Planetary gear train type speed reduction differential transmission mechanism and transmission method thereof

Abstract

The invention discloses a planetary gear train type speed reduction differential transmission mechanism and a transmission method thereof, and belongs to the technical field of speed reducers. A stator of the motor is connected with the shell, a rotor of the motor is connected with a first sun gear and arranged outside the first output shaft in a sleeving mode, the first sun gear is meshed with a first planet gear, the first planet gear is meshed with a first gear ring, the first planet gear is installed on a first planet carrier, and the first planet carrier is connected with the first output shaft. The second sun gear is meshed with the second planet gear, the second planet gear is meshed with the third planet gear, the third planet gear is meshed with the second gear ring, and the second planet gear and the third planet gear are both installed on the second planet carrier. The first gear ring is connected with the second planet carrier, and the second sun gear is connected with the second output shaft. Or the gear ring I is connected with the sun gear II, and the planet carrier II is connected with the second output shaft; the first output shaft, the second output shaft, the first planetary gear train, the second planetary gear train and the motor are coaxially arranged. The differential mechanism is compact in structure, large in transmission ratio and easy to manufacture, the differential function is achieved through the planetary gear train, and the technical bottleneck of a traditional transmission mechanism is broken through.

Description

Technical Field

[0001] The present invention relates to a planetary gear train type reduction differential transmission mechanism and its transmission method, belonging to the technical field of reducers. Background Art

[0002] To optimize the torque output characteristics and improve the system energy efficiency, the transmission device needs to have a large reduction ratio design and requires a separate differential to ensure that the motor output torque can be effectively transmitted to the drive wheels. At the same time, restricted by the vehicle lightweight design and space layout, the structural complexity of the transmission mechanism needs to be significantly reduced, and the overall mass needs to be strictly controlled at a low level. In addition, modern electric drive systems have higher requirements for functional integration, and the traditional decentralized differential and reduction modules are difficult to meet the high-efficiency and compact integration needs. It is urgent to achieve the collaborative integration of multiple functions through structural design innovation. Under this background, how to break through the technical bottlenecks of the existing transmission mechanism in terms of reduction ratio, structural simplification, lightweight and functional integration has become a key problem to be solved in this field. Summary of the Invention

[0003] To solve the problems in the background art, the present invention provides a planetary gear train type reduction differential transmission mechanism and its transmission method.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] Solution 1:

[0006] A planetary gear train type reduction differential transmission mechanism includes a first planetary gear train, a second planetary gear train, a motor, a housing, a first output shaft and a second output shaft; the first planetary gear train includes a first sun gear, a first planet carrier, a first ring gear and a first planet gear; the stator of the motor is rigidly connected to the housing, the rotor of the motor is rigidly connected to the first sun gear, the first sun gear meshes with the first planet gear, the first planet gear also meshes with the first ring gear, and the first planet gear is installed on the first planet carrier, forming a first-stage planetary gear reduction mechanism; the first planet carrier is rigidly connected to the first output shaft, and the rotor of the motor is sleeved outside the first output shaft; the second planetary gear train includes a second sun gear, a second planet carrier, a second ring gear, a second planet gear and a third planet gear; the second sun gear meshes with the second planet gear, the second planet gear meshes with the third planet gear, the third planet gear meshes with the second ring gear fixed to the housing, and the second planet gear and the third planet gear are both installed on the second planet carrier, forming a second-stage planetary gear reduction mechanism; the first ring gear is rigidly connected to the second sun gear, constituting the coupling of the two-stage planetary gear train; the second planet carrier is rigidly connected to the second output shaft; the first output shaft, the second output shaft, the first planetary gear train, the second planetary gear train and the motor are coaxially arranged.

[0007] The tooth number relationship of the transmission mechanism is:

[0008] Z11 / Z13 + 2 = Z23 / Z21 (1)

[0009] In Equation (1):

[0010] Z11 is the number of teeth of the first sun gear;

[0011] Z13 is the number of teeth of the first ring gear;

[0012] Z21 is the number of teeth of the second sun gear;

[0013] Z23 is the number of teeth of the second ring gear.

