A transmission box with crawler gear for small crawler tractor

Abstract

A transmission box with a crawler gear for a small crawler tractor relates to the technical field of tractors. The present invention realizes 9 forward gears and 3 reverse gears through the combination of a main speed change transmission mechanism, an auxiliary speed change transmission mechanism, a crawler gear transmission mechanism and a central transmission mechanism, and can meet the requirements of various operating conditions of the small crawler tractor on vehicle speed. The present invention has a clear transmission route, a simple structure, and a low manufacturing cost. The power of the small crawler tractor engine can be transmitted to the small crawler tractor walking device and the required agricultural implements, and is suitable for large-scale promotion and application.

Description

Technical Field

[0001] The invention relates to the technical field of tractors, in particular to a transmission box, and specifically to a transmission box with a crawler gear for a small crawler tractor. Background Art

[0002] As is known, among the small crawler tractor products in my country, most of the transmission boxes are modified and designed based on the transmission boxes of medium and large crawler tractors, and basically do not have the crawler gear function, and the internal structure of the transmission box has not changed significantly. Such a design result will cause the transmission box structure to be complicated and not suitable for the needs of orchard gardening and crawling operations.

[0003] With the urgent need for the development of orchard horticulture and crawling operations, the development and production of small crawler tractors has become more urgent. Therefore, it is urgent to develop a transmission box that is simple and compact in structure and can adapt to the needs of orchard horticulture and crawling operations, give full play to the strong adaptability of small crawler tractors, better meet the needs of orchard horticulture and crawling operations, and be easy to operate and use, so as to realize the diversity of small crawler tractor operation modes. Summary of the invention

[0004] In order to overcome the shortcomings of the background technology, the present invention provides a transmission box with a crawler gear for a small crawler tractor. The present invention realizes 9 forward gears and 3 reverse gears through a combination of a main speed transmission mechanism, a sub-speed transmission mechanism, a crawler gear transmission mechanism and a central transmission mechanism, which can meet the vehicle speed requirements of various operating conditions of the small crawler tractor.

[0005] In order to achieve the above-mentioned purpose of the invention, the present invention adopts the following technical solution:

[0006] A transmission case with a crawler gear for a small crawler tractor comprises a main speed transmission mechanism, an auxiliary speed transmission mechanism, a crawler gear transmission mechanism, a central transmission mechanism and a transmission case housing, wherein the main speed transmission mechanism, the auxiliary speed transmission mechanism, the crawler gear transmission mechanism and the central transmission mechanism are arranged in sequence from left to right in the transmission case housing, the left end of the main speed driving shaft in the main speed transmission mechanism is connected to the engine, the right end of the main speed driven shaft in the main speed transmission mechanism is connected to the power input end of the auxiliary speed transmission mechanism, the auxiliary speed driven shaft in the auxiliary speed transmission mechanism is respectively connected to the power input end of the crawler gear transmission mechanism and the power input end of the central transmission mechanism, and the two ends of the power output end of the central transmission mechanism are respectively connected to a walking mechanism to form the transmission case with a crawler gear for a small crawler tractor.

[0007] The transmission box with crawler gear for the small crawler tractor, the main speed transmission mechanism includes a main speed driving shaft, I-II gear double gears, a reverse gear driven gear, III-reverse gear double gears, a main speed driven shaft, I gear driven gear, II gear driven gear and III gear driven gear, the main speed driving shaft is arranged on the upper part of the transmission box housing, and the I-II gear double gears and III-reverse gear double gears are arranged in sequence from left to right on the outer edge surface of the main speed driving shaft, and the main speed driven shaft is arranged below the main speed driving shaft, and the I gear driven gear, II gear driven gear, reverse gear driven gear and III gear driven gear are arranged in sequence from left to right on the outer edge surface of the main speed driven shaft, and the right end of the main speed driven shaft is connected to the auxiliary speed constant meshing driving gear.

[0008] The transmission box with crawler gear for the small crawler tractor is arranged in parallel with the main speed change driven shaft and at intervals.

[0009] The transmission box with crawler gear for the small crawler tractor has a reverse idler shaft below the reverse driven gear, a reverse idler wheel is provided on the outer edge of the reverse idler shaft, and the reverse idler wheel is respectively meshed with the reverse driven gear and the III-reverse double gear.

