Patent Description:
A turbine is a mechanical device that obtains a rotational force by an impulsive force or reaction force using a flow of a compressible fluid such as steam or gas. A turbine may be a steam turbine using steam, or a gas turbine using a high temperature combustion gas.

Among them, the gas turbine is mainly composed of a compressor, a combustor, and a turbine. The compressor is provided with an air inlet for introducing air, and a plurality of compressor vanes and compressor blades, which are alternately arranged in a compressor housing.

The combustor supplies fuel to the compressed air compressed in the compressor and ignites a fuel-air mixture with a burner to produce a high temperature and high pressure combustion gas.

The turbine has a plurality of turbine vanes and turbine blades disposed alternately in a turbine casing. Further, a rotor is arranged to pass through the center of the compressor, the combustor, the turbine and an exhaust chamber.

Both ends of the rotor are rotatably supported by bearings. A plurality of disks is fixed to the rotor so that the respective blades are connected. A drive shaft such as a generator is connected to an end of the exhaust chamber. An example is shown in <CIT>.

Since these gas turbines have no reciprocating mechanism such as a piston found in a <NUM>-stroke engine, and consequently have no frictional parts like piston-cylinder, they have several advantages. These include minimal consumption of lubricating oil, a significant reduction in amplitude, which is a characteristic of a reciprocating machine, and the ability to operate at high speed operation.

Briefly describing the operation of the gas turbine, the compressed air compressed in the compressor is mixed with fuel and combusted to produce a high-temperature combustion gas in the combustor, which is then injected toward the turbine. The injected combustion gas passes through the turbine vanes and the turbine blades to generate a rotational force, which causes the rotor to rotate.

The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an objective of the present invention is to provide a tie rod-locking nut assembly capable of preventing a tie rod-locking nut from being loosened during operation of a gas turbine, and a gas turbine including the same.

To this end, the present invention provides a tie rod-locking nut assembly in accordance with claim <NUM> and a gas turbine in accordance with claim <NUM>. Advantageous embodiments are subject to the dependent claims and the following description, referring to the drawings.

In a first aspect of the present invention, a tie rod-locking nut assembly includes: a tie rod-locking nut engaged with or fastened to a jack bolt, e.g., in that the jack bolt is inserted or introduced into the tie rod-locking nut; a jack bolt-locking nut inserted between the tie rod-locking nut and the jack bolt; an anti-loosening washer formed to wrap around an outer circumferential surface of the jack bolt-locking nut to prevent loosening of the jack bolt-locking nut; and a locking plate formed to cover the anti-loosening washer and engaging with an outer circumferential surface of the tie rod.

It is one of the ideas of the present invention to prevent loosening of the jack bolt-locking nut by an anti-loosening washer which engages outer circumferential surface of the jack bolt-locking nut. The anti-loosening washer may be configured for being coupled to the tie rod and may engaged with the jack bolt-locking nut such that rotation of the jack bolt-locking nut is prevented.

In some embodiments, the tie rod-locking nut may have a jack bolt-insertion hole formed at a position corresponding to a position in which the jack bolt is formed, and the jack bolt-insertion hole has a stepped portion formed at an end of the jack bolt-insertion hole.

In some embodiments, the jack bolt-locking nut has a shape of hollow pipe with both ends open and may be inserted into a gap formed between the stepped portion and the jack bolt during engagement with the jack bolt. Generally, the jack bolt-insertion hole may include a step dividing the jack bolt-insertion hole into an outer portion formed at an end of the jack bolt-insertion hole and an inner portion formed on an opposite side of the step, wherein the outer portion has a greater diameter than the inner portion. The outer portion, herein, may also be referred to as stepped portion.

In some embodiments, the jack bolt-locking nut may be formed with a length greater than the stepped portion such that, when inserted into the gap, a distal end thereof is exposed externally from the tie rod-locking nut, wherein the jack bolt-locking nut is in a shape such that a cross-section of the jack bolt-locking nut has an outer circumference in a circular shape corresponding to the stepped portion and has an inner circumference in a preferably polygonal shape corresponding to the jack bolt.

In some embodiments, a contact area between the jack bolt-locking nut and the anti-loosening washer may be caulked.

In some embodiments, the anti-loosening washer may be a circular plate member having a plurality of insertion holes formed in positions corresponding to the plurality of jack bolt-locking nuts.

