Weed guard head and weed trimmer using the same

Abstract

The present invention discloses a grass trimmer head and a grass trimmer using the grass trimmer head, comprising: a grass trimmer head; a motor for driving the grass trimmer head to rotate about a rotation axis; the grass trimmer head includes: a spool that can rotate about a rotation axis, for winding a grass trimming rope and formed with a first transmission tooth; a head shell for accommodating at least part of the spool and formed with a second transmission tooth for cooperating with the first transmission tooth; when the motor drives the grass trimmer head to rotate about the rotation axis and in a first rotation direction, the first transmission tooth cooperates with the second transmission tooth to drive the head shell and the spool to rotate synchronously in the first rotation direction; when the head shell rotates synchronously with the spool, there is a circumferential acting force around the circumference of the rotation axis, the acting force includes a first component force and a second component force, the first component force is distributed radially along the circumference and towards the rotation axis, and the second component force is distributed circumferentially. The grass trimmer head and the grass trimmer using the grass trimmer head have stable operation and high operation comfort.

Description

Technical Field

[0001] The present invention relates to a gardening tool, and more particularly to a grass trimmer head and a grass trimmer using the grass trimmer head. Background Art

[0002] As a gardening tool, a grass trimmer is used for trimming lawns. The grass trimmer includes a motor and a grass trimmer head. The grass trimmer head rotates at a high speed to drive the grass trimming rope mounted thereon to rotate to achieve a cutting function. When the motor drives the grass trimmer head to rotate at a high speed, the grass trimmer head will generate a large vibration, resulting in insufficient strength of the grass trimmer, thereby affecting the service life of the grass trimmer. Summary of the Invention

[0003] To solve the deficiencies of the prior art, the purpose of the present invention is to provide a grass trimmer head with an extended service life and a grass trimmer using the grass trimmer head.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A grass trimmer head includes: a spool that can rotate about a rotation axis, for winding a grass trimming rope and formed with a first transmission tooth; a head shell for accommodating at least a part of the spool and formed with a second transmission tooth for cooperating with the first transmission tooth; when the grass trimmer head rotates about the rotation axis and towards a preset direction, the first transmission tooth cooperates with the second transmission tooth to transmit a force between the head shell and the spool, the force acts on a point of action on one of the head shell and the spool to drive the head shell and the spool to rotate synchronously towards the preset direction; on a circumference that passes through the point of action and is around the rotation axis, there is a tangential direction at the point of action, the force has a first component force in the radial direction perpendicular to the tangential direction, and the first component force is directed towards the rotation axis along the radial direction; the second component force of the force in the tangential direction along the rotation axis drives one of the head shell and the spool to rotate following the other, and the second component force and the first component force are combined into the force.

[0006] Further, the first transmission tooth is formed with a first contact surface, the second transmission tooth is formed with a second contact surface for contacting the first contact surface, and at least part of the second component force acts on the second contact surface.

[0007] Further, in a straight line direction that passes through the rotation axis and intersects with the first component force, the first component force has a third component force parallel to the straight line and directed towards the rotation axis; the first component force also has a fourth component force perpendicular to the straight line; the third component force and the fourth component force are combined into the first component force.

[0008] Further, the number of the second transmission teeth is multiple, the multiple second transmission teeth are sequentially distributed on the circumference around the rotation axis, the rotation axis is in the plane where the second contact surface is located, and the rotation axis is parallel to this plane.

[0009] Further, the height of the second contact surface along the rotation axis is less than or equal to 5 mm.

[0010] Further, it further includes a drive shaft connected to the grass trimmer head. The head shell forms a through hole for the drive shaft to pass through around the rotation axis, and the second transmission teeth are distributed around the through hole.

[0011] Further, the cross-section of the hole wall of the through hole in a plane perpendicular to the rotation axis is circular, and the ratio of the length of the second transmission teeth along a direction perpendicular to the rotation axis and substantially along the radial direction of the circle to the radius of the circle is greater than 1.

[0012] Further, the ratio of the area of the circle to the area of the circumference where the head shell is located around the rotation axis is less than or equal to 0.6.

[0013] Further, the number of the first transmission teeth is a divisor of the number of the second transmission teeth.

[0014] Further, the ratio of the height of the second transmission teeth along the rotation axis to the width along a direction perpendicular to the rotation axis and substantially along the circumferential direction around the rotation axis is greater than 0.4.

