Work equipment

Abstract

To inhibit an oil of a gear case from leaking from a respiratory pore of a breather device to the outside.SOLUTION: A breather device 14 of a gear case 82 defining a gear chamber 83 includes: a breather chamber 146 defined in the gear case 82; a respiratory pore 152 which allows an upper part of the breather chamber 146 to communicate with the outside; a front communication hole 148 and a rear communication hole 150 which allow a lower part of the breather chamber 146 and the gear chamber 83 to communicate with each other; and a partition wall 154 extending in a direction such that the partition wall 154 traverses an area between the respiratory pore 152 and the front and rear communication holes 148 and 150.SELECTED DRAWING: Figure 6

Description

Technical Field

[0008] To solve the above problems, one aspect of the present invention provides a breather device (140) for a gear case (82) defining a gear chamber (83), comprising: a breather chamber (146) defined in the gear case; a breathing hole (152) connecting the upper part of the breather chamber to the outside; communication holes (148, 150) connecting the lower part of the breather chamber to the gear chamber; and a partition wall (154) extending in a direction transverse between the breathing hole and the communication hole.

[0009] According to this embodiment, leakage of oil from the gear case to the outside through the breathing holes is suppressed.

[0010] In the above embodiment, preferably, the breather chamber extends in the front-rear direction, and the partition wall includes a first portion (154A) that extends vertically at a position rearward of the breathing hole and a second portion (154B) that extends forward from the lower end of the first portion, with a gap (156) between the front end of the second portion and the front wall of the breather chamber that connects the breathing hole and the communication hole.

[0011] In this configuration, when the vehicle is tilted backward, the partition wall effectively prevents oil from moving towards the breathing holes.

[0012] In the above embodiment, the communication hole may be provided in the front part of the breather chamber.

[0013] According to this embodiment, the oil that has entered the breather chamber is returned to the gear chamber effectively when the vehicle is tilted forward.

[0014] In the above embodiment, the communication holes may be provided at the front and rear of the breather chamber.

[0015] According to this aspect, the return of the oil that has entered the breather chamber to the gear chamber is well performed both during forward tilt and backward tilt.

[0016] In the above aspect, the communication hole may have a larger opening area at the rear than at the front.

[0017] According to this aspect, the oil return during backward tilt is well performed.

[0018] In the above aspect, the breather chamber may be defined above the gear case, and the breathing hole may be formed near the upper wall (146A) that defines the breather chamber.

[0019] According to this aspect, the leakage of the oil in the gear case from the breathing hole to the outside is surely suppressed.

[0020] In the above aspect, a working machine (10) having a breather device (140) for the gear case (82) of the above aspect, the working machine includes a traveling frame (12) provided with a traveling part (32) and a main body frame (14) that is displaceable relative to the traveling frame and has a work part (56) whose height can be adjusted, and the breather device (140) of the gear case is provided on the main body frame.

[0021] According to this aspect, even when the main body frame is displaced relative to the traveling frame by adjusting the height of the work part, the leakage of the oil in the gear case provided on the main body frame from the breathing hole of the breather device to the outside is suppressed.

Advantages of the Invention

[0022] According to the above aspects, the leakage of the oil in the gear case from the breathing hole of the breather device to the outside is suppressed.

Brief Description of the Drawings

[0023] [Figure 1] Side view of a snow remover to which the breather device of the gear case according to the present invention is applied [Figure 2] Perspective view showing the traveling device and the rotating device of the snow removal machine [Figure 3] Cross-sectional view showing the main part of the motor case breather device according to the present embodiment [Figure 4] Partial cross-sectional perspective view of the connection part between the motor case and the gear case according to the present embodiment [Figure 5] Perspective view of the gear case according to the present embodiment [Figure 6] Perspective view showing an enlarged breather device of the gear case according to the present embodiment [Figure 7] Explanatory view showing the inclination of the gear case and the liquid level of the oil in the snow removal machine according to the present embodiment

Mode for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the present invention is applied to the snow removal machine 10. Hereinafter, terms indicating directions such as front and rear, left and right, up and down, etc. are used based on the direction seen from an operator who operates the snow removal machine 10.

[0025] First, the overall configuration of the snow removal machine 10 will be described while referring to FIGS. 1 and 2. The snow removal machine 10 is a walk-behind type snow removal machine in which an operator walks and performs snow removal work at the rear thereof.

