Dual-motor four-gear transmission and gear shifting control method thereof

Abstract

The double-motor four-gear gearbox comprises two motors and a gear shifting assembly with two-gear shifting function, characterized in that it further comprises a double planetary gear structure and a brake assembly installed in the double planetary gear structure, the gear shifting assembly is of a parallel shaft structure, the motors are connected with the input end of the gear shifting assembly, the double planetary gear structure is connected with the output end of the gear shifting assembly, and the double planetary gear structure forms two-gear ratio switching with the control of the brake assembly. The application precisely matches the driving requirements of low-speed high-torque and high-speed high-efficiency of the vehicle, widens the coverage range of the high-efficiency interval of the motor, reduces the axial space layout and weight of the gearbox, improves the power density of the output torque, improves the transmission stability, improves the torque connection efficiency between gears, reduces the gear shifting impact, improves the driving experience, and improves the robustness of the gear shifting system. The application further provides a gear shifting control method of the double-motor four-gear gearbox.

Description

Technical Field

[0001] This invention relates to a dual-motor four-speed gearbox and its shift control method, belonging to the field of pure electric transmission technology. Background Technology

[0002] As electric vehicles increasingly demand high-efficiency and multi-scenario power output, single-motor electric drive axle solutions suffer from significant limitations. This is because single high-power motors are expensive and inefficient under low load conditions, often resulting in high overall vehicle energy consumption and unsatisfactory power performance. With technological advancements, dual-motor electric drive axles have become a research hotspot. By combining two relatively smaller-power motors, system costs are reduced, and precise speed ratio configurations allow the motors to operate more frequently in their efficient operating range, significantly improving vehicle economy and driving experience. In the field of dual-motor electric drive axles, planetary gear mechanisms and parallel shaft structures are widely used to achieve flexible motor coupling and intelligent power distribution, utilizing clutches for gear control. However, existing multi-speed electric drive systems suffer from issues such as volume redundancy, power interruption during gear shifts, and limited torque capacity. Especially in high-performance vehicle applications, dual-motor coupled drive and multi-gear coordinated drive schemes present the following problems: 1. The parallel shaft structure with multiple gear positions occupies a lot of axial space, is heavy, has high mechanical loss, and low power density.

[0003] 2. Poor torque diversion capability, large load on single-stage gears, rapid wear, and impact on transmission stability.

[0004] 3. The uneven torque distribution across multiple gears causes shift shocks and reduces the driving experience. Summary of the Invention

[0005] The dual-motor four-speed gearbox and its shift control method provided by this invention accurately match the driving requirements of low-speed high torque and high-speed high efficiency of vehicles, broaden the coverage of the high-efficiency range of the motor, reduce the axial space layout and weight of the gearbox, increase the power density of output torque, improve transmission stability, improve the torque connection efficiency between gears, reduce shift shock, improve the driving experience, and enhance the robustness of the transmission system.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A dual-motor four-speed gearbox includes two motors and a gearbox assembly with two-speed shifting function. The gearbox assembly is characterized by further including a dual planetary gearbox structure and a braking assembly installed in the dual planetary gearbox structure. The gearbox assembly is a parallel shaft structure. The motors are connected to the input end of the gearbox assembly, and the dual planetary gearbox structure is connected to the output end of the gearbox assembly. The dual planetary gearbox structure switches between two speed ratios under the control of the braking assembly.

[0007] Preferably, the dual planetary gear structure includes a first planetary gear and a second planetary gear, the ring gear of the first planetary gear is fixedly connected to the ring gear of the second planetary gear, the output end of the transmission component is connected to the ring gear of the first planetary gear, the planet carrier of the first planetary gear is fixedly connected to the sun gear of the second planetary gear, and the braking component controls the sun gear of the first planetary gear or the sun gear of the second planetary gear to be fixed.

[0008] Preferably, the transmission assembly includes an input shaft connected to the motor shaft end, an intermediate shaft parallel to the two input shafts, a low-gear drive gear coaxially fixed on the input shaft, a high-gear drive gear coaxially fixed on the input shaft, a low-gear driven gear meshing with the low-gear drive gear, a high-gear driven gear meshing with the high-gear drive gear, and a shift sleeve slidably mounted on the intermediate shaft along the axial direction. The low-gear driven gear and the high-gear driven gear are rotatably mounted on the intermediate shaft, and the shift sleeve is located between the low-gear driven gear and the high-gear driven gear. The shift sleeve slides to the left to engage with the low-gear driven gear and slides to the right to engage with the high-gear driven gear. The intermediate shaft is coaxially connected to the gear ring of the first planetary gear set.