[0015] A grass trimmer includes the grass trimmer head according to any one of the foregoing.

[0016] The beneficial effect of the present invention is that: by the mutual cooperation of the first transmission teeth on the spool and the second transmission teeth on the head shell to generate a force, the force has a component force that can offset the eccentric force between the head shell and the spool, thereby increasing the stability of the grass trimmer head, reducing the jitter of the grass trimmer head, and extending the service life of the grass trimmer. Description of the Drawings

[0017] Figure 1 is a perspective view of a grass trimmer of an embodiment;

[0018] Figure 2 is Figure 1 the perspective view of the grass trimmer head in

[0019] Figure 3 is Figure 2 the sectional view of the grass trimmer head in

[0020] Figure 4 is Figure 2 the exploded view of the grass trimmer head installing the first type of connecting piece in

[0021] Figure 5 is Figure 4 the exploded view of the grass trimmer head installing the first type of connecting piece from another perspective in

[0022] Figure 6 is Figure 2Exploded view of the installation of the second type of connecting member on the grass cutting head;

[0023] Figure 7 is Figure 2 Front view of the spool of the grass cutting head in;

[0024] Figure 8 is Figure 7 Top view of the spool of the grass cutting head in;

[0025] Figure 9 is Figure 2 Bottom view of the first housing part of the grass cutting head in;

[0026] Figure 10 is Figure 9 Force analysis diagram at any point on the second drive gear of the first housing part of the grass cutting head in. Detailed implementation manners

[0027] The following specifically introduces the present application in conjunction with the accompanying drawings and specific embodiments.

[0028] Figure 1 The shown lawn mower 100 includes: a grass cutting head 11, a driving device 12, an operating device 13, and a connecting device 14. The grass cutting head 11 is used to install a grass cutting rope 15 to realize the grass cutting function. The driving device 12 is used to provide rotational power for the grass cutting head 11. The driving device 12 includes a motor (not shown in the figure) and a first housing 121. The motor is arranged in the first housing 121, and the motor drives the grass cutting head 11 to rotate about the rotation axis 101. The operating device 13 includes: a handle 131, an auxiliary handle 132, a main switch 133, and a second housing 134. The handle 131 and the auxiliary handle 132 are respectively used for the user's two hands to hold, so as to operate the lawn mower 100 more stably. The main switch 133 can be arranged on the handle 131, and the user can directly operate the main switch 133 when holding the handle 131 to control the lawn mower 100 to cut grass. The second housing 134 is used to form a combining part 135 for combining a power supply device. For example, the combining part 135 can combine a battery pack to supply power to the lawn mower 100. In this embodiment, the handle 131 and the second housing 134 are separately formed. It can be understood that in some other embodiments, the handle can also be integrally formed with the second housing. The connecting device 14 includes a connecting rod for connecting the first housing 121 and the second housing 134. The auxiliary handle 132 is also installed on the connecting rod, and the auxiliary handle 132 can also be located between the first housing 121 and the second housing 134. The lawn mower 100 further includes a guard 122, and the guard 122 is at least partially distributed around the grass cutting head 11, which can prevent grass clippings from flying into the user's operation direction when the grass cutting head 11 cuts grass.

[0029] As Figure 2 and Figure 3As shown, the grass trimmer head 11 further includes: a head shell 111, a spool 112, a drive shaft 113, and a first fitting 114. The head shell 111 forms an accommodation space 111a around the rotation axis 101 that can accommodate at least part of the spool 112. The side of the head shell 111 that forms the accommodation space 111a is the inner side of the head shell 111, and the other side of the head shell 111 opposite to the inner side is the outer side. The first fitting 114 is provided on the head shell 111 and can rotate synchronously with the head shell 111. As an alternative embodiment, the first fitting 114 is fixedly connected to or integrally formed with the head shell 111. The first fitting 114 is connected to or forms a fan 114a and an anti-tangling cover 114b. The fan 114a is used to dissipate heat from the motor, and the anti-tangling cover 114b is used to prevent grass clippings from entering the interior of the grass trimmer head 11 and avoid the failure of the grass trimmer head 11.