[0026] The snow removal machine 10 has a lower body 12 and an upper body 14 that is rotatably attached to a front shaft (not shown) provided on the lower body 12. A traveling device 16 and a handle device 18 are attached to the lower body 12. A auger device 20 for snow removal and a blower device 22 are attached to the upper body 14.

[0027] The running gear 16 includes a front axle 24 and a rear axle 26 rotatably mounted on the lower body 12 so as to extend horizontally in the left-right direction, drive wheels 28 attached to both the left and right ends of the front axle 24, driven wheels 30 attached to both the left and right ends of the rear axle 26, left and right crawlers (endless running belts) 32 stretched between the left and right drive wheels 28 and driven wheels 30, and a running drive unit 34 attached to the lower body 12, which includes an electric motor that rotates the drive wheels 28 via the front axle 24. Figure 2 shows the left crawler 32 detached from the drive wheel 28 and driven wheel 30.

[0028] The handle device 18 has left and right arms 36 extending upward and rearward from the rear of the lower body 12, and left and right grips 38 and an input device 40 attached to the upper ends of the arms 36. The grips 38 are grasped by the operator.

[0029] The input device 40 is a device that accepts input operations from an operator and includes, for example, a travel lever 42 that accepts the travel operation of the snowblower 10, a snow removal switch 44 that accepts the operation of snow removal work by the auger device 20 and the blower device 22, a height adjustment switch 46 that accepts the rotation operation (height adjustment operation) of the upper body 14 described later, and a clutch lever 48 that accepts the operation of the deadman clutch 72 described later.

[0030] The auger device 20 includes an auger housing 50 attached to the upper body 14 via a blower housing 58 described later, a screw gear case 52 attached to the auger housing 50, an auger rotation shaft 54 ​​extending horizontally from the screw gear case 52 into the auger housing 50 in the left-right direction, and auger claws 56 attached to the auger rotation shaft 54.

[0031] The blower device 22 includes a blower housing 58 attached to the upper body 14, a blower 60 rotatably mounted inside the blower housing 58, and a chute 62 attached to the top of the blower housing 58.

[0032] Snow removal is performed by the rotation of the auger claws 56 as the snowblower 10 moves, which pulverizes the snow in front of the snowblower 10 and collects it in the auger housing 50. The snow collected in the auger housing 50 is guided into the blower housing 58 by the rotation of the blower 60 and discharged outwards from the chute 62.

[0033] A rotating shaft 64 is provided within the auger housing 50 and the blower housing 58, extending horizontally from the screw gear case 52 toward the rear. The rotating shaft 64 rotates the auger jaws 56 via the screw gears (not shown) in the screw gear case 52 and the auger rotating shaft 54. The rotating shaft 64 supports the blower 60 and rotates the blower 60.

[0034] The rear end of the rotating shaft 64 extends into the upper body 14. A large-diameter driven pulley 66 is attached to the rear end of this rotating shaft 64. An internal combustion engine 68 is mounted on the upper part of the upper body 14. A small-diameter drive pulley 74 is attached to the output shaft 70 of the internal combustion engine 68 via a deadman clutch 72. An endless belt 76 is stretched between the drive pulley 74 and the driven pulley 66.

[0035] As a result, the rotation of the output shaft 70 of the internal combustion engine 68 is transmitted to the rotating shaft 64 via the deadman clutch 72, drive pulley 74, endless belt 76, and driven pulley 66, and the auger claws 56 and blower 60 are driven synchronously.

[0036] Next, the rotational operation of the upper body 14 relative to the lower body 12, in other words, the operation of the auger claw 56's ground height, will be explained. The ground height of the auger claw 56 is adjusted by the rotation device 80, which causes the upper body 14 to rotate relative to the lower body 12 around the central axis of the front shaft 24.

[0037] The rotating device 80 includes a gear case 82 fixed to the upper body 14 and an electric motor 84 fixed to the rear of the gear case 82 by a flange connection.

