Indoor unit of air conditioner

Abstract

The utility model relates to the technical field of air conditioners, and provides an air conditioner indoor unit. The air conditioner indoor unit comprises a main face frame and a bottom face frame, and a dismounting opening is formed in the bottom of the main face frame; the bottom surface frame is detachably connected with the main surface frame so as to cover or expose the dismounting opening, the bottom surface frame is provided with an elastic buckle extending towards the main surface frame in a protruding mode, the main surface frame is provided with a clamping hole corresponding to the elastic buckle, and the elastic buckle is configured to elastically deform when the bottom surface frame moves towards the main surface frame in the first direction and is matched with the clamping hole in a clamped mode. According to the air conditioner indoor unit provided by the invention, an installation person only needs to push the bottom face frame in the first direction, the elastic buckles can elastically deform until the elastic buckles can penetrate through the clamping holes, then clamping fit of the elastic buckles and the clamping holes is achieved, and therefore detachable connection between the bottom face frame and the main face frame is achieved; the installation difficulty can be reduced, and the installation efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of air conditioning technology, and in particular to an indoor air conditioning unit. Background Technology

[0002] Most air conditioner indoor units on the market have a single, integral frame. To ensure sufficient operating space when connecting pipes, installers typically remove the frame, which is cumbersome and expensive. While some air conditioner indoor units utilize detachable top and bottom frame assemblies, allowing for easier pipe connection after removing the bottom frame, these units are usually installed at a higher position. Connecting the top and bottom frames using screws is tedious and inefficient for installers. Utility Model Content

[0003] In order to solve the above-mentioned technical problems, or at least partially solve the above-mentioned technical problems, this application provides an air conditioning indoor unit.

[0004] This application provides an indoor unit for an air conditioner, comprising:

[0005] The main frame has a disassembly opening at its bottom;

[0006] The bottom frame is detachably connected to the main frame to cover or expose the disassembly / removal port;

[0007] The bottom frame is provided with an elastic buckle that protrudes toward the main frame, and the main frame is provided with a locking hole corresponding to the elastic buckle. The elastic buckle is configured to elastically deform when the bottom frame moves toward the main frame in a first direction and engage with the locking hole.

[0008] The air conditioner indoor unit provided in this application includes a main frame and a bottom frame. The main frame and the bottom frame can be detachably connected by the engagement of elastic clips and locking holes. After the bottom frame is connected to the main frame, the disassembly port on the main frame is covered by the bottom frame, and the outer surface of the air conditioner indoor unit remains flat. When the bottom frame is removed from the main frame, the disassembly port on the main frame is exposed. The disassembly port provides space for the installer to connect pipes, facilitating pipe connection operations. Furthermore, the installer only needs to push the bottom frame in the first direction, and the elastic clip will elastically deform until it can pass through the locking hole, thereby achieving the engagement of the elastic clip and the locking hole, thus connecting the bottom frame and the main frame. This reduces installation difficulty and improves installation efficiency.

[0009] In some embodiments, the elastic buckle includes a buckle arm and a buckle position, one end of the buckle arm is connected to the bottom frame, and the buckle position is connected to the other end of the buckle arm;

[0010] The fastening part is configured to press against the wall of the locking hole when the bottom frame moves toward the main frame in a first direction, and the locking arm undergoes elastic deformation so that the fastening part passes through the locking hole and is locked onto the side of the locking hole away from the bottom frame.

[0011] In some embodiments, a first guide slope is formed on the side surface of the latching portion away from the bottom frame, and the first guide slope is configured to slide into the wall of the card hole when the bottom frame moves toward the main frame in a first direction.

[0012] In some embodiments, a second guide slope is formed on one side surface of the latching portion facing the bottom frame, and the second guide slope is configured to slide into the wall of the card hole when the bottom frame moves away from the main frame in a first direction.

[0013] In some embodiments, a support boss is provided on the side of the card hole away from the bottom frame, and the fastening part is engaged with the support boss.

