CN118665154A - Wheel hub motor drive system and vehicle - Google Patents

Abstract

The present application provides a wheel hub motor drive system and a vehicle. In the wheel hub motor drive system, the motor, the planetary gear reduction mechanism and the wet brake mechanism are arranged side by side in the axial direction, and the planetary gear reduction mechanism and the wet brake mechanism overlap in the radial direction. Therefore, the axial length of the entire wheel hub motor drive system can be determined by the motor and the wet brake mechanism, that is, the axial length of the entire wheel hub motor drive system is substantially equal to the sum of the axial lengths of the motor and the wet brake mechanism. As a result, compared with the existing wheel hub motor drive system, the overall size of the system can be reduced, especially the axial size can be shortened, thereby reducing the adverse effects of the axial length of the wheel hub motor drive system on the size of the wheel and the structural layout of the vehicle.

Description

Wheel hub motor drive system and vehicle

Technical Field

The present application relates to the field of vehicles such as electric vehicles, and in particular to a wheel hub motor drive system for a vehicle and a vehicle including the wheel hub motor drive system.

Background Art

In the prior art, new energy vehicles such as electric vehicles still mainly use a drive system consisting of a central motor, a clutch, a transmission and a differential, which results in too many components in the drive system and a long torque transmission path, resulting in high power loss and low efficiency in the drive system, which seriously affects the driving distance of new energy vehicles. Therefore, technicians have developed a wheel hub motor drive system with a shorter torque transmission path to overcome the above problems.

The existing wheel hub motor drive system integrates the motor, the speed change mechanism and the wheel brake mechanism, etc. However, the layout of these components in the existing wheel hub motor drive system is not reasonable, resulting in the size of the entire wheel hub motor drive system (especially the axial size) being too large, thus occupying too much space, which in turn has an adverse effect on the size of the wheel including the wheel hub motor drive system and the structural layout of the vehicle (for example, the layout of the suspension system).

Summary of the invention

This application is made based on the defects of the above-mentioned prior art. One purpose of this application is to provide a new wheel hub motor drive system, which can reduce the overall size of the system compared with the existing wheel hub motor drive system, especially shorten the axial size, thereby reducing the adverse effects of the wheel hub motor drive system on the size of the wheel and the structural layout of the vehicle. Another purpose of this application is to provide a vehicle including the above-mentioned wheel hub motor drive system.

In order to achieve the above-mentioned invention objectives, this application adopts the following technical solutions.

The present application provides a wheel hub motor drive system as follows, which has axial, radial and circumferential directions, and the wheel hub motor drive system includes:

An output shaft, which is used to be fixed to the hub of the wheel;

A motor including a stator and a rotor;

a planetary gear reduction mechanism, which is arranged side by side with the motor in the axial direction, the planetary gear reduction mechanism comprising a sun gear and a planetary gear carrier, the sun gear is drivingly connected to the rotor, and the planetary gear carrier is drivingly connected to the output shaft; and

A wet brake mechanism is arranged side by side with the motor in the axial direction and overlaps with the planetary gear reduction mechanism in the radial direction, and the wet brake mechanism can controllably generate friction torque and transmit it to the output shaft.

In an optional solution, it also includes:

a housing assembly fixed relative to a suspension system of a vehicle and forming a first space and a second space, wherein the first space accommodates the motor and the second space accommodates the planetary gear reduction mechanism and the wet brake mechanism; and

A cooling jacket is fixed to the housing assembly and is located in the first space and the second space, and the cooling jacket is used to cool the stator and the wet brake mechanism.

In another optional scheme, the wet brake mechanism includes multiple brake discs, multiple brake linings and brake pistons, and the multiple brake discs and the multiple brake linings are alternately arranged in the axial direction. The brake piston can press the multiple brake discs and the multiple brake linings against each other to generate the friction torque.

In another optional solution, one of the plurality of brake discs and the plurality of brake linings is mounted on the cooling jacket in a rotationally fixed manner, and the other of the plurality of brake discs and the plurality of brake linings is mounted on the planetary carrier in a rotationally fixed manner.

In another optional solution, the plurality of brake discs and the plurality of brake linings completely overlap with the planetary gear reduction mechanism in the radial direction.

