JPH09114553A - High performance air-cooled electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the structure of a housing, to unify the kind of a cooling fan and to reduce a space by respectively arranging the cooling fan on an air supplying side and an air exhausting side so as to supply air from the side of an electronic equipment and so as to exhaust air through the rear. SOLUTION: A CPU cooling fan unit 28 and a DC/DC cooling fan 29 are provided at the forward part of the side of the electronic equipment as cooling fans for supplying air, and the DC/DC cooling fan 29 is provided with a duct 50 with an angle. Then cooling air 40 is supplied by the CPU cooling fan unit 28, passes through the inside of a CPU unit 20, his a side plate 41 to bend its flow route at right angle, passes through the inside of an I/O package 22 to be exhausted to the rear of the equipment by an air exhausting fan unit 31. In addition cooling air 40 to the other units are similarly exhausted to the rear side of the equipment by the duct 50 with an angle. Consequently cooling air 40 is effectively used, the equipment is miniaturized and the space is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling structure for an electronic device such as a computer. Furthermore, the present invention relates to a housing structure of an electronic device in which a main body of a computer processing device, a communication device or the like can be mounted in a cabinet in a box shape.

[0002]

2. Description of the Related Art As described in Japanese Patent Application No. 5-89695, a cooling method for an electronic device such as a computer has a structure in which two or more channels are provided, and a dual structure is provided below the device. Was exhausting to.

Further, a plurality of types of cooling fans are provided between the heating elements or at the corners of the flow path for cooling. Further, the conventional casing structure of electronic devices such as computer processing devices and communication devices has a vertically long or horizontally long main body and has a self-standing box shape provided with casters, leveling bolts and the like.

[0004]

The above prior art is disclosed in FIG.
As shown in Fig. 5, the structure of the housing is complicated due to the double structure of the flow path, the number of mounting members is increased by using plural kinds of cooling fans, the cost is increased, and the installation space is increased by adding or expanding the device. There was a problem, and it was necessary to consider the simplification of the housing structure, unification of the types of cooling fans, and space saving without considering this point.

[0005]

In order to achieve the above object, a plurality of devices can be mounted in one cabinet,
A cooling fan is provided on each of the air supply side and the air discharge side of the device, and air is supplied from the side surface of the device and exhausted to the back surface.

Further, a platter board for connecting electric and signals between the boards is arranged on the bottom surface of the device, and the board is fitted vertically on the platter board by a connector, and the board is parallel to the air supply direction and the exhaust direction. Further, the guide rail mounting plate of the exhaust side substrate is provided with a rectangular hole so as to also serve as a partition plate parallel to the air supply side substrate.

Further, an angled duct shape is provided in the lower portion of the discharge side of the air supply side cooling fan, and the cooling air is blown into two systems from one fan.

Further, the air supply port of the power supply unit having a built-in cooling fan has a structure in which a partition plate is provided on the side surface of the fan on the air supply side of the apparatus in parallel with the air supply direction to separate from other air supply. Is.

Further, in the present electronic equipment in which a plurality of types of CPU units having different heat generating parts can be mounted, a plurality of mounting holes are provided in the bracket for mounting the cooling fan for the CPU unit in the housing, and the mounting holes are cooled. A cooling fan is attached so that the position of the cooling fan can be moved according to the mounted CPU unit.

A U-shaped handle is provided on the upper surface of the CPU unit to improve workability and safety with respect to vertical insertion and removal.

Further, the handle is pressed by the top cover of the device through the cushioning material, so that the connection failure between the CPU unit and the platter board due to the vibration during transportation can be prevented. It is a thing.

Further, a fan cover of the exhaust fan unit.
Is formed into a box shape, a plurality of holes each having a diameter of 4 mm are formed on the exhaust surface, and an appropriate space is provided between the fan cover and the exhaust fan.

Further, the exhaust fan unit is disposed in the vertically inserted space for vertically mounting the board, and the exhaust fan unit is connected to the housing by a hinge so as to be rotatable by 90 ° or more. By rotating the fan unit for use, the board mounted under the exhaust fan unit can be inserted and removed.

