Corn head gear box with separation device

Abstract

The utility model provides a corn header gear box with separating device, the corn header gear box with separating device includes main shaft box, pull stem roller, flail frame, power gear, transmission gear and switching gear. The utility model installs switching gear between transmission gear and power gear, switching gear keeps the state of intermeshing with power gear all the time, and switching gear is along its axial direction and is slidably arranged on flail frame. When switching gear changes position, the teeth on switching gear are separated from the teeth on transmission gear, thereby can realize the disconnection of power gear and transmission gear, and only pull stem roller rotates in the operation process. When the power gear and transmission gear need to be connected, the teeth on switching gear can be engaged with the teeth on transmission gear. The application can freely switch the working state of flail according to the on -the -spot demand, satisfies the diversified operation demand in the corn harvesting process.

Description

Technical Field

[0001] This utility model belongs to the field of agricultural machinery equipment technology, specifically relating to a corn header gearbox with a separation device. Background Technology

[0002] Currently, most corn harvester equipment on the market consists of a stalk-pulling roller and a chopping box located on one side of the roller. The stalks pulled by the roller are chopped and separated by blades on the chopping box. Furthermore, the stalk-pulling roller and the blades on the chopping box are mostly synchronized through the same gearbox. During operation, the main shaft inside the gearbox rotates, transmitting power to the stalk-pulling roller and blades via gears. However, in existing corn harvester technology, the blades always rotate with the stalk-pulling roller, making it impossible to operate the roller independently. This fails to meet the diverse operational needs of different users during corn harvesting. Utility Model Content

[0003] This utility model provides a corn header gearbox with a separation device, which aims to solve the technical problem that corn headers in the prior art cannot be diversified in operation.

[0004] To achieve the above objectives, the technical solution adopted by this utility model is: to provide a corn header gearbox with a separation device, comprising: A spindle box, on which a spindle is rotatably mounted; A stem-pulling roller is rotatably mounted on one side of the main shaft box and is connected to the main shaft drive. A tool holder is mounted on the spindle box, and a tool is rotatably mounted on the tool holder; A power gear is rotatably mounted on the tool holder and is connected to the main shaft via a transmission. A transmission gear is rotatably mounted on the blade holder and is connected to the blade drive. The switching gear meshes between the power gear and the transmission gear, and its position on the cutter holder has a degree of freedom that can be adjusted along its own axis. The switching gear can disengage from the transmission gear to cut off the transmission between the power gear and the transmission gear.

[0005] In one possible implementation, a drive shaft is rotatably mounted on the blade holder, the switching gear is slidably mounted on the drive shaft, and an anti-rotation key is protruding from the outer side wall of the drive shaft. An anti-rotation keyway corresponding to the anti-rotation key is provided on the inner hole of the switching gear.

[0006] In one possible implementation, a plurality of anti-rotation keys are provided on the outer side of the drive shaft, and the plurality of anti-rotation keys are evenly spaced along the circumference of the drive shaft.

[0007] In one possible implementation, a movable sleeve is fixedly mounted on the switching gear and slidably disposed on the transmission shaft. An annular groove is recessed in the middle of the movable sleeve. A drive rod is oscillatingly disposed on the tool holder. A guide rod is fixedly mounted on the drive rod and slidably disposed inside the annular groove. The tool holder is also provided with a limiting component for limiting the swing angle of the drive rod.

[0008] In one possible implementation, the limiting component includes: The positioning seat is fixedly installed on the swing shaft of the drive rod, and the outer side wall of the positioning seat is provided with two adjacent grooves. The pin is slidably mounted on the blade holder, and when the drive rod swings, the pin can switch between the two grooves. An elastic element is installed between the blade holder and the pin to push the pin toward the positioning seat.

[0009] In one possible implementation, a sleeve is fixedly installed on the blade holder, the pin and the elastic element are both installed inside the sleeve, and one end of the pin can slide out of the end of the sleeve to slide into the groove of the positioning seat.

[0010] In one possible implementation, there are two drive rods, both of which are fixedly mounted on the same swing axis, and the two drive rods are located on opposite sides of the movable sleeve.

[0011] In one possible implementation, the switching gear remains engaged with the power gear as it slides on the cutter holder.