In some embodiments, an inner circumferential surface of the locking plate may be threaded to engage with the outer circumferential surface of the tie rod.

In a second aspect of the present invention, a gas turbine includes: a compressor suctioning and compressing external air and having a plurality of compressor rotor disks; a combustor mixing fuel with compressed air and combusting an air-fuel mixture; a turbine section having a plurality of turbine blades mounted on a plurality of turbine rotor disks so that the turbine blades is rotated by the combustion gases discharged from the combustor; and a tie rod having one end engaged with a most upstream-side one of the compressor rotor disks and the other end engaged with a tie rod-locking nut assembly, the tie rod-locking nut assembly including: a tie rod-locking nut threaded onto a jack bolt formed; a jack bolt-locking nut inserted between the tie rod-locking nut and the jack bolt; an anti-loosening washer formed to wrap around an outer circumferential surface of the jack bolt-locking nut to prevent loosening of the jack bolt-locking nut; and a locking plate formed to cover the anti-loosening washer and engaging with an outer circumferential surface of the tie rod. The tie rod-locking nut assembly, thus, may be the tie rod-locking nut assembly of the first aspect of the invention.

In some embodiments, the jack bolt-locking nut may have a shape of hollow pipe with both ends open and may be inserted into a gap formed between the stepped portion and the jack bolt during engagement with the jack bolt.

In some embodiments, the jack bolt-locking nut may be formed with a length greater than the stepped portion such that, when inserted into the gap, a distal end thereof is exposed externally from the tie rod-locking nut, wherein the jack bolt-locking nut is in a shape such that a cross-section of the jack bolt-locking nut has an outer circumference in a circular shape corresponding to the stepped portion and has an inner circumference in a polygonal shape corresponding to the jack bolt.

Specific details of other implementations of various aspects of the present invention are included in the following detailed description.

According to embodiments of the present invention, it is possible to prevent the tie rod-locking nut from being loosened from the jack bolt due to vibration generated during operation of the gas turbine, thereby improving the operational stability of the gas turbine.

However, it should be noted that the present invention is not limited thereto.

Terms used herein are used to merely describe specific embodiments, and are not intended to limit the present invention. As used herein, an element expressed as a singular form includes a plurality of elements, unless the context clearly indicates otherwise. Further, it will be understood that the term "comprising" or "including" specifies the presence of stated features, numbers, steps, operations, elements, parts, or combinations thereof, but does not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, parts, or combinations thereof.

It is noted that like elements are denoted in the drawings by like reference symbols as whenever possible. Further, the detailed description of known functions and configurations that may obscure the gist of the present invention will be omitted. For the same reason, some of the elements in the drawings are exaggerated, omitted, or schematically illustrated.

<FIG> is a partially cut-away perspective view of a gas turbine according to an embodiment of the present invention, and <FIG> is a cross-sectional view illustrating a schematic structure of a gas turbine according to an embodiment of the present invention.

As illustrated in <FIG>, a gas turbine <NUM> according to an embodiment of the present invention includes a compressor <NUM>, a combustor <NUM>, and a turbine <NUM>. The compressor <NUM> includes a plurality of compressor blades <NUM> radially installed. The compressor <NUM> rotates the compressor blade <NUM> so that air flows while being compressed by the rotation of the compressor blade <NUM>. The size and installation angle of the blade <NUM> may vary depending on the installation location. In one embodiment, the compressor <NUM> is connected directly or indirectly to the turbine <NUM>, and receives a portion of the power generated from the turbine <NUM> to rotate the compressor blade <NUM>.

Air compressed by the compressor <NUM> flows to the combustor <NUM>. The combustor <NUM> includes a plurality of combustion chambers <NUM> and a fuel nozzle module <NUM> arranged in an annular shape.

The gas turbine <NUM> includes a housing <NUM> and a diffuser <NUM> which is disposed on a rear side of the housing <NUM> and through which a combustion gas passing through a turbine is discharged. A combustor <NUM> is disposed in front of the diffuser <NUM> so as to receive and burn compressed air.

Referring to the flow direction of the air, a compressor section <NUM> is located on the upstream side of the housing <NUM>, and a turbine section <NUM> is located on the downstream side of the housing. A torque tube <NUM> is disposed as a torque transmission member between the compressor section <NUM> and the turbine section <NUM> to transmit the rotational torque generated in the turbine section to the compressor section.

