WO2025153434A1

WO2025153434A1 - Wind turbine gearbox

Info

Publication number: WO2025153434A1
Application number: PCT/EP2025/050664
Authority: WO
Inventors: Wang QIE; Jun He; Xue MA; Jin Yu ZHAO
Original assignee: Flender GmbH
Current assignee: Flender GmbH
Priority date: 2024-01-15
Filing date: 2025-01-13
Publication date: 2025-07-24
Anticipated expiration: 2026-07-15
Also published as: CN222415865U

Abstract

A wind turbine gearbox is disclosed and comprises: an output shaft (20) which has a central axis extending in an axial direction (L) and is configured to be engaged with a rotor of a generator to drive it to rotate; a housing (10) which comprises a flange (12) defining a through-hole (14) that allows the output shaft (20) to pass through; a pair of bearings (22, 24) that rotatably support the output shaft (20); and a spacer ring (26) that spaces the pair of bearings (22, 24) apart from each other in the axial direction (L), wherein the wind turbine gearbox further comprises: a bearing bushing (30) arranged around the pair of bearings (22, 24) and detachably fastened to the flange (12), wherein the bearing bushing (30) and the spacer ring (26) are configured to be fastened to each other and sized so that they can be moved out of the through hole (14) in the axial direction (L) when fastened together.

Description

Wind Turbine Gearbox

TECHNICAL FIELD

This application relates to the technical field of a wind power generation. In particular, the application relates to a wind turbine gearbox and, more particularly, a high-power semi direct drive wind turbine gearbox.

BACKGROUND

As a key component of a wind turbine generator, a wind turbine gearbox is one of the most important parts of a transmission chain of the wind turbine generator, and thus the reliability and convenience of maintenance of its design are of great importance.

The wind turbine gearbox includes a housing, transmission components including at least one or typically a multiple of planetary gear transmission assemblies housed in the housing, and an output shaft driven by the highest stage (or referred to as an output stage) planetary gear transmission assembly. The output shaft of the wind turbine gearbox extends out of the housing through a through-hole formed in a flange of the housing to be connected to a rotor or rotor shaft of a generator, for transmitting a torque from a blade assembly to the generator for power generation. Specifically, the output shaft is rotatably supported in the through-hole of the flange by a pair of bearings which are spaced apart by a spacer ring, and bolts extend radially inwardly from the flange of the housing into the spacer ring between the bearings, fixing the spacer ring to the flange. However, the limited operation space would not allow disassembly of this bolt on a tower. With such structures, if the components inside the wind turbine gearbox, especially the output stage transmission assembly, fail, the disassembling, repairing or replacing operations can’t be carried out on (top of) the tower.

SUMMARY OF THE INVENTION

An object of the present application is to solve the problem of maintenance or replacement of components of an output stage of a wind turbine gearbox on top of its tower.

The object is solved by a novel wind power gearbox of the present application. The wind power gearbox comprises: an output shaft which has a central axis extending in an axial direction and is configured to be engaged with a rotor of a generator to drive it to rotate; a housing which comprises a flange defining a through-hole that allows the output shaft to pass through; a pair of bearings that rotatably support the output shaft; and a spacer ring that spaces the pair of bearings apart from each other in the axial direction, wherein the wind power gearbox further comprises: a bearing bushing arranged around the pair of bearings and detachably fastened to the flange, wherein the bearing bushing and the spacer ring are configured to be fastened to each other and sized so that they can be moved out of the through hole in the axial direction when fastened together.

In an embodiment, the wind turbine gearbox further comprises a first fastener for fastening the bearing bushing and the spacer ring together, wherein the first fastener extends from the bearing bushing into the spacer ring in a radial direction perpendicular to the axial direction, and a radial outer end of the first fastener is completely submerged within the bearing bushing.

In an embodiment, the wind turbine gearbox further comprises a second fastener for fastening the bearing bushing to the flange, wherein the second fastener extends from the bearing bushing into the flange in the axial direction.

In an embodiment, the wind turbine gearbox further comprises an end cap defining an end cap hole that allows the output shaft to pass through, and a third fastener for fastening the end cap to the bearing bushing, wherein the third fastener extends from the end cap into the bearing bushing in the axial direction.

