected through an interlocking means 39, rotation of the primary first balancer 8 causes rotation of the secondary first balancer 10 in linkage with rotation of the primary second balancer. hereby, there is no need to provide a means to rotate the secondary second balancer 10 independently and in linkage with a crank shaft.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a balancer device for an internal combustion engine.

(Prior art) A balancer device for an internal combustion engine such as a motorcycle engine is
In order to reduce vibrations during operation of an internal combustion engine, the primary balancer weight (hereinafter referred to as the primary balancer) is rotated at the same speed as the crankshaft in the opposite direction to reduce the primary vibrations. Accordingly, secondary vibrations are reduced by rotating a secondary balancer weight C (hereinafter referred to as secondary balancer) at twice the speed of the crankshaft.

As this type of balancer device, for example, one equipped with a pair of primary balancers is disclosed in Japanese Utility Model Application Publication No. 55-142733, and another device equipped with a pair of secondary balancers is known. Jitsukai 58-2075
The one disclosed in Publication No. 0 is known, but in these, each primary balancer and each secondary balancer are supported on a dedicated balancer shaft installed parallel to the crankshaft, and the crankshaft is rotated around the axis of the balancer shaft. It is designed to rotate in conjunction with the

Thus, in conventional balancer devices, each balancer is typically supported on its own dedicated balancer shaft.

However, in order to provide a balancer shaft for supporting each balancer, the number of parts in the balancer device increases, which hinders the reduction in weight and size of the internal combustion engine. The means for rotating the balancer has also become complicated, which has also been a factor in increasing the number of parts in the balancer device.

(11B to be Solved) The present invention eliminates such disadvantages and reduces the number of parts in a balancer device for an internal combustion engine that includes a pair of primary balancers and a pair of secondary balancers, thereby making the internal combustion engine more compact. It is an object of the present invention to provide a balancer device that can achieve weight reduction.

(Means for Solving the Problems) In order to achieve the above object, the balancer device for an internal combustion engine of the present invention includes a main shaft that is provided parallel to and interlocks with a crankshaft that is rotatably supported in a crankcase; A transmission having a subshaft installed parallel to the main shaft and interlocked with the subshaft via a transmission gear train, and a pair of transmissions that are rotated about an axis parallel to the crankshaft in the opposite direction at the same speed as the crankshaft. a pair of secondary first and second balancers that are rotated about axes parallel to the crankshaft in opposite directions at twice the speed of the crankshaft; In an internal combustion engine equipped with a balancer device having a primary
The balancer and the secondary first balancer are respectively supported by the main shaft and the sub-shaft so as to be rotatable thereabout.

The primary first balancer and the secondary first balancer are interlocked with the primary first balancer to rotate the secondary first balancer at twice the speed of the crankshaft. It is characterized by being connected through.

Furthermore, the interlocking means includes a drive gear integrally provided with the primary first balancer so as to be rotatable around the main shaft, and a drive gear meshed with the drive gear and integrally provided with the secondary first balancer. and a driven gear rotatably provided around a shaft, and the primary first balancer is connected to the driven gear and the secondary first balancer.
It is characterized by being rotatably provided between the balancers.

Further, the internal combustion engine is a single-cylinder engine, and the crankshaft includes a first crank half that includes a crank pin that connects one of a pair of crank webs housed in the crankcase and a crankshaft. , a second crank comprising the other of said webs.

The outer surface of the portion of the crank web of the first crank half where the crank pin is integrally provided is formed into a thin wall to form a gap between the first crank half and the crankcase, and the drive gear is It is characterized in that it is rotatably provided around the main shaft at the position of the gap when the crankshaft rotates.

The first and second secondary balancer weights are provided in the crankcase in close proximity to a plane that passes through a substantially central portion of the crankshaft and is orthogonal to the crankshaft.

Further, the primary second balancer is rotatably supported around the axis of a balancer shaft provided parallel to the crankshaft, and the secondary second balancer is rotatably supported around the balancer shaft. It is characterized by being supported in a freely movable manner.

Furthermore, the primary first and second balancer weights are
The first and second secondary shafts are provided on opposite sides of the crankshaft, respectively, across a plane perpendicular to the crankshaft, and at positions closer to the outer side in the axial direction of the main shaft and the balancer shaft, respectively. The second balancer weight is provided at a position inside the first and second primary balancer weights in the axial direction of the secondary shaft and the balancer shaft, respectively.

