A tractor pneumatic gear shifting device

Abstract

This invention relates to the field of gearbox shift control technology and discloses a pneumatically controlled shifting device for a tractor. It includes a top cover fixedly mounted on the gearbox, shift paddles, and cylinder assemblies. Multiple shift paddles are slidably installed inside the top cover. The shift paddles are pushed and pulled left and right by the telescopic ends of each cylinder assembly. Each cylinder assembly includes a cylinder body, with a first piston and a second piston slidably mounted on it. The surface of the cylinder body has a first air injection hole, a second air injection hole, and a third air injection hole. This pneumatically controlled shifting device, by setting up a cylinder assembly capable of three-gear positioning, can drive the shift paddles to switch between high gear, neutral, and low gear, meeting the requirement of controlling the left and right sliding of the engagement sleeve. Furthermore, multiple cylinder assemblies independently control the movement of each shift paddle, eliminating the need for a separate gear selection cylinder group, simplifying the overall structure of the shifting mechanism, reducing its size, lowering the failure rate, and providing convenience for later use, maintenance, and debugging.

Description

Technical Field

[0001] This invention relates to the field of gearbox shift control technology, and more particularly to a pneumatically controlled gear shifting device for tractors. Background Technology

[0002] Common gear shifting methods include mechanical, hydraulic, and electronic shifting. Transmissions achieve gear shifting through different mechanisms and control methods, meeting the needs of various operating conditions. Existing technology, patent document CN103629342B, discloses a pneumatic gear shifting device based on parallel double-acting cylinders. This device includes an electronic control command signal unit, a command execution unit connected to the electronic control command signal unit via an electrical signal line, a shift cylinder group and a selector cylinder group connected to the command execution unit via air pipes, and a connector connected to the transmission rocker arm. The shift cylinder group is directly or indirectly connected to the rocker arm, while the selector cylinder group is indirectly connected to the connector. Compared with existing technologies, this invention has strong universality, enabling modular and integrated production. When updating or replacing automobiles, there is no need to consider the design of the transmission operating mechanism, and installation and debugging are simple and convenient. Because the pressure exerted on the transmission rocker arm by the selector cylinder group and the shift cylinder group continues after gear engagement, the phenomenon of gear slippage will not occur.

[0003] Tractor gearboxes typically use a sleeve shifter, a common gearbox structure. Its working principle involves the movement of the sleeve to shift between different gears. It has unique advantages in tractor applications. First, shifting is smooth. Because the sleeve moves slowly, the engagement between gears is smoother, reducing shock and vibration during shifting and improving driving comfort. Second, it has a simple structure. Compared to other complex shifting structures, the sleeve shifter only requires one sleeve and one gear, resulting in a smaller size and weight, and easier maintenance. However, sleeve shifting also has some disadvantages, primarily a slower shifting speed. Because the sleeve needs to move slowly, the shifting speed is relatively slow, so it is generally suitable for low-speed vehicles such as tractors.

[0004] If the above-mentioned pneumatic shifting device is used to control the left and right sliding of the engagement sleeve, the following problems exist:

[0005] 1) Since the gear shifter needs to switch between high gear, neutral and low gear, the cylinder is required to achieve three-gear positioning to avoid gear slippage, but the existing cylinder can only achieve positioning at the beginning and end.

[0006] 2) When switching between different gears, a gear selector cylinder group is required, which results in a complex overall structure, large size, and high failure rate, causing inconvenience for later maintenance and debugging. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a pneumatic gear shifting device for tractors.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A pneumatic gear shifting device for a tractor includes a top cover, shift paddles, and cylinder assemblies fixedly mounted on a gearbox. Multiple shift paddles are slidably mounted inside the top cover, with the bottom ends of the shift paddles extending into the gearbox. Multiple cylinder assemblies are fixedly mounted on the upper side of the top cover, and the shift paddles are pushed and pulled left and right by the telescopic ends of each cylinder assembly.

