Grass trimmer

Abstract

A grass trimmer comprises a working head, the working head comprises an outer shell 11 and a motor contained in the outer shell, the motor comprises a rotating shaft 13 axially extending out of the outer shell and a rotor shell 14 connected to the rotating shaft, the side wall of the outer shell is provided with an air inlet 101 allowing cooling airflow to enter the rotor shell, the rotor shell is arranged in the outer shell, and the rotor shell is arranged in the outer shell. The height between the top and the bottom of the rotor shell is H1, the minimum distance between the top of the rotor shell and the top wall of the inner side of the shell is L. The working process comprises a wire pressing plate 15 located between the air inlet and the rotor shell, the height between the top of the wire pressing plate and the bottom of the rotor shell is H2, and H1, H2 and L meet the conditions that H2 is larger than or equal to 0.75 H1 and smaller than or equal to H1, and L is larger than or equal to H1-H2. According to the grass trimmer, the resistance of cooling airflow is reduced, the overload capacity of the working head is improved, and the service life of the working head is prolonged.

Description

Technical Field

[0001] This utility model relates to the field of grass cutting equipment technology, and in particular to a grass cutter. Background Technology

[0002] In commercially available lawn mowers, the drive motor is typically located inside the housing of the working head, while the PCBA control board is placed in the grip area. In this case, the motor, reduction or direct drive structure, wiring box, mowing rope (brush cutter blade), and protective cover are highly integrated in the design, reducing transmission vibration and loss and improving operating comfort.

[0003] When lawnmowers operate outdoors, they sometimes face temperatures exceeding 35°C. The constant cutting of grass by the trimming ropes causes dust and grass clippings to fly around the working head, placing higher demands on the heat dissipation and dust prevention of the core power component—the motor. In some land clearing scenarios, the motor needs to have a high continuous overload capacity, and the motor cannot frequently trigger temperature protection due to high temperatures, which would affect the user's work efficiency and reduce the operating experience.

[0004] The drive motors used in the mowing heads can be either brushed DC motors (such as the Greenworks ST48B2210 dual 24V front-mounted lawnmower), which are equipped with a single-stage reduction gear mechanism. The overall structure is relatively complex, resulting in a complex motor cooling airflow. In addition, brushed motors have relatively low power and are not suitable for high-load and high-power motor conditions. Alternatively, brushless DC BLDC motors can be used (such as the Worx WG185E dual 20V front-mounted lawnmower). This type of motor directly drives the cooling fan, the mowing head, and the trimming rope. The structure is simple and compact, but the motor uses centrifugal cooling with mixed flow. The air outlet is partially blocked and hidden by the casing, and some airflow is designed. Although this can provide some cooling, it cannot meet the cooling requirements of the motor under high power and overload conditions. There is still a risk that the motor will frequently trip protection or even burn out under heavy load. Utility Model Content

[0005] In view of this, the present invention provides a grass cutter that reduces the resistance of cooling airflow and improves the overload capacity and service life of the working head.

[0006] A lawn mower includes a working head, the working head comprising a housing and a motor housed within the housing, the motor comprising a rotating shaft extending axially out of the housing and a rotor housing connected to the rotating shaft, the side wall of the housing having an air inlet for cooling airflow to enter therein, the rotor housing being disposed within the housing, the height between the top and bottom of the rotor housing being H1, the minimum distance between the top of the rotor housing and the inner top wall of the housing being L, the working head including a pressure plate located between the air inlet and the rotor housing, the height between the top of the pressure plate and the bottom of the rotor housing being H2, wherein H1, H2, and L satisfy: 0.75H1≤H2≤H1, L≥H1-H2.

[0007] In an embodiment of this utility model, the top of the rotor housing is provided with multiple ventilation holes for the cooling airflow to pass through. The ventilation holes are oblong in shape, and are arranged at intervals around the rotating shaft, with each ventilation hole curved around the rotating shaft. The radius of the rotor housing relative to the rotating shaft is R1, and the total area S of the multiple ventilation holes satisfies: S ≥ 0.3πR1 2 The distance between two adjacent ventilation holes is T, where T ≥ 5 mm.