The compressor section <NUM> is provided with a plurality (for example, <NUM>) of compressor rotor disks <NUM>, which are fastened by a tie rod <NUM> to prevent axial separation thereof.

Specifically, the compressor rotor disks <NUM> are axially arranged, wherein the tie rod <NUM> constituting a rotary shaft passes through substantially central portions of the compressor rotor disks <NUM>. Here, the neighboring compressor rotor disks <NUM> are disposed so that opposed surfaces thereof are pressed against each other by an axial force applied through the tie rod <NUM>, so that the neighboring compressor rotor disks do not rotate relative to each other.

A plurality of compressor blades <NUM> are radially coupled to an outer circumferential surface of each compressor rotor disk <NUM>. Each of the compressor blades <NUM> may have a dovetail part <NUM> which is fastened to the compressor rotor disk <NUM>. The invention is not limited to a dovetail part <NUM> but the compressor blades <NUM> may comprise, generally, a coupling member which has a cross-section corresponding to a coupling groove formed in the compressor rotor disk <NUM>.

Compressor vanes (not shown) fixed to the housing are respectively positioned between the rotor disks <NUM>. Unlike the compressor rotor disks, the compressor vanes are fixed to the housing and do not rotate. The compressor vane serves to align a flow of compressed air that has passed through the compressor blades <NUM> of the compressor rotor disk <NUM> and guide the air to the compressor blades <NUM> of the rotor disk <NUM> located on the downstream side.

The fastening method of the dovetail part <NUM> includes a tangential type and an axial type. These may be chosen according to the required structure of the commercial gas turbine, and may have a generally known dovetail or fir-tree shape. In some cases, it is possible to fasten the blades to the rotor disk by using other fasteners such as keys or bolts in addition to the fastening shape.

The tie rod <NUM> is arranged to pass through the center of the compressor rotor disks <NUM> and turbine rotor disks <NUM> such that one end thereof is engaged with an engaging member, such as the compressor rotor disk located on the most upstream side, and the other end thereof is engaged with a tie rod-locking nut assembly <NUM>. The tie rod <NUM> may be composed of a single tie rod or a plurality of tie rods. Generally, the tie rod <NUM> extends longitudinally between a first end and a second end. The tie rod-locking nut assembly <NUM> according to the present invention will be described later with reference to <FIG>.

The shape of the tie rod <NUM> is not limited to that shown in <FIG>, but may have a variety of structures depending on the gas turbine. That is, as shown in the drawing, one tie rod may have a shape passing through a central portion of the rotor disk, a plurality of tie rods may be arranged in a circumferential manner, or a combination thereof may be used. Generally, the engagement member, e.g., the compressor rotor disk located on the most upstream side, and the tie rod-locking nut assembly <NUM> are engaged with opposite ends of the tie rod <NUM> and, together, apply an axial force to the compressor rotor disks <NUM> and turbine rotor disks <NUM> so that they are clamped axially between the engagement member and the tie rod-locking nut assembly <NUM>.

Although not shown, the compressor of the gas turbine may be provided with a vane serving as a guide element at the next position of the diffuser in order to adjust a flow angle of a pressurized fluid entering a combustor inlet to a designed flow angle. The vane is referred to as a deswirler.

The combustor <NUM> mixes the introduced compressed air with fuel and combusts the air-fuel mixture to produce a high-temperature and high-pressure combustion gas. With an isobaric combustion process in the compressor, the temperature of the combustion gas is increased to the heat resistance limit that the combustor and the turbine components can withstand.

The combustor consists of a plurality of combustors, which is arranged in the housing formed in a cell shape, and includes a burner having a fuel injection nozzle and the like, a combustor liner forming a combustion chamber, and a transition piece as a connection between the combustor and the turbine, thereby constituting a combustion system of a gas turbine.

Specifically, the combustor liner provides a combustion space in which the fuel injected by the fuel nozzle is mixed with the compressed air of the compressor and the fuel-air mixture is combusted. Such a liner may include a flame canister providing a combustion space in which the fuel-air mixture is combusted, and a flow sleeve forming an annular space surrounding the flame canister. A fuel nozzle is coupled to the front end of the liner, and an igniter plug is coupled to the side wall of the liner.

