Drive power transmission mechanism

Abstract

To provide a drive power transmission mechanism for an electric vehicle which can prevent an increase in size of the whole device while providing with a torque limiter mechanism.SOLUTION: The drive power transmission mechanism has a cylindrical shaft housing 22 fixed to an inner diameter part of a motor core 20 and extending in an axial direction. A shaft 9 is arranged at a center on an inner diameter side of the shaft housing 22, and is rotationally supported to the shaft housing 22. The drive power transmission mechanism includes: a plurality of annular friction plates 30 provided on one of an inner peripheral face of the shaft housing 22 and an outer peripheral face of the shaft 9; a plurality of annular separator plates 40 provided on the other of the inner peripheral face of the shaft housing 22 and the outer peripheral face of the shaft 9 and provided alternately with the plurality of friction plates 30 in the axial direction; and a plate spring 65 for urging the plurality of friction plates 30 and the plurality of separator plates 40 at all times in a friction engagement direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a driving force transmission mechanism for transmitting driving force generated by an electric motor that is a driving source of an electric vehicle. [Background technology]

[0002] Depending on the driving conditions, excessive transmission torque may be input to components that transmit driving force from a driving source, such as a vehicle's transmission, gears, or drive shaft. For example, in a vehicle powered by an electric motor, excessive transmission torque is input when the vehicle travels on rough roads, such as uneven terrain. When the tires are off the road and spinning, the motor control program recognizes that the load on the electric motor is decreasing and controls the electric motor to increase its rotation speed, thereby increasing the tire rotation speed. When the tires return to contact with the road while the electric motor is rotating at high speed, excessive transmission torque is input to the components that transmit driving force. Therefore, to ensure safety, components that transmit driving force are designed with sufficient torque transmission capacity to prevent damage even when such excessive transmission torque is input.

[0003] However, if each part is designed to have sufficient torque transmission capacity for safety reasons, each part will become larger, resulting in a design with strength that is unnecessary for normal driving.As a countermeasure to this, Patent Document 1 discloses a power transmission device that protects parts from excessive torque input by providing a torque limiter mechanism using a friction clutch. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5354103 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the power transmission device of Patent Document 1 requires securing space for providing the torque limiter mechanism, which results in an increase in the size of the entire power transmission device.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a driving force transmission mechanism for an electric vehicle that is equipped with a torque limiter mechanism while avoiding an increase in the size of the entire device. [Means for solving the problem]

[0007] In order to solve the above problems, the driving force transmission mechanism according to the present invention comprises: A driving force transmission mechanism for an electric vehicle that transmits driving force of an electric motor generated by rotation of a motor core to a shaft of the electric motor, a cylindrical shaft housing fixed to an inner diameter portion of the motor core and extending in the axial direction; the shaft is disposed at the center of the inner diameter side of the shaft housing and is rotatably supported by the shaft housing, a plurality of annular friction plates provided on either an inner peripheral surface of the shaft housing or an outer peripheral surface of the shaft, the friction plates rotating integrally with either the shaft housing or the shaft; a plurality of annular separator plates provided on the other of the inner peripheral surface of the shaft housing and the outer peripheral surface of the shaft, rotating integrally with the other of the shaft housing and the shaft, and arranged alternately with the plurality of friction plates in the axial direction; and a biasing means for constantly biasing the plurality of friction plates and the plurality of separator plates in a direction in which they are frictionally engaged with each other. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a driving force transmission mechanism for an electric vehicle that is equipped with a torque limiter mechanism while preventing the entire device from becoming large. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a skeleton diagram showing the overall configuration of a driving force transmission path of an electric vehicle including a driving force transmission mechanism according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a typical electric motor used as a drive source for an electric vehicle. [Figure 3] FIG. 3 is a cross-sectional view taken along the axial direction of a main part of an electric motor including a driving force transmission mechanism according to this embodiment. [Figure 4] Figure 4(a) is an enlarged view of the friction plate as viewed from the axial direction, Figure 4(b) is an enlarged view of the friction plate as viewed from the radial direction, and Figure 4(c) is a cross-sectional view taken along the arrow 4c-4c in Figure 4(a). [Figure 5] Figure 5(a) is an enlarged view of the separator plate as viewed from the axial direction, Figure 5(b) is an enlarged view of the separator plate as viewed from the radial direction, and Figure 5(c) is a cross-sectional view taken along the arrow 5c-5c in Figure 5(a). DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A driving force transmission mechanism for an electric vehicle according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0011] First, the directions of the driving force transmission mechanism according to the embodiment will be defined. The axial, radial, and circumferential directions of the driving force transmission mechanism refer to the axial, radial, and circumferential directions of the motor core and shaft of the electric motor, which is the driving source. Regarding the axial direction, the left side of the paper in Fig. 1 is defined as one axial side, and the right side of the paper is defined as the other axial side. Furthermore, in Fig. 3, the right side of the paper is defined as one axial side, and the left side of the paper is defined as the other axial side.

