JP2003176865A - Low noise gear mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low noise gear structure capable of certainly reducing a noise accompanied with an engagement of a gear by previously preventing an inadequate increase in an inertia mass of the gear and sufficiently exhibiting an inhibition action of a tooth-beating noise. <P>SOLUTION: An annular liquid chamber 11 is formed on an idler gear 3 engaged with a driven gear of a fuel injection pump and an oil is fed into the liquid chamber 11. The oil is stored at an outer periphery side in the liquid chamber 11 by a centrifugal force at the time of rotation of the gear. When a transmission torque between the gears is varied according to a fuel injection, a rapid variation of a rotation speed of the idler gear 3 is prevented utilizing a shearing resistance of the stored oil. Thereby, the tooth-beating noise is inhibited. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear structure that suppresses a rattling noise generated during rotation transmission through a gear to reduce noise.

[0002]

[Related Background Art] Transmission of rotation through gears is widely implemented in various fields such as machine tools and internal combustion engines.
When the transmission torque fluctuates, there is a problem that the tooth flanks collide with each other due to backlash between the gears to generate a tooth tap noise, which causes a noise increase. As a measure for suppressing the rattling noise, for example, the technique described in Japanese Utility Model Publication No. 6-32818 has been proposed. In this technique, an oil passage is formed radially from the center of the gear toward each tooth bottom on the outer peripheral side, and the oil supplied from the rotating shaft is jetted from the tooth bottom through the oil passage, which results in a rattling noise. We are trying to control it.

In addition, as another measure, the actual Kaihei 4-9354 is used.
In the technique described in Japanese Patent Publication No. 3, the annular weight is slidably fitted in the inner circumference of the rim of the gear in the circumferential direction, and the annular weight is covered with a cover to fill the viscous fluid inside. This technology functions as a so-called viscous damper, and friction resistance between the annular weight and the inner circumference of the rim when the annular weight is displaced in the circumferential direction due to the rotational fluctuation of the gear, and the annular weight sheared the viscous fluid. The shear resistance at this time is utilized to damp the rotation fluctuation of the gear, thereby suppressing the rattling noise.

[0004]

However, the former technique is merely a measure for reliably supplying the oil to the tooth surface of the gear. Therefore, the effect of suppressing the rattling noise beyond the lubrication of the tooth surface by the supplied oil cannot be obtained, and sufficient noise reduction cannot be expected. Further, in the latter technique, in order to obtain the function as the above-mentioned viscous damper, it is necessary to give a sufficient inertial mass to the annular weight, and as a result, the inertial mass of the gear itself unduly increases, and the device to which this gear is applied is increased. Another problem has arisen that interferes with the operation of the.

An object of the present invention is to prevent unduly an increase in the inertial mass of the gear and to sufficiently exert the effect of suppressing the rattling noise, thereby reliably reducing the noise associated with the gear meshing. It is to provide a low-noise gear structure that can perform.

[0006]

In order to achieve the above-mentioned object, in the invention of claim 1, the rim is connected via a disc-shaped web centering on a hub supported by a rotating shaft, and the rim is connected to the outer peripheral surface of the rim. A gear in which the formed tooth portion is meshed with a counterpart gear, a cover body that is disposed on one side surface of the gear and forms a fluid chamber between the side surface of the gear, and a viscous fluid is supplied into the fluid chamber. And a fluid supply means.

If the gear meshes with the counterpart gear to transmit the driving force to the counterpart gear, or conversely, the driving force is transmitted from the counterpart gear, and if the transmission torque at this time fluctuates, both The backlash between the gears causes the tooth flanks to collide with each other and generate a rattling noise. On the other hand, a fluid chamber is formed between the side surface of the gear having the disk-shaped web and the cover body, and the viscous fluid is supplied to the fluid chamber from the fluid supply means, and the supplied viscous fluid is applied to the rotation of the gear. Accumulated centrifugal force causes the fluid to stay on the outer peripheral side in the fluid chamber.

When the rotational speed of the gear suddenly changes due to the fluctuation of the transmission torque, shear resistance is generated between the viscous fluid staying in the fluid chamber and the outer periphery of the fluid chamber, and a damping action that prevents the sudden change in rotational speed. As a result, the collision of the tooth surfaces is alleviated. On the other hand, the shear resistance of the viscous fluid is used to mitigate the collision of the tooth surfaces, and since heavy objects such as weights are not used to mitigate the collision, it is possible to carry out without increasing the inertial mass of the gear. It is possible.