[0009] Preferably, the first planetary gear set includes a first sun gear, a first planet gear meshing with the first sun gear, a first planet carrier mounted on the first planet gear, and a first gear ring with an inner ring meshing with the first planet gear. The second planetary gear set includes a second sun gear, a second planet gear meshing with the second sun gear, a second planet carrier mounted on the second planet gear, and a second gear ring with an inner ring meshing with the second planet gear. The first gear ring and the second gear ring are fixedly connected. An intermediate shaft is connected to the first gear ring. The first planet carrier is fixedly connected to the second sun gear. The braking assembly includes a first brake mounted on the first sun gear and a second brake mounted on the second sun gear.

[0010] Preferably, the intermediate shaft, the first gear ring, and the second gear ring are integrally formed, and the output shaft is integrally formed on the second planetary carrier.

[0011] The shift control method of the dual-motor four-speed gearbox described above is characterized in that: By controlling the transmission and braking components, four-speed power output of the dual-motor four-speed gearbox is achieved; When the transmission component forms the first gear power and the braking component controls the double planetary gear structure to form the second gear ratio, the first gear power output of the dual-motor four-speed gearbox is formed. When the transmission assembly forms the first gear power and the braking assembly controls the double planetary gear structure to form the first gear ratio, the second gear power output of the dual-motor four-speed gearbox is formed. When the transmission assembly forms second-gear power and the braking assembly controls the dual planetary gear structure to form a second-gear ratio, a third-gear power output is generated in the dual-motor four-speed gearbox. When the transmission assembly forms second gear and the braking assembly controls the dual planetary gearbox structure to form first gear ratio, a four-speed power output is generated by a dual-motor four-speed gearbox. Preferably, "the transmission assembly forming first gear power" means that the shift sleeve slides to the left and engages with the lower driven gear; "the transmission assembly forming second gear power" means that the shift sleeve slides to the right and engages with the higher driven gear.

[0012] Preferably, "the dual planetary gear structure forms a two-speed ratio" means that the second brake is activated to fix the first planetary carrier and the second sun gear, the intermediate shaft drives the first and second ring gears to rotate, and the second ring gear drives the second planetary carrier to rotate, thus outputting power; "The double planetary gear structure forms a first gear ratio" means that the first brake is activated to fix the first sun gear, the intermediate shaft drives the first and second ring gears to rotate, the power of the second ring gear is transmitted to the second planet carrier, and the power of the first ring gear is transmitted to the second planet carrier via the first planet carrier and the second sun gear. The power is then combined and output on the second planet carrier.

[0013] The beneficial effects of this invention are: The present invention relates to a dual-motor four-speed gearbox. Two motors are connected to the input end of a transmission assembly, and a dual planetary gearbox structure is connected to the output end of the transmission assembly. The parallel-shaft transmission assembly couples the power of the two motors, transmitting two gears to the dual planetary gearbox structure. The dual planetary gearbox structure switches between the two gear ratios under the control of the braking assembly. The combination of the two gears of the transmission assembly and the two gear ratios of the dual planetary gearbox structure not only forms the four-speed power output of the gearbox, precisely matching the vehicle's low-speed high-torque and high-speed high-efficiency driving requirements and broadening the coverage of the motor's high-efficiency range, but also utilizes the planetary gears... The compact structure and large speed ratio of the dual planetary gearbox reduce the axial space and weight of the transmission, decrease mechanical losses during transmission, and increase the power density of output torque. The dual planetary gearbox structure effectively increases torque splitting capability, reduces single-stage gear load, and improves transmission stability. The braking components form two gear ratios for the dual planetary gearbox structure, enabling coordinated control of parallel shaft shifting and planetary gearbox braking shifting. This improves torque connection efficiency between gears, reduces shift shock, and enhances the driving experience. The dual motors form a redundant design to support limp-mode in case of single-motor failure, improving the robustness of the transmission system. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the transmission structure of the dual-motor four-speed gearbox in a specific implementation.