In another optional solution, it also includes a steering knuckle and a wheel bearing,

The output shaft includes a first flange portion and a first shaft portion fixed to each other, the first flange portion is located on one axial side of the first shaft portion and is used to be fixed to the wheel hub, and the first shaft portion extends from the first flange portion toward the other axial side.

The steering knuckle includes a second flange portion and a second shaft portion fixed to each other, the second flange portion is located at the other axial side of the second shaft portion and is used to be mounted to a suspension system of a vehicle, and the second shaft portion extends from the second flange portion toward the axial side and is inserted into the first shaft portion.

The wheel bearing is located between the first shaft portion and the second shaft portion.

In another optional solution, the planetary gear reduction mechanism and the wet brake mechanism are located on one axial side of the motor.

In another optional solution, the planetary gear reduction mechanism and the wet brake mechanism are located on the other axial side of the motor.

In another optional scheme, the planetary gear reduction mechanism includes a first planetary row and a second planetary row, the first planetary row includes a first sun gear and a first planetary wheel carrier, the second planetary row includes a second sun gear and a second planetary wheel carrier, the first sun gear is drivingly connected to the rotor, the first planetary wheel carrier is drivingly connected to the second sun gear, and the second planetary wheel carrier is drivingly connected to the output shaft.

The present application also provides a vehicle as follows, comprising the hub motor drive system described in any one of the above technical solutions.

By adopting the above technical solution, the present application provides a novel wheel hub motor drive system and a vehicle including the wheel hub motor drive system. The wheel hub motor drive system includes an output shaft, a motor, a planetary gear reduction mechanism and a wet brake mechanism assembled together. The planetary gear reduction mechanism is arranged side by side with the motor in the axial direction and is used to transmit torque between the motor and the output shaft. The wet brake mechanism is arranged side by side with the motor in the axial direction and is used to generate a friction torque that prevents the output shaft from rotating, and the wet brake mechanism overlaps with the planetary gear reduction mechanism in the radial direction.

In this way, the motor, the planetary gear reduction mechanism and the wet brake mechanism are arranged side by side in the axial direction, and the planetary gear reduction mechanism and the wet brake mechanism overlap in the radial direction, so the axial length of the entire wheel hub motor drive system can be determined by the motor and the wet brake mechanism, that is, the axial length of the entire wheel hub motor drive system is substantially equal to the sum of the axial lengths of the motor and the wet brake mechanism. Therefore, compared with the existing wheel hub motor drive system, the overall size of the system can be reduced, especially the axial size can be shortened, and the adverse effect of the axial length of the wheel hub motor drive system on the size of the wheel and the structural layout of the vehicle (for example, the layout of the suspension system) can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a wheel hub motor drive system according to a first embodiment of the present application.

FIG. 2 is a schematic cross-sectional view showing a wheel hub motor drive system according to a second embodiment of the present application.

Description of Reference Numerals

1 output shaft; 11 first flange portion; 12 first shaft portion;

2 motor; 21 stator; 22 rotor; 23 rotor bracket; 24 motor shaft;

3 planetary gear reduction mechanism; 31 first sun gear; 32 first planetary gear; 33 first planetary gear carrier; 34 first ring gear; 35 second sun gear; 36 second planetary gear; 37 second planetary gear carrier; 38 second ring gear;

4 wet brake mechanism; 41 brake disc; 42 brake lining; 43 brake piston;

5 housing assembly; 51 housing body; 52 back plate; 53 front cover; S1 first space; S2 second space;

6 Cooling jacket;

7 steering knuckle; 71 second flange portion; 72 second shaft portion;

8 wheel bearings;

A is axial; R is radial.

DETAILED DESCRIPTION

The exemplary embodiments of the present application are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are only used to teach those skilled in the art how to implement the present application, and are not intended to exhaust all feasible methods of the present application, nor to limit the scope of the present application.

