Engine

Abstract

To enable a balancer to be arranged compactly even in places other than the front of an engine, to make the engine compact.SOLUTION: In an engine, cam chains 67, 68 are mounted on the side of the engine, cam chain drive sprockets 65, 66 for driving the cam chains 67, 68 are driven by a cam chain drive gear 64 arranged coaxially on the side of the engine, the cam chain drive gear 64 is driven by an idler driven gear 63, and the idler driven gear 63 is driven by an idler drive gear 62 that meshes with a prescribed gear 61 provided on a crankshaft 10, where a balancer 80 is arranged coaxially with the idler drive gear 62.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an engine. [Background technology]

[0002] There is known an internal combustion engine equipped with a balancer that suppresses vibration. In this type of engine, a water pump shaft is fitted and fixed to one end of a front balancer shaft (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-162202 Summary of the Invention [Problem to be solved by the invention]

[0004] When arranging the balancer, it is sometimes necessary to equip it with accessories that are driven coaxially using the same drive source, but it is difficult to arrange the balancer compactly anywhere other than in the front of the engine, where there is a high degree of freedom. The present invention has been made in view of the above-mentioned circumstances, and has as its object to make the engine more compact by enabling a balancer to be arranged compactly in a location other than the front of the engine. [Means for solving the problem]

[0005] The present invention provides an engine in which a cam chain is provided on the side of the engine, a cam chain drive sprocket that drives the cam chain is driven by a cam chain drive gear (64) that is coaxially arranged on the side of the engine, the cam chain drive gear is driven by an idler driven gear, and the idler driven gear is driven by an idler drive gear that meshes with a predetermined gear provided on the crankshaft, and in which a balancer is arranged coaxially with the idler drive gear. [Effects of the Invention]

[0006] According to the present invention, the balancer can be compactly arranged in a location other than the front of the engine, thereby making the engine more compact. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of an engine according to an embodiment of the present invention. FIG. [Figure 2] 1 is a cross-sectional view of the engine taken along a plane passing through a crankshaft, a main shaft, and a front cylinder. [Figure 3] 4 is a diagram showing the peripheral structure of an idler gear support shaft and a cam chain drive shaft. FIG. [Figure 4] FIG. 2 is a perspective view showing a cross section of a crankshaft together with an idler gear support shaft and the like. [Figure 5] FIG. 2 is a perspective view showing a cross section of an idler gear support shaft together with a crankshaft and the like. [Figure 6] FIG. 2 is a perspective view showing an idler gear support shaft together with the surrounding configuration. [Figure 7] FIG. 2 is a diagram showing a cam chain drive shaft together with the surrounding configuration. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the description, directions such as front, rear, left, right, up and down are the same as directions relative to the vehicle body unless otherwise specified. In addition, in each drawing, the symbol FR indicates the front of the vehicle body, the symbol UP indicates the upper side of the vehicle body, and the symbol LH indicates the left side of the vehicle body.

[0009] [Embodiment Mode] Fig. 1 is a perspective view of an engine 1 according to an embodiment of the present invention. The engine 1 shown in Fig. 1 shows a state in which a crankcase cover 2 covering the right side of the engine 1 has been removed. Engine 1 is a V-engine mounted on a motorcycle, and can also be called an internal combustion engine and a power unit. Engine 1 includes a crankcase 11 that rotatably supports a crankshaft 10, a front cylinder 12F (also called a first bank) that extends forward and upward from the top of crankcase 11, and a rear cylinder 12R (also called a second bank) that extends rearward and upward from the top of crankcase 11. Each cylinder 12F, 12R includes a cylinder block 12a, a cylinder head 12b connected to the upper surface of the cylinder block 12a, and a head cover (not shown) that covers the upper surface of the cylinder head 12b, and a valve mechanism 13 is arranged between the cylinder head 12b and the head cover.

