Differential device

Abstract

The present invention provides a differential device that allows differential between a pair of axles. The differential device includes: a differential gear set including: side gears that can rotate about an axial direction in any one of mutually opposite first and second directions; and pinions that mesh with the side gears in a manner allowing the differential; a housing that supports the differential gear set and has a friction surface facing the differential gear set; an output member that engages with the side gears to drive-connect the side gears and the axles and has a clutch surface; a housing that supports the differential gear set and has a friction surface that faces the clutch surface and forms a friction clutch with the clutch surface to limit the differential; and a cam that has a first cam surface that converts a torque in the first direction into a first thrust in the axial direction and a second cam surface that converts a torque in the second direction into a second thrust in the axial direction, and is configured such that the first thrust and the second thrust press the clutch surface against the friction surface to operate the friction clutch, and the first cam surface and the second cam surface are sized such that the first thrust and the second thrust exceed a meshing reaction force of the side gears with respect to the pinions.

Description

Technical Field

[0001] The present invention relates to a differential device, and more particularly to a differential device that jitters less and has less noise in either the forward or reverse direction. Background Art

[0002] In an automobile, the left and right axles do not necessarily rotate at the same speed, so it is necessary to allow differential therebetween. To allow differential between the two axles, a differential device is used. When ensuring traction on two wheels, the differential device can effectively transmit torque to the two axles, but when one wheel loses traction and the other wheel is in a differential state, the torque is not transmitted to any axle. One means to avoid such a situation is a so-called limited-slip differential (LSD). The LSD includes, for example, a friction clutch that operates by sensing torque, and the friction clutch operates in a manner that limits differential (torque-sensing type LSD).

[0003] There are various forms of torque-sensing type LSDs, such as a planetary gear type that uses the tooth surface resistance of planetary gears as the pressing force on the clutch, a multi-plate clutch type that uses a multi-plate clutch for the friction clutch, a tapered clutch type that uses a tapered clutch, and the like. Although the planetary gear type and the multi-plate clutch type are likely to exhibit a relatively large differential limiting force, they have the disadvantage that the device tends to become large.

[0004] Patent Document 1 discloses a technique of a compact tapered clutch type LSD. According to the disclosure, a cam mechanism is used to obtain a large pressing force. That is, when the differential device rotates in the direction of vehicle travel (driving direction), the cam mechanism partially converts torque into thrust, and this thrust presses the tapered clutch, thereby limiting differential.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-49345 Summary of the Invention

[0008] Although not explicitly described in Patent Document 1, differential limitation can also be performed in the direction of vehicle reverse (coasting direction). However, according to further research by the present inventors, a phenomenon called so-called chatter occurs in the coasting direction, and the driver may feel discomfort.

[0009] The following disclosure has been made in view of such problems and observations. According to one aspect, a differential device that allows differential between a pair of axles includes: a differential gear set including: side gears that can rotate about an axial direction in either a first direction or a second direction opposite to each other; and pinions that mesh with the side gears in a manner that allows the differential; an output member that engages with the side gears and drivesly connects the side gears and the axles; a housing that supports the differential set and includes a friction surface that faces the clutch surface and forms a friction clutch with the clutch surface combination to limit the differential; and a cam that includes a first cam surface that converts torque in the first direction into a first thrust in the axial direction and a second cam surface that converts torque in the second direction into a second thrust in the axial direction, and is configured such that the first thrust and the second thrust press the clutch surface against the friction surface to operate the friction clutch, wherein the first cam surface and the second cam surface are sized such that both the first thrust and the second thrust exceed the meshing reaction force of the side gears relative to the pinions. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is an elevation cross-sectional view of the differential device.

[0011] Figure 2 is an exploded perspective view with the output member and the side gears removed.

[0012] Figure 3 is a perspective view showing the surface of the output member facing the side gears.

[0013] Figure 4 is a top cross-sectional view of the differential device, which is a view along Figure 1 line IV-IV.

[0014] Figure 5 is Figure 4 a partial enlarged view, particularly a top cross-sectional view showing the cam.

[0015] Figure 6 is a top cross-sectional view showing the relationship between the meshing pinions and side gears, which is a view corresponding to Figure 1 line VI-VI. DETAILED DESCRIPTION

[0016] Several exemplary embodiments will be described below with reference to the accompanying drawings. Through the following description and technical solutions, unless otherwise specified, the axis is the rotation axis of the differential device, and the axial direction is the direction parallel thereto, and the radial direction is the direction orthogonal thereto.

[0017] For example, referring to Figure 1, as an example, the differential device according to the present embodiment can be used to allow the torque around the axis C to be output to a pair of (usually, right and left) axles while allowing differential. Alternatively, it can be used to sandwich the drive shafts connecting the front and rear and distribute the torque to the front and rear drive wheels. Of course, it can also be used for various other purposes of mediating torque transmission. The following description relates to an example of distributing torque to the axles, but this is only for convenience of explanation.

