JP7432474B2 - centrifugal compressor - Google Patents

Description

The present invention relates to a centrifugal compressor for compressing gas, and in particular to a multi-stage centrifugal compressor equipped with a plurality of impellers.

As a centrifugal compressor, there is a multi-stage centrifugal compressor equipped with a plurality of impellers. Such a multistage centrifugal compressor is used, for example, to compress refrigerant gas used in a refrigerator. A multistage centrifugal compressor generally has multiple (multiple stages) impellers fixed to a main shaft, a drive source such as an electric motor that rotates the main shaft, a casing that houses the impellers, and two adjacent impellers. The vehicle is equipped with a plurality of guide vanes arranged in a return flow path that guides gas discharged from the front-stage impeller of the vehicle to the rear-stage impeller. A multistage centrifugal compressor is configured to discharge gas compressed by a plurality of impellers that are rotated together with a main shaft by a driving source. The plurality of guide vanes are arranged radially at equal intervals within the return passage, and the plurality of guide vanes rectify the flow of gas within the return passage into a flow radially inward of the centrifugal compressor. be done.

An example of such a guide vane is one that includes a fixed guide vane fixed to the return flow path and a variable guide vane disposed continuously downstream of the fixed guide vane in the gas flow direction. The variable guide vane is pivotably disposed in the return flow path relative to the fixed guide vane. By changing the swing angle of the variable guide vanes (ie, the degree of opening of the variable guide vanes relative to the solid guide vanes), a multistage centrifugal compressor can be operated efficiently at a desired flow rate and pressure head.

FIG. 13 is a diagram for explaining the opening degree of the variable guide vane. FIG. 13 is a diagram of the fixed guide vane 130 and the variable guide vane 132 viewed from the axial direction of the main shaft 101 (the direction in which the main shaft 101 extends). In FIG. 13, only two fixed guide vanes 130 and two variable guide vanes 132 are illustrated, and other fixed guide vanes 130 and other variable guide vanes 132 are not illustrated. In FIG. 13, the position of the variable guide vane 132 indicated by a solid line indicates the position where the opening degree of the variable guide vane 132 with respect to the fixed guide vane 130 is 100%, and the position of the variable guide vane 132 indicated by a dotted line indicates the position where the opening degree of the variable guide vane 132 with respect to the fixed guide vane 130 is 100%. The position where the opening degree of variable guide vane 132 with respect to 130 is 0% is shown. In other words, the opening degree of the variable guide vane 132 corresponds to the turning angle α of the variable guide vane 132 with respect to the fixed guide vane 130. When the variable guide vane 132 is in the position shown by the dotted line in FIG. 13, the turning angle α is zero.

Generally, the cross-sectional shape of the variable guide vane in a direction parallel to the main axis is constant (ie, does not change). In other words, the chord of the variable guide vane (the straight line connecting the leading edge and the trailing edge of the variable guide vane when viewed in a plane perpendicular to the axis of the main shaft) is the height direction of the variable guide vane (the axis of the main shaft It does not change depending on the position (direction parallel to the heart).

Japanese Patent Application Publication No. 2011-43130

The multistage centrifugal compressor changes the opening degree of the variable guide vane depending on the flow rate of gas flowing through the multistage centrifugal compressor. For example, when increasing the flow rate of gas flowing through a centrifugal compressor, the centrifugal compressor increases the opening degree of the variable guide vane, and when decreasing the flow rate of gas flowing through the centrifugal compressor, the opening degree of the variable guide vane increases. Make it smaller.

However, when the opening degree of the variable guide vane is increased, the diversion (bending of the flow) of the gas flowing along the variable guide vane increases, which may cause separation of the gas flow or the blades near the exit of the return flow path. Gas swirl in the opposite direction to the rotation of the car (reverse pre-swirling) may occur. In the return flow path, the gas flow on the hub side (the front impeller side in the direction in which the main shaft extends) has a higher boundary layer energy than the gas flow in the shroud side (the latter impeller side in the direction in which the main shaft extends). Because low-energy fluid caused by loss tends to accumulate, reverse pre-swirling at the inlet of the impeller in the latter stage due to separation of the gas flow or deterioration of the flow diversion function of the guide vane due to separation occurs on the hub side rather than on the shroud side. It is likely to occur in

Separation and reverse pre-swirling of the gas flow impede the stable flow of the gas. The unstable gas flow can be a contributing factor to reducing the operating efficiency of the centrifugal compressor and reducing the maximum flow rate of gas that the centrifugal compressor can flow. A reduction in the maximum gas flow rate leads to a reduction in the operating range of the centrifugal compressor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a centrifugal compressor that can form a stable flow of gas and reduce the decrease in operating efficiency of the centrifugal compressor and the maximum flow rate of gas that the centrifugal compressor can flow. .

