JP2022122325A - Speed reducer for electric motor, and vehicle drive device - Google Patents

Abstract

To provide a speed reducer for an electric motor, which can effectively suppress deterioration of NVH (Noise, Vibration and Harshness) while having a relatively simple configuration, and to provide a vehicle drive device including the same.SOLUTION: A speed reducer 2 for an electric motor includes a motor M, a speed reduction mechanism T, and a differential mechanism D. The speed reduction mechanism T includes two planetary gear mechanisms of a first planetary gear mechanism PG1 and a second planetary gear mechanism PG2. A carrier C1 of the first planetary gear mechanism PG1 and a carrier C2 of the second planetary gear mechanism PG2 are rotatably connected to each other by a connecting portion 30. The connecting portion 30 has a radial bearing 32, and a ring-shaped elastic body 34 fixed to an outer ring 32c of the radial bearing, in which the carrier C1 is fixed to an inner ring 32a, and the carrier C2 is fixed to the elastic body 34. Even at a non-driving time when torque is not transmitted and there is no gear surface reaction force, the carrier C1 is prevented from collapsing by the elasticity of the elastic body 34 in a state of not hindering the self-aligning function, thereby suppressing NVH.SELECTED DRAWING: Figure 1

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction gear for an electric motor that reduces the output of an electric motor, and a vehicle drive system including the same.

2. Description of the Related Art In recent years, development of an electric vehicle (hereinafter referred to as “EV”) using an electric motor (motor) as a drive source has been progressing. An EV is provided with a drive transmission device having a speed reducer that reduces the output of a motor and transmits the output to an axle. For EVs, it is important to reduce the size and weight of the vehicle from the viewpoint of improving the driving performance and energy efficiency of the vehicle. Accordingly, there is a demand for a drive transmission device having a speed reducer as described above to be as small and light as possible while having a structure capable of obtaining a high speed reduction ratio. Moreover, in order to increase the degree of freedom in the exterior design of the vehicle, it is desirable to make the reduction gear and the drive transmission device as compact as possible.

In order to meet such demands, Patent Document 1 discloses an electric motor having a hollow cylindrical output shaft, a speed reduction mechanism to which driving force is input from the output shaft of the electric motor, and a driving force reduced by the speed reduction mechanism. A differential mechanism that distributes and transmits power to the left and right axles is arranged coaxially, and the speed reduction mechanism consists of a planetary gear mechanism. A reduction gear for an electric motor has been proposed which is installed through. The planetary gear mechanism includes a first planetary gear mechanism to which the driving force from the output shaft is input, and a second planetary gear mechanism to output the driving force input from the first planetary gear mechanism to the differential mechanism in the output shaft direction. It has a configuration in which it is arranged in series with

Regarding the bearing structure, both ends of the output shaft are rotatably supported by bearings on the casing of the electric motor, and the gear case of the differential mechanism and the axle passing through the inside of the output shaft are rotatably supported on the casing of the electric motor by bearings. configuration is described.

In the above configuration, the electric motor, the speed reduction mechanism, and the differential mechanism are arranged coaxially with each other, and the axle through which the output of the differential mechanism is transmitted penetrates inside the output shaft of the electric motor. The diameter can be made compact, and it is possible to reduce the size and weight. In particular, by coaxially arranging the electric motor, reduction mechanism, and differential mechanism, the height or width of the reduction gear can be kept small, so the bonnet line of the vehicle can be lowered and the front overhang can be shortened. It is possible to easily take a design unique to an EV vehicle, such as In addition, since a planetary gear mechanism is used for the reduction mechanism, a high reduction ratio can be obtained.

JP 2011-102639 A

FIG. 5 is a skeleton diagram showing a state in which a reduction gear for an electric motor having a conventional configuration is driven, ie, torque is being transmitted. In the electric motor speed reducer 100 shown in FIG. 5, reference numeral B9 indicates a bearing that is fixed to the casing 10 and supports the carrier C2 of the second planetary gear mechanism PG2. In this state, since a gear tooth surface reaction force is generated between the first planetary gear mechanism PG1 and the second planetary gear mechanism PG2, the first planetary gear mechanism PG1 and the second planetary gear mechanism PG1 and the second planetary gear mechanism PG2 are separated by the tooth surface reaction force. Alignment with PG2 is maintained and there is also a self-aligning function in the first planetary gear mechanism PG1 and the second planetary gear mechanism PG2. That is, this type of planetary gear mechanism has a self-aligning function (automatic centering function) that automatically moves to a position where the rotation is stabilized as the meshing of the gears progresses when torque transmission from the motor is started. is doing.

