KR102094601B1 - Excavator having rotary arm - Google Patents

Abstract

According to an aspect of the present invention, a body having a hydraulic pump, a boom connected to one end of the vehicle body, coupled between the vehicle body and the boom, and receiving the hydraulic energy from the hydraulic pump to operate the boom boom cylinder, the other end of the boom It is coupled between the arm, the boom and the arm connected to the arm cylinder that operates the arm by receiving hydraulic energy from the hydraulic pump, the bucket connected to the end of the arm and the arm and the bucket, and the hydraulic energy from the hydraulic pump. It includes a bucket cylinder that is supplied and operates the bucket, the arm is a first member connected to the other end of the boom, one end coupled to the first member so as to be rotatable 360 degrees, and the second member connected to the other end of the bucket, And a rotation module interposed between the first member and the second member to enable rotational movement of the second member, wherein the rotation module rotates on the inner ring and the inner ring coupled to the first member. A bearing comprising an outer ring, which is coupled to the second member, and is coupled to the first member and receives hydraulic energy from a hydraulic pump to generate a rotational force for rotational movement of the second member, one end of a rotating shaft of the hydraulic motor An excavator provided with a rotatable arm including a worm wheel formed on an outer circumferential surface of a worm and an outer ring coupled to orthogonal to the worm and receiving the rotational force of a hydraulic motor through the worm is provided.

Description

Excavator with rotatable arm {EXCAVATOR HAVING ROTARY ARM}

The present invention relates to an excavator, and more particularly, to an excavator having a rotatable arm.

1 shows an excavator according to the prior art. In addition to the basic excavation work, these excavators are used for various purposes such as stop work, landscaping work, demolition work, compaction work, and crushing work. In addition, work equipment (attachment) suitable for each work characteristic has been developed in various ways, such as various buckets, breakers, crushers, cutters, rippers, grabs, and compacts, and is widely used in industrial fields.

Due to the basic structure of the excavator, that is, the structure of the operation part composed of a boom, an arm, a bucket, a hydraulic cylinder, etc., there is a restriction to move on a two-dimensional plane. That is, basically, only the vertical motion is possible. Reference numeral 100 in FIG. 1 denotes a vehicle body including a cab.

Therefore, in order to realize a three-dimensional work from various angles, a rotating device needs to be basically installed in each work device, but otherwise, the work itself in a specific direction must be abandoned.

Republic of Korea Patent Publication No. 10-2013-0070744 (2013. June 28.)

The present invention provides an excavator in which the arm is rotatable to realize a three-dimensional operation.

According to an aspect of the present invention, a body having a hydraulic pump, a boom connected to one end of the vehicle body, coupled between the vehicle body and the boom, and receiving the hydraulic energy from the hydraulic pump to operate the boom boom cylinder, the other end of the boom It is coupled between the arm, the boom and the arm connected to the arm cylinder that operates the arm by receiving hydraulic energy from the hydraulic pump, the bucket connected to the end of the arm and the arm and the bucket, and the hydraulic energy from the hydraulic pump. It includes a bucket cylinder that is supplied and operates the bucket, the arm is a first member connected to the other end of the boom, one end coupled to the first member so as to be rotatable 360 degrees, and the second member connected to the other end of the bucket, An arm cylinder and a bucket cylinder from a hydraulic pump interposed between the first member and the second member to enable rotational movement of the second member and the rotational movement of the second member A rotary joint interposed between the first member and the second member to transfer oil so that hydraulic energy transfer to the furnace is maintained, and the rotating module includes an inner ring coupled to the first member and a second rotatably coupled member to the inner ring. A bearing including an outer ring coupled to a member, a hydraulic motor coupled to the first member and receiving hydraulic energy from a hydraulic pump to generate rotational force for rotational movement of the second member, a worm coupled to one end of a rotating shaft of the hydraulic motor, and An excavator is provided with a rotatable arm that is formed on the outer circumferential surface of the outer ring and meshes orthogonally with the worm, and includes a worm wheel that receives the rotational force of the hydraulic motor through the worm.