Further, a CPU unit and a board which are frequently exchanged are mounted at a front position of the apparatus, and an upper surface or a bar is divided into front and rear in accordance with the position of the parts, and further, the female-side slad rail and the male-side slad rail. In addition, a stopper is provided to stop at the dividing point of the top cover.

Further, a battery unit can be mounted by providing a handle for insertion / removal on the upper surface of the power supply unit to be mounted inside the apparatus, and by designing the handle to have a flat upper surface and a wider area than the lower surface, the handle can be mounted on the power supply. It has a structure that can be used for two purposes: unit insertion / removal and battery unit mounting bracket.

Further, a connector having expandability is mounted on the front side of the apparatus, and further, an opening to which the connector can be connected is provided on the front panel of the apparatus, and the opening is easily opened from the front of the apparatus with a maintenance tool. It has a removable panel cover attached.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an external perspective view from the front of an electronic device 1 according to an embodiment of the present invention. FIG. 2 is a rear perspective view of the electronic device 1 according to an embodiment of the present invention. FIG. 14 is a perspective view showing a state in which a plurality of electronic device apparatuses 1 according to an embodiment of the present invention are mounted in a cabinet 45.

FIG. 3 is a perspective view showing a state in which the electronic device 1 according to an embodiment of the present invention is mounted in the cabinet 45, pulled out forward, and temporarily stopped. Front panel 2 on the front
There is an operation panel 3 on the front panel 2, and there are a power-on display, a system operation display, an operating state display and the like. Further, there is an opening 65 on the front panel 2 corresponding to the expandable connector built into the device, and is closed by the easily removable panel cover 4.

Further, on both sides of the front panel 2, there are flange portions 12 for attaching and fixing to the cabinet frame 48 when mounted on the cabinet 45. The rear surface has a package slit 11 for projecting the connector portion of the package and connecting a cable. On the upper surface, there are an upper front cover 5 and an upper rear cover 6 which are divided into two in the front and back. In front of the side surface, there is an air supply panel 7 in which a plurality of holes with a diameter of 4 mm are provided for air supply, and a magic tape is provided outside the air supply panel 7 to suck dust into the electronic device 1. An air filter 8 for prevention is attached.

Further, male slide rails for engaging the female slide rails 9 mounted on the cabinet 45 to move the apparatus forward and temporarily stop the pulled-out state at the upper portions of both side surfaces. 10 is attached.

A plurality of the electronic equipments 1 can be mounted in one cabinet 45, and the top cover is divided into two, so that the electronic equipments 1 are pulled out from the cabinet 45 and are provided on the slide rails. The upper front cover 5 can be removed in the state of being temporarily stopped by 13, and the electronic device 1 can be maintained without lowering it from the cabinet 45. Also, the air filter 8 that is frequently replaced can be easily replaced.

FIG. 4 shows an internal mounting diagram of the electronic device 1 according to one embodiment of the present invention. A CPU cooling fan unit 28 and a DC / DC cooling fan 29 are provided on the front side surface of the electronic device 1 as air supply cooling fans.
The DC cooling fan 29 is provided with an angled duct 50. The CPU unit 20, which is the heart of the device, is arranged in parallel with the direction of the air flow of the air supply cooling fan.
A DC / DC converter 21, which is an electric converter, is arranged.

A CPU base board 20e is mounted inside the CPU unit 20, and RI of a high heat generating element is mounted thereon.
RISC processor module 20 equipped with an SC chip package and a cache memory for temporarily storing data
a, an OSC (oscillator) package 20b for controlling the operating frequency of the RISC chip, a BA (bus adapter) package 20c having a role of mediating different signal lines,
An MS middle card 20d capable of mounting a maximum of eight memory packages is vertically mounted.