FIG. 6 is a skeleton diagram showing a state in which the conventional speed reducer for an electric motor is not driven, that is, when torque is not being transmitted. For example, when the driver releases the accelerator pedal (stops the output of the motor) from the state shown in FIG. The tooth surface reaction force of the gear between the 2-planetary gear mechanism PG2 is eliminated. When the gear tooth surface reaction force disappears, as shown in FIG. 6, the carrier C1 of the first planetary gear mechanism PG1 is tilted by the backlash because it is supported only by the bearing B4. In particular, when there is a sudden change from a state in which torque is being transmitted to a state in which torque is not being transmitted, the alignment between the first planetary gear mechanism PG1 and the second planetary gear mechanism PG2 changes or becomes inappropriate. As a result, NVH (Noise, Vibration and Harshness: mechanical vibration and noise) may temporarily deteriorate. In addition, in FIG. 6, the tilting of the carrier C1 is exaggerated.

In this way, in the prior art, in a configuration in which two planetary gear mechanisms (planetary gear sets) are coaxially arranged in series, for example, when the accelerator pedal is suddenly released from the accelerating state, the coasting state When the gear tooth surface reaction force suddenly disappears, such as when the vehicle is coasting without transmitting torque to the drive wheels, the alignment of the planetary gear mechanism changes or becomes inappropriate. There is a possibility that NVH, which is an index of vehicle comfort, cannot be sufficiently suppressed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a speed reducer for an electric motor capable of effectively suppressing deterioration of NVH with a relatively simple structure, and a vehicle drive having the same. It is to provide a device.

In order to solve the above problems, a speed reducer for an electric motor according to the present invention is a speed reducer for an electric motor that includes a speed reduction mechanism (T) to which driving force from an electric motor (M) is input, the speed reduction mechanism (T) , at least two sets of planetary gear mechanisms including a first planetary planetary gear mechanism (PG1) and a second planetary gear mechanism (PG2), and one rotating element (C1) of the first planetary planetary gear mechanism (PG1) It has a connecting part (30 or 40) that relatively rotatably connects with one rotating element (C2) of the second planetary planetary gear mechanism (PG2), and the connecting part (30 or 40) is the first planetary planetary gear An intermediate bearing (32 or 42) consisting of a radial bearing that supports the rotating element (C1) of the mechanism (PG1) and the rotating element (C2) of the second planetary planetary gear mechanism (PG2) in a relatively rotatable manner, and an intermediate bearing ( 32 or 42) and the rotating element (C1) of the first planetary planetary gear mechanism (PG1), or between the intermediate bearings (32, 42) and the rotating element (C2) of the second planetary planetary gear mechanism (PG2) and an elastic body (34 or 44) provided in at least one of the gaps.

According to the speed reducer for an electric motor of the present invention, the intermediate bearing is a radial bearing that supports one rotating element of the first planetary planetary gear mechanism and one rotating element of the second planetary planetary gear mechanism so as to be relatively rotatable. With this provision, when the speed reduction mechanism does not transmit torque from the electric motor, the gear reaction force disappears and the rotating element that is about to fall is supported by this intermediate bearing, so the rotating element falls (rotating shaft falls) is minimized. Therefore, it is possible to effectively prevent the alignment of the planetary gear mechanism from changing or being in an inappropriate state, and it is possible to sufficiently suppress NVH. Further, by providing an elastic body provided at least either between the intermediate bearing and the rotating element of the first planetary gear mechanism or between the intermediate bearing and the rotating element of the second planetary planetary gear mechanism, the speed reduction mechanism are transmitting torque from the electric motor, the elastic action of the elastic body does not hinder the self-aligning action due to the reaction force on the gear tooth surface, and the respective rotating elements are properly aligned. Therefore, it is possible to effectively prevent the alignment of the planetary gear mechanism from changing or being in an inappropriate state even when torque is being transmitted, and it is possible to sufficiently suppress NVH. With these features, the reduction gear for the electric motor can always maintain the alignment of the planetary gear mechanism in an appropriate state both when torque is transmitted from the electric motor to the reduction mechanism and when it is not, and can sufficiently suppress NVH. Become.

