Motor devices, construction machinery

Abstract

This motor device 1 comprises: a stator 6 provided with a plurality of coils 61 serving as electromagnets through energization; a rotor 4 which is provided with a plurality of permanent magnets 41 facing one-side surfaces of the plurality of coils 61 and is provided to be rotatable relative to the stator 6; a housing 2 which accommodates the stator 6 and the rotor 4 so as to seal the stator and the rotor, the housing being provided with end spaces 10, 11 positioned on both end sections of the rotor 4 along the rotation axis O, and a cavity 7 communicating with each of the end spaces 10, 11 on the other-side surfaces of the plurality of coils 61; and a fan 8 which causes a gas inside the housing 2 to flow through a cooling flow passage formed by a gap 5, which communicates with the one-side surfaces of the plurality of coils 61 and each of the end spaces 10, 11 between the plurality of permanent magnets 41, the end spaces 10, 11, and the cavity 7.

Description

[Technical Field]

[0001] The present invention relates to a driving technique using an electric motor. [Background technology]

[0002] Known construction machines (hereinafter also referred to as construction machines) used at construction sites include electric construction machines driven by electric motors (hereinafter also referred to as electric motors or motors) and hybrid construction machines that use hydraulic equipment and electric motors together (hereinafter also referred to collectively as electric construction machines). An actuator that directly drives each drive unit of an electric construction machine using mechanical elements such as ball screws driven by the rotational power of a motor is called an electro-mechanical actuator (EMA), while an actuator that indirectly drives each drive unit of an electric construction machine using hydraulic equipment such as hydraulic pumps driven by the rotational power of a motor is called an electro-hydraulic actuator (EHA). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2020-502990 Summary of the Invention [Problem to be solved by the invention]

[0004] Among the drive units of electric construction machinery, the undercarriage and bucket, which come into direct contact with the ground or the work object, may have soil and mud adhere to the motor housing. If a motor equipped with multiple cooling fins outside the housing, as disclosed in Patent Document 1, is used in such a drive unit, the cooling fins will become buried in soil and mud, making it impossible to properly cool the motor.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a motor device that can be appropriately cooled even in a poor environment. [Means for solving the problem]

[0006] In order to solve the above problem, a motor device of one embodiment of the present invention comprises: a stator having a coil that becomes an electromagnet when current is applied; a rotor having a permanent magnet facing one side of the coil and rotatably arranged relative to the stator; a housing that hermetically houses the stator and rotor, the housing having end spaces located at both ends of the rotor's rotation axis and a cavity on the other side of the coil that connects the end spaces; and a fan that circulates gas within the housing through a cooling flow path consisting of a gap connecting the end spaces between the one side and the permanent magnet, the end spaces, and the cavity.

[0007] According to this aspect, the cooling flow path formed by the gap between the stator and rotor, the end spaces, and the cavity is formed inside the sealed housing, so that the stator coil can be appropriately cooled even in a poor environment where soil and mud may adhere to the outside of the housing. Note that, although the following embodiment illustrates an electric construction machine to which the motor device of the present invention is applied, the application of the motor device of the present invention is not limited to electric construction machines.

[0008] Another aspect of the present invention is a construction machine. The construction machine includes a lower traveling body capable of traveling on the ground, an upper rotating body rotatably attached to the lower traveling body, a boom attached to the upper rotating body so as to be able to be raised and lowered, an arm flexibly attached to the boom, a bucket flexibly attached to the arm, and a motor device that drives at least one of the lower traveling body and the bucket. The motor device includes a stator including a coil that becomes an electromagnet when energized, a rotor including a permanent magnet facing one face of the coil and rotatably attached to the stator, a housing that hermetically houses the stator and the rotor, the housing having end spaces located at both ends of the rotor's rotation shaft and a cavity on the other face of the coil that communicates with the end spaces, and a fan that circulates gas within the housing through a cooling flow path formed by the end spaces and the cavity, a gap that communicates the end spaces between the one face and the permanent magnet.