[0010] The transmission box with crawler gear for the small crawler tractor, the auxiliary speed transmission mechanism includes an auxiliary speed constant meshing driven-low gear driving double gear, an auxiliary speed constant meshing driving gear, a meshing sleeve, a low gear driven-crawler gear first-level driving double gear and an auxiliary speed driven shaft, the left end of the auxiliary speed constant meshing driving gear is connected to the end of the main speed driven shaft, the auxiliary speed constant meshing driven-low gear driving double gear is sleeved on the outer edge surface of the main speed driving shaft, and a meshing sleeve that can slide left and right is arranged at intervals on the right end of the auxiliary speed constant meshing driving gear, the meshing sleeve is connected to the auxiliary speed driven shaft, and a low gear driven-crawler gear first-level driving double gear is sleeved on the outer edge surface of the left end of the auxiliary speed driven shaft, and the crawler gear first-level driving gear at the right end of the low gear driven-crawler gear first-level driving double gear is meshed with the crawler gear first-level driven gear at the left end of the crawler gear first-level driven-crawler gear second-level driving double gear.

[0011] The transmission box with crawler gear for the small crawler tractor has axes of the auxiliary speed-changing driven shaft and the main speed-changing driven shaft on the same straight line.

[0012] The small crawler tractor is provided with a transmission box with a crawler gear, wherein the crawler gear transmission mechanism comprises a crawler gear primary driven-crawler gear secondary active double gear and a crawler gear secondary driven gear, wherein the crawler gear primary driven-crawler gear secondary active double gear is loosely sleeved on the outer edge surface of the main speed change driving shaft, and the crawler gear secondary driven gear is arranged on the outer edge surface of the auxiliary speed change driven shaft, and the crawler gear secondary driven gear can be selected to mesh with or idle with the crawler gear secondary active gear at the right end of the crawler gear primary driven-crawler gear secondary active double gear.

[0013] The small crawler tractor has a transmission box with a crawler gear, and the central transmission mechanism includes a central transmission output shaft, a central transmission small bevel gear and a central transmission large bevel gear. The central transmission small bevel gear is connected to the right end of the auxiliary speed change driven shaft, the central transmission small bevel gear is meshed with the central transmission large bevel gear, and the central transmission large bevel gear is fixed on the outer edge surface of the central transmission output shaft. The central transmission output shaft is set at 90 degrees to the auxiliary speed change driven shaft, and the two ends of the central transmission output shaft are respectively connected to the walking mechanism.

[0014] The transmission box with crawler gear for the small crawler tractor is provided with a central transmission pinion gear and a right end of the auxiliary speed change driven shaft as an integral structure.

[0015] The small crawler tractor uses a transmission box with a crawler gear, and the right end of the main speed change driving shaft is connected to a power output mechanism.

[0016] By adopting the above technical solution, the present invention has the following advantages:

[0017] The present invention realizes 9 forward gears and 3 reverse gears through the combination of the main speed transmission mechanism, the auxiliary speed transmission mechanism, the crawler gear transmission mechanism and the central transmission mechanism, and can meet the vehicle speed requirements of various operating conditions of the small crawler tractor. The present invention has a clear transmission route, a simple structure, and a low manufacturing cost. The power of the small crawler tractor engine can be transmitted to the small crawler tractor walking device and the required agricultural implements, and is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of the present invention;

[0019] In the figure: 1. main speed driving shaft; 2. I-II gear double gear; 3. reverse gear driven gear; 4. III-reverse gear double gear; 5. auxiliary speed constant meshing driven-low gear driving double gear; 6. crawler gear first driven-crawler gear second driving double gear; 7. central transmission output shaft; 8. power output mechanism; 9. main speed driven shaft; 10. I gear driven gear; 11. II gear driven gear; 12. reverse gear idler; 13. reverse gear idler shaft; 14. III gear driven gear; 15. auxiliary speed constant meshing driving gear; 16. meshing sleeve; 17. low gear driven-crawler gear first driving double gear; 18. crawler gear second driven gear; 19. auxiliary speed driven shaft; 20. central transmission small bevel gear; 21. central transmission large bevel gear; 22. transmission box housing. DETAILED DESCRIPTION

[0020] The present invention can be explained in more detail by the following examples, but the present invention is not limited to the following examples;

