CN112279078B

CN112279078B - Tower drum lifting appliance

Info

Publication number: CN112279078B
Application number: CN201910677329.4A
Authority: CN
Inventors: 方晶; 张竹; 沈星星; 张新刚
Original assignee: Jiangsu Goldwind Science and Technology Co Ltd
Current assignee: Jiangsu Goldwind Science and Technology Co Ltd
Priority date: 2019-07-25
Filing date: 2019-07-25
Publication date: 2022-07-08
Anticipated expiration: 2039-07-25
Also published as: CN112279078A

Abstract

The invention provides a tower drum lifting appliance. This tower section of thick bamboo hoist includes: connecting a bracket; the telescopic part comprises a plurality of telescopic parts, the telescopic parts are arranged in a radial equiangular interval mode, one end of each telescopic part is connected to the connecting support, the other end of one telescopic part in the telescopic parts hooks the tower cylinder flange through the lifting hook, and the other end of each telescopic part in the rest telescopic parts is fixed to the tower cylinder flange. The tower drum lifting appliance can correct the roundness of the tower drum flange in the transportation, transportation and lifting processes so as to ensure that the tower drum is smoothly installed.

Description

Tower drum lifting appliance

Technical Field

The invention relates to the technical field of wind power generation, in particular to a tower drum lifting appliance for correcting roundness of a tower drum flange and preventing the tower drum flange from deforming in the processes of tower drum transportation, lifting and the like.

Background

The deformation of the tower drum flange is always a prominent problem in the large-scale tower drum diameter. As for the existing tower with the diameter of seven meters, the deformation of a tower flange is large due to the self weight, the storage period is long and the like, so that the installation and butt joint of the tower on site are difficult. Once the tower drum flange is deformed, huge potential safety hazards can exist in the whole machine hoisting and unit operation, and the roundness of the tower drum flange is very necessary to be ensured. Therefore, a device for solving the problem of deformation of a large-diameter tower barrel in the processes of transportation, hoisting and the like is needed.

Disclosure of Invention

In order to solve the problem that the large-diameter tower barrel deforms in the processes of transportation, hoisting and the like, the invention provides the tower barrel lifting appliance which can correct the roundness of a tower barrel flange.

According to an aspect of the invention, there is provided a tower spreader comprising: connecting a bracket; the telescopic part comprises a plurality of telescopic parts, the telescopic parts are arranged in a radial equiangular interval mode, one end of each telescopic part is connected to the connecting support, the other end of one telescopic part in the telescopic parts hooks the tower cylinder flange through the lifting hook, and the other end of each telescopic part in the rest telescopic parts is fixed to the tower cylinder flange. The roundness of the tower drum flange can be corrected according to the tower drum lifting appliance.

According to an exemplary embodiment of the invention, the hook may comprise a hook body, one end of which is hinged to said other end of one of the telescoping sections, the other end of the hook body being for attachment of a harness.

According to an exemplary embodiment of the invention, the lifting hook may further comprise a support rotatably arranged with respect to the hook body on an inner side of the hook body for hooking the tower flange to protect the tower flange from damage.

According to an exemplary embodiment of the invention, the other end of each of the remaining telescopable portions may be fixed to the tower flange by means of a castellated plate structure.

According to an exemplary embodiment of the present invention, the castellated plate structure may include a first castellated plate and a second castellated plate, the castellated surfaces of the first castellated plate and the second castellated plate being stacked facing each other such that the teeth formed on the castellated surfaces are engaged with each other, such that the tower hanger is more stably stressed and does not slip due to a tensile force during hoisting, facilitating more stable hoisting.

According to an exemplary embodiment of the present invention, the first and second tooth plates may be correspondingly formed with first connection holes connected with the other ends of the remaining telescoping portions, the first and second tooth plates being selectively rotatable with respect to the remaining telescoping portions, thereby facilitating installation and removal of the tower spreader.

According to an exemplary embodiment of the present invention, the first and second tooth plates may be correspondingly formed with second coupling holes to be coupled with the tower flange.

According to an exemplary embodiment of the present invention, each of the first and second tooth plates may be divided into left and right blade bodies, and the left and right blade bodies are respectively formed with grooves at sides opposite to each other, the grooves forming the first and second connection holes in a state in which the left and right blade bodies are detachably assembled together, thereby facilitating installation and disassembly of the tower hanger.

