CN213064588U

CN213064588U - Hydrostatic gearbox

Info

Publication number: CN213064588U
Application number: CN202021472076.1U
Authority: CN
Inventors: 郭燕; 张逵; 赵继明; 陈利东
Original assignee: Weifang Ruichi Transmission Machinery Co ltd
Current assignee: Weifang Ruichi Transmission Machinery Co ltd
Priority date: 2020-07-23
Filing date: 2020-07-23
Publication date: 2021-04-27
Anticipated expiration: 2030-07-23

Abstract

A high-gear driving gear and a low-gear driving gear are arranged on an input gear shaft, power transmission is achieved through the high-gear driven gear and the low-gear driven gear which are meshed with the high-gear driven gear and the low-gear driven gear respectively, a synchronizer is arranged between the high-gear driven gear and the low-gear driven gear, a shifting fork of the synchronizer is connected with a shifting fork shaft driven by a hydraulic cylinder, hydraulic oil is injected into or pumped out of the hydraulic cylinder to drive the shifting fork shaft and the shifting fork to move, and therefore power of the input gear shaft is transmitted to an output gear shaft through the high-gear driven gear or the low-gear driven gear. The utility model discloses an installation synchronous ware, later recycle hydraulic cylinder and drive the declutch shift shaft and remove, and then the shift fork of control synchronous ware meshes between high-grade driven gear and low-grade driven gear, has realized the function that the not parking was shifted, has reduced intensity of labour, has improved equipment work efficiency.

Description

Hydrostatic gearbox

Technical Field

The utility model relates to a gearbox, specific quiet hydraulic pressure gearbox that says so for engineering machine tool equipment.

Background

In the field of engineering machinery, the schemes for driving the axle to run by the hydraulic motor are gradually increased, and the hydraulic motor and the axle are generally switched at high and low speeds through a gearbox.

However, since the transmission is directly connected to the hydraulic motor, when a gear shift is required, the hydraulic motor will generate a large resisting torque to the transmission, which results in that the rotation speed of the gear to be engaged is quickly reduced to 0, and the gear shift mechanism still has a high rotation speed under the driving of the vehicle running inertia, so as to avoid gear rattling of the gear shift mechanism and the gear, the current hydrostatic transmission usually needs to be stopped and shifted. This results in a reduction in the working efficiency of the equipment and an increase in the labor intensity of the personnel.

In order to solve such problems, the prior art also provides various solutions, such as that described in patent CN206971304U, for shift protection by means of a control system, however, although this patent avoids gear rattling, it still requires a parking operation during shifting. For example, as disclosed in patent CN206971305U, a friction plate is used to replace a shift mechanism, although the shift mechanism can realize shifting during driving, the system is complex, the lubrication and cooling are troublesome, the cost is high, and the friction plate is assembled at the output end, and the friction plate is subjected to a large torque, which accelerates the wear of the friction plate.

SUMMERY OF THE UTILITY MODEL

In order to solve the problem that the hydrostatic gearbox in the current engineering machine tool needs the state of stopping just can shift, the utility model provides a hydrostatic gearbox, this gearbox adopt the synchronous ware to shift, have realized shifting under the state of not stopping, have reduced intensity of labour, have improved equipment work efficiency.

The utility model discloses a solve the technical scheme that above-mentioned technical problem adopted and be: a hydrostatic transmission is provided with an input gear shaft and an output gear shaft, a high-gear driving gear and a low-gear driving gear are arranged on the input gear shaft, the high-gear driving gear and the low-gear driving gear are respectively meshed with a high-gear driven gear and a low-gear driven gear to realize power transmission, a synchronizer is arranged at a position, located between the high-gear driven gear and the low-gear driven gear, on the output gear shaft, a shifting fork of the synchronizer is connected with a shifting fork shaft driven by a hydraulic cylinder, and hydraulic oil is injected into or pumped out of the hydraulic cylinder to drive the shifting fork shaft and the shifting fork to move, so that the power of the input gear shaft is transmitted to the output gear shaft through the high-gear driven gear or the low-gear driven gear.