[0038] The gear case 82 defines the gear chamber 83 (see Figure 3). The gear case 82 rotatably supports a worm 88, which extends approximately in the front-to-back direction and is connected to the output shaft 86 of the electric motor 84, within the gear chamber 83. The gear case 82 rotatably supports an intermediate shaft 90 and an output shaft 92, which extend horizontally in the left-to-right direction within the gear chamber 83. A wheel gear 94 and a pinion (not shown), which mesh with the worm 88, are fixed to the intermediate shaft 90. A sector gear 96, which meshes with the pinion (not shown), is fixed to the output shaft 92. This gear train 97 reduces the rotation of the output shaft 86 of the electric motor 84 and transmits it to the output shaft 92 of the gear case 82.

[0039] The gear chamber 83 is filled with oil for lubrication of the gear train 97. The amount of oil filled in the gear chamber 83 is set so that the oil level X is kept above the meshing portion between the worm 88 and the wheel gear 94, which are located higher up in the gear train 97, in all three positions: the horizontal position shown in (A) of Figure 7, the maximum forward tilt shown in (B) of Figure 7, and the maximum backward tilt shown in (C) of Figure 7.

[0040] The output shaft 92 includes an end that extends outside the gear case 82. One end of a link (arm) 98 is fixed to this end of the output shaft 92. The other end of the link 98 is pivotally connected to one end of another link 100 by a pivot 101. A bracket 104 is fixed to the rear of the lower body 12. The other end of the link 100 is pivotally connected to the bracket 104 by a pivot 105.

[0041] In other words, the output shaft 92 of the gear case 82 on the upper body 14 is connected to the lower body 12 by a linkage mechanism consisting of links 98 and 100.

[0042] The rotation of the output shaft 92 by the electric motor 84 changes the bending angle of the links 98 and 100, causing the upper body 14 to tilt approximately vertically relative to the lower body 12 with the front shaft 24 as the pivot point, thereby adjusting the ground clearance of the auger claws 56.

[0043] The motor case 102, which houses the rotor (not shown) of the electric motor 84, is connected to the rear of the gear case 82.

[0044] Next, the breather device 132 of the motor case 102 will be described with reference to Figures 3 to 5. Note that the output shaft 86 of the electric motor 84 is tilted forward when the snowblower 10 is in a horizontal position (see Figures 2 and 7(A)), as shown in Figure 2, but including this, the output shaft 86 extends in a substantially horizontal direction.

[0045] The motor case 102 has a cylindrical main section 102A and a flange section 102B formed at the front end of the main section 102A. The main section 102A defines an internal chamber 103 (see Figure 3) for housing a stator and rotor (not shown), etc. Three bolt holes 102C are formed in the flange section 102B. The gear case 82 has a box-shaped main section 82A for housing the aforementioned gear train 97, an end wall 82B provided at the rear of the main section 82A, a cylindrical section 82C extending rearward from the end wall 82B, and a flange section 82D formed at the rear end of the cylindrical section 82C. Three screw holes 82E are formed in the flange section 82D.

[0046] A bolt 107 (see Figure 4) is inserted into each bolt hole 102C via a collar member (not shown). Each bolt 107 is screw-engaged into the corresponding screw hole 82E. This connects the motor case 102 to the rear of the gear case 82.

[0047] The motor case 102 has a circular end wall 102D at its front. A motor shaft through hole 102E is formed in the center of the end wall 102D through which the output shaft 86 of the electric motor 84 passes. As shown in Figure 4, the end wall 102D protrudes toward the gear case 82 side from the flange portion 102B, and its outer circumference is complementaryly fitted into a corresponding recess 82F defined in the cylindrical portion 82C of the gear case 82.

[0048] As shown in Figure 3, a through-hole 82G is formed in the end wall 82B of the gear case 82, through which the rear shaft 88A of the worm 88 passes. The gear case 82 rotatably supports the rear shaft 88A of the worm 88 in the through-hole 82G by a rolling bearing 106. An O-ring 110 and an oil seal 112, held by an annular holder 108, are provided between the inner circumferential surface of the through-hole 82G and the outer circumferential surface of the rear shaft 88A.

[0049] The gear chamber 83 is filled with oil for lubrication of the gear train 97. The amount of oil filled in the gear chamber 83 is set so that the oil level X is kept above the meshing portion between the worm 88 and the wheel gear 94, which are located higher up in the gear train 97, in all three positions: the horizontal position shown in (A) of Figure 7, the maximum forward tilt shown in (B) of Figure 7, and the maximum backward tilt shown in (C) of Figure 7.