[0012] In one possible implementation, a first gear is fixedly installed at the end of the pull roller, and a second gear meshing with the first gear is installed on the main shaft. The inner wall of the second gear is recessed with a plurality of limiting grooves. A top pin for engaging with the limiting groove is slidably arranged on the main shaft. The top pin is provided with a chamfer for guiding it to slide out of the limiting groove. Furthermore, an elastic pusher is provided on the main shaft for pushing the top pin into the limiting groove.

[0013] The solution shown in this application, compared with the prior art, features a main shaft box with a main shaft rotatably mounted inside. The main shaft connects to the output shaft of the harvester and is connected to both the stalk-pulling roller and the stalk-sweeping blade. This application also includes a rotatable drive gear mounted on the stalk-sweeping blade holder, which is connected to the main shaft. When the main shaft rotates, it synchronously drives the drive gear. A transmission gear is also rotatably mounted on the stalk-sweeping blade holder, connected to the stalk-sweeping blade, with its axis parallel to the axis of the drive gear. A switching gear is installed between the transmission gear and the drive gear, always meshing with the drive gear and sliding along its axis on the stalk-sweeping blade holder. When the switching gear changes position, its teeth disengage from the transmission gear, thus disconnecting the drive gear from the transmission gear, allowing only the stalk-pulling roller to rotate during operation. When it is necessary to reconnect the drive gear and transmission gear, the stalk-sweeping blade can be manually rotated slightly, driving the switching gear upwards to mesh with the teeth of the transmission gear. This application allows for free switching of the cutting blade's working state according to on-site needs, meeting diverse operational requirements during corn harvesting. Attached Figure Description

[0014] Figure 1 A schematic diagram of the structure of a corn header gearbox with a separation device provided in an embodiment of this utility model; Figure 2 A schematic diagram of the installation structure of the transmission gear provided in an embodiment of this utility model; Figure 3 A schematic diagram of the installation structure of the limiting component provided in an embodiment of this utility model; Figure 4 A schematic diagram of the connection structure between the main shaft and the second gear provided in an embodiment of this utility model.

[0015] Explanation of reference numerals in the attached figures: 1. Spindle box; 11. Spindle; 111. Second gear; 112. Top pin; 113. Elastic pusher; 12. Pulling roller; 121. First gear; 2. Blade holder; 3. Power gear; 4. Transmission gear; 5. Switching gear; 51. Moving sleeve; 6. Transmission shaft; 61. Anti-rotation key; 7. Drive rod; 71. Guide rod; 8. Limiting assembly; 81. Positioning seat; 82. Pin; 83. Elastic element; 84. Sleeve. Detailed Implementation To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0016] Please refer to the following: Figures 1 to 4 The following describes the corn header gearbox with a separation device provided by this utility model. The corn header gearbox with a separation device includes a main shaft housing 1, a stalk-pulling roller 12, a blade holder 2, a power gear 3, a transmission gear 4, and a switching gear 5. A main shaft 11 is rotatably mounted on the main shaft housing 1; the stalk-pulling roller 12 is rotatably mounted on one side of the main shaft housing 1 and is drive-connected to the main shaft 11; the blade holder 2 is mounted on the main shaft housing 1, and blades are rotatably mounted on the blade holder 2; the power gear 3 is rotatably mounted on the blade holder 2 and is drive-connected to the main shaft 11; the transmission gear 4 is rotatably mounted on the blade holder 2 and is drive-connected to the blades; the switching gear 5 meshes between the power gear 3 and the transmission gear 4, and its position on the blade holder 2 has a degree of freedom that can be adjusted along its own axis. The switching gear 5 can disengage from the transmission gear 4 to cut off the transmission between the power gear 3 and the transmission gear 4.