As an optimized scheme of the hydrostatic transmission, an inner spline hole is formed in one end of the input gear shaft and connected with an outer spline shaft of the motor through the inner spline hole, so that power output by the motor is transmitted to the input gear shaft.

As another optimized scheme of the hydrostatic transmission, one end of the input gear shaft is provided with an internal spline hole, and is connected with an output shaft of a clutch through the internal spline hole, and an internal spline input shaft of the clutch is connected with an external spline shaft of the motor, so that power transmission between the motor and the input gear shaft is controlled through the clutch.

As another optimization scheme of the hydrostatic gearbox, one end of the shifting fork shaft extends into the hydraulic cylinder, a fixed piston driving the shifting fork shaft to synchronously move and a sliding piston moving on the shifting fork shaft are arranged on the part of the shifting fork shaft in the hydraulic cylinder, the edges of the fixed piston and the sliding piston are matched with the inner wall of the hydraulic cylinder, and divides the interior of the hydraulic cylinder into a first oil chamber, a second oil chamber and a third oil chamber along the axial direction of the shifting fork shaft, the wall of the hydraulic cylinder is respectively provided with an L-gear oil port, an H-gear oil port and an N-gear oil port which are respectively communicated with the three oil cavities in a one-to-one correspondence manner, hydraulic oil is respectively injected into or extracted from the three oil cavities through the three oil ports, so that the fixed piston drives the shifting fork shaft to move in a reciprocating manner, and then the synchronizer is combined with the high-gear driven gear or the low-gear driven gear through the shifting fork to transmit power.

As another optimization scheme of the hydrostatic transmission, the L-shift oil port and the N-shift oil port are respectively located at two ends of the shifting fork shaft in the moving direction and are respectively communicated with the first oil cavity and the third oil cavity, and the H-shift oil port is located between the L-shift oil port and the third oil cavity and is communicated with the second oil cavity;

when the L-gear oil port and the N-gear oil port simultaneously feed oil, and the H-gear oil port returns oil, the fixed piston and the sliding piston move oppositely until the fixed piston and the sliding piston touch each other, at the moment, the shifting fork shaft drives the shifting fork of the synchronizer to move, the high-gear driven gear and the low-gear driven gear are both separated from each other and combined, and the gearbox is in a neutral position;

when the oil inlet of the H-gear oil port and the oil inlet of the N-gear oil port are simultaneous, and the oil return of the L-gear oil port is performed, the fixed piston and the sliding piston both move to the limit position towards one side of the L-gear oil port, at the moment, the shifting fork shaft drives the shifting fork of the synchronizer to move, the high-gear driven gear is combined with the synchronizer and the output shaft, and the gearbox is in a high-gear position;

when the L-gear oil port is used for feeding oil, and the H-gear oil port and the N-gear oil port are used for returning oil at the same time, the fixed piston and the sliding piston both move to the limit position towards one side of the N-gear oil port, at the moment, the shifting fork shaft drives the shifting fork of the synchronizer to move, the low-gear driven gear is combined with the synchronizer and the output shaft, and the gearbox is located at the low-gear position.

As another optimized scheme of the hydrostatic transmission, the inner wall of the hydraulic cylinder is in a convex structure formed by connecting a large diameter part and a small diameter part with different diameters, a clamping table is formed at the joint of the large diameter part and the small diameter part, one side of the sliding piston is provided with a thin extension section which extends into the small diameter part, the thin extension section is cylindrical, the inner wall of the sliding piston is matched with the shifting fork shaft to form a second oil cavity, an oil passing channel which is communicated with the second oil cavity and an H-gear oil port is formed between the outer wall of the thin extension section and the inner wall of the hydraulic cylinder, the other side of the sliding piston is provided with a thick extension section which is matched with the large diameter part, the outer wall of the thick extension section is also cylindrical, the inner wall of the thick extension section is matched with the large diameter part, a cavity is formed between the inner wall and the surface of the shifting fork shaft, a second clamping ring is arranged at the end part of the shifting fork shaft, the moving range of the sliding piston is formed between the second, the thin extension section is against the side of the fixed piston.