[0010] The crankcase 11 is formed as a hollow case that supports the crankshaft 10 and the surrounding structure, and is divided into left and right halves. However, the shape and structure of the crankcase 11 may be changed as appropriate depending on the specifications of the engine 1, etc. The crankcase 11 rotatably supports the crankshaft 10 along the vehicle width direction. The crankcase 11 also rotatably supports a main shaft 21 below and rearward of the crankshaft 10, and a counter shaft 22 below the crankshaft 12 and the main shaft 21. The crankcase 11 also rotatably supports an idler gear support shaft 31 above and rearward of the crankshaft 10 and on the right side of the crankcase 11, and a cam chain drive shaft 32 above the idler gear support shaft 31 and on the right side of the crankcase 11. The crankshaft 10, main shaft 21, counter shaft 22, idler gear support shaft 31, and cam chain drive shaft 32 are parallel to one another.

[0011] 2 is a cross-sectional view of the engine 1 taken along a plane passing through the crankshaft 10, the main shaft 21, and the front cylinder. The crankshaft 10 includes left and right journals 10a rotatably supported in a crankcase 11, and a crank 10b disposed between the left and right journals 10a and housed in a crank chamber 14. The crank 10b includes crank webs 10c integrated with the journals 10a, and crank pins 10d connecting the crank webs 10c to each other. A crank weight 10e is integrally formed on the crank web 10c on the opposite side of the crank pin 10d with respect to the axis of the crankshaft 10.

[0012] A cylinder bore 15 is provided in the cylinder block 12a above the crank chamber 14, and a piston 16 is provided in the cylinder bore 15. The piston 16 is connected to the crankshaft 10 via a connecting rod 17. In the engine 1 of this configuration, the front and rear cylinders are out of phase with each other, and the connecting rod big ends 17a of the front and rear cylinders that are adjacent on the crank pin 10d are adjacent to each other with the crank web 10c interposed therebetween. A right (one) end of the crankshaft 10 protrudes to the right of the crankcase 11, and a primary drive gear 41 is provided at this end. The primary drive gear 41 meshes with a primary driven gear 42 provided on the main shaft 21.

[0013] A transmission chamber 18 is provided at the rear of the crankcase 11, and a constant mesh gear transmission 19 is housed in the transmission chamber 18. The transmission chamber 18 and the crank chamber 14 are separated by a partition wall 11w. The gear transmission 19 includes a main shaft 21 provided parallel to the crankshaft 10, a counter shaft 22 provided parallel to the main shaft 21, and a gear train group 19g provided on the main shaft 21 and the counter shaft 22. The counter shaft 22 functions as the output shaft of the engine 1, and drives the rear wheels, which are drive wheels, via a power transmission mechanism (for example, a chain transmission mechanism).

[0014] A clutch mechanism 51 capable of interrupting power transmission between the crankshaft 10 and the power transmission mechanism is provided at the right end of the main shaft 21. The clutch mechanism 51 includes a clutch outer 53 connected to the primary driven gear 42 via a damper mechanism 52, a clutch inner 54 fixed to the main shaft 21, and a friction plate 55 provided between the clutch outer 53 and the clutch inner 54. The clutch mechanism 51 is covered from the outside in the vehicle width direction by a crankcase cover 2. The crankcase cover 2 can also be referred to as a clutch cover.

[0015] 2, a primary drive gear 41, a timing gear 61, and a balancer drive gear 71 are disposed on the right end of the crankshaft 10. These gears 41, 61, and 71 are disposed in the space between the crankcase 11 and the crankcase cover 2. The crankcase cover 2 has a cylindrical portion 2t that protrudes toward the inside of the engine so as to surround the periphery of a pipe 3 connected to the crankshaft 10. The space between the cylindrical portion 2t and the pipe 3 is sealed with a seal member 4, and the opening of this cylindrical portion 2t on the outer side in the vehicle width direction is closed with a cap 5.

[0016] FIG. 3 is a diagram showing the peripheral structure of the idler gear support shaft 31 and the cam chain drive shaft 32. As shown in FIG. This engine 1 employs a semi-cam gear train system that uses a combination of gears and a cam chain to drive the valve trains 13 of the front and rear cylinders. In this engine 1, the rotation of the crankshaft 10 is transmitted to an idler drive gear 62 provided on the idler gear support shaft 31 via a timing gear 61 fixed to the crankshaft 10. Next, the rotation of the idler drive gear 62 is transmitted to a cam chain drive gear 64 provided on the cam chain drive shaft 32 via an idler driven gear 63 provided on the idler gear support shaft 31.