In the present application, the wheel hub motor drive system includes an output shaft, and other components are arranged coaxially with the output shaft. Unless otherwise specified, "axial", "radial" and "circumferential" refer to the axial, radial and circumferential directions of the output shaft, respectively. "Axial side" refers to the left side in Figures 1 and 2, and "axial other side" refers to the right side in Figures 1 and 2. "Radially outer side" refers to the side radially away from the central axis of the output shaft, and "radially inner side" refers to the side radially close to the central axis of the output shaft.

In this application, "drive connection" refers to the connection between two components in a way that can transmit torque. "Direct drive connection" refers to the drive connection between two components using direct connection methods such as splines or direct fixation; "indirect drive connection" refers to the drive connection between two components through indirect connection methods such as connectors or other transmission mechanisms.

In the present application, two components overlapping in a certain direction means that when viewed along the direction, there is at least a partial overlap between the projections of the two components on a projection plane perpendicular to the direction.

The following describes a wheel hub motor drive system according to a first embodiment of the present application in conjunction with the accompanying drawings.

(In-wheel motor drive system according to the first embodiment of the present application)

As shown in FIG1 , the wheel hub motor drive system according to the first embodiment of the present application includes an output shaft 1, a motor 2, a planetary gear reduction mechanism 3, a wet brake mechanism 4, a housing assembly 5, a cooling jacket 6, a steering knuckle 7 and a wheel bearing 8 assembled together. In this embodiment, the axial size of the wheel hub motor drive system is basically determined by the motor 2 and the wet brake mechanism 4 arranged side by side in the axial direction A. The planetary gear reduction mechanism 3 is located radially inside the wet brake mechanism 4 and overlaps with the wet brake mechanism 4 in the radial direction R, and the axial length of the wheel hub motor drive system will not be additionally increased due to the planetary gear reduction mechanism 3.

In the present embodiment, as shown in FIG1 , the output shaft 1 is a hollow flange shaft extending along the axial direction A. Specifically, the output shaft 1 includes a first flange portion 11 and a first shaft portion 12 formed as one body. The first flange portion 11 extends from one axial side end portion of the first shaft portion 12 toward the radial outside, and the first flange portion 11 extends continuously along the entire circumference. The first flange portion 11 is formed with a plurality of mounting holes, and mounting members such as hub bolts passing through the plurality of mounting holes can fix the first flange portion 11 to the hub of the wheel of the vehicle. The first shaft portion 12 extends linearly from the inner circumference of the first flange portion 11 toward the other axial side, and the first shaft portion 12 is directly transmission-connected to the second planetary wheel carrier 37 of the planetary gear reduction mechanism 3.

In this embodiment, the motor 2 is a radial magnetic field motor (or radial flux motor). As shown in FIG1 , specifically, the motor 2 includes a stator 21, a rotor 22, a rotor bracket 23 and a motor shaft 24. The stator 21 is fixed to the housing assembly 5 via a cooling jacket 6. The rotor 22 is located radially inside the stator 21 and is opposite to the stator 21 in the radial direction R, and the rotor 22 can rotate relative to the stator 21. The rotor bracket 23 is located radially inside the rotor 22 and is fixed to the rotor 22. The rotor bracket 23 is also fixed to the motor shaft 24, so that the rotor 22 and the motor shaft 24 are indirectly connected via the rotor bracket 23.

In this embodiment, the planetary gear reduction mechanism 3 can transmit the torque from the motor 2 to the output shaft 1. Specifically, as shown in FIG1 , the planetary gear reduction mechanism 3 includes a first planetary row and a second planetary row, the second planetary row and the first planetary row are arranged side by side in the axial direction A, and the second planetary row is located on the other side of the axial direction relative to the first planetary row.