As another optimized scheme of the hydrostatic transmission, one side of the fixed piston abuts against a positioning shoulder on the shifting fork shaft, and the other side of the fixed piston is fixed by using a first snap ring on the shifting fork shaft, so that the fixed piston drives the shifting fork shaft to move synchronously.

As another optimization scheme of the hydrostatic gearbox, the hydraulic cylinder comprises a cylinder body with an opening at one end and an end cover arranged on the opening through a limiting screw.

Compared with the prior art, the utility model discloses following beneficial effect has:

1) the utility model discloses an install the synchronous ware between high-gear driven gear and low-gear driven gear on the output gear shaft of gearbox, later recycle hydraulic cylinder and drive the shift fork axle and remove, and then control the shift fork of synchronous ware and mesh between high-gear driven gear and low-gear driven gear, realized the function of not stopping to shift gears, reduced intensity of labour, improved equipment work efficiency;

2) in order to avoid the influence of the resisting moment of the motor on the gearbox during gear shifting, the input gear shaft of the gearbox is connected with a clutch, so that the power input by the motor is transmitted to the input gear shaft after passing through the clutch, and the clutch is disconnected during gear shifting, so that the influence of the resisting moment of the motor on the gearbox can be avoided;

3) the utility model discloses a design and the combination of pneumatic cylinder business turn over hydraulic fluid port only can control high, low, empty three gear with a pneumatic cylinder and two pistons, simplifies the structure of shifting, improves product life.

Drawings

FIG. 1 is a schematic view of the transmission principle of the present invention;

FIG. 2 is a schematic view of the transmission principle after the clutch is added;

FIG. 3 is a schematic view of a hydraulic cylinder;

FIG. 4 is a detailed view of two pistons of the hydraulic cylinder;

FIG. 5 is a diagram of two piston positions with the transmission in the high range;

FIG. 6 is a diagram of two piston positions with the transmission in neutral;

FIG. 7 is a diagram of two piston positions with the transmission in a low range;

reference numerals: m, a motor, K1, an internal spline hole, K2, an internal spline input shaft, Z1, a high-gear driving gear, Z2, a low-gear driving gear, Z3, a high-gear driven gear, Z4, a low-gear driven gear, S1, a transmission input gear shaft, S2, a transmission output gear shaft, T1, a synchronizer, C, a clutch, 1, a shifting fork, 2, a shifting fork shaft, 201, a positioning shoulder, 202, a second clamping ring, 203, a first clamping ring, 3, a hydraulic cylinder, 301, a cylinder body, 302, an end cover, 303, a limiting screw, 304, an L-gear oil port, 305, an H-gear oil port, 306, an N-gear oil port, 307, a small-diameter part, 308, a large-diameter part, 4, a fixed piston, 401, a first oil cavity, 402, a second oil cavity, 403, a third oil cavity, 404, an oil passing channel, 5, a sliding piston, 501, a thin extension section, 502 and a thick extension section.

Detailed Description

The technical solution of the present invention will be further illustrated and described with reference to the following specific embodiments. The structure and connection of the various components and equipment units (such as the motor, the hydraulic cylinder, the piston, the seal of the piston, the gear shaft, the gear and synchronizer, the clutch, etc.) used in the following embodiments of the present invention are well known to those skilled in the art, and therefore, are not described herein.

Example 1

As shown in fig. 1, a hydrostatic transmission is provided with an input gear shaft S1 and an output gear shaft S2, an input gear shaft S1 is provided with a high-gear driving gear Z1 and a low-gear driving gear Z2, the high-gear driving gear Z1 and the low-gear driving gear Z2 are respectively provided with a high-gear driven gear Z3 and a low-gear driven gear Z4 which are engaged with each other, a synchronizer T1 is provided at a position between the high-gear driven gear Z3 and the low-gear driven gear Z4 on the output gear shaft S2, a fork 1 of the synchronizer T1 is connected to a fork shaft 2 driven by a hydraulic cylinder 3, and the fork shaft 2 and the fork 1 are driven to move by injecting or extracting hydraulic oil into or from the hydraulic cylinder 3, so that the power of the input gear shaft S1 is transmitted to the output gear shaft S2 through the high-gear Z3 or the low-gear Z4.