In an embodiment, the first fastener comprises a plurality of first fasteners distributed in a circumferential direction around the axial direction, the second fastener comprises a plurality of second fasteners distributed in the circumferential direction, and the third fastener comprises a plurality of third fasteners distributed in the circumferential direction, wherein the second fasteners and the third fasteners are arranged offset from each other in the circumferential direction and/or in the radial direction.

In an embodiment, each of the first fasteners, the second fasteners and the third fasteners are threaded fasteners.

In an embodiment, the pair of bearings are two self-aligning roller bearings arranged opposite to each other.

In an embodiment, the pair of bearings and the bearing bushing are located within the through hole in the axial direction.

In an embodiment, the wind turbine gearbox further comprises inner and outer positioning rings arranged on opposite sides of the pair of bearings in the axial direction and configured to position the pair of bearings.

In an embodiment, the inner positioning ring is a flange extending radially inward from an inner end of the bearing bushing where the bearing bushing abuts the flange, is a separately provided collar, or is provided by a portion of the flange, and/or the outer positioning ring is a collar sandwiched between the end cap and the pair of bearings, or an annular portion formed integrally with the end cap.

In an embodiment, an interface is formed between the end cap and the output shaft in the radial direction, and the end cap comprises a sealing structure provided at the interface.

In an embodiment, the sealing structure is a labyrinth sealing structure formed on the end cap.

In an embodiment, the end cap comprises a discharge passage for discharging lubricating oil at the interface out of the wind turbine gearbox, and the housing comprises a flange passage in fluid communication with the discharge passage and leading to outside of the flange for installing a tube fitting. According to a wind power gearbox of a present application, a bearing bushing is provided radially outside of a pair of bearings supporting the output shaft and a spacer ring therebetween and itself is fastened to the spacer ring between the bearings to form an assembly. The components of the assembly can be assembled into a through hole in an axial direction formed in a flange of a housing of the wind power gearbox and can be removed together out of the through hole in the flange in the axial direction. This solves the technical problem of lack of sufficient operation space to disassemble any radially-extending bolts in the prior art. In addition, the flange and an end cap of the wind power gearbox of the present application include an end cap discharge passage and a flange discharge passage, respectively, that are in fluid communication with each other to discharge leaked lubricating oil at an interface between the end cap and the output shaft out of the wind power gearbox. The flange discharge passage leads to outside of the wind power gearbox for installing a tube fitting, achieving inspection and/or recovery of the leaked lubricating oil. The tube fitting is installed on the flange, instead of on the end cap, which allows for maintenance of a seal inside of the end cap or maintenance of internal components of the wind turbine gearbox without disassembling the tube fitting. Aperations are simplified and operating time is saved. The flange discharge passage has an outlet opening formed in the flange of the wind turbine gearbox, which facilitates the inspection and recovery of the leaked lubricating oil.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic longitudinal sectional view of a portion of a wind turbine gearbox according to the present application.

Figure 2 is another schematic longitudinal sectional view of the portion shown in Figure 1.

Figure 3 is an illustrative view of a longitudinal section of a portion that is symmetrical with the portion shown in Figures 1 and 2 about a central axis of an output shaft.

DETAILED DESCRIPTION

Figures 1 and 2 are sectional views at two different longitudinal sections of a portion of a wind turbine gearbox constructed according to the principles of the present application, and Figure 3 is an illustrative view of a portion symmetrical with the portion shown in Figures 1 and 2 about a central axis of an output shaft. It should be understood for the skilled in the art that the accompanying drawings are not drawn to scale and merely intends to illustrate the principles of the present application, without limiting the scope of protection of the present application.

Reference is initially made to Figures 1 and 2, in which a housing 10 including a flange 12 is shown and an output shaft 20 extends out of the housing 10 in an axial direction L through a through-hole 14 formed in the flange 12 and has a central axis extending in the axial direction L. Although only portions related to improvements of the present application are shown in the drawings, it should be understood that an outer side 12a of the housing 10, in particular of the flange 12, is proximate to a generator (not shown) of the wind turbine gearbox, and a gear transmission assembly (not shown) is accommodated inside the housing 10 on an inner side 12b of the flange 12. The output shaft 20 extends out of the housing 10 in the axial direction L from the inner side 12b towards the outer side 12a, with one end of the output shaft 20 on the inner side 12b of the flange 12 configured to be engaged with one or more planetary gear transmission assemblies of the wind turbine gearbox driven by blades of a wind turbine generator system and configured to be driven to rotate, and the other end of the output shaft 20 on the outer side 12a of the flange 12 configured to be engaged with a rotor or rotating shaft of the generator and configured to drive it to rotate. As shown in Figure 1, a radial direction R is perpendicular to the axial direction L, in which a radial inward direction is from the flange 12 towards the output shaft 20 and a radial outward direction is from the output shaft 20 towards the flange 12. A circumferential direction recited herein is defined as a direction around the axial direction L.

