Hydraulically controlled cog-type clutch four-wheel drive mechanism and method of operation

Abstract

The application discloses a hydraulic control cog-type clutch four-wheel drive mechanism and a working method thereof, and belongs to the technical field of four-wheel drive mechanisms.The hydraulic control cog-type clutch four-wheel drive mechanism comprises a four-wheel drive piston and a hydraulic cylinder forming a sealed hydraulic cavity, wherein the hydraulic cavity is connected with a main oil path, the main oil path is provided with a switch valve, and the main oil path supplies oil to the hydraulic cavity when the switch valve is opened; the hydraulic cylinder is provided with an oil discharge hole; the oil discharge hole is communicated with the hydraulic cavity and discharges oil to a gearbox; the end faces of the four-wheel drive piston and the four-wheel drive output shaft are respectively provided with trapezoidal teeth capable of being engaged; the four-wheel drive output shaft is connected with a transmission output shaft through a mandrel; and the mandrel and the transmission output shaft realize radial positioning constraint of the four-wheel drive output shaft through a cylindrical roller bearing.The four-wheel drive piston is controlled by hydraulic pressure, the four-wheel drive piston and the four-wheel drive output shaft are combined or separated, power switching between two-wheel drive and four-wheel drive is realized, the tooth part structure of the cog-type clutch is designed, the cog-type clutch realizes self-centering function through the tooth end face inclination angle, and the mechanism realizes stable engagement, accurate limiting and self-locking function.

Description

Technical Field

[0001] This invention belongs to the field of transmission technology and relates to a hydraulically controlled four-wheel drive mechanism with a jaw clutch and its working method. Background Technology

[0002] Addressing the power issues of construction machinery such as wheeled loaders, off-road cranes, and forklifts: Under normal operating conditions, two-wheel drive is sufficient for power requirements. However, in special conditions (such as getting stuck in mud, climbing slopes, or undulating terrain), the drive wheels may spin freely, resulting in insufficient traction. Therefore, a clutch-based four-wheel drive mechanism needs to be designed. Under normal operating conditions, it operates with two-wheel drive; under special conditions, it engages all four wheels for real-time four-wheel drive, functioning similarly to a differential lock to help the vehicle escape difficult situations and increase its passability and power on rough terrain.

[0003] Currently, the most commonly used clutch that can meet the above functions is the wet friction plate clutch, because it has the advantages of transmitting large torque and smooth engagement and disengagement. However, wet clutches require a sufficiently large friction area or a method of stacking friction plates to achieve the requirement of transmitting large torque, which is a very big challenge for the powertrain of off-road engineering machinery with limited space. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of switching between four-wheel drive and two-wheel drive with a clutch in the case of limited space in the prior art, and to provide a hydraulically controlled dog clutch four-wheel drive mechanism and its working method.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A hydraulically controlled dog clutch four-wheel drive mechanism includes: a four-wheel drive piston, a four-wheel drive output shaft, a hydraulic cylinder, a four-wheel drive output shaft seat, a return spring, a cylindrical roller bearing, a deep groove ball bearing, a spindle, a transmission housing, and a transmission output shaft;

[0007] One end of the transmission output shaft is located inside the hydraulic cylinder. The four-wheel drive piston is positioned between the hydraulic cylinder and the transmission output shaft, forming a sealed hydraulic chamber. The hydraulic chamber is connected to the main oil circuit, which is equipped with a switching valve. When the switching valve is open, the main oil circuit supplies oil to the hydraulic chamber. The hydraulic cylinder has an oil drain hole, which communicates with the hydraulic chamber for draining oil to the transmission. The end faces of the four-wheel drive piston and the four-wheel drive output shaft are respectively provided with meshing trapezoidal teeth. The four-wheel drive output shaft is connected to the transmission output shaft via a spindle. The spindle and the transmission output shaft are radially positioned and constrained by cylindrical roller bearings. A return spring is fitted on the transmission output shaft, with one end of the return spring contacting the four-wheel drive piston and the other end contacting the four-wheel drive output shaft. A four-wheel drive output shaft seat and a deep groove ball bearing are both fitted on the four-wheel drive output shaft. The deep groove ball bearing is located in the inner hole of the four-wheel drive output shaft seat and supports the rotation of the four-wheel drive output shaft. Bolts pass through the four-wheel drive output shaft seat and the hydraulic cylinder in sequence to fix the hydraulic cylinder to the rear end of the transmission housing.