[0014] In some embodiments, the side surface of the support boss facing the latching part is formed as a third guide slope, and the latching part slides with the third guide slope when the bottom frame moves away from the main frame in a first direction.

[0015] In some embodiments, the end of the clamping arm near the bottom frame is provided with a reinforcing rib, and the reinforcing rib is obliquely supported between the clamping arm and the bottom frame.

[0016] In some embodiments, the number of the latches is at least two, and they are respectively disposed on both sides of the disassembly port along the second direction. The number of the elastic buckles is equal to the number of the latches and they are disposed in a one-to-one correspondence.

[0017] In some embodiments, the elastic buckle includes a buckle arm and a buckle position, one end of the buckle arm is connected to the bottom frame, and the buckle position is connected to the other end of the buckle arm;

[0018] The buckle portion of the elastic buckle located on both sides of the disassembly port along the second direction is respectively connected to the two buckle arms on the side facing away from each other.

[0019] In some embodiments, the bottom frame is provided with a handle position to apply a force to the bottom frame to move away from the main frame in the first direction.

[0020] In some embodiments, the bottom frame is a flat plate, the bottom of the main frame has a groove, the bottom frame is accommodated in the groove, and the outer surface of the bottom frame is flush with the outer surface of the bottom of the main frame.

[0021] In some embodiments, the bottom frame is an integral injection-molded structure, the bottom frame includes a middle region and two end regions located around the middle region, the thickness of the middle region is less than the thickness of the two end regions, and there is a smooth transition between the middle region and the two end regions. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of an indoor air conditioner unit according to an embodiment of the present invention;

[0025] Figure 2 This is an exploded view of an indoor air conditioner unit according to an embodiment of the present invention;

[0026] Figure 3 for Figure 2 Enlarged view of part A in the middle;

[0027] Figure 4 This is a front view of the main frame according to an embodiment of the present invention;

[0028] Figure 5 for Figure 4 Sectional view along the BB direction;

[0029] Figure 6 This is a bottom view of the main frame of an embodiment of the present invention;

[0030] Figure 7 This is a top view of the bottom frame of an embodiment of the present invention;

[0031] Figure 8 for Figure 7 A cross-sectional view along the CC direction;

[0032] Figure 9 for Figure 8 Enlarged view of a section in part D;

[0033] Figure 10 This is a schematic diagram of the assembly of the main frame and the bottom frame according to an embodiment of the present invention;

[0034] Figure 11 for Figure 10A magnified view of a section in part E;

[0035] Figure 12 This is a bottom view of the indoor unit of an air conditioner according to an embodiment of the present invention;

[0036] Figure 13 This is a schematic diagram of the pipe connection of an indoor air conditioner unit according to an embodiment of the present invention. Figure 1 ;

[0037] Figure 14 This is a schematic diagram of the pipe connection of an indoor air conditioner unit according to an embodiment of the present invention. Figure 2 .

[0038] In the diagram: 1. Main frame; 11. Disassembly / removal port; 12. Clip hole; 13. Support boss; 131. Third guide slope; 14. Groove; 2. Bottom frame; 21. Handle position; 22. Middle area; 23. Both end areas; 3. Elastic buckle; 31. Clip arm; 32. Buckle position; 321. First guide slope; 322. Second guide slope; 33. Reinforcing rib; 4. Support leg. Detailed Implementation

[0039] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0040] Many specific details are set forth in the following description in order to provide a full understanding of this application, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0041] The following is a detailed description of the indoor unit of this air conditioner through specific embodiments:

[0042] Reference Figures 1 to 14 As shown in the figure, some embodiments of the present invention provide an indoor air conditioning unit, including a main frame 1 and a bottom frame 2.

[0043] The main frame 1 has a disassembly opening 11 at its bottom, and the bottom frame 2 is detachably connected to the main frame 1 to cover or expose the disassembly opening 11.

[0044] The bottom frame 2 is provided with an elastic buckle 3 that protrudes toward the main frame 1. The main frame 1 is provided with a locking hole 12 corresponding to the elastic buckle 3. The elastic buckle 3 is configured to elastically deform when the bottom frame 2 moves toward the main frame 1 in a first direction and engage with the locking hole 12.