[0017] As shown in Fig. 3, a first cam chain drive sprocket 65 for the rear cylinders and a second cam chain drive sprocket 66 for the front cylinders are fixed to the cam chain drive shaft 32. A first cam chain 67 wound around the first cam chain drive sprocket 65 drives the valve mechanism 13 for the rear cylinders (the camshaft of the valve mechanism 13), and a second cam chain 68 wound around the second cam chain drive sprocket 66 drives the valve mechanism 13 for the front cylinders (the camshaft of the valve mechanism 13). As shown in Figs. 1 and 3, the configuration that realizes the semi-cam gear train system is concentrated on the right side of the engine.

[0018] Fig. 4 is a perspective view showing a cross section of the crankshaft 10 together with the idler gear support shaft 31, etc. Fig. 5 is a perspective view showing a cross section of the idler gear support shaft 31 together with the crankshaft 10, etc. Fig. 6 is a perspective view showing the idler gear support shaft 31 together with the surrounding configuration. As shown in FIG. 4, a balancer drive gear 71 is fixed to the rightmost side (outside the engine) of the crankshaft 10, a timing gear 61 is fixed to the inner side of the balancer drive gear 71 in the crankshaft direction (inside the engine), and a primary drive gear 41 is fixed to the inner side of the timing gear 61 in the crankshaft direction (inside the engine).

[0019] The number of teeth and diameters of these gears 71, 61, and 41 are set appropriately according to the specifications of the engine 1, but in this embodiment, the primary drive gear 41 is formed as the gear with the largest diameter. The balancer drive gear 71 drives a balancer 80 (described below) to suppress primary vibrations of the engine 1, so the gear ratio with the crankshaft 10 is 1:1, and the balancer drive gear 71 drives the balancer 80 at the same rotational speed as the crankshaft 10.

[0020] The timing gear 61 is a gear that reduces the rotation of the crankshaft 10 by half and transmits the rotation to the valve mechanism 13 (the camshaft of the valve mechanism 13). For this reason, the timing gear 61 is formed with a smaller diameter than the balancer drive gear 71. 5, the idler gear support shaft 31 is a hollow body with a bottom separate from the crankcase 11, and is fixed to the crankcase 11 by a fastening member 31k inserted from the outside in the vehicle width direction with the bottom abutting against the crankcase 11. The fastening member 31k in this embodiment is a single bolt. Note that the structure for fixing the idler gear support shaft 31 to the crankcase 11 may be changed as appropriate.

[0021] Two bearings 31a and 31b, each made up of a needle bearing, are disposed adjacent to the idler gear support shaft 31. An idler driven gear 63 that meshes with the timing gear 61 and an idler drive gear 62 are attached to the outer peripheral surface of the bearing 31a on the inner side in the crankshaft direction (corresponding to the inner side of the engine). Therefore, the idler driven gear 63 and the idler drive gear 62 are rotatable relative to the idler gear support shaft 31. These gears 63 and 62 are fixed to each other and thus rotate synchronously.

[0022] A setting gear 62s having the same diameter as the idler drive gear 62 is fitted onto the idler drive gear 62 so as to be relatively rotatable. The setting gear 62s meshes with the timing gear 61 and is biased by an elastic member in the direction opposite to the rotational direction of the timing gear 61, absorbing backlash between the timing gear 61 and the idler drive gear 62. This setting gear 62s is also called a scissors gear and is an example of the "backlash absorption mechanism" of the present disclosure.

[0023] A balancer driven gear 72 that meshes with the balancer drive gear 71 is attached to the outer peripheral surface of a bearing 31b on the crankshaft outer side (corresponding to the outer side of the engine) of the idler gear support shaft 31. A balancer 80 is provided integrally with the balancer driven gear 72. As shown in FIG. 6, the balancer 80 is formed by forming a part of the balancer driven gear 72 into a thick, fan-shaped portion that bulges outward in the right side of the engine (corresponding to the outer side in the crankshaft direction). The balancer 80 rotates in synchronization with the crankshaft 10 at the same rotation speed (reverse rotation), thereby functioning as a primary balancer that suppresses primary vibrations of the engine 1. The vibration suppression effect can be adjusted appropriately by adjusting the shape and weight of the balancer 80.