[0012] FIG. 1 is a skeleton diagram showing the overall configuration of a driving force transmission path of an electric vehicle, including a driving force transmission mechanism according to this embodiment. The driving force transmission path 1 of the electric vehicle includes a driving source unit 3 including an electric motor 2 as a driving source, a reduction gear unit 4 that reduces the rotation of the electric motor 2, and a wheel drive unit 8 that transmits the driving force of the electric motor 2 transmitted from the reduction gear unit 4 to an axle 6 via a differential gear unit 5 and drives wheels 7L and 7R that are drive wheels connected to both ends of the axle 6. Note that the driving force transmission path 1 in Fig. 1 is an example, and the driving force transmission path of an electric vehicle is not limited to this. Furthermore, the axial direction in Fig. 1 is the vehicle width direction, one axial side is the left side in the vehicle width direction (the left side of the paper in Fig. 1), and the other axial side is the right side in the vehicle width direction (the right side of the paper in Fig. 1).

[0013] The shaft 9, which is the drive shaft of the electric motor 2, is arranged parallel to the axle 6 of the wheel drive unit 8. In other words, the shaft 9 is arranged along the vehicle width direction. The shaft 9 is provided with a first connecting gear 10 for transmitting the drive force of the electric motor 2, i.e., the rotation of the electric motor 2, to the reduction gear unit 4. The first connecting gear 10 is provided integrally with the shaft 9.

[0014] The reduction gear unit 4 includes a second shaft 11 disposed parallel to the shaft 9. The second shaft 11 is provided with a second connection gear 12 that meshes with the first connection gear 10 of the shaft 9. The second connection gear 12 is integral with the second shaft 11 and has a larger diameter than the first connection gear 10 of the shaft 9. Therefore, the rotation of the electric motor 2 is reduced in speed and transmitted to the second shaft 11 via the first connection gear 10 and the second connection gear 12. The second shaft 11 is further provided with a third connection gear 14. The third connection gear 14 is integral with the second shaft 11. The second connection gear 12 and the third connection gear 14 are arranged side by side in this order in the axial direction from one axial side to the other axial side. The diameter of the third connection gear 14 is smaller than the diameter of the second connection gear 12.

[0015] The wheel drive unit 8 is equipped with a fourth connection gear 16 that meshes with the third connection gear 14 of the second shaft 11 and is connected to the differential gear unit 5. The fourth connection gear 16 is disposed coaxially with the axle 6 and has a larger diameter than the third connection gear 14. The rotation of the electric motor 2 transmitted to the second shaft 11 is reduced in speed and transmitted to the differential gear unit 5 via the third connection gear 14 and the fourth connection gear 16.

[0016] The axle 6 consists of a first axle 6L, with a left wheel 7L connected to one axial end thereof, and a second axle 6R, with a right wheel 7R connected to the other axial end thereof. The driving force of the electric motor 2 is transmitted to each of the first axle 6L and second axle 6R via a differential gear unit 5, thereby driving the left and right wheels 7L and 7R.

[0017] FIG. 2 is a cross-sectional view of a conventional, well-known electric motor 102 used as a drive source for electric vehicles. The shaft 109 of the electric motor 102 is fixed by press fitting into the inner diameter portion of a motor core 120 and rotatably supported by a motor case 121 via a pair of bearings 126A and 126B. The motor core 120 is a rotor core disposed on the inner diameter side of a stator core 119 and rotates on the inner diameter side of the stator core 119. In such an electric motor 102, as shown in FIG. 2, the shaft 109 is generally hollow to reduce weight. The inventors of the present application focused on this structure of the shaft 109 and invented the driving force transmission mechanism of the present application. The detailed configuration of the driving force transmission mechanism of this embodiment will be described below.

[0018] FIG. 3 is a cross-sectional view taken along the axial direction of a main part of the electric motor 2 including the driving force transmission mechanism according to this embodiment. The electric motor 2 has a configuration in which a motor core 120, which is a rotor core, is disposed inside a stator core, similar to the electric motor 102 shown in Fig. 2, but the stator core is not shown in Fig. 3. In this embodiment, the motor core refers to the rotor of the electric motor, i.e., the rotor core.