[0015] Figure 2 A schematic diagram of the transmission structure of a dual-motor, four-speed gearbox when forming a first-speed power system.

[0016] Figure 3 A schematic diagram of the transmission structure of a dual-motor four-speed gearbox when forming a second-speed power.

[0017] Figure 4 A schematic diagram of the transmission structure of a dual-motor four-speed gearbox to form a three-speed power system.

[0018] Figure 5 A schematic diagram of the transmission structure of a dual-motor four-speed gearbox to achieve four-speed power. Detailed Implementation

[0019] The following is combined with Figures 1-5 The embodiments of the present invention will be described in detail below.

[0020] A dual-motor four-speed gearbox includes two motors 1 and a gearbox assembly 2 with two-speed shifting function. The gearbox assembly 2 is characterized by further including a dual planetary gearbox structure 3 and a braking assembly 4 installed in the dual planetary gearbox structure 3. The gearbox assembly 2 is a parallel shaft structure. The motors 1 are connected to the input end of the gearbox assembly 2, and the dual planetary gearbox structure 3 is connected to the output end of the gearbox assembly 3. The dual planetary gearbox structure 3 forms a two-speed ratio switching under the control of the braking assembly 4.

[0021] The dual-motor four-speed gearbox described above has two motors 1 connected to the input end of the transmission assembly 2, and a dual planetary gearbox structure 3 connected to the output end of the transmission assembly 2. The parallel-shaft transmission assembly 2 couples the power from the two motors 1, transmitting two gears to the dual planetary gearbox structure 3. The dual planetary gearbox structure 3, controlled by the braking assembly 4, switches between the two gear ratios. The combination of the two gears of the transmission assembly 2 and the two gear ratios of the dual planetary gearbox structure 3 not only forms the four-speed power output of the gearbox, precisely matching the vehicle's low-speed high-torque and high-speed high-efficiency driving needs, but also broadens the coverage range of the motor's high-efficiency range. Furthermore, by utilizing the compact structure and large speed ratio of the planetary gearbox, the axial space layout and weight of the transmission are reduced, mechanical losses during transmission are decreased, and the power density of output torque is increased. The dual planetary gearbox structure 3 effectively increases torque splitting capability, reduces single-stage gear load, and improves transmission stability. The braking component 4 forms two speed ratios for the dual planetary gearbox structure, forming coordinated control of parallel shaft structure shifting and planetary gearbox braking shifting, improving torque connection efficiency between gears, reducing shift shock, and improving driving experience. The dual motors form a redundant design to support limp mode under single motor failure, improving the robustness of the transmission system.

[0022] The dual planetary gear structure 3 includes a first planetary gear set 5 and a second planetary gear set 6. The ring gear of the first planetary gear set 5 is fixedly connected to the ring gear of the second planetary gear set 6. The output end of the transmission assembly 2 is connected to the ring gear of the first planetary gear set 5. The planet carrier of the first planetary gear set 5 is fixedly connected to the sun gear of the second planetary gear set 6. The braking assembly 4 controls the fixing of the sun gear of the first planetary gear set 5 or the sun gear of the second planetary gear set 6. The ring gears of the two planetary gear sets are fixedly connected as a whole, and the ring gears serve as the input end of the dual planetary gear structure 3. The output end of the transmission assembly 2 drives the ring gears to move, transmitting power to the dual planetary gear structure 3. The braking assembly can fix the sun gear of the first planetary gear set 5 or the sun gear of the second planetary gear set 6, thereby changing the speed ratio of the dual planetary gear structure 3, allowing the dual planetary gear structure 3 to switch between two speed ratios under the control of the braking assembly 4.

