KR102206092B1 - Planetary geared reducer with dual reduction ratio - Google Patents

Abstract

The present invention relates to a planetary gear reducer having a dual reduction ratio, in which a ring gear in the shape of an internal gear is formed on an inner circumferential surface, an input shaft is rotatably inserted into one side, and an output shaft is rotatably inserted into the other side; A sun gear formed at the end of the input shaft, one or more planetary gears meshed between the sun and the ring gear, and a high-deceleration carrier formed at the end of the output shaft to rotate and support the planetary gear to be rotatable by a rotation pin. In the planetary gear reducer comprising, the high reduction carrier is coupled to a reduction speed carrier covering to accommodate the planetary gear, the reduction speed carrier has a through hole through which the sun gear can penetrate, and an inner peripheral surface of the through hole A reduction gear having an internal gear shape that can be engaged with the sun gear is formed, and the sun gear is selectively interlocked with the planetary gear or the reduction gear according to the forward or backward movement of the input shaft to achieve dual deceleration. .

Description

Planetary geared reducer with dual reduction ratio

The present invention relates to a reducer, and more particularly, to a planetary gear reducer having a dual reduction ratio having a structure capable of outputting with different reduction ratios for one input.

In general, various devices such as machine tools, washing machines, and automobiles require speed reducers using various gears to vary the rotation ratio. The reducer is a device that receives rotational force from a power source such as a motor rotating at a considerable speed, converts it to a low speed, and outputs it, and uses an assembly of various types of gears.

Among these, reducers that increase power transmission efficiency by reducing the load and speed transmitted from the input shaft to the output shaft using planetary gears are widely used in all fields of industry such as shipbuilding, offshore plants, power plants, and industrial plants.

In particular, these reducers are often used to operate actuators such as valves and valve gearboxes, and are important when opening or closing valves.

1 is a cross-sectional view showing the structure of a reduction gear using a conventional planetary gear.

As shown, the conventional speed reducer includes a gear housing having an internal gear, one end connected to the motor shaft and the other end of the input shaft inserted into the input side of the gear housing and a sun gear coupled to the other end of the input shaft, and the sun gear. A plurality of planetary gears simultaneously engaged with the internal gears of the gear housing, and a plurality of connection pins fitted to the center of the planetary gear are installed at the lower portion, and a rotating plate having an output shaft installed at the upper center thereof.

With this configuration, when the input shaft rotates by receiving a rotational force from a motor, the plurality of planetary gears engaged therewith rotate around the input shaft at the same time as the rotation plate rotates at the rotational speed of the planetary gear while the output shaft Output after decelerating through.

However, although the conventional speed reducer has a simple configuration, there is a disadvantage that it cannot implement more than two kinds of reduction ratios because it has only one reduction ratio.

In addition, in order to have two or more types of reduction ratios, there is a problem that the structure becomes very complicated and the volume becomes large, and in particular, there is a problem that an output shaft corresponding to each reduction ratio must be separately provided.

In the case of a valve, since a large torque is required at the start and end of the stroke during opening and closing, it is necessary to increase the reduction ratio at this time.

Eventually, the conventional speed reducer could not satisfy this requirement at all.

-Republic of Korea Patent Registration 10-0428653 (2004.4.12) "Reduction gear device generating multiple outputs" -Korean Patent Laid-Open Publication No. 10-2017-0041069 (2017.4.14) "EGR valve including planetary gear" -Republic of Korea Patent Registration 10-1165075 (2012.7.5) "Driving device with dual output shaft"

Accordingly, the present invention is to solve the above-described problems, and an object of the present invention is to provide a planetary gear reducer having a dual reduction ratio having a structure capable of selective output with different reduction ratios for one rotational speed input.

Another object of the present invention is to provide a planetary gear reducer having a dual reduction ratio having a structure in which one output shaft can output different reduction ratios, and an input shaft and an output shaft form the same axial center.