In the embodiment, one end of the input gear shaft S1 is provided with an internal spline hole K1, K1 is directly connected with an external spline shaft of a motor, so that the power of the motor is transmitted to the input gear shaft S1, and a high-low gear driving gear Z1 and a high-low gear driving gear Z2 are fixed on S1; the driving gears Z1 and Z2 are directly meshed with the driven gears Z3 and Z4 respectively, Z3 and Z4 are mounted on an output shaft S2 through needle bearings respectively, a synchronizer T1 is mounted between Z3 and Z4 in the middle section of the output shaft S2, and flanges are mounted at two ends of the output shaft S2 respectively to be connected with front and rear axles through universal shafts. Finally, the power is transmitted from the hydraulic motor to the front axle and the rear axle.

The synchronizer T1, the shifting fork 1 and the shifting fork shaft 2 are relatively fixed together, and the shifting fork shaft 2 is connected with the piston in the hydraulic cylinder 3, so that oil pressure is applied to different positions of the hydraulic cylinder, the piston and the shifting fork shaft 2 can be driven to move, the shifting fork 1 and the synchronizer T1 are finally driven to move left and right, and the engagement of the synchronizer T1 and the gear Z3 or Z4 is realized.

In the present embodiment, the structure, installation and connection method of the synchronizer T1 are well known to those skilled in the art, and therefore, are not described in detail herein.

The basic embodiments of the present invention are described above, and further improvements, optimizations and limitations can be made on the above basis, so as to obtain the following embodiments:

example 2

The present embodiment is an optimized scheme based on embodiment 1, and the main structure of the present embodiment is the same as that of embodiment 1, and the improvement point is that: as shown in fig. 1, one end of the input gear shaft S1 is provided with an inner spline hole K1, and is connected with an outer spline shaft of the motor M through the inner spline hole K1, so that the power output by the motor M is transmitted to the input gear shaft S1.

Example 3

The present embodiment is another optimization scheme based on embodiment 1, and the main structure of the present embodiment is the same as that of embodiment 1, and the improvement point is that: as shown in fig. 2, one end of the input gear shaft S1 is provided with an inner spline hole K1, and is connected with an output shaft of a clutch C through the inner spline hole K1, and an inner spline input shaft K2 of the clutch C is connected with an outer spline shaft of the motor M, so that the power output by the motor M is transmitted to the input gear shaft S1.

In this embodiment, the externally splined output shaft of the motor is directly connected to the internally splined input shaft K2 of the hydraulic clutch C, and the output shaft of the clutch C is connected to the internally splined bore K1 of the transmission input gear shaft S1, thereby transmitting motor power to the input gear shaft S1; the clutch C can be disconnected during gear shifting, so that the resistance torque of the motor is prevented from influencing the gearbox;

the input gear shaft S1 of the gearbox is fixed with high and low gear driving gears Z1 and Z2; driving gears Z1 and Z2 are directly meshed with driven gears Z3 and Z4 respectively, Z3 and Z4 are mounted on an output shaft S2 through needle bearings respectively, a synchronizer T1 is mounted between the Z3 and Z4 in the middle section of the output shaft S2, the synchronizer T1 can move left and right to be combined with the Z3 or Z4, so that power is transmitted to an output shaft S2 from the Z3 or Z4, flanges are mounted at two ends of the output shaft S2 respectively to be connected with front and rear axles through universal shafts, and finally the power is transmitted to the front and rear axles from a hydraulic motor.

In this embodiment, the clutch C is mounted on the transmission as an optional module, and has the following features:

1) the clutch C can be in a hydraulic, pneumatic, electromagnetic or other form;

2) the clutch C is installed at the input end of the gearbox as a module, and if the specification of the hydraulic motor is small, namely the resisting moment is small, and the influence on the gearbox is not large, the clutch can be omitted, and the shifting during running can be realized only by matching with a synchronizer;

3) with the development of the technology, the adjustment of the resistance torque of the motor in the gear shifting process can be realized through an electric control liquid and other modes, and in this case, the clutch module can be eliminated.

