Transmission structure and electric drive axle

Abstract

The application provides a transmission structure and an electric drive axle, wherein the transmission structure comprises an input shaft and an intermediate shaft, a plurality of input gears are arranged on the input shaft, the input gears comprise a first input gear and a second input gear, the radial dimension of the second input gear is larger than that of the first input gear, the plurality of input gears are arranged at intervals along the axial direction of the input shaft, and the first input gear and the input shaft are integrally formed. The transmission structure and the electric drive axle, by integrally forming part of the input gears with a smaller radial dimension and the input shaft, compared with a separate assembly mode, a connecting part is omitted to reduce the size of the input shaft, meanwhile, the input gears integrally formed on the input shaft have relatively higher strength, part of the input gears with a larger radial dimension and the input shaft are connected through a separate structure by assembly to reduce part of the processing cost.

Description

Technical Field

[0001] This invention relates to the field of electric drive bridges, and more particularly to a transmission structure and an electric drive bridge. Background Technology

[0002] An electric drive axle is an assembly consisting of a motor, gearbox, etc., used to drive the wheels. For example, the transmission structure disclosed in publication number CN202098528U includes a motor, gearbox, and half-shafts. The electric drive axle generates power from the motor and transmits the power to the gearbox connected to it. The gearbox drives the vehicle through the half-shafts connected to it. The gearbox has an output shaft and a drive shaft to transmit power from the power source.

[0003] In the transmission structure of traditional electric drive axles, the input gear on the power input shaft is mounted on the input shaft using splines and parallel keys. The manufacturing of splines requires advanced technology and equipment, and the processing is relatively complex. It requires specialized processing equipment and processes. Factors such as the hardness of the processing material and the size of the workpiece also affect the processing cost, resulting in high processing costs for splines. Spline processing requires high-precision manufacturing equipment and highly skilled workers. At the same time, different workpiece hardnesses can lead to greater processing difficulties. Summary of the Invention

[0004] The purpose of this invention is to provide a transmission structure and electric drive bridge that can reduce the machining cost of input gears on the input shaft.

[0005] To achieve the above objectives, the present invention provides a transmission structure, comprising: The system includes an input shaft and an intermediate shaft. The input shaft is equipped with a plurality of input gears, including a first input gear and a second input gear. The radial dimension of the second input gear is larger than that of the first input gear. The plurality of input gears are arranged at intervals along the axial direction of the input shaft. The first input gear and the input shaft are integrally formed, while the second input gear and the input shaft are assembled together. The intermediate shaft is equipped with a plurality of intermediate gears, which mesh with the input gears.

[0006] Preferably, the second input gear is a ring-shaped input gear, which is sleeved on the outside of the input shaft. The outer wall of the input shaft and the inner wall of the ring of the second input gear are interference-fitted and fixed by riveting with a pin.

[0007] Preferably, the intermediate gear includes a first intermediate gear and a second intermediate gear, wherein the first input gear meshes with the first intermediate gear, and the second input gear meshes with the second intermediate gear.

[0008] Preferably, the first input gear includes a plurality of first input tooth blocks, which are arranged circumferentially along the input shaft, wherein a first input tooth groove is formed between adjacent first input tooth blocks, and wherein the top surface of the first input tooth block is flush with the outer wall of the input shaft.

[0009] Preferably, the connection between the bottom surface of the first input tooth groove and the radial outer surface of the input shaft is a smooth transition in the axial direction of the input shaft.

[0010] Preferably, the input gear further includes a third input gear, and the intermediate gear further includes a third intermediate gear. The radial dimension of the third input gear is smaller than that of the second input gear. The third input gear and the third intermediate gear mesh. The third input gear and the input shaft are integrally formed. The third input gear includes a third input gear ring and a third input gear block. The outer wall of the input shaft extends outward to form the third input gear ring and the third input gear block in sequence. The third input gear blocks are arranged at circumferential intervals along the third input gear ring.

[0011] Preferably, the intermediate shaft is provided with a shaft hole connecting both ends of the intermediate shaft along the axial direction, and the intermediate shaft is provided with an oil outlet hole connecting the inside and outside of the intermediate shaft; The transmission structure also includes: an intermediate bearing and a fastener. The intermediate bearing is connected to the intermediate shaft through the fastener. The fastener has a connecting hole that connects the two ends of the fastener's axial direction. The connecting hole is connected to the shaft hole. An oil storage step is formed between the inner wall of the connecting hole and the inner wall of the shaft hole.

