Power transmission device

Abstract

To provide a power transmission device capable of mitigating impact shock on a gear body.SOLUTION: A power transmission device 70 includes a shaft 40, a gear body 60, a rotary body 73 provided on the shaft 40 in an integrally rotatable manner, and an elastic member 90 provided between the gear body 60 and the rotary body 73, the gear body 60 having a plurality of gear side engagement parts 63 at spaces in an axial periphery direction C, the rotary body 73 having a plurality of rotation side engagement parts 78 at spaces in the axial periphery direction C, the elastic member 90 being provided between the gear side engagement part 63 and the rotation side engagement part 78 in the axial periphery direction C, and having a plurality of elastic body parts 91 capable of abutting on the gear side engagement part 63 and the rotation side engagement part 78 from the axial periphery direction, the plurality of elastic body parts 91 being of a plurality of types having different spring constants in the axial periphery direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This disclosure relates to a power transmission device.

Background Art

[0002] Patent Document 1 discloses an assembly structure of a balance shaft in which four stopper rubbers are arranged between a gear body and a rotating body. In the above assembly structure, the driven gear is provided with four collision protrusions at equal intervals in the circumferential direction of the balance shaft, and the damper cover is provided with four support protrusions at equal intervals in the shaft circumferential direction. The collision protrusions and the support protrusions are arranged alternately at equal intervals in the circumferential direction of the balance shaft. The stopper rubber is composed of eight elastic deformation parts (hereinafter referred to as elastic main body parts) of the same shape and four connecting parts connecting the ends of the respective elastic main body parts. The elastic main body parts of the stopper rubber are arranged at equal intervals between the collision protrusion parts and the support protrusion parts in the circumferential direction of the balance shaft. The elastic main body part of the stopper rubber is compressed by the collision with the collision protrusion and functions as a damper.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above assembly structure, the elastic main body parts of the same shape are arranged at the same interval. Due to the rotation of the crankshaft, vibration is applied to each stopper rubber. Here, when vibration of the same or nearly the same frequency as the spring constant of the elastic main body part is applied, the four stopper rubbers resonate simultaneously, and the input torque value to the gear body suddenly increases. There is a problem that the impact on the gear body increases due to the resonance of each stopper rubber, and a load is generated on the gear body. ​

[0005] This disclosure aims to provide a power transmission device capable of mitigating impact on the gear body. [Means for solving the problem]

[0006] A shaft that can rotate around an axis, A gear body is provided on the aforementioned shaft so as to be rotatable relative to it, and rotational force from the drive shaft is transmitted to it. A rotating body is provided on the aforementioned shaft so as to be rotatable integrally with it, A power transmission device comprising an elastic member provided between the gear body and the rotating body, which transmits the rotational force between the gear body and the rotating body, The gear body has a plurality of gear-side engaging portions spaced apart in the direction around the axis, The rotating body has a plurality of rotating engagement parts spaced apart in the direction of the axis, The elastic member is provided between the gear-side engaging portion and the rotation-side engaging portion in the axial direction, and has a plurality of elastic body portions that can contact the gear-side engaging portion and the rotation-side engaging portion from the axial direction. The aforementioned multiple elastic body parts are composed of multiple types having different spring constants in the direction of the axis, forming a power transmission device. [Effects of the Invention]

[0007] Each elastic body is composed of multiple types with different spring constants. This power transmission device can avoid resonance caused by the matching of the vibration frequency transmitted from the drive body with the natural frequencies of all the elastic body parts. As a result, the power transmission device can distribute the input torque among the multiple types of elastic body parts, thereby mitigating the impact on the gear body. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of an internal combustion engine including a power transmission device in this embodiment. [Figure 2] Figure 2 is a schematic diagram showing a cross-section of the end of the power transmission device in this embodiment. [Figure 3]Figure 3 is a cross-sectional view of the power transmission device in this embodiment, as seen from the axial direction of the first balance shaft. [Figure 4] Figure 4 is a vibration characteristic graph of the power transmission device in this embodiment. [Figure 5] Figure 5 is a cross-sectional view of the power transmission device in the comparative example, viewed from the axial direction of the first balance shaft. [Figure 6] Figure 6 shows the vibration characteristics graph of the power transmission device in the comparative example. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. The multiple elastic body parts are preferably made of rubber and composed of several types with different thicknesses in the axial direction. In this case, the elastic member can be made of a single rubber member, thus suppressing variations in the material properties of each elastic body part.