[0030] As Figures 3 to 5 As shown, the head shell 111 includes a first shell part 111b and a second shell part 111c. The first shell part 111b and the second shell part 111c are connected by snap connection to form a whole. As other alternative embodiments, the first shell part 111b and the second shell part 111c can also be connected by other means such as bonding and screw connection, which will not be elaborated here. As a specific embodiment, the first shell part 111b forms a through hole 111d through which the drive shaft 113 can pass. One end of the drive shaft 113 is connected to a motor shaft (not shown in the figure), and the other end passes through the through hole 111d and forms a flat portion to constitute a connection with the spool 112. The spool 112 forms a connection hole 112a that cooperates with the flat portion of the drive shaft 113. The drive shaft 113 and the spool 112 are connected into a whole by interference press-fitting and can rotate synchronously under the drive of the motor. In some other embodiments, the drive shaft and the spool can also be connected by other connection means. The spool forms a screw hole and a locking member, and the drive shaft forms an external thread that cooperates with the screw hole, and the connection is constituted by thread cooperation and cannot be rotated out through the locking of the locking member.

[0031] In this embodiment, the trimmer 100 includes a grass trimming mode and a line winding mode. When the trimmer 100 is in the grass trimming mode, the motor drives the spool 112 to rotate in the first rotation direction 102. The spool 112 drives the head shell 111 to rotate synchronously, and drives the trimming line 15 to rotate at a high speed to achieve grass trimming. When the trimmer 100 is in the line winding mode, the spool 112 rotates in the second rotation direction 103, and the spool 112 and the head shell 111 rotate relative to each other. At this time, the trimming line 15 can be wound onto the spool 112. The line winding mode includes two modes: an automatic line winding mode and a manual line winding mode. When the trimmer 100 is in the automatic line winding mode, the motor drives the spool 112 to rotate in the second rotation direction 103, and the spool 112 and the head shell 111 rotate relative to each other, so that the trimming line 15 can be wound onto the spool 112. When the trimmer 100 is in the manual line winding mode, the user holds the first accessory 114 with one hand and manually rotates the head shell 111 with the other hand, so that the head shell 111 and the spool 112 rotate relative to each other. At this time, the trimming line 15 can be wound onto the spool 112.

[0032] As Figures 7 to 8 shown, in a direction of a first straight line 104 parallel to the rotation axis 101, the spool 112 is a cylinder formed around the first straight line 104. The connection holes 112a for mating with the flat portion of the drive shaft 113 are distributed along the first straight line 104. The connection holes 112a penetrate through the spool 112 itself, and a first transmission portion for transmission is formed around the connection holes 112a. The spool 112 further includes a first flange 112f and a second flange 112g. A wire groove 112h for accommodating the trimming line 15 is formed between the first flange 112f and the second flange 112g.

[0033] A second transmission part that cooperates with the first transmission part is further formed on the head shell 111. The first transmission part is used to transmit the power of the motor to the second transmission part, so as to drive the head shell 111 to rotate synchronously. Specifically, the first transmission part is the first transmission teeth 112b evenly distributed around the rotation axis 101, and the second transmission part is the second transmission teeth 111h distributed around the first straight line 104. When the motor drives the grass cutting head 11 to rotate at a high speed, there will be vibrations between the spool 112 and the head shell 111 due to problems such as gaps or weights during assembly or production processes, and the imbalance in the high-speed rotation state will cause a large eccentric force F0 between the head shell 111 and the spool 112. In this embodiment, each tooth of the second transmission teeth 111h deviates from the second rotation direction 103 to a preset angle. In this way, during the high-speed rotation of the head shell 111 with the spool 112, the second transmission teeth 111h will generate a reaction force on the first transmission teeth 112b that deviates from the above-mentioned eccentric force F0, so as to offset the eccentric force F0 generated between the head shell 111 and the spool 112 due to their own assembly or technological barriers, reduce or even eliminate the mutual acting force between the head shell 111 and the spool 112, effectively reduce the vibration between the head shell 111 and the spool 112, and further reduce the strength requirements for each component of the grass cutting head 11.