[0023] The transmission assembly 2 includes an input shaft 21 connected to the shaft end of the motor 1, an intermediate shaft 22 parallel to the two input shafts 21, a low-gear drive gear 23 coaxially fixed on the input shaft 21, a high-gear drive gear 24 coaxially fixed on the input shaft 21, a low-gear driven gear 25 meshing with the low-gear drive gear 23, a high-gear driven gear 26 meshing with the high-gear drive gear 24, and a shift sleeve 27 slidably mounted on the intermediate shaft 22. The low-gear driven gear 25 and the high-gear driven gear 26 are rotatably mounted on the intermediate shaft 22, and the shift sleeve 27 is located between the low-gear driven gear 25 and the high-gear driven gear 26. The shift sleeve 27 slides to the left to engage with the low-gear driven gear 25 and slides to the right to engage with the high-gear driven gear 26. The intermediate shaft 22 is coaxially connected to the gear ring of the first planetary gear set 5. In its initial state, the shift sleeve 27 is in the neutral position between the low-gear driven gear 25 and the high-gear driven gear 26. Since both the low-gear driven gear 25 and the high-gear driven gear 26 are rotatably mounted on the intermediate shaft 22, the shift sleeve 27 cannot transmit power from the input shaft to the intermediate shaft 22 when it is in neutral. When the shift sleeve 27 engages with the low-gear driven gear 25, the motor's power is transmitted to the intermediate shaft 22 via the input shaft 21, the low-gear drive gear 23, the low-gear driven gear 25, and the shift sleeve 27. The intermediate shaft 22 then transmits the power to the double planetary gear structure 3. When the shift sleeve 27 engages with the high-gear driven gear 26, the motor's power is transmitted to the intermediate shaft 22 via the input shaft 21, the high-gear drive gear 24, the high-gear driven gear 26, and the shift sleeve 27. The intermediate shaft 22 then transmits the power to the double planetary gear structure 3. Therefore, two gears can be transmitted to the double planetary gear structure 3 on the intermediate shaft 22.

[0024] The first planetary gear set 5 includes a first sun gear 51, a first planet gear meshing with the first sun gear 51, a first planet carrier 52 mounted on the first planet gear, and a first gear ring 53 with an inner ring meshing with the first planet gear. The second planetary gear set 6 includes a second sun gear 61, a second planet gear meshing with the second sun gear 51, a second planet carrier 62 mounted on the second planet gear, and a second gear ring 63 with an inner ring meshing with the second planet gear. The first gear ring 53 and the second gear ring 63 are fixedly connected. The intermediate shaft 22 is connected to the first gear ring 53. The first planet carrier 52 is fixedly connected to the second sun gear 61. The braking assembly 4 includes a first brake 41 mounted on the first sun gear 51 and a second brake 42 mounted on the second sun gear 64.When the first brake 41 is activated, the first sun gear 51 is fixed. The power from the intermediate shaft 22 is transmitted to the first ring gear 53 and the second ring gear 63. The power from the first ring gear 53 is transmitted to the second planetary carrier via the first and second planetary gear sets. The power from the second ring gear 63 is transmitted to the second planetary carrier via the second planetary gear set. The power is combined and output on the second planetary carrier, forming the first gear ratio of the double planetary gear set structure 3. When the second brake 42 is activated, the second sun gear 61 is fixed, meaning the first planetary carrier is fixed. The first planetary gear set does not transmit power; only the second planetary gear set is driven. The power from the intermediate shaft 22 is transmitted from the second ring gear 63 to the second planetary carrier, forming the second gear ratio of the double planetary gear set structure 3. The value of the first gear ratio is less than the value of the second gear ratio. When the planetary gearbox structure 3 forms the first gear ratio, its output speed is high and its torque is low. When the double planetary gearbox structure 3 forms the second gear ratio, its output speed is low and its torque is high. When the meshing sleeve 27 engages with the low-gear driven gear 25 and the second brake is activated, the power of the motor 11 is transmitted to the intermediate shaft 22 via the input shaft 21, the low-gear drive gear 23, the low-gear driven gear 25, and the meshing sleeve 27. The intermediate shaft 22 drives the first gear ring 51 and the second gear ring 61. The second gear ring 61 drives the second planetary carrier 62 through the second planetary gears. The second planetary carrier 62 outputs power, forming the first gear of the gearbox. When the meshing sleeve 27 engages with the low-gear driven gear 25 and the first brake is activated, the power of the motor 11 is transmitted to the intermediate shaft 22 via the input shaft 21, the low-gear drive gear 23, the low-gear driven gear 25, and the meshing sleeve 27. Gear 23, low-gear driven gear 25, and meshing sleeve 27 transmit power to intermediate shaft 22. Intermediate shaft 22 drives the first gear ring 53 and the second gear ring 63. The power of the first gear ring 51 is transmitted to the second planetary carrier 62 via the first planetary carrier 52, the second sun gear 61, and the second planetary gears. The power of the second gear ring 63 is transmitted to the second planetary carrier 62 via the second planetary gears. The power is combined and output on the second planetary carrier 62, forming the second gear of the gearbox. When meshing sleeve 27 engages with high-gear driven gear 26 and the second brake 42 is activated, the power of motor 11 is transmitted to intermediate shaft 22 via input shaft 21, high-gear drive gear 24, high-gear driven gear 26, and meshing sleeve 27. Intermediate shaft 22 drives the first gear ring 51 and the second gear ring 63. The second gear ring 61 drives the second planetary carrier 62 via the second planetary gears, and the second planetary carrier 62 outputs power to form the third gear of the gearbox. When the meshing sleeve engages with the high-speed driven gear 26 and the first brake is activated, the power of the motor 11 is transmitted to the intermediate shaft 22 via the input shaft 21, the high-speed driving gear 24, the high-speed driven gear 26, and the meshing sleeve 27. The intermediate shaft 22 drives the first gear ring 53 and the second gear ring 63 to move. The power of the first gear ring 51 is transmitted to the second planetary carrier 62 via the first planetary carrier 52, the second sun gear 61, and the second planetary gears. The power of the second gear ring 63 is transmitted to the second planetary carrier 62 via the second planetary gears. The power is combined and output on the second planetary carrier 62 to form the fourth gear of the gearbox.