The wind turbine gearbox includes a pair of bearings 22 and 24 that are arranged radially outward of the output shaft 20 to support it. A spacer ring 26 is provided between a first one 22 of the bearings relatively inwardly in the axial direction L and a second one 24 of the bearings relatively outwardly in the axial direction L, and, in particular, the spacer ring 26 is arranged between outer rings of the two bearings 22 and 24 to space them apart from each other.

The wind turbine gearbox further includes a bearing bushing 30 located radially outward of the spacer ring 26 and the bearings 22 and 24. In the radial direction R, the bearing bushing 30 is positioned between the flange 12 and both the spacer ring 26 and the bearings 22 and 24. In particular, the through-hole 14 includes a first hole segment 14a on the inner side 12b having a first inner diameter and a second hole segment 14b on the outer side 12a having a second inner diameter larger than the first inner diameter, thereby defining a stepped surface 15 facing the outer side 12a. The bearing bushing 30 is positioned in the second hole segment 14b of the through-hole 14 with its inner end 30a in contact with the stepped surface 15 of the flange 12.

The bearing bushing 30 can be fastened to the spacer ring 26 by any means known in the art, so that the bearing bushing 30 and the spacer ring 26 fastened together can be removed from the through hole 14 (in particular from the second hole segment 14b) together in the axial direction L. For example, in the illustrated example, the bearing bushing 30 is fastened to the spacer ring 26 by means of at least one (e.g., a plurality of) first fastener 32 arranged in a circumferential direction, the first fastener 32 being illustrated in Figure 1. The first fastener 32 extends radially into the spacer ring 26 through a radial through-hole 122 formed in the flange 12 and a first hole 322 formed in the bearing bushing 30. A hole 262 in the spacer ring 26 for receiving the first fastener 32 can be a blind hole as shown, or it may extend radially through the entire spacer ring 26. The first fastener 32 can be a bolt, and the first hole 322 in the bearing bushing 30 can be formed as a countersunk hole suitable for housing the bolt including a bolt head. Alternatively, the first fastener 32 can also be other types of fasteners. It should be understood that the fastening or attachment between the bearing bushing 30 and the spacer ring 26 is not limited to the fastening manner as shown, as long as the first fastener 32 that connects the bearing bushing 30 and the spacer ring 26 together does not protrude outwardly beyond an outer circumferential surface of the bearing bushing 30 in the radial direction R, that is, does not protrude into the radial through-hole 122 in the flange 12 (and thus would not interfere with the movement of the bearing bushing 30 out of the through-hole 14 in the axial direction L). In cases that the above functions are achieved, the first fastener 32 does not have to extend perpendicular to the axial direction L (e.g., does not have to be in the radial direction R). The bearing bushing 30 can be fastened to the flange 12 in any manner known in the art. For example, as shown in Figure 2, a second fastener 34 passes through a second hole 304 which extends through the bearing bushing 30 in the axial direction L and enters the flange 12. The second fastener 34 may be a plurality of second fasteners 34 arranged in the circumferential direction. Similar to the first fastener 32, the second fastener 34 is not limited to a bolt. The second hole 304 can be in the form of a countersunk hole, so that a bolt head of the second fastener 34 is fully received in the second hole 304 without protruding out of the bearing bushing 30.