[0034] The first transmission gear 112b includes a first arc portion 112c and a second arc portion 112d distributed around the rotation axis 101. The first arc portion 112c and the second arc portion 112d are connected by a first contact surface 112e. On a connection surface connecting the rotation axis 101 and the connection point of the first arc portion 112c and the first contact surface 112e, the second arc portion 112d is located at both ends of the connection surface. The first contact surface 112e of the first transmission gear 112b is distributed towards the first rotation direction 102. The angle between the tangent line at the connection point of the first arc portion 112c and the first contact surface 112e and the straight line passing through this tangent line on the first contact surface 112e is an acute angle, and this angle faces the first rotation direction 102. In order to increase the transmission force between the spool 112 and the head shell 111, the first transmission gear 112b is distributed within a preset circumferential range. Here, the radius of the circle where the first transmission gear 112b is located is defined as R1, and the circumferential radius of the spool 112 is R2. R1 is less than R2, and the ratio of the area of the circle where R1 is located to the area of the circle where R2 is located is less than or equal to 0.6, that is, the ratio of the area of the circle formed by the connection line between the farthest point of the first transmission gear from the rotation axis and the rotation axis to the area of the circle formed by the spool around the rotation axis is less than or equal to 0.6. Along the direction of the first straight line 104, the first transmission gear 112b also protrudes from the first flange 112f where the spool 112 body is located and has a certain height. Along the direction of the first straight line 104, the vertical distance H1 from the highest point of the first transmission gear 112b to the first flange 112f is less than or equal to 5 mm. Through this setting, on the one hand, the radial space occupied by the first transmission gear 112b is reduced, increasing the convenience of assembly; on the other hand, the transmission force between the first transmission gear 112b and the second transmission gear 111h is also increased, making it easier for the first transmission gear 112b and the second transmission gear 111h to mesh. The spool 112 in this embodiment includes a first spool portion 112 and a second spool portion 112. The first spool portion 112 and the second spool portion 112 are connected by a fixing member. The first spool portion 112 is formed with fixing holes (not shown in the figure) for connecting the second spool portion 112, and the fixing holes are provided on the first transmission gear 112b.

[0035] As Figures 8 to 10 shown, as a preferred embodiment, the number of the first transmission gears 112b is a divisor of the number of the second transmission gears 111h. In this way, when the first transmission gears 112b and the second transmission gears 111h need to cooperate, they can mesh at any position, and when one of the first transmission gears 112b meshes with the second transmission gear 111h, the remaining first transmission gears 112b can also mesh with the second transmission gear 111h at the same time. As Figure 9As shown, as an alternative embodiment, there are 3 first transmission teeth 112b provided, and 6 second transmission teeth 111h provided. The second transmission teeth 111h are distributed on the first housing portion 111b. In the circumferential direction around the through hole 111d of the first housing portion 111b, the second transmission teeth 111h are evenly distributed. In any second straight line direction passing through the center of the through hole 111d of the first housing portion 111b, the second transmission teeth 111h are formed with second contact surfaces 111k that cooperate with the first contact surfaces 112e, and the extending directions of the second contact surfaces 111k all deviate from the second straight line direction. In fact, it can be understood that one end of the drive shaft 113 is connected to the motor shaft, and the other end is connected to the spool 112 through the through hole 111d. During the process of the motor driving the spool 112 to rotate through the drive shaft 113, the spool 112 drives the head shell 111 to rotate synchronously through the cooperation of the first transmission teeth 112b and the second transmission teeth 111h of the head shell 111. Due to limitations in technologies such as process or assembly, neither the spool 112 nor the head shell 111 can form a true circle. Therefore, under the drive of the motor, both the head shell 111 and the spool 112 have a centrifugal force perpendicular to the rotation axis 101 direction. In fact, the spool 112 is directly driven by the motor, has a first center C1, and can rotate around the first center C1; there is a certain gap between the head shell 111 and the drive shaft 113, and this gap is not uniform, resulting in the head shell 111 rotating around the second center C2 under the drive of the spool 112. Within a certain error range, the first center C1 and the second center C2 do not coincide, resulting in different centrifugal forces acting on the head shell 111 and the spool 112 under the same rotational speed condition, thereby generating an eccentric force F0. At this time, the eccentric force F0 causes a certain displacement between the head shell 111 and the spool 112. And when such an eccentric force F0 exists at each angle around the circumferential direction, relatively intense vibrations will occur between the head shell 111 and the spool 112. Since the spool 112 and the head shell 111 only transmit the acting force through the engagement of the first transmission teeth 112b and the second transmission teeth 111h, the above vibrations will increase the acting force between the first transmission teeth 112b and the second transmission teeth 111h, thereby affecting the structural stability of the grass cutting head 11 itself and also affecting the service life of the grass cutting head 11.