[0010] The multiple elastic body sections are preferably composed of a first elastic body section and a second elastic body section having a greater thickness in the axial direction than the first elastic body section. In this case, since only two types of elastic body sections with different thicknesses are needed, the number of parts does not increase unnecessarily.

[0011] The multiple gear-side engaging portions are preferably configured by arranging alternately in the axial direction a first gear-side engaging portion, positioned between a pair of first elastic body portions arranged in the axial direction, and a second gear-side engaging portion, positioned between a pair of second elastic body portions arranged in the axial direction. In this case, since the elastic body portions of the same shape are paired with the gear-side engaging portion in the axial direction, the impact between the rotating-side engaging portion and the gear-side engaging portion can be made the same. Furthermore, the power transmission device can maintain balance during rotation by having the first gear-side engaging portion, which is positioned between the first elastic body portions that are paired in the axial direction, and the second gear-side engaging portion, which is positioned between the second elastic body portions that are paired in the axial direction, arranged alternately.

[0012] The plurality of gear-side engagement portions may be arranged at equal intervals in the circumferential direction around the axis. In this case, the power transmission device does not need to change the arrangement of the gear-side engagement portions of the existing gear body, and has excellent versatility.

[0013] [Details of Embodiments of the Present Disclosure] Embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is shown by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

[0014] Preferred embodiments of the present disclosure are shown below. In the following description, regarding the front-rear direction, one axial end portion (the left side in FIG. 1) of the shaft 40 described later is defined as the front side.

[0015] [Example 1] As shown in FIG. 1, the power transmission device 70 of Example 1 of the present disclosure exemplifies a balancer device, and includes a housing 72, a shaft 40 (hereinafter also referred to as the first balance shaft 40), a rotating body 73 as a damper cover, an elastic member 90 as a stopper rubber, a gear body 60 as a driven gear, a friction damper 77, a first driven gear 61, and a balance weight 41.

[0016] As shown in FIGS. 1 and 2, the power transmission device 70 of Embodiment 1 is used in an internal combustion engine. The internal combustion engine is a four-cylinder reciprocating engine. When the crankshaft 10 (hereinafter also referred to as the drive shaft) rotates in conjunction with the reciprocating motion of the piston 25, the rotational force of the drive shaft 10 is transmitted to the first balance shaft 40 via the drive gear 20 and the gear body 60. The rotational force transmitted to the first balance shaft 40 is transmitted to the second balance shaft 50 via the first driven gear 61 and the second driven gear 64. Both the first balance shaft 40 and the second balance shaft 50 rotate at twice the speed of the drive shaft 10, and rotate at the same speed in opposite directions to each other. For this reason, the secondary inertial force of the reciprocating piston 25 is canceled out, and the vibrations generated between the first balance shaft 40 and the second balance shaft 50 are also canceled out.

[0017] The first balance shaft 40 of the power transmission device 70 is rotatably supported via a bearing (not shown) of the housing 72. As shown in FIG. 2, the first balance shaft 40 has a shaft main body portion 83 extending in the axial direction, and a flange portion 81 protruding radially outward at the front end portion of the shaft main body portion 83. The flange portion 81 constitutes the outer peripheral portion of the shaft main body portion 83 and is integrally connected to the shaft main body portion 83. The shaft main body portion 83 has an oil passage (not shown) extending in the axial direction at the center portion, and a branch passage (not shown) branching radially from the oil passage. The lubricating oil flowing through the oil passage is supplied to the bearing and the inner surface of the through hole of the gear body 60 via the branch passage.