[0024] The structure of the balancer 80 is not limited to the above. For example, the balancer 80 may be manufactured as a separate part from the idler drive gear 62, and the balancer 80 and the idler drive gear 62 may be connected to each other so as to be integrated. Also, vibrations other than the primary vibration may be suppressed by adjusting the number of teeth of the gears in the balancer drive system or by adjusting the balancer 80.

[0025] 5, a plurality of oil supply holes 31h are provided in the idler gear support shaft 31. Lubricating oil is supplied into the idler gear support shaft 31, and the supplied lubricating oil is supplied to the bearings 31a, 31b and the gears 62, 63 through each oil supply hole 31h.

[0026] 3, a cam chain drive gear 64 that meshes with an idler driven gear 63 provided on the idler gear support shaft 31 is provided on the right end of the cam chain drive shaft 32. A second cam chain drive sprocket 66 for the front cylinders is provided on the cam chain drive shaft 32 on the inner side in the vehicle width direction of the cam chain drive gear 64 (corresponding to the inner side of the engine), and a first cam chain drive sprocket 65 for the rear cylinders is provided on the inner side in the vehicle width direction of the second cam chain drive sprocket 66 (corresponding to the inner side of the engine).

[0027] FIG. 7 is a diagram showing the cam chain drive shaft 32 together with the surrounding structure. As shown in FIG. 7, the cam chain drive shaft 32, the cam chain drive gear 64, and the first and second cam chain drive sprockets 66 are manufactured as a single unit. Bearings 33, 34, which are rolling bearings, are press-fitted onto both ends of the cam chain drive shaft 32, and a first cam chain drive sprocket 65 is manufactured integrally with the outer periphery of the press-fit portion of the bearing 33 on the crankcase 11 side. Also, a cam chain drive gear 64 is manufactured integrally with the outer periphery of the press-fit portion of the bearing 34 on the crankcase cover 2 side. The first cam chain drive sprocket 65, second cam chain drive sprocket 66, and cam chain drive gear 64 are arranged coaxially.

[0028] In this configuration, the cam chain drive shaft 32, cam chain drive gear 64, first cam chain drive sprocket 65, and second cam chain drive sprocket 66 are manufactured as a single unit, thereby reducing the number of parts. Moreover, the first cam chain drive sprocket 65 is provided using the press-fit portion of the bearing 33, so the first cam chain drive sprocket 65 can be positioned closer to the inside in the vehicle width direction (inside the engine).

[0029] 3, 5, etc., the first cam chain drive sprocket 65 is positioned so as to overlap the crank weight 10e or the connecting rod big end 17a in the up-down direction perpendicular to the crankshaft direction. This allows the first cam chain drive sprocket 65 and the first cam chain 67 to be positioned closer to the inside in the left-right direction of the engine 1. This allows the engine 1 to be made more compact in the left-right direction (crankshaft direction).

[0030] As described above, the engine 1 of this embodiment has a crankshaft 10 in which the connecting rod big ends 17a of adjacent front and rear cylinders on the crank pin 10d are adjacent to each other via the crank web 10c, and cam chains 67, 68 are respectively provided on one side of the engine for the front and rear cylinders 12F. Cam chain drive sprockets 65, 66 that drive the cam chains 67, 68 are driven by a cam chain drive gear 64 that is coaxially disposed on the side of the engine. The cam chain drive gear 64 is driven by an idler driven gear 63, and the idler driven gear 63 is driven by an idler drive gear 62 that meshes with the drive gear of the crankshaft 10. As shown in Figures 3 and 5, etc., in this embodiment, the first cam chain drive sprocket 65 of the cam chain drive sprockets 65, 66 is positioned so as to overlap with the crank weight 10e or the connecting rod big end 17a in the engine up-down direction, which is perpendicular to the crankshaft direction. Therefore, the first cam chain drive sprocket 65 and the first cam chain 67 can be positioned closer to the inside on the left and right sides of the engine 1, allowing the engine 1 to be made more compact in the width direction.