[0036] Specifically, as Figure 10As shown, any point A on the second transmission gear 111h is taken for force analysis. When the first transmission gear 112b meshes with the second transmission gear 111h, the first contact surface 112e of the first transmission gear 112b contacts the second contact surface 111k of the second transmission gear 111h. In the state where the grass cutting head 11 rotates at a high speed, due to the action of torque, a force F1 perpendicular to both the first contact surface 112e and the second contact surface 111k will be generated between the head shell 111 and the spool 112. This force F1 will generate two mutually perpendicular component forces. These two component forces include the first component force F2 and the second component force F3. Among them, the first component force F2 extends along the direction of the first center C1 and can pass through the first center C1; the second component force F3 is distributed along a direction that intersects the meshing surface of the first transmission gear 112b and the second transmission gear 111h at the same time, and can drive one of the head shell and the spool to rotate with the other. It can be understood that when the second transmission gear 111h does not deviate towards the second rotation direction 103, then the above-mentioned force F1 has no component forces, and all of it acts in a direction perpendicular to the meshing surface of the first transmission gear 112b and the second transmission gear 111h at the same time, thus posing higher requirements on the first transmission gear 112b and the transmission gear itself. Here, by setting the second transmission gear 111h to deviate towards the second rotation direction 103, the force directly acting in the direction perpendicular to the meshing surface of the first transmission gear 112b and the second transmission gear 111h at the same time can be effectively reduced. Thus, the requirements for the structural strength of the first transmission gear 112b and the second transmission gear 111h are reduced. In fact, the first component force F2 can be further decomposed into two mutually perpendicular component forces, and these two component forces include the third component force F4 and the fourth component force F5. Among them, the third component force F4 is similar in magnitude to the above-mentioned eccentric force F0 and has the opposite direction. At an appropriate angle, the third component force F4 is the same in magnitude as the eccentric force F0 and has the opposite direction. In theory, it can be completely offset, thus effectively solving the vibration problem between the head shell 111 and the spool 112 due to the eccentric force F0. In fact, in a straight line direction passing through the first center C1, the second transmission gear 111h includes a set of first component forces F2 and first component forces F20 that are the same in magnitude and opposite in direction. The first component force F2 offsets the eccentric force F00, and while the first component force F20 eliminates the eccentric force F0, the first component force F2 and the first component force F20 can also restrain each other to prevent the head shell 11 from jittering relative to the spool 12, so that the resultant force between the head shell 11 and the spool 12 is directed towards the first center C1. As an optional implementation manner, in order to achieve better meshing with the second transmission gear 111h, each tooth of the first transmission gear 112b can also be set to deviate towards the first rotation direction 102 by a preset angle.Thus, when the first transmission tooth 112b mates with the second transmission tooth 111h, the first contact surface 112e of the first transmission tooth 112b and the second contact surface 111k of the second transmission tooth 111h can be effectively fitted, so that the force between the two first contact surfaces 112e is more uniform.

[0037] It can be understood that by deflecting the second transmission tooth 111h to a preset angle in the second rotation direction 103, the vibration problem between the head shell 111 and the spool 112 is effectively solved, thereby reducing the material requirements for the head shell 111 to form the second transmission tooth 111h. In fact, under the above settings, the head shell 111 for forming the second transmission tooth 111h can be made thinner along the rotation axis 101 direction. And the tooth height of the second transmission tooth 111h along the rotation axis 101 direction is less than or equal to 5 mm, thereby saving the material for forming the second transmission tooth 111h and making the engagement and disengagement between the second transmission tooth 111h and the first transmission tooth 112b more convenient.

