Differential device

Abstract

To provide a differential device capable of improving lubricity of a sliding part and stabilizing differential limiting characteristics.SOLUTION: A differential device includes a differential case that is rotatably disposed, a pinion gear that is rotatably supported in the differential case and revolves by rotation of the differential case, a pair of side gears that mesh with the pinion gear and are relatively rotatable, and a differential limiting portion that limits a differential between the differential case and the side gears. The differential limiting portion includes two sliding portions 2939 and that are slidable with respect to each other. At least one of the two sliding portions 2939 and has the nitride layer 47 including the porous 45 formed on the surface of the base material 43 and the diamond-like carbon layer 49 formed on the surface of the nitride layer 47.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a differential device. [Background technology]

[0002] Conventionally, a differential device has been known that includes a rotatably arranged differential case, a pinion gear that is rotatably supported within the differential case and revolves with the rotation of the differential case, a pair of side gears that mesh with the pinion gear and are rotatable relative to the pinion gear, and a differential limiting unit that limits the differential between the differential case and the side gear (see Patent Document 1).

[0003] In this differential, the differential limiting unit has two sliding parts that can slide against each other. At least one of the two sliding parts has numerous recesses formed by shot blasting. The sliding part with the recesses has been treated with nitriding, diamond-like carbon, or the like. By providing the recesses and surface treatment to the sliding parts, lubricating oil is retained in the sliding parts, stabilizing the differential limiting characteristics of the differential limiting unit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-242377 Summary of the Invention [Problem to be solved by the invention]

[0005] In the differential gear of Patent Document 1, the sliding parts are subjected to shot blasting and then surface treatment. When shot blasting is performed on the sliding parts, the numerous recesses formed can increase the surface roughness of the sliding surface, potentially affecting the differential limiting characteristics. On the other hand, when only nitriding is performed as surface treatment, the formed nitride layer contains numerous pores, improving lubricant retention, but the surface hardness is insufficient, potentially promoting wear. Furthermore, accelerated wear can destroy the pores, potentially reducing lubricant retention.

[0006] The present invention has been made in view of the problems inherent in the prior art, and an object of the present invention is to provide a differential device that can improve the lubrication of the sliding parts and stabilize the differential limiting characteristics. [Means for solving the problem]

[0007] The differential device according to this embodiment comprises a rotatably arranged differential case, a pinion gear rotatably supported within the differential case and revolving with the rotation of the differential case, a pair of side gears that mesh with the pinion gear and are rotatable relative to each other, and a differential limiting unit that limits the differential between the differential case and the side gear, wherein the differential limiting unit has two sliding parts that can slide against each other, and at least one of the two sliding parts has a porous nitride layer formed on the surface of a substrate and a diamond-like carbon layer formed on the surface of the nitride layer. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a differential device that can improve the lubrication of sliding parts and stabilize the differential limiting characteristics. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the differential device according to the embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a sliding portion of the differential device according to the embodiment. [Figure 3] 10 is an image of a cross section of a sliding portion of a differential device according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The differential device according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0011] 1, a differential device 1 according to this embodiment is disposed between a drive source (not shown), such as an engine or an electric motor, and left and right wheels (not shown). Driving force from the drive source is transmitted to the differential device 1 via a transmission (not shown), and the driving force is distributed to the left and right wheels via a pair of output shafts (not shown).

[0012] As shown in FIG. 1, the differential device 1 includes a differential mechanism 3 and a differential limiting unit 5.

[0013] The differential mechanism 3 includes a differential case 7, a pinion shaft 9, a pinion gear 11, and a pair of side gears 13 and 15.

[0014] The differential case 7 is rotatably supported by a stationary member (not shown) such as a carrier via bearings (not shown) at the outer peripheries of bosses 17, 19 formed on both axial sides. A flange 21 to which a ring gear (not shown) is fixed is formed on the differential case 7. The ring gear fixed to the flange 21 meshes with a power transmission gear (not shown) that transmits driving force, and the driving force is transmitted to rotate the differential case 7. A pinion shaft 9, a pinion gear 11, a pair of side gears 13, 15, etc. are housed and arranged within the differential case 7.

[0015] The pinion shaft 9 has an end that engages with a hole formed in the differential case 7 and is prevented from coming off and rotating by a pin 23, and is rotatably driven integrally with the differential case 7. Note that while the pinion shaft 9 is configured as a single long pinion shaft 9, the configuration is not limited to this, and the pinion shaft 9 may be configured as a single long pinion shaft 9 and two short pinion shafts 9. In this case, a hole may be formed in the center of the long pinion shaft 9, and the ends of the two short pinion shafts 9 may be engaged with the hole to be rotatably driven integrally with the differential case 7. Pinion gears 11 are supported on both axial ends of the pinion shaft 9, respectively.