Further, in the above speed reducer for electric motor, the first planetary planetary gear mechanism (PG1) and the second planetary planetary gear mechanism (PG2) are coaxially arranged in series, and the first planetary planetary gear mechanism (PG1) The rotating element (C1) is the carrier (C1) of the first planetary gear mechanism (PG1), and the rotating element (C2) of the second planetary gear mechanism (PG2) is the second planetary gear mechanism (PG2 ) is preferably the carrier (C2). According to this, the elasticity (elastic force) of the elastic body acts between the carrier of the first planetary gear mechanism and the carrier of the second planetary gear mechanism, which are main elements supporting the meshing of the gears. The alignment of the mechanism can be maintained in a more appropriate state, and NVH can be suppressed with higher accuracy.

Further, in the electric motor speed reducer described above, the elastic body (34 or 44) is fixed to the outer ring (32c) or the inner ring (42a) of the intermediate bearing (32 or 42), and the first planetary planetary gear mechanism (PG1). Either the carrier (C1) or the carrier (C2) of the second planetary planetary gear mechanism (PG2) is preferably fixed to the elastic body (34 or 44). According to this configuration, a general-purpose radial bearing is used as the intermediate bearing, and a connecting portion that can effectively suppress NVH with a relatively simple and inexpensive configuration can be realized.

Moreover, in the above speed reducer for electric motor, it is preferable that the elastic body (34 or 44) is formed in a ring shape. According to this configuration, manufacturing of the elastic body is facilitated, and assembly (fixation) to the intermediate bearing is also facilitated.

Further, in the above speed reducer for electric motor, the carrier (C1) of the first planetary planetary gear mechanism (PG1) and the carrier (C2) of the second planetary planetary gear mechanism (PG2) are connected from the connecting portion (30 or 40) to the electric motor. It is rotatably supported by bearings (B4, B5) fixed directly or indirectly to the casing (10) of the motor speed reducer at a position separated in the axial direction of the output shaft (L1) of (M). is desirable. According to this, the rotational stability of each carrier (C1, C2) is further improved, and the NVH suppression accuracy is further improved.

Further, a vehicle drive device of the present invention includes an electric motor (M) and a speed reducer for the electric motor having any one of the configurations according to the present invention, which includes a speed reduction mechanism (T) to which driving force from the electric motor (M) is input. and a differential mechanism (D) for distributing and transmitting the driving force reduced by the reduction mechanism (T) to the left and right axles.

ADVANTAGE OF THE INVENTION According to the reduction gear for electric motors of this invention, and the drive device for vehicles provided with the same, although it is a comparatively simple structure, deterioration of NVH can be effectively suppressed.

1 is a skeleton diagram showing the configuration of a vehicle drive device provided with an electric motor speed reducer according to a first embodiment of the present invention; FIG. 2A is a front view, and FIG. 2B is a schematic cross-sectional view taken along line X1-X1 of FIG. 2A. FIG. FIG. 6 is a skeleton diagram showing the configuration of a vehicle drive device including a speed reducer for an electric motor according to a second embodiment of the present invention; 4A is a front view, and FIG. 4B is a schematic cross-sectional view taken along the line X2-X2 of FIG. 3A. FIG. FIG. 10 is a diagram for explaining a problem of the conventional configuration, and is a skeleton diagram showing a state when a speed reducer for an electric motor (driving device) is driven. FIG. 10 is a diagram for explaining a problem of the conventional configuration, and is a skeleton diagram showing a state when the speed reducer for the electric motor (driving device) is not driven.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a skeleton diagram showing the configuration of a vehicle drive system provided with a speed reducer for an electric motor (hereinafter simply referred to as "speed reducer") according to a first embodiment of the present invention. The vehicle drive device 1 includes a motor M as an electric motor having a rotor shaft L1 which is a hollow cylindrical output shaft, and a planetary gear mechanism to which the driving force from the rotor shaft L1 of the motor M is input. It comprises a speed reducer 2 for electric motor having a mechanism T, and a differential mechanism D as a differential mechanism for distributing and transmitting the driving force reduced by the speed reduction mechanism T of the speed reducer for electric motor 2 to left and right axles L2 and L3. ing. The motor M, speed reduction mechanism T, and differential mechanism D are arranged coaxially with each other, and one axle L2, to which the output from the differential mechanism D is transmitted, is installed so as to pass through the inside of the rotor shaft L1. The tip of axle L2 is connected to a wheel (drive wheel) not shown. The reduction mechanism T includes two planetary gear mechanisms (planetary gear sets), a first planetary gear mechanism PG1 located on the motor M side and a second planetary gear mechanism PG2 located on the differential mechanism D side.