[0018] A rotating body 73, an elastic member 90, a gear body 60, a friction damper 77, and a first driven gear 61 are attached to the first balance shaft 40. The elastic member 90 is disposed between the rotating body 73 and the gear body 60. The gear body 60 meshes with the drive gear 20, and the housing 72 is attached to a cylinder block (not shown).

[0019] As shown in Figures 1 and 2, the first driven gear 61 is mounted on the rear side of the gear body 60 of the shaft 40. The first driven gear 61 is disc-shaped with a through hole in the center and has a helical gear-shaped first driven gear portion 66 on its outermost circumference. The first driven gear 61 is mounted on the shaft 40 by passing through the through hole of the first driven gear 61. The second driven gear 64 is disc-shaped with a through hole in the center, similar to the first driven gear 61, and has a helical gear-shaped second driven gear portion 67 on its outermost circumference. The pair of balance shafts (40, 50) rotate with the first driven gear 61 and the second driven gear 64 meshed with each other.

[0020] The gear body 60 has helical gear-shaped gear teeth 62 on its outer circumference, and at least the outer circumference portion having the gear teeth 62 is made of resin. The gear body 60 is mounted so as to be rotatable relative to the first balance shaft 40. The gear body 60 has a plurality of rectangular parallelepiped-shaped gear-side engaging portions 63 extending from the front to the front. The gear-side engaging portions 63 have a collision surface 65 that collides with the elastic body portion 91, which will be described later, in the direction around the axis of the first balance shaft 40 (hereinafter simply referred to as the direction around the axis C). Four gear-side engaging portions 63 are arranged at equal intervals in the direction around the axis C. That is, as shown in Figure 3, four gear-side engaging portions 63 are provided at 90-degree intervals. Hereinafter, of the pairs of gear-side engaging portions 63 that face each other radially, the pair of gear-side engaging portions that face each other vertically in Figure 3 will be referred to as the first gear-side engaging portion 63a, and the pair of gear-side engaging portions that face each other horizontally in Figure 3 will be referred to as the second gear-side engaging portion 63b. The gear body 60 houses a friction damper 77. The friction damper 77 is an annular elastic body that generates friction between the shaft 40 and the gear body 60, suppressing the movement of the shaft 40.

[0021] The rotating body 73 has a disc-shaped end wall 75 and a circumferential wall 76 extending from the outer peripheral edge of the end wall 75 toward the rear end. As shown in Figure 3, the end wall 75 has a through hole in the center and eight engagement holes 74 spaced apart in the axial direction C. The rotating body 73 is fixed to the front end of the shaft 40, with the shaft 40 passing through the through hole. The rotating body 73 rotates together with the rotation of the shaft 40.

[0022] The rotating body 73 houses four elastic members 90 inside. Each elastic member 90 has a projection 94 that protrudes forward. The elastic members 90 are fixed to the rotating body 73 with the projections 94 inserted into the engagement holes 74.

[0023] The rotating body 73 has a plurality of rotating engagement portions 78 that protrude radially inward from the circumferential wall 76 behind the end wall 75. Each rotating engagement portion 78 is located at four positions within the rotating body 73, spaced apart in the axial direction C. Each rotating engagement portion 78 is composed of a pair of radially opposing first rotating engagement portions 78a and second rotating engagement portions 78b.

[0024] In Figure 3, the distance between the first rotational engagement portion 78a and the second rotational engagement portion 78b adjacent in the axial direction C on the upper and lower sides is smaller than the distance between the first rotational engagement portion 78a and the second rotational engagement portion 78b adjacent in the axial direction C on both the left and right sides of Figure 3. In other words, the space between the first rotational engagement portion 78a and the second rotational engagement portion 78b is composed of multiple wide and narrow spacings in the axial direction C.