An I / O (input / output) package 22 which is an expansion board vertically to the CPU unit 20 and the DC / DC converter 21, an SSU package 23 for system control, a PSU package 24 for controlling power supply, and an auxiliary power supply. 25, AC / which is the electricity supply unit
The DC converter unit 26 is arranged. A platter board 27 is provided on these bottom surfaces, and mediates electricity and signals between the packages. An exhaust cooling fan unit 31 for discharging the internal heat to the outside is rotatably coupled to the device casing by a hinge 59 on the I / O package 22 on the rear surface of the device, and the exhaust air blows to the I / O package 22. It is arranged so as to flow in parallel with the O package and the like.

FIG. 5 shows a flow path of the cooling air 40 inside the electronic device 1 which is an embodiment of the present invention as viewed from above. There are three channels, and the first channel is supplied by the CPU fan unit 28 from the air supply panel 7 on the front side.
After passing through the inside of the CPU unit 20, hitting the side plate 41, bending the flow path at a right angle, passing through the inside of the I / O package 22, and discharged to the back side of the device by the exhaust fan unit 31 on the back side of the device.

The second flow path is supplied with air by the DC / DC cooling fan 29 from the air supply panel 7 on the front side, and is mainly DC.
/ It passes through the inside of the DC converter 21, hits the side plate 41,
It merges with the first path and is similarly discharged to the back surface of the device.
Further, the DC / DC cooling fan 29 has the SSU packages 23, P through the rectangular holes of the air flow direction plate 42 and the partition plate 43.
The cooling air 40 is also sent to the SU package 24 and the auxiliary power supply 25, and is discharged by the exhaust cooling fan unit 31 on the rear surface of the device. Further, the cooling air 40 is also sent to the lower layer portion of the CPU unit 20 by the angled duct 50, and is discharged to the back surface like the first flow path.

The third route is to supply air from the air supply panel 7 in front of the side by the AC / DC cooling fan 30 mounted inside the AC / DC converter unit 26, and to the upper part of the AC / DC converter unit 26 and the auxiliary power supply. It is discharged from the side surface on the 25 side, and is discharged to the outside by the exhaust cooling fan unit 31 on the rear surface of the apparatus. Further, the air supply port of the AC / DC converter unit 26 is provided with a partition plate 47 on the side surface of the DC / DC cooling fan 29.

By implementing the mounting and the flow path as shown in FIGS. 4 and 5, it is possible to reduce the size of the electronic device 1 and to efficiently cool the heating elements at various places. Is. Further, when the electronic device 1 is mounted on the cabinet 45 by supplying air from the side surface, the side surface of the device is covered by the cabinet side surface plate 46, so that the noise of the air supply fan is not directly output to the front surface. Noise can be reduced.

Further, by supplying air from the side surface, it is not necessary to provide the air filter 8 on the front surface, and the front surface of the apparatus can be beautifully finished. Further, by providing the partition plate 47 in the third flow path, it is possible to adjust the air pressure balance with the DC / DC cooling fan having a larger air volume than the AC / DC cooling fan 30, and thus the AC / DC converter unit. 26, stable air supply can be performed.

FIG. 6 shows an exploded perspective view of the front portion of the electronic device apparatus 1 according to one embodiment of the present invention. FIG. 7 shows a flow path of the cooling air 40 in the CPU unit 20 in a cross section AA including the upper front cover of FIG. As shown in FIG. 7, the flow path of the cooling air 40 inside the CPU unit 20 cools the RISC processor module 20a, which is a high heating element, by the CPU cooling fan unit 28, and further cools the MS middle card 20d on the downstream side. The CPU cooling fan unit 28 mainly cools the upper layer side, and the lower layer OSC package 20.
b, the cooling capacity for the BA package 20d is weak.

In this embodiment, as shown in FIG. 6, DC / D
The DC / DC cooling fan 29 for cooling the C converter 21 is provided with an angled duct 50 so as to distribute to the lower layer side of the CPU unit 20 as well, so that the entire CPU unit 20 can be efficiently cooled. Can be cooled without increasing the number of fans.