The first planetary gear mechanism PG1 has a sun gear S1, a carrier C1, a pinion gear P1 and a ring gear R1, and the second planetary gear mechanism PG2 has a sun gear S2, a carrier C2, a pinion gear P2 and a ring gear R2. The sun gear S1 of the first planetary gear mechanism PG1 is connected to the rotor shaft L1 of the motor M, and the carrier C1 is connected to the sun gear S2 of the second planetary gear mechanism PG2. A pinion gear P1 is rotatably held on a carrier C1 by a bearing B1. The carrier C2 of the second planetary gear mechanism PG2 is configured integrally with the gear case 20 of the differential mechanism D. As shown in FIG. The pinion gear P2 is rotatably held on the carrier C2 by the bearing B2. Both the ring gear R1 of the first planetary gear mechanism PG1 and the ring gear R2 of the second planetary gear mechanism PG2 are fixed to the casing 10 of the vehicle drive device 1 . A thrust direction bearing B3 is arranged between the first planetary gear mechanism PG1 and the second planetary gear mechanism PG2.

A carrier C1, which is one rotating element of the first planetary gear mechanism PG1, and a carrier C2, which is one rotating element of the second planetary gear mechanism PG2, are connected to each other by a connecting portion 30 so as to be relatively rotatable. The carrier C1 is directly supported by a bearing B4 fixed to the casing 10 at a position away from the connecting portion 30 in the axial direction of the rotor shaft L1 (on the right side in the drawing), and the carrier C2 extends from the connecting portion 30 to the rotor shaft L1. It is indirectly supported via a gear case 20 by a bearing B5 fixed to the casing 10 at a position separated in the axial direction (left side in the drawing). Reference numerals B6 and B7 shown in FIG. 1 denote bearings that support the rotor shaft L1, and reference numeral B8 denotes a bearing that supports one end of the axle L2.

In the vehicle drive device 1, the ring gear R1 of the first planetary gear mechanism PG1 is fixed to the casing 10, and the output from the rotor shaft L1 of the motor M is input to the sun gear S1. Then, the driving force reduced by the first planetary gear mechanism PG1 is output from the carrier C1, and the output from the carrier C1 is input to the sun gear S2 of the second planetary gear mechanism PG2. Since the ring gear R2 of the second planetary gear mechanism PG2 is fixed to the casing 10, the driving force reduced by the second planetary gear mechanism PG2 is output from the carrier C2 to the differential mechanism D. there is

In the vehicle drive system 1 of the present embodiment, as described above, the motor M, the speed reduction mechanism T, and the differential mechanism D are coaxially arranged, and one axle L2 to which the output of the differential mechanism D is transmitted is the rotor shaft. By penetrating the inner side of L1, the outer diameter of the vehicle drive device 1 can be made compact, and it is possible to reduce the size and weight. In particular, by coaxially arranging the motor M, the speed reduction mechanism T, and the differential mechanism D, the height dimension of the vehicle drive device 1 or the width dimension in the direction perpendicular to the axial direction of the rotor shaft L1 can be kept small. As a result, it is possible to easily create designs unique to EV vehicles, such as lowering the vehicle's bonnet line and shortening the front overhang.