According to the second aspect of the present invention, the rim is connected through a web having a through hole centering on the hub supported by the rotary shaft, and the tooth portion formed on the outer peripheral surface of the rim is meshed with the mating gear. And a pair of cover bodies that are respectively disposed on both side surfaces of the gear and that form a pair of fluid chambers that communicate with each other through the through holes of the web between the both sides of the gear and the respective fluid chambers. And a fluid supply means for respectively supplying a viscous fluid.

Therefore, a pair of fluid chambers communicating with each other through the through holes of the web are formed between the both side surfaces of the gear and the cover body, and these fluid chambers are defined by the unit of claim 1. The same action as one fluid chamber is exhibited. Therefore,
As described in claim 1, when the transmission torque between the gears fluctuates, the collision of the tooth surfaces is mitigated by utilizing the shear resistance of the viscous fluid, and it can be performed without increasing the inertial mass of the gear. Become.

As a preferred mode, it is desirable that the fluid supply means is configured to supply the viscous fluid supplied from the rotating shaft into the fluid chamber through the supply passage formed in the hub. In this case, the viscous fluid supplied from the rotating shaft is supplied into the fluid chamber through the supply path of the hub and stays on the outer peripheral side of the fluid chamber. As another preferable aspect, it is desirable that the fluid supply unit is configured to supply the viscous fluid ejected from the ejection nozzles facing each other into the fluid chamber via the supply port formed in the cover body. . In this case, the viscous fluid ejected from the ejection nozzle is supplied into the fluid chamber through the supply port of the cover body and stays on the outer peripheral side of the fluid chamber.

According to the third aspect of the present invention, the gear is provided with a discharge passage for communicating the fluid chamber with one side of the tooth portion of the gear. Therefore, when the transmission torque between both gears fluctuates, the viscous fluid discharged from the discharge path adheres to the tooth surface, and the viscous resistance also reduces the collision of the tooth surfaces, resulting in suppression of the rattling noise. It According to the invention of claim 4, the gear transmits rotation with the counterpart gear with periodic torque fluctuation, and the discharge path is formed at the position of the tooth portion that meshes with the counterpart gear when the torque varies. It was done.

Therefore, when the transmission torque between the two gears fluctuates, the gear discharge path has reached the meshing position with the mating gear, so that the collision of the tooth surfaces in the viscous fluid discharged from the discharge path. Therefore, the collision mitigation due to the viscous resistance is more reliably exhibited. In a preferred embodiment, the counterpart gear is supported by an input shaft of a fuel injection pump that pressure-feeds fuel to a plurality of cylinders of an internal combustion engine, and a discharge passage of the gear is generated along with fuel injection into each cylinder. It is desirable to form at the position of the tooth portion that meshes with the counterpart gear when the driving torque of the fuel injection pump changes. Therefore, at the time of fuel injection of each cylinder, the discharge passage of the gear reaches the meshing position with the counterpart gear, and the collision of the tooth surface is surely alleviated in the viscous fluid. The sound is suppressed.

In another preferred embodiment, the mating gear is supported by a cam shaft that opens and closes an intake valve or an exhaust valve of an internal combustion engine, and an exhaust passage of the gear is opened and closed by an intake valve or an exhaust valve. It is desirable to form it at the position of the tooth portion that meshes with the mating gear when the driving torque of the cam shaft changes due to driving. Therefore, when the intake valve or the exhaust valve is driven to open or close, the discharge path of the gear reaches the meshing position with the mating gear, and the collision of the tooth surface is reliably alleviated in the viscous fluid, so that the intake valve or the exhaust valve is opened or closed. The rattling noise caused by driving is suppressed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment in which the present invention is applied to an idler gear for driving a fuel injection pump of a diesel internal combustion engine will be described below.
The present embodiment corresponds to the invention of claims 1, 3, and 4.