[0019] The electric motor 2 includes a motor case 21, a cylindrical motor core 20 housed in the motor case 21, a shaft housing 22 press-fitted onto the inner periphery of the motor core 20, and a shaft 9 rotatably supported by the shaft housing 22. Note that the outer diameter portion of the motor case 21 is not shown in FIG. 3. The motor core 20 has the same configuration as known motor cores and is made of a permanent magnet. A coil (not shown) through which a current flows is wound a predetermined length around a stator core (not shown). When a current flows through the coil (not shown), the motor core 20 rotates. In this embodiment, the shaft housing 22 is fixed to the center of the motor core 20 by press-fitting. As a result, the shaft housing 22 rotates integrally with the motor core 20.

[0020] The shaft housing 22 is formed in a cylindrical shape and is disposed so as to axially penetrate the inner diameter portion of the motor core 20. A first bushing 23 and a second bushing 24 for centering are provided at one axial end and the other axial end of the shaft housing 22, respectively. The shaft 9 is rotatably supported at the center of the inner diameter side of the shaft housing 22 via the first and second bushings 23, 24.

[0021] The shaft 9 is made of solid metal. The shaft 9 extends axially and penetrates the shaft housing 22 in the axial direction. Specifically, the shaft 9 has a portion that protrudes in one axial direction from a first bushing 23 at one axial end of the shaft housing 22, and a portion that protrudes in the other axial direction from a second bushing 24 at the other axial end of the shaft housing 22. A first rolling bearing 26 is fitted via an annular spacer 25 to the portion of the shaft 9 that protrudes from the first bushing 23 on one axial side. A second rolling bearing 28 is fitted via an annular spacer 27 to the portion of the shaft 9 that protrudes from the second bushing 24 on the other axial side. The shaft 9 is rotatably supported by an external member (not shown) via these first and second rolling bearings 26 and 28. Furthermore, a first connecting gear 10 that transmits the output of the electric motor 2 to the reduction gear unit 4 is provided on the portion of the shaft 9 that protrudes from the second bushing 24 on the other axial side, as shown in FIG. 1 .

[0022] With this configuration of the shaft housing 22 and the shaft 9, an annular space extending in the axial direction is formed between the shaft housing 22 and the shaft 9. Within the annular space, a plurality of annular friction plates 30 and a plurality of annular separator plates 40 are arranged alternately in the axial direction.

[0023] Figure 4(a) is an enlarged view of the friction plate 30 as seen from the axial direction, Figure 4(b) is an enlarged view of the friction plate 30 as seen from the radial direction, and Figure 4(c) is a cross-sectional view taken along the arrow 4c-4c in Figure 4(a).

[0024] The friction plate 30 is formed by bonding an annular friction material 33 made of paper to the surface of an annular core plate 32, which is a metal substrate. The friction material 33 is bonded to both sides of the core plate 32. A plurality of teeth 35 are formed circumferentially on the inner diameter edge of the friction plate 30. Male splines 36 are provided circumferentially on the outer peripheral surface of the shaft 9, and the shapes of the plurality of teeth 35 of the friction plate 30 correspond to the shapes of the male splines 36 of the shaft 9. The inner diameter teeth 35 fit into the male splines 36 of the shaft 9, so that the friction plate 30 is disposed on the outer peripheral surface of the shaft 9 so as to be axially movable relative to the shaft 9 but unable to rotate relative to the shaft 9. In other words, the friction plate 30 rotates integrally with the shaft 9. The outer peripheral surface of the friction plate 30 and the inner peripheral surface of the shaft housing 22 face each other circumferentially with a predetermined space between them. In other words, the friction plate 30 and the shaft housing 22 are not in contact with each other.

[0025] Figure 5(a) is an enlarged view of the separator plate 40 as viewed from the axial direction, Figure 5(b) is an enlarged view of the separator plate 40 as viewed from the radial direction, and Figure 5(c) is a cross-sectional view taken along the arrow 5c-5c in Figure 5(a).

[0026] The separator plate 40 is made of a single annular plate such as a metal plate and serves as a frictionally engaging member for the friction plate 30. A plurality of teeth 45 are formed circumferentially on the outer edge of the separator plate 40. A female spline 46 is provided circumferentially on the inner surface of the shaft housing 22, and the shape of the plurality of teeth 45 on the separator plate 40 corresponds to the shape of the female spline 46 on the shaft housing 22. The outer teeth 45 of the separator plate 40 are fitted into the female spline 46 of the shaft housing 22, so that the separator plate 40 is disposed on the inner surface of the shaft housing 22, axially movable relative to the shaft housing 22 but unable to rotate relative to the shaft housing 22. In other words, the separator plate 40 rotates integrally with the shaft housing 22. The shaft 9 is disposed axially penetrating the center holes of the plurality of separator plates 40. The inner surface of the separator plate 40 and the outer surface of the shaft 9 face each other circumferentially with a predetermined gap between them. In other words, the separator plate 40 and the shaft 9 are not in contact with each other.

