Vehicle differential device

Abstract

To provide a vehicle differential having a differential limiting mechanism that can adequately achieve the differential function and differential limiting function of the vehicle differential even when the vehicle differential is used for a long period of time, and can suppress deterioration of tooth contact between the pinion gear and the side gear. [Solution] A vehicle differential device 10 comprising a differential case 16, a pinion gear 20 provided inside the differential case 16 and rotatably supported around the pinion shaft 18 by a pinion shaft 18, a pair of side gears 22, 24 meshed with the pinion gear 20, and a differential limiting mechanism 32 having a plurality of friction plates 26, 28 between the side gears 22, 24 and the differential case 16 and a preloading spring 30 that preloads the friction plates 26, 28, wherein the friction plates of the differential limiting mechanism 32 are made of a friction plate material whose plate thickness increases with use of the vehicle differential device 10.

Description

Technical Field

[0001] The present invention relates to a vehicle differential device provided with a differential limiting mechanism.

Background Art

[0002] A vehicle differential device including a differential case (hereinafter referred to as a "diff case"), a pinion gear provided in the diff case and rotatably supported around the pinion shaft by the pinion shaft, a pair of side gears meshed with the pinion gear, a plurality of friction plates interposed between the side gears and the diff case, and a pressure spring for applying pressure to these friction plates, and capable of directly transmitting the rotational torque of the diff case to the side gears is well known. For example, the vehicle differential device described in Patent Document 1 is such a device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when the above-described differential device is used for a long time, sliding wear of a plurality of friction plates constituting the differential limiting mechanism progresses, seizure occurs between the friction plates, and the differential function of the differential device may not operate normally. Further, when each plate thickness becomes thinner due to the sliding wear of the friction plate, the force transmitted from the pressure spring disposed between the pair of left and right side gears through the side gears weakens, and the frictional force acting on the wear plate weakens, so that the differential limiting function may not be sufficiently obtained. Further, when the both side gears move in a direction away from each other as the friction plates wear, the tooth contact between each side gear and the pinion gear meshed therewith may deteriorate.

[0005] The present invention has been made to solve the above-mentioned problems, and its objective is to provide a vehicle differential device having a differential limiting mechanism that can adequately obtain the differential function and differential limiting function of the differential device even when the differential device is used for a long period of time, and can suppress deterioration of tooth contact between the pinion gear and the side gear. [Means for solving the problem]

[0006] The gist of the present invention is a vehicle differential device comprising: a differential case; a pinion gear provided within the differential case and rotatably supported around the pinion shaft by a pinion shaft; a pair of side gears meshed with the pinion gear; and a differential limiting mechanism having a plurality of friction plates interposed between the side gears and the differential case, and a preloading spring for preloading the friction plates, wherein the friction plates of the differential limiting mechanism are made of a friction plate material whose thickness increases with use of the differential device. [Effects of the Invention]

[0007] According to the differential limiting mechanism of the present invention, even if the differential device is used for a long period of time, the reduction in plate thickness due to wear of the friction plates arranged in the differential limiting mechanism is suppressed by the increase in the thickness of the friction plates. As a result, the differential function and differential limiting function of the differential device can be operated normally, and deterioration of tooth contact with the pinion gear and side gear can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view illustrating the configuration of a vehicle differential device to which the present invention is suitably applied. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in the following embodiments, the drawings have been simplified or modified as appropriate, and the dimensional ratios and shapes of each part are not necessarily depicted accurately. [Examples]

[0010] Figure 1 is a cross-sectional view illustrating the configuration of a vehicle differential device 10 to which the present invention is suitably applied. Hereinafter, the vehicle differential device 10 will be referred to as the differential device 10. The differential device 10 is provided in the power transmission path between a vehicle power source, such as an engine (not shown), and drive shafts 12 and 14 that rotate a pair of left and right drive wheels (not shown).

[0011] As shown in Figure 1, the differential device 10 comprises a differential case 16, a pinion shaft 18 fixed to the differential case 16, a pinion gear 20 rotatably supported around the pinion shaft 18, a pair of side gears 22 and 24 meshing with the pinion gear 20 and arranged facing each other across the pinion shaft 18 and rotatably supported by the differential case 16 around the axis of rotation CL, and a differential limiting mechanism 32 having a plurality of friction plates 26 and 28 interposed between the side gears 22 and 24 and the differential case 16 in a stacked state, and a preloading spring 30 that preloads the friction plates 26 and 28.

[0012] In the case shown in Figure 1, the pinion shaft 18 is configured in a Y-shape from three radial shafts, including two shafts not shown, and the ends of each shaft are fixed to the differential case 16 by a method not shown. Two pinion gears (not shown) are rotatably supported around the two shafts (not shown). The differential case 16 is composed of two parts, which are integrally fastened together with fastening bolts 34. The pinion gear 20 is pressed against a pinion washer 36 disposed between it and the inner wall surface of the differential case 16 by the reaction force generated by its meshing with the side gears 22 and 24. The pinion washer 36 is a partially spherical shape with the pinion shaft 18 inserted through its central hole, and is, for example, a circular plate made of bearing metal.

[0013] A ring gear 40 is fixed to an outer peripheral projection 16a projecting outward from the outer peripheral surface of the differential case 16 by fastening bolts 38. The drive torque from the vehicle drive source is transmitted to the differential case 16 via a drive pinion (not shown) that meshes with the ring gear 40. The drive torque is transmitted to side gears 22 and 24 via a pinion shaft 18, a pinion gear 20, and two pinion gears (not shown), and then transmitted to a pair of left and right drive wheels (not shown) via drive shafts 12 and 14, which are spline-fitted to the side gears 22 and 24 so that they cannot rotate relative to each other.