[0017] The corn header gearbox with a separation device provided in this embodiment, compared with the prior art, features a main shaft box 1 with a main shaft 11 rotatably mounted inside. The main shaft 11 is connected to the output shaft of the harvester and is connected to the stalk-pulling roller 12 and the sling cutter. In this application, a power gear 3 is rotatably mounted on the sling cutter holder 2, and is connected to the main shaft 11. When the main shaft 11 rotates, it synchronously drives the power gear 3. A transmission gear 4 is also rotatably mounted on the sling cutter holder 2, connected to the sling cutter, and its axis is parallel to the axis of the power gear 3. A switching gear 5 is installed between the transmission gear 4 and the power gear 3. The switching gear 5 is always meshed with the power gear 3 and slides along its axis on the sling cutter holder 2. When the switching gear 5 changes position, the teeth on the switching gear 5 disengage from the teeth on the transmission gear 4, thereby disconnecting the power gear 3 from the transmission gear 4, allowing only the stalk-pulling roller 12 to rotate during operation. When it is necessary to connect the power gear 3 and the transmission gear 4, the cutter can be manually rotated slightly to drive the switching gear 5 upward, so that the teeth on the switching gear 5 mesh with the teeth on the transmission gear 4. This application can freely switch the working state of the cutter according to the needs of the site, meeting the diverse operational requirements during corn harvesting.

[0018] Specifically, in this embodiment, the gear carrier is a box structure with a removable cover plate, which protects each gear set. The power gear 3, transmission gear 4, and switching gear 5 are all spur gears. The main shaft 11 is connected to the power gear 3 by a bevel gear transmission, and the transmission gear 4 is connected to the spur gear transmission, thus ensuring an effective transmission ratio.

[0019] In some embodiments, the aforementioned blade holder 2 may be adopted as follows: Figure 2 , Figure 3 The structure shown. See also... Figure 2 , Figure 3 A drive shaft 6 is rotatably mounted on the tool holder 2. A switching gear 5 is slidably mounted on the drive shaft 6, and an anti-rotation key 61 protrudes from the outer wall of the drive shaft 6. An anti-rotation keyway corresponding to the anti-rotation key 61 is provided on the inner hole of the switching gear 5. The axis of the drive shaft 6 is parallel to the axes of the power gear 3 and the transmission gear 4, and is located between the power gear 3 and the transmission gear 4. The switching gear 5 is slidably mounted on the drive shaft 6 along the axial direction of the drive shaft 6, and the anti-rotation key 61 protrudes from the outer wall of the drive shaft 6. An anti-rotation keyway that slides with the anti-rotation key 61 is provided on the inner wall of the inner hole of the switching gear 5. The anti-rotation key 61 is slidably mounted inside the anti-rotation keyway, so that the switching gear 5 can only slide along the axial direction of the drive shaft 6. When the switching gear 5 rotates, the drive shaft 6 rotates together with the switching gear 5.

[0020] Specifically, in this embodiment, both ends of the drive shaft 6 are rotatably mounted on the tool holder 2 via bearings.

[0021] In some embodiments, the drive shaft 6 may be as follows: Figure 2 , Figure 3 The structure shown. See also... Figure 2 , Figure 3 Multiple anti-rotation keys 61 protrude from the outer side of the drive shaft 6, and these keys are evenly spaced along the circumference of the drive shaft 6. The anti-rotation keys 61 are integrally formed with the drive shaft 6, and their length is aligned with the axis of the drive shaft 6. The multiple anti-rotation keys 61 enhance the connection strength between the switching gear 5 and the drive shaft 6, and the presence of anti-rotation keys 61 around the circumference of the drive shaft 6 improves the stability of the switching gear 5 sliding along the axis of the drive shaft 6.

[0022] In some embodiments, the switching gear 5 may be as follows: Figure 2 , Figure 3 The structure shown. See also... Figure 2 , Figure 3A movable sleeve 51, which is slidably mounted on the transmission shaft 6, is fixedly installed on the switching gear 5. An annular groove is recessed in the middle of the movable sleeve 51. A drive rod 7 is oscillatingly mounted on the tool holder 2. A guide rod 71, which is slidably mounted inside the annular groove, is fixedly installed on the drive rod 7. A limiting component 8 is also provided on the tool holder 2 to limit the swing angle of the drive rod 7. The movable sleeve 51 protrudes from one end of the switching gear 5, is coaxial with the switching gear 5, and is an integral structure with the switching gear 5. An anti-rotation keyway penetrates the inner wall of the movable sleeve 51 and the switching gear 5, thereby increasing the contact area between the switching gear 5 and the transmission shaft 6. Meanwhile, an annular groove is recessed in the middle of the movable sleeve 51, and a guide rod 71 is slidably arranged inside the annular groove. One end of the guide rod 71 located outside the annular groove is fixedly connected to a drive rod 7. One end of the drive rod 7 is hinged to the tool holder 2, and the swing axis of the drive rod 7 on the tool holder 2 is perpendicular to the drive rod 7, so that the end of the drive rod 7 with the guide rod 71 can swing up and down. When the guide rod 71 swings up and down, it can drive the movable sleeve 51 and the switching gear 5 to move up and down, thereby realizing the switching of the connection state between the transmission gear 4 and the power gear 3.