[0010] The cylinder assembly includes a cylinder body, inside which are a first stepped cavity and a second stepped cavity. A first piston is slidably installed in the first stepped cavity, dividing the first stepped cavity into two chambers, left and right. A second piston is slidably installed in the second stepped cavity. A first air injection port, a second air injection port and a third air injection port are respectively opened on the surface of the cylinder body. The first air injection port and the second air injection port are respectively connected to the two chambers on both sides of the first piston, and the third air injection port is connected to the second stepped cavity.

[0011] A drive shaft is slidably mounted inside the cylinder block. The first piston is connected to the end of the drive shaft via a connecting sleeve. The end of the drive shaft away from the first piston extends into the upper cover and is fixedly connected to the shift lever. Compressed air is injected from the first air injection port, the second air injection port, and the third air injection port respectively, which can realize the three-speed positioning of the cylinder assembly.

[0012] Preferably, a plurality of Hall sensors are fixedly installed on the upper surface of the cover, and the plurality of Hall sensors are arranged one-to-one above each shift lever. The function of the Hall sensors is to detect whether the shift lever is in the neutral position.

[0013] Preferably, the connecting sleeve is fixedly connected to the end of the first piston. A liquid storage chamber is provided inside the connecting sleeve. The drive shaft slides through the connecting sleeve and through the liquid storage chamber. A separator is slidably installed inside the liquid storage chamber. The separator is fixedly installed on the surface of the drive shaft. A connecting port is provided on the surface of the separator. The separator divides the liquid storage chamber into two liquid storage chambers, left and right. The liquid storage chamber contains a flowing medium. The flowing medium can convect between the two liquid storage chambers through the connecting port to absorb the instantaneous impact force of the cylinder assembly and delay the meshing of the primary and secondary gears in the gearbox.

[0014] Preferably, a first inlet hole and a second inlet hole are respectively opened on both sides of the separator plate, and a first plunger and a second plunger are respectively fixedly installed inside the connecting sleeve. When the transmission shaft drives the separator plate to move left and right, the first plunger can slide into the first inlet hole and the second plunger can slide into the second inlet hole.

[0015] The drive shaft has two sets of sliding holes on its surface and two independent flow channel holes inside. The two sets of sliding holes are connected to the first inlet hole and the second inlet hole through the flow channel holes respectively. The first positioning pin and the second positioning pin are slidably installed in the two sets of sliding holes respectively. The cylinder body has two annular grooves. The first positioning pin and the second positioning pin can slide into the two annular grooves respectively by telescoping, which can lock the drive shaft in high and low gear positions.

[0016] Preferably, the inner wall of the cylinder is embedded with two electrode plates, which are respectively arranged on the upper and lower sides of the connecting sleeve. The flowing medium is an electrorheological fluid. The two electrode plates provide a changing electric field for the electrorheological fluid, so that the viscosity of the electrorheological fluid changes with the change of the electric field strength, thereby controlling the convection velocity of the flowing medium.

[0017] Preferably, multiple sliding shafts are fixedly installed inside the upper cover, and the shift lever is slidably installed on the surface of the sliding shaft. Two return springs are sleeved on the surface of the sliding shaft, and the two return springs abut against both sides of the shift lever to assist the shift lever in returning to the neutral position.

[0018] The gearbox is equipped with a shift shaft, a shift fork, and a engagement sleeve. The end of the shift shaft is provided with a recessed groove, and the bottom end of the shift fork is movably inserted into the recessed groove.

[0019] The present invention has the following beneficial effects:

[0020] 1. This pneumatic gear shifting device, through the setting of a cylinder assembly that can be positioned in three gears, can drive the shift paddle to switch between high gear, neutral and low gear, meet the requirements of controlling the left and right sliding of the engagement sleeve. Moreover, multiple sets of cylinder assemblies control the independent operation of each shift paddle, eliminating the need for a gear selection cylinder group, simplifying the overall structure of the gear shifting mechanism, reducing its size, reducing the failure rate, and providing convenience for later use, maintenance and debugging.