[0008] In an embodiment of this utility model, a fixed post is provided in the middle of the outer shell, the rotating shaft passes through the fixed post, the motor further includes a rotor and a stator, the rotor is fixed to the inner wall of the rotor shell, the stator is disposed opposite to the rotor and fixed to the fixed post; the inner diameter of the stator relative to the rotating shaft is R2, the radius of the circle containing the innermost side of each ventilation hole relative to the rotating shaft is R5, and R2 and R5 satisfy: R5≤R2; the outer diameter of the stator relative to the rotating shaft is R4, the radius of the circle containing the outermost side of each ventilation hole relative to the rotating shaft is R3, and R2, R4, and R3 satisfy 0.5(R2+R4)≤R3≤R4.

[0009] In an embodiment of this utility model, the working head further includes an air guide shroud, which is fixed to the bottom of the outer shell. The air guide shroud is arranged around the rotating shaft, and the inner radial direction of the air guide shroud gradually decreases in the direction away from the outer shell.

[0010] In an embodiment of this utility model, the working head further includes a rotating sleeve and a locking pin quick-release mechanism. The rotating sleeve is fixed on the rotating shaft and has a positioning port. The locking pin quick-release mechanism is fixed to the bottom of the outer shell. The locking pin quick-release mechanism cooperates with the positioning port to lock or unlock the rotating shaft. And / or, the air guide cover has a notch to avoid the locking pin quick-release mechanism, and the width of the notch W≤15mm.

[0011] In an embodiment of this utility model, a fixed seat is provided in the middle of the outer shell, a bearing is installed on the fixed seat, the rotating shaft is connected to the bearing, the bottom of the fixed seat is located in the air guide shroud, the bottom outer diameter of the fixed seat is R6, the minimum inner diameter of the air guide shroud is R7, and R6 and R7 satisfy: R7≤R6; and / or, the distance between the bottom end face of the fixed seat and the bottom end face of the air guide shroud is m, and m satisfies: 3mm≤m≤5mm.

[0012] In an embodiment of this utility model, the working head further includes a cooling fan, which is disposed at the bottom of the housing and connected to the rotating shaft. The cooling fan includes multiple blades, each blade including a protrusion protruding toward the air guide shroud. The radius of the highest point of the protrusion relative to the rotating shaft is R8, and R7 and R8 satisfy: R8≤R7.

[0013] In an embodiment of this utility model, the lawn mower further includes a connecting rod and a handle assembly. One end of the connecting rod is connected to the working head, and the other end of the connecting rod is connected to the handle assembly. The connecting rod has a hollow channel inside, which communicates with the air inlet. The connecting rod has multiple through holes that communicate with the hollow channel.

[0014] In an embodiment of this utility model, the cross-section of the connecting rod is circular, and the radius of the connecting rod is R9; and / or, the total air inlet area of ​​the plurality of air inlets is ≥2πR9. 2 .

[0015] In an embodiment of this utility model, the handle assembly includes a handle shell and a control circuit board. The handle shell has a receiving cavity, the connecting rod is connected to the handle shell, and the hollow channel communicates with the receiving cavity. The control circuit board is installed inside the handle shell, and the control circuit board is correspondingly positioned to the opening of the hollow channel, with the thickness direction of the control circuit board parallel to the axial direction of the hollow channel; and / or, the handle shell has two air inlets on both sides, and the total air inlet area of ​​the two air inlets is ≥2πR⁹. 2 .