Further, the electronic device 1 has a platter board 27 arranged on the bottom thereof, and the CPU unit 20 is disposed vertically to the platter board 27.
Are connected by a connector 53, and the insertion / removal is performed in the vertical direction. U-shaped handles 51 are provided on the left and right on the upper surface of the CPU unit 20, and by having the U-shaped handles 51, the CPU unit 20 can be reliably inserted and removed, and fall prevention during insertion and removal can be achieved. Further, a cushioning material 52 is adhered to the upper front cover 5 at a position facing the U-shaped handle 51, and the upper front cover 5 is attached, so that the CPU unit 20 has a structure to be pressed down through the cushioning material 52 and is transported. It is possible to prevent disconnection of the connector 53 due to vibration such as time, and prevent malfunction of the device due to poor contact of the connector 53.

FIG. 8 shows an exploded perspective view of the CPU cooling fan unit 28. A fan cover 55 is attached to the CPU cooling fan 57 in order to efficiently send air to the CPU unit 20, and the fan cover 55 is provided to a bracket 54 for attaching the CPU cooling fan unit 28 to the electronic device 1. Multiple mounting holes 56
Via a mounting screw 70. The assembled CPU cooling fan unit 28 is a C of the electronic device 1.
It is attached to the PU fan attachment portion 58 with an attachment screw 70. As a result, the mounting position of the CPU cooling fan 57 can be changed, and the CPU cooling fan 57 can be moved to an optimum position according to the heat-generating portions of the plurality of types of CPU units 20 to be mounted.

FIG. 9 shows a mounting state when the exhaust cooling fan unit 31 is disassembled. FIG. 10 shows a cross section BB shown in FIG. The exhaust cooling fan unit 31 includes two exhaust cooling fans 61 on an exhaust fan cover 62.
Are attached by mounting screws 70. A plurality of holes having a diameter of 4 mm are formed in the exhaust fan cover 62 to prevent danger such as finger scissors, a magnetic shield, and reduce exhaust air velocity, which is effective for noise reduction. The exhaust fan cover 62 has a box shape, and an appropriate space (dimension a: 10 mm or more) is provided between the exhaust fan cover 62 and the exhaust cooling fan 61 to prevent deterioration of exhaust performance due to exhaust pressure loss. There is. The exhaust fan cover 62 is fastened to the device back plate 60 by a hinge 59 and has a structure capable of rotating by 90 ° or more.

Normally, the exhaust cooling fan unit 31 is mounted in the insertion / removal space above the I / O package 22. In this state, the I / O package cannot be inserted / removed, but the exhaust cooling fan unit 31 is opened. By doing so, it becomes possible to insert and remove. As a result, the cooling fan unit 31 for exhaust can be mounted without protruding to the back surface of the device, the depth dimension of the electronic device 1 can be reduced, and it is effective for downsizing of the device.

FIG. 11 shows an exploded perspective view of the front panel 2. There is an opening 65 in the lower part of the front panel 2, a threaded portion 63 is welded around the opening 65, and the panel cover 4 is attached from the rear surface by a nut 64. Therefore, replacement with the panel cover 4a having the connector 53 as shown in FIG. 12 can be easily performed. As a result, signal cables between devices can be connected on the front of the device, and expansion and expansion can be easily supported.

FIG. 13 shows an AC / DC converter unit 2
6 shows an exploded view of the mounting of FIG. A Z-shaped handle 66 is provided on the upper surface of the AC / DC converter unit 26 for easy insertion and removal. Hooking portion 68 of Z-shaped handle 66
By making the area flat and having a large area, the battery unit 67 for operating the memory in the SSU package 23 when the power supply of the apparatus is down can be mounted thereon.
It can be utilized for two purposes, one for inserting and removing the power supply unit and the other for mounting the battery unit. Furthermore, by mounting the battery unit 67 by floating it from the AC / DC converter unit 26 with the Z-shaped handle 66, it is possible to prevent the heat of the AC / DC converter unit 26 from being directly conducted.

[0038]

Since the present invention is configured as described above, the effects described below can be obtained.

Air is supplied from the front side of the electronic device and exhausted to the back side, cooling fans are provided on the air supply side and the exhaust side, and the substrates are arranged in parallel on the air supply side and the exhaust side.
Effective use of the cooling air can be achieved by providing a partition plate to open rectangular holes, angle the cooling fan duct, and move the position of the cooling fan with respect to the heat generation area. By reducing fan power, noise can be reduced, equipment can be made smaller, and cost can be reduced. Further, since there is no air supply port on the front surface, a beautiful appearance can be formed.