[0050] The rear shaft 88A is the input shaft of the gear train 97 and is coaxially positioned with the output shaft 86 of the electric motor 84. The output shaft 86 has a double chamfered portion 86A at its front end that protrudes forward beyond the end wall 102D. The double chamfered portion 86A is rectangular in shape and engages with an engagement groove 88B formed at the rear end of the rear shaft 88A. This engagement connects the output shaft 86 of the electric motor 84 and the rear shaft 88A, which forms the input shaft of the gear train 97, in a power transmission relationship, and the rotation of the output shaft 86 of the electric motor 84 is transmitted to the gear train 97.

[0051] The outer circumference of the end wall 102D of the motor case 102 is complementaryly fitted into the corresponding recess 82F of the cylindrical portion 82C of the gear case 82, which allows for easy and reliable coaxiality (concentricity) between the output shaft 86 of the electric motor 84 and the rear shaft 88A of the gear train 97.

[0052] The front end surface 102F of the end wall 102D of the motor case 102 and the rear end surface 82H of the end wall 82B of the gear case 82 face each other with an axial gap between them. Between these opposing front end surfaces 102F and rear end surface 82H, a breather chamber 120 is defined, which is a cylindrical space enclosed on its outer circumference by the cylindrical portion 82C of the gear case 82.

[0053] A motor communication hole (air breathing hole) 122 is formed through the end wall 102D of the motor case 102, connecting the breather chamber 120 and the internal chamber 103 of the motor case 102. The motor communication hole 122 is located diagonally above the motor shaft through-hole 102E through which the output shaft 86 passes.

[0054] The end wall 82B and flange portion 82D of the gear case 82 and the end wall 102D and flange portion 102B of the motor case 102 cooperate with each other to define an external communication hole 124. The external communication hole 124 opens the breather chamber 120 to the outside.

[0055] A partition portion 128 is formed on the end wall 82B of the gear case 82, projecting from the end wall 82B toward the end wall 102D of the motor case 102. The partition portion 128 extends in a direction that crosses between the motor shaft through hole 102E and the external communication hole 124, with a gap 130 (see Figure 3) forming a constricted portion between it and the end wall 102D.

[0056] The gear case 82 is provided with a breather device 140, as shown in Figures 5 and 6. The breather device 140 includes a breather chamber 146 defined in the upper part of the main section 82A of the gear case 82. The breather chamber 146 includes an upper wall 146A, a lower wall 146B, a front wall 146C, a rear wall 146D, and a side wall 146E, with an opening 146F on the side opposite to the side wall 146E. The breather chamber 146 has a length in the front-to-back direction that is greater than its length in the vertical direction, and extends substantially horizontally in the front-to-back direction. The opening 146F is closed by a cover plate 142 attached to the main section 82A by bolts 144.

[0057] A breathing hole 152 is formed in the side wall 146E, which connects the upper part of the breather chamber 146 to the outside. The breathing hole 152 is located close to the rear wall 146D in the front-to-back direction and near the upper wall 146A in the up-to-down direction, so that it is located above the liquid level X when the gear case 82 is in the horizontal position shown in Figure 7(A) and in the maximum forward-tilting position shown in Figure 7(B). When the gear case 82 is in the maximum backward-tilting position shown in Figure 7(C), the liquid level X is located above the breathing hole 152, but the ingress of oil into the breathing hole 152 is prevented by the partition wall 154.

[0058] A front communication hole 148 is formed at the front of the lower wall 146B. A rear communication hole 150 is formed at the rear of the lower wall 146B. The front communication hole 148 and the rear communication hole 150 penetrate the lower wall 146B and connect the lower part of the breather chamber 146 to the gear chamber 83 (see Figure 7). The opening area of ​​the rear communication hole 150 is larger than the opening area of ​​the front communication hole 148.

[0059] The main section 82A is formed with a breathing hole 152 that connects the upper part of the breather chamber 146 to the outside, a front communication hole 148 and a rear communication hole 150 that connect the lower part of the breather chamber 146 to the gear chamber 83 (see Figure 3), and a partition wall 154 that extends in a direction transverse between the breathing hole 152 and the front communication hole 148 and the rear communication hole 150.

[0060] A partition wall 154 is formed in the side wall 146E, extending in a direction that spans between the breathing hole 152 and the front communication hole 148 and the rear communication hole 150. The partition wall 154 protrudes from the side wall 146E toward the opening 146F and includes a first portion 154A that extends vertically at a position behind the breathing hole 152 and a second portion 154B that extends forward from the lower end of the first portion 154A.