FIG. 1 is a sectional view showing the low noise gear structure of this embodiment, and FIG. 2 is a sectional view taken along line II-II of FIG. 1 showing the idler gear. The internal combustion engine is configured as a 4-cycle 4-cylinder diesel engine, and the front surface of the cylinder block 1 is shown in FIG. A base end of a rotary shaft 2 is fitted and fixed in a prepared hole 1a formed in the front surface of the cylinder block 1, and an idler gear 3 (gear) is fitted in the rotary shaft 2. The idler gear 3 is restricted from moving in the axial direction by a restricting step portion 2a formed on the base end side of the rotating shaft 2 and a restricting plate 4 fixed to the tip end side of the rotating shaft 2 so that the idler gear 3 is centered on the rotating shaft 2. As it can rotate.

The idler gear 3 is located between the hub 5 on the center side fitted into the rotary shaft 2, an annular rim 6 arranged on the outer peripheral side of the hub 5, and between the hub 5 and the rim 6. It is composed of a disk-shaped web 7 that connects both members, and these hub 5, rim 6, and web 7 are integrally formed by, for example, forging. The web 7 is located on the side opposite to the engine with respect to the hub 5 and the rim 6 (hereinafter, the left side in FIG. 1 will be referred to as the engine side, and the right side will be described as the opposite engine side).
The side surface of the idler gear 3 on the engine side is annularly recessed.

A tooth portion 6a formed on the outer peripheral surface of the rim 6
Meshes with a drive gear (not shown) fixed to the crankshaft of the internal combustion engine at the lower position, and meshes with a driven gear 8 (mating gear) fixed to the input shaft of the fuel injection pump at the upper position. . The gear ratio between the driving gear and the driven gear 8 is set to 1: 2, and during operation of the internal combustion engine, the fuel injection pump is rotationally driven at a half speed via the idler gear 3 as the crankshaft rotates. . Therefore, the input shaft of the fuel injection pump makes one rotation while the crankshaft makes two revolutions to complete the combustion of each cylinder, and the input shaft has 90 ° of rotation.
Every time one of the cylinders reaches the compression top dead center, high-pressure fuel is pressure-fed to the cylinder by the fuel injection pump.

On the other hand, on the side surface of the idler gear 3 on the engine side, a disk-shaped cover body 9 corresponding to the web 7 is provided. The cover body 9 is positioned by the step formed on the hub 5 and the rim 6, and the idler gear 3 is attached by the snap ring 10 mounted on the hub 5 side.
It is fixed to. As a result, between the idler gear 3 and the cover body 9, an annular fluid chamber 1 centered on the rotating shaft 2 is provided.
1 is formed.

As shown in FIG. 2, the cover body 9 is formed with four substantially square supply ports 9a at 90 ° intervals around the rotary shaft 2, and the above-mentioned fluid is supplied through these supply ports 9a. The inside of the chamber 11 is open toward the engine side. The number and arrangement of the supply ports 9a are not limited to this, and can be arbitrarily changed. On the other hand, on the front surface of the cylinder block 1, jet nozzles 12 are arranged so as to face the cover body 9, and the jet nozzles 12 sequentially face the supply ports 9a as the idler gear 3 rotates. The jet nozzle 12 communicates with an oil passage 13 for lubricating the bearings of the internal combustion engine, and while the engine is operating, it is constantly supplied with oil from the oil passage 13 and jets oil. It is supplied into the fluid chamber 11 through each supply port 9a (fluid supply means).

As shown in FIG. 2, the rim 6 of the idler gear 3 is provided with three discharge oil passages 14 (discharge passages) at four locations at 90 ° intervals, as shown in the detailed view of FIG. Moreover, the fluid chamber 11 on the inner peripheral side of the rim 6 and the tooth bottom of the tooth portion 6a on the outer peripheral side communicate with each other by these discharge oil passages 14. The number of teeth of the idler gear 3 is set to be the same as the number of teeth of the driven gear 8 on the fuel injection pump side, and the positions of the four discharge oil passages 14 are the same as those of the driven gear 8 during fuel injection (shown in FIG. 2). It is set to the meshing position. Therefore, one of the discharge oil passages 14 reaches the meshing position of the gears 3 and 8 each time fuel is injected.

Here, the oil in the fluid chamber 11 is discharged from the discharge oil passages 14 to the outer peripheral side by the centrifugal force caused by the rotation of the idler gear 3. At this time, the oil is discharged.
The total cross-sectional area of each discharge oil passage 14 is set in consideration of the amount of oil supplied from the jet nozzle 12 to the fluid chamber 11 so that the oil is appropriately retained therein. The rotary shaft 2
A first supply oil passage 15 in the axial direction and a second supply oil passage 16 orthogonal to each other are formed in the axial direction, and the oil in the oil passage 13 is
The sliding portion of the idler gear 3 is lubricated by being guided to the outer periphery of the rotary shaft 2 through the prepared hole 1a and these oil supply passages 15 and 16.