Example 4

The present embodiment is another optimization scheme based on embodiment 1, and the main structure of the present embodiment is the same as that of embodiment 1, and the improvement point is that: as shown in fig. 3 and 4, one end of the fork shaft 2 extends into the hydraulic cylinder 3, a fixed piston 4 driving the fork shaft 2 to move synchronously and a sliding piston 5 moving on the fork shaft 2 are arranged on the part of the fork shaft 2 in the hydraulic cylinder 3, the edges of the fixed piston 4 and the sliding piston 5 are both matched with the inner wall of the hydraulic cylinder 3, and divides the inside of the cylinder 3 into a first oil chamber 401, a second oil chamber 402 and a third oil chamber 403 in the axial direction of the fork shaft 2, an L-range oil port 304, an H-range oil port 305 and an N-range oil port 306 are respectively arranged on the wall of the hydraulic cylinder 3, the three oil ports are respectively communicated with the three oil cavities in a one-to-one correspondence manner, hydraulic oil is respectively injected into or extracted from the three oil cavities through the three oil ports, so that the fixed piston 4 drives the shifting fork shaft 2 to move in a reciprocating manner, and the shifting fork 1 is used for realizing the combination of the synchronizer T1 and the high-gear driven gear Z3 or the low-gear driven gear Z4 so as to transmit power.

Example 5

The present embodiment is an optimized scheme based on embodiment 4, and the main structure of the present embodiment is the same as that of embodiment 4, and the improvement point is that: as shown in fig. 3 and 4, the L-range oil port 304 and the N-range oil port 306 are respectively located at two ends of the shifting fork shaft 2 in the moving direction and are respectively communicated with the first oil chamber 401 and the third oil chamber 403, and the H-range oil port 305 is located between the two and is communicated with the second oil chamber 402;

when the L-gear oil port 304 and the N-gear oil port 306 simultaneously feed oil, and the H-gear oil port 305 feeds oil, the fixed piston 4 and the sliding piston 5 move in opposite directions until the fixed piston and the sliding piston touch, at the moment, the shifting fork shaft 2 drives the shifting fork 1 of the synchronizer T1 to move, the high-gear driven gear Z3 and the low-gear driven gear Z4 are both separated from combination, and the gearbox is in a neutral position;

when the H-gear oil port 305 and the N-gear oil port 306 simultaneously feed oil and the L-gear oil port 304 feeds oil, the fixed piston 4 and the sliding piston 5 both move to the extreme position towards one side of the L-gear oil port 304, at the moment, the shifting fork shaft 2 drives the shifting fork 1 of the synchronizer T1 to move, the high-gear driven gear Z3 is combined with the synchronizer T1 and the output shaft S1, and the gearbox is in a high-gear position;

when the oil is fed into the L-shift oil port 304, and the oil is fed back into the H-shift oil port 305 and the N-shift oil port 306 at the same time, the fixed piston 4 and the sliding piston 5 both move to the extreme position toward one side of the N-shift oil port 306, at this time, the shift fork shaft 2 drives the shift fork 1 of the synchronizer T1 to move, the low-shift driven gear Z4 is combined with the synchronizer T1 and the output shaft S1, and the transmission case is in the low-shift position.