[0027] The plurality of friction plates 30 and the plurality of separator plates 40 are arranged alternately in the axial direction, and are arranged so that both axial ends are separator plates 40. A circumferential groove 50 is formed on the inner peripheral surface of a portion of the shaft housing 22 adjacent to the other axial side of the separator plate 40 at the other axial end, and a retaining ring 51 is engaged in the circumferential groove 50. A circumferential groove 52 is formed on the outer peripheral surface of a portion of the shaft 9 adjacent to the other axial side of the separator plate 40 at the other axial end, and a retaining ring 53 is engaged in the circumferential groove 52. These retaining rings 51, 53 restrict movement of the separator plate 40 at the other axial end in the other axial direction.

[0028] A circumferential groove 60 is formed on the inner peripheral surface of a portion of the shaft housing 22 near one axial side of the separator plate 40 at one axial end, and a retaining ring 61 is engaged in the circumferential groove 60. A circumferential groove 62 is formed on the outer peripheral surface of a portion of the shaft 9 near one axial side of the separator plate 40 at one axial end, and a retaining ring 63 is engaged in the circumferential groove 62.

[0029] A disc spring 65 is interposed between the separator plate 40 at one axial end and the two retaining rings 61, 63. The disc spring 65 is interposed in a compressed state. The two retaining rings 61, 63 restrict movement of the disc spring 65 in one axial direction. Therefore, the disc spring 65 constantly urges the multiple separator plates 40 and the multiple friction plates 30 from one axial side to the other axial side. In other words, the disc spring 65 constantly urges the friction plates 30 and the separator plates 40 in a direction that frictionally engages them. This causes the multiple friction plates 30 and the multiple separator plates 40, which are arranged alternately, to come into close contact with each other.

[0030] In this state, when motor core 20 rotates, the rotation of motor core 20 is transmitted to shaft 9 as the driving force of electric motor 2. Specifically, when motor core 20 rotates, shaft housing 22 rotates integrally with motor core 20, shaft housing 22 rotates integrally with multiple separator plates 40, and shaft 9 rotates integrally with motor core 20 and shaft housing 22 via multiple friction plates 30 that are in close contact with multiple separator plates 40. In this way, the driving force of electric motor 2 generated by the rotation of motor core 20 is transmitted to shaft 9.

[0031] As described above, the driving force transmission mechanism of this embodiment is configured to include a shaft housing 22 fitted to the motor core 20, and a plurality of friction plates 30 and a plurality of separator plates 40 that are frictionally engaged and in close contact with each other by the biasing force of the disc springs.

[0032] The driving force of the electric motor 2 transmitted to the shaft 9 is transmitted to the wheels 7L and 7R, which are drive wheels, via a driving force transmission path 1 shown in FIG.

[0033] The driving force transmission mechanism according to this embodiment is configured so that the plurality of friction plates 30 and the plurality of separator plates 40 that are frictionally engaged by the biasing force of the disc springs 65 function as a torque limiter mechanism. The torque limiter mechanism will be described below.

[0034] Due to the pressure of the disc spring 65, a friction force F [N (unit: Newton)] acts between the friction material 33 adhered to one surface of the friction plate 30 and the surface of the separator plate 40 facing the one surface of the friction plate 30. The friction force F is expressed by the following equation (1). (1) Friction force F [N] = friction coefficient μ of friction material × force N [N] pressed by disc spring

[0035] If the radius from the center of the annular friction plate 30 to which the friction material 33 made of a paper material with a high friction coefficient is r [mm (unit: millimeter)] (see FIG. 4(a)), when the number of contact surfaces between the friction plate 30 and the separator plate 40 is one, the transmission torque T (number of contact surfaces: 1) [Nm (unit: Newton meters)] generated between the annular friction plate 30 having teeth 35 formed on its inner diameter side and the shaft 9 having male splines 36 formed on its outer diameter side is expressed by the following equation (2): (2) T (Number of contact surfaces: 1)[Nm]=μ×N[N]×r[mm]

[0036] If the number of contact surfaces between the friction plate 30 and the separator plate 40 is n (n: natural number), the transmission torque T (number of contact surfaces: n) [Nm] is expressed by the following equation (3). (3) T (Number of contact surfaces: n)[Nm]=μ×N[N]×r[mm]×n

[0037] When the electric vehicle is operating normally, i.e., when the tires are in contact with the road surface, the driving force, i.e., the transmission torque, of the electric motor 2 input to the shaft 9 is defined as transmission torque T (normal). If transmission torque T (normal) is equal to or less than T (number of contact surfaces: n) expressed by equation (3), the driving force of the electric motor 2 is transmitted to the shaft 9 and becomes the propulsion force for the electric vehicle.