[0023] Specifically, in this embodiment, the limiting component 8 can limit the two position states of the switching gear 5. The two position states of the switching gear 5 are the meshing state and the disengagement state between the transmission gear 4 and the power gear 3.

[0024] Specifically, in this embodiment, the movable sleeve 51 includes a sleeve 84 fixedly installed on the switching gear 5, and two bearings fixedly installed on the outside of the sleeve 84. The two bearings are spaced apart along the axial direction of the movable sleeve 51 to form an annular groove for accommodating the guide rod 71, and the guide rod 71 abuts against the outer ring of the two bearings, thereby avoiding affecting the rotation of the switching gear 5. Both bearings are deep groove ball bearings.

[0025] In some embodiments, the limiting component 8 described above may employ, for example... Figure 3 The structure shown. See also Figure 3The limiting assembly 8 includes a positioning seat 81, a pin 82, and an elastic element 83. The positioning seat 81 is fixedly mounted on the swing shaft of the drive rod 7, and its outer wall has two adjacent recesses. The pin 82 is slidably mounted on the blade holder 2, and when the drive rod 7 swings, the pin 82 can switch between the two recesses. The elastic element 83 is installed between the blade holder 2 and the pin 82, and is used to push the pin 82 towards the positioning seat 81. The positioning seat 81 is a fan-shaped structure coaxial with the swing shaft, and its arc-shaped surface has two adjacent recesses. The inner walls of the recesses are inclined to guide the pin 82 to switch between the two recesses. During operation, the operator rotates the swing shaft, and guided by the recesses, the pin 82 slides away from the positioning seat 81 until it reaches another recess. The pin 82 is then pushed into the recess by the elastic element 83, thus switching the angle of the drive rod 7. When the pins 82 are located inside the two grooves respectively, the position of the switching gear 5 changes along its axial direction, and the teeth on the switching gear 5 and the teeth on the transmission gear 4 switch between meshing and disengaging.

[0026] Specifically, in this embodiment, the side wall of the pin 82 is provided with a chamfer that slides into the groove. When the swing shaft rotates, the chamfer on the pin 82 overcomes the force of the elastic element 83, allowing the pin 82 to move away from the positioning seat 81. This enables the pin 82 to switch between the two grooves. In the free state, the pin 82 is stabilized inside the groove by the force of the elastic element 83, preventing it from sliding out of the groove and ensuring the stability of the position of the switching gear 5.

[0027] In some embodiments, the aforementioned pin 82 may be adopted as follows: Figure 3 The structure shown. See also Figure 3 A sleeve 84 is fixedly installed on the tool holder 2. A pin 82 and an elastic element 83 are both installed inside the sleeve 84, and one end of the pin 82 can slide out of the end of the sleeve 84 to slide into the groove of the positioning seat 81. A positioning strip protrudes from the side wall of the sleeve 84. An elongated hole for installing the positioning strip is provided on the tool holder 2, with the length of the elongated hole arranged radially along the swing shaft on the drive rod 7. The positioning strip is slidably disposed inside the elongated hole, and the outer side wall of the sleeve 84 and the positioning strip are welded and fixed to the tool holder 2. The positioning strip and the elongated hole improve the connection strength between the sleeve 84 and the tool holder 2; at the same time, they facilitate the positioning of the sleeve 84, thereby ensuring a stable fit between the pin 82 and the groove on the positioning seat 81.

[0028] Specifically, in this embodiment, the end of the pin 82 is provided with a guide portion that is slidably disposed inside the sleeve 84. An anti-rotation edge is provided on the outer wall of the guide portion, and a side edge that slides and engages with the anti-rotation edge is provided on the inner wall of the sleeve 84. This prevents the pin 82 from rotating inside the sleeve 84. Simultaneously, a limiting platform is provided at the end of the sleeve 84 near the positioning seat 81 to prevent the guide portion from sliding out of the sleeve 84. Furthermore, the elastic element 83 is a spring, installed inside the sleeve 84, and a threaded plug is threaded to the end of the sleeve 84 to limit the elastic element 83 and the pin 82 within the sleeve 84. Both ends of the elastic element 83 abut against the threaded plug and the guide portion of the pin 82, respectively.