According to an exemplary embodiment of the present invention, the left blade and the right blade may be symmetrical to each other, and ends of the left blade and the right blade in a radial direction of the tower flange may be formed with through holes corresponding to each other and penetrating the left blade and the right blade, respectively, so as to facilitate assembling and disassembling the first tooth plate and the second tooth plate for disassembling the tower hanger.

According to an exemplary embodiment of the invention, the tower spreader may further comprise lifting lugs, which are arranged on at least one of the castellated plate structures, such that the tower spreader is provided.

According to the exemplary embodiment of the present invention, the number of the telescopic parts may be four, which not only is suitable for the structure, but also can achieve a good effect of correcting the roundness of the tower flange.

The tower drum lifting appliance can effectively solve the problem that a large-diameter tower drum deforms in the processes of transportation, lifting and the like, and meanwhile solves the personal safety risk caused by the traditional installation and disassembly of the tail sliding lifting lug, and is convenient to install and disassemble.

Drawings

The above and other features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating a tower spreader mounted to a tower flange according to an exemplary embodiment of the present invention;

FIG. 2 is a schematic view illustrating the tower spreader of FIG. 1 not yet fully installed to a tower;

FIG. 3 is a diagram showing a castellated plate structure of the tower spreader of FIG. 1;

FIG. 4 is an exploded schematic view of the first castellated plate;

fig. 5 to 7 are schematic diagrams illustrating a process of performing hoisting, turning and tower flange butting by using the tower spreader in fig. 1.

The reference numbers illustrate:

1: a tower drum; 2: a sling; 3: a tower drum lifting appliance; 30: connecting a bracket; 31: a stretchable portion; 32: a hook; 33: a toothed plate structure; 4: a tower drum flange; 5: a first extendable portion; 6: a second extendable portion; 7: a third extendable portion; 8: a fourth extendable portion; 10: a hook body; 11: a support; 12: a hinged seat; 13: a first pin shaft; 14: a first castellated plate; 15: a second toothed plate; 16: a second pin shaft; 17: the bolt is connected to the pair; 18: a first screw; 19: a first nut; 20: a second nut; 21: a left sheet body; 22: a right sheet body; 23: a second bolt; 24: and a third nut.

Detailed Description

Embodiments of the present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

According to an exemplary embodiment of the present invention, a tower spreader 3 is provided, the tower spreader 3 comprising: a connecting bracket 30; the tower flange is provided with a plurality of telescopic parts 31, the plurality of telescopic parts 31 are arranged in a radial equiangular interval mode, one end of each telescopic part 31 is connected to the connecting support 30, the other end of one telescopic part 31 in the plurality of telescopic parts 31 is hooked on the tower flange 4 through a hook 32, and the other end of each of the rest telescopic parts 31 is fixed to the tower flange 4.

In the drawings, the number of the stretchable and contractible portions 31 is shown as four. That is, the four telescopic parts 31 are arranged around the connecting bracket 30 at 90-degree intervals, and have a suitable structure and can achieve a good effect of correcting the roundness of the tower flange 4. However, the embodiment of the present invention is not limited thereto, and the number of the telescopic parts 31 may also be less than four, for example, three (in a Y shape) and two (in a straight shape), and as the number of the telescopic parts 31 decreases, the structure thereof becomes simpler and simpler, but the correction effect on the tower flange 4 becomes worse; or the number of the stretchable and contractible portions 31 may be set to more than four, for example, five, six, seven, eight, etc., and as the number of the stretchable and contractible portions 31 increases, the structure thereof becomes complicated. According to other examples of the invention, the number of the telescopic parts 31 may be set to a multiple of four in order to make the stress on each telescopic part 31 uniform and correct the roundness of the tower flange 4. By the form of symmetrically arranging the telescopic parts 31, the tower flange 4 is uniformly stressed, and the roundness of the tower flange 4 can be conveniently ensured.

For purposes of exemplary description, an example in which the tower spreader 3 includes four telescoping sections 31 will be described below in conjunction with fig. 1-3.