[0021] First of all, it should be explained that the directions or positional relationships indicated by “upper”, “lower”, “front”, “back”, “left”, “right”, “top”, “bottom”, “inside” and “outside” when describing the structure of the present invention are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of description and simplified description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0022] Combined with Figure 1 The transmission box with a crawler gear for a small crawler tractor comprises a main speed transmission mechanism, an auxiliary speed transmission mechanism, a crawler gear transmission mechanism, a central transmission mechanism and a transmission box housing 22. The main speed transmission mechanism, the auxiliary speed transmission mechanism, the crawler gear transmission mechanism and the central transmission mechanism are arranged in the transmission box housing 22 from left to right. The left end of the main speed driving shaft 1 in the main speed transmission mechanism is connected to the engine, the right end of the main speed driving shaft 1 is connected to the power output mechanism 8, the right end of the main speed driven shaft 9 in the main speed transmission mechanism is connected to the power input end of the auxiliary speed transmission mechanism, the auxiliary speed driven shaft 19 in the auxiliary speed transmission mechanism is respectively connected to the power input end of the crawler gear transmission mechanism and the power input end of the central transmission mechanism, and the two ends of the power output end of the central transmission mechanism are respectively connected to the walking mechanism to form the transmission box with a crawler gear for the small crawler tractor.

[0023] The main speed transmission mechanism comprises a main speed driving shaft 1, a I-II gear double gear 2, a reverse gear driven gear 3, a III-reverse gear double gear 4, a main speed driven shaft 9, an I gear driven gear 10, a II gear driven gear 11 and a III gear driven gear 14. The main speed driving shaft 1 is arranged on the upper part of the transmission case housing 22. The I-II gear double gear 2 and the III-reverse gear double gear 4 are arranged in sequence from left to right on the outer edge surface of the main speed driving shaft 1. A main speed driven shaft 9 is arranged below the main speed driving shaft 1. The main speed driving shaft 1 Parallel to the main speed driven shaft 9 and arranged at intervals, on the outer edge surface of the main speed driven shaft 9, a I gear driven gear 10, a II gear driven gear 11, a reverse gear driven gear 3 and a III gear driven gear 14 are arranged in sequence from left to right, and the right end of the main speed driven shaft 9 is connected to a secondary speed constantly meshing driving gear 15. In specific implementation, a reverse idler gear shaft 13 is provided below the reverse gear driven gear 3, and a reverse idler gear 12 is provided on the outer edge of the reverse idler gear shaft 13. The reverse idler gear 12 is meshed with the reverse driven gear 3 and the III-reverse double gear 4 respectively.

[0024] The auxiliary speed transmission mechanism includes an auxiliary speed constant mesh driven-low gear driving double gear 5, an auxiliary speed constant mesh driving gear 15, a meshing sleeve 16, a low gear driven-crawling gear first-stage driving double gear 17 and an auxiliary speed driven shaft 19. The left end of the auxiliary speed constant mesh driving gear 15 is connected to the end of the main speed driven shaft 9. The auxiliary speed constant mesh driven-low gear driving double gear 5 is loosely sleeved on the outer edge surface of the main speed driving shaft 1. The meshing sleeve 16 is spaced apart at the right end of the auxiliary speed constant mesh driving gear 15. The meshing sleeve 16 can slide left and right, and the meshing sleeve 16 is connected to the auxiliary speed-change driven shaft 19. In specific implementation, the axes of the auxiliary speed-change driven shaft 19 and the main speed-change driven shaft 9 are in the same straight line, and a low gear driven-crawler gear first-stage active double gear 17 is sleeved on the outer edge surface of the left end of the auxiliary speed-change driven shaft 19. The crawler gear first-stage active gear at the right end of the low gear driven-crawler gear first-stage active double gear 17 is meshed with the crawler gear first-stage driven gear at the left end of the crawler gear first-stage driven-crawler gear second-stage active double gear 6.

[0025] The crawler gear transmission mechanism includes a crawler gear first driven-crawler gear second active double gear 6 and a crawler gear second driven gear 18. The crawler gear first driven-crawler gear second active double gear 6 is loosely mounted on the outer edge surface of the main speed change driving shaft 1, and the crawler gear second driven gear 18 is arranged on the outer edge surface of the auxiliary speed change driven shaft 19. The crawler gear second driven gear 18 can be selected to mesh with the crawler gear second active gear at the right end of the crawler gear first driven-crawler gear second active double gear 6 or idle.