[0016] A plurality of pinion gears 11 (two in this example) are arranged at equal intervals around the circumferential direction of the differential case 7, and each is supported on the shaft end side of the pinion shaft 9 and revolves with the rotation of the differential case 7. The pinion gear 11 transmits driving force to the pair of side gears 13, 15, and is rotatably supported on the pinion shaft 9 so as to be rotationally driven when a differential rotation occurs between the pair of meshed side gears 13, 15.

[0017] The pair of side gears 13, 15 are housed in the differential case 7 so as to be capable of relative rotation. Each of the pair of side gears 13, 15 includes a gear member 25 and an output member 27. In the pair of side gears 13, 15, the gear member 25 and the output member 27 are formed symmetrically, so the following mainly describes only one of them, and a description of the other is omitted.

[0018] The gear member 25 is formed in an annular shape, and has a gear portion formed on its outer periphery that meshes with the pinion gear 11. The gear member 25 meshes with the pinion gear 11, thereby transmitting driving force from the pinion gear 11 to the pair of side gears 13, 15. In addition, when differential rotation occurs between the pair of side gears 13, 15, the gear member 25 rotates the pinion gear 11.

[0019] The output member 27 is formed in a concave annular shape capable of accommodating a portion of the gear member 25 in the axial direction so that it can be disposed axially adjacent to the gear member 25. A sliding portion 29 having a sliding surface that is conically inclined in the axial direction is provided at a portion of the output member 27 located radially outward of the gear member 25. Spline-shaped output portions 31 and 33 are formed on the inner circumferential side of the output member 27 in the pair of side gears 13 and 15 and can be connected to the pair of output shafts so as to be rotatable together with the pair of output shafts. The output member 27 outputs the driving force input from the differential case 7 to the pair of side gears 13 and 15 to the left and right wheels via the pair of output shafts.

[0020] A cam portion 35 that converts rotational torque into axial thrust force is provided between the gear member 25 and the output member 27. The cam portion 35 is made up of a plurality of engaging recesses provided on the inner circumferential side of the gear member 25 and a plurality of engaging protrusions that are provided on the outer circumferential side of the output member 27 and can engage with the plurality of engaging recesses. The cam portion 35 enables the gear member 25 and the output member 27 to rotate integrally by engaging the plurality of engaging recesses with the plurality of engaging protrusions.

[0021] On the other hand, in the cam portion 35, the engagement surface in the rotational direction between the multiple engagement recesses and the multiple engagement protrusions is inclined at a predetermined angle. When a driving force (driving torque) is input to the differential case 7, the cam surface of the cam portion 35 is actuated by the driving force branched from the pinion gear 11 and input to the pair of side gears 13, 15, causing the cam portion 35 to move the output member 27 axially outward. The axial movement of the output member 27 by the cam portion 35 can increase and strengthen the differential limiting force of the pair of differential limiting units 5, 5 arranged between the differential case 7 and the pair of side gears 13, 15.

[0022] The pair of differential limiting units 5, 5 are disposed between the differential case 7 and the pair of side gears 13, 15. The pair of differential limiting units 5, 5 are formed symmetrically, so the following mainly describes one of them, and the other is omitted. The differential limiting unit 5 has a tapered ring 37 and an output member 27 that slide against each other.

[0023] The tapered rings 37 are disposed on the differential case 7 at positions corresponding to the sliding portions 29 of the output members 27 of the pair of side gears 13, 15. The tapered rings 37 are provided with sliding portions 39 having sliding surfaces that are conically inclined in the axial direction and are capable of sliding on the sliding portions 29 of the output members 27. The tapered ring 37 rotates integrally with the differential case 7 by engaging multiple protrusions formed in the circumferential direction on the inner peripheral side with recesses formed on the inner wall surface of the differential case 7.

[0024] The sliding portion 39 of the tapered ring 37 slides against the sliding portion 29 of the output member 27 of the pair of side gears 13, 15, which is moved axially by a meshing reaction force with the pinion gear 11, depending on the magnitude of the driving force (driving torque) input to the differential case 7. At this time, the sliding friction between the sliding portions 29, 39 of the output member 27 and the tapered ring 37, which is the differential limiting force of the differential limiting unit 5, is increased and strengthened by the cam thrust force of the cam unit 35.