The first planetary gear row includes a first sun gear 31, a first planetary gear 32, a first planetary gear carrier 33 and a first gear ring 34 assembled together. As described above, the other axial end of the motor shaft 24 of the motor 2 is formed with gear teeth to form the first sun gear 31 of the planetary gear reduction mechanism 3, that is, the first sun gear 31 is formed as a whole with the motor shaft 24. A plurality of first planetary gears 32 are located radially outside the first sun gear 31 and are evenly distributed along the circumferential direction. Each first planetary gear 32 is always meshed with the first sun gear 31, so that as the first sun gear 31 rotates, each first planetary gear 32 can rotate around its own central axis and revolve around the first sun gear 31. The first planetary gear carrier 33 is located radially outside the first sun gear 31, and a plurality of first planetary gears 32 are mounted on the first planetary gear carrier 33. The first planetary gear carrier 33 is directly connected to the second sun gear 35 of the second planetary gear row. As the plurality of first planetary gears 32 revolve, the first planetary gear carrier 33 can be driven to rotate and then the second sun gear 35 can be driven to rotate. The first ring gear 34 is located radially outside the first planetary gears 32 and fixed to the housing assembly 5 . An orbit for the first planetary gears 32 to revolve is formed between the first ring gear 34 and the first sun gear 31 . The first ring gear 34 is always meshed with the first planetary gears 32 .

The second planetary gear row includes a second sun gear 35, a second planetary gear 36, a second planetary gear carrier 37 and a second gear ring 38 assembled together. As described above, the second sun gear 35 is directly connected to the first planetary gear carrier 33 of the first planetary gear row. A plurality of second planetary gears 36 are located radially outside the second sun gear 35 and are evenly distributed along the circumference. Each second planetary gear 36 is always meshed with the second sun gear 35, so that as the second sun gear 35 rotates, each second planetary gear 36 can rotate around its own central axis and revolve around the second sun gear 35. The second planetary gear carrier 37 is located radially outside the second sun gear 35, and a plurality of second planetary gears 36 are mounted on the second planetary gear carrier 37. The second planetary gear carrier 37 is directly connected to the output shaft 1. As the plurality of second planetary gears 36 revolve, the second planetary gear carrier 37 can be driven to rotate and then the output shaft 1 can be driven to rotate. The second ring gear 38 is located radially outside the second planetary gears 36 and fixed to the housing assembly 5 . An orbit for the second planetary gears 36 to revolve is formed between the second ring gear 38 and the second sun gear 35 . The second ring gear 38 is always meshed with the second planetary gears 36 .

In this embodiment, as shown in FIG1 , the wet brake mechanism 4 includes a plurality of brake discs 41, a plurality of brake linings 42 and a brake piston 43. The plurality of brake discs 41 and the plurality of brake linings 42 are alternately arranged in the axial direction A, the plurality of brake discs 41 are torsionally mounted on the cooling jacket 6, and the plurality of brake linings 42 are torsionally mounted on the second planetary carrier 37. Here, the second planetary carrier 37 may include an annular outer peripheral portion extending in the axial direction and the circumferential direction on the radial outer side of the ring gear, and the plurality of brake linings 42 may be mounted to the outer peripheral portion of the second planetary carrier 37. The brake piston 43 may be located in a hydraulic cylinder, and the brake piston 43 may be driven to move in the hydraulic cylinder by a power source, thereby applying an axial force to the brake disc 41 and the brake lining 42 in a controlled manner. When the brake piston 43 does not generate an axial force on the brake disc 41 and the brake lining 42, the multiple brake discs 41 and the multiple brake linings 42 are not pressed against each other; when the brake piston 43 generates an axial force on the brake disc 41 and the brake lining 42, the multiple brake discs 41 and the multiple brake linings 42 can be pressed against each other by the brake piston 43 to generate a friction torque. Thus, the wheel can be prevented from rotating by the friction torque to achieve braking. In this embodiment, the multiple brake discs 41 and the multiple brake linings 42 of the wet brake mechanism 4 completely overlap with the planetary gear reduction mechanism 3 in the radial direction R, thereby minimizing the axial size of the hub motor drive system.

In the present embodiment, as shown in FIG1 , the housing assembly 5 is formed as a whole in a cylindrical shape. Specifically, the housing assembly 5 may include a housing body 51 and a back plate 52 assembled together, and the back plate 52 is fixed to the housing body 51 from the other axial side. Further, as shown in FIG1 , the housing assembly 5 defines a first space S1 and a second space S2 separated from each other, and the first space S1 is adjacent to the second space S2 in the axial direction A. The stator 21, the rotor 22 and the rotor support 23 of the motor 2 are accommodated and installed in the first space S1, and the motor shaft 24 extends in the axial direction A from the position where the first space S1 is located to the position where the second space S2 is located. The planetary gear reduction mechanism 3 and the wet brake mechanism 4 are accommodated and installed in the second space S2, so that the planetary gear reduction mechanism 3 and the wet brake mechanism 4 can share the liquid medium (such as oil) in the second space S2.

