Vehicle drive force transmission device

Abstract

This power transmission device comprises a differential case, a clutch member, and a differential gear set. The differential case includes an outer case that receives a torque and rotates about an axis, and an inner case coaxial with the outer case and capable of relatively rotating about the outer case. The clutch member is fixed or engaged to the outer case, includes the inner case and a dog clutch, and transmits the torque to the inner case from the outer case when meshed with the inner case. The differential gear set includes a pair of side gears and a pinion gear. The pair of side gears are respectively rotatable about the axis, capable of moving differentially with respect to each other, and respectively include a friction clutch that, combined with the differential case, restricts the differential movement. The pinion gear is supported by the inner case so as to be capable of transmitting the torque to the side gears, and is meshed with the side gears so as to permit the differential movement.

Description

[Technical Field]

[0001] The following disclosure relates to a power transmission device that can be suitably used in the powertrain of an electric vehicle. [Background technology]

[0002] In automobiles, the left and right axles do not necessarily rotate at the same speed, so differential movement between them is necessary. A differential is used to allow differential movement between the two axles. When both wheels have traction, the differential can effectively transmit torque to both axles. However, if one wheel loses traction and the other wheel remains capable of differential movement, torque will not be transmitted to either axle. One way to avoid this situation is the so-called limited slip differential (LSD). An LSD is equipped with a friction clutch that operates in response to torque, and the friction clutch acts to limit differential movement (torque-sensitive LSD).

[0003] There are various types of torque-sensitive LSDs. For example, the cone clutch type disclosed in Patent Document 1 is not expected to provide a large differential limiting force, but it can realize an LSD with a simple structure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-49345 Summary of the Invention

[0005] Although LSDs potentially offer the above-mentioned advantages to electric vehicles, they are not typically used. This is because, while electric vehicles use the motor as a generator to regenerate excess energy during deceleration, LSDs installed without any special ingenuity consume energy by limiting the differential even during deceleration. The inventors have conceived a power transmission device that can suitably utilize an LSD in electric vehicles.

[0006] According to one aspect, For electric vehicles, combined with an electric motor equipped with a reduction gear to transmit torque The power transmission device is a ring gear that meshes with the reduction gear; The differential case includes: an outer case that receives torque and rotates around an axis; and an inner case that is coaxial with the outer case and can rotate relatively to the outer case; a clutch member that is fixed to or engages with the outer case and forms a dog clutch with the inner case, and that transmits the torque from the outer case to the inner case when meshed with the inner case; a differential gear set that includes: a pair of side gears that are each rotatable around the axis and can be differentiated from each other, and whose combination with the outer case forms a friction clutch that limits the differential; and a pinion gear that is supported by the inner case so as to be able to transmit the torque to the side gear and meshes with the side gear so as to allow the differential. [Brief explanation of the drawings]

[0007] [Figure 1A] FIG. 1A is a schematic diagram showing the powertrain of an electric vehicle according to an example, in which an electromagnetic solenoid is used to drive a clutch. [Figure 1B] FIG. 1B is a schematic diagram showing a power train in which a combination of a motor, a gear mechanism, and a cam mechanism is used to drive the clutch. [Figure 1C] FIG. 1C is a schematic diagram showing a powertrain of an electric vehicle based on another example, in which a power source and a differential are arranged coaxially. [Figure 1D] FIG. 1D is a schematic diagram showing the power train, in which the clutch arrangement is opposite to that in FIG. 1C. [Figure 1E] FIG. 1E is a schematic diagram showing a powertrain of an electric vehicle based on yet another example, in which, instead of the example shown in FIG. 1B, a planetary gear is used to reduce (double) the output of the power source. [Figure 2] FIG. 2 is a cross-sectional view of a differential device included in a power transmission device according to one embodiment. [Figure 3] FIG. 3 is a cross-sectional view of a differential device in which a combination of a motor, a gear mechanism, and a cam mechanism is used to drive the clutch. [Figure 4] FIG. 4 is an exploded perspective view of a side gear including a gear member and an output member. [Figure 5] FIG. 5 is a partial cross-sectional plan view of the side gear to particularly show the engagement at the cam surface. DETAILED DESCRIPTION OF THE INVENTION