[0012] Preferably, the intermediate gear and the intermediate shaft are rotatably connected, and the transmission structure further includes a synchronizing sleeve, which is slidably connected between the intermediate shaft and the intermediate gear in a manner along the axial direction of the intermediate shaft. In the circumferential direction of the intermediate shaft, the synchronizing sleeve is engaged with the intermediate shaft, and the synchronizing sleeve is keyed to the intermediate gear.

[0013] The present invention also provides an electric drive bridge, including the above-described transmission structure, and further comprising: A gearbox, comprising a housing, wherein a transmission structure and a differential are disposed within the housing, wherein an intermediate shaft drives and connects to the differential; Axle housing, which is connected to an axle housing connection surface on the gearbox, wherein a portion of the housing for accommodating the differential is located inside the axle housing; An axial flux motor is connected to the motor connection surface on the gearbox.

[0014] Compared with existing technologies, this technical solution has the following advantages: This transmission structure and electric drive bridge, by integrally molding some of the input gears with smaller radial dimensions and the input shaft, eliminates the connecting parts compared to the separate assembly method, thereby reducing the size of the input shaft. At the same time, the input gears integrally molded on the input shaft have relatively higher strength. The input gears with larger radial dimensions are connected to the input shaft by a separate structure through assembly, thereby reducing some processing costs. Compared to traditional motors, which have a large axial dimension and insufficient margin for multi-gear arrangement on a single shaft (otherwise they would interfere with the air chamber, frame, etc.), requiring at least three or four gear arrangements and having a relatively complex structure, this transmission structure and electric drive axle, based on the advantages of the motor, have a shorter axial dimension than traditional radial motors, and the gearbox shaft arrangement can have multiple gears on a single shaft, requiring only two gear stages to meet the requirements.

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall transmission structure described in this invention; Figure 2 This is a schematic cross-sectional view of the input shaft of the transmission structure described in this invention; Figure 3 This is a schematic cross-sectional view of the intermediate shaft of the transmission structure described in this invention; Figure 4 This is a schematic diagram of the housing of the gearbox in the electric drive axle of the present invention; Figure 5 This is a schematic diagram of the overall electric drive bridge described in this invention.

[0017] In the diagram: 100, gearbox; 110, housing; 111b, axle housing connecting surface; 112a, half-shaft connecting surface; 121, input shaft; 122, intermediate shaft; 1221, shaft hole; 1222, oil outlet hole; 1223, intermediate bearing; 1224, fastener; 1224a, abutment part; 1224b, connecting part; 12241, connecting hole; 12242, oil reservoir step; 125, intermediate gear; 125a, first intermediate gear; 125b, second intermediate gear; 1 25c, Third intermediate gear; 1255, Synchronizer ring; 126, Input gear; 126a, First input gear; 126a1, First input gear block; 126a2, First input gear groove; 126b, Second input gear; 126c, Third input gear; 126c1, Third input gear ring; 126c2, Third input gear block; 127, Synchronizer sleeve; 128, Retaining ring; 129, Shift fork; 130, Differential; 200, Axial flux motor; 300, Bridge housing Detailed Implementation The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0018] like Figure 1-3 As shown, the present invention provides a transmission structure, comprising: An input shaft 121 is provided with a plurality of input gears 126, which are spaced apart along the axial direction of the input shaft 121. The input gears 126 with smaller radial dimensions are integrally formed with the input shaft 121, while the input gears 126 with larger radial dimensions are assembled with the input shaft 121. An intermediate shaft 122 is provided with a plurality of intermediate gears 125, which are meshed with the input gear 126.

[0019] Based on the above limitations, the input gear 126 with a smaller radial dimension and the input shaft 121 are integrally formed. Compared with the separate assembly method, the connecting part is eliminated, thereby reducing the size of the input shaft 121. At the same time, the input gear 126 integrally formed on the input shaft 121 has relatively higher strength. The input gear 126 with a larger radial dimension and the input shaft 121 are connected by assembly using a separate structure to reduce some processing costs.