[0038] Such as Figures 5 to 6As shown, in this embodiment, the lawn mower 100 further has a first use state and a second use state that can be switched. To facilitate the switching of the use state, a first type of connecting member 16 or a second type of connecting member 17 is also connected to or formed on the drive shaft 113. Specifically, when the first type of connecting member 16 is connected to the drive shaft 113, the lawn mower 100 is in the first use state; when the second type of connecting member 17 is connected to the drive shaft 113, the lawn mower 100 is in the second use state. As an alternative embodiment, the first use state is the state when the lawn mower 100 is in the automatic winding mode; the second use state is the state when the lawn mower 100 is in the manual winding mode. To enable the lawn mower 100 to switch between the automatic winding mode and the manual winding mode, a head shell 111 that allows the grass head 11 to be suitable for different operation modes is also provided. As an alternative embodiment, the through hole 111d of the head shell 111 is arranged in a form that allows switching between two operation modes. When the lawn mower 100 is in the automatic winding mode, the drive shaft 113 in the through hole 111d is provided with a first type of connecting member 16, and the first type of connecting member 16 is movably connected to the drive shaft 113 and can rotate relative to the drive shaft 113. When the lawn mower 100 is in the manual winding mode, the drive shaft 113 in the through hole 111d is provided with a second type of connecting member 17, and the second type of connecting member 17 is fixedly connected to the drive shaft 113 and can form synchronous rotation. Specifically, the through hole 111d forms a first circumferential surface 111e and a second circumferential surface 111f around the rotation axis 101, the radius R3 of the first circumferential surface 111e is smaller than the radius R4 of the second circumferential surface 111f, and an internal transmission part 111g for transmission is formed between the first circumferential surface 111e and the second circumferential surface 111f. In fact, whether the drive shaft 113 is installed with the first type of connecting member 16 or the second type of connecting member 17, the through hole 111d of the head shell 111 can pass through. In fact, the ratio of the area of the first circumferential surface 111e of the through hole 111d to the area of the circumference where the head shell 111 is located around the rotation axis 101 is greater than or equal to 0.4. Through this setting, on the one hand, the effective cooperation between the through hole 111d and the drive shaft 113 is achieved, reducing the vibration between the head shell 111 and the spool 112; on the other hand, the space for forming the through hole 111d can also be reduced, thereby increasing the structural strength of the head shell 111 and avoiding the reduction of the strength of the head shell 111 due to the over-large through hole 111d. In fact, through this size setting and ratio matching, the material for forming the head shell 111 can also be effectively reduced, and at the same time, the thickness of the head shell 111 is reduced, thereby reducing the load of the motor, increasing the battery life and operation convenience of the lawn mower 100. We can understand that for the lawn mower 100, it is necessary to hold the handle 131 provided on the connecting rod for a long time to operate for mowing. When the weight of the grass head 11 is lighter, the weight borne on the human hand is smaller, and the user operation is more comfortable.In addition, since the circumference where the through hole 111d is located is small, the part of the head shell 111 for forming the second transmission gear 111h is large, so that the first contact surface 112e of the second transmission gear 111h is longer in the radial direction of the head shell 111. In this way, a more reliable fit between the first transmission gear 112b and the second transmission gear 111h can be achieved. In fact, in this embodiment, the ratio of the length of the first contact surface 112e of the second transmission gear 111h in the radial direction to the radius of the circumference where the first circumferential surface 111e of the through hole 111d is located is greater than 1.

[0039] As an alternative embodiment, the inner transmission part 111g may exist in the form of a transmission gear. Here, the first type of connector 16 is connected to or forms an outer transmission part 161 that cooperates with the inner transmission part 111g. When the inner transmission part 111g cooperates with the outer transmission part 161, the drive shaft 113 can drive the head shell 111 to rotate synchronously. The second type of connector 17 is a smooth-surfaced ring that is installed on the drive shaft 113 and can pass through the through hole 111d, and it does not generate mutual forces with the inner transmission part 111g and does not drive the head shell 111 to rotate. In fact, when the drive shaft 113 is installed with the second type of connector 17 and passes through the through hole 111d, the second type of connector 17 does not contact the inner transmission part 111g; or, the inner transmission part 111g is in partial contact with the second type of connector 17, but no mutual forces are generated.

[0040] More specifically, after the drive shaft 113 is connected to the first type of connector 16 or the second type of connector 17, a fixed connection is formed with the first fitting 114 through the first type of connector 16 or the second type of connector 17. In fact, the first fitting 114 and the drive shaft 113 always rotate synchronously. In some alternative embodiments, the first fitting 114 is fixedly connected to the drive shaft 113 through the first type of connector 16 or the second type of connector 17. Or, the first fitting 114 is directly fixedly connected to the drive shaft 113 and can rotate synchronously with the drive shaft 113.