As shown in fig. 1 to 3, the four stretchable parts 31 may include a first stretchable part 5, a second stretchable part 6, a third stretchable part 7, and a fourth stretchable part 8. According to an example, the connecting bracket 30 may be formed in a rectangular parallelepiped or cubic shape, and the first to fourth stretchable and contractible portions may be connected to four faces of the connecting bracket 30, respectively. However, the embodiment of the present invention is not limited thereto, and the linking bracket 30 may be formed in a substantially spherical, disc-like or other irregular shape, etc., as long as it can provide the mounting points of the first to fourth stretchable and contractible portions. In addition, the shape of the connecting bracket 30 may also be designed according to the formation of the first telescopic part 5, the second telescopic part 6, the third telescopic part 7 and the fourth telescopic part 8, so that the tower sling 3 can be connected to the tower flange 4 and the roundness of the tower flange 4 can be corrected.

According to an exemplary embodiment of the present invention, the hook 32 includes a hook body 10, one end of the hook body 10 is hinged to the other end of one stretchable part 31 (i.e., the fourth stretchable part 8), and the other end of the hook body 10 is used to connect the hanging strip 2 to form a lifting device.

To facilitate the hinging of one end of the hook body 10 to the fourth flexible portion 8, the hook 32 may further comprise a hinge seat 12, the hinge seat 12 being provided at one end of the hook body 10, such that the other end of the fourth flexible portion 8 may be hinged to the hook body 10 by hinging to the hinge seat 12. As an example, the other end of the fourth stretchable and contractible portion 8 may be formed with a through hole, and the fourth stretchable and contractible portion 8 may be coupled to the hook 32 by using the first pin 13 through the through hole formed in the hinge base 12 and the through hole of the other end of the fourth stretchable and contractible portion 8. By arranging the hinge seat 12, the tower drum lifting appliance 3 can be uniformly stressed up and down during lifting, and the tower drum flange 4 is not easy to deform.

In order to better hook the tower flange 4 and protect the tower flange 4, the hook 32 may further include: a support 11, the support 11 being rotatably arranged inside the hook body 10 with respect to the hook body 10 for contacting and hooking the tower flange 4. For example, the inner side of the hook body 10 may be provided with a slide rail, and the seat 11 may be provided with a slider that can be received in and slid along the slide rail of the hook body 10, however, embodiments of the present invention are not limited thereto, and the seat 11 may be provided in any relatively rotatably provided structure as understood by those skilled in the art without limitation.

According to an example, the support 11 may be made of a polymer material (e.g., polyurethane), rubber, etc., but the present invention is not limited thereto as long as it can hook the flange and play a role in protecting the tower flange 4 from damage. Furthermore, the shape of the support 11 is not limited as long as it can contact and hook the tower flange 4. The shape of the support 11 may correspond to the shape of the tower flange 4, for example, the support 11 may be substantially U-shaped to receive the tower flange 4 therein to hook and protect the tower flange 4. According to an example of the present invention, the support 11 may be configured as an elastic support with elasticity, while ensuring that the support 11 can hook and protect the tower flange 11.

The outside of the hook body 10 is also provided with a U-shaped loop for providing an anchoring point for the adjustment cord to facilitate adjustment of the position of the hook 32, e.g. by applying a force through the adjustment cord to place the hook 32 in an upright position.

To facilitate mounting and dismounting, the other end of each of the remaining telescoping sections 31 may be secured to the tower flange 4 by a castellated plate structure 33. In other words, the tower spreader 3 may further include a castellated plate structure 33, and the two ends of the castellated plate structure 33 in the radial direction of the tower flange 4 are respectively connected to the other end of the telescopic part 31 and the tower flange 4. Specifically, in the illustrated example, the castellated plate structure 33 may be disposed between the other ends of the first, second and

third telescoping parts

5, 6, 7, respectively, and the tower flange 4 to secure the first, second and

third telescoping parts

5, 6, 7, respectively, to the tower flange 4.