In one aspect, a main shaft, a plurality of impellers fixed to the main shaft, a casing that accommodates the plurality of impellers, and a gas discharged from a first impeller of the plurality of impellers are provided. a plurality of guide vanes arranged in a return flow path leading to a second impeller that is the next stage impeller of the first impeller; each guide vane includes a fixed guide vane; and a variable guide vane arranged continuously in the variable guide vane, the angle between the chord of the variable guide vane and the reference straight line increasing from the shroud side to the hub side. A centrifugal compressor is provided in which the reference straight line is a straight line connecting the axial center of the main shaft and the axial center of the rotating shaft of the variable guide vane.

In one aspect, the variable guide vane has a flange on a rear edge, and when the variable guide vane is placed at an initial position, the first variable guide vane of two adjacent variable guide vanes Only the collar portion of the guide vane contacts the second variable guide vane.
In one aspect, a rear edge of the first variable guide vane is located radially outward of the centrifugal compressor from a contact position of the flange.

According to the present invention, the deflection of the gas flow along the suction surface of the variable guide vane on the hub side is smaller than the deflection of the gas flow along the suction surface of the variable guide vane on the shroud side. can do. That is, the blade load on the hub side of the variable guide vane can be reduced more than the blade load on the shroud side of the variable guide vane. As a result, the occurrence of gas flow separation and reverse pre-swirling is reduced, and the centrifugal compressor is able to form a uniform gas flow within the return flow path. Therefore, the centrifugal compressor can reduce a decrease in the operating efficiency of the centrifugal compressor and a decrease in the maximum flow rate of gas that the centrifugal compressor can flow.

FIG. 1 is a schematic diagram showing an embodiment of a centrifugal compressor. FIG. 3 is a schematic diagram of the guide vane viewed from the axial direction of the main shaft. It is a schematic diagram which shows the state when a variable guide vane is open. It is a perspective view of a variable guide vane. 5 is a view of the variable guide vane of FIG. 4 viewed from the direction indicated by arrow A in FIG. 4. FIG. 5 is a view of the variable guide vane of FIG. 4 viewed from the direction indicated by arrow B in FIG. 4. FIG. FIG. 3 is a plan view of the variable guide vane. 8 is a side view of the variable guide vane of FIG. 7 viewed from the direction indicated by arrow D in FIG. 7. FIG. 8 is a sectional view taken along line CC in FIG. 7. FIG. 10(a) is a diagram showing the shroud surface, FIG. 10(b) is an end view taken along line EE in FIG. 8, and FIG. 10(c) is an end view taken along line FF in FIG. FIG. 10(d) is an end view taken along the line GG in FIG. 8, and FIG. 10(e) is an inverted view of the hub surface. It is a figure explaining a reference straight line. FIG. 6 is a diagram showing details of the flow of gas flowing along the negative pressure surface of the variable guide vane of the present embodiment. It is a figure for explaining the opening degree of a variable guide vane.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of a centrifugal compressor. The centrifugal compressor of this embodiment is a device that compresses gas. A centrifugal compressor is used, for example, in a centrifugal refrigerator to compress refrigerant gas.

As shown in FIG. 1, the centrifugal compressor houses a main shaft 1, a plurality of (multiple stages) (two in FIG. 1) impellers 3a, 3b fixed to the main shaft 1, and impellers 3a, 3b. a casing 2, a plurality of guide vanes 5 disposed on the discharge side of the impeller 3a, and a drive source (not shown) such as an electric motor connected to the end of the main shaft 1 to rotate the main shaft 1. ing. The main shaft 1 is rotatably supported by a bearing 9. The plurality of impellers 3a and 3b are rotated together with the main shaft 1 by the drive source.