The planetary gear reducer having a dual reduction ratio according to the present invention for achieving the above object has a cylindrical shape in which an internal gear-shaped ring gear is formed on an inner circumferential surface, an input shaft is rotatably inserted into one side, and an output shaft is rotatably inserted into the other side. A housing of, a sun gear formed at an end of the input shaft, at least one planetary gear meshing between the sun and a ring gear, and formed at the end of the output shaft to rotate and support the planetary gear to be rotatable by a rotation pin In the planetary gear reducer comprising a high reduction carrier, the high reduction carrier is coupled to a reduction speed carrier covering to accommodate the planetary gear, and a through hole through which the sun gear can penetrate is formed in the reduction speed carrier, , On the inner circumferential surface of the through hole, a reduction gear having an internal gear shape that can be engaged with the sun gear is formed, so that the sun gear is selectively interlocked with the planetary gear or the reduction gear according to the forward or backward movement of the input shaft, so that dual reduction is achieved. Can be done.

Here, a protruding guide rod is formed at the center of the reduction carrier, and a guide hole into which the guide rod is inserted is formed at the center of the input shaft, and the center of the guide rod and the guide hole coincides with the center of the input shaft and the output shaft. You can guide the movement.

In this case, a restoring spring for reversing the input shaft may be provided between the guide hole and the guide rod.

In addition, a locking groove may be formed on an outer circumference of the input shaft, and a locking pin may be inserted into the locking groove at one side of the housing.

In addition, the locking pin is elastically supported by the locking spring.

Meanwhile, between the high-deceleration carrier and the reduced-speed carrier, a first sun gear meshed with the planetary gear; A first reduction carrier spline-coupled to the first sun gear; At least one first planetary gear rotatably coupled to the first reduction carrier with a first rotation pin and meshed with the sun gear; And a first housing in which the housing is separable into an input-side housing and an output-side housing, the first housing coupled therebetween and having a first ring gear meshing with the first planetary gear formed on an inner circumferential surface thereof, the first rotation The pin may be coupled to the reduction speed carrier, and a first reduction means to which a first auxiliary carrier for preventing separation of the planetary gear is coupled may be further mounted on the rotation pin.

Here, between the first reduction means and the reduction speed carrier, a second reduction means having the same configuration as the first reduction means may be further mounted.

According to the present invention constituted as described above, first, despite providing two types of reduction ratios, the structure is simple and the volume is small, so it is possible to reduce the size and weight.

Second, when applying to valve opening/closing, by selecting a high reduction ratio at the beginning and end of opening and closing, the torque is generated large to facilitate opening and closing, and a large torque is not required at the intermediate opening/closing, so selecting a low reduction ratio operates without large torque You can quickly open and close by increasing the speed.

1 is a cross-sectional view showing the structure of a reduction gear using a conventional planetary gear
2 is a perspective view showing the overall appearance of a planetary gear reducer having a dual reduction ratio according to an embodiment of the present invention
3 is a longitudinal sectional view of the present invention shown in FIG. 2
4 is a cross-sectional view of a planetary gear reducer having a dual reduction ratio according to another embodiment of the present invention
Figure 5 is an operating state diagram of the present invention shown in Figure 4
6 is a cross-sectional view showing the structure of a planetary gear reducer having a dual reduction ratio according to another embodiment of the present invention
7 is an operating state diagram of the present invention shown in FIG. 6
8 is a cross-sectional view showing the structure of a planetary gear reducer having a dual reduction ratio according to another embodiment of the present invention

Hereinafter, an embodiment according to the present invention will be described in more detail with reference to the accompanying drawings.

For reference, the description with reference to the drawings is for easier understanding of the present invention, and the scope of the present invention is not limited thereto. Further, in describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, a detailed description will be omitted.

2 is a perspective view showing the overall appearance of a planetary gear reducer having a dual reduction ratio according to an embodiment of the present invention, and FIG. 3 is a longitudinal sectional view of the present invention shown in FIG.

The present invention is a device such as a gearbox that, when a rotational force is input to an input shaft by a power source such as a motor (not shown), is decelerated and the rotational force reduced to the output shaft is output.

An embodiment of the present invention largely includes a housing 10, an input shaft 20, an output shaft 30, a planetary gear 40, a sun gear 50, a high reduction carrier 60, and a reduced speed carrier 70. It can be configured.

First, the housing 10 will be described.

The housing 10 is configured to accommodate and support all of the input shaft 20, the output shaft 30, the planetary gear 40, the sun gear 50, the high reduction carrier 60, and the reduction speed carrier 70 inside. to be.

The housing 10 may have a substantially cylindrical shape, but may have a structure that is separated into an input-side housing 11 and an output-side housing 13 so as to be disassembled and assembled.