[0008] Several exemplary embodiments will be described below with reference to the accompanying drawings. Throughout the following description and claims, unless otherwise specified, the term "axis" refers to the rotation axis of the differential device, the axial direction refers to a direction parallel to the axis, and the radial direction refers to a direction perpendicular to the axis. The distinctions between front, rear, right, and left are based on the state in which the device is mounted on a vehicle, but of course, the front and rear or left and right may be reversed. It should be noted that the drawings are not necessarily drawn to exact scale, and therefore the mutual dimensional relationships are not limited to those shown.

[0009] The power transmission device according to this embodiment can be used in any type of automobile, but is particularly suitable for use in the powertrain of an electric vehicle that can regenerate energy in a rechargeable battery. Here, electric vehicles are not limited to purely electric vehicles, but can also include so-called (plug-in) hybrid vehicles that combine a rechargeable battery with an internal combustion engine, and hybrid fuel cell vehicles that combine a fuel cell with a rechargeable battery.

[0010] 1A, the powertrain of an electric vehicle includes, for example, an electric motor M as a power source, a reduction gear set 7 that reduces the rotation (i.e., multiplies the torque), and a differential device 1 that outputs torque while allowing differential movement. The entire arrangement is accommodated and supported in a single or separable housing.

[0011] The motor M includes, but is not limited to, a stator MS fixed to a motor housing and a rotor MR coupled to and rotating with a shaft 11. In response to a high-frequency current applied by a power source, the rotor MR generates torque on the stator MS, and the generated torque is output via the shaft 11.

[0012] The shaft 11 may be pulled out from the motor housing and serve directly as the input shaft of the reduction gear set 7, or a coupling 15 may be interposed between the shaft 11 and the input shaft 13. The drive train including the reduction gear set 7 and the differential device 1 is housed and supported in a gear housing that encloses a chamber separate from the motor housing. This electrically isolates the motor M from the drive train, which helps to reduce the leakage of high-frequency noise. The gear housing may be molded integrally with the motor housing, which helps to reduce the weight of the entire device, or it may be a separate component.

[0013] In either case, the reduction gear set 7 includes one or more reduction gear sets, and reduces the speed of the input rotation while multiplying the torque, and transmits it to the differential 1. The differential 1 receives torque by meshing with the reduction gear set 7 via, for example, a ring gear 9, and outputs the torque to the right axle 5R and the left axle 5L while allowing differential motion.

[0014] The reduction gear set 7 may be composed of two or more parallel shafts as shown in Figures 1A and 1B. In this case, the differential device 1 belongs to the third or fourth shaft in the drive train. This structure is advantageous for reducing the axial dimensions of the power train or drive train. It also provides design freedom in that each element of the power transmission device can be positioned without interference from the motor M.

[0015] However, the arrangements illustrated in FIGS. 1A and 1B require a considerable vertical dimension. The arrangements illustrated in FIGS. 1C and 1D are effective in reducing the radial dimension. In these examples, the motor M and the differential 1 are coaxially adjacent to each other in the axial direction, and the shaft 11 of the motor M is hollow, with the left axle 5L (or the right axle 5R) extending to the outside through the shaft 11. The reduction gear set 7 has only one axis parallel to these axles, but still has two reduction gears, as in the example illustrated in FIGS. 1A and 1B, and can achieve a sufficient reduction ratio. Furthermore, in the example illustrated in FIG. 1C, the actuator 3 can be placed in the space between the motor M and the differential 1, which is usually a dead space, which is advantageous in terms of space saving. On the other hand, in the example illustrated in FIG. 1D, the motor M and the actuator 3, which are prone to magnetic flux interference, are placed apart, which is expected to result in more stable operation.