[0016] In this invention, the pressure plate of the grass trimmer has a small H2 value, causing the cooling airflow to bypass through the gaps between the outer shell and the rotor shell, as well as between the rotor shell and the pressure plate, resulting in a significant waste of cooling airflow. Conversely, if the pressure plate's H2 value is too large, it increases the difficulty for the cooling airflow to reach the space between the rotor shell and the top cover. Therefore, this application redesigns the pressure plate to ensure that its dimensions satisfy L≥H1-H2, reducing the resistance to cooling airflow and ensuring that the majority of the cooling airflow smoothly enters the rotor shell through the ventilation holes. This effectively cools the windings, improves the overload capacity and service life of the working head, and ultimately enhances work efficiency and user experience. Attached Figure Description

[0017] Figure 1 This is a side view structural diagram of the lawn mower of this application.

[0018] Figure 2 This is a top view structural diagram of the lawn mower of this application.

[0019] Figure 3 yes Figure 1 The diagram shows a cross-sectional view of the lawn mower.

[0020] Figure 4 yes Figure 3 The diagram shows a cross-sectional view of the working head.

[0021] Figure 5 This is a top view of the working head of this application after the outer shell and top cover have been removed.

[0022] Figure 6 This is a top view of the air guide shield of this application.

[0023] Figure 7 This is a cross-sectional structural schematic diagram of the air guide shroud of this application. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification.

[0025] In the following description, reference is made to the accompanying drawings, which illustrate several embodiments of the present application. It should be understood that other embodiments may also be used, and changes in mechanical composition, structure, electrical and operational aspects may be made without departing from the spirit and scope of the present application. The following detailed description should not be considered limiting, and the terminology used herein is for describing particular embodiments only and is not intended to limit the present application.

[0026] Although the terms first, second, etc., are used in some instances to describe various elements herein, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0027] Furthermore, as used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of a feature, step, operation, element, component, item, kind, and / or group, but do not exclude the presence, occurrence, or addition of one or more other features, steps, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are interpreted as inclusive, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition arise only when combinations of elements, functions, steps, or operations are inherently mutually exclusive in some way.

[0028] Figure 1 This is a side view structural diagram of the lawn mower of this application. Figure 2 This is a top view structural diagram of the lawn mower of this application. Figure 3 yes Figure 1 The diagram shows a cross-sectional view of the lawn mower. Figure 4 yes Figure 3 Please refer to the cross-sectional structural diagram of the working head shown. Figures 1 to 4 The lawn mower includes a working head 10, which comprises a housing 11, a top cover 12, a rotating shaft 13, a rotor housing 14, and a pressure plate 15. The side wall of the housing 11 has an air inlet 101 for cooling airflow to enter its interior. The top cover 12 is fixed to the top of the housing 11. The rotating shaft 13 is rotatably connected to the middle of the housing 11 and the top cover 12. The rotor housing 14 is disposed within the housing 11 and connected to the rotating shaft 13. The top of the rotor housing 14 has multiple ventilation holes 102 for cooling airflow to pass through. The top of the rotor housing 14 is connected to... The height between the bottoms is H1, and the minimum distance between the top of the rotor housing 14 and the inner top wall of the top cover 12 is L. The pressure plate 15 is fixed inside the outer casing 11 and is correspondingly arranged with the air inlet 101. The pressure plate 15 is used to guide the cooling airflow to the space between the rotor housing 14 and the top cover 12. The height of the top of the pressure plate 15 relative to the bottom of the rotor housing 14 is H2, that is, the height of the pressure plate 15 above the bottom of the rotor housing 14 is H2. H1, H2, and L satisfy: 0.75H1≤H2≤H1, L≥H1-H2. In this embodiment, the bottom of the pressure plate 15 exceeds the bottom of the rotor housing 14 and is used to press on the wire, while the top of the pressure plate 15 does not exceed the top of the rotor housing 14.