In this embodiment, when the L range oil port 304 and the N range oil port 306 simultaneously feed oil, and the H range oil port 305 returns oil, the fixed piston 4 moves rightward, the sliding piston 5 moves leftward, and when the sliding piston 5 moves leftward to a certain position and is tightly pressed against the fixed piston 4, the sliding piston 5 does not move any more; similarly, the fixed piston 4 moves right to a certain position and is not moved when being tightly pressed against the sliding piston 5, and the position is a neutral position, which is shown in figure 6;

when the H-shift oil port 305 and the N-shift oil port 306 simultaneously feed oil, and the L-shift oil port 304 returns oil, the fixed piston 4 moves leftward, the force applied to the right side of the sliding piston 5 is greater than the force applied to the left side, that is, the thrust force on the right side of the sliding piston 5 is greater, so that the hydraulic oil pushes the sliding piston 5 to move leftward as well until the sliding piston 5 abuts against the fixed piston 4, and meanwhile, due to the limitation of the second snap ring 202, when the fork shaft 2 moves leftward to a certain position, the second snap ring 202 contacts with the sliding piston 5, and the sliding piston 5 is limited (i.e., cannot continue to move leftward), so that the fork shaft 2 does not move any more after reaching the position, which is a high-grade position, as shown in;

when the oil is fed into the L-shift oil port 304 and the oil is fed into the N-shift oil port 306 and the H-shift oil port 305, the fixed piston 4 moves rightwards and pushes the sliding piston 5 to move rightwards together, until the fork shaft 2 touches the limit position in the hydraulic cylinder 3, the fork shaft 2 stops moving, and the position is the low shift position, as shown in fig. 7.

Example 6

The present embodiment is another optimization scheme based on embodiment 4, and the main structure of the present embodiment is the same as that of embodiment 4, and the improvement point is that: as shown in fig. 3 and 4, the inner wall of the hydraulic cylinder 3 is of a convex structure formed by connecting a large diameter portion 308 and a small diameter portion 307 with different diameters, a clamping table is formed at the joint of the large diameter portion 308 and the small diameter portion 307, one side of the sliding piston 5 is provided with a thin extension section 501 extending into the small diameter portion 307, the thin extension section 501 is cylindrical, the inner wall of the thin extension section is matched with the fork shaft 2 to form a second oil chamber 402, an oil passing channel 404 communicating the second oil chamber 402 and the H-range oil port 305 is arranged between the outer wall of the thin extension section 501 and the inner wall of the hydraulic cylinder 3, the other side of the sliding piston 5 is provided with a thick extension section 502 matched with the large diameter portion 308, the thick extension section 502 is also cylindrical, the outer wall of the thick extension section is matched with the large diameter portion 308, the inner wall of the thin extension section forms a cavity with the surface of the fork shaft 2, a second clamping ring 202 is arranged at the end of the fork shaft 2, and, and the thin extension 501 abuts against the side surface of the fixed piston 4 when the thick extension 502 abuts against the abutment formed at the junction of the large diameter portion 308 and the small diameter portion 307.

The oil passing channel 404 in this embodiment is actually a gap between the outer wall of the thin extension 501 and the inner wall of the hydraulic cylinder 3, and the gap is communicated with the H-range oil port 305, but since the second oil chamber 402 is formed by the inner wall of the thin extension 501 and the fork shaft 2 in a matching manner, and the sliding piston 5 slides on the fork shaft 2, even if the sliding piston moves to the left limit position and cooperates with the fixed piston 4 to close the second oil chamber 402, when oil is injected through the H-range oil port 305, the sliding piston 5 and the fixed piston 4 can generate a gap under the action of oil pressure, so that hydraulic oil enters the second oil chamber 402;

of course, in order to facilitate the entry of the hydraulic oil into the second oil chamber 402 more smoothly in the above case, a through hole penetrating through the inner and outer walls of the thin extension section 501 may be provided, and the second oil chamber 402 and the oil passing passage 404 may be communicated by the through hole.

This embodiment can be further modified based on embodiment 5, and in this case, the main structure is the same as embodiment 5, and the modified point is the same as the modified point described above in this embodiment.