Further, by providing the cooling fan unit with an angled duct shape and blowing air from one fan to two systems, the cooling air can be effectively used, and the size of the apparatus can be reduced.
Cost reduction can be achieved.

Further, by separating each flow path by a partition plate in the air supply unit, it is possible to prevent adverse effects due to airflow between cooling fans having different outputs, to perform stable air supply, and to perform efficient cooling.

Further, by providing a handle on the upper surface of the unit which is vertically inserted and withdrawn, and further pressing the handle with a cushioning material by the top cover of the device, the insertability of the unit is improved and there is a risk of damage due to dropping or the like. And the connector can be prevented from being disengaged during transportation, etc., and reliability can be improved.

Further, by providing an opening in the front panel and closing the panel with an easily removable panel cover, it is possible to easily cope with expansion and expansion.

Further, by dividing the upper cover of the apparatus into two parts and providing the slide rail with a stopper that temporarily stops at the dividing point of the upper cover, maintenance of the main parts can be performed without lowering the entire heavy apparatus from the cabinet. The maintenance work time can be shortened.

[Brief description of the drawings]

FIG. 1 is an external perspective view from the front of an electronic device according to an embodiment of the present invention.

FIG. 2 is an external perspective view from the rear of the electronic device showing an embodiment of the present invention.

FIG. 3 is a perspective view of an electronic device according to an embodiment of the present invention in a state of being pulled out from a cabinet.

FIG. 4 is an internal mounting diagram of an electronic device according to an embodiment of the present invention.

FIG. 5 is a cooling channel diagram viewed from the top of an electronic device according to an embodiment of the present invention.

FIG. 6 is an exploded perspective view of an air supply side of an electronic device according to an embodiment of the present invention.

FIG. 7 is a sectional view taken along line AA of FIG. 6 showing an embodiment of the present invention.

FIG. 8 is an exploded perspective view of a CPU fan unit portion showing an embodiment of the present invention.

FIG. 9 is an exploded perspective view showing an exhaust fan unit in an opened state according to an embodiment of the present invention.

FIG. 10 is a sectional view taken along line BB of FIG. 9 showing an embodiment of the present invention.

FIG. 11 is an exploded perspective view of a front panel portion showing an embodiment of the present invention.

FIG. 12 is a perspective view of a panel cover showing an embodiment of the present invention.

FIG. 13 is an exploded perspective view of an AC / DC converter unit part showing an embodiment of the present invention.

FIG. 14 is a perspective view in which a plurality of electronic equipment devices according to an embodiment of the present invention are mounted in a cabinet.

FIG. 15 is a perspective view of an electronic apparatus device showing a conventional example.

[Explanation of symbols]

1 ... Electronic device, 2 ... Front panel, 3 ... Operation panel,
4 ... Panel cover, 4a ... Panel cover, 5 ... Top front cover, 6 ... Top back cover, 7 ... Air supply panel, 8 ... Air filter, 9 ... Female slide rail, 10 ... Male slide rail, 11 ... Package Slit, 12 ... Flange portion, 13 ... Stopper, 20 ... CPU unit, 20a ...
RISC processor module, 20b ... OSC package, 20c ... BA package, 20d ... MS middle card, 20e ... CPU base board, 21 ... DC / DC
Converter, 22 ... I / O package, 23 ... SSU package, 24 ... PSU package, 25 ... Auxiliary power supply,
26 ... AC / DC converter unit, 27 ... Platter board, 28 ... CPU cooling fan unit, 29 ... D
C / DC cooling fan, 30 ... AC / DC cooling fan, 31 ... Exhaust cooling fan unit, 40 ... Cooling air,
41 ... Side plate, 42 ... Wind direction plate, 43 ... Partition plate, 45 ... Cabinet, 46 ... Cabinet side plate, 47 ... Air supply duct, 48 ... Cabinet frame, 50 ... Duct, 5
1 ... U-shaped handle, 52 ... Buffer material, 53 ... Connector, 54
… Bracket part, 55… Fan cover, 56… Mounting hole,
57 ... CPU cooling fan, 58 ... CPU fan mounting portion, 59 ... Hinge, 60 ... Back plate, 61 ... Exhaust cooling fan, 62 ... Exhaust fan cover, 63 ... Screw portion, 64
... nut, 65 ... opening, 66 ... Z-shaped handle, 67 ... battery unit, 68 ... hooking portion, 70 ... mounting screw, 71 ...
Hard disk, 72 ... Upper cross flow fan unit, 73 ... Lower cross flow fan unit, 74 ... D
AT, 75 ... Caster