On the other hand, a transition piece is connected to a rear end of the liner so as to transmit the combustion gas combusted by the igniter plug to the turbine side. An outer wall of the transition piece is cooled by the compressed air supplied from the compressor so as to prevent thermal breakage due to the high temperature combustion gas.

To this end, the transition piece is provided with cooling holes through which compressed air is injected into and cools the inside of the transition piece and flows towards the liner.

The air that has cooled the transition piece flows into the annular space of the liner and compressed air is supplied as a cooling air to the outer wall of the liner from the outside of the flow sleeve through cooling holes provided in the flow sleeve so that both air flows may collide with each other.

In the meantime, the high-temperature and high-pressure combustion gas from the combustor is supplied to the turbine <NUM>. The supplied high-temperature and high-pressure combustion gas expands and collides with the rotating blades of the turbine, generating a reaction force that imparts a rotational torque. This torque is subsequently transferred to the compressor via the torque tube <NUM>. Here, any surplus power needed to drive the compressor is used to drive a generator or similar equipment.

The turbine <NUM> is basically similar in structure to the compressor. That is, the turbine <NUM> is also provided with a plurality of turbine rotor disks <NUM> similar to the compressor rotor disks of the compressor. Thus, the turbine rotor disk <NUM> also includes a plurality of turbine blades <NUM> disposed radially. The turbine blade <NUM> may also be coupled to the turbine rotor disk <NUM> in a dovetail coupling manner, for example. That is, the turbine blades <NUM> may comprise, generally, a coupling member which has a cross-section corresponding to a coupling groove formed in the turbine rotor disk <NUM>.

Between the turbine blades <NUM>, a turbine vane (not shown) fixed to a turbine casing <NUM> is provided to guide a flow direction of the combustion gas passing through the turbine blades.

<FIG> are views illustrating the process of assembling a tie rod-locking nut according to the related art, and <FIG> is a perspective view illustrating a tie rod-locking nut assembled on a tie rod according to the related art.

Referring to <FIG>, and <FIG>, a jack bolt <NUM> is formed at an end of the tie rod <NUM>, and the tie rod-locking nut <NUM> is fastened inserting the jack bolt <NUM> into the tie-rod locking nut <NUM>. The tie rod-locking nut <NUM> is able to provide a high tension force and tightening force to the tie rod <NUM> as it is threaded onto the jack bolt <NUM>.

Large-scale gas turbines rotate at approximately <NUM> RPM and are exposed to a variety of high-temperature/high-pressure environments. In particular, the tie rod-locking nut <NUM> may be loosened from the jack bolt <NUM> by vibrations generated during operation. However, conventional gas turbines are not equipped with means to prevent the tie rod-locking nut <NUM> from being loosened. Accordingly, the present invention discloses a tie rod-locking nut assembly capable of preventing the tie rod-locking nut from being loosened during operation of the gas turbine, and a gas turbine including the tie rod-locking nut.

<FIG> is a perspective view illustrating a tie rod-locking nut assembly according to an embodiment of the present invention, <FIG> is a cross-sectional view illustrating the tie rod-locking nut assembly according to the embodiment of the present invention, <FIG> is a perspective view illustrating a jack bolt-locking nut inserted between the tie rod-locking nut and the jack bolt, <FIG> is a cross-sectional view of <FIG>, <FIG> is a perspective view illustrating the state of an anti-loosening washer being engaged in the configuration of <FIG>, and <FIG> is a cross-sectional view of <FIG>.

Referring to <FIG>, the tie rod-locking nut assembly <NUM> includes a tie rod-locking nut <NUM>, a jack bolt-locking nut <NUM>, an anti-loosening washer <NUM>, and a locking plate <NUM>.

At an end of the tie rod <NUM>, a plurality of jack bolts <NUM> are arranged. For example, the jack bolts <NUM> may be circularly arranged to form a circle around a central axis of the tie rod <NUM>. The circle formed by the plurality of jack bolts <NUM> may be arranged in two concentric circles centered on the tie rod <NUM>. In other words, the plurality of jack bolts <NUM> may be inserted in the rod-locking nut <NUM> such that they form two concentric circles centered on the central axis of the tie rod <NUM>. The jack bolts <NUM> may be coupled to the tie rod <NUM>. In particular, the jack bolts <NUM> may axially protrude from a stepped portion formed in the tie rod <NUM>, as exemplarily shown in <FIG>.