[0029] Preferably, in this embodiment, the two outer walls of the two grooves on the positioning seat 81 that are relatively far apart can abut against the end of the sleeve 84 to limit the rotation angle of the positioning seat 81 and prevent the pin 82 from disengaging from the positioning seat.

[0030] In some embodiments, the drive rod 7 described above may be as follows: Figure 3 The structure shown. See also Figure 3 There are two drive rods 7, both fixedly mounted on the same swing shaft, and the two drive rods 7 are located on opposite sides of the movable sleeve 51. A swing shaft is rotatably mounted on the knife holder 2, and a handle for driving the swing shaft to rotate is fixedly mounted at the end of the swing shaft, located on the outside of the knife holder 2. The two drive rods 7 are fixedly mounted on the swing shaft, located on opposite sides of the movable sleeve 51, thereby improving the stability of the movable sleeve 51 when moving up and down.

[0031] Specifically, in this embodiment, guide rods 71 ​​are fixedly installed at the ends of both drive rods 7. Within the swing stroke range of the drive rods 7, that is, when the pin 82 switches between the two grooves on the positioning seat 81, the guide rods 71 ​​on the two drive rods 7 are always located inside the annular groove on the outer wall of the movable sleeve 51. This ensures that the two guide rods 71 ​​always limit the position of the movable sleeve 51.

[0032] In some embodiments, the aforementioned blade holder 2 may be adopted as follows: Figure 2 The structure shown. See also Figure 2 When the switching gear 5 slides on the cutter holder 2, it always remains engaged with the drive gear 3. Along the axial direction of the drive gear 3, the length of the teeth on the drive gear 3 is greater than the length of the teeth on the transmission gear 4. Furthermore, within the stroke range of the switching gear 5 moving along its axial direction, the switching gear 5 always remains engaged with the drive gear 3, and it also completes the disengagement or engagement of the teeth with the transmission gear 4.

[0033] Specifically, in this embodiment, the switching gear 5 and the power gear 3 are always engaged, thus avoiding the inconvenience of adjusting the tooth position after the teeth of the switching gear 5 and the power gear 3 disengage, which would prevent the teeth on the switching gear 5 from engaging with the teeth on the power gear 3 later. Simultaneously, the switching gear 5 and the transmission gear 4 can switch between engagement states. During operation, the operator can manually rotate the cutter to change the position of the transmission gear 4, thereby facilitating the engagement of the switching gear 5 and the transmission gear 4.

[0034] In some embodiments, the spindle box 1 described above can be as follows: Figure 4 The structure shown. See also Figure 4 A first gear 121 is fixedly installed at the end of the stem-pulling roller 12. A second gear 111, meshing with the first gear 121, is installed on the main shaft 11. Multiple limiting grooves are recessed on the inner wall of the second gear 111. A top pin 112, for engaging with the limiting groove, is slidably mounted on the main shaft 11. The top pin 112 has a chamfer for guiding it out of the limiting groove. An elastic pusher 113 is also provided on the main shaft 11 to push the top pin 112 into the limiting groove. Both the first gear 121 and the second gear 111 are bevel gears. The first gear 121 is fixedly mounted on the stem-pulling roller 12 and meshes with the second gear 111, thus enabling the stem-pulling roller 12 to rotate together when the main shaft 11 rotates.

[0035] Specifically, in this embodiment, a mounting hole for mounting a top pin 112 is provided on the outer wall of the main shaft 1`1. The top pin 112 is slidably disposed inside the mounting hole, and the top pin 112 can be completely moved into the mounting hole. This facilitates the installation of the second gear 111 onto the main shaft 11. After the second gear 111 is installed onto the main shaft 11, the top pin 112 slides into the limiting groove on the inner wall of the second gear 111 under the push of the elastic pusher 113. Thus, when the force between the second gear 111 and the main shaft 11 in the rotational direction is within a safe range, the top pin 112 is always located inside the limiting groove of the second gear 111, thereby ensuring the transmission connection between the main shaft 11 and the second gear 111. When a material with high hardness is caught between the two pull rollers 12, the rotational resistance of the pull rollers 12 increases, thereby increasing the force between the second gear 111 and the main shaft 11. When the force between the second gear 111 and the main shaft 11 exceeds the safe range, the force exerted by the chamfer on the top pin 112 sliding into the main shaft 11 is greater than the force exerted by the elastic pusher 113. This causes the top pin 112 to slide into the main shaft 11, allowing the second gear 111 to rotate relative to the main shaft 11, thus providing a safety protection function.