(Operation) According to this means, since the primary first balancer and the secondary first balancer are supported on the main shaft and the secondary shaft, respectively, the primary first balancer and the second balancer are supported. There is no need to provide a dedicated balancer shaft for this purpose.

When the primary first balancer and the secondary first balancer are connected via the interlocking means, the secondary second balancer rotates in conjunction with the rotation of the primary first balancer. Therefore, there is no need to provide means for independently rotating the second secondary balancer in conjunction with the crankshaft.

Further, the interlocking means includes the drive gear and the driven gear, and the primary first balancer is connected to the driven gear and the secondary first balancer.
When the balancer is provided rotatably between the balancers, the first
By making it possible to provide a balancer and a secondary first balancer close to the subshaft and main shaft, respectively, and by making both the first balancers and interlocking means close to each other in the axial direction of the main shaft and subshaft, It becomes possible to shorten the length of the main shaft and sub-shaft that support these.

Further, the internal combustion engine is a single-cylinder engine, the crankshaft is composed of the first and second crank halves, and the outer surface of a portion of the crank web of the first crank half is integrally provided with the crank pin. When a gap is formed between the crankcase and the crankcase, and the drive gear is provided so as to be rotatable around the main shaft at the position of the gap when the crankshaft rotates, the primary The first balancer and the drive gear can be provided close to the crank web of the crankshaft.

Further, when the secondary first and second balancer weights are provided close to a plane that passes through the approximate center of the crankshaft in the crankcase and is orthogonal to the crankshaft, the secondary first and second balancer weights By rotating the second balancer weights in opposite directions, the couple generated on the crankshaft or the like is reduced.

Further, when the second balancer weight of the secondary is supported on a balancer shaft that supports the second balancer weight of the primary, the balance bolt is shared by both balancers, and a separate balancer shaft is provided for each. There will be no need.

Furthermore, the primary first and second balancer weights,
The first and second secondary shafts are provided on opposite sides of the crankshaft, respectively, across a plane perpendicular to the crankshaft, and at positions closer to the outer side in the axial direction of the main shaft and the balancer shaft, respectively. When the two balancer weights are provided at positions inside the first and second primary balancer weights in the axial direction of the secondary shaft and balancer shaft, respectively, both primary balancer weights that are rotated in the same direction are cranked. Both secondary balancer weights are arranged at positions where the distances in the axial direction from the center of the shaft are approximately equal to cancel out the couples generated by these rotations, and the secondary balancer weights are rotated in opposite directions. It is possible to prevent a couple from occurring due to the rotation of the crankshafts by arranging them on substantially the same plane passing through the approximate center of the crankshaft and perpendicular thereto.

(Example) A single-air H4 cycle engine for a motorcycle equipped with an example of the balancer device for an internal combustion engine of the present invention will be described with reference to FIGS. 1 to 3. FIGS. 1 to 3 are explanatory cross-sectional views of main parts of the engine in a front view, a plan view, and a side view, respectively.

In Figures 1 to 3, 1 is a crankshaft rotatably supported by a crankcase 2, 3 is a main shaft 4 installed parallel to the crankshaft 1, and 3 is a main shaft 4 installed parallel to the main shaft 4 for speed change. a transmission having a countershaft 6 connected via a gear train 5;
Reference numeral 7 denotes a balancer device having a primary balancer 8 and a second balancer 9, and a secondary balancer IO and second balancer 11.

As shown in the first diagram, the crankshaft l has a pair of crank webs 12.13 housed in the crank case 2, and is connected to the crank case 2 at both sides of the crank webs 12.13 through bearings 14.15. It is rotatably supported.

This crankshaft l consists of a first crank half 16 with a crank web 13 and a second crank half 17 with a crank web 12, which are connected to the crank web 13.
The crank pin 18 is formed integrally with the crank web 12 and is press-fitted into the crank web 12. The crankcase 2 is connected via a connecting rod 21 to a piston 20 that is slidable within a cylinder 19 mounted on the crankcase 2, and the reciprocating motion of the piston 20 rotates the crankshaft l around its axis. I try to keep it moving.

Further, the outer surface of the portion of the crank web 13 where the crank pin 18 is provided is cut into a slope shape and made thin, thereby forming a gap between the crankcases 2.