In this embodiment, as shown in FIG1 , the cooling jacket 6 is fixed to the housing body 51, and a flow path for a cooling fluid (such as water) to flow through is formed between the cooling jacket 6 and the housing body 51. The cooling jacket 6 extends from the first space S1 to the second space S2, the stator 21 of the motor 2 is fixed to the cooling jacket 6, and the brake disc 41 of the wet brake mechanism 4 is also installed on the cooling jacket 6, so that the cooling jacket 6 can simultaneously reduce the temperature of the stator 21 during the operation of the motor 2 and the temperature of the wet brake mechanism 4 during the operation.

In the present embodiment, as shown in FIG. 1 , the steering knuckle 7 is formed as a flange shaft extending along the axial direction A. Specifically, the steering knuckle 7 includes a second flange portion 71 and a second shaft portion 72 formed as one body. The second flange portion 71 extends from the other axial side end of the second shaft portion 72 toward the radial outer side, and the second flange portion 71 extends continuously along the circumference over the entire circumference. The second flange portion 71 is fixed to the back plate 52 of the housing assembly 5, and the second flange portion 71 is formed with a plurality of mounting holes, and mounting members such as bolts passing through the plurality of mounting holes can enable the second flange portion 71 to be mounted together with the suspension system of the vehicle. The second shaft portion 72 extends linearly from the inner circumference of the second flange portion 71 toward one axial side. The second shaft portion 72 extends into the interior of the first shaft portion 12 of the output shaft 1.

In this embodiment, as shown in FIG1 , the wheel bearing 8 may be a double-row tapered roller bearing. The wheel bearing 8 includes an inner ring, an outer ring, and rolling elements, wherein the inner ring is fixed to the steering knuckle 7, the outer ring is fixed to the output shaft 1, and the rolling elements are located between the inner ring and the outer ring. Thus, the second shaft portion 72 of the steering knuckle 7 can support the first shaft portion 12 of the output shaft 1 through the wheel bearing 8.

In this way, in the wheel hub motor drive system according to the first embodiment of the present application, the following working modes can be implemented.

In the first working mode, the torque is transmitted toward the wheel hub through the motor 2 to drive the wheel to rotate. In this working mode, the transmission path of the torque from the motor 2 is as follows: rotor 22→rotor support 23→motor shaft 24→first sun gear 31→first planetary gear 32→first planetary gear carrier 33→second sun gear 35→second planetary gear 36→second planetary gear carrier 37→output shaft 1→wheel hub.

In the second working mode, braking energy recovery is performed during vehicle braking. In this working mode, the transmission path of the torque from the wheel hub is as follows: wheel hub→output shaft 1→second planetary carrier 37→second planetary gear 36→second sun gear 35→first planetary carrier 33→first planetary gear 32→first sun gear 31→motor shaft 24→rotor support 23→rotor 22.

In the third working mode, the friction torque generated by the wet brake mechanism 4 during vehicle braking is transmitted to the wheel hub, and the kinetic energy of the vehicle is converted into thermal energy of the wet brake mechanism 4. In this working mode, the transmission path of the friction torque from the wet brake mechanism 4 is as follows: brake disc 41 and brake lining 42 → second planetary carrier 37 → output shaft 1 → wheel hub.