The direction in which the jack bolts <NUM> are inserted in the rod-locking nut <NUM> may be referred to as an upstream direction, which is parallel to the central axis of the tie rod <NUM>. The direction opposite to the upstream direction may be referred to as a downstream direction.

The tie rod-locking nut <NUM> is fastened by inserting the plurality of jack bolts <NUM> formed at the end of the tie rod <NUM> into the tie-rod locking nut <NUM>. The tie rod-locking nut <NUM> has a plurality of jack bolt-insertion holes <NUM> formed at locations corresponding to the locations in which the plurality of jack bolts <NUM> are formed. For example, the plurality of jack bolt-insertion holes <NUM> may form a circle centered on the tie rod <NUM>, as in the plurality of jack bolts <NUM>. In other words, the plurality of jack bolt-insertion holes <NUM> may be circularly arranged, being spaced apart from each other with regular intervals and having the tie rod <NUM> at the center. According to an embodiment, the plurality of jack bolt-insertion holes <NUM> may be arranged to form double concentric circles centered on the tie rod <NUM>.

According to an embodiment, each of the plurality of jack bolt-insertion holes <NUM> may be in a cylindrical shape. The plurality of jack bolt-insertion holes <NUM> may be formed by being grooved toward the upstream direction from a downstream end surface of the tie rod-locking nut <NUM>. In other words, the jack bolt-insertion holes <NUM> may open on a first axial end face of the tie rod-locking nut <NUM>. Each of the plurality of jack bolt-insertion holes <NUM> may be in a cylindrical shape having an inner circumferential surface. The inner circumferential surface of the insertion hole <NUM> may comprise a step, wherein an outer portion <NUM> or downstream portion jack bolt-insertion holes <NUM> extending between the first axial end face of the tie rod-locking nut <NUM> and the step has a greater diameter than an inner portion of jack bolt-insertion hole <NUM> extending from the step oppositely to the outer portion. Thus, generally, an outer portion <NUM> is formed at a downstream end portion or outer end portion of the jack bolt-insertion holes <NUM>. The outer end portion is adjacent to the first axial end face of the tie rod-locking nut <NUM>. When a diameter of the jack bolt-insertion hole <NUM> measured at an upstream side of the step is defined as a first diameter, and a diameter of the jack bolt-insertion hole <NUM> measured on a downstream side of the step is defined as a second diameter, the second diameter is larger than the first diameter. The first and second diameters may be constant. In other words, the cylindrical shape of the jack bolt-insertion hole <NUM> includes a front part or inner part at relatively upstream and an end part or outer part <NUM> at relatively downstream of the step, while the front part and the end part are concentric, the end part has a larger diameter than the front part.

Generally, each jack bolt <NUM> is inserted into one of the jack bolt-insertion holes <NUM>. When the jack bolt <NUM> is inserted into the jack bolt-insertion hole <NUM>, the jack bolt <NUM> is engaged with a thread formed on the inner surface of the first part of the jack bolt-insertion hole <NUM> and there is formed a space between the jack bolt <NUM> and the end part of the jack bolt-insertion hole <NUM> (i.e., a space between the jack bolt <NUM> and the stepped portion <NUM>).

A jack bolt-locking nut <NUM> is formed to have a shape of hollow pipe with both ends open, and is inserted between the tie rod-locking nut <NUM> and the jack bolt <NUM>. In other words, the jack bolt-locking nut <NUM> is inserted in the space between the jack bolt <NUM> and the end part of the tie rod-locking nut <NUM>. When the jack bolt-locking nut <NUM> engages with the jack bolt <NUM>, the jack bolt-locking nut may be inserted into a gap formed between the jack bolt <NUM> and the outer portion <NUM> formed at the end of the jack bolt-insertion hole <NUM>. The cross-section of the jack bolt-locking nut <NUM> may be in a shape such that the outer circumference is a circular shape corresponding to the outer portion <NUM> of the jack bolt-insertion hole <NUM> and the inner circumference may be a polygonal shape corresponding to an outer surface of an end portion of the jack bolt <NUM>. Generally, the outer surface of the end portion of the jack bolt <NUM> and the inner circumference of the jack bolt-locking nut <NUM> may be formed to form fittingly engage. The jack bolt-locking nut <NUM> may be formed with a length greater than a length of the outer portion <NUM>, such that when inserted into the gap, an downstream end of the jack bolt-locking nut <NUM> may be exposed externally from the tie rod-locking nut <NUM>. In other words, when inserted into the gap, a downstream end of the jack bolt-locking nut <NUM> may be exposed by protruding further downstream than the downstream end surface of the tie rod-locking nut <NUM>. Generally, when inserted into the gap, the jack bolt-locking nut <NUM> may protrude from the first axial end face of the tie rod-locking nut <NUM>.