[0025] The intermediate shaft 22, the first gear ring 53, and the second gear ring 53 are integrally formed, and the output shaft 7 is integrally formed on the second planetary carrier 62. This improves the stability and reliability of the double planetary gear structure 3 and effectively reduces maintenance costs.

[0026] This invention also protects the shift control method of the dual-motor four-speed gearbox described above, characterized in that: By controlling the transmission assembly 2 and the braking assembly 4, the four-speed power output of the dual-motor four-speed gearbox is realized; When the transmission component 2 forms the first gear power and the braking component 4 controls the double planetary gear structure 3 to form the second gear ratio, the first gear power output of the dual motor four-speed gearbox is formed. When the transmission component 2 forms the first gear power and the braking component 4 controls the double planetary gear structure 3 to form the first gear ratio, the second gear power output of the dual motor four-speed gearbox is formed. When the transmission component 2 forms a second-gear power and the braking component 4 controls the double planetary gear structure 3 to form a second-gear speed ratio, a third-gear power output is formed in the dual-motor four-speed gearbox. When the transmission component 2 forms a second-gear power and the braking component 4 controls the double planetary gear structure 3 to form a first-gear speed ratio, a four-gear power output is formed by the dual-motor four-speed gearbox. Since the speed ratio is directly proportional to torque and inversely proportional to speed, a larger speed ratio results in greater torque and lower speed. The first gear ratio of the double planetary gearbox 3 is smaller than its second gear ratio. When the double planetary gearbox 3 forms a first gear ratio, the output speed is higher and the torque is lower; when it forms a second gear ratio, the output speed is lower and the torque is higher. Therefore, when the transmission assembly 2 forms a first gear and the double planetary gearbox 3 forms a second gear ratio, it forms the first gear output of a dual-motor four-speed gearbox, meeting the high-torque drive requirements for escaping difficult situations under heavy loads and harsh conditions. The second-gear power output of the four-speed transmission meets the driving requirements of high-speed driving under heavy load conditions. When the transmission assembly 2 forms the second-gear power and the double planetary gear structure 3 forms the second-gear ratio, the third-gear power output of the dual-motor four-speed transmission is formed, meeting the driving requirements of rapid passage under light load and harsh conditions. When the transmission assembly forms the second-gear power and the double planetary gear structure forms the first-gear ratio, the fourth-gear power output of the dual-motor four-speed transmission is formed, meeting the driving requirements of high-speed driving under light load conditions. The four-gear power output of the transmission precisely matches the driving requirements of low-speed high torque and high-speed high efficiency of the vehicle, and widens the coverage of the high-efficiency range of the motor.