The inner end 30a of the bearing bushing 30 includes a radially inwardly protruding flange 36 which is configured to abut the outer ring of the first bearing 22 on its axial inner side of the first bearing 22, providing positioning and stopping functions. With the bearing bushing 30 fastened to the flange 12, the first bearing 22 is positioned and fixed in the axial direction L between the flange 36 of the bearing bushing 30 and the spacer ring 26 fastened to the bearing bushing 30. Therefore, with the second fastener 34 removed, the bearing bushing 30, the first bearing 22, and the spacer ring 26 can be moved out of the through-hole 14 from the outer side 12a in the axial direction L as an integral. It can be understood for the skilled in the art that a separate collar, instead of the flange 36 integrated with the bearing bushing 30, can be used to position the first bearing 22 on its axial inner side. Alternatively, in some embodiments, instead of providing the separate collar or the flange 36, the flange 12 can be used to directly abut the outer ring of the first bearing 22 on its axial inner side to position the first bearing 22.

In the axial direction L, the second bearing 24 is positioned between the spacer ring 26 which is located on an axial inner side of the second bearing 24 and a collar 28 which is located on an opposite axial outer side of the second bearing 24. The collar 28 is fixed in place by an end cap 40 which is fastened to the bearing bushing 30 from the outer side 12a.

In the illustrated embodiment, the fastening of the end cap 40 to the bearing bushing 30 can be achieved by means of a third fastener 38 (Figure 1). The third fastener 38 passes through an end cap through-hole 408 that extends through the end cap 40 in the axial direction L and enters a third hole 308 formed in the bearing bushing 30. The third fastener 38 can include a plurality of third fasteners 38 arranged in the circumferential direction. Similar to the first fastener 32 and the second fastener 34, the third fastener 38 can be, but not limited to, a bolt.

In the illustrated embodiment, the collar 28 may be a separately provided component located between the outer ring of the second bearing 24 and the end cap 40. In some embodiments, the collar 28 may be an integral part of the end cap 40.

Although not shown in the drawings, it can be understood that the plurality of second fasteners 34 and the plurality of third fasteners 38 can be distributed in a manner of being offset relative to each other in the circumferential direction or in the radial direction R, so that the second and third holes 304 and 308 in the bearing bushing 30 for the second and third fasteners 34 and 38, respectively, do not interfere with each other. It should also be understood that the arrangement in the circumferential direction of the first fasteners 32 extending radially through the bearing bushing 30 and the arrangement in the circumferential direction of the second fasteners 34 extending axially through the bearing bushing 30 are configured so that the first holes 302 through which the first fasteners 32 pass and the second holes 304 through which the second fasteners 34 pass do not interfere with each other.

With the structure shown in the drawings and described as above, the bearing bushing 30 is fastened to the spacer ring 26 between the bearings 22 and 24 in the radial direction R by the first fastener 32, and is fastened to the flange 12 of the housing 10 in the axial direction L by the second fastener 34. The end cap 40 is fastened to the bearing bushing 30 by the third fastener 38. Figure 1 also illustrates a plug 124 which is configured and used to block or cover the flange through-hole 122 for the first fastener 32, an end seal 13 which is positioned between the inner end 30a of the bearing bushing 30 and the stepped surface 15 of the flange 12, and an outer circumferential seal 17 which is positioned between the outer circumferential surface of the bearing bushing 30 and the opposite surface of the flange 12. Preferably, the outer circumferential seal 17 is positioned on an outer side of the first fastener 32 in the axial direction L.

The wind turbine gearbox in the present application is advantages. In particular, providing the bearing bushing 30 between the flange 12 and the two bearings 22 and 24 and having the first fastener 32 extending radially into the bearing bushing 30 to be completely submerged within the bearing bushing 30 are beneficial in maintaining and preparing internal components of the wind turbine gearbox, especially those of an output stage transmission assembly, in that: the bearing bushing 30, the spacer ring 26 and the first bearing 22 can be removed from the through- hole 14 in the axial direction L together as an integral, without having to remove the first fastener 32, after the third fastener 38, the end cap 40, the collar 28, the second bearing 24 and the second fastener 34 are removed in the axial direction L. This makes it possible to replace the components of the output stage transmission assembly on a tower of the wind turbine generator system by solving the problem of being unable to remove the first fastener 32 on top of the tower.

In addition, the wind turbine gearbox of the present application provides an improved structure for discharging leaked lubricating oil. Referring to Figure 3, the end cap 40 includes an interface

45 formed between the end cap 40 and the output shaft 20, and includes a sealing structure at the interface 45. The wind turbine gearbox also includes a seal 42 located on an inner side of the interface 45 in the axial direction L, that is, the side proximate to the bearing 24. The sealing structure at interface 45 can be a labyrinth sealing structure 44 formed on end cap 40. In this way, most of the lubricating oil used to lubricate the bearings 22 and 24 is blocked by seal 42 with a small portion still leaking and reaching the interface 45 mentioned above.