[0009] Any combination of the above components, and any transformation of the present invention into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present invention. [Effects of the Invention]

[0010] According to the present invention, the motor device can be appropriately cooled even in a poor environment. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic configuration diagram of an electric construction machine. [Figure 2] FIG. [Figure 3] FIG. 2 is a cross-sectional view including a rotation shaft of the motor device. [Figure 4] FIG. 4 is a cross-sectional view of the motor device taken along the line AA in FIG. 3. [Figure 5] 1 shows multiple permanent magnets arranged according to a Halbach array. [Figure 6] 10 shows a modified example of the motor device. DETAILED DESCRIPTION OF THE INVENTION

[0012] The motor device or drive device of the present invention can be applied to any device or machine that has a drive unit or movable unit that is rotationally driven by a motor. Therefore, the device or equipment to which the present invention is applied is not particularly limited. In this embodiment, an example of an electric construction machine that has multiple drive units driven by actuators that include a motor and a reducer is described. In this embodiment, an EMA that directly drives each drive unit of the electric construction machine using mechanical elements driven by the rotational power of a motor is used as an example of an actuator. However, the present invention can also be applied to an EHA that indirectly drives each drive unit of the electric construction machine using hydraulic equipment driven by the rotational power of a motor.

[0013] Fig. 1 is a schematic configuration diagram of the electric construction machine 100. Fig. 2 is a top view of the electric construction machine 100. In the following description, the directions of front, back, up, down, left, right, etc. are the same as the directions of the electric construction machine 100. That is, in the following description, the front in the traveling direction of the electric construction machine 100 will be simply referred to as the front, the rear in the traveling direction of the electric construction machine 100 will be simply referred to as the rear, the upper side in the direction of gravity will be simply referred to as the upper side, the lower side in the direction of gravity will be simply referred to as the lower side, the right side in the vehicle width direction when facing forward will be simply referred to as the right side, and the left side in the vehicle width direction will be simply referred to as the left side.

[0014] In an electric construction machine 100, which is a construction machine, an upper rotating body 102 is rotatably attached to a lower traveling body 101 that can travel forward and backward on the ground. A cab 103 is provided on the front left side of the upper rotating body 102, and a boom 104 is attached to the front center portion so that it can be raised and lowered. An arm 105 is attached to the tip of the boom 104 so that it can be bent up and down. A bucket 106 is attached to the tip of the arm 105 so that it can be bent up and down.

[0015] A gyro sensor 110 is attached to the front left side of the cab 103. In other words, the gyro sensor 110 is attached to the upper rotating body 102 at a position that is farthest from the center of rotation C1. The gyro sensor 110 is attached to the cab 103 (lower running The sensor is capable of detecting the tilt angle, tilt direction, rotation position, and rotation angular velocity of the rotating body 101 and the upper rotating body 102. The tilt direction refers to the uphill or downhill direction of the tilt.

[0016] Hereinafter, the lower traveling body 101, the upper rotating body 102, the boom 104, the arm 105, and the bucket 106 will be collectively referred to as the drive unit of the electric construction machine 100. Therefore, the electric construction machine 100 in FIGS. 1 and 2 is a construction machine having five drive units. The lower traveling body 101 constitutes a traveling unit capable of traveling on the ground, the upper rotating body 102 constitutes a rotating unit capable of rotating relative to the traveling unit, and the boom 104, the arm 105, and the bucket 106 constitute a working unit attached to the rotating unit to perform work. Each actuator, which serves as a drive device for driving each drive unit of the electric construction machine 100, includes an inverter that converts DC power from a DC power source such as a battery into AC power, a motor device that generates rotational power based on the AC power supplied from the inverter, and a reducer that decelerates the rotation of the motor device to obtain torque according to a reduction ratio. The detailed configuration of the motor device will be described below.

[0017] 3 is a cross-sectional view of the motor device 1 including the rotation axis O, and FIG. 4 is a cross-sectional view of the motor device 1 taken along the line AA in FIG. 3, which is perpendicular to the rotation axis O. The motor device 1 includes a housing 2 that hermetically houses the following components of the motor device 1; a shaft member 3 that is rotatable about a rotation axis O and outputs rotational power from its tip (left end in FIG. 3 ) protruding outside the housing 2; a rotor 4 that is fixed to the shaft member 3 and can rotate in conjunction with the shaft member 3; a stator 6 that is fixed to the housing 2 and faces the rotor 4 across a gap 5 as a radial gap (up and down in FIG. 3 ); a cavity 7 that is located on the back side of the stator 6, i.e., on the side opposite the surface of the stator 6 that faces the rotor 4 and gap 5, and through which a cooling gas can flow; a fan 8 that is connected or fixed to the base end (right end in FIG. 3 ) of the shaft member 3 by a connector 83 and generates a circulating flow of cooling gas in the gap 5 and cavity 7; and a heat dissipation unit 9 that is fixed to both end surfaces of the housing 2 in the axial direction (left and right in FIG. 3 ) and has an uneven surface that absorbs heat stored in the cooling gas and dissipates it outside the housing 2. Arrows in FIG. 3 schematically represent the flow of air as cooling gas.