[0008] A further improvement of the present invention is that:

[0009] Furthermore, a stepped hole is provided at one end of the four-wheel drive output shaft; the stepped hole is radially positioned with one end of the spindle through an interference fit; the other end of the spindle is inserted into the inner hole of the transmission output shaft.

[0010] Furthermore, an output flange is fitted onto the four-wheel drive output shaft; a spline is provided in the middle part of the four-wheel drive output shaft, which meshes with the output flange to transmit the output torque of the jaw clutch.

[0011] Furthermore, a stepped groove is provided next to the spline of the four-wheel drive output shaft, and an O-ring is installed in the stepped groove. The O-ring prevents the lubricating oil entering the four-wheel drive mechanism from leaking to the outside of the housing and causing a dripping failure. An external thread is provided on one side of the stepped groove, which is used to install and tighten the nut to lock the axial movement and disengagement of the output flange.

[0012] A radial hole is provided in the stepped groove next to the spline of the four-wheel drive output shaft. The radial hole communicates with the stepped hole of the four-wheel drive output shaft and plays a role in venting during interference fit.

[0013] Furthermore, the end faces of the four-wheel drive piston and the four-wheel drive output shaft that come into contact with each other are evenly distributed with meshing trapezoidal teeth; the working surface tooth inclination angle of the trapezoidal teeth of the paired four-wheel drive piston and the four-wheel drive output shaft is designed to be 8°, so that the four-wheel drive piston and the four-wheel drive output shaft can mesh smoothly under small speed difference, and achieve self-locking function by relying on tooth side friction during operation; when the four-wheel drive piston and the four-wheel drive output shaft are fully meshed, the tooth tip of the four-wheel drive output shaft abuts against the tooth root of the four-wheel drive piston to achieve axial positioning; at the same time, the single-sided backlash generated by the tooth working surface of the four-wheel drive piston and the four-wheel drive output shaft is 0.04mm; the end faces of the trapezoidal teeth of the four-wheel drive piston and the four-wheel drive output shaft have the same inclination angle of 1.3°.

[0014] Furthermore, a spring retaining ring is provided between the return spring and the four-wheel drive output shaft; the spring retaining ring fixes the axial movement of the return spring.

[0015] Furthermore, a rotary seal ring is installed between the four-wheel drive piston and the hydraulic cylinder. The rotary seal ring cooperates with the hydraulic cylinder to ensure the sealing of the hydraulic system of the four-wheel drive mechanism.

[0016] Furthermore, the inner ring end face of the deep groove ball bearing fits against the shoulder of the four-wheel drive output shaft, achieving axial positioning of the four-wheel drive output shaft.

[0017] Furthermore, a tapered roller bearing is provided between the transmission output shaft and the transmission housing; the tapered roller bearing is used for positioning and constraining the transmission output shaft within the transmission housing.

[0018] A method for operating a hydraulically controlled four-wheel drive clutch includes: when the switching valve is opened and the drain hole is closed, hydraulic oil from the main oil circuit enters the hydraulic chamber sealed by the four-wheel drive piston and the hydraulic cylinder, and the hydraulic oil pushes the four-wheel drive piston to move in the hydraulic chamber and engage with the four-wheel drive output shaft; at the same time, the return spring is compressed; when the four-wheel drive piston engages with the four-wheel drive output shaft, the transmission changes from two-wheel drive to four-wheel drive, increasing the driving capability; when the switching valve is closed and the drain hole is opened, the main oil circuit stops supplying oil to the hydraulic chamber, and at the same time, the hydraulic oil in the hydraulic chamber is quickly discharged into the transmission through the drain hole, the return spring is reset, the four-wheel drive piston is separated from the four-wheel drive output shaft, the power of the four-wheel drive mechanism is cut off, and the two-wheel drive working state is restored.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention achieves power switching between two-wheel drive and four-wheel drive by hydraulically controlling the movement of the four-wheel drive piston, enabling engagement or disengagement of the piston and output shaft. Simultaneously, through the design of the jaw clutch's tooth structure, the jaw clutch achieves self-centering via the tooth end face angle, resulting in smooth meshing, accurate positioning, and self-locking. The uniform design of the jaw clutch's teeth ensures that each tooth experiences equal force, evenly bearing the torque transmitted from the output shaft, giving the jaw clutch sufficient strength to transmit the ultimate torque. Its compact structure is integrated into the transmission housing, achieving the design goal of a small structure with high torque in a limited space. Furthermore, through the design of the solenoid valve, hydraulic cylinder, four-wheel drive piston, and rotary seal ring, this invention achieves precise hydraulic control of the jaw clutch four-wheel drive mechanism, rapidly and sensitively responding to engagement and disengagement signals. The cooperation between the rotary seal ring and the hydraulic cylinder ensures excellent sealing of the four-wheel drive hydraulic system. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a cross-sectional view of the assembly structure of the four-wheel drive mechanism of the jaw clutch of the present invention;