Next, the function of suppressing deterioration of NVH in the vehicle drive system 1 will be described. As shown in FIG. 2, the connecting portion 30 includes a radial bearing (intermediate bearing) 32 that supports the carrier C1 and the carrier C2 so as to be relatively rotatable. The radial bearing 32 has an inner ring 32a, rolling elements (rollers) 32b, and an outer ring 32c. A ring-shaped elastic body 34 having elasticity is fixed to the outer peripheral surface of the outer ring 32c in a state of being laminated in a direction perpendicular to the axial direction of the rotor shaft L1. In this embodiment, the carrier C1 of the first planetary gear mechanism PG1 is fixed to the inner ring 32a, and the carrier C2 of the second planetary gear mechanism PG2 is fixed to the elastic body . That is, the elastic body 34 is provided between the carrier C1 and the carrier C2, which are the rotating elements in the connecting portion 30. As shown in FIG. Therefore, between the carrier C1 of the first planetary gear mechanism PG1 and the carrier C2 of the second planetary gear mechanism PG2, the elastic force of the elastic body 34 acts in the direction crossing the axial direction of the rotor shaft L1. ing.

As described above, in this embodiment, the carrier C1 and the carrier C2 are provided so as to be relatively rotatable with the elastic body 34 interposed therebetween, so that the self-aligning function by the gear tooth surface reaction force can be achieved. Without hindrance, the first planetary gear mechanism PG1 and the second planetary gear mechanism PG2 are in proper alignment. Therefore, the torque is not transmitted between the first planetary gear mechanism PG1 and the second planetary gear mechanism PG2, and the tooth surface reaction force of the gears disappears. Alignment remains unchanged. Further, even if torque is transmitted, the elasticity of the elastic body 34 does not interfere with the automatic centering function. In other words, the elasticity of the elastic body 34 absorbs the displacement when the meshing of the gears advances and the rotation shifts to a stable position.

As shown in FIG. 1, in this embodiment, during driving (when torque is transmitted from the motor M to the speed reduction mechanism T), the carrier C1 of the first planetary gear mechanism PG1 includes the bearing B4, the sun gear S2, and the pinion gear. The carrier C2 of the second planetary gear mechanism PG2 is supported by the bearing B5 and the tooth surfaces of the sun gear S2 and the pinion gear P2. Further, when not driven (when torque is not transmitted from the motor M to the speed reduction mechanism T), the carrier C1 of the first planetary gear mechanism PG1 is supported by the bearing B4 and the connecting portion 30, and the carrier C1 of the second planetary gear mechanism PG2 is supported. , the carrier C2 is supported by the bearing B5 and the connecting portion 30. As shown in FIG. As a result, NVH can be effectively suppressed regardless of whether the device is driven or not.

If the modulus of elasticity of the elastic body 34 is extremely small, sufficient elasticity cannot be exhibited, and the carrier C1 may fall down as shown in FIG. 6 of the conventional structure. It may not be possible to control it. Conversely, if the elastic modulus is excessively large, the rigidity hinders the self-aligning function, and in that case also, there is a possibility that NVH cannot be sufficiently suppressed. Therefore, the material of the elastic body 34 is appropriately selected within a range that has appropriate rigidity and damping characteristics that do not interfere with the self-aligning function.

If the carrier C1 and the carrier C2 are connected only by the radial bearing 43 without providing the elastic body 34, the carrier C1 and the carrier C2 can be prevented from falling down by the support of the radial bearing 32. Since the restraint of the bearing 32 hinders the self-aligning function due to the gear tooth surface reaction force, there is a possibility that the NVH cannot be sufficiently suppressed.

[Second embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. Parts that are the same as or can be regarded as the same as those of the above-described embodiment are denoted by the same reference numerals, and descriptions thereof are omitted as appropriate.