[0025] The differential limiting unit 5 transmits friction torque between the differential case 7 and the pair of side gears 13, 15 in response to the magnitude of the cam thrust force, thereby limiting the differential movement of the differential mechanism 3. The differential limiting unit 5 is a cone clutch type torque-sensitive friction clutch. A preload is applied to the differential limiting unit 5 by a biasing member 41.

[0026] The biasing member 41 is made of, for example, a disc spring, and is arranged axially between the gear member 25 and the output member 27. The biasing member 41 biases the gear member 25 axially inward (toward the pinion gear 11), and biases the output member 27 axially outward (toward the differential limiting unit 5). By arranging the biasing member 41 between the gear member 25 and the output member 27, a preload is applied to the differential limiting unit 5, and the differential limiting characteristic (intermittent characteristic) of the differential limiting unit 5 can be stabilized.

[0027] In the limited slip differential unit 5 of the differential gear 1, as shown in FIGS. 2 and 3, the sliding portions 29, 39 between the differential case 7 and the side gears 13, 15 are subjected to a surface treatment to enhance lubricant retention. It is sufficient that at least one of the two sliding portions 29, 39 is surface-treated. For example, the sliding portion 39 of the tapered ring 37 is disposed radially outward of the sliding portion 29 of the output member 27. Therefore, the lubricant flowing between the sliding portions 29, 39 is more likely to flow through the sliding portion 39 of the tapered ring 37 due to centrifugal force generated by the rotation of the differential case 7. Additionally, when handling the tapered ring 37 and the output member 27 as a single unit, the tapered ring 37 is easier to handle than the output member 27. Therefore, it is preferable to perform a surface treatment on at least the sliding portion 39 of the tapered ring 37.

[0028] The surface treatment of the sliding parts 29, 39 begins by subjecting the base material 43 of the tapered ring 37 and the output member 27 to a nitriding treatment such as salt bath nitriding, salt bath soft nitriding, gas nitriding, or gas soft nitriding. The nitriding treatment forms a nitride layer 47 containing a plurality of pores 45 on the surface of the base material 43 of the sliding parts 29, 39. The pores 45 contained in the nitride layer 47 are open facing the opposite side of the base material 43. Therefore, the openings of the pores 45 face each other toward the sliding parts 29, 39. Lubricating oil flowing between the sliding parts 29, 39 flows into the openings of the pores 45, and the lubricating oil is retained in the pores 45. In the sliding part 39 of the tapered ring 37, the openings of the pores 45 face the rotational axis of the differential case 7. Therefore, the lubricating oil flowing on the sliding portion 39 side of the tapered ring 37 due to the centrifugal force caused by the rotation of the differential case 7 can be stably retained by the pores 45. By increasing the lubricating oil retention capacity by the pores 45 of the nitride layer 47, the lubrication of the sliding portions 29, 39 can be improved, and the differential limiting characteristics of the differential limiting unit 5 can be stabilized.

[0029] The surface treatment of the sliding parts 29, 39 involves forming a nitride layer 47 and then performing a diamond-like carbon treatment. By performing the diamond-like carbon treatment, a diamond-like carbon layer 49 is formed on the surface of the nitride layer 47. The diamond-like carbon layer 49 is not formed inside the holes 45, but is formed on the surface of the nitride layer 47 located around the openings of the holes 45 so as to expose the insides of the holes 45. This prevents the holes 45 from being blocked by the diamond-like carbon layer 49, improving the lubricant retention. The area of ​​the diamond-like carbon layer 49 is in the range of 50% to 90% of the total sliding area of ​​the sliding parts 29, 39. The thickness of the diamond-like carbon layer 49 is in the range of 1 μm to 10 μm. By forming the diamond-like carbon layer 49 on the surface of the nitride layer 47, the hardness of the sliding surfaces of the sliding parts 29, 39 can be improved. Therefore, the wear of the sliding portions 29, 39 can be prevented from being accelerated, the destruction of the pores 45 can be prevented, and the deterioration of the lubricating oil retention can be prevented.

[0030] Such a differential device 1 includes a rotatably arranged differential case 7 and a pinion gear 11 that is rotatably supported within the differential case 7 and revolves with the rotation of the differential case 7. The differential device 1 also includes a pair of side gears 13, 15 that mesh with the pinion gear 11 and are rotatable relative to each other, and a differential limiting unit 5 that limits the differential between the differential case 7 and the side gears 13, 15. The differential limiting unit 5 also has two sliding units 29, 39 that can slide on each other. At least one of the two sliding units 29, 39 has a nitride layer 47 including pores 45 formed on the surface of a substrate 43, and a diamond-like carbon layer 49 formed on the surface of the nitride layer 47.