As shown in the drawings, the end cap 40 includes at least one (e.g. two) oil-returning passage

46 that opens to the interface 45 so that the interface 45 is in fluid communication with an interior of the gearbox, and a discharge passage 48 for discharging the leaked lubricating oil at the interface 45 out of the wind turbine gearbox. As illustrated, it is preferable that an opening 46a of the oil-returning passage 46 opening to the interface 45 is located closer to the seal 42 or bearing 24 than an opening 48a of the discharge passage 48 opening to the interface 45. In other words, the opening 48a is arranged outwardly relative to the opening 46a in the axial direction L. In this way, most of the leaked lubricating oil will be returned to the gearbox through the oil-returning passage 46, and the rest of the leaked lubricating oil can be discharged out of the wind turbine gearbox through the discharge passage 48.

As further illustrated, the bearing bushing 30 and the housing 10 (or the flange 12, in particular) include a bushing passage 31 and a flange passage 11, respectively, configured to be in fluid communication with the oil-returning passage 46 of the end cap 40 to direct the (leaked) lubricating oil at the interface 45 back to the gearbox. Optionally, in some embodiments, according to the actual dimensions and designs of the bearing bushing 30, the flange 12 and the end cap 40, the passages used to direct the lubricating oil at the interface 45 back to the gearbox may not run through the bearing bushing 30 (and thus the bearing bushing 30 does not include the bushing passage 31), and the oil-returning passage 46 is in direct fluid communication with the flange passage 11.

As illustrated, the housing 10 (in particular, the flange 12) includes a flange discharge passage 18 that is in fluid communication with the discharge passage 48 of the end cap 40 and leads to the outside of the wind turbine gearbox, and a discharge port (it is a tube fitting 58 installed at the discharge port that is shown in Figure 3, to perform inspection and/or recovery of the leaked lubricating oil) formed in the housing 10 (in particular, the flange 12) and configured to discharge the leaked lubricating oil at the interface 45 out of the wind turbine gearbox.

Advantageously, the discharge port is provided in the housing in the present application, in particular, on the flange 12, rather than on the end cap 40. In one hand, this makes it easier for an operator to collect the discharged lubricating oil by grasping a lubricating oil container (for example, an oil pot). On the other hand, in case there is a problem with the seal 42, only the third fastener 38 and the end cap 40 need to be removed by the operator and the tube fitting 58 doesn’t have to be removed, which simplifies the process and saves time.

Examples of the wind turbine gearbox of the present application have been described in detail with reference to the accompanying drawings. The present application is particularly advantageous in the maintenance of the components of the output stage (or high-speed stage) transmission assembly of the wind turbine gearbox and in the inspection and/or discharge of leaked lubricating oil. For the former aspect, the bearing bushing is added between the housing (the flange) and the spacer ring between the internal bearings of the present application, and the radially extending connectors or fasteners are completely submerged in the bearing bushing, which solves the technical problem that the first fastener can’t be removed radially outwardly from the flange due to an insufficient operation space. Merely by removing the second and third fasteners extending in the axial direction, the operator can easily remove the bearings, the bearing bushing and the spacers ring, among other components, out of the flange at one time. And then, maintenance and replacement operations can be performed to the components of the output stage transmission assemblies of the wind turbine gearbox on the tower. For the latter aspect, the tube fitting for oil leakage inspection or recovery is provided on the housing, which makes it possible to maintain or replace the seal 42 or maintain or replace the components of the output stage transmission assembly without need to remove and then to reinstall the tube fitting for oil leakage inspection. Compared to the structures in which the tube fitting is installed on the end cap, a simplified structure is provided, which is particularly advantageous in cases where a compact space makes it inconvenient to operate, because the tube fitting if installed on the end cap has to be removed before the maintenance or replacement of the internal components of the output stage transmission assembly and reinstallation of the tube fitting is needed afterwards.