[0027] Specifically, "transmission assembly 2 forming first gear power" means that the shift sleeve 37 slides to the left and engages with the low-gear driven gear 25; "transmission assembly 2 forming second gear power" means that the shift sleeve 27 slides to the right and engages with the high-gear driven gear 26. When the shift sleeve 27 engages with the low-gear driven gear 25, the motor power is transmitted to the intermediate shaft 22 via the input shaft 21, the low-gear drive gear 23, the low-gear driven gear 25, and the shift sleeve 27. The intermediate shaft 22 then transmits the power to the double planetary gear set 3. When the shift sleeve 27 engages with the high-gear driven gear 26, the motor power is transmitted to the intermediate shaft 22 via the input shaft 21, the high-gear drive gear 24, the high-gear driven gear 26, and the shift sleeve 27. The intermediate shaft 22 then transmits the power to the double planetary gear set 3. Therefore, two gears can be transmitted to the double planetary gear set 3 via the intermediate shaft 22.

[0028] Preferably, "the double planetary gear structure 3 forms a second gear ratio" means that the second brake 42 is activated to fix the first planetary carrier 52 and the second sun gear 61, the intermediate shaft 22 drives the first gear ring 53 and the second gear ring 63 to rotate, and the second gear ring 63 drives the second planetary carrier 62 to rotate, thus outputting power; "The double planetary gear structure 3 forms a first gear ratio" means that the first brake 41 is activated to fix the first sun gear 51, the intermediate shaft 22 drives the first ring gear 53 and the second ring gear 63 to rotate, the power of the second ring gear 63 is transmitted to the second planet carrier 62, and the power of the first ring gear 53 is also transmitted to the second planet carrier 62 through the first planet carrier 52 and the second sun gear 61. The power is combined and output on the second planet carrier.

[0029] When the first brake 41 is activated, the first sun gear 51 is fixed. The power from the intermediate shaft 22 is transmitted to the first ring gear 53 and the second ring gear 63. The power from the first ring gear 53 is transmitted to the second planetary carrier 62 via the first planetary carrier 52 and the second sun gear 61. The power from the second ring gear 63 is also transmitted to the second planetary carrier 62. The power is combined and output on the second planetary carrier, forming the first gear ratio of the double planetary gear set 3. When the second brake 42 is activated, the second sun gear 61 is fixed, i.e., the first planetary carrier 52 is fixed. The first planetary gear set does not transmit power; only the second planetary gear set is driven. The power from the intermediate shaft 22 is transmitted from the second ring gear 63 to the second planetary carrier 62, forming the second gear ratio of the double planetary gear set 3. The value of the first gear ratio is less than the value of the second gear ratio. When the double planetary gear set 3 forms the first gear ratio, its output speed is high and its torque is low. When the double planetary gear set 3 forms the second gear ratio, its output speed is high and its torque is low. The output speed is low but the torque is high. Therefore, when the transmission component 2 provides first-gear power and the double planetary gear structure 3 provides second-gear ratio, it forms the first-gear power of the dual-motor four-speed transmission. When the transmission component 2 provides first-gear power and the double planetary gear structure 3 provides first-gear ratio, it forms the second-gear power of the dual-motor four-speed transmission. The speed of the second-gear power is higher than that of the first-gear power, but the torque is lower. When the transmission component 2 provides second-gear power and the double planetary gear structure 3 provides second-gear ratio, it forms the third-gear power of the dual-motor four-speed transmission. The speed of the third-gear power is higher than that of the second-gear power, but the torque is lower. When the transmission component provides second-gear power and the double planetary gear structure provides first-gear ratio, it forms the fourth-gear power of the dual-motor four-speed transmission. The speed of the fourth-gear power is higher than that of the third-gear power, but the torque is lower. This precisely matches the vehicle's low-speed high torque and high-speed high efficiency driving needs, and broadens the coverage range of the motor's high-efficiency range.