A gas flow path 20 is formed inside the casing 2 and extends from the front impeller 3a to the rear impeller 3b of the two adjacent impellers 3a and 3b. The casing 2 has a suction port 12 and a scroll flow path 13, and the gas sucked from the suction port 12 passes through the impeller 3a, the gas flow path 20, the impeller 3b, and the scroll flow path 13, and enters the scroll flow path. It is discharged from a discharge port (not shown) communicating with the passage 13. The impellers 3a and 3b are arranged in series facing the same direction (the direction of the suction port 12). In the following description, the impellers 3a and 3b may be collectively referred to simply as an impeller 3. The centrifugal compressor of this embodiment is a multistage centrifugal compressor including a plurality of impellers 3.

The gas flow path 20 has a diffuser flow path 21, a crossover flow path 22, and a return flow path 23. The diffuser flow path 21 is a flow path arranged on the radially outer side of the impeller 3a, and communicates with the gas outlet of the impeller 3a. The crossover flow path 22 is connected to the diffuser flow path 21 and is a flow path for reversing the flow direction of the gas discharged from the impeller 3a to a direction radially inward. The return flow path 23 is a flow path that is connected to the crossover flow path 22 and guides the gas that has passed through the diffuser flow path 21 and the crossover flow path 22 (that is, the gas discharged from the impeller 3a) to the impeller 3b. be.

The plurality of guide vanes 5 are arranged in the return flow path 23 of the gas flow path 20. In this embodiment, the plurality of guide vanes 5 are arranged in a return passage 23 formed between the casing 2 and a disk 7 arranged on the back side of the impeller 3a (on the impeller 3b side). . The main shaft 1 extends through the disk 7. The position of the disk 7 is fixed, and the disk 7 does not rotate as the main shaft 1 rotates.

Each guide vane 5 includes a fixed guide vane 30 and a variable guide vane 32. The variable guide vane 32 is arranged downstream of the fixed guide vane 30 in the gas flow direction. The variable guide vane 32 is arranged continuously with the fixed guide vane 30. The position of the fixed guide vane 30 is fixed within the return channel 23, while the variable guide vane 32 is arranged in the return channel 23 so as to be pivotable relative to the fixed guide vane 30.

The centrifugal compressor further includes a vane controller 8 coupled to the variable guide vane 32. The vane controller 8 controls the opening degree of the variable guide vane 32 (that is, the turning angle with respect to the fixed guide vane 30) according to the flow rate of gas flowing through the centrifugal compressor.

When the main shaft 1 is rotated by a drive source (not shown), the impeller 3 rotates, and gas flows into the impeller 3a through the suction port 12. Gas is compressed by the rotating impeller 3a, and the compressed gas flows into the gas flow path 20 from the outlet of the impeller 3a. The gas that has reached the return flow path 23 of the gas flow path 20 flows along the guide vane 5, flows into the next stage impeller 3b, and is further compressed by the rotating impeller 3b. The gas discharged from the outlet of the impeller 3b passes through the scroll passage 13 and is discharged from a discharge port (not shown).

Although the centrifugal compressor of this embodiment is a multistage centrifugal compressor including two stages of impellers 3a and 3b, the number of impellers 3 is not limited to this embodiment. In one embodiment, the centrifugal compressor may include three or more stages of impellers 3. In this case, a plurality of gas channels 20 are formed in the casing 2 and a plurality of guide vanes 5 are arranged in the return channel 23 of each gas channel 20. Each return flow path 23 is formed between the impeller 3 of one stage and the impeller 3 of the next stage. The pressure of the gas is increased sequentially by the plurality of impellers 3 and the plurality of guide vanes 5, and the gas is finally collected in the scroll passage 13, passed through the scroll passage 13, and discharged from a discharge port (not shown).

FIG. 2 is a schematic diagram of the guide vane 5 viewed from the direction of the axis CP of the main shaft 1. More specifically, FIG. 2 is a diagram of the guide vane 5 viewed from the shroud side (impeller 3b side). As shown in FIG. 2, the fixed guide vanes 30 have curved side surfaces and are arranged at equal intervals along the circumferential direction of the disk 7. The vane controller 8 that adjusts the opening degrees of the plurality of variable guide vanes 32 may be connected to the casing 2 or may be disposed apart from the casing 2.