[0014] The transmission ratio K of the described transmission mechanism is:

[0015] K = 2×W1 / (W2 + W3) = 1 + (Z13 / Z11)×(Z23 / Z21) (2)

[0016] In Equation (2):

[0017] W1 is the rotational speed of the motor rotor;

[0018] W2 is the rotational speed of the first output shaft;

[0019] W3 is the rotational speed of the second output shaft.

[0020] A transmission method for a planetary gear train type reduction differential transmission mechanism of the first solution. The method includes the following steps:

[0021] S1: Power input: The rotation of the rotor of the motor drives the rotation of the first sun gear;

[0022] S2: First planetary gear train transmission: When the first sun gear rotates, it meshes and drives the rotation of the first planetary gear. While rotating, the first planetary gear drives the rotation of the first ring gear and the first planet carrier;

[0023] S3: Second planetary gear train transmission: The first ring gear drives the rotation of the second sun gear. The second sun gear meshes and drives the rotation of the second planetary gear. The second planetary gear meshes and drives the rotation of the third planetary gear. Under the constraint of the second ring gear, the second planetary gear and the third planetary gear drive the rotation of the second planet carrier;

[0024] S4: Power output: The first planet carrier drives the first output shaft to output power, and the second planet carrier drives the second output shaft to output power, realizing the same-speed rotation of the first output shaft and the second output shaft when the vehicle is driving straight, and the differential rotation of the first output shaft and the second output shaft when the vehicle is turning.

[0025] Solution two:

[0026] A planetary gear train type reduction and differential transmission mechanism includes a first planetary gear train, a second planetary gear train, a motor, a housing, a first output shaft, and a second output shaft; the first planetary gear train includes a first sun gear, a first planet carrier, a first ring gear, and a first planet gear; the stator of the motor is rigidly connected to the housing, the rotor of the motor is rigidly connected to the first sun gear, the first sun gear meshes with the first planet gear for transmission, the first planet gear simultaneously meshes with the first ring gear for transmission, and the first planet gear is installed on the first planet carrier to form a first-stage planetary gear reduction mechanism; the first planet carrier is rigidly connected to the first output shaft, and the rotor of the motor is sleeved outside the first output shaft; the second planetary gear train includes a second sun gear, a second planet carrier, a second ring gear, a second planet gear, and a third planet gear; the second sun gear meshes with the second planet gear for transmission, the second planet gear meshes with the third planet gear for transmission, the third planet gear meshes with the second ring gear fixed to the housing for transmission, and the second planet gear and the third planet gear are both installed on the second planet carrier to form a second-stage planetary gear reduction mechanism; the first ring gear is rigidly connected to the second planet carrier to form the coupling of the two-stage planetary gear train; the second sun gear is rigidly connected to the second output shaft; the first output shaft, the second output shaft, the first planetary gear train, the second planetary gear train, and the motor are coaxially arranged.

[0027] The tooth number relationship of the transmission mechanism is:

[0028] Z11 / Z13 + 1 = Z21 / (Z23 - Z21) (3)

[0029] In formula (3):

[0030] Z11 is the tooth number of the first sun gear;

[0031] Z13 is the tooth number of the first ring gear;

[0032] Z21 is the tooth number of the second sun gear;

[0033] Z23 is the tooth number of the second ring gear.

[0034] The transmission ratio K of the transmission mechanism is:

[0035] K = 2×W1 / (W2 + W3) = 1 + Z13 / Z11 + (Z13 / Z11)×Z21 / (Z23 - Z21) (4)

[0036] In formula (4):

[0037] W1 is the rotational speed of the motor rotor;

[0038] W2 is the rotational speed of the first output shaft;

[0039] W3 is the rotational speed of the second output shaft.