[0025] As shown in Figure 3, the power transmission device 70 is divided by a line A1 connecting the centers of a pair of first rotation-side engaging parts 78a and a line B1 connecting the centers of a pair of second rotation-side engaging parts 78b. As will be described in detail later, a high spring constant region E1 with a narrow spacing is formed on both the upper and lower sides of Figure 3, and a low spring constant region E2 with a wider spacing is formed on both the left and right sides of Figure 3. In the case of Embodiment 1, the ratio of the thickness of the low spring constant region E2 in the axial direction C to the thickness of the high spring constant region E1 in the axial direction C is set to approximately 1:2.

[0026] The elastic members 90 mitigate the impact of vibration torque input from the drive gear 20. The elastic members 90 are made of a single rubber composition, and in Example 1, four identical members are provided. Each elastic member 90 comprises a pair of elastic body parts 91 and a connecting part 92. As shown in Figure 3, each pair of elastic body parts 91 is approximately rectangular in cross-section, arranged opposite each other in the axial direction C, and connected on the inner circumference by the connecting part 92. The pair of elastic body portions 91 consist of a first elastic body portion 91a with a smaller thickness in the axial direction C, and a second elastic body portion 91b with a greater thickness than the first elastic body portion 91a in the axial direction C. Both ends of each elastic body portion 91 on the circumferential wall 76 side are chamfered to be rounded. The elastic body portion 91 has thickness in the axial direction C and in the front-rear direction. The thickness of the first elastic body portion 91a and the second elastic body portion 91b in the front-rear direction is the same. In the first embodiment, the ratio of the thickness of the second elastic body portion 91b to the thickness of the first elastic body portion 91a in the axial direction C is 1:2. The spring constant of the first elastic body portion 91a is lower than the spring constant of the second elastic body portion 91b. Each elastic member 90 is positioned between the gear-side engaging portions 63 in the axial direction C. The connecting portion 92 of each elastic member 90 is positioned radially inward of the rotation-side engaging portion 78.

[0027] As shown in Figure 3, a pair of first elastic body portions 91a are arranged on both sides of the first gear-side engaging portion 63a in the axial direction C. A pair of second elastic body portions 91b are arranged on both sides of the second gear-side engaging portion 63b in the axial direction C. In other words, the gear-side engaging portion 63 is composed of a first gear-side engaging portion 63a positioned to be sandwiched between a pair of first elastic body portions 91a in the axial direction C, and a second gear-side engaging portion 63b positioned to be sandwiched between a pair of second elastic body portions 91b in the axial direction C, arranged alternately in the axial direction C.

[0028] As described above, the power transmission device 70 of Embodiment 1 is configured with high spring constant region E1 and low spring constant region E2 arranged alternately in the axial direction C. A pair of first elastic body portions 91a are arranged in the high spring constant region E1, and a pair of second elastic body portions 91b are arranged in the low spring constant region E2. The elastic member 90 is fixed to the rotating body 73 by fitting the rotating side engaging portion 78 into a recess formed between the pair of elastic body portions 91 and on the radially outer side of the connecting portion 92. In other words, the pair of elastic body portions 91 are supported by being sandwiched in the axial direction C between a pair of support surfaces 93, which are the end faces of the rotating side engaging portion 78 in the axial direction C.

[0029] The pair of first elastic body portions 91a, positioned on both sides of the first gear-side engaging portion 63a in the axial direction C, consist of an acceleration-side elastic body portion 91c located on the side that collides with the collision surface 65 of the first gear-side engaging portion 63a when the gear body 60 accelerates due to the rotation of the drive gear 20, and a deceleration-side elastic body portion 91d located on the side that collides with the collision surface 65 of the gear-side engaging portion 63 when decelerating. A gap is formed between the first gear-side engaging portion 63a and the first elastic body portions 91a.

[0030] Similarly, the pair of second elastic body portions 91b, which are arranged on both sides of the second gear-side engaging portion 63b in the axial direction C, consist of an acceleration-side elastic body portion 91c, which is located on the side that collides with the collision surface 65 of the second gear-side engaging portion 63b when the gear body 60 accelerates due to the rotation of the drive gear 20, and a deceleration-side elastic body portion 91d, which is located on the side that collides with the collision surface 65 of the gear-side engaging portion 63 when decelerating. A gap is formed between the second gear-side engaging portion 63b and the second elastic body portions 91b.