The castellated plate structure 33 may include a first castellated plate 14 and a second castellated plate 15, the toothed surfaces of the first and second castellated

plates

14, 15 being stacked facing each other such that the teeth formed on the toothed surfaces mesh with each other. For example, the toothed surface of the second toothed plate 15 and the toothed surface of the first toothed plate 14 may respectively have teeth of a concavo-convex structure corresponding to each other. The specific shape of the teeth is not limited, and the cross section thereof may be substantially triangular, rectangular, etc., as long as they can be engaged with each other to ensure that the first and

second tooth plates

14 and 15 do not slip. Compared with the common steel plate structure, the tower drum lifting appliance adopting the toothed plate structure 33 is more stable in stress and cannot slide due to tension during lifting, and the lifting is more stably executed.

In order to realize connection and fixation between the castellated plate structure 33 and the telescopic portion 31 and the tower flange 4, the first castellated plate 14 and the second castellated plate 15 are correspondingly formed with a first connection hole connected with the other end of the other telescopic portion 31, and the first castellated plate 14 and the second castellated plate 15 are correspondingly formed with a second connection hole connected with the tower flange 4.

According to an example of the present disclosure, the first and second

toothed plates

14, 15 may be designed to be selectively rotatable relative to the remaining telescoping portion 31, and in particular, the first and

second toothed plates

14, 15 may be selectively arranged to be fixed relative to the remaining telescoping portion 31 during the lifting and/or roundness correction of the tower flange 4; during disassembly of the tower spreader 3, the first and second

toothed plates

14, 15 may be selectively arranged to be rotatable relative to the remaining telescopable portion 31 to facilitate and ease the disassembly operation. For example, holes for passing through pins, for example, may be provided on the first toothed plate 14, the second toothed plate 15 and the retractable part 31, and the pins may be inserted during the process of hoisting and/or correcting the roundness of the tower flange 4 to achieve a fixed connection; during the disassembly of the tower spreader 3, the retaining pins are pulled out so that the first and second

toothed plates

14, 15 are rotatable relative to the remaining telescopable portion 31 to facilitate the disassembly. However, the present invention is not limited thereto, and the manner of achieving the connection of the first and second

toothed plates

14 and 15 and the remaining telescopic part 31 may adopt any manner known to those skilled in the art as long as it can achieve the selectively rotatable connection manner.

The first and second connection holes penetrate the first and

second tooth plates

14 and 15 in the thickness direction. The first connecting holes are used for connecting the extendable portions 31 (specifically, the first extendable portion 5, the second extendable portion 6, and the third extendable portion 7), and the second connecting holes are used for connecting the tower flange 4. Preferably, the second connection hole may be formed as a waist-shaped hole, and the waist-shaped hole may extend along the circumferential direction of the tower flange 4 in a state where the tower hanger 3 is mounted on the tower flange 4, so as to match the bolt hole positions of different tower flanges 4. According to an example, the other end of the stretchable part 31 may be formed with a through hole, and the second pin 16 may be used to pass through the first connecting hole and the through hole to fix the tooth plate structure 33 to the other end of the stretchable part 31; the other end of the castellated plate structure 33 may be fixed to the tower flange 4 by using a bolt connection pair 17 through the second connection hole and the bolt hole of the tower flange 4.

As shown in fig. 4, in order to facilitate the disassembly of the tower hanger, each of the first and

second tooth plates

14 and 15 may be designed to include left and

right bodies

21 and 22 symmetrical to each other, and the left and

right bodies

21 and 22 are respectively formed with grooves at sides opposite to each other to form the first and second connection holes described above in a state where the left and

right bodies

21 and 22 are detachably assembled together. Through the adoption with the sectional type dentate plate of every dentate plate divide into two, can solve the technical problem that is difficult to dismantle after correcting the frock installation, this kind of sectional type dentate plate is reuse still moreover to can improve the installation of product, dismantle efficiency and reuse rate, reduction in production cost.

The left and

right blades

21 and 22 are formed with through holes corresponding to each other at the ends in the radial direction of the tower flange 4 and penetrating the left and

right blades

21 and 22, respectively, so that the left and

right blades

21 and 22 are combined together by fasteners penetrating the through holes formed in the left and

right blades

21 and 22, respectively.

In the above-described example, each of the plurality of stretchable and contractible portions 31 may be provided as a cylinder, however, embodiments of the present invention are not limited thereto, and the stretchable and contractible portions 31 may be provided as other elements capable of providing an adjustable stroke, for example, a cylinder, a rack, and the like. In order to facilitate adjustment of the stroke for correcting the roundness of the tower flange 4, the telescopic part 31, such as a cylinder, may have a self-locking function.