[0021] 2. This pneumatic gear shifting device, by setting a connecting sleeve and setting a first positioning pin and a second positioning pin on the surface of the drive shaft, the first piston is connected to the end of the drive shaft through the connecting sleeve. The drive shaft drives the partition plate to move left and right in the connecting sleeve, which can control the extension and retraction of the first positioning pin and the second positioning pin. The first positioning pin or the second positioning pin is inserted into the annular groove, which can lock the drive shaft in high and low gear positions, and prevent the engagement sleeve from sliding accidentally, thereby achieving the effect of preventing gear skipping.

[0022] 3. This pneumatic gear shifting device uses a cylinder assembly to drive the shift paddle to move left and right for gear shifting. Because the connecting sleeve contains a flowing medium, the relative movement between the separator plate and the connecting sleeve allows the flowing medium to convect through the two liquid reservoirs in the connecting sleeve via the connecting port. This absorbs the instantaneous impact force of the cylinder assembly and delays the meshing of the primary and secondary gears in the gearbox, making the linear velocity of the primary and secondary gear teeth closer together, facilitating meshing, reducing gear grinding, making gear shifting smoother, reducing impact and vibration during gear shifting, and improving driving comfort.

[0023] 4. Due to frequent gear shifting during tractor operation, the piston seals in the cylinder assembly wear out quickly or age rapidly, which can easily lead to air leakage between the high and low pressure chambers of the cylinder. This results in a decrease in the response accuracy of the cylinder assembly. It is not advisable to directly control the shifting speed and prevent gear slippage through the cylinder assembly. Otherwise, the manufacturing cost of the cylinder assembly will be high, the failure rate will be high, and subsequent maintenance will be troublesome.

[0024] In this pneumatic gear shifting device, the fluid medium inside the connecting sleeve is an electrorheological fluid. The electrode plates on the upper and lower sides of the connecting sleeve provide a changing electric field for the electrorheological fluid, so that the viscosity of the electrorheological fluid changes with the change of the electric field strength, thus realizing adjustable shifting speed.

[0025] Meanwhile, by inserting the first or second locating pin into the annular groove, the drive shaft can be locked in high or low gear positions, preventing the engagement sleeve from slipping unexpectedly and thus preventing gear skipping.

[0026] There is no need to directly control the shift speed and prevent gear slippage through the cylinder assembly. The cylinder assembly only provides the force for the extension and retraction action, which reduces the precision requirements of the cylinder assembly, reduces the frequency and burden of later maintenance, extends its service life, and makes it more reliable. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the three-dimensional structure of the upper cover proposed in this invention;

[0028] Figure 2 This is a schematic diagram (partial cross-section) of the three-dimensional structure of the upper cover proposed in this invention;

[0029] Figure 3 This is a schematic diagram of the front section structure of the upper cover proposed in this invention (with an added schematic diagram of the gearbox);

[0030] Figure 4 This is a schematic plan view of the three-cylinder assembly proposed in this invention;

[0031] Figure 5 This is a partial cross-sectional structural diagram of the upper cover proposed in this invention;

[0032] Figure 6 A partially enlarged cross-sectional view of the first cylinder block (I);

[0033] Figure 7 A partially enlarged cross-sectional view of the first cylinder block (II);

[0034] Figure 8 A partially enlarged cross-sectional view of the first cylinder block (Part 3);

[0035] Figure 9 This is a schematic diagram of the side profile of the connecting sleeve proposed in this invention.