[0031] Next, the operation of the internal combustion engine will be explained. When the internal combustion engine accelerates, the rotational speed of the drive gear 20 on the drive shaft 10 increases, and the gear body 60 that meshes with the drive gear 20 rotates in a driven motion. At this time, the gear body 60 rotates freely while being damped by the friction damper 77 until the collision surface 65 of its gear-side engaging portion 63 collides with the acceleration-side elastic body portion 91c housed in the rotating body 73. Then, with the collision surface 65 in a state of collision with the acceleration-side elastic body portion 91c, the shaft 40 rotates due to the gear body 60, and the second balance shaft 50 rotates in a driven motion via the first driven gear 61 and the second driven gear 64.

[0032] On the other hand, when the internal combustion engine decelerates, the rotational speed of the drive gear 20 on the drive shaft 10 and the rotational speed of the gear body 60 that meshes with the drive gear 20 decrease, while the pair of balance shafts (40, 50) continue to rotate at their pre-deceleration rotational speed due to inertia. At this time, the pair of balance shafts (40, 50) spin freely until the deceleration-side elastic body portion 91d housed in the rotating body 73 collides with the collision surface 65 of the gear-side engaging portion 63. Then, with the deceleration-side elastic body portion 91d in contact with the collision surface 65, the rotational speed of the pair of balance shafts (40, 50) decreases, and thereafter, the pair of balance shafts (40, 50) rotate in accordance with the rotation of the drive gear 20 and the gear body 60.

[0033] In the power transmission device 70 of Embodiment 1, the first gear-side engaging portion 63a is positioned to sandwich a pair of first elastic body portions 91a. The pair of first elastic body portions 91a deform alternately in response to acceleration and deceleration. Since the pair of elastic body portions 91 have the same thickness in the axial direction C, the impact caused by the collision between the first elastic body portions 91a and the collision surface 65 during acceleration and deceleration of the internal combustion engine can be kept constant.

[0034] Similarly, the second gear-side engaging portion 63b of the power transmission device 70 of Embodiment 1 is positioned to sandwich a pair of second elastic body portions 91b. The pair of second elastic body portions 91b deform alternately with acceleration and deceleration. Since the pair of second elastic body portions 91b have the same thickness in the axial direction C, the impact caused by the collision between the second elastic body portions 91b and the collision surface 65 during acceleration and deceleration of the internal combustion engine can be kept constant.

[0035] The elastic member 90 absorbs the input torque from the drive gear 20 during the collision described above. However, the elastic member 90 resonates with other members of the same spring constant range at specific frequencies. Resonance is a phenomenon in which an object (the elastic main body) vibrates significantly when it receives an external frequency that is the same as or close to the spring constant (natural frequency) of the object.

[0036] As shown in Figure 3, the power transmission device 70 housed in the rotating body 73 alternately arranges a low spring constant region E2, where a pair of second elastic body parts 91b and second gear-side engaging parts 63b are located, and a high spring constant region E1, where a pair of first elastic body parts 91a and first gear-side engaging parts 63a are located, in the axial direction C. As shown in Figure 4, the frequency characteristics of the power transmission device 70 resulting from the collision between the elastic body part 91 and the collision surface 65 can be divided into two types: one originating from the high spring constant region E1 (dashed line indicated by arrow H in Figure 4) and one originating from the low spring constant region E2 (dotted line indicated by arrow L in Figure 4). Since the spring constants of the high spring constant region E1 and the low spring constant region E2 are different, the two types of frequency characteristics do not coincide. Therefore, the peak of the input torque in the combined frequency characteristics of the two types (solid line indicated by arrow HL in Figure 4) becomes smaller.