In this case, the input-side housing 11 and the output-side housing 13 may be mutually fastened with a plurality of fastening bolts 16 at the edges.

In addition, an input port 12 into which the input shaft 20 is inserted is formed in the input-side housing 11, and an output port 14 through which the output shaft 30 is inserted is formed in the output-side housing 13.

In addition, a ring gear 15, which is an internal gear, is formed on the inner circumferential surface of the housing 10, and preferably may be formed on the inner circumferential surface of the output-side housing 13.

Next, the input shaft 20 and the output shaft 30 will be described.

The input shaft 20 is inserted into the input port of the housing 10 and rotated by various power sources.

A bushing and an O-ring are inserted between the input shaft 20 and the input port 12 so as to be rotatable and sealing. In addition, the input shaft 20 is slidable to move forward or backward along the input port 12.

The output shaft 30 is installed rotatably by being inserted into the output port 14 of the housing 10.

To this end, a bearing (b) may be installed between the output shaft 30 and the output port 14, and an O-ring may be provided for sealing. And the output shaft 30 may be a hollow type or a solid type.

Next, the sun gear 50 and the planetary gear 40 will be described.

The sun gear 50 is coupled to an end of the input shaft 20 and rotates by rotation of the input shaft 20. Gear teeth are formed on the outer periphery of the sun gear 50.

And one or more planetary gears 40 are engaged around the outside of the sun gear 50.

Two to four planetary gears 40 are usually arranged at regular intervals and are interlocked by rotation of the sun gear 50 to rotate at the same direction and speed.

In addition, the planetary gears 40 are respectively engaged with the ring gears.

Therefore, when the sun gear 50 rotates, the planetary gears 40 rotate. Since the planetary gears 40 are interlocked with the ring gear 15, the planetary gears 40 also rotate the ring gear 15. ) And move along the circle trajectory. As a result, the planetary gears 40 rotate and at the same time orbit around the sun gear 50.

At this time, the planetary gear 40 may be rotatably fixed on the high-deceleration carrier 60 and the low-speed carrier 70 to be described later by separate rotation pins 41, respectively.

Next, the high-deceleration carrier 60 and the reduction-speed carrier 70 will be described.

The high-deceleration carrier 60 is coupled to or formed at an end of the output shaft 30 to rotate together with the output shaft 30.

The high-deceleration carrier 60 may be formed in an approximately disk shape, and a seating groove 61 may be formed in the center so that the end of the input shaft 20 can be inserted. And the seating groove 61 is provided with a bearing (b) for supporting the end of the input shaft 20 to be inserted and rotatable.

In addition, rotation pins 41 are vertically fixed to the high-deceleration carrier 60 at regular intervals along the circumferential direction, and the planetary gears 40 are rotatably coupled and supported to the rotation pins 41, respectively.

Therefore, as the planetary gear 40 revolves, the high-deceleration carrier 60 rotates, and thus the output shaft 30 rotates.

Meanwhile, the reduced speed carrier 70 is coupled to each other by the high speed reduction carrier 60 and the rotation pin 41, and accommodates the planetary gears 40 therein. Accordingly, as the planetary gear 40 revolves, the reduced speed carrier 70 also rotates together with the high speed reduction carrier 60.

For reference, a bearing (b) is also posted between the reduced speed carrier 70 and the input-side housing 11.

A through hole is formed in the center of the reduction speed carrier 70, and a reduction speed gear 71 having an internal gear shape is formed on an inner peripheral surface of the through hole.

In this case, the reduction gear 71 may be engaged with the sun gear 50. Accordingly, the rotational force of the sun gear 50 is transmitted to the reduced speed carrier 70, whereby the high speed reduction carrier 60 and the output shaft 30 rotate.

For example, when the sun gear 50 is engaged with the reduced speed gear 71 and rotates in a state in which the input shaft 20 is retracted, the output shaft 30 is formed with the reduction speed carrier 70 and the high speed reduction carrier ( It rotates at the same speed as the input shaft 20 through 60). In other words, it is transmitted at constant speed without actual deceleration (reduction ratio 1: 1).

