Sub-assembly for e-axle

Abstract

To impart a differential limiting function to an eAxle without substantially increasing a dimension in the axial direction.SOLUTION: A sub-assembly for providing a differential limiting function to an eAxle including a differential for differentially outputting torque about an axis comprises: an actuator configured to generate a rotational force; a cam mechanism configured to convert the rotational force into a thrust force in a direction of the axis; a clutch assembly including a first drum separably coupled to a casing of the differential, a second drum separably coupled to a side gear of the differential, and a friction clutch configured to brake the second drum relative to the first drum, the clutch assembly being disposed adjacent to the cam mechanism so as to receive the thrust force to actuate the friction clutch; and a cover dimensioned to enclose the cam mechanism and the clutch assembly, the cover being coupled to the eAxle so as to support any one of the cam mechanism and the clutch assembly against the thrust force or a thrust reaction force, the cover having an opening surrounding the axis.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The following disclosure relates to a sub - assembly for imparting a differential limiting function to an electric axle.

Background Art

[0002] Technologies for driving a vehicle solely by an electric motor instead of an internal combustion engine have been intensively studied. Usually, the torque generated by an electric motor is multiplied by a reduction gear set and output to an axle. A drive device in which a reduction gear set and an inverter are integrated with an electric motor is called an electric axle or eAxle, etc. Patent Documents 1 and 2 propose an electric axle that further includes a differential for allowing differential between the left and right axles.

[0003] Since an electric axle includes many devices by itself and can be handled as a whole, it facilitates the assembly of a vehicle. Also, compared with the combination of an internal combustion engine and a transmission, an electric axle is compact and lightweight. These features enhance the design freedom of the vehicle and contribute to the improvement of energy efficiency.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When attempting to add further functions to an electric axle, several problems are encountered. For example, when attempting to mechanically interrupt the output to the axle, at least a clutch and a device for operating the clutch must be incorporated inside the electric axle. This requires an extension of the axial dimension of the electric axle, and inevitably a design change on the vehicle side where it is mounted is necessary. Also, since an electric axle is inherently long in the axial direction, that is, long in the width direction of the vehicle, it is difficult to ensure sufficient length for the axles that extend further on both sides thereof. When attempting to extend the electric axle in the axial direction, a further shortening of the axle length is required, and then the room for the axle to swing about the joint as a fulcrum decreases, thus affecting the ride comfort of the vehicle. Alternatively, even if a device is added outside the electric axle, if the device is to be supported separately from the support of the electric axle, a design change on the vehicle side is inevitable.

[0006] The technology disclosed below was created in view of these problems.

Means for Solving the Problems

[0007] According to one aspect, a sub-assembly for imparting a differential limiting function to an electric axle having a differential that differentially outputs torque around an axis includes an actuator that generates a rotational force around the axis, a cam mechanism that converts the rotational force into a thrust force in the direction of the axis, a first drum that is separably coupled to the casing of the differential, a second drum that is separably coupled to the side gear of the differential, and a friction clutch that brakes the second drum with respect to the first drum. The clutch assembly includes a clutch assembly disposed adjacent to the cam mechanism to receive the thrust force and operate the friction clutch, and a cover dimensioned to surround the cam mechanism and the clutch assembly and coupled to the electric axle to support either the cam mechanism or the clutch assembly against the thrust force or thrust reaction force. The cover includes an opening surrounding the axis.

[0008] Preferably, the actuator is fixed to the cover or interposed between the cam mechanism and the electric axle, and is coupled to the cam mechanism to transmit the rotational force. Also preferably, the cam mechanism is interposed between the clutch assembly and the cover or the electric axle. Alternatively preferably, the friction clutch is a multi-plate clutch including a first clutch plate engaged with the first drum and a second clutch plate engaged with the second drum and alternately laminated with the first clutch plate. Also preferably, the first drum and the second drum each include a spline for coupling to the differential, and the splines overlap each other in the circumferential direction.

Advantages of the Invention

[0009] There is provided a sub-assembly of an electric axle that can easily impart a differential limiting function simply by being incorporated at one end of the electric axle, and moreover hardly increases its axial dimension.