[0029] The H2 of the pressure plate 15 in the grass trimmer of this application is too small, causing the cooling airflow to bypass through the gap between the outer shell 11 and the rotor shell 14, as well as the gap between the rotor shell 14 and the pressure plate 15, resulting in a significant waste of cooling airflow. Conversely, if the H2 of the pressure plate 15 is too large, it increases the difficulty for the cooling airflow to reach the space between the rotor shell 14 and the top cover 12. Therefore, this application designs the structure of the pressure plate 15 to ensure that its dimensions satisfy L≥H1-H2, thereby reducing the resistance of the cooling airflow and ensuring that most of the cooling airflow smoothly enters the rotor shell 14 through the ventilation holes 102. This achieves the purpose of effectively cooling the windings, which is beneficial for improving the overload capacity and service life of the working head 10, thus improving work efficiency and user experience.

[0030] Optionally, the pressure plate 15 is provided with a positioning groove on each side, and the outer casing 11 is provided with two positioning ridges, which are set in the two positioning grooves. The pressure plate 15 is fixed to the outer casing 11 by two screws.

[0031] Optionally, Figure 5 This is a top view of the working head of this application after removing the outer shell and top cover, as shown below. Figure 5 As shown, each ventilation hole 102 is an oblong hole, and multiple ventilation holes 102 are arranged at intervals around the rotating shaft 13, and each ventilation hole 102 is curved around the rotating shaft 13. In this embodiment, the top of the rotor housing 14 is provided with three ventilation holes 102, and the number of ventilation holes 102 can be freely increased or decreased according to actual needs.

[0032] Optionally, the radius of the rotor housing 14 relative to the shaft 13 is R1, and the total area S of the multiple ventilation holes 102 satisfies: S ≥ 0.3πR1 2 This ensures that the ventilation holes 102 have sufficient area to allow enough cooling airflow to enter the rotor housing 14, achieving efficient cooling of the windings; moreover, the structural strength of the rotor housing 14 can meet the strength requirements of the whole machine under conditions such as stall.

[0033] Optionally, such as Figure 5 As shown, the distance between two adjacent ventilation holes 102 is T, where T ≥ 5 mm.

[0034] Optionally, such as Figure 4 As shown, a fixing post 111 is provided in the middle of the outer casing 11, and the rotating shaft 13 is disposed through the fixing post 111. The working head 10 also includes a rotor 161 and a stator 162. The rotor 161 is fixed to the inner wall of the rotor housing 14, and the stator 162 is disposed opposite to the rotor 161 and fixed to the fixing post 111. In this embodiment, the rotor 161 and the stator 162 constitute the winding of the motor, and the cooling airflow is used to cool the rotor 161 and the stator 162 to provide them with overcurrent and overload capacity.

[0035] Optionally, the fixing column 111 has a hollow tubular structure, and the stator 162 is fixed to the outer wall of the fixing column 111.

[0036] Optionally, the inner diameter of the stator 162 relative to the rotating shaft 13 is R2, and the radius of the innermost circle of each ventilation hole 102 relative to the rotating shaft 13 is R5, wherein R2 and R5 satisfy: R5≤R2.

[0037] Optionally, the outer diameter of the stator 162 relative to the shaft 13 is R4, and the radius of the outermost circle containing each ventilation hole 102 relative to the shaft 13 is R3. R2, R4, and R3 satisfy 0.5(R2+R4)≤R3≤R4. This application optimizes the dimensions of each ventilation hole 102, ensuring sufficient cooling airflow into the rotor housing 14 while maintaining sufficient structural strength, thus ensuring effective cooling.

[0038] Optionally, Figure 6 This is a top view of the air guide shield of this application. Figure 7 This is a cross-sectional structural schematic diagram of the air guide shroud of this application, as shown below. Figure 4 , Figure 6 and Figure 7 As shown, the working head 10 also includes an air guide shroud 17, which is fixed to the bottom of the outer shell 11. The air guide shroud 17 is arranged around the rotating shaft 13, and the inner radial direction of the air guide shroud 17 gradually decreases in size away from the outer shell 11. In this embodiment, after the cooling airflow enters the rotor housing 14 through each ventilation hole 102, it cools the motor windings on one hand and rotates at high speed with the motor on the other. Therefore, the airflow is bound to be chaotic in space. Therefore, this application designs the air guide shroud 17 into a bowl-shaped form to smoothly guide the chaotic airflow to the bottom of the outer shell 11 for discharge.