[0026] The central transmission mechanism includes a central transmission output shaft 7, a central transmission small bevel gear 20 and a central transmission large bevel gear 21. The central transmission small bevel gear 20 is arranged at the right end of the auxiliary speed-changing driven shaft 19. During specific implementation, the central transmission small bevel gear 20 and the right end of the auxiliary speed-changing driven shaft 19 can be made into a whole. The central transmission small bevel gear 20 is meshed with the central transmission large bevel gear 21. The central transmission large bevel gear 21 is fixed on the outer edge surface of the central transmission output shaft 7. The central transmission output shaft 7 is arranged at 90 degrees to the auxiliary speed-changing driven shaft 19. The two ends of the central transmission output shaft 7 are respectively connected to the walking mechanism.

[0027] In the specific implementation of the present invention, the main speed transmission mechanism, the auxiliary speed transmission mechanism, the crawler gear transmission mechanism, and the central transmission mechanism are distributed in the transmission box housing 22 in sequence, wherein the left end of the main speed driving shaft 1 in the main speed transmission mechanism is connected to the engine of the small crawler tractor, and the two sides of the central transmission mechanism are respectively connected to the walking mechanism of the small crawler tractor.

[0028] A main speed transmission mechanism is respectively installed with a main speed driving shaft 1, a main speed driven shaft 9 and a reverse gear idler shaft 13, a sub-speed transmission mechanism is installed with a sub-speed driven shaft 19, and there is no separate shaft in the crawler gear transmission mechanism. A central transmission output shaft 7 is installed in the central transmission mechanism. In specific implementation, a power output driving shaft and a power output shaft can be installed in the power output mechanism 8. Since the power output mechanism 8 is not the focus of protection of the present invention, it is not specifically described; wherein the main speed driving shaft 1 is shared by the main speed transmission mechanism, the sub-speed transmission mechanism and the crawler gear transmission mechanism, the axes of the main speed driven shaft 9 and the sub-speed driven shaft 19 are on the same straight line, the axes of the main speed driving shaft 1, the main speed driven shaft 9 and the reverse gear idler shaft 13 are parallel to each other, the axis of the central transmission output shaft 7 and the axis of the sub-speed driven shaft 19 are perpendicular to each other, and the power output driving shaft in the power output mechanism 8 is on the same straight line with the axis of the main speed driving shaft 1.

[0029] In the specific implementation, in the main speed transmission mechanism, the main speed driving shaft 1 is equipped with a I-II gear double gear 2 and a III-reverse gear double gear 4 through a spline, the main speed driven shaft 9 is equipped with an I gear driven gear 10, a II gear driven gear 11, a III gear driven gear 14 and a reverse gear driven gear 3 through a spline, and a reverse idler gear 12 is installed on the reverse idler gear shaft 13. The reverse idler gear 12 can mesh with the III-reverse gear double gear 4 and the reverse gear driven gear 3 at the same time, and the main speed driven shaft 9 and the auxiliary speed constantly meshing driving gear 15 are set as an integral structure. The I-II gear double gear 2 and the III-reverse gear double gear 4 on the main speed driving shaft 1 can slide left and right along the axial direction of the main speed driving shaft 1, and respectively select to mesh with the gears on the adjacent main speed driven shaft 9.

[0030] In the auxiliary speed transmission mechanism, the auxiliary speed constant meshing driving gear 15 and the main speed driven shaft 9 are set as an integrated structure, the left end of the auxiliary speed constant meshing driven-low gear driving double gear 5 is the auxiliary speed constant meshing driven gear, and the right end is the low gear driving gear, and the meshing sleeve 16 is installed on the auxiliary speed driven shaft 19 through a spline, the left end of the low gear driven-crawler gear first-stage driving double gear 17 is the low gear driven gear, and the right end is the crawler gear first-stage driving gear, the low gear driven-crawler gear first-stage driving double gear 17 is loosely sleeved on the auxiliary speed driven shaft 19 and can rotate independently, and the meshing sleeve 16 can slide left and right along the axial direction to respectively select to mesh with the connecting teeth on the adjacent gears.