FIG. 3 is a skeleton diagram showing the configuration of a vehicle drive system provided with an electric motor speed reducer according to a second embodiment of the present invention. 4A and 4B are diagrams showing the connecting portion of the speed reducer for electric motor shown in FIG. As shown in FIG. 3, in the electric motor speed reducer 2-2 of the vehicle drive device 1-2 according to the present embodiment, the carrier C1, which is one rotating element of the first planetary gear mechanism PG1, and the second planetary gear A carrier C2, which is one rotating element of the mechanism PG2, is rotatably connected by a connecting portion 40. As shown in FIG. As shown in FIG. 4, the connecting portion 40 includes a radial bearing 42 that supports the carrier C1 and the carrier C2 so as to be relatively rotatable. The radial bearing 42 has an inner ring 42a, rolling elements (rollers) 42b, and an outer ring 42c. A ring-shaped elastic body 44 having elasticity is fixed to the inner peripheral surface of the inner ring 42a in a stacked state in a direction orthogonal to the axial direction of the rotor shaft L1. That is, in this embodiment, the elastic body 44 is interposed between the carrier C2 and the radial bearing 42, the carrier C1 of the first planetary gear mechanism PG1 is fixed to the elastic body 44, and the carrier C1 of the second planetary gear mechanism PG2 is fixed to the elastic body 44. C2 is fixed to the outer ring 42c of the radial bearing 42. Therefore, also in this embodiment, the axial direction of the rotor shaft L1 is intersected between the carrier C1 of the first planetary gear mechanism PG1 and the carrier C2 of the second planetary gear mechanism PG2, as in the first embodiment. The elastic force of the elastic body 44 acts in the direction. Therefore, the NVH suppression function similar to that of the first embodiment can be obtained in this embodiment as well.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the technical ideas described in the claims, the specification and the drawings. is possible. For example, the material of the elastic bodies 34 and 44 is not limited to rubber-based materials, and metal-based materials such as leaf springs may be employed. Moreover, the shape of the elastic bodies 34 and 44 is not limited to the ring shape, and may be discontinuous in the circumferential direction.

1, 1-2 Vehicle drive device 2, 2-2 Reducer (reducer for electric motor)
Reference Signs List 10 casing 20 gear case 30, 40 connecting portion 32, 42 radial bearing (intermediate bearing)
32a, 42a inner ring 32c, 42c outer ring 34, 44 elastic body B4, B5 bearing (other bearing)
C1, C2 Carrier (rotating element)
D differential mechanism (differential mechanism)
L1 Rotor shaft (output shaft)
L2, L3 axle M motor (electric motor)
PG1 First planetary gear mechanism PG2 Second planetary gear mechanism S1, S2 Sun gear P1, P2 Pinion gear R1, R2 Ring gear T Reduction mechanism

Claims (6)

A reduction gear for an electric motor comprising a reduction mechanism to which driving force from the electric motor is input,
The speed reduction mechanism includes at least two sets of planetary gear mechanisms including a first planetary planetary gear mechanism and a second planetary gear mechanism, and one rotating element of the first planetary planetary gear mechanism and the second planetary planetary gear mechanism. has a connecting portion that connects the one rotating element of
The connecting portion includes an intermediate bearing comprising a radial bearing that supports the rotating element of the first planetary planetary gear mechanism and the rotating element of the second planetary planetary gear mechanism so as to allow relative rotation, and the intermediate bearing and the first planetary gear. and an elastic body provided between the rotating element of the planetary gear mechanism and/or between the intermediate bearing and the rotating element of the second planetary gear mechanism. . The first planetary planetary gear mechanism and the second planetary planetary gear mechanism are coaxially arranged in series,
the rotating element of the first planetary gear mechanism is the carrier of the first planetary gear mechanism;
2. The reduction gear for an electric motor according to claim 1, wherein the rotating element of said second planetary gear mechanism is a carrier of said second planetary gear mechanism. The elastic body is fixed to the outer ring or the inner ring of the intermediate bearing, and either one of the carrier of the first planetary planetary gear mechanism and the carrier of the second planetary planetary gear mechanism is fixed to the elastic body. 3. A speed reducer for an electric motor according to claim 2. 4. A reduction gear for an electric motor according to claim 3, wherein said elastic body is formed in a ring shape. The carrier of the first planetary planetary gear mechanism and the carrier of the second planetary planetary gear mechanism are directly or indirectly connected to the casing of the reduction gear for the electric motor at a position separated from the connecting portion in the axial direction of the output shaft of the electric motor. 5. The speed reducer for an electric motor according to claim 1, wherein the speed reducer for an electric motor is rotatably supported by another bearing fixed to the speed reducer. an electric motor;
The speed reducer for electric motor according to any one of claims 1 to 5, comprising a speed reduction mechanism to which driving force from the electric motor is input;
and a differential mechanism that distributes and transmits the driving force reduced by the reduction mechanism to left and right axles.

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