[0040] A transmission method for a planetary gear train type reduction and differential transmission mechanism of the second solution, the method comprising the following steps:

[0041] S1: Power input: The rotation of the rotor of the motor drives the first sun gear to rotate;

[0042] S2: First planetary gear train transmission: When the first sun gear rotates, it meshes with and drives the first planetary gear to rotate. While rotating, the first planetary gear drives the first ring gear and the first planet carrier to rotate, and the first planet carrier further drives the first output shaft to output power;

[0043] S3: Second planetary gear train transmission: The first ring gear drives the second planet carrier to rotate. The rotation of the second planet carrier drives the meshing second planetary gear and third planetary gear to move. Under the constraint of the second ring gear, the second planetary gear drives the second sun gear to rotate;

[0044] S4: Power output: The first planet carrier drives the first output shaft to output power, and the second sun gear drives the second output shaft to output power, realizing the same-speed rotation of the first output shaft and the second output shaft when the vehicle is driving straight, and the differential rotation of the first output shaft and the second output shaft when the vehicle is turning.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] Through the coupling of two-stage planetary gear trains and the optimization of the tooth number relationship, the present invention realizes the compound reduction effect of the transmission ratio and improves the torque output ability; utilizes the differential characteristics of the planetary gear train to realize the dynamic distribution of the rotational speeds of the two output shafts and meet the vehicle steering differential requirements; adopts the coaxial arrangement method of nesting the motor rotor and the first output shaft, combined with the spatial symmetry of the planetary gear train, significantly reduces the axial dimension while realizing function integration, and meets the requirements of lightweight and compact layout; reduces the transmission link by directly coupling the ring gear with the sun gear or the planet carrier, and the standardized planetary gear train structure reduces the processing cost and assembly complexity; the optimized tooth number matching ensures the balanced distribution of the load, reduces the energy loss, and improves the transmission efficiency. It has the advantages of compact structure, large transmission ratio, easy manufacturing, etc., realizes the differential function through the planetary gear train, and breaks through the technical bottlenecks of the traditional transmission mechanism in terms of reduction ratio, structural complexity and energy efficiency. Brief Description of the Drawings

[0047] Figure 1 is the structural schematic diagram of the first solution of the present invention;

[0048] Figure 2 is the tooth number relationship lever diagram of the first solution of the present invention;

[0049] Figure 3 is the structural schematic diagram of the second solution of the present invention;

[0050] Figure 4 is the tooth number relationship lever diagram of the second solution of the present invention. Detailed implementation mode

[0051] The following will clearly and completely describe the technical solutions in the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0052] Embodiment 1:

[0053] A planetary gear train type speed reduction and differential transmission mechanism includes a first planetary gear train 41, a second planetary gear train 42, a motor 33, a housing 34, a first output shaft 31 and a second output shaft 32; the first planetary gear train 41 includes a first sun gear 11, a first planet carrier 12, a first ring gear 13 and a first planet gear 14; the stator of the motor 33 is rigidly connected to the housing 34, the rotor of the motor 33 is rigidly connected to the first sun gear 11, the first sun gear 11 meshes and drives with at least three circumferentially evenly distributed first planet gears 14, the first planet gear 14 meshes and drives with the first ring gear 13 at the same time, and the first planet gear 14 is installed on the first planet carrier 12 to form a first-stage planetary gear reduction mechanism; the first planet carrier 12 is rigidly connected to the first output shaft 31, and the rotor of the motor 33 is sleeved outside the first output shaft 31; the second planetary gear train 42 includes a second sun gear 21, a second planet carrier 22, a second ring gear 23, a second planet gear 24 and a third planet gear 25; the second sun gear 21 meshes and drives with at least four circumferentially evenly distributed second planet gears 24, the second planet gear 24 meshes and drives with the third planet gear 25, the third planet gear 25 meshes and drives with the second ring gear 23 fixed to the housing 34, and the second planet gear 24 and the third planet gear 25 are both installed on the second planet carrier 22 to form a second-stage planetary gear reduction mechanism; the first ring gear 13 is rigidly connected to the second sun gear 21 to form the coupling of the two-stage planetary gear train; the second planet carrier 22 is rigidly connected to the second output shaft 32; the first output shaft 31, the second output shaft 32, the first planetary gear train 41, the second planetary gear train 42 and the motor 33 are coaxially arranged.

[0054] The above-mentioned form of rigid connection can be one or a combination of several of bolt connection, spline connection, keyway connection, welding connection, riveting connection and integral molding.