[0039] Optionally, such as Figure 4 As shown, the working head 10 also includes a rotating sleeve 18 and a locking pin quick-release mechanism (not shown). The rotating sleeve 18 is fixed on the rotating shaft 13 and has a positioning port. The locking pin quick-release mechanism is fixed to the bottom of the outer casing 11. The locking pin quick-release mechanism cooperates with the positioning port to lock or unlock the rotating shaft 13. The lawn mower of this application can meet the user's needs for cutting hard grass and shrubs, as well as clearing land. By setting the locking pin quick-release mechanism, it can switch to a structure such as a three-blade rotary cutting structure to meet the needs of different occasions.

[0040] Optionally, the quick-release mechanism includes a locking pin and a spring sleeved on the locking pin; pressing the locking pin can drive its end to insert into the positioning port to fix the rotating shaft 13, and pressing the locking pin again can unlock the rotating shaft 13, at which time the spring drives the locking pin to return to its original position.

[0041] Optionally, the air guide cover 17 has a notch 103 with a width W ≤ 15mm to avoid the quick-release mechanism of the locking pin. This application designs a notch 103 on the air guide cover 17 to avoid the quick-release mechanism of the locking pin. This notch 103 affects the air guiding effect to a certain extent. The width W ≤ 15mm of the notch 103 in this application can reduce the impact on the air guiding effect.

[0042] Optionally, such as Figure 4 As shown, a fixing seat 112 is provided in the middle of the outer casing 11, and a bearing 113 is installed on the fixing seat 112. The rotating shaft 13 is connected to the bearing 113. The bottom of the fixing seat 112 is located in the air guide shroud 17. The outer diameter of the bottom of the fixing seat 112 is R6, and the minimum inner diameter of the air guide shroud 17 is R7. R6 and R7 satisfy: R7≤R6. In this embodiment, another fixing seat 112 is provided on the inner wall of the top cover 12, and a bearing 113 connected to the rotating shaft 13 is installed on this fixing seat 112.

[0043] Optionally, the distance between the bottom end face of the fixed base 112 and the bottom end face of the air guide shroud 17 is m, where m satisfies: 3mm≤m≤5mm.

[0044] This application designs the dimensions of m, R6, and R7 to achieve a compact structure without increasing airflow resistance. If R7 is too large, the airflow will not be easily drawn into the negative pressure zone; if it is too small, the airflow will increase resistance and reduce flow rate. If m is too large, the overall height of the working head 10 will increase; if it is too small, the flow channel area will be reduced and the motor cooling flow rate will be reduced.

[0045] Optionally, such as Figure 4 As shown, the working head 10 also includes a cooling fan 19, which is located at the bottom of the housing 11 and connected to the rotating shaft 13. The cooling fan 19 includes multiple blades 191, each blade 191 including a protrusion 192 protruding towards the air guide shroud 17. The radius of the highest point of the protrusion 192 relative to the rotating shaft 13 is R8, and R7 and R8 satisfy: R8≤R7. In this embodiment, the cooling fan 19 uses the centrifugal force generated by high-speed rotation to throw the airflow from the negative pressure area to the high pressure area and discharge it outside the housing 11. The key to its working efficiency and heat dissipation effect lies in the air guide shroud 17 being able to smoothly guide the airflow to the negative pressure area of ​​the cooling fan 19, and the cooperation between the air outlet of the whole machine and the blades 191. In order to achieve the above purpose and avoid the aforementioned locking pin quick release mechanism, while making full use of the structural space, this application designs "irregular" blades 191, which have the characteristic that the upper part of the middle is higher than the edge.