[0018] The rotor 4 includes a plurality of permanent magnets 41 periodically arranged in the circumferential direction or rotational direction around the rotation axis O, and support members 42 that interconnect the plurality of permanent magnets 41. The plurality of permanent magnets 41 are disposed facing the gap 5 between the rotor 4 and the stator 6, and are connected by the support members 42 on the opposite side. The support members 42 are formed of a soft magnetic material with high magnetic permeability, such as iron, carbon steel, silicon steel, permalloy, sendust, permendur, soft ferrite, amorphous magnetic alloy, or nanocrystalline magnetic alloy. Note that the support members 42 containing iron are also called yokes. Note that the support members 42 may also be formed of a non-magnetic material.

[0019] The multiple permanent magnets 41 are arranged so that their magnetic poles appear periodically along the circumferential direction on the surface facing the stator 6. For example, the multiple permanent magnets 41 may be arranged so that north and south poles appear alternately along the circumferential direction on the surface facing the stator 6, or the multiple permanent magnets 41 may be arranged in a Halbach array as shown in FIG. 5. The Halbach array is an array in which the magnetic pole directions of adjacent permanent magnets 41 along the circumferential direction are rotated by N equal parts of 2π (N is an integer greater than or equal to 3 or less than -3). In the illustrated example, N=4, and the magnetic pole directions of adjacent permanent magnets 41 along the circumferential direction are rotated by π / 2, or 90 degrees. Such a Halbach array can increase the magnetic field or magnetic field strength of the multiple permanent magnets 41 on the surface facing the stator 6, thereby enabling higher efficiency and higher torque of the motor device 1.

[0020] The stator 6 includes a plurality of coils 61 arranged circumferentially and configured to become electromagnets when energized, and a yoke 62 interconnecting the coils 61. As shown in FIG. 5, the coils 61 are arranged at equal intervals along the rotational or circumferential direction of the motor device 1, with one surface or end surface (the inner end surface in FIG. 5 or the lower end surface in FIG. 3) of each coil facing the plurality of permanent magnets 41 of the rotor 4 across a gap 5. When a current of controlled magnitude and direction is passed through each coil 61 while the motor device 1 is rotating, a periodic magnetic pole pattern of N and S poles rotating circumferentially or a rotating magnetic field is generated on the surface facing the rotor 4, causing the rotor 4, equipped with the plurality of permanent magnets 41, to rotate relative to the stator 6. The yoke 62 is made of a soft magnetic material containing iron.

[0021] Here, it is known that by arranging the multiple permanent magnets 41 in the rotor 4 in a Halbach array as shown in FIG. 5, the (radial) magnetic field appearing on the surface facing the stator 6 varies sinusoidally along the circumferential direction, allowing the stator 6 to have a coreless structure. A coreless stator 6 does not have a core or iron core around which the coils 61 are wound, and therefore the coils 61 are not confined by slots formed between the cores. Therefore, as shown schematically in FIG. 5, there are many gaps inside and between the coils 61 through which air can flow as cooling gas, allowing each coil 61 to be efficiently cooled. Furthermore, by using a coreless structure for the stator 6, the radial thickness of the coils 61 can be reduced, thereby increasing the gap 5 between the rotor 4. This increases the amount of cooling gas flowing through the gap 5, further improving cooling efficiency.