[0055] The tooth number relationship of the transmission mechanism is as follows:

[0056] Z11 / Z13 + 2 = Z23 / Z21 (1)

[0057] In formula (1):

[0058] Z11 is the tooth number of the first sun gear 11;

[0059] Z13 is the number of teeth of the first ring gear 13;

[0060] Z21 is the number of teeth of the second sun gear 21;

[0061] Z23 is the number of teeth of the second ring gear 23.

[0062] The transmission ratio K of the said transmission mechanism is:

[0063] K = 2×W1 / (W2 + W3) = 1 + (Z13 / Z11)×(Z23 / Z21) (2)

[0064] In formula (2):

[0065] W1 is the rotational speed of the rotor of the motor 33;

[0066] W2 is the rotational speed of the first output shaft 31;

[0067] W3 is the rotational speed of the second output shaft 32.

[0068] A transmission method of a planetary gear train type reduction differential transmission mechanism in this embodiment, the said method comprises the following steps:

[0069] S1: Power input: The rotation of the rotor of the motor 33 drives the rotation of the first sun gear 11;

[0070] S2: First planetary gear train transmission: When the first sun gear 11 rotates, it meshes and drives the rotation of the first planet gear 14, and while rotating, the first planet gear 14 drives the rotation of the first ring gear 13 and the first planet carrier 12;

[0071] S3: Second planetary gear train transmission: The first ring gear 13 drives the rotation of the second sun gear 21, the second sun gear 21 meshes and drives the rotation of the second planet gear 24, the second planet gear 24 meshes and drives the rotation of the third planet gear 25, and under the constraint of the second ring gear 23, the second planet gear 24 and the third planet gear 25 drive the rotation of the second planet carrier 22;

[0072] S4: Power output: The first planet carrier 12 further drives the first output shaft 31 to output power, and the second planet carrier 22 drives the second output shaft 32 to output power, realizing the same-speed rotation of the first output shaft 31 and the second output shaft 32 when the vehicle travels straight, and the differential rotation of the first output shaft 31 and the second output shaft 32 when the vehicle turns.

[0073] When the vehicle is driving straight, the resistance of the wheels on both sides is balanced. The sun gear two (21) rotates with the ring gear one (13). Since the ring gear two (23) is stationary, the planet gear two (24) and the planet gear three (25) rotate on the planet carrier two (22). Therefore, under the combined action of the sun gear two (21) and the ring gear two (23), the planet gear two (24) and the planet gear three (25) drive the planet carrier two (22) to rotate. The rotation speed of the planet carrier two (22) is determined by the rotation speed of the sun gear two (21). When the tooth number relationship (Equation 1) is satisfied, the planet carrier one (12) and the planet carrier two (22) rotate at the same speed, and the rotation speeds of the first output shaft (31) and the second output shaft (32) are the same and satisfy the speed ratio relationship of (Equation 2).

[0074] When the vehicle is turning, the travel distances of the inner and outer wheels of the vehicle are different. The rotation speeds of the first output shaft (31) and the second output shaft (32) are different, and the rotation speeds of the planet carrier one (12) and the planet carrier two (22) are different. When the tooth number relationship (Equation 1) is satisfied, the change amount of the rotation speed of the planet carrier one (12) is equal to the change amount of the rotation speed of the planet carrier two (22), and the average value of the rotation speeds of the planet carrier one (12) and the planet carrier two (22) satisfies the speed ratio relationship of (Equation 2).

[0075] Embodiment 2:

[0076] The difference between this embodiment and Embodiment 1 is that:

[0077] The ring gear one 13 is rigidly connected to the planet carrier two 22 to form the coupling of the two-stage planetary gear train; the sun gear two 21 is rigidly connected to the second output shaft 32.

[0078] The tooth number relationship of the transmission mechanism is:

[0079] Z11 / Z13 + 1 = Z21 / (Z23 - Z21) (3)

[0080] In Equation (3):

[0081] Z11 is the tooth number of the sun gear one 11;

[0082] Z13 is the tooth number of the ring gear one 13;

[0083] Z21 is the tooth number of the sun gear two 21;

[0084] Z23 is the tooth number of the ring gear two 23.