The variable guide vane 32 is provided with a rotating shaft 35, and the variable guide vane 32 is configured to pivot around the rotating shaft 35 in the direction indicated by the arrow in FIG. The vane controller 8 controls the rotation angle (opening degree) of the variable guide vanes 32 so that all of the plurality of variable guide vanes 32 have the same rotation angle. The variable guide vane 32 closes or opens a gas flow path formed between two adjacent fixed guide vanes 30 by pivoting around the rotating shaft 35.

FIG. 2 shows the variable guide vane 32 in a closed state. The position of the variable guide vane 32 shown in FIG. 2 is a position where the opening degree of the variable guide vane 32 is 0%, and corresponds to the initial position of the variable guide vane 32. When the plurality of variable guide vanes 32 are in the initial position, each variable guide vane 32 contacts another adjacent variable guide vane 32. Specifically, only the flange 49 formed at the rear edge of each variable guide vane 32 contacts the front edge 45 of the adjacent variable guide vane 32 .

The variable guide vane 32 in the initial position closes the gas flow path formed between two adjacent guide vanes 5 and prevents gas from flowing through this flow path. Therefore, at the start and end of operation of the centrifugal compressor, the variable guide vane 32 is moved to the initial position to prevent gas from flowing backward from the discharge port. Further, when assembling the variable guide vane 32 to the centrifugal compressor, the variable guide vane 32 is arranged at the initial position. Each variable guide vane 32 can be positioned by bringing the flange 49 of one of the two adjacent variable guide vanes 32 into contact with the front edge 45 of the other variable guide vane 32. can.

FIG. 3 is a schematic diagram showing a state when the variable guide vane 32 is open. More specifically, the position of the variable guide vane 32 shown in FIG. 3 is a position where the opening degree of the variable guide vane 32 is 100%. The vane controller 8 controls the opening degree of the variable guide vane 32 between 0% shown in FIG. 2 and 100% shown in FIG. 3. In one embodiment, vane controller 8 may open the variable guide vanes to greater than 100% opening as shown in FIG. When the variable guide vanes 32 open from the closed state (see FIG. 2), a gas flow path is formed between adjacent guide vanes 5, and the gas flows along the variable guide vanes 32 in the radial direction of the centrifugal compressor. It flows inward (in the direction indicated by the arrow in FIG. 3). Guide vanes 5, including fixed guide vanes 30 and variable guide vanes 32, rectify the flow of gas in return passage 23 into a flow radially inward of the centrifugal compressor.

The vane controller 8 controls the opening degree of the variable guide vane 32 according to the flow rate of gas flowing through the centrifugal compressor. Specifically, the vane controller 8 increases (decreases) the opening degree of the variable guide vane 32 as the flow rate of gas flowing through the centrifugal compressor increases (decreases).

As mentioned above, the variable guide vanes 32 are arranged in succession with the fixed guide vanes 30. The total length of the variable guide vane 32 is preferably 20% to 60% of the total length of the guide vane 5 (the combined length of the fixed guide vane 30 and the variable guide vane 32).

4 is a perspective view of the variable guide vane 32, FIG. 5 is a view of the variable guide vane 32 of FIG. 4 viewed from the direction indicated by arrow A in FIG. 4, and FIG. 6 is a perspective view of the variable guide vane 32 of FIG. 5 is a view of the vane 32 viewed from the direction indicated by arrow B in FIG. 4. FIG. As shown in FIGS. 4 to 6, the variable guide vane 32 has a shroud surface 37 located on the shroud side (impeller 3b side) and a shroud surface 37 located on the hub side (impeller 3a side) and opposite to the shroud surface 37. It has a hub surface 38 which is a side surface.

The variable guide vane 32 has a twisted three-dimensional shape between the shroud surface 37 and the hub surface 38. In other words, the variable guide vane 32 extends in a direction parallel to the main axis 1 (see FIG. 1) while changing the cross-sectional shape of the variable guide vane 32. Hereinafter, in this specification, the height direction of the variable guide vanes 32 is defined as the direction perpendicular to the shroud surface 37 and the hub surface 38 (direction of the axis CP of the main shaft 1), and the height direction of the variable guide vanes 32 is It is defined as the distance from the surface 37 to the hub surface 38.