Brief Description of the Drawings

[0010]

Fig. 1A

Fig. 1B

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6A

Fig. 6B

Fig. 6C

Fig. 6D

[0011] Some exemplary embodiments will be described below with reference to the accompanying drawings. It should be noted in particular that the drawings are not necessarily drawn to scale, and thus the mutual dimensional relationships are not limited to those shown. Throughout the following description and the appended claims, unless otherwise specified, the axis means a common rotational axis for the differential and the subassembly, and the terms "radial direction" and "circumferential direction" are defined with respect to the axis. Also, for the sake of convenience of description, right and left are distinguished with respect to the traveling direction of the vehicle, but it goes without saying that embodiments with the right and left reversed are possible.

[0012] Referring to FIGS. 1A and 1B, an electric axle including a differential includes an electric motor 1 that generates torque in response to the output of an inverter, a reduction gear set 3 that reduces its rotation (doubles the torque), and a differential 5 that differentially distributes the doubled torque to the left and right axles 9R and 9L. The differential 5 includes, for example, a bevel gear type differential gear set inside, outputs torque to the left and right side gears 5R and 5L while allowing differential, and further outputs the torque to the axles 9R and 9L coupled to the side gears 5R and 5L.

[0013] The output shaft of the electric motor 1 is a hollow shaft, and the right axle shaft 9R is drawn out to the outside through such a hollow shaft, whereby the electric motor 1 and the differential 5 are arranged coaxially. In this case, the reduction gear set 3 can be provided with an offset shaft as illustrated in FIG. 1A. Alternatively, as illustrated in FIG. 1B, by applying a planetary gear set to the reduction gear set 3, the reduction gear set 3 can also be made coaxial with the electric motor 1 and the differential 5.

[0014] The differential 5 included in a normal electric axle cannot limit differential, so for example, if one of the left and right drive wheels loses traction, torque cannot be output to the other. The sub-assembly 7 according to the present embodiment imparts a differential limiting function to an electric axle including the differential 5 by combining them. The differential 5 can be combined with any type of electric axle as long as it is arranged at one end of the electric axle. Needless to say, it can be combined with either the offset shaft type illustrated in FIG. 1A or the coaxial type illustrated in FIG. 1B.

[0015] Referring mainly to FIG. 2 in combination with FIGS. 1A and 1B, the sub-assembly 7 generally includes an actuator 11 for controllably increasing or decreasing the differential limiting ability, a cam mechanism 13 that operates in response to an input by the actuator 11, and a clutch assembly 15 that generates a braking force in response to a thrust force by the cam mechanism 13. The cover 17 houses and supports these. At least the actuator 11 and the cam mechanism 13 can be separated from or coupled to the differential 5 integrally, and the cover 17 is coupled to the casing of the electric axle at its end portion 17E and covers these.

[0016] For the actuator 11, for example, a combination of a motor 21 and a toothed (gear-toothed) wheel 23 meshing with its shaft can be used. The motor 21 may be fixed to the cover and partially exposed to the outside, but the toothed wheel 23 is exposed within the cover 17 and meshes with the cam mechanism 13 to transmit the output of the motor 21 to the cam mechanism 13. Alternatively, when the motor 21 can exert sufficient output, its shaft may directly include a toothed wheel and mesh with the cam mechanism 13. Further alternatively, the combination of the toothed wheel 23 and the cam mechanism 13 may constitute a reduction gear, thereby doubling the output of the motor 21. Also, instead of these structures, as will be described later with reference to FIGS. 6B and 6D, the actuator 11 may directly transmit a rotational motion to the cam mechanism 13. In any case, the actuator 11 generates a rotational force around the axis in the cam mechanism 13.

[0017] Referring to FIG. 3 in combination with FIG. 2, for example, the cam mechanism 13 includes, for example, a base member 31, a cam ball 33, and a thrust member 35. The base member 31 and the thrust member 35 are each annular members around the axis X, and either or both of them include grooves running in their circumferential directions. The cam ball 33 is sandwiched between the members 31 and 35 and rolls on such grooves. Also, such grooves are gentle slopes in the circumferential direction, and as the cam ball 33 rolls on the grooves, the thrust member 35 is pushed up or lowered.

[0018] The base member 31 is seated on and supported by an appropriate stationary member of the electric axle, such as its casing or the carrier of the planetary gear set. Alternatively, as shown in Fig. 4, the cam mechanism 13 can be arranged closer to the end wall of the cover 17 than the clutch assembly 15, and in such an arrangement, the base member 31 may be seated on the end wall. In any case, the base member 31 is stationary both in the direction of the axis X and around the axis X. On the other hand, the thrust member 35 is movable both in the direction of the axis X and around the axis X, and its outer periphery is provided with gear teeth that mesh with the wheel 23. When receiving the rotational force from the actuator 11 through such a meshing relationship, the thrust member 35 rotates around the axis, the cam ball 33 moves up and down along the groove, and thus the cam mechanism 13 converts the rotational force generated by the actuator 11 into an axial thrust force.