The rotary joint is rotatably coupled with the second member by being rotatably coupled to the fixed part by surrounding the outer circumferential surface of the fixed part and the fixed part, which is inserted into the first member on one side and the second member, and rotates integrally with the second member. Included, the fixed portion is formed with a flow path for transferring oil supplied from the hydraulic pump, the flow path extends from one side of the fixed portion to the other side through the inside of the fixed portion to communicate with the outer peripheral surface of the fixed portion, and the outer peripheral surface of the fixed portion In, it may be characterized in that a groove connected to the flow path and a groove formed around the outer circumference of the fixing part is formed, and a port for transmitting oil to the arm cylinder or the bucket cylinder in communication with the groove is formed on the rotating part.

A plurality of flow paths, ditches, and ports may be formed, and the number of flow paths, ditches, and ports may be the same.

 A plurality of ports may be characterized in that they are located on one side of the rotating portion so as to face the same direction with each other.

A sealing groove may be formed between two adjacent grooves among the plurality of grooves, and a sealing member may be inserted into the sealing groove.

A locking protrusion is formed on an outer circumferential surface of the rotating part, and a stopper that engages the locking protrusion is formed on the second member so that the rotating part rotates integrally with the second member.

The rotating module may further include a relief valve to prevent the pressure of the oil supplied to the hydraulic motor from exceeding a predetermined limit value.

The arm protrudes outwardly of the first member, and may further include a motor bracket that supports the hydraulic motor.

The arm may be characterized by further comprising a first gear cover coupled to the motor bracket to protect the worm.

The arm may further include a second gear cover coupled to the first member to protect the worm wheel.

According to a preferred embodiment of the present invention, the arm can rotate freely to realize a three-dimensional working environment.

1 is a side view showing an excavator according to the prior art.
Figure 2 is a side view showing an excavator having a rotatable arm according to an embodiment of the present invention.
Figure 3 is a cross-sectional view showing the arm of the excavator having a rotatable arm according to an embodiment of the present invention.
4 and 5 are diagrams showing a worm wheel and a worm according to an embodiment of the present invention.
Figure 6 is a cross-sectional view showing a rotary joint of an excavator having a rotatable arm according to an embodiment of the present invention.
7 is a view showing a fixing part of a rotary joint according to an embodiment of the present invention.
FIG. 8 is an enlarged view of a portion showing a portion 'C' of FIG. 6.

The present invention can be applied to a variety of transformations and may have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all conversions, equivalents, and substitutes included in the spirit and scope of the present invention. In the description of the present invention, when it is determined that a detailed description of known technologies related to the present invention may obscure the subject matter of the present invention, the detailed description will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Hereinafter, a preferred embodiment of an excavator having a rotatable arm according to the present invention will be described in detail with reference to the accompanying drawings, and in describing with reference to the accompanying drawings, identical or corresponding components are given the same reference numbers. And redundant description thereof will be omitted.

As shown in FIG. 1, the excavator is coupled between the vehicle body 100 having a hydraulic pump, the boom 200 connected to one end of the vehicle body 100, the vehicle body 100 and the boom 200, and the hydraulic pump Hydraulic energy supplied from the boom cylinder 300 to operate the boom 200, the arm 400 connected to the other end of the boom 200, coupled between the boom 200 and the arm 400, hydraulic pump Arm cylinder 500 that receives hydraulic energy from the arm 400 to operate the arm, the bucket 600 connected to the end of the arm 400, coupled between the arm 400 and the bucket 600, from the hydraulic pump It has a bucket cylinder 700 for operating the bucket 600 receives hydraulic energy as a component.

Excavator having a structure as shown in FIG. 1 has a limitation of moving on a two-dimensional plane due to the structure of an operation unit composed of a boom 200, an arm 400, a bucket 600, and the like. That is, basically, only the vertical motion is possible. Therefore, in order to realize a three-dimensional work from various angles, a rotating device needs to be basically installed in each work device, but otherwise, the work itself in a specific direction must be abandoned.

In order to solve this problem, the present embodiment proposes a structure in which the arm 400 can rotate 360 degrees. As illustrated in FIG. 2, when the arm 400 is freely rotated 360 degrees around its longitudinal axis, it is possible to perform operations in various directions up, down, left, and right with a simple operation, thereby improving work efficiency. It will be.