The anti-loosening washer <NUM> is formed to wrap around an outer circumferential surface of the jack bolt-locking nut <NUM>, especially the protruding portions of the jack bolt-locking nut <NUM>. The anti-loosening washer <NUM> is in close contact with the tie rod-locking nut <NUM>. The area in which the jack bolt-locking nut <NUM> and the anti-loosening washer <NUM> contact may be caulked to prevent rotation of the jack bolt-locking nut <NUM>, thereby preventing the jack bolt-locking nut <NUM> from being loosened. "Caulking" in this context may be understood as a process of sealing a gap or joint between the two facing surfaces of the jack bolt-locking nut <NUM> and the anti-loosening washer <NUM> using a material such as caulk. The anti-loosening washer <NUM> is a circular plate member or a disk-shaped plate member having a plurality of insertion holes <NUM> formed in positions corresponding to the plurality of jack bolt-locking nuts <NUM>. The diameter and the location of the insertion holes <NUM> formed in the anti-loosening washer <NUM> may be the same as the diameter and the location of the outer portions <NUM> of the plurality of jack bolt-insertion holes <NUM> in the tie rod-locking nut <NUM>. The thickness, in other words, an axial length of the anti-loosening washer <NUM> may be the same with the length of the protruding portions of the jack bolt-locking nut <NUM>. The inner diameters of the insertion holes <NUM> are formed to be sized to allow the jack bolt-locking nuts <NUM> to be inserted. The plurality of insertion holes <NUM> are arranged to form a circle centered on the tie rod <NUM> as in the plurality of jack bolts <NUM>. According to an embodiment, the plurality of insertion holes <NUM> may be arranged to form double centric circles centered on the tie rod <NUM>. A through-hole is formed at the center of the anti-loosening washer <NUM> such that the tie rod <NUM> passes therethrough. For example, the anti-loosening washer <NUM> may be provided with a thread on the through-hole so that it may be threaded onto the tie rod <NUM>. The outer diameter of the anti-loosening washer <NUM> may be the same with the outer diameter of the tie rod-locking nut <NUM>.

The locking plate <NUM> is formed and arranged to cover the jack bolt-locking nut <NUM> and the anti-loosening washer <NUM> at their downstream ends. The locking plate <NUM> is formed in the same shape as the anti-loosening washer <NUM> except that the locking plate <NUM> does not have insertion holes <NUM> and that the locking plate <NUM> may be thicker than the anti-loosening washer <NUM> (i.e., longer axial length). That is, the locking plate <NUM> is a circular plate member or a disk-shaped plate member of the same size (i.e., same outer diameters) as the anti-loosening washer <NUM>, and has a through-hole formed at the center such that the tie rod <NUM> passes therethrough. A thread may be formed on an inner circumferential surface of the locking plate <NUM> to engage with a thread formed on the outer circumferential surface of the tie rod <NUM>.

Claim 1:
A tie rod-locking nut assembly (<NUM>) comprising:
a tie rod-locking nut (<NUM>) engaged with a jack bolt (<NUM>); characterised by
a jack bolt-locking nut (<NUM>) inserted between the tie rod-locking nut (<NUM>) and the jack bolt (<NUM>);
an anti-loosening washer (<NUM>) formed to wrap around an outer circumferential surface of the jack bolt-locking nut (<NUM>) to prevent loosening of the jack bolt-locking nut (<NUM>); and
a locking plate (<NUM>) formed to cover the anti-loosening washer (<NUM>) and engaging with an outer circumferential surface of the tie rod (<NUM>).