[0023] Figure 2 This is an isometric view of the four-wheel drive mechanism of the jaw clutch of the present invention;

[0024] Figure 3 This is a structural diagram of the active end of the four-wheel drive mechanism of the tooth clutch of the present invention - the four-wheel drive piston tooth end;

[0025] Figure 4 This is a structural diagram of the driven end of the toothed clutch of the present invention - the tooth end of the four-wheel drive shaft;

[0026] Figure 5 This is a schematic diagram of the hydraulic system of the four-wheel drive mechanism of the jaw clutch of the present invention.

[0027] Among them, 1-four-wheel drive piston; 2-four-wheel drive output shaft; 3-hydraulic cylinder; 4-four-wheel drive output shaft seat; 5-return spring; 6-rotary seal ring; 7-cylindrical roller bearing; 8-deep groove ball bearing; 9-spindle; 10-output flange; 11-transmission housing; 12-tapered roller bearing; 13-transmission output shaft; 14-tightening nut; 15-spring elastic retaining ring; 16-switching valve. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present 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, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0033] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0034] The present invention will now be described in further detail with reference to the accompanying drawings:

[0035] See Figure 1 and Figure 2 This invention discloses a hydraulically controlled dog clutch four-wheel drive mechanism, comprising: a four-wheel drive piston 1, a four-wheel drive output shaft 2, a hydraulic cylinder 3, a four-wheel drive output shaft seat 4, a return spring 5, a cylindrical roller bearing 7, a deep groove ball bearing 8, a spindle 9, a transmission housing 11, and a transmission output shaft 13.

[0036] One end of the transmission output shaft 13 is located inside the hydraulic cylinder 3. The four-wheel drive piston 1 is located between the hydraulic cylinder 3 and the transmission output shaft 13, forming a sealed hydraulic chamber with the hydraulic cylinder 3. The hydraulic chamber is connected to the main oil circuit, which is equipped with a switching valve 16. When the switching valve 16 is open, the main oil circuit supplies oil to the hydraulic chamber. The hydraulic cylinder 3 is equipped with an oil drain hole, which communicates with the hydraulic chamber and is used to drain oil from the transmission. The end face of the four-wheel drive piston 1 and the end face of the four-wheel drive output shaft 2 are respectively provided with meshing trapezoidal teeth. The four-wheel drive output shaft 2 is connected to the transmission output shaft 13 via a spindle 9. The spindle 9 and the transmission output shaft 13 are radially positioned and constrained by the cylindrical roller bearing 7; the return spring 5 is sleeved on the transmission output shaft 13, one end of the return spring 5 is in contact with the four-wheel drive piston 1, and the other end of the return spring 5 is in contact with the four-wheel drive output shaft 2; the four-wheel drive output shaft seat 4 and the deep groove ball bearing 8 are both sleeved on the four-wheel drive output shaft 2, the deep groove ball bearing 8 is set in the inner hole of the four-wheel drive output shaft seat 4, and the deep groove ball bearing 8 supports the rotation of the four-wheel drive output shaft 2; the bolt passes through the four-wheel drive output shaft seat 4 and the hydraulic cylinder 3 in sequence to fix the hydraulic cylinder 3 to the rear end of the transmission housing 11.

[0037] The inner cavity of the four-wheel drive piston 1 is machined with an internal spline. The internal spline transmits part of the torque distributed by the transmission output shaft 13. At the same time, the spline guides the axial movement of the four-wheel drive piston 1. The other end of the spline has a boss, which mainly serves the purpose of axial positioning and constrains the end point of the piston's stroke in the disengaged state. There are four notches evenly distributed on the boss, and through holes are machined in the notches. The purpose of this feature is mainly to facilitate oil passage, connecting the lubrication oil passage between the four-wheel drive clutch system and the transmission housing, and ensuring that all components of the four-wheel drive mechanism receive sufficient lubrication.