In order to implement such a structure, the arm 400 of the excavator according to the present embodiment, the first member 410 connected to the other end of the boom 200, one end can be rotated 360 degrees to the first member 410 The second member 420 is coupled to the other end is connected to the bucket 600, and is interposed between the first member 410 and the second member 420 to enable rotational movement of the second member 420 It includes a rotating module 430. As described above, when the structure of the arm 400 is dualized to the first member 410 and the second member 420 to implement a rotational operation, there is an advantage of realizing a three-dimensional working environment while minimizing design changes compared to the conventional structure. .

As shown in FIG. 3, in a concrete form of the rotating module 430, in an embodiment of the present invention, a hydraulic motor 431 generating a rotating force, a worm 432 and a worm wheel 433 transmitting the rotating force, And a bearing 434 in which the worm wheel 433 is formed on the outer circumferential surface is presented. Hereinafter, each element of the rotation module 430 according to an embodiment will be described in more detail.

The rotation of the arm 400, that is, the operation of the rotation module 430, may be implemented by the operator's manipulation in the cab located in the vehicle body 100. Since the operation of the excavator typically uses hydraulic pressure, a hydraulic pump is provided on the vehicle body 100. In this embodiment, the hydraulic motor 431 using the oil of the above-described hydraulic pump is used as a power source of the rotation module 430.

The hydraulic motor 431 is coupled to the first member 410 and receives hydraulic energy from a hydraulic pump to generate rotational force for rotational movement of the second member 420. That is, the hydraulic motor 431 is installed on the first member 410 which does not rotate to generate rotational force using the hydraulic pressure supplied from the hydraulic pump of the vehicle body 100. 3 and 4, the generated rotational force is transmitted to the worm 432 coupled to the rotating shaft of the hydraulic motor 431.

Meanwhile, as illustrated in FIG. 5, a bearing 434 may be interposed between the first member 410 and the second member 420, and the bearing 434 is an inner ring coupled to the first member 410. And, it may be made of an outer ring that is rotatably coupled to the inner ring and coupled to the second member (420).

Here, a worm wheel 433 may be formed on the outer circumferential surface of the outer ring of the bearing 434 as illustrated in FIGS. 4 and 5. The worm wheel 433 is formed on the outer circumferential surface of the outer ring of the bearing 434 and can be orthogonally engaged with the worm 432 described above. Accordingly, the rotational force of the hydraulic motor 431 includes the worm 432 and the worm wheel 433. Is transmitted to the outer ring of the bearing 434, and consequently, is finally delivered to the second member 420 coupled with the outer ring of the bearing 434 to rotate the second member 420 relative to the first member 410. .

The worm 432 is coupled to one end of the rotating shaft of the hydraulic motor 431 and the gear teeth may be formed in a spiral structure along the outer circumferential surface. In addition, the worm wheel 433 is orthogonally engaged with the helical structure of the worm 432 and can receive the rotational force of the hydraulic motor 431 through the worm 432.

When the second member 420 is rotated using a spur gear or the like, some rotational motion may occur even if the hydraulic motor 431 is stopped, so a separate device such as a brake may be required to prevent this. On the other hand, in the case of the worm gear, the worm 432 cannot rotate due to the rotation of the worm wheel 433 according to the tooth surface angle of the worm 432, so that the second member 420 is rotated without a separate member such as a brake. It can be prevented from moving in place.

In this way, when the worm wheel 433 is formed on the outer ring of the bearing 434, and this is meshed in a circumferential manner with the worm 432 receiving the rotational force directly from the hydraulic motor 431, the power transmission structure can be simplified and maintained later. Also, it is greatly advantageous for maintenance and power loss can be minimized.

Meanwhile, a relief valve may be provided at the oil inlet / outlet of the hydraulic motor 431. Such a relief valve can prevent the pressure of the oil supplied to the hydraulic motor from rising above a preset limit value, thereby minimizing malfunctions or malfunctions caused by overpressure.

Meanwhile, as illustrated in FIG. 5, the arm 400 includes a motor bracket 440 for supporting the hydraulic motor 431, a first gear cover 450 protecting the worm 432, and a worm wheel 433. ) May be further provided with a second gear cover 460 to protect.