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Matsushima 502 Jinritsucho, Tsuchiura-shi, Ibaraki Hiritsu Manufacturing Co., Ltd.Mechanical Research Laboratory (72) Inventor Kazuo Morita 810 Shimoimaizumi, Ebina-shi, Kanagawa Hitachi, Ltd. Office system division

Claims (11)

[Claims] 1. An electronic device apparatus comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, wherein cooling fans are arranged on the air supply side and the exhaust side, respectively. A high-performance air-cooled electronic device that supplies air from the side of the device and exhausts air to the back. 2. The electronic device apparatus according to claim 1, comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, and cooling fans are arranged on the air supply side and the exhaust side, respectively. The high heat generating substrate is arranged parallel to the air supply direction, the other substrates are arranged parallel to the exhaust direction, and the partition plate parallel to the air supply side substrate is provided with a rectangular hole. High-performance air-cooled electronic equipment. 3. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, wherein cooling fans are arranged on the air supply side and the air discharge side, respectively. A high-performance air-cooled electronic device device characterized in that the fan has a duct shape, and the duct shape provided on the air supply side fan blows air to two systems. 4. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, wherein cooling fans are arranged on the air supply side and the exhaust side, respectively. A high-performance air-cooled electronic device device, wherein a partition plate is provided on the air supply side to form a path of a power supply unit having a built-in cooling fan in an electronic device device that cools a high heat generating substrate with an air side fan. 5. The electronic device according to any one of claims 1 to 4, which comprises a substrate having a heating element such as an IC chip and an LSI package, a power source and the like, and which can be mounted in a cabinet, wherein a plurality of types of CPU units having different heat generating parts are provided. With a mountable structure,
Set the position of the fan for the CPU unit on the air supply side to the CPU
A high-performance air-cooled electronic device that is movable according to the unit. 6. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, wherein a handle is provided on the cover of the CPU unit according to claim 5. High-performance air-cooled electronic equipment. 7. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, and the handle of claim 6 is attached to a top cover of the electronic equipment device. A high-performance air-cooled electronic device having a structure in which it is pressed down via a cushioning material. 8. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source and the like, which can be mounted in a cabinet, and a cooling fan unit on the exhaust side between a cooling fan and a fan cover. A high-performance air-cooled electronic device device characterized in that an appropriate space is provided and a hinge for opening and closing the fan cover by 90 ° or more is provided. 9. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, has an expandable connector mounted on the front surface, and has an opening on the front panel. A high-performance air-cooled electronic device device, characterized in that a panel cover is provided, and a panel cover that is easily removable is provided in the opening. 10. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be mounted in a cabinet, and a top cover of the electronic equipment device is divided into two parts, front and rear, and the device. A high-performance air-cooled electronic device characterized in that a male mouth slide rail is provided on the side surface of the device and a female mouth slide rail is provided on the cabinet side, and when the device is pulled out from the cabinet, the device temporarily stops at the dividing point of the top cover. Equipment equipment. 11. An electronic equipment device comprising a substrate having a heating element such as an IC chip and an LSI package, a power source, etc., which can be installed in a cabinet, and a Z-shaped handle is provided on the upper surface of the mounted power source unit, and the handle is provided. A high-performance air-cooled electronic device device characterized by having a flat upper part and a larger area than the lower part.