Next, the operation of the low noise gear structure configured as described above will be described. During operation of the internal combustion engine, the fuel injection pump is rotationally driven via the idler gear 3 in accordance with the rotation of the crankshaft, and the fuel pumped from the fuel injection pump injects fuel in the vicinity of the compression top dead center of each cylinder. . On the other hand, the oil from the oil passage 13 is ejected from the ejection nozzle 12 and is supplied into the fluid chamber 11 via each supply port 9a of the cover body 9. The supplied oil stays on the outer peripheral side in the fluid chamber 11 as shown in FIG. 2 due to the centrifugal force associated with the rotation of the idler gear 3, and is sequentially discharged to the outer peripheral side through the respective discharge oil passages 14.

The driving load of the fuel injection pump is not constant, and has a characteristic of rapidly increasing at the moment of pumping fuel. Therefore, the torque transmitted from the idler gear 3 to the driven gear 8 fluctuates each time fuel is injected, and the tooth flanks collide with each other due to backlash between the gears 3 and 8 to generate a rattling noise. Here, the oil staying in the fluid chamber 11 can be stored in the fluid chamber 1 when the rotation speed of the idler gear 3 suddenly changes due to the transmission torque variation.
A shearing resistance is generated between the inner circumference and the outer circumference, and a damping action that prevents a sudden change in the rotation speed is achieved. Therefore, the collision of the tooth surfaces is mitigated, and the rattling noise is significantly suppressed.

Further, when fuel is injected into each cylinder, one of the discharge oil passages 14 of the idler gear 3 has reached the meshing position with the driven gear 8, so that the collision of the tooth surfaces is discharged from the discharge oil passage 14. Will be done in oil. Unlike the case where the oil is jetted over the entire circumference of the gear as in the prior art described in Japanese Utility Model Laid-Open No. 6-32818, the oil is jetted intensively at the meshing point, and therefore the tooth surface Will collide in sufficient oil, and the collision of the tooth surface will be alleviated not only by the shear resistance but also by the viscous resistance of the oil. As a result, the rattling noise is further suppressed, and the noise accompanying the meshing of the gears 3 and 8 can be reliably reduced.

Moreover, the above noise reducing action is achieved by the gear 3,
Can be obtained regardless of the magnitude of the transmission torque between the gears 8, and for example, in a driving state where the transmission torque is high (the driving load of the fuel injection pump is large), such as a scissors gear that suppresses the rattling noise by the spring force, the spring force is high. There is no problem such as noise being insufficient and noise cannot be reduced, and sufficient effects can be obtained in all operating regions.

FIG. 4 shows the damping state of the vibration generated in the idler gear 3 due to the fuel injection. In this embodiment, the vibration amplitude W at the time of fuel injection is small and the vibration is small in comparison with the prior art. It can be seen that the time T required for the damping is short, and the rattling noise correlated with this vibration can be sufficiently suppressed. Needless to say, this noise reduction effect is exhibited both inside and outside the vehicle.

Further, by reducing the noise as described above, another advantage that the high pressure of the fuel injection pump can be realized can be obtained. That is, there has recently been a demand for a high pressure for the purpose of reducing emissions, but the load fluctuation of the fuel injection pump increases, which limits the noise. Here, if the rattling noise can be suppressed by the above-described action, it is possible to realize high pressure while maintaining low noise.

On the other hand, as is clear from the above description, the oil supplied from the jet nozzle 12 is temporarily retained in the fluid chamber 11 and the shear resistance thereof is utilized for mitigating the collision of the tooth surface, and then the discharged oil is discharged. It is discharged from the passage 14 and its viscous resistance is used for cushioning the collision of the tooth surfaces. The configuration is such that the cover body 9 is fixed to the idler gear 3 and the supply oil passages 15, 1
6, 22 and the discharge oil passage 14 are simply formed, and the existing idler gear can be easily modified by changing the specifications. Moreover, since the annular weight, which is a heavy load, is not used unlike the conventional technique described in Japanese Utility Model Laid-Open No. 4-93543, the inertial mass of the idler gear 3 is almost the same as that of a general gear. Therefore, it is possible to prevent adverse effects when the inertial mass of the idler gear 3 is increased, for example, adverse effects such as deterioration of the rotational response of the internal combustion engine.