[0038] One end of the four-wheel drive output shaft 2 is provided with a stepped hole; the stepped hole is radially positioned with one end of the spindle 9 through an interference fit; the other end of the spindle 9 is inserted into the inner hole of the transmission output shaft 13. An output flange 10 is fitted on the four-wheel drive output shaft 2; a spline is provided in the middle part of the four-wheel drive output shaft 2, which meshes with the output flange 10 to transmit the output torque of the jaw clutch. A stepped groove is provided next to the spline of the four-wheel drive output shaft 2, and an O-ring is installed in the stepped groove. The O-ring prevents the lubricating oil entering the four-wheel drive mechanism from leaking to the outside of the housing and causing a dripping failure; an external thread is provided on one side of the stepped groove, which is used to install and tighten the nut 14 to lock the axial movement and disengagement of the output flange 10;

[0039] See Figure 3 and Figure 4A radial hole is provided in the stepped groove next to the spline of the four-wheel drive output shaft 2. The radial hole communicates with the stepped hole of the four-wheel drive output shaft 2, which serves to release air during the interference fit. The end faces of the four-wheel drive piston 1 and the four-wheel drive output shaft 2 that are in contact are evenly distributed with meshing trapezoidal teeth; there are 14 teeth in total. The working surface tooth inclination angle of the trapezoidal teeth of the four-wheel drive piston 1 and the four-wheel drive output shaft 2 are designed to be 8°, so that the four-wheel drive piston 1 and the four-wheel drive output shaft 2 can mesh smoothly under small speed difference, and achieve self-locking function by relying on the friction of the tooth side during operation. The trapezoidal tooth height of the four-wheel drive piston 1 is 6.2mm and the tooth root height is 3.2mm; the trapezoidal tooth height of the four-wheel drive output shaft 2 is 7.0mm and the tooth tip height is 3.3mm. This height design allows the tooth tip of the four-wheel drive output shaft 2 to abut against the tooth root of the four-wheel drive piston 1 when the two are fully meshed, thereby axially positioning them; at the same time, the single-sided backlash generated by the tooth working surface is 0.04, which is beneficial to the low noise impact during the tooth meshing process and switching process. Meanwhile, the trapezoidal tooth end faces of the four-wheel drive piston 1 and the four-wheel drive output shaft 2 have the same inclination angle of 1.3°, which provides good alignment during their meshing process.

[0040] A spring retaining ring 15 is provided between the return spring 5 and the four-wheel drive output shaft 2; the spring retaining ring 15 fixes the axial movement of the return spring 5. A rotary seal ring 6 is provided between the four-wheel drive piston 1 and the hydraulic cylinder 3. The rotary seal ring 6 cooperates with the hydraulic cylinder 3 to ensure the sealing of the hydraulic system of the four-wheel drive mechanism. The inner ring end face of the deep groove ball bearing 8 is in contact with the shoulder of the four-wheel drive output shaft 2 to achieve axial positioning of the four-wheel drive output shaft 2. The deep groove ball bearing 8 restricts the five degrees of freedom of the four-wheel drive output shaft 2, so that the four-wheel drive output shaft 2 can only rotate with the inner ring of the bearing; the end face of the four-wheel drive output shaft 2 is machined with 14 trapezoidal teeth that mate with the four-wheel drive piston 1. The trapezoidal teeth are evenly distributed along the circumference, and the working surface of the teeth is machined with a tooth inclination angle of 8°, the same as the trapezoidal teeth of the four-wheel drive piston 1, to achieve a self-locking function.

[0041] A tapered roller bearing 12 is provided between the transmission output shaft 13 and the transmission housing 11; the tapered roller bearing 12 is used for positioning and constraining the transmission output shaft 13 in the transmission housing 11.

[0042] The electromagnetic switch valve 16, hydraulic cylinder 3, four-wheel drive piston 1, and spring 5 constitute the hydraulic system of the four-wheel drive jaw clutch. By controlling the electrical signal, the electromagnetic valve 16 is turned on (off), so that the high-pressure oil drives the four-wheel drive piston to move axially in the hydraulic cylinder, thereby realizing the real-time engagement (disengagement) of the jaw clutch.