However, it should be appreciated for the skilled in the art that the drawings and the description are only for exemplary embodiments of the present application to provide a comprehensive understanding of the present application. It is apparent to those skilled in the art that this application can be implemented without some of the specific details. Only the parts of the wind turbine gearbox related to the improvements of the present application are illustrated, in order to avoid unnecessary blurring of the present application. The skilled in the art can make various modifications, additions or omissions to various features or details after reading the above description, and these are considered as falling within the scope of protection of this application.

Claims

1. A wind turbine gearbox comprising: an output shaft (20) which has a central axis extending in an axial direction (L) and is configured to be engaged with a rotor of a generator to drive it to rotate; a housing (10) which comprises a flange (12) defining a through-hole (14) that allows the output shaft (20) to pass through; a pair of bearings (22, 24) that rotatably support the output shaft (20); and a spacer ring (26) that spaces the pair of bearings (22, 24) apart from each other in the axial direction (L), characterized by further comprising: a bearing bushing (30) arranged around the pair of bearings (22, 24) and detachably fastened to the flange (12), wherein the bearing bushing (30) and the spacer ring (26) are configured to be fastened to each other and sized so that they can be moved out of the through hole (14) in the axial direction (L) when fastened together.

2. The wind turbine gearbox according to claim 1, characterized by further comprising a first fastener (32) for fastening the bearing bushing (30) and the spacer ring (26) together, wherein the first fastener extends from the bearing bushing (30) into the spacer ring (26) in a radial direction (R) perpendicular to the axial direction (L), and a radial outer end of the first fastener is completely submerged within the bearing bushing (30).

3. The wind turbine gearbox according to claim 2, characterized by further comprising a second fastener (34) for fastening the bearing bushing (30) to the flange (12), wherein the second fastener (34) extends from the bearing bushing (30) into the flange (12) in the axial direction (L).

4. The wind turbine gearbox according to claim 3, characterized by further comprising an end cap (40) defining an end cap hole that allows the output shaft (20) to pass through, and a third fastener (38) for fastening the end cap (40) to the bearing bushing (30), wherein the third fastener extends from the end cap (40) into the bearing bushing (30) in the axial direction (L).

5. The wind turbine gearbox as claimed in claim 4, characterized in that the first fastener (32) comprises a plurality of first fasteners distributed in a circumferential direction around the axial direction (L), the second fastener (34) comprises a plurality of second fasteners distributed in the circumferential direction, and the third fastener (38) comprises a plurality of third fasteners distributed in the circumferential direction, wherein the second fasteners (34) and the third fasteners (38) are arranged offset from each other in the circumferential direction and/or in the radial direction.

6. The wind turbine gearbox according to claim 5, characterized in that each of the first fasteners (32), the second fasteners (34) and the third fasteners (38) are threaded fasteners.

7. The wind turbine gearbox according to any one of claims 1-6, characterized in that the pair of bearings (22, 24) are two self-aligning roller bearings arranged opposite to each other.

8. The wind turbine gearbox according to claim 7, characterized in that the pair of bearings (22, 24) and the bearing bushing (30) are located within the through hole (14) in the axial direction (L).

9. The wind turbine gearbox according to any one of claims 4-6, characterized by further comprising inner and outer positioning rings arranged on opposite sides of the pair of bearings (22, 24) in the axial direction (L) and configured to position the pair of bearings (22, 24).

10. The wind turbine gearbox according to claim 9, characterized in that: the inner positioning ring is a flange (36) extending radially inward from an inner end (30a) of the bearing bushing (30) where the bearing bushing (30) abuts the flange (12), is a separately provided collar, or is provided by a portion of the flange (12), and/or the outer positioning ring is a collar (28) sandwiched between the end cap (40) and the pair of bearings (22, 24), or an annular portion formed integrally with the end cap (40).

11. The wind turbine gearbox according to any one of claims 4-6, characterized in that an interface (45) is formed between the end cap (40) and the output shaft (20) in the radial direction, and the end cap (40) comprises a sealing structure provided at the interface (45).

12. The wind turbine gearbox according to claim 11, characterized in that the sealing structure is a labyrinth sealing structure (44) formed on the end cap (40).

13. The wind turbine gearbox according to claim 11, characterized in that the end cap (40) comprises a discharge passage (48) for discharging lubricating oil at the interface (45) out of the wind turbine gearbox, and the housing (10) comprises a flange passage (18) in fluid communication with the discharge passage (48) and leading to outside of the flange (12) for installing a tube fitting (58).