Differential device

Abstract

To provide a differential device that suppresses breakage of a welding part with a simple structure, and has a high transmission torque capacity.SOLUTION: A differential device 10 having a welding part 60 where a ring gear 20 and a differential case 30 are welded includes: (a) a fitting part 40 where the ring gear 20 and the differential case 30 are fitted; (b) a key groove 52 disposed in the fitting part 40 so as to straddle both of the ring gear 20 and the differential case 30; and (c) a key material 54 press-fitted into the inside of the key groove 52 in the circumferential direction of the ring gear 20. With this, in the differential device 10, the load in torque transmission is shared by the welding part 60, and the key groove 52 and the key material 54, i.e., a key part 50. Due to that the load shared by the welding part 60 is suppressed from becoming excessive, breakage in the welding part 60 is suppressed, and the differential device 10 has a high transmission torque capacity Tc.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] It relates to a differential device having a welded portion where a ring gear and a differential case are welded.

Background Art

[0002] There is known a differential device having a fitting portion where an insertion portion of a differential case is press-fitted (i.e., shrink-fitted) into a fitting hole of a ring gear and having a welded portion where the fitting portion is welded. For example, the one 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, excessive torque may be input to the ring gear due to some factor. When such excessive torque is input to the differential device described in Patent Document 1 exceeding the frictional force of the fitting portion, the amount (i.e., load) borne by the welded portion among the torque transmitted by the differential device (hereinafter referred to as "transmitted torque") rapidly increases. As a result, if the welded portion is damaged, there is a risk that the transmitted torque capacity, which is the maximum value of the transmitted torque that the differential device can transmit, will be limited to a torque value based on the frictional force of the fitting portion or less.

[0005] The present invention has been made against the background of the above circumstances, and an object thereof is to provide a differential device having a high transmitted torque capacity by suppressing damage to the welded portion with a simple structure.

Means for Solving the Problems

[0006] The gist of the present invention is to have a welded portion where a ring gear and a differential case are welded Furthermore, the differential case has openings in part for assembling the side gears, and its rigidity differs depending on the circumferential position around the axis of rotation, and the stress on the welded portion differs according to the circumferential position of the differential case.A differential gear comprising: (a) a fitting portion into which the ring gear and the differential case are fitted; (b) a keyway provided in the fitting portion so as to span both the ring gear and the differential case; and (c) a key material pressed into the inside of the keyway in the circumferential direction of the ring gear. (d) The keyway is provided at the circumferential position where the stress on the welded portion is locally high, and at a position opposite the circumferential position across the axis of rotation. It is about that. [Effects of the Invention]

[0007] The differential of the present invention includes (a) a fitting portion into which the ring gear and the differential case are fitted, (b) a keyway provided in the fitting portion so as to span both the ring gear and the differential case, and (c) a key material pressed into the inside of the keyway in the circumferential direction of the ring gear. As a result, the differential distributes the load in torque transmission between the welded portion and the keyway and key material, i.e., the key portion. This prevents the load borne by the welded portion from becoming excessive, thereby suppressing damage to the welded portion, and the differential has a high torque transmission capacity. Furthermore, the differential case of the differential gear has openings in part for assembling side gears, and its rigidity varies depending on the circumferential position around the axis of rotation. The stress on the welded portion varies according to the circumferential position of the differential case, and the keyway is provided at the circumferential position where the stress on the welded portion is locally high, and at a position opposite the circumferential position across the axis of rotation. As a result, the stress value at the location where the stress on the welded portion is locally high is reduced, and eccentricity due to the rotation of the differential gear is suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This is an explanatory diagram of the differential gear, where Figure 1(a) is a cross-sectional view along the cutting line aa shown in Figure 1(b), and Figure 1(b) is a view of the ring gear and differential case from the direction of arrow b shown in Figure 1(a). [Figure 2] This figure shows the relationship between the circumferential position of the ring gear in the circumferential direction and the stress at the welded joint, in the case where a key portion is not provided in this embodiment. [Figure 3] This diagram illustrates the load distribution in torque transmission at the welded and keyed sections of a differential gear. [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 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 an explanatory diagram of the differential gear 10, where Figure 1(a) is a cross-sectional view of the cutting line aa shown in Figure 1(b), and Figure 1(b) is the ring gear 20 and differential case 30 viewed from the direction of arrow b shown in Figure 1(a). Note that in Figure 1(a), the pinion shaft and pair of pinions provided inside the differential case 30 are not shown. Also, of the key portion 50 shown in Figure 1(a), the upper side is the state before the key material 54 is fitted into the keyway 52, and the lower side is the state after the key material 54 is fitted into the keyway 52.