[0020] Optionally, the input gear 126 with a small radial dimension is integrally formed on the input shaft 121 by machining or casting, while the input gear 126 with a large radial dimension is interference-fitted with the input shaft 121 and fixed by pin riveting.

[0021] As a preferred embodiment, see Figure 1-3 The input gear 126 includes a first input gear 126a, a second input gear 126b and a third input gear 126c arranged sequentially at intervals along the axial direction of the input shaft 121; The intermediate gear 125 includes a first intermediate gear 125a, a second intermediate gear 125b and a third intermediate gear 125c arranged sequentially at intervals along the axial direction of the intermediate shaft 122. The first input gear 126a is meshed with the first intermediate gear 125a, the second input gear 126b is meshed with the second intermediate gear 125b, and the third input gear 126c is meshed with the third intermediate gear 125c.

[0022] See Figure 2 The radial dimension of the first input gear 126a is smaller than that of the second input gear 126b, and the radial dimension of the third input gear 126c is smaller than that of the second input gear 126b. The first input gear 126a and the input shaft 121 are integrally formed, the third input gear 126c and the input shaft 121 are integrally formed, and the second input gear 126b and the input shaft 121 are assembled together. The radial dimension of the first input gear 126a is smaller than that of the third input gear 126c.

[0023] The radial dimensions of the first input gear 126a and the third input gear 126c are both no more than twice the radial dimension of the input shaft 121. The smaller radial dimension of the input gear 126a results in less torque during transmission. The input shaft 121 outputs a smaller torque through this smaller torque, which helps to reduce the burden on the power source driving the input shaft 121 and improve the efficiency of the gearbox. In addition, the smaller torque of the input shaft 121 reduces the impact and jerking between gears during shifting, which helps to improve the smoothness of shifting and reduce vibration and noise.

[0024] For more details, see Figure 1-2 The first input gear 126a includes a plurality of first input tooth blocks 126a1, which are arranged circumferentially along the input shaft 121. A first input tooth groove 126a2 is formed between adjacent first input tooth blocks 126a1, wherein the top surface of the first input tooth block 126a1 is flush with the outer wall of the input shaft 121. Along the axial direction of the input shaft 121, the connection between the bottom surface of the first input tooth groove 126a2 and the radial outer surface of the input shaft 121 is a smooth transition, so as to form a gentle slope between the first input tooth groove 126a2 and the outer wall of the input shaft 121, avoiding the reduction of its structural stability by slotting on the outer wall of the input shaft 121.

[0025] See Figure 1 and 2 The third input gear 126c includes a third input gear ring 126c1 and a third input gear block 126c2. The outer wall of the input shaft 121 extends outward to form the third input gear ring 126c1 and the third input gear block 126c2 in sequence. The third input gear block 126c2 is arranged circumferentially along the third input gear ring 126c1.

[0026] The second input gear 126b is a ring-shaped second input gear 126b, which is sleeved on the outside of the input shaft 121. The outer wall of the input shaft 121 and the inner wall of the second input gear 126b are interference-fitted. The input shaft 121 and the second input gear 126b are fixed by riveting with pins.

[0027] It can be seen that the assembly method of the second input gear 126b and the input shaft 121 in this solution, as well as the assembly of the first input gear 126a, the third input gear 126c and the input shaft 121, do not use spline and flat key assembly methods, thus avoiding the problems of high production cost of spline and difficult assembly of flat key.

[0028] For the specific construction of the intermediate shaft 122, see the preferred embodiment. Figure 3 The intermediate shaft 122 is hollow and has oil outlet holes 1222 connecting its interior and exterior. Multiple sets of oil outlet holes 1222 are provided, with multiple holes in each set. Adjacent sets of oil outlet holes 1222 are spaced apart along the axial direction of the intermediate shaft 122, while the oil outlet holes 1222 in each set are spaced apart circumferentially along the intermediate shaft 122. During use, lubricating oil from the external oil passage structure of the intermediate shaft 122 can enter the intermediate shaft 122. During high-speed rotation of the intermediate shaft 122, the oil can be ejected through the oil outlet holes 1222, achieving lubrication of the external gears.