5, the first member 410 may be formed with a motor bracket 440 protruding outward. 3 and 4, the hydraulic motor 431 may be installed on the motor bracket 440 using a fastening means such as a bolt.

In addition, a first gear cover 450 surrounding the outer circumferential surface of the worm 432 may be coupled to the motor bracket 440 as illustrated in FIGS. 3 and 5. Since the outer peripheral surface of the worm 432 can be mostly enclosed by the first gear cover 450, the worm 432 can be more effectively protected from external contamination or impact.

Also, as illustrated in FIGS. 3 to 5, a second gear cover 460 for protecting the worm wheel 433 may be coupled to the first member 410. The second gear cover 460 may be installed on the first member 410 to surround the outer circumferential surface of the remaining worm wheel 433 except for the portion where the worm 432 and the worm wheel 433 are engaged. In addition, the second gear cover 460 may be divided into two parts, a left side and a right side.

Next, the rotary joint 800 for maintaining the supply of hydraulic energy even during the rotation of the second member 420 will be described.

Boom cylinder 300, arm cylinder 500, bucket cylinder 700 is operated by receiving hydraulic energy from a hydraulic pump (not shown) provided on the vehicle body 100, each cylinder (300, 500, 700) There is connected a hydraulic hose (not shown) for the supply of hydraulic pressure, when the arm 400 rotates freely, the hydraulic hoses for supplying hydraulic pressure to the arm cylinder 500 and the bucket cylinder 700 are twisted There is a danger of bursting.

In order to solve this problem, in the present embodiment, the first member 410 so that hydraulic energy transfer from the hydraulic pump to the arm cylinder 500 and the bucket cylinder 700 is maintained even during the rotational movement of the second member 420. ) And the second member 420 to present the rotary joint 800 interposed between the oil and the oil (see FIG. 3).

3 and 6, the rotary joint 800 is large, one side is inserted into the first member 410 and the other side is fixed into the second member 420, the fixing portion 810, and the fixing portion Surrounding the other side of the (810) it is rotatably coupled to the fixed portion 810 can be composed of a rotating portion 820 that rotates integrally with the second member 420.

In this case, as illustrated in FIG. 6, a locking protrusion 821 is formed on an outer circumferential surface of the rotating part 820, and as shown in FIGS. 3 and 6, the second member 420 includes a rotating part 820. A stopper 470 engaged with the locking protrusion 821 may be formed to rotate integrally with the two members 420. That is, the rotation part 820 and the second member 420 are integrally rotatable due to interference between the locking protrusion 821 of the rotation part 820 and the stopper 470 of the second member 420.

As shown in Figure 6, the fixing portion 810 is formed with a flow path 830 for delivering oil supplied from a hydraulic pump to each cylinder through a hydraulic hose or the like, the flow path 830 is a fixing portion 810 It is formed from one side of the extend through the inside of the fixing portion 810 in the other direction and has a structure in communication with the outer peripheral surface of the fixing portion 810. That is, one end of the flow path 830 is exposed at one side of the fixing portion 810, and the other end of the flow path 830 is exposed at the other outer peripheral surface of the fixing portion 810. The arrow in FIG. 6 represents a path through which hydraulic pressure is transmitted through the flow path 830.

6 and 7, a groove 815 having a shape surrounding the outer circumferential surface of the fixing portion 810 is formed on the other outer circumferential surface of the fixing portion 810 to which the other end of the flow path 830 is exposed. Since the ditch 815 communicates with the flow path 830, hydraulic pressure, that is, oil supplied through the flow path 830, can be circulated along the outer circumferential surface of the fixing part 810 by the ditch 815.

As shown in FIG. 6, the other end of the fixing part 810 is surrounded by the rotating part 820. As the rotating part 820 covers the upper side of the groove 815, as a result, the inner peripheral surface of the rotating part 820 A circulation flow path that can be connected anywhere at 360 degrees may be implemented by the outer circumferential surface of the fixing part 810 and the groove 815.

As shown in FIG. 7, a port 840 communicating with a trench 815 is formed in the rotating part 820, and a hydraulic hose or the like is connected to the port 840 to arm cylinder 500 or bucket cylinder 700. To oil.