[0030] The technical solutions of the embodiments of the present invention have been fully described above with reference to the accompanying drawings. It should be noted that the described embodiments are only a part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A dual-motor four-speed gearbox, comprising two motors and a gearbox assembly with two-speed shifting function, characterized in that: It also includes a double planetary gear structure and a braking component installed in the double planetary gear structure. The transmission component is a parallel shaft structure. The motor is connected to the input end of the transmission component, and the double planetary gear structure is connected to the output end of the transmission component. The double planetary gear structure forms a two-speed ratio switching according to the control of the braking component. The dual planetary gear structure includes a first planetary gear and a second planetary gear. The gear ring of the first planetary gear is fixedly connected to the gear ring of the second planetary gear. The output end of the transmission component is connected to the gear ring of the first planetary gear. The planet carrier of the first planetary gear is fixedly connected to the sun gear of the second planetary gear. The braking component controls the sun gear of the first planetary gear or the sun gear of the second planetary gear to be fixed. The speed transmission assembly includes an input shaft connected to the motor shaft end, an intermediate shaft parallel to the two input shafts, a low-gear drive gear coaxially fixed on the input shaft, a high-gear drive gear coaxially fixed on the input shaft, a low-gear driven gear meshing with the low-gear drive gear, a high-gear driven gear meshing with the high-gear drive gear, and a shift sleeve slidably mounted on the intermediate shaft along the axial direction. The low-gear driven gear and the high-gear driven gear are rotatably mounted on the intermediate shaft, and the shift sleeve is located between the low-gear driven gear and the high-gear driven gear. The shift sleeve slides to the left to engage with the low-gear driven gear and slides to the right to engage with the high-gear driven gear. The intermediate shaft is coaxially connected to the gear ring of the first planetary gear set. The first planetary gear set includes a first sun gear, first planet gears meshing with the first sun gear, a first planet carrier mounted on the first planet gear, and a first gear ring with an inner ring meshing with the first planet gear. The second planetary gear set includes a second sun gear, second planet gears meshing with the second sun gear, a second planet carrier mounted on the second planet gear, and a second gear ring with an inner ring meshing with the second planet gear. The first gear ring and the second gear ring are fixedly connected. An intermediate shaft is connected to the first gear ring. The first planet carrier is fixedly connected to the second sun gear. The braking assembly includes a first brake mounted on the first sun gear and a second brake mounted on the second sun gear.

2. The dual-motor four-speed gearbox according to claim 1, characterized in that: The intermediate shaft, the first gear ring, and the second gear ring are integrally formed, and the output shaft is integrally formed on the second planetary carrier.

3. The shift control method of the dual-motor four-speed gearbox according to any one of claims 1 to 2, characterized in that: By controlling the transmission and braking components, four-speed power output of the dual-motor four-speed gearbox is achieved; When the transmission assembly forms the first gear and the braking assembly controls the dual planetary gear structure to form the second gear ratio, the first gear power output of the dual-motor four-speed gearbox is formed. When the transmission assembly forms the first gear and the braking assembly controls the dual planetary gear structure to form the first gear ratio, the second gear power output of the dual-motor four-speed gearbox is formed. When the transmission assembly forms second gear and the braking assembly controls the dual planetary gearbox structure to form a second gear ratio, a third gear output is generated in the dual-motor four-speed gearbox. When the transmission assembly forms second gear and the braking assembly controls the dual planetary gearbox structure to form first gear ratio, a four-speed power output is generated in the dual-motor four-speed gearbox.

4. The shift control method of the dual-motor four-speed gearbox as described in claim 3, characterized in that: "The transmission assembly forms first gear power" means that the shift sleeve slides to the left and engages with the lower driven gear; "The transmission assembly forms second gear power" means that the shift sleeve slides to the right and engages with the higher driven gear.

5. The shift control method of the dual-motor four-speed gearbox according to claim 4, characterized in that: "The double planetary gear structure forms a two-speed ratio" means that the second brake is activated to fix the first planetary carrier and the second sun gear, the intermediate shaft drives the first and second ring gears to rotate, the second ring gear drives the second planetary carrier to rotate, and outputs power; "The double planetary gear structure forms a first gear ratio" means that the first brake is activated to fix the first sun gear, the intermediate shaft drives the first and second ring gears to rotate, the power of the second ring gear is transmitted to the second planet carrier, and the power of the first ring gear is transmitted to the second planet carrier via the first planet carrier and the second sun gear. The power is then combined and output on the second planet carrier.

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