[0018] The differential device generally includes: a housing 1 that receives torque and rotates around the axis C; a differential gear set 3 that is drivingly coupled to the housing 1 to transmit torque while allowing differential; an output member 5 that outputs the transmitted torque to the axles respectively; a cam 7 that partially converts the torque into thrust; and a friction clutch 9 that uses the thrust to limit the differential.

[0019] The housing 1 is generally cylindrical and is rotatably supported by protruding portions protruding from both ends thereof. The housing 1 can have a flange protruding radially from the outer periphery of the cylindrical portion and can receive torque via an annular gear coupled thereto. However, the support and the reception of torque do not necessarily have to rely on this structure.

[0020] In addition, the housing 1 can be in a two-piece form that can be divided into multiple parts for convenience of moving parts inside, or it can be in a one-piece form. In the case of the one-piece form, as Figure 4 shown, one or more openings 37 can be provided on its side, and the differential gear set 3 and the output member 5 can be moved in through the opening 37. The inner surface of the housing 1 has a friction surface 31 facing the output member 5. As will be described later, the friction surface 31 is an element constituting the friction clutch 9.

[0021] Referring again to Figure 1 , the differential gear set 3 includes a pair of side gears 13 corresponding to a pair of axles. The differential gear set 3 also includes a pinion shaft 33 drivingly coupled to the housing 1 and a plurality of pinions 11 rotatably supported on the shaft 33. By meshing the pinions 11 with the side gears 13 respectively, the torque is transmitted while allowing differential to the pair of side gears 13.

[0022] As shown in the figure, the differential gear set 3 can be a so-called bevel gear type in which the gear teeth of the pinions and the side gears are inclined respectively, or it can be a flat gear type (not shown). The bevel gear type or the flat gear type can easily achieve the following disclosure, or other forms can be adopted if possible.

[0023] Combining Figure 1 , 4 and referring to Figure 2, In either case, the side gear 13 can be directly coupled to the axle. However, unlike a general differential gear, it can also be separated from the axle without direct coupling. Interposed between the side gear 13 and the axle for driving is the output member 5 that is integral with or separate from the side gear 13.

[0024] Coupling Figure 2 And referring to Figure 3 , each output member 5 is generally composed of a hub 23 and a flange portion 25 that extends radially outward from the hub 23. A corresponding side gear 13 is fitted on the outer peripheral surface of each hub 23, and a corresponding axle is coupled to the inner surface. In order to couple with the axle, the inner surface has, for example, a spline, but the coupling does not necessarily have to rely on a spline.

[0025] Details will be described later, but in the case of being separate, the side gear 13 and the output member 5 each have a structure capable of meshing with each other to transmit torque. That is, in either the integral or separate case, the torque output by the side gear 13 is also transmitted to the axle via the output member 5.

[0026] Coupling Figure 2 , 3 , mainly referring to Figure 1 , the outer periphery of the flange portion 25 is a conical surface 27 facing the friction surface 31, and the conical surface 27 abuts against the friction surface 31 to form a friction clutch 9. The conical surface 27 and the friction surface 31 can be formed, for example, as conical surfaces that taper outward in the axial direction, which is the form of a so-called conical clutch. Or it can also be other appropriate rotationally symmetric shapes instead of the conical surface. These methods can control the braking force of the friction clutch 9 according to the pressing force.

[0027] In addition, an appropriate friction ring 29 can be interposed between the conical surface 27 and the friction surface 31, and the inner surface of the friction ring 29 can also be formed as a conical surface suitable for the conical surface 27. In this case, the conical surface 27 abuts against the friction surface 31 of the housing 1 via the friction ring 29. The friction ring 29 can rotate relative to the housing 1, but for example, it can also have an engaging portion to be non-rotatable relative to the housing 1.

[0028] The above description mainly relates to a conical clutch with a conical surface as the clutch surface, but this is only for convenience of explanation. Instead of the conical clutch, the combination of the output member 5 and the housing 1 can form other types of clutches such as a disk clutch or a drum clutch. In addition, of course, it can also be a multi-plate clutch.

[0029] Mainly referring to Figure 2 , the side gear 13 has, for example, a recess that opens outward in the axial direction, that is, a socket 19. Referring to Figure 3 Instead of Figure 2, corresponding to the socket 19, the output members 5 each have lugs 21. The lugs 21 are configured and sized to be respectively inserted into the sockets 19, so that the output members 5 are respectively meshed with the side gears 13 to transmit torque.

[0030] The relationship between the socket and the lug can be opposite to the above description, or the side gear can have lugs and the output member can have sockets. Alternatively, it can also be other suitable structures that mesh with each other to transmit torque.