However, when the input shaft 20 advances and the sun gear 50 is meshed with the planetary gear 40 and rotates, the output shaft 30 is formed with the planetary gears 40, the ring gear 15, and the high reduction carrier. Through 60, it rotates at a speed smaller than that of the input shaft 20. In other words, deceleration is achieved with a reduction ratio N:1.

That is, the sun gear 50 may be selectively interlocked with the planetary gear 40 or the reduction gear 71 according to the forward or backward movement of the input shaft 20 to achieve dual deceleration.

Hereinafter, another embodiment of the present invention will be described with reference to 4 and 5. 4 is a cross-sectional view of a planetary gear reducer having a dual reduction ratio according to another embodiment of the present invention, and FIG. 5 is an operational state diagram of the present invention shown in FIG. 4.

Another embodiment of the present invention discloses a structure in which the input shaft 20 is elastically supported so that the input shaft 20 can be moved back smoothly in the forward state.

To this end, a guide rod 62 having a protruding shape may be formed at the inner center of the high reduction carrier 60.

In addition, a guide hole 21 is formed at the center of the end of the input shaft 20.

At this time, the guide rod 62 is processed so that the guide rod 62 can be inserted into the guide hole 21.

Accordingly, the input shaft 20 can slide while maintaining concentricity with the center of the output shaft 30 when moving forward and backward.

However, a restoring spring 23 is provided in the guide hole 21.

The restoring spring 23 is a compression spring, and one end is seated on the upper end of the guide rod 62. Therefore, when the input shaft 20 is pushed forward by an external force, the guide rod 62 is inserted into the guide hole 21 while compressing the restoration spring 23, so that the sun gear 50 is transferred to the planetary gear 40 ).

Conversely, when the external force is removed, the input shaft 20 is pushed back by the elastic force of the restoring spring 23 and the sun gear 50 is interlocked with the reduced speed gear 71.

Further, on the outer circumference of the input shaft 20, a locking groove 22 is continuously formed along the circumference.

In addition, a locking pin 24 is installed on one side of the housing 10, specifically on the input port 12, to pass through. The front end of the locking pin 24 may be inserted into the locking groove 22, and the rear end may be elastically supported by the locking spring 25.

Therefore, when the input shaft 20 advances, the locking pin 24 is pushed and separated from the locking groove 22, and when the input shaft 20 moves backward, the locking pin 24 becomes the locking groove 22 The input shaft 20 is prevented from moving backwards while being caught in.

When the present invention is used to open and close a valve, the input shaft 20 is moved backward and the sun gear 50 is interlocked with the reduced speed gear 71 in the middle of a stroke where a large torque is not required. The output shaft 30 may rotate rapidly.

However, when opening and closing the valve, a large torque is required at the start and end of the stroke, so it is necessary to increase the reduction ratio. Therefore, by moving the input shaft 20 forward so that the sun gear 50 is interlocked with the planetary gear 40, the output shaft 30 can be greatly decelerated.

Hereinafter, another embodiment of the present invention will be described with reference to FIGS. 6 and 7. 6 is a cross-sectional view showing the structure of a planetary gear reducer having a dual reduction ratio according to another embodiment of the present invention, and FIG. 7 is a diagram illustrating an operating state of the present invention shown in FIG.

Another embodiment of the present invention is to propose a reduction gear having a larger reduction ratio, and a structure in which the first reduction means 80 can be additionally mounted between the high reduction carrier 60 and the reduction speed carrier 70 to be. In this case, in order to add the first reduction means 80, the input side housing 11 and the output side housing 13 may be separated, and the first reduction means 80 may be mounted and connected therebetween.

Specifically, the first reduction means 80 includes a first sun gear 81, a first reduction carrier 82, a first planetary gear 83, a first housing 84, and a first auxiliary carrier 85. It can be configured.

The first sun gear 81 has a gear tooth formed on its outer periphery and is meshed with the planetary gear 40.

One end of the first sun gear 81 is seated and supported in a seating groove of the high-deceleration carrier 60, and a spline is formed at the other end to be spline-coupled with the first reduction-carrier 82.

The first reduction carrier 82 has a structure and shape similar to that of the high reduction carrier 60.

The other end of the first sun gear 81 is inserted into the center of the first reduction carrier 82 in one direction to be spline-coupled, and the end of the input shaft 20 may be inserted and seated in the other direction.

At this time, a bearing (b) is provided between the first reduction carrier 82 and the input shaft 20 to rotatably support the end of the input shaft 20.