A brief description of a method of using a tower spreader according to an exemplary embodiment of the present invention follows.

The hook body 10 is connected with the support 11 and then acts on the tower flange 4, one end of the hook body 10 is hinged to the other end of the fourth telescopic portion 8, one end of the fourth telescopic portion 8 is connected to one side of the connecting bracket 30, and the other three sides of the connecting bracket 30 are respectively fixed with the tower flange 4 through the corresponding telescopic portions 31 (specifically, the first telescopic portion 5, the second telescopic portion 6 and the third telescopic portion 7) and the toothed plate structure 33.

When the tower 1 is in a horizontal state, the hanging strip 2 is connected with the hook 32 of the tower hanger 3 to form a lifting device. The tower 1 can be horizontally lifted with the hooks 32 in the vertical position and hooked on the upper portion of the tower flange 4. Because the upper part of the tower drum lifting appliance 3 is connected with the tower drum flange 4 through the lifting hook 32, and the left, right and lower parts of the tower drum lifting appliance 3 are locked and fixed through the toothed plate structure 33 and the tower drum flange 4, the tower drum flange 4 can not deform during the lifting of the large-diameter tower drum, namely, the tower drum lifting appliance 3 can prevent the tower drum flange 4 of the tower drum from deforming.

The roundness of the tower flange 4 can also be corrected by means of the tower spreader 3 according to the invention if the tower flange 4 has been deformed. After the roundness of the tower drum flange 4 is corrected, the stress load of each oil cylinder is ensured to be unchanged, and the turning process of the tower drum 1 is completed, as shown in fig. 5. The displacement of the fourth stretchable and contractible portion 8 is adjusted to release the hook 32, and the hook 32 is detached as shown in fig. 6. At this time, the first telescopic part 5 and the third telescopic part 7 can also ensure the roundness of the tower flange 4, and the roundness of the symmetrical part of the tower flange 4 is slightly influenced by the disassembly of the fourth telescopic part 8. And then, the tower barrel 1 is turned over and butted, the bolt holes at the position, corresponding to the position of the lifting hook 32, of the tower barrel flange 4 are firstly ensured to be installed in the hole pairs through adjustment in the butting process of the tower barrel flange 4, and after about 5-10 bolts are installed, the displacement of the second telescopic part 6 is adjusted to adjust the roundness of the tower barrel flange 4, so that the bolt holes at the opposite side are ensured to be installed smoothly. Based on the same principle, bolts at the position of the third telescopic part 7 are installed as required, and the roundness of the tower flange 4 can be corrected by adjusting the displacement of the first telescopic part 5 at the opposite side of the third telescopic part, so that the complete installation of the whole tower flange 4 with the non-circular diameter is ensured. As described above, the tower drum lifting appliance 3 of the present invention can dynamically correct the flange during the lifting process, and can correct the roundness of the tower drum flange 4 at any time.

The tower tube lifting appliance 3 can prevent the tower tube flange 4 from deforming in the transportation, transportation and lifting processes of the tower tube 1 (especially a large-diameter tower tube), and can correct the deformed tower tube flange 4 to restore the roundness of the tower tube flange.

The process of dismantling the tower spreader 3 according to the invention will be briefly described below.

After the straightened tower flange 4 and the tower flange of the tower located therebelow are installed and positioned with each other (i.e. the bolts are inserted into the bolt holes of the tower flanges of the upper and lower towers, and the two tower flanges are not completely attached), the first nuts 19, the first screws 18, the second nuts 20, the third nuts 24, the second bolts 23 and the like for connecting the left sheet body 21 and the right sheet body 22 are sequentially disassembled, and the first toothed plate 14 and the second toothed plate 15 are disassembled into the left sheet body 21 and the right sheet body 22, so that the tower hanger 3 is disassembled from the tower flange 4.

After the tower drum lifting appliance 3 is disassembled, the tower drum 1 can continuously fall down until the tower drum flange 4 of the tower drum 1 is completely attached to the flange of the tower drum to be butted, and bolts in the bolt holes are screwed and fixed to complete the butting of the two tower drums.