[0031] By forming a nitride layer 47 containing pores 45 and a diamond-like carbon layer 49 on at least one of the sliding portions 29, 39, it is not necessary to perform a shot blasting process to form multiple recesses. This prevents the sliding surfaces of the sliding portions 29, 39 from becoming too rough, and does not affect the differential limiting characteristics of the differential limiting unit 5. The nitride layer 47 contains pores 45, which enhance the retention of lubricant. This improves the lubrication of the sliding portions 29, 39 and stabilizes the differential limiting characteristics of the differential limiting unit 5. The diamond-like carbon layer 49 is formed on the surface of the nitride layer 47, which improves the hardness of the sliding surfaces of the sliding portions 29, 39. This prevents accelerated wear of the sliding portions 29, 39, suppresses damage to the pores 45, and suppresses a decrease in the retention of lubricant.

[0032] Therefore, in such a differential device 1, the lubrication of the sliding parts 29, 39 can be improved, and the differential limiting characteristics can be stabilized.

[0033] The diamond-like carbon layer 49 is formed on the surface of the nitride layer 47 so as to expose the pores 45 .

[0034] Therefore, the pores 45 are not blocked by the diamond-like carbon layer 49, and the lubricant retention can be improved.

[0035] A tapered ring 37 is provided on the differential case 7 so as to rotate integrally therewith. An output member 27, which is slidable with the tapered ring 37, is provided on the side gears 13, 15 so as to rotate integrally therewith. Sliding portions 29, 39 are provided on the tapered ring 37 and the output member 27, respectively. A nitride layer 47 and a diamond-like carbon layer 49 are provided on at least the sliding portion 39 of the tapered ring 37. An opening of the porous portion 45 in the sliding portion 39 of the tapered ring 37 faces the rotational axis of the differential case 7.

[0036] The differential case 7 is located radially outward of the side gears 13, 15. Therefore, the sliding portion 39 of the tapered ring 37 is located radially outward of the sliding portion 29 of the output member 27. The lubricating oil flowing between the sliding portions 29, 39 is easily guided along the sliding portion 39 side of the tapered ring 37 by centrifugal force generated by the rotation of the differential case 7. The openings of the pores 45 in the sliding portion 39 of the tapered ring 37 face the direction of the rotation axis of the differential case 7. Therefore, the lubricating oil flowing along the sliding portion 39 side of the tapered ring 37 due to centrifugal force generated by the rotation of the differential case 7 can be stably retained by the pores 45.

[0037] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

[0038] For example, in this embodiment, a tapered ring is provided so as to be rotatable integrally with the differential case, but this is not limiting, and a sliding portion may be formed on the inner surface of the differential case without providing a tapered ring.

[0039] Furthermore, the side gear is composed of a gear member and an output member, but this is not limited thereto. The side gear may be formed from a single continuous member and provided with a sliding portion that slides against a sliding portion on the differential case side. [Explanation of symbols]

[0040] 1 Differential device 5. Limited slip differential 7 Differential case 11 Pinion gear 13,15 Side gear 27 Output member 29,39 Sliding part 37 Tapering 43 Base material 45 Porous 47 Nitrided layer 49 Diamond-like carbon layer

Claims

1. A rotatably arranged differential case; a pinion gear rotatably supported in the differential case and revolving with the rotation of the differential case; a pair of side gears that mesh with the pinion gear and are rotatable relative to each other; a differential limiting unit that limits differential between the differential case and the side gear; Equipped with the differential limiting unit has two sliding units that are slidable relative to each other, At least one of the two sliding portions has a nitride layer including a porous material formed on the surface of a substrate, and a diamond-like carbon layer formed on the surface of the nitride layer.

2. 2. The differential device according to claim 1, wherein the diamond-like carbon layer is formed on the surface of the nitride layer so as to expose the pores.

3. A tapered ring is provided on the differential case so as to be integrally rotatable, an output member slidable with the tapered ring is provided on the side gear so as to rotate integrally with the tapered ring; the sliding portion is provided on the tapered ring and the output member, the nitride layer and the diamond-like carbon layer are provided at least on the sliding portion of the tapered ring, 3. The differential device according to claim 1, wherein the opening of the porous portion in the sliding portion of the tapered ring faces in the direction of the rotation axis of the differential case.

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