[0037] Figure 5 is a cross-sectional view of the comparative example power transmission device 70. The difference from the power transmission device 70 of this embodiment is that the comparative example power transmission device 70 has the same thickness in the axial direction C of each elastic body portion 111. The comparative example power transmission device 70 has the same spring constant in the region E3 to E6 formed by lines A2 and B2 connecting the centers of a pair of radially opposing rotating side engaging portions 113. Because the comparative example power transmission device 70 has the same spring constant in E3 to E6, when it receives vibrations of a specific frequency from the drive gear 20, E3 to E6 resonate simultaneously. Therefore, as shown in Figure 6, the peak input torque of the frequency characteristics of the comparative example power transmission device 70 is larger than the peak input torque of the frequency characteristics of the combined power transmission device 70 of Example 1 shown in Figure 4.

[0038] As described above, in the case of Embodiment 1, the power transmission device 70 is provided with a high spring constant region E1 and a low spring constant region E2, and the high spring constant region E1 and the low spring constant region E2 have different spring constants. Therefore, the timing at which the peak of the input torque occurs can be staggered in the high spring constant region E1 and the low spring constant region E2, and simultaneous resonance of the high spring constant region E1 and the low spring constant region E2 can be avoided. Thus, according to Embodiment 1, the input torque can be distributed between the high spring constant region E1 (the region having the first elastic body part 91a) and the low spring constant region E2 (the region having the second elastic body part 91b), so that the impact on the gear body 60 can be mitigated.

[0039] [Other embodiments of this disclosure] This disclosure is not limited to these examples and includes all modifications within the meaning and scope of the claims, as shown in the claims. (1) The power transmission device 70 of this embodiment is composed of multiple types with different thicknesses in the direction C around the axis. The power transmission device 70 may use, for example, four types of elastic members 90 with different compound compositions. (2) The multiple elastic body portions 91 in this embodiment are composed of a first elastic body portion 91a and a second elastic body portion 91b having a greater thickness in the axial direction C than the first elastic body portion 91a. In contrast, the elastic member may also use a third elastic body portion having a thickness in the axial direction C that is smaller than the first elastic body portion and smaller than the second elastic body portion. (3) The elastic body portion 91 of the embodiment is configured by arranging a high spring constant region E1 consisting of a first elastic body portion 91a and a low spring constant region E2 consisting of a second elastic body portion 91b alternately in the direction C around the axis. In contrast, the power transmission device may be configured, for example, by arranging the high spring constant region E1 and the low spring constant region E2 continuously in the direction around the axis. (4) In the embodiment, the thickness of the first elastic body portion 91a arranged on both sides in the axial direction C with respect to the first gear-side engaging portion 63a is the same, and the thickness of the second elastic body portion 91b arranged on both sides in the axial direction C with respect to the second gear-side engaging portion 63b is the same. In contrast, the thickness of the first elastic body portion 91a arranged on both sides in the axial direction C with respect to the first gear-side engaging portion 63a may be different, and the thickness of the second elastic body portion 91b arranged on both sides in the axial direction C with respect to the second gear-side engaging portion 63b may be different. (5) In the embodiment, the thickness of the first gear-side engaging portion 63a and the second gear-side engaging portion 63b in the axial direction C was the same. In contrast, the thickness of the first gear-side engaging portion 63a and the second gear-side engaging portion 63b in the axial direction C may be different. (6) In the embodiment, the ratio of the thickness of the second elastic body portion 91b to the thickness of the first elastic body portion 91a in the axial direction C is 1:2. In contrast, the ratio of the thickness of the second elastic body portion 91b to the thickness of the first elastic body portion 91a in the axial direction C is arbitrary, but from the viewpoint of rotational balance and mitigating impact on the gear body, it is preferably 1:3 to 2:3. (7) The power transmission device 70 of the embodiment is equipped with four elastic members 90. There is no limit to the number of rotating bodies 73 used. Preferably, 2 to 8 rotating bodies are used. (8) The power transmission device 70 of the embodiment is equipped with four rotating engagement parts 78. There is no limit to the number of rotating engagement parts. The number of rotating engagement parts is preferably 2 to 8. (9) The power transmission device 70 of the embodiment is equipped with four gear-side engaging parts. There is no limit to the number of gear-side engaging parts. The number of gear-side engaging parts is preferably 2 to 8. (10) In the power transmission device 70 of the embodiment, four regions are formed by a line A1 connecting the centers of a pair of radially opposing first rotation-side engaging portions 78a and a line B1 connecting the centers of a pair of radially opposing second rotation-side engaging portions 78b. There is no limit to the number of regions that can be formed. Preferably, 2 to 8 regions can be formed. (11) The elastic member 90 of the embodiment comprises a pair of elastic main bodies 91 and a connecting portion 92. The elastic member may also comprise three elastic main bodies and two connecting portions that connect the ends of each elastic main body. Alternatively, the connecting portions that connect each elastic main body from the elastic member may be omitted, and the elastic member may consist only of a plurality of elastic main bodies. (12) In the power transmission device 70 of the embodiment, the gear-side engaging portions are arranged at equal intervals in the axial direction C, and the spacing between each rotating-side engaging portion 78 is made different in the axial direction C, thereby forming regions E1 and E2. The power transmission device may also be arranged with the rotating-side engaging portions at equal intervals in the axial direction, and the spacing between each gear-side engaging portion is made different in the axial direction C, thereby forming regions E1 and E2. (13) The power transmission device 70 of the embodiment has a gap between the rotating engagement portion 78 and the elastic body portion 91, and during engine acceleration and deceleration, the acceleration or deceleration side elastic body portions 91c and 91d housed in the rotating body 73 rotate freely until they collide with the collision surface 65 of the gear side engagement portion 63. The power transmission device 70 does not necessarily have to be configured to have a gap between the rotating engagement portion 78 and the elastic body portion 91. (14) The internal combustion engine in the embodiment is a four-cylinder reciprocating engine. The internal combustion engine may also be a diesel engine, and there is no restriction on the number of cylinders. (15) The present disclosure is not limited to the balancer devices of the embodiments, but is broadly applicable to internal combustion engines equipped with power transmission devices. [Explanation of Symbols]