[0022] The cavity 7 provided in the housing 2 is provided on the other side or end face (upper face in FIG. 3 ) of the coil 61, facing the yoke 62, and allows the cooling gas to flow through the gap 5 between one end face (lower face in FIG. 3 ) of the coil 61 and the permanent magnet 41. As shown in FIG. 3 , the gap 5 and the cavity 7 are provided parallel to each other along the rotation axis O of the rotor 4, and the flow directions of the cooling gas flowing through each of them along the rotation axis O are opposite to each other. That is, in the gap 5, the cooling gas flows leftward from the base end side (right side in FIG. 3 ) to the tip end side (left side in FIG. 3 ) of the shaft member 3, and in the cavity 7, the cooling gas flows rightward from the tip end side to the base end side of the shaft member 3. A tip end space 10 is provided on the tip end side of the shaft member 3 as an end space communicating between the gap 5 and the cavity 7. The direction of the cooling gas flowing leftward from the gap 5 is redirected by the inner wall of the housing 2 and a tip end heat dissipation section 92 (described later), causing the cooling gas to flow rightward into the cavity 7. Further, a base end space 11 is provided on the base end side of the shaft member 3 as an end space that communicates with the gap 5 and the cavity 7. In the base end space 11, a fan 8 that circulates or circulates the cooling gas inside the housing 2 together with a base end heat dissipation section 91 (described later) is provided, and the fan 8 changes the direction of the cooling gas that flows out to the right from the cavity 7 and causes the cooling gas to flow to the left into the gap 5.

[0023] In this way, a cooling flow path through which air as cooling gas circulates is formed around the coil 61, which generates heat when current is applied during rotational driving of the motor device 1, by the gap 5 on one end face of the coil 61, the cavity 7 on the other end face, and the distal end space 10 and proximal end space 11 that communicate with the gap 5 and cavity 7. This allows the coil 61 to be efficiently cooled. Note that the flow direction of the cooling gas flowing through the gap 5 and cavity 7 along the rotation axis O may be opposite to that shown in FIG. 3. That is, in the cavity 7, the cooling gas may flow leftward from the proximal end side (right side in FIG. 3) to the distal end side (left side in FIG. 3) of the shaft member 3, and in the gap 5, the cooling gas may flow rightward from the distal end side to the proximal end side. This circulation direction of the cooling gas can be adjusted by the fan 8 and / or the heat dissipation unit 9, which will be described later.

[0024] 3, the cavity 7 is formed in a straight line parallel to the rotation axis O and the gap 5, but the cavity 7 can be formed in any direction as long as it connects the spaces on the tip and base ends of the shaft member 3 and allows the cooling gas to circulate. For example, the cavity 7 may be formed in a curved or spiral shape that connects the spaces on the tip and base ends of the shaft member 3 while meandering. Such a cavity 7 increases the distance the cooling gas flows while being in thermal contact with the stator 6, thereby improving cooling efficiency.

[0025] As shown in FIG. 4, multiple cavities 7 are provided around the end face (the other end face) of the stator 6 on the yoke 62 side. Providing multiple thin tubular cavities 7 in this manner increases the area of ​​thermal contact between the cooling gas flowing through the cavities 7 and the stator 6, thereby improving cooling efficiency. As shown as a modified example in FIG. 6, multiple cavities 71, 72 may be provided at multiple positions at different distances from the rotation axis O to increase the thermal contact area between the cooling gas and the stator 6. As shown in the figure, the cross-sectional area of ​​the cavity (72) increases with increasing distance from the rotation axis O, thereby reducing thermal resistance. The outer cavities 72 are indicated by dotted lines in FIG. 4. The inner cavities 71 closer to the rotation axis O and the outer cavities 72 farther from the rotation axis O form a grid-like or mesh-like cooling channel network on the outside of the stator 6.

[0026] The fan 8 rotates in conjunction with the shaft member 3 and the rotor 4 at the base end side of the rotation axis O (the right end side in FIG. 3 ), generating a flow of cooling gas in the gap 5 and the cavity 7. The fan 8 includes a first fan 81 that faces one end of the gap 5 (the right end in FIG. 3 ) and generates a flow of cooling gas in the gap 5, and a second fan 82 that faces one end of the cavity 7 (the right end in FIG. 3 ) and generates a flow of cooling gas in the cavity 7. The first fan 81 and the second fan 82 blow out cooling gas in opposite directions along the rotation axis O. In the example of FIG. 3 , the first fan 81 blows out cooling gas to the left, approaching the gap 5, and the second fan 82 blows out cooling gas to the right, away from the cavity 7. In other words, the first fan 81 blows cooling gas into the gap 5, and the second fan 82 sucks out cooling gas from the cavity 7. The direction in which the cooling gas is blown out from each of the fans 81 and 82 is determined by the installation direction or inclination direction of the blades. As shown schematically by the diagonal lines in each of the fans 81 and 82 in Figure 3, the installation direction or inclination direction of the blades of the first fan 81 and the second fan 82 are opposite to each other.