[0036] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A corn header gearbox with a separation device, characterized in that, include: A spindle box (1) on which a spindle (11) is rotatably mounted; The stem-pulling roller (12) is rotatably disposed on one side of the main shaft box (1) and is connected to the main shaft (11) for transmission. A tool holder (2) is mounted on the spindle box (1), and a tool is rotatably mounted on the tool holder (2); The power gear (3) is rotatably mounted on the tool holder (2) and is connected to the main shaft (11) for transmission. The transmission gear (4) is rotatably mounted on the blade holder (2) and is connected to the blade drive; The switching gear (5) meshes between the power gear (3) and the transmission gear (4), and its position on the slinger (2) has a degree of freedom to be adjusted along its own axis. The switching gear (5) can disengage from the transmission gear (4) to cut off the transmission between the power gear (3) and the transmission gear (4).

2. The corn header gearbox with a separation device as described in claim 1, characterized in that, The blade holder (2) is rotatably provided with a drive shaft (6), the switching gear (5) is slidably provided on the drive shaft (6), and the outer side wall of the drive shaft (6) is provided with an anti-rotation key (61), and the inner hole of the switching gear (5) is provided with an anti-rotation keyway corresponding to the anti-rotation key (61).

3. The corn header gearbox with a separation device as described in claim 2, characterized in that, The transmission shaft (6) has a plurality of anti-rotation keys (61) protruding from its outer side, and the plurality of anti-rotation keys (61) are evenly spaced along the circumference of the transmission shaft (6).

4. The corn header gearbox with a separation device as described in claim 2, characterized in that, A movable sleeve (51) is fixedly installed on the switching gear (5) and slidably disposed on the transmission shaft (6). An annular groove is recessed in the middle of the movable sleeve (51). A drive rod (7) is swayingly disposed on the tool holder (2). A guide rod (71) is fixedly installed on the drive rod (7) and slidably disposed inside the annular groove. A limiting component (8) for limiting the swing angle of the drive rod (7) is also provided on the tool holder (2).

5. The corn header gearbox with a separation device as described in claim 4, characterized in that, The limiting component (8) includes: The positioning seat (81) is fixedly installed on the swing shaft of the drive rod (7), and the outer side wall of the positioning seat (81) is provided with two adjacent grooves; The pin (82) is slidably disposed on the blade holder (2), and when the drive rod (7) swings, the pin (82) can switch between the two grooves; An elastic element (83) is installed between the blade holder (2) and the pin (82) to push the pin (82) to move closer to the positioning seat (81).

6. The corn header gearbox with a separation device as described in claim 5, characterized in that, A sleeve (84) is fixedly installed on the blade holder (2). The pin (82) and the elastic element (83) are both installed inside the sleeve (84). One end of the pin (82) can slide out of the end of the sleeve (84) to slide into the groove of the positioning seat (81).

7. The corn header gearbox with a separation device as described in claim 4, characterized in that, There are two drive rods (7), both of which are fixedly installed on the same swing shaft, and the two drive rods (7) are located on both sides of the movable sleeve (51).

8. The corn header gearbox with a separation device as described in claim 1, characterized in that, When the switching gear (5) slides on the blade holder (2), it always remains engaged with the power gear (3).

9. The corn header gearbox with a separation device as described in claim 1, characterized in that, A first gear (121) is fixedly installed at the end of the pull roller (12), and a second gear (111) meshing with the first gear (121) is installed on the main shaft (11). The inner wall of the second gear (111) is recessed with a plurality of limiting grooves. A top pin (112) for engaging with the limiting groove is slidably provided on the main shaft (11). The top pin (112) is provided with a chamfer for guiding it to slide out of the limiting groove. The main shaft (11) is also provided with an elastic pusher (113) for pushing the top pin (112) to slide into the limiting groove.

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