[0040] 40... Shaft (First Balance Shaft) 60... Gear body 63...Gear-side engagement part 63a...Engaging part on the first gear side 63b...Engaging part on the second gear side 70... Power transmission device 73…Rotational body 78 (78a, 78b) ... Rotating side engagement part 90... Stopper rubber (elastic material) 91...Elastic main body 91a...First elastic body section 91b...Second elastic main body E1... High spring constant region E2... Low spring constant region

Claims

1. A shaft that can rotate around an axis, A gear body is provided on the aforementioned shaft so as to be rotatable relative to it, and rotational force from the drive shaft is transmitted to it. A rotating body is provided on the aforementioned shaft so as to be rotatable integrally with it, A power transmission device comprising an elastic member provided between the gear body and the rotating body, which transmits the rotational force between the gear body and the rotating body, The gear body has a plurality of gear-side engaging portions spaced apart in the direction around the axis, The rotating body has a plurality of rotating engagement parts spaced apart in the direction of the axis, The elastic member is provided between the gear-side engaging portion and the rotation-side engaging portion in the axial direction, and has a plurality of elastic body portions that can contact the gear-side engaging portion and the rotation-side engaging portion from the axial direction. The aforementioned plurality of elastic body parts are made of rubber and consist of a first elastic body part and a second elastic body part, each having different spring constants in the axial direction. The second elastic body portion has a greater thickness in the axial direction than the first elastic body portion. A power transmission device comprising a plurality of gear-side engaging portions, each consisting of a first gear-side engaging portion positioned between a pair of first elastic body portions arranged in the axial direction, and a second gear-side engaging portion positioned between a pair of second elastic body portions arranged in the axial direction, arranged alternately in the axial direction.

2. The power transmission device according to claim 1, wherein the plurality of gear-side engaging portions are arranged at equal intervals in the direction around the axis.

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