[0061] A gap 156 is provided between the front end of the second part 154B and the front wall 146C, which connects the breathing hole 152, the front communication hole 148, and the rear communication hole 150.

[0062] Next, the operation of the snowblower 10 will be explained with reference to Figure 1. When the operator operates the snowblower 10 using the travel lever 42 of the input device 40, the travel drive unit 34 is driven, and the drive wheels 28 are rotated via the front axle 24. As a result, the crawler 32 rotates, and the snowblower 10 moves.

[0063] When the operator operates the blower 60 and auger claws 56 using the snow removal switch 44 on the input device 40, the output shaft 70 of the internal combustion engine 68 rotates. The rotation of the output shaft 70 is transmitted to the rotating shaft 64 via the deadman clutch 72, drive pulley 74, endless belt 76, and driven pulley 66, causing the blower 60 and auger claws 56 to rotate. The rotation of the auger claws 56 crushes the snow in the snowblower 10, and the snow is collected in the center of the auger housing 50 in the left-right direction. This collected snow is introduced into the blower housing 58 and ejected from the chute 62 in the desired direction by the rotation of the blower 60.

[0064] In this snow removal operation, when the operator operates the height adjustment switch 46, the electric motor 84 is driven to rotate, and the rotation of the electric motor 84 is transmitted to the output shaft 92 via the gear train 97 in the gear case 82. As a result, the upper body 14 rotates approximately vertically relative to the lower body 12 with the front shaft 24 as the pivot point, and the ground height of the auger claws 56 is adjusted.

[0065] When the internal pressure of the gear chamber 83 rises due to the heat generated by the rotation of the gear train 97, air from the gear chamber 83 enters the breather chamber 146 through the front communication hole 148 and the rear communication hole 150 and is released to the outside through the breathing hole 152. When the internal pressure of the gear chamber 83 falls, an airflow opposite to that during the internal pressure rise occurs. This maintains the internal pressure of the gear chamber 83 at a predetermined value.

[0066] When the oil level X in the gear chamber 83 fluctuates due to vibration or other factors, the oil in the gear chamber 83 may seep into the breather chamber 146 through the front communication hole 148 or the rear communication hole 150. This intrusion of oil into the breather chamber 146 is more likely to occur when the gear is tilted to the maximum forward position as shown in Figure 7(B) and when it is tilted to the maximum backward position as shown in Figure 7(C).

[0067] However, even if oil from the gear chamber 83 enters the breather chamber 146, the partition wall 154 makes it difficult for the oil to reach the breathing hole 152. This makes it difficult for oil from the gear chamber 83 to leak out of the breathing hole 152.

[0068] Since the breathing hole 152 is formed near the upper wall 146A that defines the breather chamber 146, oil from the gear chamber 83 is less likely to leak out of the breathing hole 152 than if it were located lower down.

[0069] In particular, because the partition wall 154 includes a first portion 154A that extends vertically at a position behind the breathing hole 152 and a second portion 154B that extends forward from the lower end of the first portion 154A, the partition wall 154 effectively prevents oil from flowing toward the breathing hole 152 when the device is tilted backward as shown in Figure 7(C).

[0070] Oil that enters the breather chamber 146 returns to the gear chamber 83 through the front communication hole 148 when the engine is tilted forward, and returns to the gear chamber 83 through the rear communication hole 150 when the engine is tilted backward. This prevents a large amount of oil from accumulating in the breather chamber 146. Because the opening area of ​​the rear communication hole 150 is larger than that of the front communication hole 148, the oil returns to the gear chamber 83 from the rear communication hole 150 (oil return) when the engine is tilted backward.

[0071] Even if oil that has entered the breather chamber 146 seeps into the side of the breathing hole 152 of the partition wall 154, when the vehicle is tilted forward, this oil returns to the lower wall 146B through the gap 156 and returns to the gear chamber 83 through the front communication hole 148. As a result, oil does not accumulate on the side of the breathing hole 152 of the partition wall 154.

[0072] This also makes it less likely for oil in the gear chamber 83 to leak out through the breathing hole 152.