[0045] In practice, the main frame 1 and the bottom frame 2 can be detachably connected by the snap-fit ​​of the elastic buckle 3 and the snap-fit ​​of the hole 12. After the bottom frame 2 is connected to the main frame 1, the disassembly port 11 on the main frame 1 is covered by the bottom frame 2, and the outer surface of the air conditioner indoor unit remains flat. When the bottom frame 2 is removed from the main frame 1, the disassembly port 11 on the main frame 1 is exposed. The disassembly port 11 can provide space for the installer to connect pipes, making it convenient to carry out pipe connection operations.

[0046] Furthermore, the installer only needs to push the bottom frame 2 in the first direction, and the elastic buckle 3 will elastically deform until the elastic buckle 3 can pass through the buckle hole 12, thereby realizing the snap-fit ​​between the elastic buckle 3 and the buckle hole 12, so as to connect the bottom frame 2 and the main frame 1, which can reduce the installation difficulty and improve the installation efficiency.

[0047] Specifically, the first direction can be vertical. The installer only needs to stand on the ground and push the bottom frame 2 upward in the vertical direction to push the elastic buckle 3 to engage with the buckle hole 12, thereby completing the connection between the bottom frame 2 and the main frame 1. When disassembling, the bottom frame 2 can be removed downward in the vertical direction, which is convenient for disassembly and assembly.

[0048] In some embodiments, refer to Figure 3 and Figure 9 As shown, the elastic buckle 3 includes a buckle arm 31 and a buckle part 32. One end of the buckle arm 31 is connected to the bottom frame 2, and the buckle part 32 is connected to the other end of the buckle arm 31. The buckle part 32 is configured to press against the wall of the buckle hole 12 when the bottom frame 2 moves toward the main frame 1 in the first direction. The buckle arm 31 undergoes elastic deformation so that the buckle part 32 passes through the buckle hole 12 and is engaged on the side of the buckle hole 12 away from the bottom frame 2.

[0049] In other words, during the movement of the latching part 32 toward the main frame 1 in the first direction, it can press and cooperate with the hole wall of the locking hole 12, so as to drive the locking arm 31 to elastically deform in the direction away from the pressed hole wall, thereby allowing the latching part 32 to pass through the locking hole 12 and abut against the other side of the locking hole 12 away from the bottom frame 2. The main frame 1 can restrict the latching part 32 from coming out, thereby ensuring the connection performance between the main frame 1 and the bottom frame 2.

[0050] It should be noted that during the movement of the latching part 32 away from the main frame 1 in the first direction, it can also be squeezed and engaged with the hole wall of the locking hole 12, so as to drive the locking arm 31 to undergo elastic deformation in the direction away from the squeezed hole wall, thereby enabling the latching part 32 to pass through the locking hole 12 and disengage from the locking hole 12, thereby removing the bottom frame 2 from the main frame 1.

[0051] In specific implementation, refer to Figure 9As shown, a first guide slope 321 is formed on the side surface of the latching part 32 away from the bottom frame 2. The first guide slope 321 is configured to slide and engage with the wall of the locking hole 12 when the bottom frame 2 moves toward the main frame 1 in the first direction, so as to compress the locking arm 31 to undergo elastic deformation until the latching part 32 can pass through the locking hole 12. After the latching part 32 passes through the locking hole 12, the wall of the hole no longer compresses the latching part 32, and the locking arm 31 can recover its deformation and make the latching part 32 abut against the side of the locking hole 12 away from the bottom frame 2.

[0052] Furthermore, continue to refer to Figure 9 As shown, a second guide slope 322 is formed on the side surface of the latching part 32 facing the bottom frame 2. The second guide slope 322 is configured to slide and engage with the wall of the locking hole 12 when the bottom frame 2 moves away from the main frame 1 in the first direction, so as to compress the locking arm 31 to undergo elastic deformation until the latching part 32 passes through the locking hole 12 from the side away from the bottom frame 2, thereby releasing the restriction between the latching part 32 and the main frame 1. After the latching part 32 passes through the locking hole 12, the hole wall no longer compresses the latching part 32, and the locking arm 31 can recover its deformation and allow the latching part 32 to abut against the side of the locking hole 12 away from the bottom frame 2.