[0014] The differential limiting mechanism 32 consists of a group of overlapping friction plates 26, 28 arranged on either side of the pinion shaft 18, a preload spring 30 disposed in a through hole in the central part 42 of the pinion shaft 18 and acting on the left and right side gears 22, 24 in a direction away from each other, and two spring supports 44, 46 on both ends of the preload spring 30 that receive the force of the preload spring 30. The friction plate 26 is an annular disc shape, and its inner circumference 26a is fitted to the spline portions 22a, 24a on the outer circumference of the cylindrical parts of the side gears 22, 24 so as to be movable in the direction of the rotation axis CL but not rotatable around the rotation axis CL. The friction plate 28 is an annular disc shape, and its outer circumference 28a is fitted to two spline portions 16b on the left and right inside the differential case 16 so as to be movable in the direction of the rotation axis CL but not rotatable around the rotation axis CL. The central shaft portion of the spring retainer 44 and the central cylindrical hollow portion of the spring retainer 46 are fitted together so as to be able to move relative to each other in the direction of the rotation axis CL. The spring retainer 46 is positioned on the outer circumference of the through hole in the central portion 42 of the pinion shaft 18 by a knock pin 48 so as not to rotate around the rotation axis CL. The force from the preload spring 30 is transmitted to the side gears 22 and 24 via the spring retainers 44 and 46. The friction plates 26 and 28 located on the left side are preloaded by the preload spring 30 by being sandwiched between the side gear 22 and the left side wall 16c inside the differential case 16, while the friction plates 26 and 28 located on the right side are preloaded by the preload spring 30 by being sandwiched between the side gear 24 and the right side wall 16d inside the differential case 16.

[0015] When a difference in rotational speed occurs between the left and right drive wheels (not shown), a difference in rotational speed occurs between the differential case 16 and the side gears 22 and 24. This difference in rotational speed generates frictional heat due to sliding between the friction plate 26 fitted to the side gears 22 and 24 and the friction plate 28 fitted to the differential case 16, causing the surfaces of the friction plates 26 and 28 to become hot. Due to the action of this frictional heat, the thickness of the friction plates 26 and 28 increases due to the formation of an oxide film formed by the reaction of iron and other metallic elements contained on the surface of the friction plates 26 and 28 with the surrounding oxygen. If the friction plates 26 and 28 are made of carbon steel, for example, an oxide scale (oxide film) is formed at around 500°C, increasing the thickness. This oxide scale contains ferrous oxide (wustite), triiron tetroxide (magnetite, black rust), and ferric oxide (hematite).

[0016] Alternatively, due to the action of the aforementioned frictional heat, the thickness of the friction plates 26 and 28 increases due to a chemical reaction between the surface metal of the friction plates 26 and 28 and the chemical substances present in the surrounding area, such as additives in the lubricating oil (e.g., ZnDTP (ZincDialkyldithiophosphate)), which forms a chemical reaction film (e.g., a ZnDTP film) on the surface of the friction plates 26 and 28.

[0017] Alternatively, the friction plates 26 and 28 are made of a material having the following properties: As friction occurs between the surfaces of the friction plates 26 and 28, the protruding parts of the surfaces come into contact and deform, causing fractures to occur internally. The fractured wear particles accumulate on the surfaces of the friction plates 26 and 28, and the thickness of the friction plates 26 and 28 increases due to the deposition film that is baked onto the surfaces of the friction plates 26 and 28 by the heat effect of the friction plates and the pressure applied between the friction plates 26 and 28.

[0018] As described above, with the differential device 10 of this embodiment, even if the differential device 10 is used for a long period of time, the decrease in plate thickness due to wear of the friction plates 26 and 28 arranged in the differential limiting mechanism 32 is suppressed by the increase in the thickness of the friction plates 26 and 28. Therefore, the differential function and differential limiting function of the differential device 10 can be operated normally, and deterioration of tooth contact with the pinion gear 20 and side gears 22 and 24 can be suppressed.

[0019] As described above, the embodiments of the present invention have been described in detail based on the drawings, but the present invention is also applicable in other aspects.

[0020] For example, in the foregoing embodiment, the pinion shaft 18 is composed of three radial shafts and three pinion gears are used, but it may be composed of one shaft and two pinion gears, or may be composed of four or more shafts and four or more pinion gears.

[0021] Also, for example, in the foregoing embodiment, a coil spring is used as the biasing spring 30 between the left and right side gears 22 and 24 in FIG. 1, but any elastic body that applies a force in a direction separating the left and right side gears 22 and 24 as a function may be used. For example, spring materials such as conical spring washers may be arranged singly or in plurality facing each other alternately.

[0022] Also, for example, in the foregoing embodiment, a plurality of friction plates are provided as the friction plates 26 and 28 in FIG. 1, but each may be composed of a single member made of a material having a frictional force equivalent to that of a plurality of members.

[0023] Note that the above is merely one embodiment, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

Explanation of Reference Numerals

[0024] 10: Differential device for vehicle 12, 14: Drive shaft 16: Differential case 18: Pinion shaft 20: Pinion gear 22, 24: Side gear 26, 28: Friction plate 30: Biasing spring 32: Differential limiting mechanism 40: Ring gear CL: Axis of rotation

Claims

[Claim 1] A vehicle differential device comprising: a differential case; a pinion gear provided within the differential case and rotatably supported around the pinion shaft by a pinion shaft; a pair of side gears meshed with the pinion gear; and a differential limiting mechanism having a plurality of friction plates interposed between the side gears and the differential case, and a preloading spring for preloading the friction plates, wherein The friction plates of the differential limiting mechanism are made of a friction plate material whose thickness increases with use of the differential device. A vehicle differential device characterized by the following features.

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