In the wheel hub motor drive system according to the first embodiment of the present application, the motor 2 and the wet brake mechanism 4 are arranged side by side in the axial direction A, and other components are substantially completely overlapped with the motor 2 and the wet brake mechanism 4 in the radial direction R. Therefore, the axial length of the entire wheel hub motor drive system can be determined by the motor 2 and the wet brake mechanism 4, thereby reducing the axial dimension compared with the wheel hub motor drive system of the prior art, and reducing the adverse effect of the axial dimension of the wheel hub motor drive system on the size of the wheel and the overall layout of the vehicle (for example, the layout of the suspension system). In particular, the planetary gear reduction mechanism 3 does not increase the axial length of the entire wheel hub motor drive system. In addition, in this embodiment, due to the use of the wet brake mechanism 4, compared with the transmission caliper dry brake mechanism, dust is not generated during the braking process. Further, the wet brake mechanism 4 and the planetary gear reduction mechanism 3 use the liquid medium in the second space S2 together, and the wet brake mechanism 4 and the motor 2 use the cooling jacket 6 together to reduce the temperature, thereby simplifying the structure of the entire wheel hub motor drive system, improving performance and reducing costs. In fact, when the in-wheel motor drive system is installed on a vehicle, the wet brake mechanism 4 will be located on the side of the suspension system of the vehicle, thereby facilitating maintenance of the wet brake mechanism 4 .

The following describes a wheel hub motor drive system according to a second embodiment of the present application in conjunction with the accompanying drawings.

(In-wheel motor drive system according to the second embodiment of the present application)

The structure of the wheel hub motor drive system according to the second embodiment of the present application is substantially the same as the structure of the wheel hub motor drive system according to the first embodiment of the present application, and the differences between the two are mainly described below.

In this embodiment, compared with the scheme in which the motor 2 is arranged between the planetary gear reduction mechanism 3 and the wet brake mechanism 4 and the wheel hub or spokes described in the first embodiment, in this embodiment, as shown in FIG. 2 , the planetary gear reduction mechanism 3 and the wet brake mechanism 4 are arranged between the motor 2 and the wheel hub or spokes. Therefore, by comparing FIG. 1 and FIG. 2 , it can be seen that the structural layout of the motor 2, the planetary gear mechanism 3 and the wet brake mechanism 4 in this embodiment and the structural layout of the motor 2, the planetary gear mechanism 3 and the wet brake mechanism 4 in the first embodiment can be considered to have a mirror-symmetric relationship. In addition, in this embodiment, as shown in FIG. 2 , the housing assembly 5 omits the back plate 52 and includes a housing body 51 and a front cover 53, the front cover 53 is fixed to the housing body 51 from one axial side, and the housing body 51 is installed on the suspension system of the vehicle via the bogie 7. By adopting the above structure, the same effect as the first embodiment can be achieved.

The present application is not limited to the above embodiments, and those skilled in the art can make various modifications to the above embodiments of the present application under the guidance of the present application without departing from the scope of the present application. In addition, the following description is also made.

i. The present application also provides a vehicle including the above-mentioned wheel hub motor drive system, which may be an electric vehicle with more than two wheels. In an optional example of the vehicle according to the present application, the vehicle includes four wheels, and the wheel hub motor drive system may be installed in two or four wheels.

ii. It can be understood that in order to achieve the necessary separation and sealing effects, a sealing assembly and a sealing ring can be provided as needed in the hub motor drive system of the present application.

In addition, in order to support the motor shaft 24, a plurality of support bearings may be provided between the motor shaft 24 and the housing assembly 5. For example, as shown in FIGS. 1 and 2, two support bearings may be spaced apart from each other and respectively located on both axial sides of the rotor bracket 23, and the two support bearings may be deep groove ball bearings.

iii. In the wheel hub motor drive system of the present application, the brake disc 41 of the wet brake mechanism 4 is torsionally mounted on the cooling jacket 6, and the brake lining 42 is torsionally mounted on the second planetary carrier 37, but the present application is not limited thereto. For example, the brake disc 41 can be torsionally mounted on the second planetary carrier 37, and the brake lining 42 can be torsionally mounted on the cooling jacket 6.

iv. It can be understood that in each embodiment of the present application, the first space S1 and the second space S2 separated by the housing assembly 5 can both be closed spaces.

v. It can be understood that the second shaft portion 72 of the steering knuckle 7 is inserted into the first shaft portion 11 of the output shaft 1, so that the first shaft portion 12 of the output shaft 1 and the second shaft portion 72 of the steering knuckle 7 partially overlap in the radial direction R, and the overall length of both the output shaft 1 and the steering knuckle 7 in the axial direction A may not exceed or slightly exceed the axial length limited by the motor 2 and the wet brake mechanism 4.