[0016] Alternatively, a drivetrain using a planetary gear 7P is also possible, as shown in Figure 1E. In the illustrated example, the outer gear is fixed to the gear housing, the sun gear is fixed to the input shaft, and the planetary carrier is coupled to the differential case of the differential device 1, thereby achieving a large reduction ratio in torque transmission from the input shaft to the differential device 1. Of course, other configurations may be adopted, such as using the outer gear as the input. As can be easily understood from Figure 1E, with planetary gears, large diameter gears do not protrude off the axis as in Figures 1C and 1D.

[0017] 2 in combination with FIGS. 1A to 1E, the differential case 21 of the differential device 1 includes an outer case 31 that receives torque and rotates around an axis X, and an inner case 33 that is coaxially fitted to the outer case 31. The outer case 31 has bosses 32 at both ends, for example, and the gear housing has bearings 34 corresponding to the bosses, so that the outer case 31 is rotatably supported by the gear housing. The inner case 33 is rotatable relative to the outer case 31, but when the clutch 23 is engaged, the two are drivingly connected, and input torque is transmitted to the differential gear set 25. In other words, only when the clutch 23 is engaged is torque from the motor M output to the axles 5R, 5L via the differential gear set 25 and used to propel the vehicle. However, when the clutch 23 is disengaged, no torque is output to either axle 5R, 5L. On the other hand, when the vehicle is decelerated, if the clutch 23 is engaged, the motor M can generate braking force and regenerate surplus energy, but when the clutch 23 is disengaged, no energy regeneration occurs.

[0018] The clutch 23 may be composed of, for example, clutch teeth engraved on the edge of the inner case 33 and a clutch member 29 equipped with corresponding clutch teeth. The clutch member 29 may be generally annular, with the clutch teeth engraved on one surface and one or more legs protruding from the other surface. Corresponding to the legs, the outer case 31 has one or more openings 39 penetrating it at least axially. The openings 39 may also be open radially, which is advantageous for circulating lubricating oil. The legs of the clutch member 29 are exposed to the outside of the outer case 31 through the openings 39. The exposed legs may also be coupled to a member such as a ring plate 55 for easy external operation. By engaging the legs of the clutch member 29 with the openings 39, the clutch member 29 is immovable circumferentially relative to the outer case 31 and receives torque, but is movable axially.

[0019] The clutch 23 can be operated from outside the drivetrain by an actuator 3. As shown in FIG. 2, the actuator 3 can utilize an electromagnetic solenoid 61 that electromagnetically drives a plunger. The electromagnetic solenoid 61 is, for example, ring-shaped and slidably fitted around one boss portion 32 of the differential case 21 and is prevented from rotating. The plunger is fitted, for example, to the inner periphery of the electromagnetic solenoid and is movable in the axial direction. It also abuts, engages, or is fixed to the clutch member 29 or a ring plate 55 connected thereto. A cable C is electrically connected to the electromagnetic solenoid 61, and as shown in FIGS. 1A, 1C, and 1D, the cable C is drawn out to the outside of the gear housing. When an electric current is applied to the electromagnetic solenoid 61 from outside through the cable C, the plunger is driven in the axial direction, and the clutch 23 can be operated via the ring plate 55.

[0020] Alternatively, instead of the stationary electromagnetic solenoid 61 driving the movable plunger, the electromagnetic solenoid 61 itself may be movable and driven by itself relative to a fixed member, thereby operating the clutch 23.