[0036] In the diagram: 1. Gearbox, 2. Top cover, 3. Shift lever, 4. Cylinder block, 5. First stepped cavity, 6. Second stepped cavity, 7. First piston, 8. Second piston, 9. First air inlet, 10. Second air inlet, 11. Third air inlet, 12. Drive shaft, 13. Connecting sleeve, 14. Hall sensor, 15. Divider plate, 16. Connecting port, 17. First inlet hole, 18. Second inlet hole, 19. First plunger, 20. Second plunger, 21. First locating pin, 22. Second locating pin, 23. Electrode plate, 24. Sliding shaft, 25. Return spring, 26. Shift shaft, 27. Shift fork, 28. Engaging sleeve, 29. First cylinder, 30. Second cylinder, 31. Third cylinder, 32. Annular groove. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] Example 1

[0040] Reference Figure 1-9 A pneumatically controlled gear shifting device for a tractor includes a top cover 2, a shift paddle 3, and a cylinder assembly fixedly mounted on a gearbox 1, such as... Figure 1 As shown, taking three cylinder assemblies with the same internal structure as an example, the three cylinder assemblies are the first cylinder 29, the second cylinder 30 and the third cylinder 31.

[0041] like Figure 3As shown, the gearbox 1 is equipped with a shift shaft 26, a shift fork 27, and a meshing sleeve 28. The end of the shift shaft 26 is provided with a recessed groove. The internal structure of the gearbox 1 and how to use the meshing sleeve 28 for shifting are prior art and will not be described in detail here. Figure 3 The gearbox 1 is only used as an illustration to aid understanding.

[0042] Three shift paddles 3 are slidably installed inside the upper cover 2. Specifically, multiple sliding shafts 24 are fixedly installed inside the upper cover 2. The shift paddles 3 are slidably installed on the surface of the sliding shafts 24. Two return springs 25 are sleeved on the surface of the sliding shafts 24, and the two return springs 25 respectively abut against both sides of the shift paddle 3. The bottom end of the shift paddle 3 extends into the gearbox 1, and the bottom end of the shift paddle 3 is movably inserted into the recessed groove of the shift shaft 26. Three cylinder assemblies are fixedly installed on the upper side of the upper cover 2. The telescopic ends of each cylinder assembly push and pull each shift paddle 3 to move left and right. Each shift paddle 3 controls the engagement sleeve 28 to be in three different positions: neutral, high gear, and low gear. The first cylinder 29, the second cylinder 30, and the third cylinder 31 correspond to the first gear area, the second gear area, and the third gear area, respectively. See Figure 4 .

[0043] The following is a detailed explanation using the example of the first cylinder 29 controlling the shifting of the first gear area.

[0044] refer to Figure 5 The cylinder assembly includes a cylinder body 4. The cylinder body 4 has a first stepped cavity 5 and a second stepped cavity 6 inside. A first piston 7 is slidably installed in the first stepped cavity 5, which divides the first stepped cavity 5 into two chambers, left and right. A second piston 8 is slidably installed in the second stepped cavity 6. A first air injection hole 9, a second air injection hole 10 and a third air injection hole 11 are respectively opened on the surface of the cylinder body 4. The first air injection hole 9 and the second air injection hole 10 are respectively connected to the two chambers on both sides of the first piston 7, and the third air injection hole 11 is connected to the second stepped cavity 6.

[0045] A drive shaft 12 is slidably mounted inside the cylinder 4. The first piston 7 is connected to the end of the drive shaft 12 via a connecting sleeve 13. The end of the drive shaft 12 away from the first piston 7 extends into the upper cover 2 and is fixedly connected to the shift knob 3.

[0046] Multiple Hall sensors 14 are fixedly installed on the upper surface of the cover 2. The multiple Hall sensors 14 are arranged one by one above each shift knob 3. The function of the Hall sensors 14 is to detect whether the shift knob 3 is in the neutral position.

[0047] refer to Figure 3 , Figure 5When compressed air is injected into the first stepped cavity 5 through the first air injection hole 9, the air pushes the first piston 7 to move to the right, that is, the shift head 3 drives the engagement sleeve 28 to the low gear position, continuously inputting compressed air to achieve low gear positioning.

[0048] When compressed air is injected into the first stepped cavity 5 through the second air injection hole 10, the air pushes the first piston 7 to move to the left, that is, the shift head 3 drives the engagement sleeve 28 to the high gear position, continuously inputting compressed air to achieve high gear positioning.