[0019] The above description relates to an example using a cam ball, but rollers or other rolling members may be used instead of the cam ball, or a cam structure or ball screw provided in either or both of the members 31, 35 may be used. Also, instead of the thrust member 35, the base member 31 may mesh with the wheel 23 and rotate around the axis X, and the thrust member 35 may be locked against rotation. In any of these examples, the cam mechanism 13 can convert the rotational force generated by the actuator 11 into an axial thrust force.

[0020] The clutch assembly 15 includes, for example, an inner drum 51, an outer drum 53, and a friction clutch that frictionally brakes the outer drum 53 with respect to the inner drum 51. As shown in FIG. 3, the inner drum 51 is drivingly engaged with the differential case 5C of the differential 5. A boss portion of the side gear 5L is drawn out from the differential case 5C, and the outer drum 53 is drivingly engaged therewith. The relationship between the drums 51 and 53 may be the opposite, for example, as shown in FIGS. 4 and 5, the inner drum 51 may be engaged with the side gear 5L and the outer drum 53 may be engaged with the differential case 5C. Further, without the boss portion being drawn out greatly, instead, the clutch assembly 15 may enter and engage within the differential case 5C. For example, as shown in FIG. 4, the inner drum 51 may enter into the differential case 5C and engage with the side gear 5L. Furthermore, such an engaging portion may overlap in the circumferential direction with the engaging portion between the outer drum 53 and the differential case 5C. Such an arrangement helps to reduce at least the axial dimension of the sub-assembly 7.

[0021] In any case, these engagements can be by spline or keyway connection. Spline or keyway connection is easy to connect and disconnect, and yet provides sufficient coupling force for torque transmission, but it is not necessarily limited to these. Due to such a connection, when the friction clutch exerts a braking force, the differential of the side gear 5L is restricted with respect to the differential case 5C.

[0022] When a differential occurs between the side gears 5R and 5L, a relative rotation occurs between the inner drum 51 and the outer drum 53 according to such a differential. Although not essential, as shown in FIGS. 3 and 5, a bearing 63 may be interposed between the drums 51 and 53, and the bearing 63 is, for example, a ball bearing or a needle bearing. Alternatively, in the case of the arrangement as shown in FIG. 4, a bearing may be interposed between the differential case 5C and the inner drum 51.

[0023] The friction clutch is a clutch that frictionally limits the differential between such drums 51 and 53, and is, for example, a multi-plate clutch composed of a plurality of clutch plates 55. One group thereof is drivingly engaged with the inner drum 51, and the other group is drivingly engaged with the outer drum 53. These groups are alternately laminated, and when a thrust force acts on the whole, friction occurs between the plates, and the outer drum 53 is frictionally braked with respect to the inner drum 51.

[0024] In order to receive the thrust force from the cam mechanism 13 and operate, as shown in FIGS. 2 and 3, the clutch assembly 15 is disposed adjacent to the cam mechanism 13. The clutch assembly 15 may be adjacent to the end wall of the cover 17, but as already described with reference to FIG. 4, the cam mechanism 13 may be adjacent to the end wall. Although not depicted in FIG. 4, a bearing may be interposed between the outer drum 53 and the cover 17 to support the back surface thereof. According to such a structure, the thrust force by the cam mechanism 13 is borne by the cover 17, and the alignment of the clutch assembly 15 with respect to the axis X is easy.

[0025] Alternatively, the clutch plate 55 does not necessarily have to be axially adjacent to the cam mechanism 13. For example, as shown in FIG. 5, it may be disposed radially outward, and the clutch plate 55 and the cam mechanism 13 may be partially overlapped. Such an arrangement helps to reduce at least the axial dimension of the sub-assembly 7.

[0026] According to such an aspect, the intermediate member 59 extending radially outward along the outer drum 53 transmits the thrust reaction force by the cam mechanism 13 to the clutch plate 55. The intermediate member 59 is generally a disk around the axis X, and abuts against the thrust member 35 on one surface thereof. The other surface is provided with one or more protrusions penetrating the outer drum 53, and the outer drum 53 is provided with corresponding through holes, whereby the intermediate member 59 transmits the thrust force by the cam mechanism 13 to the clutch plate 55. Needless to say, a thrust bearing may be interposed between the thrust member 35 and the intermediate member 59.