The main shaft 4 of the transmission 3 has a bearing 2 as shown in the first diagram.
2.23, the crank web 1 is rotatably supported on the crank case 2 through the crank case 2, and the crank web 1 is
A clutch inner 25 of a clutch device 24 is concentrically and rotatably attached to the end protruding toward the third side.

As shown in the second figure, the clutch inner 25 is connected to the clutch outer 28 via a plurality of clutch plates 27 which are overlapped and pressed together between the clutch inner 25 and the lifter plate 26 when the clutch device 24 is connected. It is connected concentrically and rotatably. The clutch outer 28 has a primary driven gear 29 fixed to its end face on the crankcase 2 side concentrically with the main shaft 4, and a crank web 1 from inside the crankcase 2 of the crankshaft l.
The primary driven gear 30 is integrally rotatably mounted on the end protruding from the primary driven gear 29 and meshed with the primary driven gear 29 at a gear ratio of 1:1. The rotation of the crankshaft 1 is transmitted to the main shaft 4 via the primary drive gear 30, the primary driven gear 29, and the clutch device 24 in this order, and the main shaft 4 is rotated in conjunction with the crankshaft 1. I have to.

As shown in the first diagram, the subshaft 6 of the transmission 3 is rotatably supported by the crankcase 2 via bearings 31 and 32, and is rotated along the subshaft 6 and the main shaft 4 within the crankcase 2. It is connected to the main shaft 4 via a transmission gear train 5 disposed near the end of the crank web 12, and operates the subshaft 6 at several speeds depending on the meshing combination of the transmission gear train 5. It is designed to rotate in conjunction with the main shaft 4. The subshaft 6 is connected to a wheel of a motorcycle (not shown) via a chain 34 from a drive sprocket 33 that is integrally rotatably attached to an end protruding from inside the crankcase 2 toward the crank web 12. As a result, the rotation of the subshaft 6 transmitted from the crankshaft 1 via the main shaft 4 is output to the wheels.

The primary first balancer 8 of the balancer device 7 has a hollow shaft 36 interposed between the main shaft 4 and the bearing 23 and rotatably fitted onto the main shaft 4 via a needle bearing 35, as shown in the second figure. It is provided integrally at an end inside the crankcase 2 and is rotatably supported by the main shaft 4 via the hollow shaft 36. The primary driven gear 29 is integrally and rotatably fitted to the outer circumferential surface of the end of the hollow shaft 36 protruding from the inside of the crankcase 2 by means of a spline connection, thereby causing rotation of the crankshaft 1. is transmitted to the hollow shaft 36 via the primary drive gear 30 and the primary driven gear 29, and together with the hollow shaft 36, the primary first balancer 8 is linked to the crankshaft 1 as shown in the third figure. It rotates around the main shaft 4 in the opposite direction at high speed.

The secondary first balancer lO of the balancer device 7 is a hollow shaft which is rotatably fitted onto the countershaft 6 via a needle bearing 37 at a position facing the hollow shaft 36 within the crankcase 2, as shown in the second figure. It is provided integrally with one end of the shaft 38, and is rotatably supported by the subshaft 6 via the hollow shaft 38. The other end of the hollow shaft 38 is connected to the hollow shaft 36 via an interlocking means 39.

This interlocking means 39 includes a drive gear 40 integrally provided on the hollow shaft 36 between the primary balancer 8 and the crankcase 2, and a driven gear 4 integrally provided on the other end of the hollow shaft 38.
1, and a hollow shaft 36 that is interlocked with the crankshaft 1 by meshing these gears 40 and 41 with a gear ratio of 2:1.
The rotation of the primary first balancer 8 is transmitted to the hollow shaft 38 at twice the speed, and as shown in the third figure, the secondary first balancer 10 and the hollow shaft 38 are linked to the crankshaft 1 and rotated at twice the speed. It is made to rotate in the same direction at the same speed.

In addition, these art book 1 balancers 8, 10 and interlocking means 3
Reference numeral 9 denotes an interlocking means 39 and a primary linking means 39 along the main shaft 4 and counter shaft 6 in the crankcase 2 from a position near the end on the crank web 13 side toward the speed change gear train 5 side, as shown in the second figure. first balancer 8 and secondary first balancer 1
The first balancers 8 of the first order are arranged close to each other in the order of 0, and the first balancers 8 of the first order are connected to the first balancers 10 of the second order as shown by the imaginary line in FIG.
and interlocking means 39, and the secondary first balancer 10 is located closer to the inside of the crankcase 2 with respect to the primary first balancer 8, as shown in FIGS. 1 and 2. At the position, the axis of the crankshaft 1 and the piston 20
passes through the center point O of the crankshaft l, which is the intersection with the axis of
Moreover, it is provided close to the center plane X perpendicular to the crankshaft 1.