[0053] It is understandable that both the first guide slope 321 and the second guide slope 322 can guide the latching part 32 to slide and engage with the hole wall of the locking hole 12, so as to squeeze and drive the locking arm 31 to elastically deform in a direction away from the squeezed hole wall, which can reduce the installation difficulty, improve the operability of assembly and disassembly, and facilitate the operation of installers.

[0054] In some embodiments, a support boss 13 is provided on the side of the latch 12 away from the bottom frame 2, and the latching part 32 is engaged with the support boss 13. It is understood that the sum of the height of the support boss 13 and the thickness of the latch 12 is adapted to the length of the latch arm 31. By providing the support boss 13, the mounting surface of the elastic buckle 3 can be increased, thereby increasing the height of the elastic buckle 3 and improving its elasticity, making it easier to assemble and disassemble. Specifically, the support boss 13 is located at the edge of the latch 12 and protrudes from the surface of the main frame 1 in a direction away from the bottom frame 2, thereby increasing the mounting surface of the elastic buckle 3.

[0055] Reference Figure 11As shown, the surface of the support boss 13 facing the latching part 32 is formed as a third guide slope 131. When the bottom frame 2 moves away from the main frame 1 along the first direction, the latching part 32 slides with the third guide slope 131 to compress the latching part 32 and the locking arm 31, causing elastic deformation until the latching part 32 disengages from the third guide slope 131 on the support boss 13, thereby removing the bottom frame 2 from the main frame 1. The third guide slope 131 reduces the installation difficulty and facilitates the operation of the installer. Specifically, the second guide slope 322 slides with the third guide slope 131.

[0056] In some embodiments, refer to Figure 9 As shown, a reinforcing rib 33 is provided at the end of the clamping arm 31 near the bottom frame 2, and the reinforcing rib 33 is inclined and supported between the clamping arm 31 and the bottom frame 2. The reinforcing rib 33 increases the structural strength of the elastic buckle 3, avoids damage to the elastic buckle 3 after a lot of disassembly and assembly, and can extend the service life.

[0057] In practice, the height of the reinforcing rib 33 should not exceed half the height of the elastic buckle 3. That is, the reinforcing rib 33 is connected in the area of ​​half of the elastic buckle 3 facing the bottom frame 2. This can ensure the structural strength of the elastic buckle 3 while avoiding the elastic deformation effect of the elastic buckle 3 due to excessive structural strength of the reinforcing rib 33.

[0058] Specifically, the reinforcing rib 33 can be a rib structure or a triangular reinforcing rib structure. This application does not limit this, as long as it can be supported between the clip arm 31 and the bottom frame 2 to increase the structural strength of the elastic buckle 3.

[0059] In some embodiments, refer to Figure 7 As shown, there are at least two locking holes 12, which are respectively located on both sides of the disassembly port 11 along the second direction. This ensures that the bottom frame 2 can be detachably connected to the area of ​​the main frame 1 other than the disassembly port 11. It can be understood that the bottom frame 2 and the main frame 1 can be connected by elastic buckles 3 at multiple different positions, which can ensure the stability of the connection and avoid unevenness of the surface such as warping. The second direction can be the length direction of the main frame 1, so that the bottom frame 2 can completely cover the disassembly port 11 after installation.

[0060] In practice, the number of elastic buckles 3 is equal to the number of buckle holes 12 and they are set in a one-to-one correspondence so that multiple elastic buckles 3 and multiple buckle holes 12 can be snapped together in a one-to-one correspondence during installation, thereby ensuring the connection strength between the main frame 1 and the bottom frame 2.