[0027] Although not essential, a ball bearing 67 may be interposed, for example, between a base member 31 and an outer drum 53 of the cam mechanism 13. This, together with the needle bearing 63, helps to align the respective elements with respect to the axis X.

[0028] Although the entire cam mechanism 13 is substantially stationary about the axis X, the clutch assembly 15 rotates about the axis X together with the differential 5. A thrust bearing 41 may be interposed therebetween to allow transmission of thrust force while allowing relative rotation. A pressure plate 57 may also be interposed between the thrust bearing 41 and the clutch plate 55 to achieve uniform application of the thrust force.

[0029] As can be easily understood, when the actuator 11 operates the cam mechanism 13 to exert a thrust force on the clutch assembly 15, the differential between the axles 9R, 9L is restricted. The differential restricting ability increases as the thrust force increases in response to the input to the actuator 11, and decreases as the thrust force decreases.

[0030] The clutch assembly 15 is rotatably supported by the cover 17. To allow rotation, a bearing 61 is interposed, for example, between the outer drum 53 and the cover 17. Such a bearing 61 preferably also contacts the back surface of the outer drum 53 and is supported by the end wall of the cover 17 to bear the thrust force. In FIGS. 2 and 3, the bearing 61 is depicted as a ball bearing, but it may be a roller bearing. Also, any of radial, angular and thrust bearings may be used. Further, as shown in FIG. 5, a bearing 65 may also be interposed between the inner drum 51 and the cover 17.

[0031] The cover 17 is generally a bowl or pot-shaped container comprising a peripheral wall surrounding the axis X and an end wall extending from the peripheral wall towards the axis X, and is dimensioned to enclose the cam mechanism 13 and the clutch assembly 15 and their associated members. At the end 17E of the peripheral wall, the cover 17 is coupled or integrated with the casing of the electric axle. Also, when coupled or integrated, in the embodiment shown in FIGS. 3 and 5, the cover 17 is dimensioned such that the base member 31 seats on a suitable stationary member of the electric axle. Alternatively, in the embodiment shown in FIG. 4, the outer drum 53 seats on a stationary member via a bearing such as a thrust bearing. The stationary member is, for example, the casing of the electric axle or the carrier of the planetary gear set, etc. Alternatively, the cover 17 may be provided with a structure for seating, and the base member 31 to the bearing may seat on such a structure. Further, when coupled or integrated, the inner drum 51 and the outer drum 53 are respectively coupled to the differential case 5C and the side gear 5L, and the cover 17 also covers these. The end wall of the cover 17 is provided with an opening 71 surrounding the axis X, and the axle 9L is inserted into the cover 17 through such an opening 71 and coupled to the side gear 5L.

[0032] In the embodiment shown in FIGS. 3 and 5, the end wall of the cover 17 supports the clutch assembly 15 against the thrust force via the bearings 61 and 65. As already described, at the end portion 17E on the opposite side of such an end wall, since the cover 17 is coupled to the casing of the electric axle, ultimately such a thrust force is borne by the cover 17 and the casing. The thrust reaction force generated in the cam mechanism 13 in pair with the thrust force is borne by the stationary member on which the base member 31 is seated. Further, in the embodiment shown in FIG. 4, the end wall of the cover 17 supports the cam mechanism 13 against the thrust reaction force, and the casing of the electric axle bears the thrust force received by the clutch assembly 15. That is, in any of the embodiments, the thrust force and its reaction force are borne by the cover 17 coupled to the electric axle, so the vehicle side does not need to bear the thrust force and does not need a structure for supporting the member against the thrust force. Also, as can be more easily understood from FIGS. 2 and 3, the sub-assembly 7 only slightly projects axially from the end of the differential 5. That is, even if the sub-assembly 7 is incorporated into the electric axle, no design change is required for the vehicle on which it is mounted.

[0033] Referring to FIG. 6A in combination with FIGS. 2, 3 or 5, in the above-described embodiment, the actuator 11 is supported by the cover 17 so as to project radially outward with respect to the axis X, and the rotation is transmitted to the cam mechanism 13 by using the wheel 23 exposed within the cover 17. Instead of such a structure, as schematically shown in FIG. 6B, the actuator 11 can also be arranged within the cover 17. For example, an axially thin motor such as an axial gap motor with a hollow shaft can be used as the actuator 11, and its output shaft can be directly coupled to the base member 31. Such a motor is also coaxial with the cam mechanism 13 and can be interposed between the cam mechanism 13 and the electric axle. Although the dimension increases in the axial direction, a more compact structure is realized in the radial direction. In this case, instead of the base member 31, the actuator 11 may be seated on the electric axle side to bear the reaction force thereon. Also, the side of the motor facing the cam mechanism 13 may be a rotor surface that rotates around the axis X. In this case, the rotor surface may be directly coupled to the base member 31 or may also serve as the base member 31.