[0029] See also Figure 3 The intermediate shaft 122 is provided with shaft holes 1221 that connect the two ends of the intermediate shaft 122 along the axial direction. The transmission structure also includes an intermediate bearing 1223, which is disposed at both ends of the intermediate shaft 122 along the axial direction. The intermediate shaft 122 is rotatably connected to the housing 110 of the gearbox 100 through the intermediate bearing 1223. Fastener 1224, the intermediate bearing 1223 is connected to the intermediate shaft 122 through the fastener 1224, the fastener 1224 is provided with connecting holes 12241 connecting the two ends of the fastener 1224 along the axial direction, the connecting holes 12241 are connected to the shaft hole 1221, and an oil storage step 12242 is formed between the inner wall of the connecting hole 12241 and the inner wall of the shaft hole 1221.

[0030] Furthermore, the connecting hole 12241 and the shaft hole 1221 are coaxially arranged.

[0031] Furthermore, the fastener 1224 has a chamfer on its radially outer end face located within the shaft hole 1221. During use, some oil within the shaft hole 1221 can remain within the annular area formed by the chamfer, thus improving the oil storage effect within the shaft hole 1221.

[0032] In one embodiment, the fastener 1224 includes an abutment portion 1224a and a connecting portion 1224b connected sequentially along the axial direction. The abutment portion 1224a is connected to the intermediate bearing 1223, and the connecting portion 1224b is screwed into the shaft hole 1221.

[0033] In another embodiment, fastener 1224 and intermediate bearing 1223 are nut bearings. The transmission structure is applied to heavy trucks, which have large torque and large impact. The housing 110 is made of aluminum and has low impact resistance. The nut bearing fixation can reduce the impact.

[0034] For the specific connection structure of the intermediate gear 125 and the intermediate shaft 122, please refer to... Figure 3 The intermediate gear 125 is rotatably connected to the intermediate shaft 122. Optionally, the intermediate gear 125 is mounted on the outside of the intermediate shaft 122 by a roller bearing, and a synchronizing ring 1255 is provided on one side of the intermediate gear 125 in the axial direction. A synchronizing sleeve 127 is movably disposed along the axial direction of the intermediate shaft 122. In the circumferential direction of the intermediate shaft 122, the synchronizing sleeve 127 is engaged with the intermediate shaft 122, and the synchronizing sleeve 127 is keyed to the synchronizing ring 1255. In the axial direction of the intermediate shaft 122, the synchronizing sleeve 127 is slidably connected to the intermediate shaft 122, and the synchronizing sleeve 127 is slidably connected to the synchronizing ring 1255. The corresponding key and keyway between the synchronization sleeve 127 and the synchronization ring 1255 are in radial clearance fit. Specifically, the top surface of the key and the bottom surface of the keyway between the synchronization sleeve 127 and the synchronization ring 1255 are in clearance fit. Multiple sets of keys are provided on the synchronizing sleeve 127 or the synchronizing ring 1255. Each set contains multiple keys arranged at intervals along the circumference. A toothed positioning structure is provided between adjacent sets of keys. A limiting surface 12511 is provided on the toothed positioning structure. The limiting surface 12511 abuts against the top surface of the opposite key. The intermediate gear 125, the synchronizing sleeve 127, and the intermediate shaft 122 are arranged concentrically.

[0035] In use, by adjusting the synchronizing sleeve 127's axial position on the intermediate shaft 122, the synchronizing sleeve 127 engages with the synchronizing ring 1255 via a key connection, simultaneously engaging with the intermediate shaft 122. This allows the intermediate shaft 122 to synchronize with the target intermediate gear 125 via the intermediate gear 125, achieving gear shifting. A gap is reserved between the corresponding key and keyway between the synchronizing sleeve 127 and the intermediate gear 125 to provide sufficient redundancy when keying the synchronizing sleeve 127 and the intermediate gear 125, ensuring that the keys on both quickly enter their corresponding keyways. Furthermore, a toothed positioning structure is provided between the synchronizing sleeve 127 and the intermediate gear 125. This toothed positioning structure abuts against its corresponding key, improving the concentricity between the intermediate gear 125, the synchronizing sleeve 127, and the intermediate shaft 122. This avoids the problem of excessive friction between keys due to errors when directly connecting using flat keys or splines, which affects the service life of the transmission structure.

[0036] To ensure that the missing tooth positioning structure can press the key on the synchronization sleeve 127 at multiple angles, the number of missing tooth positioning structures is further increased, and the missing tooth positioning structures are arranged at equal intervals around the circumference of the synchronization ring 1255. As a preferred embodiment, the number of missing tooth positioning structures is three.