[0011] The differential gear 10 receives the input power for driving and transmits equal driving torque to a pair of drive wheels via a pair of drive shafts (not shown), while allowing an appropriate difference in rotational speed. The differential gear 10 includes a ring gear (= differential ring gear) 20 and a differential case 30. The configuration of the differential gear 10 other than the ring gear 20 and differential case 30 is a well-known configuration. The axis C is the rotational centerline common to the ring gear 20 and the differential case 30.

[0012] A fitting hole 22a is provided in the inner circumference 22 of the ring gear 20. The ring gear 20 has a cylindrical portion 24 that protrudes from between its inner circumference 22 and outer circumference toward one side in the direction of axis C (same direction as arrow b). The other side of the cylindrical portion 24, opposite to the one side in the direction of axis C, is connected to the ring gear 20.

[0013] A cylindrical insertion portion 32a is provided on the outer circumference 32 of the differential case 30. A flange portion 34 is provided on the outer circumference 32 of the differential case 30. The insertion portion 32a of the differential case 30 is fitted into the fitting hole 22a of the ring gear 20 by blind fit. A "blind fit" is a fitting that is intermediate between a clearance fit and a interference fit, with a gap or interference allowance depending on the tolerance. The fitting hole 22a and the insertion portion 32a into which the ring gear 20 and the differential case 30 are fitted together constitute the fitting portion 40 of the ring gear 20 and the differential case 30, and correspond to the "fitting portion" in this invention. When the ring gear 20 and the differential case 30 are fitted together, the tip of the cylindrical portion 24 and the tip of the flange portion 34 are in close proximity to each other and facing each other. Furthermore, compared to press-fitting, in this embodiment, because it is a blind fit, the positional relationship between the tip of the cylindrical portion 24 and the tip of the flange portion 34 is less affected by manufacturing tolerances in these dimensions, resulting in improved welding quality.

[0014] The tip of the cylindrical portion 24 and the tip of the flange portion 34 are welded together, for example, by laser, from one end in the direction of axis C to the other (opposite direction to arrow b) along their entire circumference. As a result, the welded joint 60 formed by welding the cylindrical portion 24 and the flange portion 34 prevents relative rotation between the ring gear 20 and the differential case 30.

[0015] A key portion 50 is provided in the mating portion 40. The key portion 50 has the function of preventing relative rotation between the ring gear 20 and the differential case 30 in the mating portion 40. The key portion 50 comprises a keyway 52 and a key material 54. The keyway 52 is a groove provided in the mating portion 40 that spans both the ring gear 20 and the differential case 30, with multiple grooves (four in this embodiment). Preferred positions for arranging the keyway 52 in the circumferential direction will be described later. The keyway 52 is, for example, a rectangular parallelepiped groove extending in the circumferential direction in the mating portion 40. A key material 54 is press-fitted into the interior of each keyway 52 in the circumferential direction. The key material 54 is, for example, a rectangular parallelepiped shape that can be fitted into the keyway 52 and extends in the circumferential direction. The key material 54 maintains its press-fitted state in the circumferential direction even when the temperature of the differential 10 changes. Preferably, the key material 54 is made of a material with the same coefficient of thermal expansion as the ring gear 20 and the differential case 30, so that the circumferential press-fit state is maintained against thermal expansion or contraction.

[0016] Figure 2 shows the relationship between the circumferential position θ [deg] of the ring gear 20 in the circumferential direction and the stress F [N] at the welded portion 60, in the case where the key portion 50 is not provided in this embodiment. The circumferential position θ is shown in Figure 1(b).