One or more first planetary gears 83 are arranged on the first reduction carrier 82 along the circumferential direction. Each of the first planetary gears 83 is rotatably fixed by a first rotation pin 86.

In addition, each of the first planetary gears 83 is meshed with the sun gear 50 and rotates in the same direction and speed by the rotation of the sun gear 50.

The first housing 84 is provided around the outside of the first planetary gear 83.

A first ring gear 87 meshing with the first planetary gears 83 is formed on an inner circumferential surface of the first housing 84. The first ring gear 87 has an internal gear shape.

In order to mount the first housing 84, the input housing 11 and the output housing 13 may be separated, and the first housing 84 may be assembled therebetween.

In addition, one end of the first rotation pins 86 is fixed to the first reduction carrier 82 and the other end is fixed to the reduction speed carrier 70, so that the first reduction carrier 82 and the reduction speed carrier 70 Will rotate together.

For reference, a separate first auxiliary carrier 85 is coupled to the other end of the rotation pin 41 having one end fixed to the high deceleration carrier 60 to prevent separation of the planetary gear 40 and the high deceleration carrier ( 60) and rotates.

When explaining the operation state, when the input shaft 20 moves backward and the sun gear 50 is interlocked with the reduction gear 71, the reduction speed carrier 70 and the first reduction carrier 82 rotate together without deceleration. do.

When the first reduction carrier 82 rotates, the spline-coupled first sun gear 81 rotates, and when the first sun gear 81 rotates, the planetary gear rotates while the high reduction carrier 60 and The output shaft rotates by decelerating at a reduction ratio of N:1.

If the input shaft 20 is moved forward and the sun gear 50 is interlocked with the first planetary gear 83, the first planetary gear 83 rotates while the first reduction carrier 82 and the first sun gear (81) is the first decelerating rotation with a reduction ratio of N:1.

In addition, as the planetary gear 40 rotates by the rotation of the first sun gear 81, the high-deceleration carrier 60 and the output shaft 30 are rotated by second reduction at a reduction ratio of N:1.

As a result, by further mounting the first reduction means 80, the output shaft 30 with respect to the input shaft 20 is greatly reduced and rotated at a reduction ratio of N×N:1.

Hereinafter, another embodiment of the present invention will be described with reference to FIG. 8. 8 is a cross-sectional view showing the structure of a planetary gear reducer having a dual reduction ratio according to another embodiment of the present invention.

Another embodiment of the present invention is a structure in which a second reduction means 90 is additionally mounted between the first reduction means 80 and the reduction speed carrier 70 in order to realize a larger reduction ratio.

The structure of the second reduction means 90 is preferably made of the same configuration as the first reduction means 80.

That is, the second reduction means 90 includes a second sun gear 91, a second reduction carrier 92, a second planetary gear 93, a second housing 94, and a second auxiliary carrier 95. It can be configured.

The second sun gear 91, the second reduction carrier 92, the second planetary gear 93, the second housing 94, and the second auxiliary carrier 95 are respectively the first sun gear 81 and the first It may have the same structure and shape as the reduction carrier 82, the first planetary gear 83, the first housing 84, and the first auxiliary carrier 85.

At this time, the second sun gear 91 is meshed with the first planetary gear 83, one end is seated and supported on the first reduction carrier 82, and a spline is formed at the other end of the second reduction carrier ( 92) and spline are combined.

The other end of the second sun gear 91 is inserted into the center of the second reduction carrier 92 in one direction to be spline-coupled, and the end of the input shaft 20 may be inserted and seated in the other direction.

At this time, a bearing (b) is provided between the second reduction carrier 92 and the input shaft 20 to rotatably support the end of the input shaft 20.

A second planetary gear 93 is arranged on the second reduction carrier 92, and each of the second planetary gears 93 is rotatably fixed by a second rotation pin 96. And each second planetary gear 93 is meshed with the sun gear 50.

The second housing 94 is provided outside the second planetary gear 93, and a second ring gear 97 meshed with the second planetary gears 93 is provided on the inner circumferential surface of the second housing 94. ) Is formed.

In order to mount the second housing 94, the input housing 11 and the first housing 84 may be separated and fastened to be assembled to the second housing 94 therebetween.