[0049] When compressed air is injected through the third air injection hole 11, the second piston 8 moves to the left to the left end of the second stepped cavity 6. Then, compressed air is injected into the first air injection hole 9, causing the first piston 7 to move to the right and press against the second piston 8. Under the combined action of the two return springs 25, the shift knob 3 drives the engagement sleeve 28 to the neutral position, continuously inputting compressed air to achieve neutral positioning.

[0050] This pneumatic gear shifting device, through the setting of a cylinder assembly that can be positioned in three gears, can drive the shift head 3 to switch between high gear, neutral and low gear, meet the requirement of controlling the left and right sliding of the engagement sleeve 28. Moreover, multiple sets of cylinder assemblies control the independent operation of each shift head 3, eliminating the need for a gear selection cylinder group, simplifying the overall structure of the gear shifting mechanism, and is particularly suitable for use in tractor gearboxes with a large number of gears, reducing their size, lowering the failure rate, and providing convenience for later use, maintenance and debugging.

[0051] The above solution uses continuous compressed air for three-level positioning. However, if the cylinder assembly extends and retracts too quickly or the pressure is too high, it can easily lead to gear grinding.

[0052] In this embodiment, the connecting sleeve 13 is fixedly connected to the end of the first piston 7. A liquid storage cavity is provided inside the connecting sleeve 13. The drive shaft 12 slides through the connecting sleeve 13 and through the liquid storage cavity. A partition plate 15 is slidably installed inside the liquid storage cavity. The partition plate 15 is fixedly installed on the surface of the drive shaft 12. A communication port 16 is provided on the surface of the partition plate 15 (see reference). Figure 9 The separator 15 divides the liquid storage chamber into two liquid storage chambers, which contain a flowing medium (such as hydraulic oil). The flowing medium can circulate between the two liquid storage chambers through the connecting port 16.

[0053] The shift lever 3 is driven by the cylinder assembly to move left and right to switch gears. Since the connecting sleeve 13 contains a flowing medium, the separator 15 and the connecting sleeve 13 move relative to each other. The flowing medium can convect in the two liquid storage chambers in the connecting sleeve 13 through the connecting port 16, which can absorb the instantaneous impact force of the cylinder assembly. At the same time, it delays the meshing of the main and driven gears in the gearbox 1, so that the linear velocity of the tooth tip of the main and driven gears is closer, making it easier to mesh and reducing the occurrence of tooth knocking. The shifting is smoother, and the impact and vibration during shifting are reduced. At the appropriate shifting speed, the driving comfort is improved.

[0054] It should be noted that the shifting speed is determined by the convection velocity of the flowing medium, which is related to the size of the connecting port 16. During the manufacturing process of the separator plate 15, the size of the connecting port 16 is determined, and the convection velocity of the flowing medium in the connecting sleeve 13 can be set within a certain range.

[0055] In this embodiment, a first inlet hole 17 and a second inlet hole 18 are respectively provided on both sides of the partition disk 15. A first plunger 19 and a second plunger 20 are respectively fixedly installed inside the connecting sleeve 13. When the drive shaft 12 drives the partition disk 15 to move left and right, the first plunger 19 can be slidably inserted into the first inlet hole 17, and the second plunger 20 can be slidably inserted into the second inlet hole 18.

[0056] The surface of the drive shaft 12 is provided with two sets of sliding holes, and the interior of the drive shaft 12 is provided with two independent flow channel holes. The two sets of sliding holes are connected to the first inlet hole 17 and the second inlet hole 18 through the flow channel holes respectively. The first positioning pin 21 and the second positioning pin 22 are slidably installed in the two sets of sliding holes respectively. The cylinder body 4 is provided with two annular grooves 32. The first positioning pin 21 and the second positioning pin 22 can slide into the two annular grooves 32 respectively when they extend and retract.