[0041] When the lawn mower 100 is set to the automatic winding mode, the drive shaft 113 is connected to the first type of connecting member 16. At this time, the head shell 111 can rotate synchronously with the drive shaft 113. When winding is required, the user can control the motor to reverse through the operating device 13. At this time, the drive shaft 113 drives the spool 112 to rotate in the second rotation direction 103. Due to the reverse rotation, the first transmission gear 112b straddles the second transmission gear 111h, and the two are no longer engaged. Also, since the head shell 111 and the first fitting 114 are synchronously rotated through the first type of connecting member 16, and when the user activates the automatic winding switch, a locking pin is provided on the lawn mower 100 for locking the rotation of the head shell 111 or the spool 112. In this embodiment, the locking pin is used to lock the head shell 111. When the locking pin is inserted into the through hole 111d of the first fitting 114 along the rotation axis 101 direction, the rotation of the first fitting 114 and the head shell 111 is locked. At this time, the drive shaft 113 can freely rotate relative to the first type of connecting member 16, so as to drive the spool 112 to rotate. A relative rotation is generated between the spool 112 and the head shell 111, so that the grass string 15 can be wound around the thread groove 112h of the spool 112.

[0042] When the lawn mower 100 is set to the manual winding mode, the drive shaft 113 is connected to the second type of connecting member 17. At this time, the head shell 111 can freely rotate relative to the first fitting 114. When winding is required, the user can hold the first fitting 114 with one hand and hold the head shell 111 to rotate in the second rotation direction 103 with the other hand. At this time, a relative rotation is generated between the head shell 111 and the spool 112, so that the grass string 15 can be wound around the thread groove 112h of the spool 112.

[0043] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the above embodiments do not limit the present application in any form. Any technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present application.

Claims

1. A grass trimmer head, comprising: a spool that can rotate about a rotation axis and is used for winding a grass trimming string and forming a first transmission tooth; a head shell for accommodating at least part of the spool and forming a second transmission tooth for cooperating with the first transmission tooth; characterized in that when the grass trimmer head rotates about the rotation axis and towards a preset direction, the first transmission tooth cooperates with the second transmission tooth to transmit a force between the head shell and the spool, and the force acts on an acting point on one of the head shell and the spool to drive the head shell and the spool to rotate synchronously towards the preset direction; on a circumference that surrounds the rotation axis and passes through the acting point, there is a tangential direction at the acting point, the force has a first component force in the radial direction perpendicular to the tangential direction, and the first component force is directed radially towards the rotation axis; the force has a second component force in the tangential direction along the rotation axis to drive one of the head shell and the spool to rotate with the other, the second component force and the first component force are combined into the force, and the first component force cancels the eccentric force generated between the head shell and the spool due to their own assembly or process.

2. The grass trimmer head according to claim 1, characterized in that the first transmission tooth forms a first contact surface, the second transmission tooth forms a second contact surface for contacting the first contact surface, and at least part of the second component force acts on the second contact surface.

3. The grass trimmer head according to claim 1, characterized in that in a straight line direction that passes through the rotation axis and intersects the first component force, the first component force has a third component force parallel to the straight line and directed towards the rotation axis; the first component force also has a fourth component force perpendicular to the straight line; the third component force and the fourth component force are combined into the first component force.

4. The grass trimmer head according to claim 2, characterized in that the number of the second transmission teeth is multiple, and the multiple second transmission teeth are sequentially distributed on the circumference surrounding the rotation axis, the rotation axis is in the plane where the second contact surface is located, and the rotation axis is parallel to the plane.

5. The grass trimmer head according to claim 2, characterized in that the height of the second contact surface in the direction of the rotation axis is less than or equal to 5 mm.

6. The grass trimmer head according to claim 1, characterized in that it further includes a drive shaft connecting the grass trimmer head, the head shell forms a through hole for the drive shaft to pass through around the rotation axis, and the second transmission teeth are distributed around the through hole.

7. The grass trimmer head according to claim 6, characterized in that the cross-section of the hole wall of the through hole in a plane perpendicular to the rotation axis is circular, and the ratio of the length of the second transmission tooth in a direction perpendicular to the rotation axis and substantially along the radial direction of the circle to the radius of the circle is greater than 1.

8. The grass trimmer head according to claim 7, characterized in that the ratio of the area of the circle to the area of the circumference of the head shell around the rotation axis is less than or equal to 0.

6.

9. The grass cutting head according to claim 1, wherein the height of the second transmission gear in the direction of the rotation axis and the ratio of the width in a direction perpendicular to the rotation axis and substantially along the circumference around the rotation axis is greater than 0.

4.

10. A grass trimmer, characterized in that it includes the grass cutting head according to any one of claims 1 to 9.

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