[0037] See Figure 3 The transmission structure also includes: A fixing ring 128 is fixedly connected to the intermediate shaft 122. In the circumferential direction of the intermediate shaft 122, the fixing ring 128 and the synchronization sleeve 127 are keyed together, and in the circumferential direction of the intermediate shaft 122, the fixing ring 128 and the synchronization sleeve 127 are slidably connected together.

[0038] The shift fork 129 is rotatably connected to the synchronizing sleeve 127. The shift fork 129 is movably mounted on the housing 110 of the gearbox 100. The shift fork 129 is driven to connect to the synchronizing sleeve 127.

[0039] It should be noted that the shift fork 129 is connected to the shift execution structure, and the shift execution structure drives the shift fork 129 to move within the gearbox 100. This is a mature existing technology and is well known to those skilled in the art, so it will not be described in detail here.

[0040] In addition, the present invention also provides an electric drive bridge, see [link to relevant documentation]. Figure 4 and 5 The transmission structure described above is also included, as well as a gearbox 100. The gearbox 100 includes a housing 110, and a transmission structure and a differential 130 are provided inside the housing 110. The intermediate shaft 122 drives and connects to the differential 130. Axle housing 300 is connected to axle housing connection surface 111b on the gearbox 100, and the portion of the housing 110 of the gearbox 100 for accommodating the differential 130 is located inside the axle housing 300. An axial flux motor 200 is provided, which is connected to a motor connection surface 111a on the gearbox 100. The axial flux motor 200 has the advantage of a small thickness, resulting in a smaller volume for the electric drive axle.

[0041] The transmission structure and electric drive axle adopt a three-speed transmission. When the synchronizing sleeve 127 and the first intermediate gear 125a are connected, the first input gear 126a, the first intermediate gear 125a and the differential are sequentially connected to form the first gear. When the synchronizing sleeve 127 and the second intermediate gear 125b are connected, the second input gear 126b, the second intermediate gear 125b and the differential are sequentially connected to form the second gear. When the synchronizing sleeve 127 and the third intermediate gear 125c are connected, the third input gear 126c, the third intermediate gear 125c and the differential are sequentially connected to form the third gear.

[0042] In summary, this transmission structure and electric drive axle have the following advantages: 1. Structural advantages: Based on the advantages of motors, the axial dimension of motors is half that of traditional motors, and the gearbox shaft system can be arranged with multiple gears on one shaft. Only two gears are needed to meet the requirements. In contrast, the axial dimension of traditional motors is large, and there is not enough margin for multiple gears on one shaft. Otherwise, it will interfere with the air chamber, frame, etc. Therefore, at least three or four gears are required, and the structure is more complex.

[0043] 2. High transmission efficiency: ①. Compared to traditional gearboxes that use at least three or four stages, resulting in more gear meshing and greater oil churning losses, the gearbox provided in this embodiment has only two stages of transmission, with fewer gear meshing and higher transmission efficiency; ②. The gearbox uses a three-speed transmission. Because the disc motor has a large efficiency range, the motor is basically in the high-efficiency range at almost every vehicle speed. 3. The transmission is a three-speed gearbox, which has good power performance and economy, with a maximum gradeability of >37.1% and a maximum speed of >115 km / h; 4. Good NVH performance: Each gear has a dedicated gear mesh, and the working conditions of each gear are different. It is designed and micro-tuned specifically for each gear. Traditional gearboxes have many transmission stages and share many gears, so they cannot be designed and tuned specifically for each gear, resulting in poor NVH. 5. The manufacturing and processing technology and assembly technology are simpler than those of traditional gearboxes, making it easier to achieve mass production. 6. By fully utilizing the advantages of axial flux motors, such as fast speed regulation, the clutch is eliminated, thus avoiding the difficulties in controlling slippage and heat dissipation of traditional gearbox clutches. 7. By fully utilizing the characteristics of axial flux motors, such as fast speed regulation and small error, the synchronizer is eliminated, avoiding the control of shifting force when the synchronizer is working, thus reducing the control difficulty; 8. No synchronizer, no clutch, lower cost, less shifting noise, and lower after-sales service costs.