[0085] The transmission ratio K of the transmission mechanism is:

[0086] K = 2×W1 / (W2 + W3) = 1 + Z13 / Z11 + (Z13 / Z11)×Z21 / (Z23 - Z21) (4)

[0087] In Equation (4):

[0088] W1 is the rotational speed of the rotor of the motor 33;

[0089] W2 is the rotational speed of the first output shaft 31;

[0090] W3 is the rotational speed of the second output shaft 32.

[0091] A transmission method of a planetary gear train type reduction differential transmission mechanism according to this embodiment, the method includes the following steps:

[0092] S1: Power input: The rotation of the rotor of the motor 33 drives the rotation of the first sun gear 11;

[0093] S2: First planetary gear train transmission: When the first sun gear 11 rotates, it meshes and drives the rotation of the first planet gear 14. While rotating, the first planet gear 14 drives the first ring gear 13 and the first planet carrier 12 to rotate. The first planet carrier 12 further drives the first output shaft 31 to output power;

[0094] S3: Second planetary gear train transmission: The first ring gear 13 drives the second planet carrier 22 to rotate. The rotation of the second planet carrier 22 drives the meshing movement of the second planet gear 24 and the third planet gear 25 thereon. Under the constraint of the second ring gear 23, the second planet gear 24 drives the second sun gear 21 to rotate;

[0095] S4: Power output: The first planet carrier 12 further drives the first output shaft 31 to output power, and the second sun gear 21 drives the second output shaft 32 to output power, realizing the same-speed rotation of the first output shaft 31 and the second output shaft 32 when the vehicle is driving straight, and the differential rotation of the first output shaft 31 and the second output shaft 32 when the vehicle is turning.

[0096] When the vehicle is driving straight, the resistance on both sides of the wheels is balanced. The second planet carrier (22) rotates with the first ring gear (13), the second ring gear (23) is stationary, and the second planet gear (24) and the third planet gear (25) rotate on the second planet carrier (22). Under the combined action of the second planet carrier (22) and the second ring gear (23), the second planet gear (24) and the third planet gear (25) jointly drive the second sun gear (21) to rotate. The rotational speed of the second sun gear (21) is determined by the rotational speed of the second planet carrier (22). When the tooth number relationship (Equation 3) is satisfied, the first planet carrier (12) and the second sun gear (21) rotate at the same speed, the first output shaft (31) and the second output shaft (32) have the same rotational speed, and the speed ratio relationship of (Equation 4) is satisfied.

[0097] When the vehicle is turning, the travel distances of the inner and outer wheels of the vehicle are different. The rotational speeds of the first output shaft (31) and the second output shaft (32) are different, and the rotational speeds of the first planet carrier (12) and the second sun gear (21) are different. When the tooth number relationship (Equation 3) is satisfied, the change amount of the rotational speed of the first planet carrier (12) is equal to the change amount of the rotational speed of the second sun gear (21), and the average value of the rotational speeds of the first planet carrier (12) and the second sun gear (21) satisfies the speed ratio relationship of (Equation 4).

[0098] Through the collaborative work of the two-stage planetary gear train and the self-rotation and revolution characteristics of the planetary gears, the present invention realizes:

[0099] Straight driving: The two output shafts rotate at the same speed to ensure the stability of the vehicle.

[0100] Turning driving: The two output shafts rotate differentially to adapt to the different rotational speed requirements of the inner and outer wheels.

[0101] This design not only improves the transmission efficiency but also significantly enhances the controllability and passability of the vehicle.

[0102] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent conditions of the claims are intended to be encompassed by the present invention. Any reference signs in the claims should not be regarded as limiting the claimed claims.