[0031] As shown in Figures 3 and 5, the idler drive gear 62 and the idler driven gear 63 rotate synchronously and rotate relative to the idler gear support shaft 31 that supports these gears 62, 63, and the idler gear support shaft 31 is fixed to the crankcase 11 of the engine 1. According to this configuration, there is no need to provide a bearing between the idler gear support shaft 31 and the crankcase 11, so the area around the idler gear support shaft 31 can be made compact.

[0032] In addition, a set gear 62s that functions as a backlash absorption mechanism is provided on the idler drive gear 62. According to this configuration, the backlash absorption mechanism can be provided in a compact manner.

[0033] The idler gear support shaft 31 is hollow and has a bottom, the bottom of which abuts against the crankcase 11 and is fixed to the crankcase 11, and is provided with an oil supply hole 31h for supplying oil from the inside to the idler driving gear 62 and the idler driven gear 63. With this configuration, the lubrication structure for the gears provided on the idler gear support shaft 31 can be provided compactly. An oil supply hole 31h for supplying oil to at least one of the idler driving gear 62 and the idler driven gear 63 may be provided.

[0034] 1, the idler gear support shaft 31 is disposed between the crankshaft 10 and the main shaft 21, which is provided parallel to the crankshaft 10, in a side view of the engine. With this configuration, the space between the crankshaft 10 and the main shaft 21 can be effectively utilized, allowing the idler gear support shaft 31 to be disposed compactly.

[0035] 5, there is provided a primary drive gear 41 that transmits the rotation of crankshaft 10 to main shaft 21, and primary drive gear 41 is disposed closer to the engine inner side than idler driven gear 63. With this configuration, primary drive gear 41 can be disposed closer to the engine inner side, which reduces the torsional torque acting on crankshaft 10 and allows the area around crankshaft 10 to be made compact.

[0036] Furthermore, the first cam chain drive sprocket 65, the second cam chain drive sprocket 66, and the cam chain drive gear 64 are provided coaxially and integrally, and the bearings 33, 34 are press-fitted into both ends of this integral member, with the first cam chain drive sprocket 65 formed on the outer periphery of the portion of the crankcase 11 where the bearing 33 is press-fitted. With this configuration, the member having the cam chain drive sprockets 65, 66 and the cam chain drive gear 64 can be easily formed compactly in the axial direction, which is advantageous for reducing the width of the engine 1.

[0037] Furthermore, as shown in Fig. 3, engine 1 of this embodiment has cam chains 67, 68 provided on the sides of the engine, and cam chain drive sprockets 65, 66 that drive the cam chains 67, 68 are driven by a cam chain drive gear 64 that is coaxially arranged on the side of the engine. Cam chain drive gear 64 is driven by an idler driven gear 63, and idler driven gear 63 is driven by an idler drive gear 62 that meshes with a timing gear 61 (a specified gear) provided on crankshaft 10. A balancer 80 is arranged coaxially with idler drive gear 62. According to this configuration, the balancer 80 can be compactly arranged in a location other than the location with a high degree of freedom in front of the engine, and the engine 1 can be made compact.

[0038] Furthermore, the idler driven gear 63 and the idler drive gear 62 rotate synchronously and also rotate relative to the idler gear support shaft 31 that supports these gears, and the balancer 80 rotates relative to the idler gear support shaft 31 and rotates at a different rotation speed from the idler drive gear 62. With this configuration, while the balancer 80 is arranged coaxially with the idler drive gear 62, the rotation speeds of the cam chain drive system including the idler drive gear 62 and the balancer drive system can be set independently, ensuring freedom in the design of each drive system.

[0039] The crankshaft 10 also has a balancer driven gear 72 that is driven by a balancer drive gear 71, and the balancer 80 is provided integrally with the balancer driven gear 72. With this configuration, since the balancer drive gear 71 is provided specifically for the balancer, the number of teeth can be set differently between the balancer drive system and the cam chain drive system, increasing the degree of freedom in the gear ratio of each drive system. Furthermore, since the balancer 80 is integral with the balancer driven gear 72, this is advantageous for reducing the number of parts and making the unit more compact.