When the improvement is performed on the basis of the embodiment 5, when the H-range oil port 305 and the N-range oil port 306 simultaneously feed oil, and the L-range oil port 304 feeds oil, the fixed piston 4 moves leftward, the force applied to the right side of the sliding piston 5 is greater than the force applied to the left side, that is, the thrust force applied to the right side of the sliding piston 5 is greater, so that the hydraulic oil pushes the sliding piston 5 to move leftward until the sliding piston tightly abuts against the clamping table; at this time, the fixed piston 4 continues to move rightwards, and does not move any more until the sliding piston 5 is reached (because the force bearing area of the sliding piston 5 is larger than that of the fixed piston 4, the fixed piston 4 is limited by the sliding piston 5, and the sliding piston 5 is positioned by a clamping table at the end part of the large-diameter part 308); meanwhile, due to the limitation of the second snap ring 202, when the declutch shift shaft 2 moves to a certain position to the left, the second snap ring 202 contacts with the sliding piston 5, and the sliding piston 5 is limited (i.e. cannot move to the left), so that the declutch shift shaft 2 does not move any more after reaching the position, which is a high-grade position, as shown in fig. 5;

the remaining gear positions are the same as embodiment 4.

Example 7

The present embodiment is another optimization scheme based on embodiment 4, and the main structure of the present embodiment is the same as that of embodiment 4, and the improvement point is that: as shown in fig. 3 and 4, one side of the fixed piston 4 abuts against a positioning shoulder 201 on the fork shaft 2, and the other side of the fixed piston is fixed by using a first snap ring 203 on the fork shaft 2, so that the fixed piston drives the fork shaft 2 to move synchronously.

Example 8

The present embodiment is another optimization scheme based on embodiment 4, and the main structure of the present embodiment is the same as that of embodiment 4, and the improvement point is that: as shown in fig. 3 and 4, the hydraulic cylinder 3 includes a cylinder body 301 having an opening at one end and an end cap 302 provided on the opening by a stopper screw 303.

Claims

1. A hydrostatic transmission is provided with an input gear shaft (S1) and an output gear shaft (S2) therein, a high-gear driving gear (Z1) and a low-gear driving gear (Z2) are provided on the input gear shaft (S1), and the high-gear driving gear (Z1) and the low-gear driving gear (Z2) realize the transmission of power through a high-gear driven gear (Z3) and a low-gear driven gear (Z4) which are engaged with both, respectively, and is characterized in that: the output gear shaft (S2) is provided with a synchronizer (T1) at a position between the high-gear driven gear (Z3) and the low-gear driven gear (Z4), a shifting fork (1) of the synchronizer (T1) is connected with a shifting fork shaft (2) driven by a hydraulic cylinder (3), hydraulic oil is injected into or pumped out of the hydraulic cylinder (3) to drive the shifting fork shaft (2) and the shifting fork (1) to move, and then the power of the input gear shaft (S1) is transmitted to the output gear shaft (S2) through the high-gear driven gear (Z3) or the low-gear driven gear (Z4).

2. The hydrostatic transmission of claim 1, wherein: one end of the input gear shaft (S1) is provided with an inner spline hole (K1) and is connected with an outer spline shaft of the motor (M) through the inner spline hole (K1), so that the power output by the motor (M) is transmitted to the input gear shaft (S1).

3. The hydrostatic transmission of claim 1, wherein: one end of the input gear shaft (S1) is provided with an inner spline hole (K1) and is connected with an output shaft of a clutch (C) through the inner spline hole (K1), and an inner spline input shaft (K2) of the clutch (C) is connected with an outer spline shaft of the motor (M), so that the power output by the motor (M) is transmitted to the input gear shaft (S1).

4. The hydrostatic transmission of claim 1, wherein: one end of the shifting fork shaft (2) extends into the hydraulic cylinder (3), a fixed piston (4) for driving the shifting fork shaft (2) to synchronously move and a sliding piston (5) for moving on the shifting fork shaft (2) are arranged on the part of the shifting fork shaft (2) in the hydraulic cylinder (3), the edges of the fixed piston (4) and the sliding piston (5) are matched with the inner wall of the hydraulic cylinder (3) and divide the interior of the hydraulic cylinder (3) into a first oil cavity (401), a second oil cavity (402) and a third oil cavity (403) along the axial direction of the shifting fork shaft (2), an L-gear oil port (304), an H-gear oil port (305) and an N-gear oil port (306) are respectively arranged on the wall of the hydraulic cylinder (3), the three oil cavities are respectively communicated with the three oil ports in a one-to-one correspondence manner, hydraulic oil is respectively injected into or extracted from the three oil ports, and the fixed piston (4) drives the shifting fork shaft (2) to reciprocate, and the shifting fork (1) is used for realizing the combination of the synchronizer (T1) and the high-gear driven gear (Z3) or the low-gear driven gear (Z4) so as to transmit power.