Furthermore, in FIG. 2, the drive gear 40 of the interlocking means 39
is located in the gap between the crank web 13 and the crankcase 2 when the crankshaft 1 rotates, and is a primary first balancer that prevents the crank web 13 and the drive gear 40 from interfering with each other. 8 and close to the crank web 13.

As shown in FIGS. 2 and 3, the primary second balancer 9 of the balancer device 7 is operated by a main balancer 9a that bears most of its weight, and a sub-balancer 9b that carries the remaining weight. The balancer shaft 44 is installed parallel to the main shaft 5 at a position opposite to the main shaft 5 with the crankshaft 1 in between, as shown in the second figure, and rotatably supported on the crankcase 2 via bearings 42 and 43. The crank web 12 is provided integrally with an end portion inside the crank case 2, and is provided on the opposite side of the primary first balancer 8 with the center plane X in between.

On the other hand, the sub-balancer 9b is inserted into the crank web 1 from inside the crankcase 2 of the balancer shaft 44 as shown in the second figure.
The balancer shaft 44 is provided integrally with a driven gear 45 that is integrally rotatably mounted on the end protruding from the third side, and is rotatable about the axis of the balancer shaft 44 together with the main balancer 9a via the driven gear 45. is supported by.

The driven gear 45 is meshed with the primary drive gear 30 at a gear ratio of 1:1, as shown in the second diagram, and thereby balances the rotation of the crankshaft l via the primary drive gear 30 and the driven gear 45. The transmission is transmitted to the shaft 44, and together with the balancer shaft 44, the primary second balancer 9 consisting of the main balancer 9a and the sub-balancer 9b is interlocked with the crankshaft 1 as shown in the third figure, and rotates at a constant speed in the opposite direction. It is designed to rotate.

In addition, in FIGS. 2 and 3, the primary second balancer 9
The main balancer 9a, which bears most of the weight of The balancers 8 and 9a are provided at positions where the distances from the center point O are approximately the same, and the moment around the center point 0 due to the centrifugal force generated in a direction perpendicular to the crankshaft when each of these balancers 8 and 9a is rotated is mutually reduced. I'm trying to cancel it out.

The secondary second balancer 11 of the balancer device 7 is integrally provided at one end of a hollow shaft 47 which is rotatably inserted into the middle part of the balancer shaft 44 via a needle bearing 46 as shown in the second diagram. is connected to the balancer 11 via the hollow shaft 47.
1144 so as to be rotatable therearound.

As shown in the second figure, this hollow shaft 47 has a driven gear 48 integrally provided at its other end, and is formed on the outer peripheral surface of the crank web 12 and meshes with the driven gear 48 at a gear ratio of 1:2. The crankshaft 1 is connected to the crankshaft l via the drive gear 12a and the driven gear 48, thereby transmitting the rotation of the crankshaft 1 to the hollow shaft 47 via the drive gear 12a and the driven gear 48,
Together with the hollow shaft 47, the secondary second balancer 11 is interlocked with the crankshaft 1 as shown in the third figure, and rotated around the balancer shaft 44 in the opposite direction at twice the speed. As shown in FIGS. 1 and 2, this secondary second balancer 11 is provided close to the center plane X at a position closer to the inside of the crankcase 2 than the primary second balancer 9. At the same time, as shown in the third diagram, the center of rotation P! and the rotation center P+ of the secondary second balancer 10
A line connecting them is provided so as to pass through a position close to the center point O of the crankshaft 1.

In addition, in FIG. 1, 49 is a camshaft 5 that is interlocked with the crankshaft 1.
0, 51 is the crankshaft 1
In FIGS. 1 and 3, reference numeral 52 indicates a speed change spindle 53 connected to a speed change pedal (not shown), a speed change drum 54 and a shift fork 55 that are interlocked with the speed change spindle 53. In FIG. 3, reference numeral 56 is a kick starter device.

Next, in this engine, the operation of the balancer device 7, which is a main part of the present invention, and the above-mentioned configuration will be explained with reference to FIGS. 2 and 3.