[0046] Optionally, such as Figure 1 , Figure 2 and Figure 3As shown, the lawn mower also includes a connecting rod 20 and a handle assembly 30. One end of the connecting rod 20 is connected to the working head 10, and the other end is connected to the handle assembly 30. The connecting rod 20 has a hollow channel 201 that communicates with the air inlet 101. The connecting rod 20 has multiple through holes 202 that communicate with the hollow channel 201. When the working head 10 is working, the cooling fan 19 rotates with the shaft 13, generating negative pressure. At this time, outside air enters the hollow channel 201 through the through holes 202, and then enters the working head 10 through the air inlet 101. The cooling airflow enters the rotor housing 14 through the ventilation holes 102 to cool the windings, and finally exits through the cooling fan 19.

[0047] Optionally, the connecting rod 20 has a circular cross-section and a radius of R9; the total air inlet area of ​​the multiple air inlets 101 is ≥2πR9. 2 .

[0048] Optionally, the handle assembly 30 includes a handle housing 31 and a control circuit board 32. The handle housing 31 has a receiving cavity 301. The connecting rod 20 is connected to the handle housing 31, and the hollow channel 201 communicates with the receiving cavity 301. The control circuit board 32 is installed inside the handle housing 31, and the control circuit board 32 is correspondingly positioned to the opening of the hollow channel 201. The thickness direction of the control circuit board 32 is parallel to the axial direction of the hollow channel 201. In this application, the control circuit board 32 is correspondingly positioned to the opening of the connecting rod 20, which facilitates heat dissipation for the control circuit board 32.

[0049] Optionally, the handle housing 31 has two air inlets 311 on both sides, and the total air inlet area of ​​the two air inlets 311 is ≥2πR9. 2 .

[0050] The heat dissipation technology of this application is applicable to the heat dissipation of the drive motor, control circuit board 32 and other three electrical systems of handheld lithium-ion tools with voltages of 12V and above (such as 16V, 18V, 20V, 40V, 56V and 80V).

[0051] This application imposes global structural dimension constraints on various key structures of the lawn mower to achieve precise control of the cooling airflow, effectively reducing the air resistance of the cooling airflow, achieving efficient cooling of the motor, directly reducing the temperature of the motor windings, and improving its overcurrent and overload capacity.

[0052] This application's lawnmower design integrates the advantages and disadvantages of existing 12V and above handheld lawnmowers / brush cutters' overall machine and motor heat dissipation methods and structures. It optimizes the design of the entire machine, cooling fan 19, and air duct, identifying key factors affecting motor heat dissipation and controlling core dimensions. Using this heat dissipation solution, not only can the daily motor heat dissipation needs of the lawnmower under light to medium loads be met, but under heavy-load conditions such as clearing land and brush cutting, the motor temperature is significantly reduced by more than 10K compared to traditional heat dissipation methods and structures, significantly improving the machine's overload capacity and reliability. Because the motor using this heat dissipation solution operates at a lower temperature, the motor power density can be made higher, and the structure more compact, offering significant advantages in terms of materials and cost.

[0053] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A lawn mower, characterized in that, The device includes a working head, which comprises a housing and a motor housed within the housing. The motor includes a rotating shaft extending axially out of the housing and a rotor housing connected to the rotating shaft. The side wall of the housing is provided with an air inlet for cooling airflow to enter its interior. The rotor housing is disposed within the housing. The height between the top and bottom of the rotor housing is H1, and the minimum distance between the top of the rotor housing and the inner top wall of the housing is L. The working head includes a pressure plate located between the air inlet and the rotor housing. The height between the top of the pressure plate and the bottom of the rotor housing is H2. H1, H2, and L satisfy: 0.75H1≤H2≤H1, L≥H1-H2.