[0103] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A planetary gear train type speed reduction differential transmission mechanism, characterized in that: The invention comprises a first planetary gear train (41), a second planetary gear train (42), a motor (33), a housing (34), a first output shaft (31) and a second output shaft (32); the first planetary gear train (41) comprises a sun gear one (11), a planet carrier one (12), a gear ring one (13) and a planetary gear one (14); the stator of the motor (33) is rigidly connected to the housing (34), the rotor of the motor (33) is rigidly connected to the sun gear one (11), the sun gear one (11) is meshed with the planetary gear one (14), the planetary gear one (14) is meshed with the gear ring one (13) at the same time, the planetary gear one (14) is mounted on the planet carrier one (12) to form a first-stage planetary gear reduction mechanism; the planet carrier one (12) is rigidly connected to the first output shaft (31), the rotor of the motor (33) is sleeved on the outside of the first output shaft (31); the second planetary gear train ( 42) comprises a sun gear 2 (21), a planet carrier 2 (22), a ring gear 2 (23), a planet gear 2 (24) and a planet gear 3 (25); the sun gear 2 (21) is meshed with the planet gear 2 (24), the planet gear 2 (24) is meshed with the planet gear 3 (25), the planet gear 3 (25) is meshed with the ring gear 2 (23) fixed on the housing (34), the planet gear 2 (24) and the planet gear 3 (25) are both mounted on the planet carrier 2 (22) to form a second-stage planetary gear reduction mechanism; the ring gear 1 (13) is rigidly connected to the sun gear 2 (21) to form a series coupling of a two-stage planetary gear train; the planet carrier 2 (22) is rigidly connected to the second output shaft (32); the first output shaft (31), the second output shaft (32), the first planetary gear train (41), the second planetary gear train (42) and the motor (33) are coaxially arranged.

2. A planetary gear train type speed reduction differential transmission mechanism according to claim 1, characterized in that: The relationship between the number of teeth of the transmission mechanism is: Z11 / Z13+2=Z23 / Z21 (1) In formula (1): Z11 is the number of teeth of sun gear 1 (11); Z13 is the number of teeth of ring gear 1 (13); Z21 is the number of teeth of sun gear 2 (21); Z23 is the number of teeth of ring gear two (23).

3. A planetary gear train type speed reduction differential transmission mechanism according to claim 2, characterized in that: The transmission ratio K of the transmission mechanism is: K=2×W1 / (W2+W3)=1+(Z13 / Z11)×(Z23 / Z21) (2) In formula (2): W1 is the rotation speed of the rotor of the motor (33); W2 is the rotation speed of the first output shaft (31); W3 is the rotation speed of the second output shaft (32).

4. A transmission method of a planetary gear train type reduction differential transmission mechanism according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1: Power input: The rotor of the motor (33) rotates to drive the sun gear 1 (11) to rotate; S2: First planetary gear train transmission: When the sun gear 1 (11) rotates, it meshes and drives the planetary gear 1 (14) to rotate. When the planetary gear 1 (14) rotates, it drives the ring gear 1 (13) and the planet carrier 1 (12) to rotate; S3: Second planetary gear train transmission: the ring gear 1 (13) drives the sun gear 2 (21) to rotate, the sun gear 2 (21) meshes with and drives the planet gear 2 (24) to rotate, the planet gear 2 (24) meshes with and drives the planet gear 3 (25) to rotate, and the planet gear 2 (24) and the planet gear 3 (25) are constrained by the ring gear 2 (23) to drive the planet carrier 2 (22) to rotate; S4: Power output: the planet carrier 1 (12) drives the first output shaft (31) to output power, and the planet carrier 2 (22) drives the second output shaft (32) to output power, so that the first output shaft (31) and the second output shaft (32) rotate at the same speed when the vehicle is traveling in a straight line, and the first output shaft (31) and the second output shaft (32) rotate at a differential speed when the vehicle is turning.