[0034] Also, according to the structure illustrated in FIG. 6A, the cam mechanism 13 is on the electric axle side, and the thrust force is borne by the end wall of the cover 17. Referring to FIG. 6C in combination with FIG. 4, the cam mechanism 13 may be arranged adjacent to and supported by the end wall of the cover 17 so as to exert a thrust force on the clutch assembly 15 toward the differential 5. In this case, the base member 31 may be seated on the end wall of the cover 17 to bear the thrust reaction force, and the bearing 61 may be seated on the electric axle side to bear the thrust force. Also, with the structure illustrated in FIG. 6C, the axial overhang of the sub-assembly 7 is small.

[0035] Even in the example where the cam mechanism 13 is arranged on the end wall side of the cover 17, as illustrated in FIG. 6D, the actuator 11 can be arranged inside the cover 17. In this case, the actuator 11 (motor) may be fixed to the end wall of the cover 17. The cam mechanism 13 is supported by the cover 17 via the actuator 11. Although the dimension increases in the axial direction, a more compact structure is realized in the radial direction.

[0036] By using the sub-assembly according to any of the embodiments described above, a differential limiting function can be easily imparted to the electric axle. Since such a sub-assembly is not incorporated inside the electric axle, it does not cause an increase in the axial dimension of the electric axle, and thus does not require a design change on the vehicle side. Nevertheless, after the sub-assembly is coupled to the electric axle, the whole can be handled integrally, and the handling is no different from that of a conventional electric axle. It facilitates the assembly of the vehicle in the same way as a conventional electric axle, and on the other hand, since only the sub-assembly part can be removed unlike the case where it is incorporated, maintenance is easy.

[0037] Although several embodiments have been described, modifications or variations of the embodiments are possible based on the above disclosure.

Industrial Applicability

[0038] There is provided a sub-assembly for an electric axle that can easily impart a differential limiting function just by incorporating it at one end of the electric axle, and moreover hardly increases the axial dimension.

Explanation of Signs

[0039] 1 Electric motor 3 Reduction gear set 5 Differential 5C Differential case 5R, 5L Side gears 7 Sub-assembly 9R, 9L Axles 11 Actuator 13 Cam mechanism 15 Clutch assembly 17 Cover 21 Motor 23 Toothed wheel 31 Base member 33 Cam ball 35 Thrust member 41 Thrust bearing 51 Inner drum 53 Outer drum 55 Clutch plate 59 Intermediate member 61, 63, 65, 67 Bearings 71 Opening

Claims

1. A subassembly for imparting a differential limiting function to an electric axle having a differential that differentially outputs torque around an axis, comprising: an actuator that generates a rotational force around the axis; a cam mechanism that converts the rotational force into a thrust force in the direction of the axis; a clutch assembly including a first drum separably coupled to the casing of the differential, a second drum separably coupled to the side gear of the differential, and a friction clutch that brakes the second drum with respect to the first drum, the clutch assembly being disposed adjacent to the cam mechanism to receive the thrust force and operate the friction clutch; a cover dimensioned to surround the cam mechanism and the clutch assembly and coupled to the electric axle by supporting either the cam mechanism or the clutch assembly to resist the thrust force or thrust reaction force, the cover having an opening surrounding the axis; The subassembly comprising the above.

2. The subassembly according to claim 1, wherein the actuator is fixed to the cover or interposed between the cam mechanism and the electric axle and is coupled to the cam mechanism to transmit the rotational force.

3. The subassembly according to claim 1, wherein the cam mechanism is interposed between the clutch assembly and the cover or the electric axle.

4. The subassembly according to claim 1, wherein the friction clutch is a multi-plate clutch including a first clutch plate engaged with the first drum and a second clutch plate engaged with the second drum and alternately laminated with the first clutch plate.

5. The subassembly according to claim 1, wherein the first drum and the second drum each have a spline for coupling to the differential, and the splines overlap each other in the circumferential direction.

Images