[0021] Furthermore, any driving device, such as a hydraulic device, a pneumatic device, or an electric motor, can be used for the actuator 3, without being limited to an electromagnetic solenoid. The device shown in FIG. 3 and schematically shown in FIGS. 1B and 1E is one example. The actuator 3 generally comprises an electric motor 63, gear mechanisms 65 and 67, and a cam structure 69. The gear mechanism comprises, for example, a pinion gear 65 rotated by the electric motor 63 and a gear ring 67 meshing with the pinion gear 65 and having a parallel shaft. The gear ring 67 has a larger diameter than the pinion gear 65 and constitutes a reduction gear mechanism. To increase the reduction ratio, other gears may be interposed. The cam structure 69 is a mechanism that converts the rotational motion of the gear ring 67 into linear motion, and may comprise, for example, a cam protrusion abutting on or formed on the gear ring 67, or a cam ball that rolls on the gear ring 67. Applying current through cable C causes gear ring 67 to rotate and cam structure 69 to press against plate 55, thereby enabling actuator 3 to engage and disengage clutch 23.

[0022] In the illustrated example, the clutch member 29 itself has clutch teeth and meshes with the inner case 33, but the clutch member 29 and the clutch teeth may be separate entities. For example, a movable member that is movable in the axial direction but fixed in the circumferential direction relative to the outer case 31 may have clutch teeth and be made to move following the clutch member 29. Alternatively, the outer case 31 itself or a member fixed thereto may have clutch teeth, and the clutch member 29 may drive the inner case 33 to mesh with it. Furthermore, the clutch 23 does not have to rely on meshing between clutch teeth, and can be configured with any appropriate meshing structure, such as a combination of axially extending lugs and grooves.

[0023] 2 and 3, the inner case 33 is connected to the differential gear set 25. For example, a pinion shaft 41 is connected to the inner case 33 by a pin, and a plurality of pinion gears 43 are rotatably supported on the pinion shaft 41. Right and left side gears 45 mesh with the pinion gear 43, and the side gears 45 can be connected to their respective axles. For this connection, for example, a structure such as a spline can be provided on the inner peripheral surface.

[0024] The combination of the axially outer surface of the side gear 45 and the inner surface of the outer case 31 forms a friction clutch 27, which functions to limit differential movement between the side gears 45. The illustrated example and the following description exclusively relate to a bevel gear and cone clutch LSD. However, it goes without saying that a face gear type may be used instead of a bevel gear type, a multi-plate clutch may be used instead of a cone clutch type, or any other suitable type may be used. In the illustrated example, the inner surface of the outer case 31 forms the friction clutch 27. However, if possible, the inner surface of the inner case 33 may form the friction clutch 27 instead of or in addition to the outer case 31. In either case, the friction clutch 27 is located radially inward of the clutch members 29 and is not directly interfering with them. Axial drive of the clutch members 29 does not affect the operation of the friction clutch 27, and operation of the friction clutch 27 does not affect the engagement of the clutch members 29. This structure efficiently utilizes the limited installation space in the differential.

[0025] The meshing reaction force between the gear teeth of the pinion gear 43 and the gear teeth of the side gear 45 presses the side gear 45 axially outward, thereby operating the friction clutch 27. Since the thrust force increases as the applied torque increases, the differential restriction by the friction clutch 27 is torque-sensitive. To further strengthen the effect, the friction surface 35 of the outer case 31 and the friction surface 51 of the side gear 45 may each be a conical surface (i.e., a cone clutch), and a friction ring 37 may be interposed between the friction surfaces 35, 51.

[0026] 4 in combination with FIGS. 2 and 3, side gears 45 do not have to be one piece, and may instead comprise, for example, a gear member 49 that meshes with pinion gear 43 and an output member 47 that engages with the gear member 49 and rotates therewith. Output member 47 can be used for connection to an axle and includes a flange portion 47F that extends radially outward to receive gear member 49. Friction surface 51 may be formed on the radially outer edge of flange portion 47F.

[0027] The gear member 49 has a socket 53, which is an axially outwardly opening recess, for engagement with the output member 47, and the output member 47 has a corresponding lug. The socket and lug relationship may be reversed, but in either case, such an engagement structure transmits torque between the gear member 49 and the output member 47 for both forward rotation R1 and reverse rotation R2.