5. A planetary gear train type speed reduction differential transmission mechanism, characterized in that: The invention comprises a first planetary gear train (41), a second planetary gear train (42), a motor (33), a housing (34), a first output shaft (31) and a second output shaft (32); the first planetary gear train (41) comprises a sun gear (11), a planet carrier (12), a ring gear (13) and a planet gear (14); the stator of the motor (33) is rigidly connected to the housing (34), the rotor of the motor (33) is rigidly connected to the sun gear (11), the sun gear (11) is meshed with the planet gear (14), the planet gear (14) is meshed with the ring gear (13), the planet gear (14) is mounted on the planet carrier (12) to form a first-stage planetary gear reduction mechanism; the planet carrier (12) is rigidly connected to the first output shaft (31), the rotor of the motor (33) is sleeved on the outside of the first output shaft (31); the second planetary gear train (41) comprises a sun gear (11), a planet carrier (12), a ring gear (13) and a planet gear (14); the stator of the motor (33) is rigidly connected to the housing (34), the rotor of the motor (33) is rigidly connected to the sun gear (11), the sun gear (11) is meshed with the planet gear (14), the planet gear (14) is meshed with the ring gear (13) at the same time, the planet gear (14) is mounted on the planet carrier (12) to form a first-stage planetary gear reduction mechanism; the planet carrier (12) is rigidly connected to the first output shaft (31), the rotor of the motor (33) is sleeved on the outside of the first output shaft (31); the second planetary gear train (41) comprises a sun gear (11), a planet carrier (12), a ring gear (13) and a planet gear (14) (42) comprises a sun gear 2 (21), a planet carrier 2 (22), a ring gear 2 (23), a planet gear 2 (24) and a planet gear 3 (25); the sun gear 2 (21) is meshed with the planet gear 2 (24), the planet gear 2 (24) is meshed with the planet gear 3 (25), the planet gear 3 (25) is meshed with the ring gear 2 (23) fixed on the housing (34), the planet gear 2 (24) and the planet gear 3 (25) are both mounted on the planet carrier 2 (22) to form a second-stage planetary gear reduction mechanism; the ring gear 1 (13) is rigidly connected to the planet carrier 2 (22) to form a series coupling of two-stage planetary gear trains; the sun gear 2 (21) is rigidly connected to the second output shaft (32); the first output shaft (31), the second output shaft (32), the first planetary gear train (41), the second planetary gear train (42) and the motor (33) are coaxially arranged.

6. A planetary gear train type speed reduction differential transmission mechanism according to claim 5, characterized in that: The relationship between the number of teeth of the transmission mechanism is: Z11 / Z13+1=Z21 / (Z23-Z21) (3) In formula (3): Z11 is the number of teeth of sun gear 1 (11); Z13 is the number of teeth of ring gear 1 (13); Z21 is the number of teeth of sun gear 2 (21); Z23 is the number of teeth of ring gear two (23).

7. A planetary gear train type speed reduction differential transmission mechanism according to claim 6, characterized in that: The transmission ratio K of the transmission mechanism is: K=2×W1 / (W2+W3)=1+Z13 / Z11+(Z13 / Z11)×Z21 / (Z23-Z21) (4) In formula (4): W1 is the rotation speed of the rotor of the motor (33); W2 is the rotation speed of the first output shaft (31); W3 is the rotation speed of the second output shaft (32).

8. A transmission method of a planetary gear train type reduction differential transmission mechanism according to any one of claims 5 to 7, characterized in that: The method comprises the following steps: S1: Power input: The rotor of the motor (33) rotates to drive the sun gear 1 (11) to rotate; S2: First planetary gear train transmission: When the sun gear 1 (11) rotates, it meshes and drives the planetary gear 1 (14) to rotate. When the planetary gear 1 (14) rotates, it drives the ring gear 1 (13) and the planet carrier 1 (12) to rotate; S3: Second planetary gear train transmission: the ring gear 1 (13) drives the planet carrier 2 (22) to rotate, and the rotation of the planet carrier 2 (22) drives the planetary gear 2 (24) and the planetary gear 3 (25) meshing with each other thereon to move, and under the constraint of the ring gear 2 (23), the planetary gear 2 (24) drives the sun gear 2 (21) to rotate; S4: Power output: the planet carrier 1 (12) drives the first output shaft (31) to output power, and the sun gear 2 (21) drives the second output shaft (32) to output power, so that the first output shaft (31) and the second output shaft (32) rotate at the same speed when the vehicle is traveling in a straight line, and the first output shaft (31) and the second output shaft (32) rotate at a differential speed when the vehicle is turning.

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