[0040] Furthermore, balancer 80 is disposed on the outside of the engine, that is, on the outside in the crankshaft direction, of idler drive gear 62. With this configuration, the cam chain drive system including idler drive gear 62 can be disposed closer to the inside of the engine, making it possible to make engine 1 more compact. Furthermore, when changing the specifications of balancer 80 or changing to specifications without balancer 80, it is not necessary to make major changes to the internal layout of engine 1, for example, the layout of the cam chain drive system.

[0041] 3 and 5, the engine is provided with a clutch mechanism 51 that cuts off power transmission from crankshaft 10, and in a cross section taken along a plane through the axis of crankshaft 10 and the axis of clutch mechanism 51 (corresponding to the axis of main shaft 21), balancer 80 overlaps with clutch mechanism 51 in a direction perpendicular to the crankshaft direction. With this configuration, balancer 80 can be disposed using the space available in the direction perpendicular to the crankshaft direction relative to clutch mechanism 51, allowing balancer 80 to be disposed compactly.

[0042] Furthermore, the idler driven gear 63 is disposed on the outside of the engine, that is, on the outside of the crankshaft direction of the primary drive gear 41 provided on the crankshaft 10, and the balancer driven gear 72 is disposed on the outside of the engine, that is, on the outside of the crankshaft direction of the idler driven gear 63. With this configuration, when changing the specifications of the balancer 80 or changing to a specification without the balancer 80, there is no need to significantly change the layout inside the engine 1, for example, the layout of the drive system including the primary drive gear 41 or the layout of the drive system including the idler driven gear 63.

[0043] [Other embodiments] The above-described embodiment merely shows one aspect of the present invention, and any modifications and applications are possible without departing from the spirit of the present invention.

[0044] For example, in the above embodiment, the first cam chain drive sprocket 65 is disposed at a position overlapping with the crank weight 10e or the connecting rod big end 17a in the vertical direction of the engine, but this is not limited thereto, and the second cam chain drive sprocket 66 may be disposed at a position overlapping with the crank weight 10e or the connecting rod big end 17a in the vertical direction of the engine.Furthermore, both the first cam chain drive sprocket 65 and the second cam chain drive sprocket 66 may be disposed at positions overlapping with the crank weight 10e or the connecting rod big end 17a in the vertical direction of the engine.

[0045] Furthermore, in the above embodiment, a case has been described in which the balancer 80 is arranged coaxially with the idler drive gear 62 in the V-type engine 1 shown in FIG. 1 etc., but this is not limited to this, and the balancer 80 may be arranged coaxially with the idler drive gear 62 in an engine other than a V-type. Furthermore, although the present invention has been described as being applied to an engine 1 mounted on a motorcycle, the present invention is not limited to this and may also be applied to engines mounted on saddle-ride vehicles including vehicles other than motorcycles, vehicles other than saddle-ride vehicles, and moving bodies other than vehicles.

[0046] [Configuration supported by the above embodiment] The above embodiment supports the following configurations.

[0047] (Configuration 1) An engine in which a cam chain is provided on the side of the engine, a cam chain drive sprocket that drives the cam chain is driven by a cam chain drive gear that is arranged coaxially on the side of the engine, the cam chain drive gear is driven by an idler driven gear, and the idler driven gear is driven by an idler drive gear that meshes with a predetermined gear provided on the crankshaft, and a balancer is arranged coaxially with the idler drive gear. This configuration allows the balancer to be arranged compactly, making the engine more compact.

[0048] (Configuration 2) The engine described in Configuration 1, wherein the idler driven gear and the idler drive gear rotate synchronously, and the idler drive gear and an idler gear support shaft that supports the idler driven gear rotate relative to each other, and the balancer rotates relative to the idler gear support shaft and at a different rotational speed from the idler drive gear. With this configuration, while the balancer is positioned coaxially with the idler drive gear, the rotation speeds of the cam chain drive system including the idler drive gear and the balancer drive system can be set independently, ensuring freedom in the design of each drive system.