[0057] When shifting into neutral, as Figure 6 As shown;

[0058] When shifting into a lower gear, such as Figure 7 As shown, after the first plunger 19 is inserted into the first inlet hole 17, it squeezes the flowing medium from the flow channel hole in the drive shaft 12 to the second positioning pin 22, pushing the second positioning pin 22 out and into the annular groove 32 to lock the gear position. When the connecting sleeve 13 moves to the left, the first plunger 19 is pulled out from the first inlet hole 17, forming a negative pressure, which causes the second positioning pin 22 to retract into the drive shaft 12, thus automatically unlocking the gear position.

[0059] When shifting into a higher gear, such as Figure 8As shown, after the second plunger 20 is inserted into the second inlet hole 18, it squeezes the flowing medium from the flow channel hole in the drive shaft 12 to the first positioning pin 21, pushing the first positioning pin 21 out and locking it into the annular groove 32 to lock the gear position. When the connecting sleeve 13 moves to the right, the second plunger 20 is pulled out from the first inlet hole 17, forming a negative pressure, which causes the first positioning pin 21 to retract into the drive shaft 12, thus automatically unlocking the gear position.

[0060] This pneumatic gear shifting device, through the setting of a connecting sleeve 13, and the setting of a first positioning pin 21 and a second positioning pin 22 on the surface of the transmission shaft 12, the first piston 7 is connected to the end of the transmission shaft 12 through the connecting sleeve 13. The transmission shaft 12 drives the partition plate 15 to move left and right within the connecting sleeve 13, which can control the extension and retraction of the first positioning pin 21 and the second positioning pin 22. The first positioning pin 21 or the second positioning pin 22 is inserted into the annular groove 32, which can lock the transmission shaft 12 in high and low gear positions, and prevent the engagement sleeve 28 from sliding accidentally, thereby achieving the effect of preventing gear skipping. It does not require continuous input of compressed air to maintain high and low gears, reducing the requirements for the airtightness of the cylinder assembly.

[0061] Example 2

[0062] Reference Figure 1-9 Unlike Embodiment 1, the inner wall of the cylinder 4 is fitted with two electrode plates 23, which are respectively arranged on the upper and lower sides of the connecting sleeve 13, and the flowing medium is electrorheological fluid.

[0063] During tractor operation, gear shifting is frequent, causing the piston seals in the cylinder assembly to wear out quickly or age rapidly. This can easily lead to air leakage between the high and low pressure chambers of the cylinder, resulting in a decrease in the response accuracy of the cylinder assembly. Therefore, it is not advisable to directly control the shifting speed and prevent gear slippage through the cylinder assembly. Otherwise, the manufacturing cost of the cylinder assembly will be high, the failure rate will be high, and subsequent maintenance will be troublesome.

[0064] In this pneumatic gear shifting device, the fluid medium flowing inside the connecting sleeve 13 is an electrorheological fluid. The electrode plates 23 on the upper and lower sides of the connecting sleeve 13 provide a changing electric field for the electrorheological fluid, so that the viscosity of the electrorheological fluid changes with the change of the electric field strength. That is, by changing the electric field strength, the convection velocity of the fluid medium can be controlled, and the shifting speed can be adjusted. Different drivers can adjust the shifting speed according to their own driving habits to meet the shifting needs under different working conditions. This design changes the traditional shifting control method, eliminating the need to control the shifting speed by changing the extension and retraction speed of the cylinder assembly.

[0065] Meanwhile, by inserting the first positioning pin 21 or the second positioning pin 22 into the annular groove 32, the transmission shaft 12 can be locked in high and low gear positions, which can prevent the engagement sleeve 28 from sliding accidentally, thereby achieving the effect of preventing gear skipping.

[0066] In summary, this pneumatic gear shifting device eliminates the need to directly control the shifting speed and prevent gear slippage through the cylinder assembly. The cylinder assembly only provides the force for the extension and retraction action, reducing the precision requirements of the cylinder assembly, decreasing the frequency and burden of later maintenance, extending its service life, and making it more reliable in use.