[0031] The socket 19 is not necessarily limited to this, but as Figure 2 best shown, it can also be formed along the inner surface that fits with the outer peripheral surface. Correspondingly, as Figure 3 best shown, the lugs 21 can be respectively formed as protrusions protruding radially outward from the hub 23. Such a structure is beneficial for processing and especially helps to improve strength and rigidity.

[0032] Thus, in the output member, a relatively wide surface (marked 5A in Figure 3 ) radially outside the lug can be used to support a relatively wide surface (marked 13A in Figure 2 ) radially outside the socket in the side gear. In addition, the surface 5A can become a recess that sinks inward in the output member 5, and as can be understood from Figure 1 , it can accommodate the bottom of the side gear 13. Of course, this structure can also be applied to the other side gear 13 and the output member 5.

[0033] This structure helps to compress the size of the combination of the side gear and the output member in the axial direction. In addition, the outer shape of this combination is the same as that of the conventional side gear, so it is advantageous in terms of interchangeability of components.

[0034] Combined Figure 2 , 3 and referring to Figure 4 , 5 , the side surfaces 21A, 21B of the lug 21 can also be tapered inward in the direction of the side gear 13, that is, in the axial direction. Alternatively, or in addition, the side surfaces 19A, 19B of the socket 19 also extend outward in the direction of the output member 5, that is, axially outward. Either one or both of the side surfaces 21A, 21B and 19A, 19B are inclined with respect to the direction of the axis C, so the combinations of the mutually abutting side surfaces 19A, 21A and the side surfaces 19B, 21B define cam surfaces 19, 21 that guide the sliding of the lug 21 relative to the socket 19. In these figures, both of the mutually abutting side surfaces are depicted flat, but it is also possible that only one is flat and the other is curved.

[0035] The cam surfaces 15, 17 are inclined with respect to the direction of the shaft C. Thus, the combination of the socket 19 and the lug 21 acts as a cam 7 that converts a part of the torque into a thrust when a torque acts. This thrust presses the output member 5 axially outward to operate the friction clutch 9.

[0036] The thrust generated by the cam 7 can be estimated by the following formula.

[0037] [Number 1]

[0038] f = T·tanθ / (2·R c )·(1)

[0039] Wherein, T is the torque input to the differential device, θ is the angle of the cam surface with respect to the shaft C, and Rc is the acting radius of the cam. As understood from the formula (1), the larger the angle of the cam surface and the smaller the acting radius of the cam, the larger the thrust obtained.

[0040] As understood from the above description, if both the cam surfaces 15, 17 are inclined with respect to the direction of the shaft C, differential limiting performance can be exerted for both the driving direction and the coasting direction. Therefore, in the present embodiment, when the angles formed by the cam surfaces 15, 17 and the direction of the shaft C are respectively set as θ1, θ2, according to Figure 4 , 5 it can be known that both θ1 and θ2 are greater than 0. That is, the cam 7 generates a thrust f1 not only with respect to the rotation R1 in the driving direction but also generates a thrust f2 with respect to the rotation R2 in the coasting direction.

[0041] Both the thrusts f1, f2 press the output member 5 axially outward to operate the friction clutch 9. The friction clutch 9 operates in a torque-sensing manner, so the differential device functions as a torque-sensing type LSD.

[0042] The thrusts f1, f2 can be equal to each other or can also be different. As understood from the formula (1), by appropriately adjusting θ1 and θ2 respectively, the thrusts f1, f2 can be adjusted independently. For example, compared with the driving direction, a large differential limiting force is not required in the coasting direction, so it can be set as f1 > f2, and in this case, it can be set as θ1 > θ2. Of course, adjustment based on the inclination of the cam surface can be replaced, or on this basis, adjustment can be made through the acting radius.

[0043] Between the side gear 13 and the output member 5, an elastic body such as a disc spring can be added. Or the elastic body can also be interposed at other appropriate positions. This elastic body presses the conical surface 27 against the friction surface 31 regardless of the operation of the cam, generating an initial torque. This can be a countermeasure for the delay of the differential limit accompanying the initial operation of the cam 7.

[0044] On the other hand, combined with Figure 5 and referring to Figure 6 , the tooth surfaces of the side gear 13 and the pinion gear 11 are in contact on the pitch circle P, and the common normal TL of these tooth surfaces forms a pressure angle a with respect to the radius line R. According to this pressure angle a, a meshing reaction force fG is generated outward in the axial direction of the side gear 13. The meshing reaction force fG can be estimated by the following formula.

[0045] [Equation 2]

[0046] f G = T·tan a·sinδ0 / d m ·(2)

[0047] where T is the torque input to the differential device, a is the pressure angle of the pinion gear, δ0 is the pitch angle of the side gear, and d m is the meshing pitch diameter of the side gear.