[0049] (Configuration 3) The engine according to configuration 1 or 2, further comprising a balancer driven gear driven by a balancer drive gear provided on the crankshaft, the balancer being integrally provided on the balancer driven gear. With this configuration, since there is a balancer drive gear dedicated to the balancer, the number of teeth can be set differently for the balancer drive system and the cam chain drive system, increasing the degree of freedom in the gear ratio of each drive system. Also, since the balancer is integrated with the balancer driven gear, it is advantageous for reducing the number of parts and making the system more compact.

[0050] (Configuration 4) The engine according to any one of configurations 1 to 3, wherein the balancer is disposed outside the engine relative to the idler drive gear. This configuration allows the cam chain drive system, including the idler drive gear, to be positioned closer to the inside of the engine, making the engine more compact. Furthermore, when changing the balancer specifications or switching to a balancer-less configuration, the internal layout of the engine does not need to be significantly altered.

[0051] (Configuration 5) An engine described in any one of configurations 1 to 4, which is provided with a clutch mechanism that cuts off power transmission from the crankshaft, and in a cross-sectional view taken along a plane that cuts the axis of the crankshaft and the axis of the clutch mechanism, the balancer overlaps with the clutch mechanism in a direction perpendicular to the crankshaft direction. According to this configuration, the balancer can be disposed in a compact manner by utilizing the space available in the direction perpendicular to the crankshaft direction relative to the clutch mechanism.

[0052] (Configuration 6) An engine according to Configuration 3, wherein the idler driven gear is positioned further outward from the engine than a primary drive gear provided on the crankshaft, and the balancer driven gear is positioned further outward from the engine than the idler driven gear. With this configuration, when changing the specifications of the balancer or changing to a specification without a balancer, there is no need to make major changes to the layout inside the engine. [Explanation of symbols]

[0053] 1...Engine (internal combustion engine) 10 crankshaft 10c Crankweb 10d crank pin 10e crank weight 11 Crankcase 12F, 12R cylinder 13 Valve train 17a Connecting rod big end 21 Main shaft 31 Idler gear support shaft 31h fuel filler hole 33,34 Bearings 41 Primary drive gear 51 Clutch mechanism 61 Timing gear 62 Idler drive gear 62s Serashi Gear (Backlash Absorption Mechanism) 63 Idler driven gear 64 Cam chain drive gear 65 No. 1 cam chain drive sprocket 66 No. 2 cam chain drive sprocket 67 First cam chain 68 Second cam chain 71 Balancer drive gear 72 Balancer driven gear 80 Balancer

Claims

1. An engine in which cam chains (67, 68) are provided on the side of the engine, cam chain drive sprockets (65, 66) that drive the cam chains (67, 68) are driven by cam chain drive gears (64) that are coaxially arranged on the side of the engine, the cam chain drive gears (64) are driven by idler driven gears (63), and the idler driven gears (63) are driven by idler drive gears (62) that mesh with a predetermined gear (61) provided on a crankshaft (10), A balancer (80) is disposed coaxially with the idler drive gear (62). engine.

2. The idler driven gear (63) and the idler driving gear (62) rotate synchronously, and the idler driving gear (62) and the idler gear support shaft (31) supporting the idler driven gear (63) rotate relative to each other. The balancer (80) rotates relative to the idler gear support shaft (31) and rotates at a different rotation speed from the idler drive gear (62).

10. The engine of claim 1.

3. a balancer driven gear (72) driven by a balancer drive gear (71) provided on the crankshaft (10); The balancer (80) is integrally provided with the balancer driven gear (72).

10. The engine of claim 1.

4. The balancer (80) is disposed outside the engine relative to the idler drive gear (62).

3. The engine of claim 2.

5. a clutch mechanism (51) for interrupting power transmission from the crankshaft (10); In a cross-sectional view taken along a plane that cuts the axis of the crankshaft (10) and the axis of the clutch mechanism (51), the balancer (80) overlaps the clutch mechanism (51) in a direction perpendicular to the direction of the crankshaft (10).

3. The engine of claim 2.

6. The idler driven gear (63) is disposed on the outer side of the engine than the primary drive gear (41) provided on the crankshaft (10), The balancer driven gear (72) is disposed outside the engine relative to the idler driven gear (63).

4. The engine of claim 3.

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