[0067] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pneumatically controlled gear shifting device for a tractor, comprising a top cover (2), a shift paddle (3), and a cylinder assembly fixedly mounted on a gearbox (1), characterized in that: Multiple shift paddles (3) are slidably installed inside the upper cover (2). The bottom end of the shift paddles (3) extends into the gearbox (1). Multiple cylinder assemblies are fixedly installed on the upper side of the upper cover (2). The shift paddles (3) are pushed and pulled left and right by the telescopic ends of each cylinder assembly. The cylinder assembly includes a cylinder body (4), and the cylinder body (4) has a first stepped cavity (5) and a second stepped cavity (6) inside. A first piston (7) is slidably installed in the first stepped cavity (5), and the first piston (7) divides the first stepped cavity (5) into two chambers on the left and right. A second piston (8) is slidably installed in the second stepped cavity (6). A first air injection hole (9), a second air injection hole (10) and a third air injection hole (11) are respectively opened on the surface of the cylinder body (4). The first air injection hole (9) and the second air injection hole (10) are respectively connected to the two chambers on both sides of the first piston (7), and the third air injection hole (11) is connected to the second stepped cavity (6). A drive shaft (12) is slidably installed inside the cylinder body (4). The first piston (7) is connected to the end of the drive shaft (12) through the connecting sleeve (13). The end of the drive shaft (12) away from the first piston (7) extends into the upper cover (2) and is fixedly connected to the shift lever (3). The connecting sleeve (13) is fixedly connected to the end of the first piston (7). A liquid storage cavity is provided inside the connecting sleeve (13). The drive shaft (12) slides through the connecting sleeve (13) and through the liquid storage cavity. A partition plate (15) is slidably installed inside the liquid storage cavity. The partition plate (15) is fixedly installed on the surface of the drive shaft (12). The surface of the partition plate (15) is provided with a communication port (16). The partition plate (15) divides the liquid storage chamber into two liquid storage chambers, which are filled with a flowing medium. The flowing medium can flow between the two liquid storage chambers through the communication port (16). The partition plate (15) has a first inlet hole (17) and a second inlet hole (18) on both sides respectively. The first plunger (19) and the second plunger (20) are fixedly installed inside the connecting sleeve (13). When the drive shaft (12) drives the partition plate (15) to move left and right, the first plunger (19) can slide into the first inlet hole (17) and the second plunger (20) can slide into the second inlet hole (18).

2. The pneumatic gear shifting device for a tractor according to claim 1, characterized in that: Multiple Hall sensors (14) are fixedly installed on the upper surface of the cover (2), and the multiple Hall sensors (14) are arranged one by one above each shift knob (3).

3. A tractor pneumatic gear shifting device according to claim 2, characterized in that: The drive shaft (12) has two sets of sliding holes on its surface and two independent flow channel holes inside. The two sets of sliding holes are connected to the first inlet hole (17) and the second inlet hole (18) through the flow channel holes respectively. The first positioning pin (21) and the second positioning pin (22) are slidably installed in the two sets of sliding holes respectively. The cylinder (4) has two annular grooves (32). The first positioning pin (21) and the second positioning pin (22) can slide into the two annular grooves (32) respectively when they extend and retract.

4. A tractor pneumatic gear shifting device according to claim 3, characterized in that: The inner wall of the cylinder (4) is fitted with two electrode plates (23), which are respectively arranged on the upper and lower sides of the connecting sleeve (13), and the flowing medium is electrorheological fluid.

5. A tractor pneumatic gear shifting device according to claim 4, characterized in that: Multiple sliding shafts (24) are fixedly installed inside the upper cover (2). The shift lever (3) is slidably installed on the surface of the sliding shaft (24). Two return springs (25) are sleeved on the surface of the sliding shaft (24). The two return springs (25) abut against the two sides of the shift lever (3) respectively.

6. A tractor pneumatic gear shifting device according to any one of claims 1-5, characterized in that: The gearbox (1) is provided with a shift shaft (26), a shift fork (27) and a meshing sleeve (28). The end of the shift shaft (26) is provided with a recessed groove, and the bottom end of the shift head (3) is movably inserted into the recessed groove.

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