[0031] There is no separate shaft in the crawler gear transmission mechanism. The right end of the low gear driven-crawler gear first-stage active double gear 17 is the crawler gear first-stage active gear, and the left end is the low gear driven gear. The low gear driven-crawler gear first-stage active double gear 17 is loosely sleeved on the auxiliary speed change driven shaft 19 and can rotate independently. The left end of the crawler gear first-stage driven-crawler gear second-stage active double gear 6 is the crawler gear first-stage driven gear, and the right end is the crawler gear second-stage active gear. The crawler gear first-stage driven-crawler gear second-stage active double gear 6 is loosely sleeved on the main speed change driving shaft 1 and can rotate independently. The crawler gear second-stage driven gear 18 is installed on the auxiliary speed change driven shaft 19 through a spline. The crawler gear second-stage driven gear 18 can slide left and right along the axial direction, and choose to mesh with the crawler gear first-stage driven-crawler gear second-stage active double gear 6 or idle.

[0032] In the central transmission mechanism, the central transmission small bevel gear 20 and the central transmission large bevel gear 21 are in a constant meshing state. The central transmission small bevel gear 20 is installed on the auxiliary speed-change driven shaft 19 through a spline, or the central transmission small bevel gear 20 and the auxiliary speed-change driven shaft 19 are set as one body, that is, they are processed into an integrated structure. The central transmission large bevel gear 21 is fixedly installed on the central transmission output shaft 7. The two ends of the central transmission output shaft 7 are respectively connected to the walking mechanism of the small crawler tractor to realize the walking of the small crawler tractor.

[0033] In specific implementation, the power of the small crawler tractor engine is divided into two output paths, as follows:

[0034] The first route: the engine of the small crawler tractor is transmitted to the power output mechanism 8 through the main transmission driving shaft 1, driving the power output shaft of the small crawler tractor.

[0035] Second route: The engine of the small crawler tractor transmits power to the main transmission mechanism through the main transmission shaft 1. The main transmission mechanism can realize 3 forward gears and 1 reverse gear according to the position state of the I-II gear double gear 2 and the III-reverse gear double gear 4 installed on the main transmission shaft 1 after sliding left and right. The power transmission path of each gear is as follows:

[0036] I gear: I-II gear double gear 2 slides to the right and meshes with I gear driven gear 10, while III-reverse gear double gear 4 does not mesh with any gear. The power is from the main transmission driving shaft 1 → I-II gear double gear 2 → I gear driven gear 10 → main transmission driven shaft 9.

[0037] II gear: I-II gear double gear 2 slides to the left and meshes with II gear driven gear 11, while III-reverse gear double gear 4 does not mesh with any gear. The power is from the main transmission driving shaft 1 → I-II gear double gear 2 → II gear driven gear 11 → main transmission driven shaft 9.

[0038] Gear III: The III-reverse gear double gear 4 slides to the right and meshes with the gear III driven gear 14, while the I-II gear double gear 2 does not mesh with any gear. The power is from the main transmission driving shaft 1 → the III-reverse gear double gear 4 → the gear III driven gear 14 → the main transmission driven shaft 9.

[0039] Reverse gear: III-reverse gear double gear 4 slides to the left and meshes with reverse gear driven gear 3, which meshes with reverse idler gear 12 on reverse idler gear shaft 13, while I-II gear double gear 2 does not mesh with any gear. Power is from main transmission driving shaft 1 → III-reverse gear double gear 4 → reverse gear driven gear 3 → reverse idler gear 12 → main transmission driven shaft 9.

[0040] Then the power is transmitted from the main speed driven shaft 9 to the auxiliary speed transmission mechanism. The auxiliary speed constant meshing driving gear 15 and the main speed driven shaft 9 are set as an integrated structure. The auxiliary speed transmission mechanism can realize the conversion of two gears according to the position state of the meshing sleeve 16 on the auxiliary speed driven shaft 19 after sliding left and right. The power transmission path of each gear is as follows:

[0041] High gear: The meshing sleeve 16 on the auxiliary speed driven shaft 19 slides to the left and meshes with the connecting teeth on the auxiliary speed constant meshing driving gear 15, and at the same time, the crawler gear secondary driven gear 18 in the crawler gear transmission mechanism does not mesh with the crawler gear secondary driving gear at the right end of the crawler gear primary driven-crawler gear secondary driving double gear 6. The power is from the main speed driven shaft 9 → the meshing sleeve 16 → the auxiliary speed driven shaft 19.