Claims (10)

1. A wheel hub motor drive system having axial (A), radial (R) and circumferential directions, characterized in that the wheel hub motor drive system comprises: An output shaft (1) is used to be fixed to a wheel hub; A motor (2) comprising a stator (21) and a rotor (22); a planetary gear reduction mechanism (3), which is arranged side by side with the motor (2) in the axial direction (A), the planetary gear reduction mechanism (3) comprising a sun gear (31) and a planetary gear carrier (37), the sun gear (31) being drivingly connected to the rotor (22), and the planetary gear carrier (37) being drivingly connected to the output shaft (1); and A wet brake mechanism (4) is arranged side by side with the motor (2) in the axial direction (A) and overlaps with the planetary gear reduction mechanism (3) in the radial direction (R), and the wet brake mechanism (4) is capable of generating friction torque in a controlled manner and transmitting it to the output shaft (1). 2. The wheel hub motor drive system according to claim 1, further comprising: A housing assembly (5) fixed relative to a suspension system of a vehicle and having a first space (S1) and a second space (S2), wherein the first space (S1) accommodates the motor (2) and the second space (S2) accommodates the planetary gear reduction mechanism (3) and the wet brake mechanism (4); and A cooling jacket (6) is fixed to the housing assembly (5) and is located in the first space (S1) and the second space (S2), and the cooling jacket (6) is used to cool the stator (21) and the wet brake mechanism (4). 3. The wheel hub motor drive system according to claim 2 is characterized in that the wet brake mechanism (4) comprises a plurality of brake discs (41), a plurality of brake linings (42) and a brake piston (43), the plurality of brake discs (41) and the plurality of brake linings (42) being alternately arranged in the axial direction (A), and the brake piston (43) can press the plurality of brake discs (41) and the plurality of brake linings (42) against each other to generate the friction torque. 4. The wheel hub motor drive system according to claim 3 is characterized in that one of the multiple brake discs (41) and the multiple brake linings (42) is torsionally mounted on the cooling jacket (6), and the other of the multiple brake discs (41) and the multiple brake linings (42) is torsionally mounted on the planetary wheel carrier (37). 5. The wheel hub motor drive system according to claim 3 or 4, characterized in that the multiple brake discs (41) and the multiple brake linings (42) completely overlap with the planetary gear reduction mechanism (3) in the radial direction (R). 6. The wheel hub motor drive system according to any one of claims 1 to 4, characterized in that it also comprises a steering knuckle (7) and a wheel bearing (8), The output shaft (1) comprises a first flange portion (11) and a first shaft portion (12) fixed to each other, the first flange portion (11) being located on one axial side of the first shaft portion (12) and being used to be fixed to the wheel hub, and the first shaft portion (12) extending from the first flange portion (11) toward the other axial side. The steering knuckle (7) comprises a second flange portion (71) and a second shaft portion (72) fixed to each other, the second flange portion (71) being located at the other axial side of the second shaft portion (72) and being used for being mounted on a suspension system of a vehicle, and the second shaft portion (72) extending from the second flange portion (71) toward the one axial side and being inserted into the first shaft portion (12). The wheel bearing (8) is located between the first shaft portion (12) and the second shaft portion (72). 7. The wheel hub motor drive system according to claim 6, characterized in that: The planetary gear reduction mechanism (3) and the wet brake mechanism (4) are located on one axial side of the motor (2). 8. The wheel hub motor drive system according to claim 6, characterized in that: The planetary gear reduction mechanism (3) and the wet brake mechanism (4) are located on the other axial side of the motor (2). 9. The hub motor drive system according to any one of claims 1 to 4, characterized in that the planetary gear reduction mechanism (3) includes a first planetary row and a second planetary row, the first planetary row includes a first sun gear (31) and a first planetary wheel carrier (33), the second planetary row includes a second sun gear (35) and a second planetary wheel carrier (37), the first sun gear (31) is transmission-connected to the rotor (22), the first planetary wheel carrier (33) is transmission-connected to the second sun gear (35), and the second planetary wheel carrier (37) is transmission-connected to the output shaft (1). 10. A vehicle, characterized by comprising the wheel hub motor drive system according to any one of claims 1 to 9.