According to the structure as described above, even if the second member 420 constituting the arm 400 rotates in any direction 360 degrees around its longitudinal axis, the flow path 830 passing through the fixing portion 810 and the fixing portion The supply of oil can be stably maintained by the trench 815 formed along the outer circumferential surface of 810.

Meanwhile, the above-described flow path 830, the trench 815, and the port 840 may be variously changed according to the number of channels to which hydraulic pressure is to be transmitted. In this case, the flow path 830, the trench 815, and the port 840 may be formed in plural, respectively, and may be formed in the same number as each other to correspond one-to-one.

In this way, when a plurality of flow paths 830, trenches 815, and ports 840 are formed, it is necessary that interference does not occur between adjacent trenches 815. To this end, as shown in FIGS. 6 and 7, a sealing groove 814 using a pair of partitions 811 between adjacent grooves 815 is formed, and a sealing member made of rubber and Teflon is formed in the sealing groove. By inserting (812, 813) it is possible to implement a solid sealing between the grooves (815).

3 and 6, the plurality of ports 840 may include first ports 841 to sixth ports 846, and one side of the rotating part 820 may face the same direction with each other Can be formed from. The first port 841, the third port 843, and the fifth port 845 are positioned on a straight line along the longitudinal direction of the rotating part 820, and the second port 842, the fourth port 844, and The sixth port 846 may be disposed in a straight line along the longitudinal direction of the rotating portion 820 and spaced apart from the first port 841, the third port 843, and the fifth port 845 by a predetermined distance. .

When a plurality of ports 840 are formed on one side of the rotating part 820, since oil flows in and out on one side having a plurality of ports 840, a structure for an oil flow path such as an oil hose is simplified. The rotary joint 800 may be easily coupled or separated, and post-maintenance may be facilitated.

In addition, the center of the second port 842 is located at the same distance from the center of the first port 841 and the center of the third port 843, and the center of the third port 843 is the second port 842 ) And the same distance from the center of the fourth port 844, the center of the fourth port 844 is the same distance from the center of the fifth port 845 and the center of the sixth port 846 Can be located.

Accordingly, the positions of the plurality of ports 840 are formed to be staggered, so that one side space of the rotating part 820 can be utilized to the maximum, and oil hoses coupled to the plurality of ports are prevented from interfering with each other to prevent problems such as twisting. Can be reduced.

Meanwhile, the two ports 840 connected to the inlet and the outlet of one hydraulic unit and paired with each other may have different diameters. That is, the first port 841 and the second port 842 have different diameters from each other, and the third port 843 and the fourth port 844, the fifth port 845 and the sixth port 846 are also mutually different. It can have different diameters.

In addition, the first port 841 and the third port 843 have the same diameter, and the second port 842, the fourth port 844, and the fifth port 845 have the same diameter, and the sixth port ( The diameter of 846 may be smaller than the first port 841 and larger than the second port 842. That is, the second port 842, the fourth port 844, and the fifth port 845 have the smallest diameter, the sixth port 846 is the middle diameter, and the first port 841 and the third port ( 843) may have the largest diameter.

The diameters of the plurality of ports 840 may vary depending on the application, and the function of the port 840 and the direction of oil in and out can be easily distinguished through the difference in diameter, so that the maintenance and management of the rotary joint can be facilitated.

Although described above with reference to preferred embodiments of the present invention, those of ordinary skill in the art may vary the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be understood that modifications and changes can be made.

Many embodiments other than the above-described embodiments exist within the claims of the present invention.

100: body
200: boom
300: boom cylinder
400: arm
410: first member
420: second member
430: rotating module
431: hydraulic motor
432: worm
433: worm wheel
434: bearing
440: motor bracket
450: first gear cover
460: second gear cover
470: stopper
500: arm cylinder
600: bucket
700: bucket cylinder
800: rotary joint
810: fixing part
811: bulkhead
812, 813: sealing member (sealing member)
814: sealing groove
815: ditch
820: rotating part
821: jam
830: Euro
840: port
841: first port
842: second port
843: port 3
844: port 4
845: port 5
846: sixth port

Claims (10)