[0073] Although the present invention has been described above in terms of preferred embodiments, as will be easily understood by those skilled in the art, the present invention is not limited to these embodiments and can be modified as appropriate without departing from the spirit of the invention. For example, the rear communication hole 150 may be omitted, leaving only the front communication hole 148. The gap 156 is not essential, and communication between the breathing hole 152 and the communication holes 148 and 150 may be achieved by holes drilled in the partition wall 154 or the like.

[0074] The motor case breather device 132 of this embodiment is not limited to the snowblower 10, but can be applied to various types of work machines and the like that have an electric motor 84 connected to a gear case 82.

[0075] Furthermore, not all of the components shown in the above embodiments are necessarily essential, and they can be appropriately selected and omitted as long as they do not deviate from the spirit of the present invention. [Explanation of symbols]

[0076] 10: Snowblower 12: Lower body (running frame) 14: Upper section (main frame) 16: Running gear 18: Handle device 20: Auger device 22: Blower device 24: Front axle 26: Rear axle 28: Drive wheels 30: Driven wheel 32: Crawler (running section) 34: Drive system 36: Arm 38: Grip 40: Input device 42: Driving lever 44: Snow removal switch 46: Height adjustment switch 48: Clutch lever 50: Ogre Housing 52: Screw gear case 54: Auger rotation axis 56: Auger claws (working part) 58: Blower Housing 60: Blower 62: Shooter 64: Rotation axis 66: Driven pulley 68: Internal combustion engine 70: Output shaft 72: Deadman's Clutch 74: Drive pulley 76: Endless belt 80: Rotating device 82: Gear case 82A: Main section 82B: End wall 82C: Cylindrical section 82D: Flange section 82E: Screw hole 82F: Corresponding recess 82G:Through hole 82H: Rear end surface 83: Gearroom 84: Electric motor 86: Output shaft 86A: Chamfered section 88: Warm 88A: Rear axle 88B: Engagement groove 90: Intermediate axis 92: Output shaft 94: Wheel gear 96: Sector gear 97: Gear train 98: Link 100: Link 101: Axis 102: Motor case 102A: Main section 102B: Flange section 102C: Bolt holes 102D: End wall 102E: Motor shaft through hole 102F: Front end surface 103:Inner chamber 104: Bracket 105: Axis 106: Rolling bearings 107: Bolt 108: Holder 110: O-ring 112: Oil seal 120: Breather Room 122: Motor connection hole 124:External communication hole 128: Partition section 130: Gap 132: Motor case breather device 140: Breather device 142: Cover board 144: Bolt 146: Breather Room 146A: Upper wall 146B: Lower wall 146C: Front wall 146D: Back wall 146E: Side wall 146F: Opening 148: Front communication hole 150: Rear communication hole 152: Breathing hole 154: Partition wall 154A: 1st part 154B :Second part

Claims

1. A work machine comprising a travel frame having a travel section, and a main frame having a work section that is rotatably attached to the travel frame around a pivot extending laterally and tilts forward and backward relative to the travel frame by rotation around the pivot, wherein a breather device for a gear case is provided on the main frame, The breather device is, The gear case comprises a gear chamber and a breather chamber, The upper part of the breather chamber has a breathing hole that communicates with the outside, A communication hole connecting the lower part of the breather chamber and the gear chamber, It has a partition wall that extends in a direction transverse between the breathing hole and the communication hole, The breather chamber extends in the front-to-back direction. The partition wall includes a first portion extending vertically at a position behind the breathing hole and a second portion extending forward from the lower end of the first portion, and the working machine has a gap between the front end of the second portion and the front wall of the breather chamber that connects the breathing hole and the communication hole.

2. The work machine according to claim 1, wherein the breathing hole is located above the oil level in the gear chamber when the work section is at its maximum forward tilt.

3. The working machine according to claim 1 or 2, wherein the front end of the second portion is formed to be positioned above the oil level in the gear chamber when the working section is tilted to its maximum rearward position.

4. The work machine according to claim 1 or 2, wherein the communication hole is provided in the front part of the breather chamber.

5. The work machine according to claim 1 or 2, wherein the communication holes are provided in the front and rear of the breather chamber.

6. The work machine according to claim 5, wherein the rear communication hole has a larger opening area than the front communication hole.

7. The breather chamber is defined in the upper part of the gear case. The work machine according to claim 1 or 2, wherein the breathing holes are formed near the upper wall defining the breather chamber.

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