In the above-described embodiment, the tower spreader 3 according to the present invention is used as a tail boom, and since the tower spreader 3 is simply disassembled without manually climbing the upper portion of the tower flange 4 to perform the aerial work for removing the hook 32, the risk of the aerial work can be reduced.

However, the tower spreader 3 according to the invention may not only be able to be used as a tail boom. According to other embodiments of the invention, the tower spreader 3 may also be used as a master spreader. For example, the tower spreader 3 may additionally comprise lifting lugs, which may be provided on at least one of the castellated plate structures 33. In the case of a tower spreader 3 with only one lifting lug, the lifting lug may be arranged at a position opposite to the lifting hook 32 in the same radial direction of the tower flange 4; in case of a plurality of lifting eyes, one lifting eye of the plurality of lifting eyes may be arranged at a position opposite to the lifting hook 32 in the same radial direction of the tower flange 4, and every two remaining lifting eyes may be arranged at a position opposite to each other in the same radial direction of the tower flange 4, so that the tower spreader 3 may also be used as a main spreader for lifting the upper flange of the tower 1.

The tooth-shaped plate structure is divided into an upper tooth-shaped plate and a lower tooth-shaped plate, and each tooth-shaped plate is divided into a left plate and a right plate, so that the tower cylinder lifting appliance can be detached even in a small operating space. The tower drum lifting appliance is convenient to install and disassemble, the on-site lifting operation time can be effectively shortened, and the construction period is shortened.

The tower drum lifting appliance provided by the invention can prevent the tower drum flange from deforming in the transportation, transportation and lifting processes of the tower drum, can correct the roundness of the deformed tower drum flange at any time, has the advantages of convenience in installation and disassembly, simplicity in operation and the like, and can effectively reduce the production cost and improve the production efficiency.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

1. A tower spreader, characterized in that the tower spreader (3) comprises:

a connecting bracket (30);

a plurality of stretchable portions (31), the plurality of stretchable portions (31) being arranged at equal angular intervals in a radial direction,

wherein one end of each of the plurality of stretchable portions (31) is connected to the connecting bracket (30), the other end of one stretchable portion (31) of the plurality of stretchable portions (31) hooks a tower flange (4) through a hook (32), the other end of each of the remaining stretchable portions (31) is fixed to the tower flange (4) through a tooth plate structure (33), the tooth plate structure (33) includes a first tooth plate (14) and a second tooth plate (15), and tooth surfaces of the first tooth plate (14) and the second tooth plate (15) are stacked facing each other such that tooth portions formed on the tooth surfaces are engaged with each other.

2. The tower spreader of claim 1, wherein the hook (32) comprises a hook body (10), one end of the hook body (10) being hinged to the other end of the one telescopic part (31), the other end of the hook body (10) being used for connecting a harness (2).

3. The tower spreader of claim 2, wherein the lifting hook (32) further comprises a support (11), the support (11) being rotatably arranged inside the hook body (10) with respect to the hook body (10) for hooking the tower flange (4).

4. The tower spreader of claim 1, wherein the first and second toothed plates (14, 15) are correspondingly formed with first connection holes to the other ends of the remaining telescoping sections (31), the first and second toothed plates (14, 15) being selectively rotatable with respect to the remaining telescoping sections (31).

5. The tower spreader of claim 4, wherein the first toothed plate (14) and the second toothed plate (15) are correspondingly formed with second connection holes to the tower flange (4).

6. The tower spreader of claim 5, wherein each of the first and second toothed plates (14, 15) is divided into a left blade (21) and a right blade (22), and the left and right blades (21, 22) are respectively formed with grooves on sides opposite to each other, the grooves forming the first and second connection holes in a state in which the left and right blades (21, 22) are detachably assembled together.

7. The tower spreader of claim 6, wherein the left and right plates (21, 22) are symmetrical to each other, and the ends of the left and right plates (21, 22) in the radial direction of the tower flange (4) are formed with through holes corresponding to each other and penetrating the left and right plates (21, 22), respectively.

8. The tower spreader according to claim 1, wherein the tower spreader (3) further comprises lifting lugs, which are provided on at least one of the castellated plate structures (33).

9. The tower spreader according to any one of claims 1-8, wherein the number of telescopable portions (31) is four.