And one end of the second rotation pins 96 is fixed to the second reduction carrier 92 and the other end is fixed to the reduction speed carrier 70, so that the second reduction carrier 92 and the reduction speed carrier 70 Will rotate together.

In addition, a separate second auxiliary carrier 95 is coupled to the other end of the first rotation pin 86 having one end fixed to the first reduction carrier 82 to prevent separation of the first planetary gear 83 It rotates together with the first reduction carrier 82.

In this case, when the input shaft 20 is moved backward, the output shaft 30 is decelerated and rotated at a reduction ratio of N×N: 1, and the output shaft 30 is rotated at a reduction ratio of N×N×N: 1. It decelerates and rotates.

In this way, the third reduction means, the fourth reduction means... can be additionally installed, and the reduction ratio gradually decreases each time the reduction means is added.

Although the exemplary embodiments of the present invention have been described above with reference to the drawings, a person of ordinary skill in the field to which the present invention belongs will be able to perform various applications and modifications within the scope of the present invention based on the above contents. Therefore, the scope of the present invention is limited to the described embodiments and should not be determined, and should not be determined by the claims to be described later, but also by those equivalents to the claims.

10: housing
11: input side housing 12: input port
13: output side housing 14: output port
15: ring gear 16: fastening bolt
20: input shaft 21: guide hole
22: locking groove 23: restoration spring
24: locking pin 25: locking spring
30: output shaft
40: planetary gear 41: rotating pin
50: sun gear
60: high deceleration carrier
61: seating groove 62: guide rod
70: reduced speed carrier 71: reduced speed gear
80: first reduction means 81: first sun gear
82: first reduction carrier 83: first planetary gear
84: first housing 85: first auxiliary carrier
86: first rotation pin 87: first ring gear
90: second reduction means 91: second sun gear
92: second reduction carrier 93: second planetary gear
94: second housing 95: second auxiliary carrier
96: second rotation pin 97: second ring gear
b: bearing

Claims (7)

An internal gear-shaped ring gear is formed on the inner circumferential surface, an input shaft is rotatably inserted into one side, and an output shaft is rotatably inserted into a cylindrical housing, a sun gear formed at the end of the input shaft, and the sun and ring gear A planetary gear reducer comprising at least one planetary gear engaged therebetween, and a high-speed reduction carrier formed at an end of the output shaft to rotate and support the planetary gear so as to be rotatable by a rotation pin,
A reduction speed carrier covering the high reduction carrier to accommodate the planetary gear is coupled, a through hole through which the sun gear can penetrate is formed in the reduction speed carrier, and an internal circumferential surface of the through hole that can be engaged with the sun gear A gear-shaped reduction gear is formed, and the sun gear is selectively interlocked with the planetary gear or the reduction gear according to the forward or backward movement of the input shaft to achieve dual reduction,
A protruding guide rod is formed at the center of the high-deceleration carrier, a guide hole into which the guide rod is inserted is formed at the center of the input shaft, and a restoring spring is provided between the guide hole and the guide rod so that the input shaft moves backward, The centers of the guide rod and the guide hole coincide with the centers of the input shaft and the output shaft, thereby guiding the movement of the input shaft,
A locking groove is formed on the outer circumference of the input shaft, a locking pin that can be inserted into the locking groove is provided on one side of the housing, and the locking pin is elastically supported by a locking spring. Gear reducer. delete delete delete delete The method of claim 1,
Between the high-deceleration carrier and the reduced-speed carrier,
A first sun gear meshed with the planetary gear;
A first reduction carrier spline-coupled to the first sun gear;
At least one first planetary gear rotatably coupled to the first reduction carrier by a first rotation pin and meshed with the sun gear; And
The housing is separable into an input-side housing and an output-side housing, the first housing coupled therebetween and having a first ring gear engaged with the first planetary gear formed on an inner circumferential surface thereof, wherein the first rotation pin is formed. Is coupled to the reduction speed carrier, and a planetary gear reducer having a dual reduction ratio, characterized in that a first reduction means to which a first auxiliary carrier for preventing separation of the planetary gear is coupled is further mounted on the rotation pin. The method of claim 6,
Between the first reduction means and the reduction speed carrier,
A planetary gear reducer having a dual reduction ratio, characterized in that a second reduction means having the same configuration as the first reduction means can be further mounted.

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