[0061] Specifically, there are four elastic buckles 3 and four buckle holes 12. The four elastic buckles 3 are arranged in pairs opposite each other at both ends of the bottom frame 2 along the second direction, and the four buckle holes 12 are arranged one-to-one with the four elastic buckles 3 on the main frame 1.

[0062] Of course, it should be noted that the number of elastic buckles 3 and buckle holes 12 can be five, six or more, and multiple elastic buckles 3 and buckle holes 12 can be distributed in other arrangements. This application does not limit this, as long as the connection between the bottom frame 2 and the main frame 1 can be achieved from multiple different positions, thereby achieving a stable connection.

[0063] The elastic buckle 3 includes a buckle arm 31 and a buckle position part 32. One end of the buckle arm 31 is connected to the bottom frame 2, and the buckle position part 32 is connected to the other end of the buckle arm 31. The buckle position parts 32 of the elastic buckle 3 located on both sides of the disassembly port 11 along the second direction are respectively connected to the two buckle arms 31 on the side facing away from each other.

[0064] It is understandable that the elastic buckle arms 31 located on both sides of the disassembly port 11 along the second direction can elastically deform in opposite directions during the installation of the bottom frame 2. The elastic forces on the two opposite buckle arms 31 cancel each other out, which can prevent the bottom frame 2 from shifting due to elastic force during installation. The installer only needs to push the bottom frame 2 along the first direction to connect the bottom frame 2 with the main frame 1.

[0065] Of course, it should be noted that the latching parts 32 of the elastic buckles 3 located on both sides of the disassembly port 11 along the second direction can also be connected to the two latching arms 31 facing each other. This application does not limit this, as long as the deformation directions on the two opposing latching arms 31 can be opposite so that the elastic forces can cancel each other out.

[0066] In some embodiments, refer to Figure 7 and Figure 12 As shown, the bottom frame 2 is provided with a handle position 21, which applies a force to the bottom frame 2 in a first direction away from the main frame 1. That is, during disassembly, by inserting fingers into the handle position 21 on the bottom frame 2 and pulling the bottom frame 2 in the first direction away from the main frame 1, the elastic buckle 3 can elastically deform, allowing the bottom frame 2 to be easily removed. The handle position 21 improves the disassembly experience. Specifically, the handle position 21 is an avoidance groove structure formed on the bottom frame 2, allowing fingers to be inserted for easy application of force.

[0067] In practice, the bottom frame 2 is a flat plate, and the bottom of the main frame 1 has a groove 14. The bottom frame 2 is housed in the groove 14, and the installer's fingers can be inserted into the space between the handle position 21 and the groove wall of the groove 14. The outer surface of the bottom frame 2 is flush with the outer surface of the bottom of the main frame 1, which can improve the aesthetic performance.

[0068] Of course, the outer surface of the bottom frame 2 can also be lower than the bottom outer surface of the main frame 1 along the first direction and away from the main frame 1, as long as the height difference between the bottom frame 2 and the main frame 1 is less than 0.5mm after the elastic buckle 3 is fastened, so as to avoid excessive gap and ensure aesthetic effect.

[0069] Furthermore, the engagement gap between the elastic buckle 3 and the buckle hole 12 is less than or equal to 0.2mm, which can prevent the bottom frame 2 from protruding from the main frame 1 due to excessive engagement gap after installation, thus preventing the bottom frame 2 from sagging and ensuring that the mounting surface at the bottom of the air conditioner indoor unit is flat.

[0070] In some embodiments, the bottom frame 2 is an integral injection molded structure. The bottom frame 2 includes a middle region 22 and two end regions 23 located around the middle region 22. The thickness of the middle region 22 is less than the thickness of the two end regions 23, and there is a smooth transition between the middle region 22 and the two end regions 23.

[0071] Understandably, wavy deformation is prone to occur during injection molding. The thickness of the middle region 22 is thinner than that of the two end regions 23. The middle region 22 can form a pre-deformation zone to compensate for deformation during injection molding, ensuring the appearance and assembly of the product. Furthermore, there is a wall thickness transition zone between the two end regions 23 and the middle region 22. The wall thickness of the transition zone is smoothly transitioned, which can avoid shrinkage marks on the appearance surface and ensure the product's appearance performance.