[0028] 5 in combination with FIGS. 2 to 4, side surfaces 53A and 53B of socket 53 may be inclined relative to the axial direction. Needless to say, the side surfaces of the lug may also be inclined correspondingly. The inclined, abutting side surfaces function as cams that convert a portion of the torque acting on gear member 49 into thrust forces f1 and f2. These thrust forces f1 and f2 press output member 47 axially outward, thereby actuating friction clutch 27.

[0029] The inclination angles θ1 and θ2 of the side surfaces 53A and 53B relative to the axis X can be set independently and appropriately, thereby independently increasing or decreasing the thrust forces f1 and f2. Because these thrust forces can be greater than those generated by the meshing reaction force of the differential gear, this structure can strengthen the differential limiting capability of the friction clutch 27. By increasing the inclination angle θ1 of the side surface 53A, on which torque in the forward direction R1 acts, a greater thrust force f1 is generated in response to torque application in the direction that accelerates the vehicle (the drive direction), thereby achieving a greater differential limiting capability. By decreasing or setting to zero the inclination angle θ2 of the side surface 53B, on which torque in the reverse direction R2 acts, the thrust force f2 is weakened or set to zero in response to torque application in the direction that decelerates the vehicle (the coasting direction), thereby reducing the differential limiting capability.

[0030] According to this embodiment, the differential has a differential limiting function, so a transmission device equipped with this can transmit torque to one of the drive wheels even if the other loses traction. Meanwhile, during deceleration, the electric motor regenerates the vehicle's surplus energy. However, since the differential limiting function is small, the energy loss associated with the differential limiting is also small, allowing for low-loss energy regeneration. Furthermore, if the energy inflow through the drivetrain is excessive compared to the capacity of the electric motor, the power transmission can be cut off by operating the clutch, preventing overload on the electric motor, regeneration circuit, or battery. Furthermore, because the speed difference between the clutch teeth before and after clutch operation is very small, abnormal noise and shock to the vehicle body associated with the operation are very small, and are much smaller than, for example, a disconnect device on a shaft.

[0031] Although several embodiments have been described, modifications or variations of the embodiments can be made based on the above disclosure.

Claims

1. A power transmission device for an electric vehicle that is combined with an electric motor equipped with a reduction gear for transmitting torque, a differential case including an outer case having a ring gear meshing with the reduction gear and rotating around an axis by receiving the torque, and an inner case coaxial with the outer case and rotatable relative to the outer case; a clutch member fixed to or engaged with the outer case, forming a dog clutch together with the inner case, the clutch member transmitting the torque from the outer case to the inner case when meshed with the inner case; a differential gear set including: a pair of side gears each rotatable about the axis and capable of mutual differential movement, each of which constitutes a friction clutch that limits the differential movement when combined with the outer case; and a pinion gear supported by the inner case so as to be capable of transmitting the torque to the side gears and meshing with the side gears so as to allow the differential movement; A power transmission device comprising:

2. 2. The power transmission device according to claim 1, wherein the friction clutch includes friction surfaces provided on the side gears and inner surfaces of the outer case that respectively correspond to the friction surfaces.

3. 3. The power transmission device of claim 2, wherein each of the side gears includes a gear member that meshes with the pinion gear and an output member that has the friction surface, and the gear member and the output member engage with each other at a cam surface that is inclined relative to the circumferential direction, whereby the cam surface converts a portion of the torque into an axial thrust force to press the friction surface toward the differential case.

4. 2. The power transmission device of claim 1, wherein said clutch member is configured to move axially to engage and disengage with said inner case.

5. an opening that penetrates the outer case in the axial direction, the opening engaging with the clutch member and exposing at least a portion of the clutch member to the outside of the outer case; The power transmission device of claim 1 further comprising:

6. 2. The power transmission device of claim 1, wherein said friction clutch is disposed radially inward from said clutch member.

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