2. The lawn mower as described in claim 1, characterized in that, Includes at least one of the following: The top of the rotor housing is provided with multiple ventilation holes for the cooling airflow to pass through. The ventilation holes are waist-shaped holes. The multiple ventilation holes are arranged at intervals around the rotating shaft, and each ventilation hole is bent around the rotating shaft. The radius of the rotor housing relative to the shaft is R1, and the total area S of the plurality of ventilation holes satisfies: S ≥ 0.3πR1 2 ; The distance between two adjacent ventilation holes is T, where T ≥ 5 mm.

3. The lawn mower as described in claim 2, characterized in that, Includes at least one of the following: A fixing post is provided in the middle of the housing, and the rotating shaft is disposed through the fixing post. The motor also includes a rotor and a stator. The rotor is fixed to the inner wall of the rotor housing, and the stator is disposed opposite to the rotor and fixed to the fixing post. The inner diameter of the stator relative to the rotating shaft is R2, and the radius of the innermost circle containing each ventilation hole relative to the rotating shaft is R5. R2 and R5 satisfy: R5≤R2; The outer diameter of the stator relative to the rotating shaft is R4, and the radius of the outermost circle containing each ventilation hole relative to the rotating shaft is R3. R2, R4, and R3 satisfy 0.5(R2+R4)≤R3≤R4.

4. The lawn mower as described in any one of claims 1 to 3, characterized in that, The working head also includes an air guide shroud, which is fixed to the bottom of the outer shell. The air guide shroud is arranged around the rotating shaft, and the inner radial direction of the air guide shroud gradually decreases in the direction away from the outer shell.

5. The lawn mower as described in claim 4, characterized in that, The working head also includes a rotating sleeve and a locking pin quick-release mechanism. The rotating sleeve is fixed to the rotating shaft and has a positioning port. The locking pin quick-release mechanism is fixed to the bottom of the outer casing. The locking pin quick-release mechanism cooperates with the positioning port to lock or unlock the rotating shaft; and / or, The air guide cover is provided with a notch to avoid the quick-release mechanism of the locking pin, and the width of the notch W≤15mm.

6. The lawn mower as described in claim 4, characterized in that, A fixed base is provided in the middle of the outer casing, and a bearing is installed on the fixed base. The rotating shaft is connected to the bearing. The bottom of the fixed base is located in the air guide shroud. The outer diameter of the bottom of the fixed base is R6, and the minimum inner diameter of the air guide shroud is R7. R6 and R7 satisfy: R7≤R6; and / or, The distance between the bottom end face of the fixed base and the bottom end face of the air guide shroud is m, where m satisfies: 3mm≤m≤5mm.

7. The lawn mower as described in claim 6, characterized in that, The working head also includes a cooling fan, which is located at the bottom of the housing and connected to the rotating shaft. The cooling fan includes multiple blades, each blade including a protrusion protruding towards the air guide shroud. The radius of the highest point of the protrusion relative to the rotating shaft is R8, and R7 and R8 satisfy: R8≤R7.

8. The lawn mower as described in claim 1, characterized in that, The lawn mower also includes a connecting rod and a handle assembly. One end of the connecting rod is connected to the working head, and the other end of the connecting rod is connected to the handle assembly. The connecting rod has a hollow channel inside, which communicates with the air inlet. The connecting rod has multiple through holes that communicate with the hollow channel.

9. The lawn mower as described in claim 8, characterized in that, The connecting rod has a circular cross-section and a radius of R9; and / or, The total air inlet area of ​​the multiple air inlets is ≥2πR9 2 .

10. The lawn mower as described in claim 9, characterized in that, The handle assembly includes a handle housing and a control circuit board. The handle housing has a receiving cavity. The connecting rod is connected to the handle housing. The hollow channel communicates with the receiving cavity. The control circuit board is installed inside the handle housing, and the control circuit board is correspondingly positioned to the opening of the hollow channel. Furthermore, the thickness direction of the control circuit board is parallel to the axial direction of the hollow channel; and / or, The handle housing has two air inlets on both sides, and the total air inlet area of ​​the two air inlets is ≥2πR9. 2 .

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