[0042] Low gear: the meshing sleeve 16 on the auxiliary speed driven shaft 19 slides to the right and meshes with the connecting teeth on the low gear driven gear at the left end of the low gear driven-crawler gear first-stage active double gear 17. At the same time, the crawler gear second-stage driven gear 18 in the crawler gear transmission mechanism does not mesh with the crawler gear second-stage active gear at the right end of the crawler gear first-stage driven-crawler gear second-stage active double gear 6. The power is transmitted from the main speed driven shaft 9 → auxiliary speed constant meshing driving gear 15 → auxiliary speed constant meshing driven gear at the left end of the auxiliary speed constant meshing driven-low gear active double gear 5 → the low gear driving gear at the right end of the auxiliary speed constant meshing driven-low gear active double gear 5 → the low gear driven gear at the left end of the low gear driven-crawler gear first-stage active double gear 17 → meshing sleeve 16 → auxiliary speed driven shaft 19.

[0043] The power is transmitted from the auxiliary speed change driven shaft 19 to the crawler gear transmission mechanism. The crawler gear transmission mechanism can realize whether the crawler gear is engaged or not according to the position state of the crawler gear secondary driven gear 18 after sliding left and right. The power transmission route of the crawler gear is as follows:

[0044] The secondary crawler gear driven gear 18 slides to the right and meshes with the secondary crawler gear driving gear at the right end of the primary crawler gear driven-secondary crawler gear driving double gear 6. At the same time, the meshing sleeve 16 on the auxiliary speed change driven shaft 19 is in a middle position, neither meshing with the connecting teeth on the auxiliary speed change normally meshing driving gear 15 nor meshing with the connecting teeth on the low gear driven gear at the left end of the low gear driven-primary crawler gear driving double gear 17. The power is transmitted from the main speed driven shaft 9 → the auxiliary speed constant mesh driving gear 15 → the auxiliary speed constant mesh driven-low gear driving double gear 5 at the left end → the low gear driving gear at the right end of the auxiliary speed constant mesh driven-low gear driving double gear 5 → the low gear driven-crawler gear first-stage driving double gear 17 at the left end → the crawler gear first-stage driving gear at the right end of the low gear driven-crawler gear first-stage driving double gear 17 → the crawler gear first-stage driven-crawler gear second-stage driving double gear 6 at the left end → the crawler gear second-stage driving gear at the right end of the crawler gear second-stage driven gear 18 → the auxiliary speed driven shaft 19.

[0045] The power is transmitted from the auxiliary speed-changing driven shaft 19 to the central transmission mechanism, and the central transmission pinion bevel gear 20 is in constant meshing with the central transmission large bevel gear 21. The power transmission route is as follows: auxiliary speed-changing driven shaft 19 → central transmission pinion bevel gear 20 → central transmission large bevel gear 21 → central transmission output shaft 7 → walking mechanism.

[0046] In summary, the combination of the main speed transmission mechanism, the auxiliary speed transmission mechanism, the crawler gear transmission mechanism and the central transmission mechanism can realize the conversion of 9 forward gears and 3 reverse gears.

[0047] Parts of the present invention not described in detail are prior art.

[0048] The embodiments selected herein for the purpose of disclosing the invention are currently considered to be suitable, but it should be understood that the invention is intended to include all changes and modifications of the embodiments that fall within the scope of the concept and invention.