Shroud surface 37 and hub surface 38 are connected by pressure surface 40 and suction surface 41 . The pressure surface 40 is a surface located on the right side with respect to the gas flow direction indicated by the arrow in FIG. 3, and is a curved surface having a concave curved surface. The negative pressure surface 41 is a surface located on the left side with respect to the gas flow direction indicated by the arrow in FIG. 3, and is a convex curved surface. The pressure surface 40 and the suction surface 41 are smoothly curved surfaces, and the pressure surface 40 and the suction surface 41 contact at the front edge 47 and the rear edge 48 of the variable guide vane 32 .

7 is a plan view of the variable guide vane 32, and FIG. 8 is a side view of the variable guide vane 32 of FIG. 7 viewed from the direction indicated by arrow D in FIG. As shown in FIGS. 7 and 8, the variable guide vane 32 has a front edge 45 which is an upstream end in the gas flow direction when the variable guide vane 32 is open, and a downstream end. It has a certain trailing edge 46.

The leading edge portion 45 includes a portion of the leading edge 47, the pressure surface 40, and the suction surface 41, and has a smooth curved surface formed by the leading edge 47, the pressure surface 40, and the suction surface 41. There is. The trailing edge portion 46 includes a portion of the trailing edge 48, the pressure surface 40, and the suction surface 41, and has a smooth curved surface formed by the trailing edge 48, the pressure surface 40, and the suction surface 41. There is. The leading edge 47 is the tip of the variable guide vane 32 on the upstream side in the gas flow direction when the variable guide vane 32 is open, and the trailing edge 48 is the tip of the variable guide vane 32 on the downstream side in the gas flow direction. It is the tip.

As shown in FIGS. 4 to 8, the variable guide vane 32 has a flange 49 at the rear edge 46. As shown in FIGS. Specifically, the variable guide vane 32 has a flange 49 at the rear edge 46 on the shroud side. The flange 49 is located downstream of the rear edge 48b on the hub side in the gas flow direction, and the rear edge 48a on the shroud side is located at the tip of the flange 49.

9 is a sectional view taken along line CC in FIG. 7, FIG. 10(a) is a view showing the shroud surface 37, and FIG. 10(b) is an end view taken along line EE in FIG. , FIG. 10(c) is an end view taken along line FF in FIG. 8, FIG. 10(d) is an end view taken along line GG in FIG. It is an inverted view. As shown in FIG. 9, the pressure surface 40 is obliquely inclined with respect to the height direction of the variable guide vane 32.

As shown in FIGS. 10(a) to 10(e), the slope of the chord L1 of the variable guide vane 32 increases from the shroud side to the hub side. The chord L1 is a straight line connecting the leading edge 47 and the trailing edge 48 of the variable guide vane 32 when viewed from a plane perpendicular to the axis CP of the main shaft 1 (a plane perpendicular to the height direction of the variable guide vane 32). It is.

Specifically, the angle θ between the blade chord L1 and the reference straight line L2 increases from the shroud side toward the hub side. The reference straight line L2 is a straight line connecting the axis CP of the main shaft 1 and the axis AX of the rotating shaft 35, as shown in FIG. In FIG. 11, only one guide vane 5 is illustrated, and illustration of the other plurality of guide vanes 5 is omitted. FIG. 11 shows the variable guide vane 32 in a closed state. Pressure surface 40 and suction surface 41 are torsionally connected to shroud surface 37 and hub surface 38.

FIG. 12 is a diagram showing details of the flow of gas flowing along the negative pressure surface 41 of the variable guide vane 32 of this embodiment. By making the variable guide vane 32 have the structure described with reference to FIGS. 9 and 10(a) to 10(e), the gas flow can be diverted along the negative pressure surface 41 of the variable guide vane 32 on the hub side. can be made smaller than the deflection of the gas flow along the suction surface 41 of the variable guide vane 32 on the shroud side. Specifically, as shown in FIG. 12, the gas flow H that has entered the negative pressure surface 41 side of the variable guide vane 32 becomes a flow I on the shroud side, and the flow is more diverted than the flow I on the hub side. It becomes a small flow J. As a result, the blade load on the hub side of the variable guide vane 32 can be reduced more than the blade load on the shroud side of the variable guide vane 32. As a result, it is possible to reduce flow separation occurring on the hub side of the gas flowing along the negative pressure surface 41 of the variable guide vane 32 and occurrence of reverse pre-swirling near the exit of the return flow path 23. Therefore, the centrifugal compressor can form a uniform gas flow within the return flow path 23, reducing the decrease in operating efficiency of the centrifugal compressor and the decrease in the maximum flow rate of gas that the centrifugal compressor can flow. can be done.