[0048] The meshing reaction force fG cancels out the thrust reaction forces f1R and f2R. When the meshing reaction force fG exceeds the thrust reaction forces f1R and f2R, the larger one is beneficial to increasing the braking force of the friction clutch 9. However, there is a problem in that the meshing reaction force is not constant. That is, when the gears start to mesh, they rotate while sliding against each other, and then, according to the disengagement process, the meshing reaction force changes over time. In particular, as described above, when the relationship f1 > f2 holds, the thrust reaction force f2R in the coasting direction is likely to become smaller than the meshing reaction force fG, so the change in the meshing reaction force fG has a strong impact on the operation of the friction clutch 9. This is presumed to be the cause of the shudder in the coasting direction.

[0049] Therefore, in the present embodiment, contrary to the general understanding that the meshing reaction force should be increased, the meshing reaction force fG is fixed at an appropriate size with respect to the thrusts f1 and f2. That is, the dimensions of the cam surfaces 15 and 17 are set such that both the thrusts f1 and f2 exceed the meshing reaction force fG. As described above repeatedly, this structure is advantageous for suppressing chattering.

[0050] On the other hand, since the thrust reaction forces f1R and f2R are borne by the gear tooth surfaces, if they are too large, it is possible to consume the differential gear set. Therefore, in order to reduce the influence of the thrust reaction forces f1R and f2R, a block 35 may be interposed between the pair of side gears 13 so as to slide with both of them. The thrust reaction forces acting on the two side gears 13 are of substantially the same magnitude and opposite to each other, so the thrust reaction forces are substantially canceled out in the block 35. As Figure 1 , 4As best shown, the block 35 is, for example, a cylinder around the axis C and has a through hole through which the pinion shaft 33 passes, but is not necessarily limited to this shape.

[0051] As understood from the above description, although various reaction forces act on the side gear 13 in the axial direction, they oppose or cancel each other out. In addition, since the block 35 protects the side gear 13 from the reaction forces, even if the torque increases, the meshing of the side gear 13 and the pinion 11 is stable, the gear operation does not become unstable, or the gear tooth surfaces are not damaged. These aspects are advantageous effects compared to the case where the side gear itself functions as a friction clutch.

[0052] In addition, based on the above structure, the differential device may further include an actuator that applies a pressing force to the clutch in order to control the differential limit from the outside. In addition, in order to lock the differential, the clutch may have a structure such as claw teeth. The clutch having the claw teeth may be independent of the friction clutch 9, and the actuator may be configured to drive the claw teeth.

[0053] In addition, the present embodiment can be applied to a so-called free-running differential. In a free-running differential, the housing is divided into an inner housing and an outer housing, and torque is transmitted to the axle only when they are connected to each other through a clutch or the like. The structure described above can be substantially directly used for the inner housing and its internal structure of the free-running differential except for the flange and the protruding portion.

[0054] Several embodiments have been described, but embodiments can be modified or deformed based on the above disclosure.

Claims

1. A differential device that allows differential between a pair of axles, characterized in that, it includes: a differential gear set, including: side gears that can rotate around the axial direction in either one of the mutually opposite first direction and second direction; and pinions that mesh with the side gears in a manner allowing the differential; an output member that engages with the side gears and drivably connects the side gears and the axles, and has a clutch surface; a housing that supports the differential gear set, and has a friction surface that faces the clutch surface and forms a friction clutch that restricts the differential in combination with the clutch surface; and a cam that has a first cam surface that converts the torque in the first direction into a first thrust in the axial direction and a second cam surface that converts the torque in the second direction into a second thrust in the axial direction, and is configured such that the first thrust and the second thrust press the clutch surface against the friction surface to operate the friction clutch, and the first cam surface and the second cam surface are sized such that both the first thrust and the second thrust exceed the meshing reaction force of the side gears relative to the pinions.

2. The differential device according to claim 1, characterized in that, the first cam surface forms a first angle (θ1) with respect to the axial direction, and the second cam surface forms a second angle (θ2) different from the first angle (θ1) with respect to the axial direction.

3. The differential device according to claim 2, characterized in that, the first angle (θ1) and the second angle (θ2) satisfy the inequality first angle (θ1) > second angle (θ2).

4. The differential device according to claim 1, characterized in that, the output member includes: a hub that has an inner surface for coupling with the axle; and a flange portion that extends radially outward from the hub and has the clutch surface on its outer periphery, and one surface of the flange portion is sized to accommodate the side gears.

5. The differential device according to claim 1, characterized in that, the output member has lugs for engaging with the side gears, the side gears have sockets for accommodating the lugs, and the surfaces where the lugs abut against the sockets form the first cam surface and the second cam surface.

6. The differential device according to claim 1, characterized in that, it further includes a block that slides with the side gears and bears the thrust reaction force brought by the cam.

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