A vehicle body having a hydraulic pump;
A boom with one end connected to the vehicle body;
A boom cylinder coupled between the vehicle body and the boom and receiving hydraulic energy from the hydraulic pump to operate the boom;
An arm connected to the other end of the boom;
An arm cylinder coupled between the boom and the arm and receiving hydraulic energy from the hydraulic pump to operate the arm;
A bucket connected to the end of the arm; And
It is coupled between the arm and the bucket, and includes a bucket cylinder for operating the bucket receiving hydraulic energy from the hydraulic pump,
The cancer,
A first member connected to the other end of the boom;
A second member coupled to the first member so that one end is rotatable 360 degrees, and the other end is connected to the bucket;
A rotation module interposed between the first member and the second member to enable rotational movement of the second member; And
And a rotary joint interposed between the first member and the second member to transfer oil so that hydraulic energy transfer from the hydraulic pump to the arm cylinder and the bucket cylinder is maintained during the rotational movement of the second member. ,
The rotation module,
A bearing including an inner ring coupled to the first member and an outer ring rotatably coupled to the inner ring and coupled to the second member;
A hydraulic motor coupled to the first member and receiving hydraulic energy from the hydraulic pump to generate a rotational force for rotational movement of the second member;
A worm coupled to one end of the rotating shaft of the hydraulic motor; And
It is formed on the outer circumferential surface of the outer ring and meshed orthogonally with the worm, and includes a worm wheel receiving the rotational force of the hydraulic motor through the worm,
The rotary joint,
One side is inserted into the first member and the other side is fixed to the second member; And
The outer peripheral surface of the other side of the fixing portion and is rotatably coupled to the fixing portion 360 degrees, and includes a rotating portion integrally rotating with the second member,
A flow path for transferring oil supplied from the hydraulic pump is formed in the fixing part,
The flow path extends from one side of the fixing portion to the other side through the inside of the fixing portion to communicate with the outer peripheral surface of the fixing portion,
On the outer circumferential surface of the fixing part, a groove having a shape connected to the flow path and surrounding the outer circumferential surface of the fixing part is formed,
A port for communicating oil to the arm cylinder or the bucket cylinder in communication with the groove is formed in the rotating part,
The plurality of ports are located on one side of the rotating portion so as to face the same direction with each other,
The plurality of ports are arranged in two rows on one side of the rotating portion,
The plurality of ports,
A first port, a third port, and a fifth port located on a straight line along the longitudinal direction of the rotating portion; And
The second port, the fourth port and the sixth port are disposed to be spaced apart from the first port, the third port, and the fifth port along the circumference of the rotating part and are positioned in a straight line along the longitudinal direction of the rotating part. and,
The first port, the third port and the fifth port and the second port, the fourth port and the sixth port are arranged to be staggered with each other,
The first port and the second port have different diameters from each other,
The third port and the fourth port have different diameters from each other,
The fifth port and the sixth port are excavators having different diameters and rotatable arms.
delete According to claim 1,
The flow path, the groove and the port are each formed in plural,
Excavator having a rotatable arm, characterized in that the number of the flow path, the groove and the port are the same.
delete According to claim 3,
A sealing groove is formed between two adjacent ones of the plurality of grooves,
Excavator having a rotatable arm, characterized in that the sealing member is inserted into the sealing groove.
The method of claim 5,
A locking protrusion is formed on the outer peripheral surface of the rotating part,
Excavator having a rotatable arm, wherein the second member is provided with a stopper engaged with the locking protrusion so that the rotating part is integrally rotated with the second member.
According to claim 1,
The rotation module,
Excavator having a rotatable arm, characterized in that it further comprises a relief valve for preventing the pressure of the oil supplied to the hydraulic motor exceeds a predetermined limit value.
According to claim 1,
The arm protrudes in the outer direction of the first member, characterized in that it further comprises a motor bracket for supporting the hydraulic motor, the excavator having a rotatable arm
The method of claim 8,
The arm is coupled to the motor bracket, characterized in that it further comprises a first gear cover to protect the worm, excavator with a rotatable arm.
The method of claim 9,
The cancer,
Excavator having a rotatable arm, characterized in that it further comprises a second gear cover coupled to the first member to protect the worm wheel.

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