Claims

1. A transmission box with a crawler gear for a small crawler tractor, comprising a main speed change transmission mechanism, a secondary speed change transmission mechanism, a crawler gear transmission mechanism, a central transmission mechanism and a transmission box housing (22), wherein: The transmission case housing (22) is provided with a main speed transmission mechanism, a sub-speed transmission mechanism, a crawler gear transmission mechanism and a central transmission mechanism in sequence from left to right. The left end of the main speed driving shaft (1) in the main speed transmission mechanism is connected to the engine, the right end of the main speed driven shaft (9) in the main speed transmission mechanism is connected to the power input end of the sub-speed transmission mechanism, the sub-speed driven shaft (19) in the sub-speed transmission mechanism is respectively connected to the power input end of the crawler gear transmission mechanism and the power input end of the central transmission mechanism, and both ends of the power output end of the central transmission mechanism are respectively connected to the walking mechanism to form the transmission case with crawler gear for the small crawler tractor; The main speed transmission mechanism comprises a main speed driving shaft (1), a I-II gear double gear (2), a reverse gear driven gear (3), a III-reverse gear double gear (4), a main speed driven shaft (9), an I gear driven gear (10), a II gear driven gear (11) and a III gear driven gear (14). The main speed driving shaft (1) is arranged on the upper part of the transmission case housing (22), and the outer edge surface of the main speed driving shaft (1) is sequentially arranged from left to right at intervals. A main speed transmission driven shaft (9) is provided below the main speed transmission driving shaft (1); a main speed transmission driven shaft (10), a main speed transmission driven gear (11), a reverse speed transmission driven gear (3) and a main speed transmission driven gear (14) are provided on the outer edge surface of the main speed transmission driven shaft (9) in sequence from left to right; and the right end of the main speed transmission driven shaft (9) is connected to a secondary speed transmission constantly meshing driving gear (15); The auxiliary speed transmission mechanism comprises an auxiliary speed constant mesh driven-low gear driving double gear (5), an auxiliary speed constant mesh driving gear (15), a meshing sleeve (16), a low gear driven-crawling gear first-stage driving double gear (17) and an auxiliary speed driven shaft (19), wherein the left end of the auxiliary speed constant mesh driving gear (15) is connected to the end of the main speed driven shaft (9), the auxiliary speed constant mesh driven-low gear driving double gear (5) is loosely sleeved on the outer edge surface of the main speed driving shaft (1), and the auxiliary speed constant mesh driving gear (15) is loosely sleeved on the outer edge surface of the main speed driven shaft (1). A meshing sleeve (16) capable of sliding left and right is provided at the right end of the meshing driving gear (15). The meshing sleeve (16) is connected to the auxiliary speed change driven shaft (19). A low gear driven-crawler gear first-stage driving double gear (17) is sleeved on the outer edge surface of the left end of the auxiliary speed change driven shaft (19). The crawler gear first-stage driving gear at the right end of the low gear driven-crawler gear first-stage driving double gear (17) is meshed with the crawler gear first-stage driven gear at the left end of the crawler gear first-stage driven-crawler gear second-stage driving double gear (6).

2. The transmission box with crawler gear for a small crawler tractor according to claim 1, characterized in that: The main speed change driving shaft (1) and the main speed change driven shaft (9) are arranged in parallel and at intervals.

3. The transmission box with crawler gear for a small crawler tractor according to claim 1, characterized in that: A reverse idler gear shaft (13) is provided below the reverse gear driven gear (3), a reverse idler gear (12) is provided on the outer edge of the reverse idler gear shaft (13), and the reverse idler gear (12) is respectively meshed with the reverse gear driven gear (3) and the III-reverse double gear (4).

4. The transmission box with crawler gear for a small crawler tractor according to claim 1, characterized in that: The axes of the auxiliary speed-change driven shaft (19) and the main speed-change driven shaft (9) are on the same straight line.

5. The transmission box with crawler gear for a small crawler tractor according to claim 1, characterized in that: The crawler gear transmission mechanism comprises a crawler gear primary driven-crawler gear secondary active double gear (6) and a crawler gear secondary driven gear (18), wherein the crawler gear primary driven-crawler gear secondary active double gear (6) is loosely sleeved on the outer edge surface of the main speed change driving shaft (1), and the crawler gear secondary driven gear (18) is arranged on the outer edge surface of the auxiliary speed change driven shaft (19), and the crawler gear secondary driven gear (18) can be selected to mesh with the crawler gear secondary active gear at the right end of the crawler gear primary driven-crawler gear secondary active double gear (6) or to idle.

6. The transmission box with crawler gear for a small crawler tractor according to claim 1, characterized in that: The central transmission mechanism comprises a central transmission output shaft (7), a central transmission small bevel gear (20) and a central transmission large bevel gear (21); the central transmission small bevel gear (20) is connected to the right end of the auxiliary speed change driven shaft (19); the central transmission small bevel gear (20) is meshed with the central transmission large bevel gear (21); the central transmission large bevel gear (21) is fixed on the outer edge surface of the central transmission output shaft (7); the central transmission output shaft (7) and the auxiliary speed change driven shaft (19) are arranged at 90 degrees; and the two ends of the central transmission output shaft (7) are respectively connected to the walking mechanism.

7. The transmission box with crawler gear for a small crawler tractor according to claim 6, characterized in that: The central transmission bevel gear (20) and the right end of the auxiliary speed change driven shaft (19) are arranged as an integral structure.

8. The transmission box with crawler gear for a small crawler tractor according to claim 1, characterized in that: The right end of the main speed change driving shaft (1) is connected to a power output mechanism (8).

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