[0044] The embodiments described above are only used to illustrate the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The scope of patent application of the present invention should not be limited by these embodiments. That is, any equivalent changes or modifications made in accordance with the spirit disclosed in the present invention still fall within the patent scope of the present invention.

Claims

1. An electric drive bridge, characterized in that, include: Transmission structure; The gearbox (100) includes a housing (110) and a transmission structure and a differential (130) are provided inside the housing (110), wherein an intermediate shaft (122) drives the differential (130). Axle housing (300) is connected to an axle housing connection surface (111b) on the gearbox (100), and a portion of the housing (110) for accommodating the differential (130) is located inside the axle housing (300). An axial flux motor (200) is connected to a motor connection surface (111a) on the gearbox (100); The transmission structure includes an input shaft (121) and an intermediate shaft (122). The input shaft (121) is provided with a plurality of input gears (126). The input gears (126) include a first input gear (126a) and a second input gear (126b). The radial dimension of the second input gear (126b) is larger than that of the first input gear (126a). The plurality of input gears (126) are arranged at intervals along the axial direction of the input shaft (121). The first input gear (126a) and the input shaft (121) are integrally formed. The second input gear (126b) and the input shaft (121) are assembled together. The intermediate shaft (122) is provided with a plurality of intermediate gears (125). The intermediate gears (125) are meshed with the input gears (126). The intermediate gear (125) includes a first intermediate gear (125a) and a second intermediate gear (125b), the first input gear (126a) meshes with the first intermediate gear (125a), and the second input gear (126b) meshes with the second intermediate gear (125b); The input gear (126) further includes a third input gear (126c), and the intermediate gear (125) further includes a third intermediate gear (125c). The radial dimension of the third input gear (126c) is smaller than that of the second input gear (126b). The third input gear (126c) and the third intermediate gear (125c) mesh. The third input gear (126c) and the input shaft (121) are integrally formed. The third input gear (126c) includes a third input gear ring (126c1) and a third input gear block (126c2). The outer wall of the input shaft (121) extends outward to form the third input gear ring (126c1) and the third input gear block (126c2) in sequence. The third input gear block (126c2) is arranged at intervals along the circumference of the third input gear ring (126c1). The intermediate shaft (122) is provided with a shaft hole (1221) that connects the two ends of the axis of the intermediate shaft (122), and an oil outlet hole (1222) that connects the inside and outside of the intermediate shaft (122) is provided on the intermediate shaft (122). The transmission structure also includes an intermediate bearing (1223) and a fastener (1224). The intermediate bearing (1223) is connected to the intermediate shaft (122) through the fastener (1224). The fastener (1224) is provided with a connecting hole (12241) that connects the two ends of the fastener (1224) in the axial direction. The connecting hole (12241) is connected to the shaft hole (1221). An oil storage step (12242) is formed between the inner wall of the connecting hole (12241) and the inner wall of the shaft hole (1221).

2. The transmission structure as described in claim 1, characterized in that, The second input gear (126b) is an annular input gear, which is sleeved on the outside of the input shaft (121). The outer wall of the input shaft (121) and the inner wall of the second input gear (126b) are interference-fitted and fixed by riveting with pins.

3. The electric drive bridge as described in claim 1, characterized in that, The first input gear (126a) includes a plurality of first input tooth blocks (126a1), which are arranged circumferentially along the input shaft (121). A first input tooth groove (126a2) is formed between adjacent first input tooth blocks (126a1), wherein the top surface of the first input tooth block (126a1) is flush with the outer wall of the input shaft (121).

4. The electric drive bridge as described in claim 3, characterized in that, In the axial direction of the input shaft (121), the connection between the bottom surface of the first input tooth groove (126a2) and the radial outer surface of the input shaft (121) is a smooth transition.

5. The electric drive bridge as described in claim 1, characterized in that, The intermediate gear (125) and the intermediate shaft (122) are rotatably connected. The transmission structure also includes a synchronizing sleeve (127). The synchronizing sleeve (127) is slidably connected between the intermediate shaft (122) and the intermediate gear (125) in an axial manner along the intermediate shaft (122). The synchronizing sleeve (127) and the intermediate shaft (122) are engaged in the circumferential direction of the intermediate shaft (122). The synchronizing sleeve (127) and the intermediate gear (125) are keyed together.

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