By making the shape of the variable guide vane into a three-dimensional shape twisted between the shroud surface and the hub surface, when the variable guide vane is moved to the initial position, there is a relatively large gap between adjacent variable guide vanes. Gaps may occur. Such a gap may cause gas to flow backward from the discharge port or prevent accurate positioning of the variable guide vane during assembly.

As described above, the variable guide vane 32 of this embodiment has the flange 49 at the rear edge 46. The flange portion 49 is configured to be able to come into contact with other adjacent variable guide vanes 32, and the rear edge portion 46 on the hub side is configured so as not to come into contact with other adjacent variable guide vanes 32. When the plurality of variable guide vanes 32 are arranged at the initial position, only the flange portion 49 of one of the two adjacent variable guide vanes 32 contacts the other variable guide vane 32 (see FIG. (see 2). Specifically, the collar 49 contacts the pressure surface 40 (not shown in FIG. 2) of the leading edge 45 of the other variable guide vane 32. At this time, the rear edge 48b (not shown in FIG. 2) of the variable guide vane 32 is located radially outward of the centrifugal compressor from the contact position of the flange 49.

Therefore, the range of motion of the variable guide vane 32 is increased, and the variable guide vane 32 can be closed without a large gap. As a result, backflow of gas from the discharge port can be prevented. Further, since the variable guide vane 32 can be closed without a large gap, the operator can accurately position the variable guide vane 32.

The collar portion 49 may or may not be twisted. In other words, the angle θ may be the same from the height position of the collar portion 49 closest to the hub to the shroud surface 37. Even if the angle θ is the same between the height position of the flange 49 closest to the hub and the shroud surface 37, between the height position of the flange 49 closest to the hub and the hub surface 38, If the angle θ increases from the shroud side toward the hub side, it is possible to reduce the turning of the flow on the hub side and close the variable guide vane 32 without a large gap.

The embodiments described above have been described to enable those skilled in the art to carry out the invention. Various modifications of the above embodiments can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Therefore, the invention is not limited to the described embodiments, but is to be construed in the broadest scope according to the spirit defined by the claims.

1 Main shaft 2 Casing 3, 3a, 3b Impeller 5 Guide vane 7 Disk 8 Vane controller 9 Bearing 12 Suction port 13 Scroll passage 20 Gas passage 21 Diffuser passage 22 Crossover passage 23 Return passage 30 Fixed guide vane 32 Variable guide vane 35 Rotating shaft 37 Shroud surface 38 Hub surface 40 Pressure surface 41 Negative pressure surface 45 Front edge 46 Rear edge 47 Front edge 48 Rear edge 49 Flange 101 Main shaft 130 Fixed guide vane 132 Variable guide vane

Claims (3)

The main shaft and
a plurality of impellers fixed to the main shaft;
a casing that accommodates the plurality of impellers;
A plurality of guides arranged in a return flow path that guides gas discharged from a first impeller of the plurality of impellers to a second impeller that is the next impeller of the first impeller. comprising a vane;
Each guide vane includes a fixed guide vane and a variable guide vane arranged in succession to the fixed guide vane,
The variable guide vane is configured such that the angle between the chord of the variable guide vane and the reference straight line increases from the shroud side toward the hub side,
In the centrifugal compressor, the reference straight line is a straight line connecting the axis of the main shaft and the axis of the rotating shaft of the variable guide vane. The variable guide vane has a flange at a rear edge,
When the variable guide vane is placed at the initial position, only the flange of the first variable guide vane of the two adjacent variable guide vanes comes into contact with the second variable guide vane. , The centrifugal compressor according to claim 1. The centrifugal compressor according to claim 2, wherein a rear edge of the first variable guide vane is located radially outward of the centrifugal compressor from a contact position of the collar portion.

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