In this balancer device 7, as described above in FIG. 3, a primary first balancer 8 and a primary second balancer 9 consisting of the main balancer 9a and the sub-balancer 9b move in conjunction with the crankshaft l and move at a constant speed therewith. By rotating in the opposite direction, the primary vibration of the engine is reduced, and furthermore,
The secondary first balancer 10 and second balancer 11 rotate in opposite directions at twice the speed of the crankshaft 1, thereby reducing secondary vibrations of the engine.

, At this time, in Fig. 2, both secondary balancers 10°1
As described above, the third
As shown in the figure, a line connecting these rotation centers P and P8 is provided so as to pass through a position close to the center point 0 of the crankshaft l, so that both secondary balancers 10 and 11 are opposite to each other. Generation of couples due to rotation in the direction is suppressed. And such a secondary balancer io,
The arrangement of xi is such that these are both primary balancers 8.
This is possible because it is provided closer to the inside of the crankcase 2 than the crank case 9.

In addition, in FIG. 2, the balancer device 7 includes a primary first balancer 8 and a secondary first balancer l as described above.
The main shaft 4 and the counter shaft 6 of the transmission 3 are supported as balancer shafts, respectively, and the primary second balancer 9 and the secondary second balancer 11 are supported on one balancer shaft 44.
By supporting the balancers 8 to 11, the number of balancer shafts supporting the balancers 8 to 11 is reduced as much as possible to reduce the number of parts of the balancer device 7, thereby making the engine smaller and lighter.

In particular, the secondary first balancer 10 is connected to the crankshaft l.
By interlocking the primary first balancer 8 which is interlocked with the crankshaft 1 via the interlocking means 39 without independently providing a means for interlocking with the crankshaft 1, the interlocking means 39 is connected to the driving gear 40 and the driven gear 41. The balancer device 70 has a simple configuration, which suppresses an increase in the number of parts.

Further, in the balancer device 7, as described above, the primary first balancer 8 is connected to the secondary first balancer 11 and the interlocking means 3.
9 are rotatable between the crank web 13 and the crank case 2, and the structure is made smaller and lighter by providing them close to each other. By providing the drive gear 40 and the primary first balancer 8 close to the crank web 13 in the gap between them, the distance between them and the crankshaft l is shortened, thereby reducing the size of the engine.

In order to form the above-mentioned gap between the crank club 13 and the crank case 2, the outer surface of the crank web 13 is made thin, and the crank pin 18 is integrally provided on the thin part. This does not reduce the strength of the crankshaft 10.

Further, in this embodiment, the primary second balancer 9 is composed of the main balancer 9a and the sub-balancer 9b, but the sub-balancer 9b is not provided in the driven gear 45, but is integrated with the main balancer 9a, and the second Of course, even if the balancer 9 is configured, the above effects can be achieved.

(Effects) As is clear from the above description, according to the balancer device for an internal combustion engine of the present invention, the primary balancer and the secondary
By supporting the balancer on the main shaft and subshaft of the transmission, respectively, the number of parts of the balancer device can be reduced, and the internal combustion engine can be made smaller and lighter.

By connecting the primary first balancer and the secondary first balancer via an interlocking means and interlocking the secondary first balancer with the primary first balancer, the secondary first balancer The number of parts of the balancer device can be reduced by simplifying the structure of the means for interlocking the balancer with the crankshaft.

Further, by providing the interlocking means horizontally by a driving gear and a driven gear, or by providing the primary first balancer rotatably between the driven gear and the secondary first balancer, both the first balancers and the interlocking means are provided. These structures can be made smaller by placing them closer to each other.

Furthermore, in a single-cylinder engine, the crankshaft is constituted by first and second crank halves, and a crank web integrally provided with the crank pin of the first crank half is shaped into a thin wall, and the crank web and the crankcase are formed into a thin shape. A gap is formed between the crank web and the drive gear of the interlocking means is positioned in the gap when the crankshaft rotates, so that the first balancer and the drive gear of the primary are brought close to the crank web. This allows the engine to be made smaller.

In addition, by providing both secondary balancers in the crankcase in close proximity to a plane that passes through the approximate center of the crankshaft and is orthogonal to the crankshaft, both balancers with the nuclear secondary can rotate in opposite directions. The couple caused by this can be reduced.