[0072] Reference Figure 13 and Figure 14 As shown, during the pipe connection process, after removing the bottom frame 2, the support leg 4 can be supported between the main frame 1 and the wall surface to be installed. The disassembly port 11 on the main frame 1 and the wall surface together form a pipe connection space. The larger space of the pipe connection space can be used by the installer to perform pipe connection, pipe alignment and other operations.

[0073] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0074] The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to these embodiments, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An indoor unit for an air conditioner, characterized in that, include: The main frame has a disassembly opening at its bottom; The bottom frame is detachably connected to the main frame to cover or expose the disassembly / removal port; The bottom frame is provided with an elastic buckle that protrudes toward the main frame, and the main frame is provided with a locking hole corresponding to the elastic buckle. The elastic buckle is configured to elastically deform when the bottom frame moves toward the main frame in a first direction and engage with the locking hole.

2. The indoor unit of the air conditioner according to claim 1, characterized in that, The elastic buckle includes a buckle arm and a buckle position, one end of the buckle arm is connected to the bottom frame, and the buckle position is connected to the other end of the buckle arm; The fastening part is configured to press against the wall of the locking hole when the bottom frame moves toward the main frame in a first direction, and the locking arm undergoes elastic deformation so that the fastening part passes through the locking hole and is locked onto the side of the locking hole away from the bottom frame.

3. The indoor unit of the air conditioner according to claim 2, characterized in that, A first guide slope is formed on the side surface of the fastening part away from the bottom frame. The first guide slope is configured to slide in engagement with the wall of the card hole when the bottom frame moves toward the main frame in a first direction.

4. The indoor unit of the air conditioner according to claim 2, characterized in that, The fastening part has a second guide slope on one side surface facing the bottom frame. The second guide slope is configured to slide against the wall of the card hole when the bottom frame moves away from the main frame in a first direction.

5. The indoor unit of the air conditioner according to claim 2, characterized in that, A support boss is provided on the side of the card hole away from the bottom frame, and the fastening part is engaged with the support boss.

6. The indoor unit of the air conditioner according to claim 5, characterized in that, The side surface of the support boss facing the fastening part is formed as a third guide slope, and the fastening part slides with the third guide slope when the bottom frame moves away from the main frame in the first direction.

7. The indoor unit of the air conditioner according to claim 2, characterized in that, The end of the clamping arm near the bottom frame is provided with a reinforcing rib, and the reinforcing rib is inclinedly supported between the clamping arm and the bottom frame.

8. The indoor unit of the air conditioner according to claim 1, characterized in that, The number of the card holes is at least two, and they are respectively set on both sides of the disassembly port along the second direction. The number of the elastic buckles is equal to the number of the card holes and they are set one-to-one.

9. The indoor unit of the air conditioner according to claim 8, characterized in that, The elastic buckle includes a buckle arm and a buckle position, one end of the buckle arm is connected to the bottom frame, and the buckle position is connected to the other end of the buckle arm; The buckle portion of the elastic buckle located on both sides of the disassembly port along the second direction is respectively connected to the two buckle arms on the side facing away from each other.

10. The indoor unit of an air conditioner according to any one of claims 1 to 9, characterized in that, The bottom frame is provided with a handle position, so as to apply a force to the bottom frame to move away from the main frame in the first direction through the handle position.

11. The indoor unit of the air conditioner according to claim 10, characterized in that, The bottom frame is a flat plate, and the bottom of the main frame has a groove. The bottom frame is accommodated in the groove, and the outer surface of the bottom frame is flush with the outer surface of the bottom of the main frame.

12. The air conditioning indoor unit according to any one of claims 1 to 9, characterized in that, The bottom frame is an integral injection molded structure. The bottom frame includes a middle area and two end areas located around the middle area. The thickness of the middle area is less than the thickness of the two end areas, and there is a smooth transition between the middle area and the two end areas.

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