[0027] The heat dissipation unit 9 includes a base-side heat dissipation unit 91 fixed to the end face (right end face in FIG. 3) or inner wall of the housing 2 on the base end side of the rotating shaft O, and a tip-side heat dissipation unit 92 fixed to the end face (left end face in FIG. 3) or inner wall of the housing 2 on the tip end side of the rotating shaft O. Each heat dissipation unit 91, 92 is formed from a material with low thermal resistance such as aluminum, and efficiently absorbs heat stored in the cooling gas using an uneven surface shape such as fins, and releases the heat from the rear surface to the outside of the housing 2. Air is blown onto the base-side heat dissipation unit 91 as cooling gas from the second fan 82, so heat is efficiently dissipated in the same manner as a heat sink and fan commonly used in personal computers, etc. In addition, it is preferable to change the direction in which the unevenness is formed on the surface shape of each heat dissipation section 91, 92 so that air naturally flows in the direction of circulation shown in Figure 3, i.e., from top (outside) to bottom (inside) in the base end heat dissipation section 91, and from bottom (inside) to top (outside) in the tip end heat dissipation section 92.

[0028] When the motor device 1 configured as described above is driven to rotate, the rotor 4, shaft member 3, and fan 8 rotate integrally relative to the stator 6 and housing 2 due to the rotating magnetic field generated by the multiple coils 61 of the energized stator 6. The rotation of the fan 8 forms a circulating cooling flow path for cooling gas passing through the gap 5 and cavity 7 as shown by the arrows in Figure 3, thereby efficiently cooling the coil 61 that has generated heat due to the energization. In addition, the heat stored in the cooling gas is efficiently released to the outside of the housing 2 by a heat dissipation unit 9 provided on the circulating cooling flow path for cooling gas.

[0029] According to this embodiment, a cooling flow path constituted by the gap 5 between the stator 6 and rotor 4, the cavity 7, the tip end space 10, and the base end space 11 is formed inside the sealed housing 2, so that the coil 61 of the stator 6 can be appropriately cooled even in a poor environment where earth and sand may adhere to the outside of the housing 2. In an electric construction machine 100 such as that shown in Figures 1 and 2, it is preferable to apply the motor device 1 of this embodiment to the undercarriage 101 and the bucket 106, which are likely to be subject to the adhesion of earth and sand.

[0030] The present invention has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention.

[0031] In the embodiment, an example of an EMA in which the motor device 1 directly drives each drive unit of the electric construction machine 100 has been described, but each drive unit of the electric construction machine 100 may be indirectly driven by the motor device 1. For example, if each drive unit is directly driven by hydraulic equipment such as a hydraulic motor or hydraulic cylinder, the actuator may be configured as an EHA by using the motor device 1 to control a hydraulic valve that controls the hydraulic pressure to each hydraulic equipment.

[0032] Although air has been exemplified as the cooling gas in the embodiment, other gases may be used as the cooling gas.

[0033] 3, in the embodiment, the rotor 4 is provided on the inside (bottom) and the stator 6 is provided on the outside, but the rotor 4 may be provided on the outside and the stator 6 on the inside. In this case, the cavity 7 is formed further inside than the stator 6.

[0034] The functional configuration of each device described in the embodiments can be realized by hardware resources, software resources, or a combination of hardware and software resources. Examples of hardware resources include processors, ROMs, RAMs, and other LSIs. Examples of software resources include operating systems, applications, and other programs.

[0035] Among the embodiments disclosed in this specification, those in which multiple functions are provided in a distributed manner may have some or all of the multiple functions integrated together, and conversely, those in which multiple functions are provided in a distributed manner may have some or all of the multiple functions integrated together. Regardless of whether the functions are integrated or distributed, it is sufficient that the configuration can achieve the object of the invention. [Industrial Applicability]

[0036] The present invention relates to a driving technique using an electric motor. [Explanation of symbols]

[0037] 1 motor device, 2 housing, 3 shaft member, 4 rotor, 5 gap, 6 stator, 7 cavity, 8 fan, 9 heat dissipation section, 10 tip space, 11 base end space, 41 permanent magnet, 61 coil, 62 yoke, 81 first fan, 82 second fan, 83 connecting section, 100 electric construction machine, 101 lower running body, 102 upper rotating body, 104 boom, 105 arm, 106 bucket.