Furthermore, by supporting the secondary second balancer on the balancer shaft that supports the primary second balancer, the balancer shaft of the two-cylinder dual balancer can be shared, further reducing the number of parts of the balancer device. I can do it.

Furthermore, both primary balancer shafts are provided on opposite sides of a plane that passes through the approximate center of the crankshaft and is orthogonal to the crankshaft, and at positions closer to the outside in the axial direction of the main shaft and the balancer shaft. , by providing both secondary balancer weights at positions inside of both primary balancer weights in the axial direction of the counter shaft and balancer shaft, respectively, the two primary balancer weights that are rotated in the same direction as each other can be cranked. Both secondary balancer weights, which are arranged at approximately equal distances in the axial direction from the center of the crankshaft and are rotated in opposite directions, pass through the center of the crankshaft and are orthogonal thereto. The two primary balancer weights and the secondary two balancer weights can be arranged on substantially the same plane, and the generation of a couple due to the rotation of both the primary balancer weights and both the secondary balancer weights can be suppressed.

[Brief explanation of drawings]

1 to 3 are explanatory cross-sectional views of essential parts of a single-cylinder engine of a motorcycle equipped with an example of the balancer device of the present invention in a front view, a plan view, and a side view, respectively. 7... Balancer device 8... Primary first balancer way 9... Primary second balancer way 10... Secondary first balancer way 11... Secondary second balancer way 12, 13. ... Crank web (6... First crank half body 17... Second crank half body 18... Crank pin 39... Interlocking means 40... Drive gear 41... Driven gear 44
・・・Balancer axis

Claims (1)

[Scope of Claims] 1. A main shaft that is installed parallel to and interlocks with a crankshaft that is rotatably supported in the crankcase, and a main shaft that is installed parallel to the main shaft and interlocks with it via a transmission gear train. a pair of first and second balancer weights that are rotated about axes parallel to the crankshaft at a constant speed and in opposite directions to the crankshaft; A balancer device having a pair of secondary first and second balancer weights that are rotated about axes parallel to the crankshaft in opposite directions at a speed of A balancer device for an internal combustion engine, characterized in that a balancer weight and a secondary first balancer weight are respectively supported by the main shaft and the subshaft so as to be rotatable therearound. 2. The primary first balancer weight and the secondary first balancer weight
The balancer weight is connected to the primary balancer weight through an interlocking means that rotates the secondary first balancer weight at twice the speed of the crankshaft in conjunction with the primary first balancer weight. A balancer device for an internal combustion engine according to claim 1. 3. The interlocking means includes a drive gear provided integrally with the primary first balancer weight so as to be rotatable around the main shaft, and meshed with the drive gear to be integrated with the secondary first balancer weight. and a driven gear rotatably provided around the counter shaft, and the primary first balancer weight is rotatably provided between the driven gear and the secondary first balancer weight. A balancer device for an internal combustion engine according to claim 2. 4. The internal combustion engine is a single-cylinder engine, and the crankshaft includes a first crank half including one of a pair of crank webs housed in the crankcase and a crank pin that connects the two webs; and a second crank half having the other of the two webs, and the outer surface of the portion of the crank web of the first crank half where the crank pin is integrally provided is formed with a thin wall so that there is a gap between the crankcase and the crankcase. 4. The balancer device for an internal combustion engine according to claim 3, wherein a gap is formed, and the drive gear is rotatably provided around the main shaft at a position of the gap when the crankshaft rotates. 5. Claim characterized in that the secondary first and second balancer weights are provided close to a plane passing through a substantially central portion of the crankshaft in the crankcase and orthogonal to the crankshaft. 1. The balancer device for an internal combustion engine according to 1. 6. The primary second balancer weight is rotatably supported on a balancer shaft installed parallel to the crankshaft about its axis, and the secondary second balancer weight is supported around the balancer shaft in parallel with the crankshaft. 2. The balancer device for an internal combustion engine according to claim 1, wherein the balancer device is rotatably supported by the balancer device. 7. The primary first and second balancer weights each pass through a substantially central portion of the crankshaft and are opposite to each other across a plane perpendicular to the crankshaft, and are located outside in the axial direction of the main shaft and balancer shaft. The secondary first and second balancer weights are provided at positions inner than the primary first and second balancer weights in the axial direction of the secondary shaft and the balancer shaft, respectively. 7. A balancer device for an internal combustion engine according to claim 6.