[0038] On the other hand, when a large driving force is generated, such as when the tires of the electric vehicle return to contact with the road after having left the road surface and are spinning, the driving force of the electric motor 2 input to the shaft 9, i.e., the transmission torque, is defined as T (excessive). If the transmission torque T (excessive) exceeds T (number of contact surfaces: n) expressed by Equation (3), the frictional engagement between the friction plates 30 and the separator plates 40 caused by the frictional force of the friction material 33 is released, and the friction plates 30 and the separator plates 40 slip. In this state, torque transmission from the separator plates 40 to the friction plates 30 is interrupted. In other words, the rotation of the motor core 20 is not transmitted to the shaft 9. As a result, excessive driving force is prevented from being transmitted to the driving force transmission path shown in FIG. 1, and damage to the components of the driving force transmission path can be prevented. In this way, the friction plates 30 and the separator plates 40 in this embodiment function as torque limiters.

[0039] In this embodiment, the torque limiter mechanism is provided in a space corresponding to the internal space of the shaft in a conventional electric motor, so that the torque limiter mechanism can be added without changing the size of the conventional electric motor. This makes it possible to provide a power transmission mechanism for an electric vehicle that is equipped with a torque limiter mechanism but does not increase the size of the entire device.

[0040] In this embodiment, the teeth 35 on the inner diameter portion of the friction plate 30 are fitted into the male splines 36 on the outer peripheral surface of the shaft 9, and the teeth 45 on the outer diameter portion of the separator plate 40 are fitted into the female splines 46 on the inner peripheral surface of the shaft housing 22. However, the configuration may also be such that the teeth on the outer diameter portion of the friction plate 30 are fitted into the female splines 46 on the inner peripheral surface of the shaft housing 22, and the teeth on the inner diameter portion of the separator plate 40 are fitted into the male splines 35 on the outer peripheral surface of the shaft 9.

[0041] Furthermore, by using the above-mentioned formulas (1) to (3), the magnitude of the transmission torque at which the friction plates 30 and the separator plates 40 slip, the number of friction plates 30 and the separator plates 40, etc. can be appropriately designed. [Explanation of symbols]

[0042] 1. Driving force transmission path 2 electric motors 9 Shaft 20 Motor Core 21 Motor case 22 Shaft housing 23 First Bush 24 Second Bush 25, 27 Spacer 26, 28 Rolling bearings 30 Friction Plate 33 Friction material 35 teeth 36 male spline 40 Separator Plate 45 teeth 46 female spline 50, 52, 60, 62 circumferential groove 51, 53, 61, 63 Retaining ring 65 Disc spring

Claims

1. A driving force transmission mechanism for an electric vehicle that transmits driving force of an electric motor generated by rotation of a motor core to a shaft of the electric motor, a cylindrical shaft housing fixed to an inner diameter portion of the motor core and extending in the axial direction; the shaft is disposed at the center of the inner diameter side of the shaft housing and is rotatably supported by the shaft housing, a plurality of annular friction plates provided on either an inner peripheral surface of the shaft housing or an outer peripheral surface of the shaft, the friction plates rotating integrally with either the shaft housing or the shaft; a plurality of annular separator plates provided on the other of the inner peripheral surface of the shaft housing and the outer peripheral surface of the shaft, rotating integrally with the other of the shaft housing and the shaft, and arranged alternately with the plurality of friction plates in the axial direction; and biasing means for constantly biasing the plurality of friction plates and the plurality of separator plates in a direction in which they are frictionally engaged with each other.

2. 2. The driving force transmission mechanism according to claim 1, wherein the frictional engagement between the plurality of friction plates and the plurality of separator plates is released when the driving force exceeds a predetermined magnitude.

3. the plurality of friction plates are fitted to splines provided on either the inner circumferential surface of the shaft housing or the outer circumferential surface of the shaft, 3. The driving force transmission mechanism according to claim 1, wherein the plurality of separator plates are fitted to splines provided on the other of the inner peripheral surface of the shaft housing and the outer peripheral surface of the shaft.

4. 2. The driving force transmission mechanism according to claim 1, wherein the biasing means is a disc spring.

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