5. The hydrostatic transmission of claim 4, wherein: the L-gear oil port (304) and the N-gear oil port (306) are respectively positioned at two ends of the shifting fork shaft (2) in the moving direction and are respectively communicated with the first oil cavity (401) and the third oil cavity (403), and the H-gear oil port (305) is positioned between the L-gear oil port and the third oil cavity and is communicated with the second oil cavity (402);

when the L-gear oil port (304) and the N-gear oil port (306) simultaneously feed oil and the H-gear oil port (305) feeds oil, the fixed piston (4) and the sliding piston (5) move in opposite directions until the fixed piston and the sliding piston touch, at the moment, the shifting fork shaft (2) drives the shifting fork (1) of the synchronizer (T1) to move, the high-gear driven gear (Z3) and the low-gear driven gear (Z4) are both separated from each other and combined, and the gearbox is in a neutral position;

when the H-gear oil port (305) and the N-gear oil port (306) simultaneously feed oil, and the L-gear oil port (304) returns oil, the fixed piston (4) and the sliding piston (5) both move to the extreme position towards one side of the L-gear oil port (304), at the moment, the shifting fork shaft (2) drives the shifting fork (1) of the synchronizer (T1) to move, the high-gear driven gear (Z3) is combined with the synchronizer (T1) and the output shaft, and the gearbox is in the high-gear position;

when the L-gear oil port (304) is filled with oil, and the H-gear oil port (305) and the N-gear oil port (306) are simultaneously returned with oil, the fixed piston (4) and the sliding piston (5) both move to the limit position towards one side of the N-gear oil port (306), at the moment, the shifting fork shaft (2) drives the shifting fork (1) of the synchronizer (T1) to move, the low-gear driven gear (Z4) is combined with the synchronizer (T1) and the output shaft, and the gearbox is located at the low-gear position.

6. A hydrostatic gearbox according to claim 4 or 5, characterised in that: the inner wall of the hydraulic cylinder (3) is of a convex structure formed by connecting a large diameter part (308) and a small diameter part (307) with different diameters, a clamping table is formed at the joint of the large diameter part (308) and the small diameter part (307), a thin extension section (501) extending into the small diameter part (307) is arranged on one side of the sliding piston (5), the thin extension section (501) is cylindrical, the inner wall of the thin extension section is matched with the shifting fork shaft (2) to form a second oil cavity (402), an oil passing channel (404) communicated with the second oil cavity (402) and an H-gear oil port (305) is arranged between the outer wall of the thin extension section (501) and the inner wall of the hydraulic cylinder (3), a thick extension section (502) matched with the large diameter part (308) is arranged on the other side of the sliding piston (5), the thick extension section (502) is cylindrical, the outer wall of the thick extension section is matched with the large diameter part (308), and the inner wall of the shifting fork shaft (2), a second snap ring (202) is arranged at the end part of the shifting fork shaft (2), a moving range of the sliding piston (5) is formed between the second snap ring (202) and the fixed piston (4), and when the thick extension section (502) abuts against a snap table formed at the joint of the large-diameter part (308) and the small-diameter part (307), the thin extension section (501) abuts against the side surface of the fixed piston (4).

7. The hydrostatic transmission of claim 4, wherein: one side of the fixed piston (4) is tightly abutted to a positioning shoulder (201) on the shifting fork shaft (2), and the other side of the fixed piston is fixed by a first snap ring (203) on the shifting fork shaft (2), so that the shifting fork shaft (2) is driven to synchronously move.

8. The hydrostatic transmission of claim 4, wherein: the hydraulic cylinder (3) comprises a cylinder body (301) with an opening at one end and an end cover (302) arranged on the opening through a limiting screw (303).