[Second Embodiment] Next, a second embodiment in which the present invention is embodied in another idler gear will be described. The present embodiment corresponds to the invention of claims 2 to 4. The low noise gear structure of the present embodiment is different from that of the first embodiment in the oil supply method and the configuration of the fluid chamber 11, and the support structure of the idler gear 3 with respect to the rotating shaft 2 and each gear. The relationship of the number of teeth, etc. is the same as in the first embodiment. Therefore, the description of the common parts will be omitted, and the differences will be mainly described.

FIG. 5 is a sectional view showing the low noise gear structure of this embodiment, and FIG. 6 is a sectional view taken along line VI-VI of FIG. 5 showing the idler gear with the cover body removed. In this embodiment,
The web 7 of the idler gear 3 is in the shape of a spoke having a through hole 7a, and is located at the center of the hub 5 and the rim 6 in the axial direction of the rotary shaft 2, and the cover bodies 9 are provided on both side surfaces of the idler gear 3, respectively. It is mounted by the same structure as the first embodiment. It should be noted that the supply port 9a described in the first embodiment is omitted in the cover body 9, and the jet nozzle 12 on the engine side is also omitted.

With these cover bodies 9, the idler gear 3
The fluid chambers 11 are formed on both sides of the
1 communicate with each other through the through holes 7a of the spoke-shaped web 7 to form a single fluid chamber. Further, the discharge oil passages 14 are individually formed corresponding to the fluid chambers 11, and the positions of the discharge oil passages 14 are the same as in the first embodiment.
It is set to a position where it meshes with the driven gear 8 during fuel injection.

On the other hand, two second supply oil passages 16 are formed on the rotary shaft 2 together with the first supply oil passage 15, and each second supply oil passage 16 is open to the outer periphery of the rotary shaft 2. Each second
Two oil grooves 21 are formed in the circumferential direction on the inner periphery of the hub 5 of the idler gear 3 so as to correspond to the opening portions of the oil supply passage 16, and each oil groove 21 has a third oil supply passage 22 interposed therebetween. And communicates with the fluid chamber 11, respectively. Each oil groove 21 is formed around the entire circumference of the hub 5, and the idler gear 3
The second supply oil passage 16 and the third supply oil passage 22 are always communicated with each other regardless of the rotation angle. In FIG. 6, the third supply oil passage 22 is formed at four positions at 90 ° intervals in correspondence with the discharge oil passage 14, but the number and arrangement of the third supply oil passage 22 are not limited to this, and are arbitrary. Can be changed to.

The oil from the oil passage 13 is
While being guided to the sliding portion of the idler gear 3 through the first supply oil passage 15 and the second supply oil passage 16 for lubrication,
Further, it is supplied to each fluid chamber 11 via the oil groove 21 and the third supply oil passage 22 (fluid supply means). After that, the same as in the first embodiment, the supplied oil is sequentially discharged from the respective discharge oil passages 14 toward the outer periphery while staying on the outer peripheral side in the fluid chamber 11 by the centrifugal force caused by the rotation of the idler gear 3. Although not described again, it is possible to obtain the same operational effects as the first embodiment.

Although the embodiment has been described above, the aspect of the present invention is not limited to this embodiment. For example, in each of the above-described embodiments, the idler gear 3 for driving the fuel injection pump of the diesel internal combustion engine is embodied, but the application portion is not limited to this, and is applied to, for example, a gear for driving the cam shaft of the internal combustion engine. May be. That is, as in the case of the fuel injection pump, the cam shaft that drives the intake / exhaust valve to open and close also undergoes load fluctuations due to the reaction force of the valve spring. When it is transmitted to, gear rattle is generated between the gears. Therefore, if the gears forming the gear train have the same structure as the idler gear 3 of the above-described embodiment, it is possible to suppress the rattling noise caused by the opening and closing drive of the intake and exhaust valves. Further, the invention is not limited to such an idler gear, and may be embodied in other driving side or driven side gears. For example, in the case of the above-described embodiment, if the same function is added to the driven gear 8 on the pump side instead of the idler gear 3, the same operational effect can be obtained.