[0043] A method for operating a hydraulically controlled four-wheel drive clutch includes: when the switching valve 16 is opened and the oil drain hole is closed, hydraulic oil from the main oil circuit enters the hydraulic chamber formed by the four-wheel drive piston 1 and the hydraulic cylinder 3, which is sealed. The hydraulic oil in the hydraulic chamber pushes the four-wheel drive piston 1 to move and engage with the four-wheel drive output shaft 2; at the same time, the return spring 5 is compressed; when the four-wheel drive piston 1 engages with the four-wheel drive output shaft 2, the transmission changes from two-wheel drive to four-wheel drive, increasing the driving capability; when the switching valve 16 is closed and the oil drain hole is opened, the main oil circuit stops supplying oil to the hydraulic chamber, and the hydraulic oil in the hydraulic chamber is quickly discharged into the transmission through the oil drain hole. The return spring 5 is reset, the four-wheel drive piston 1 separates from the four-wheel drive output shaft 2, the power of the four-wheel drive mechanism is cut off, and the two-wheel drive working state is restored.

[0044] See Figure 5 , Figure 5 A hydraulic system for a four-wheel drive mechanism with a jaw clutch is disclosed. Specifically, the jaw clutch four-wheel drive mechanism has an independent hydraulic pipeline. The hydraulic oil is pressurized by a hydraulic pump and then enters an oil filter to ensure the cleanliness of the hydraulic oil entering the pipeline. Furthermore, a pressure regulating valve ensures stable hydraulic oil pressure entering the switching valve body, preventing oil pressure pulsation caused by abnormal pump operation from damaging the precision switching valve-valve body / valve core assembly. Further, the switching valve receives on / off signals from the transmission controller. When it receives an "open" signal, the switching valve is in the right working position, the piston chamber is connected to the hydraulic pipeline, and the piston begins to move to the right, engaging the four-wheel drive piston with the four-wheel drive shaft, activating the four-wheel drive mode. When it receives a "closed" signal, the switching valve is in the left working position, the piston chamber is disconnected from the hydraulic pipeline, the hydraulic oil in the piston chamber is depressurized and flows into the oil pan of the transmission housing, and the piston begins to move to the left under the force of the return spring, disengaging the four-wheel drive piston from the four-wheel drive shaft, activating the two-wheel drive mode.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydraulically controlled dog clutch four-wheel drive mechanism, characterized in that, include: Four-wheel drive piston (1), four-wheel drive output shaft (2), hydraulic cylinder (3), four-wheel drive output shaft seat (4), return spring (5), cylindrical roller bearing (7), deep groove ball bearing (8), spindle (9), transmission housing (11), transmission output shaft (13) and bolts; One end of the transmission output shaft (13) is located inside the hydraulic cylinder (3). The four-wheel drive piston (1) is located between the hydraulic cylinder (3) and the transmission output shaft (13). The four-wheel drive piston (1) and the hydraulic cylinder (3) form a sealed hydraulic chamber. The hydraulic chamber is connected to the main oil circuit. The main oil circuit is equipped with a switching valve (16). When the switching valve (16) is open, the main oil circuit supplies oil to the hydraulic chamber. The hydraulic cylinder (3) is equipped with an oil discharge hole. The oil discharge hole is connected to the hydraulic chamber and is used to drain oil from the transmission. The end face of the four-wheel drive piston (1) and the end face of the four-wheel drive output shaft (2) are respectively provided with meshing trapezoidal teeth. The four-wheel drive output shaft (2) is connected to the transmission output shaft (13) through a spindle (9). The shaft (9) and the transmission output shaft (13) are radially positioned and constrained by the cylindrical roller bearing (7) for the four-wheel drive output shaft (2); the return spring (5) is sleeved on the transmission output shaft (13), one end of the return spring (5) is in contact with the four-wheel drive piston (1), and the other end of the return spring (5) is in contact with the four-wheel drive output shaft (2); the four-wheel drive output shaft seat (4) and the deep groove ball bearing (8) are both sleeved on the four-wheel drive output shaft (2), the deep groove ball bearing (8) is set in the inner hole of the four-wheel drive output shaft seat (4), and the deep groove ball bearing (8) supports the rotation of the four-wheel drive output shaft (2); the bolt passes through the four-wheel drive output shaft seat (4) and the hydraulic cylinder (3) in sequence to fix the hydraulic cylinder (3) to the rear end of the transmission housing (11).

2. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 1, characterized in that, One end of the four-wheel drive output shaft (2) is provided with a stepped hole; the stepped hole is radially positioned with one end of the spindle (9) through an interference fit; the other end of the spindle (9) is inserted into the inner hole of the transmission output shaft (13).

3. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 2, characterized in that, An output flange (10) is fitted on the four-wheel drive output shaft (2); a spline is provided in the middle part of the four-wheel drive output shaft (2), and the spline meshes with the output flange (10) to transmit the output torque of the dog clutch.

4. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 3, characterized in that, A stepped groove is provided next to the spline of the four-wheel drive output shaft (2), and an O-ring is installed in the stepped groove. The O-ring prevents the lubricating oil entering the four-wheel drive mechanism from leaking to the outside of the housing and causing a dripping fault. An external thread is provided on one side of the stepped groove. The external thread is used to install and tighten the nut (14) to lock the output flange (10) from axial movement and disengagement. A radial hole is provided in the stepped groove next to the spline of the four-wheel drive output shaft (2). The radial hole communicates with the stepped hole of the four-wheel drive output shaft (2) and plays a role in venting when the interference fit is applied.

5. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 4, characterized in that, The four-wheel drive piston (1) and the four-wheel drive output shaft (2) have evenly distributed meshing trapezoidal teeth on their contacting end faces; the working surface tooth inclination angle of the trapezoidal teeth of the paired four-wheel drive piston (1) and the four-wheel drive output shaft (2) is designed to be 8°, so that the four-wheel drive piston (1) and the four-wheel drive output shaft (2) can mesh smoothly under small speed difference, and achieve self-locking function by relying on tooth side friction during operation; when the four-wheel drive piston (1) and the four-wheel drive output shaft (2) are fully meshed, the tooth tip of the four-wheel drive output shaft (2) abuts against the tooth root of the four-wheel drive piston (1) to achieve axial positioning; at the same time, the single-sided backlash generated by the tooth working surface of the four-wheel drive piston (1) and the four-wheel drive output shaft (2) is 0.04mm; the end faces of the trapezoidal teeth of the four-wheel drive piston (1) and the four-wheel drive output shaft (2) have the same inclination angle of 1.3°.

6. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 5, characterized in that, A spring elastic retaining ring (15) is provided between the return spring (5) and the four-wheel drive output shaft (2); the spring elastic retaining ring (15) fixes the axial movement of the return spring (5).

7. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 6, characterized in that, A rotary seal ring (6) is provided between the four-wheel drive piston (1) and the hydraulic cylinder (3). The rotary seal ring (6) cooperates with the hydraulic cylinder (3) to ensure the sealing of the hydraulic system of the four-wheel drive mechanism.

8. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 7, characterized in that, The inner ring end face of the deep groove ball bearing (8) is in contact with the shoulder of the four-wheel drive output shaft (2) to achieve axial positioning of the four-wheel drive output shaft (2).

9. The hydraulically controlled dog clutch four-wheel drive mechanism according to claim 8, characterized in that, A tapered roller bearing (12) is provided between the transmission output shaft (13) and the transmission housing (11); the tapered roller bearing (12) is used for positioning constraint of the transmission output shaft (13) in the transmission housing (11).

10. A method for operating a hydraulically controlled dog clutch four-wheel drive mechanism according to any one of claims 1 to 9, characterized in that, include: When the switch valve (16) is opened and the oil drain hole is closed, the hydraulic oil in the main oil circuit enters the hydraulic chamber formed by the four-wheel drive piston (1) and the hydraulic cylinder (3). The hydraulic oil pushes the four-wheel drive piston (1) to move in the hydraulic chamber and engage with the four-wheel drive output shaft (2). At the same time, the return spring (5) is compressed. When the four-wheel drive piston (1) engages with the four-wheel drive output shaft (2), the transmission changes from two-wheel drive to four-wheel drive, increasing the driving capability. When the switch valve (16) is closed and the oil drain hole is opened, the main oil circuit stops supplying oil to the hydraulic chamber. At the same time, the hydraulic oil in the hydraulic chamber is quickly discharged into the transmission through the oil drain hole. The return spring (5) is reset, the four-wheel drive piston (1) and the four-wheel drive output shaft (2) are separated, the power of the four-wheel drive mechanism is cut off, and the two-wheel drive working state is restored.

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