Claims

1. a stator having a coil that becomes an electromagnet when energized; a rotor provided rotatably with respect to the stator and including a permanent magnet facing one surface of the coil; a housing that hermetically houses the stator and the rotor, the housing having end spaces located at both ends of the rotation shaft of the rotor and a cavity that communicates with the end spaces on the other surface side of the coil; a shaft member that is rotatable around the rotation axis and outputs rotational power from a tip end thereof; a fan that circulates gas within the housing through a cooling flow path that is formed by gaps that communicate the end spaces between the one surface and the permanent magnet, the end spaces, and the cavity; a heat dissipation unit fixed to both end surfaces of the rotary shaft in the housing in the axial direction, which absorbs heat stored in the gas and dissipates it to the outside of the housing; Equipped with the heat dissipation portion includes a tip-side heat dissipation portion fixed to an end surface or an inner wall of the housing on the tip side of the shaft member, The gas from the fan is blown onto the tip-end heat dissipation portion, a plurality of the cavities are provided at a plurality of positions having different distances from the rotation axis; The cavity is formed linearly, A motor device, wherein the cross-sectional areas of the multiple cavities taken along a cross section perpendicular to the rotation axis increase as they become farther from the rotation axis.

2. the gap and the cavity are provided along the rotation axis, The motor device according to claim 1 , wherein the gas flows through the gap and the cavity in opposite directions along the rotation axis.

3. The motor device according to claim 1 , further comprising a coupling portion that couples the fan to a rotation shaft of the rotor.

4. The motor device according to claim 1 , wherein the fan is provided in at least one of the end spaces.

5. the fans include a first fan facing one end of the gap in the direction of the rotation axis to generate the gas flow in the gap, and a second fan facing one end of the cavity in the direction of the rotation axis to generate the gas flow in the cavity, The first fan and the second fan blow out the gas in opposite directions along the rotation axis. The motor device according to claim 1 .

6. The motor device according to claim 1 , wherein a plurality of the cavities are provided surrounding the other surface of the stator.

7. 7. The motor device according to claim 1, wherein the stator has a coreless structure in which no core is provided around which the coil is wound.

8. The motor device according to claim 7, wherein the rotor has a Halbach array in which the directions of the magnetic poles of the permanent magnets adjacent to each other along the rotation direction are rotated by N equal parts of 2π (N is an integer greater than or equal to 3 or less than or equal to −3).

9. a lower running body capable of running on the ground; an upper rotating body rotatably attached to the lower traveling body; a boom attached to the upper rotating body so as to be able to be raised and lowered; an arm bendably attached to the boom; a bucket bendably attached to the arm; a motor device that drives at least one of the lower traveling body and the bucket; Equipped with The motor device a stator having a coil that becomes an electromagnet when energized; a rotor provided rotatably with respect to the stator and including a permanent magnet facing one surface of the coil; a housing that hermetically houses the stator and the rotor, the housing having end spaces located at both ends of the rotation shaft of the rotor and a cavity that communicates with the end spaces on the other surface side of the coil; a shaft member that is rotatable around the rotation axis and outputs rotational power from a tip end thereof; a fan that circulates gas within the housing through a cooling flow path that is formed by gaps that communicate the end spaces between the one surface and the permanent magnet, the end spaces, and the cavity; a heat dissipation unit fixed to both end surfaces of the rotary shaft in the housing in the axial direction, which absorbs heat stored in the gas and dissipates it to the outside of the housing; Equipped with the heat dissipation portion includes a tip-side heat dissipation portion fixed to an end surface or an inner wall of the housing on the tip side of the shaft member, The gas from the fan is blown onto the tip-end heat dissipation portion, a plurality of the cavities are provided at a plurality of positions having different distances from the rotation axis; The cavity is formed linearly, A construction machine, wherein the cross-sectional areas of the multiple cavities perpendicular to the rotation axis increase as they become farther from the rotation axis.

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