In each of the above embodiments, the idler gear 3 is used.
Although the discharge oil passage 14 is formed at a position that meshes with the driven gear 8 at the time of fuel injection, it may be changed to another position. In this case, the collision of the tooth surfaces cannot be done in oil,
Since the oil discharged from the discharge oil passage 14 adheres to the tooth surface, its viscous resistance can alleviate the collision of the tooth surface. Further, the collision mitigation due to the shear resistance of the oil can be obtained in the same manner as in the embodiment, and even in this case, the rattling noise can be sufficiently suppressed.

Furthermore, in each of the above-described embodiments, the fluid chamber 11 is formed by utilizing the concave portion on the side surface of the idler gear 3, but the fluid chamber 1 is formed by using the concave cover body 9 instead.
1 may be formed. On the other hand, in the second embodiment, the oil is supplied into the fluid chamber 11 via the supply oil passages 15, 16 and 22, but the jet nozzle 12 may be used to supply the oil as in the first embodiment. Good. In addition, idler gear 3
Since the web 7 is of a spoke shape, the oil from the jet nozzle 12 is reliably supplied to the fluid chamber 11 on the side opposite to the engine through the fluid chamber 11 on the engine side.

In the second embodiment, the web 7 of the idler gear 3 has a spoke shape, but it may have a disk shape as in the first embodiment so that both fluid chambers 11 are completely partitioned. As described above, since each fluid chamber 11 is provided with the third supply oil passage 22 and the discharge oil passage 14 individually, even with such a configuration, there is no problem in the flow of oil to the fluid chamber 11.

[0039]

As described above, according to the low noise gear structure of the inventions of claims 1 and 2, an undesired increase in the inertial mass of the gear is prevented, and the effect of suppressing the rattling noise is sufficient. Therefore, it is possible to reliably reduce the noise associated with the meshing of the gears. According to the low noise gear structure of the inventions of claims 3 and 4, in addition to the inventions of claims 1 and 2, it is possible to more reliably exhibit collision mitigation due to viscous resistance and further reduce noise.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a low noise gear structure of a first embodiment.

FIG. 2 is a sectional view taken along line II-II of FIG. 1 showing an idler gear.

FIG. 3 is an enlarged cross-sectional view showing details of a discharge oil passage.

FIG. 4 is an explanatory diagram showing a damping state of vibration generated in an idler gear.

FIG. 5 is a sectional view showing a low noise gear structure according to a second embodiment.

6 is a sectional view taken along line VI-VI of FIG. 5, showing the idler gear with the cover body removed.

[Explanation of symbols] 2 rotation axes 3 idler gear (gear) 5 hubs 6 rims 6a Teeth 7 Web 7a through hole 8 Driven gear (counter gear) 9 cover body 9a Supply port (fluid supply means) 11 Fluid chamber 12 Jet nozzle (fluid supply means) 14 Discharge oil passage (discharge passage) 15 First supply oil passage (fluid supply means) 16 Second supply oil passage (fluid supply means) 22 Third supply oil passage (fluid supply means)

Claims (4)

[Claims] 1. A gear in which a rim is connected via a disc-shaped web centering on a hub supported by a rotating shaft, and a tooth portion formed on an outer peripheral surface of the rim is meshed with a mating gear, Low noise, comprising a cover body which is disposed on one side surface of the gear and forms a fluid chamber with the side surface of the gear, and a fluid supply means for supplying a viscous fluid into the fluid chamber. Gear structure. 2. A gear in which a rim is connected via a web having a through hole centered on a hub supported by a rotating shaft, and a tooth portion formed on an outer peripheral surface of the rim is meshed with a mating gear, A pair of cover bodies which are respectively disposed on both side surfaces of the gear and which form a pair of fluid chambers communicating with each other through the through holes of the web between the both sides of the gear, and the respective fluid chambers. A low-noise gear structure comprising: 3. The low-noise gear structure according to claim 1, wherein the gear has a discharge passage that connects the fluid chamber and one side of a tooth portion of the gear. 4. The gear transmits rotation with the counterpart gear with periodic torque fluctuation, and the discharge path is located at a position of a tooth portion meshing with the counterpart gear during the torque fluctuation. The low noise gear structure according to claim 3, wherein the low noise gear structure is formed.