[0017] As shown in Figure 2, when the differential 10 rotates, the stress F applied to the welded joint 60 differs for each circumferential position θ. This is because the differential case 30 has openings in some parts for assembling a pair of side gears, and therefore the rigidity of the differential case 30 differs depending on the circumferential position θ. As a result, for example as shown in Figure 2, there are areas where the stress F at the welded joint 60 is high and areas where it is low for each circumferential position θ, and for example, the stress F is high at intervals of 90 degrees, such as at circumferential positions θ of 45 [deg], 135 [deg], 225 [deg], and 315 [deg], for either forward torque or reverse torque.

[0018] The key portion 50 is provided at the circumferential positions θ where the stress F at the welded portion 60 in the forward and reverse directions shown in FIG. 2 is high, for example. Thereby, the load in torque transmission in the differential device 10 is shared not only by the welded portion 60 but also by the key portion 50 in addition to the welded portion 60. By providing the key portion 50 at such a circumferential position θ, the stress value at the location where the stress F at the welded portion 60 is high is reduced as shown by the white arrow in FIG. 2. For example, by providing the key portions 50 at positions facing each other across the axis C, the centroid of the differential device 10 is suppressed from deviating from the axis C, and eccentricity during rotation of the differential device 10 is suppressed.

[0019] FIG. 3 is a diagram for explaining the load sharing in torque transmission at the welded portion 60 and the key portion 50 in the differential device 10. The input torque Tin [Nm] input to the differential device 10 is shown by a solid line, the load shared by the key portion 50 in this embodiment is shown by a broken line, and the load shared by a fitting portion 140 (described later) in the comparative example is shown by a two-dot chain line.

[0020] The comparative example is different from this embodiment in that a fitting portion 140 (not shown) fitted by press-fitting is provided instead of the fitting portion 40 in this embodiment and the key portion 50 is not provided.

[0021] In the comparative example, the load due to the transmission torque Td [Nm] is shared by the press-fitted fitting portion 140 and the welded portion 60. The amount of the transmission torque Td shared by the fitting portion 140 is defined as the fitting portion transmission torque Tp [Nm], and the amount of the transmission torque Td shared by the welded portion 60 is defined as the welded portion transmission torque Ty [Nm]. The fitting portion transmission torque Tp and the welded portion transmission torque Ty are load torques applied to the press-fitted fitting portion 140 and the welded portion 60, respectively, when viewed from another perspective. The welded portion transmission torque Ty is the remainder obtained by subtracting the fitting portion transmission torque Tp from the input torque Tin. As the input torque Tin increases, the fitting portion transmission torque Tp increases. However, when the fitting portion transmission torque Tp exceeds the fitting portion transmission torque Tps in the maximum static friction state (= the state in which the frictional force between the ring gear 20 and the differential case 30 at the fitting portion 140 is the maximum static frictional force), the fitting portion 140 can only share the fitting portion transmission torque Tpd (<Tps) in the dynamic friction state (= the state in which the frictional force between the ring gear 20 and the differential case 30 at the fitting portion 140 is the dynamic frictional force). As a result, if the load applied to the welded portion 60 suddenly becomes larger than before and the welded portion 60 is damaged, the transmission torque capacity Tc [Nm] may be limited to be less than or equal to the fitting portion transmission torque Tpd in the dynamic friction state of the fitting portion 140.

[0022] In this embodiment, the load due to the transmitted torque Td is shared between the key portion 50 and the welded portion 60. Since the fitting portion 40 is a blind fit, it bears almost no load due to the transmitted torque Td. The amount of the transmitted torque Td shared by the key portion 50 is defined as the key portion transmitted torque Tk [Nm], and the amount of the transmitted torque Td shared by the welded portion 60 is defined as the welded portion transmitted torque Ty. The key portion transmitted torque Tk and the welded portion transmitted torque Ty are, in other words, the load torques applied to the key portion 50 and the welded portion 60, respectively. The welded portion transmitted torque Ty is the remainder obtained by subtracting the key portion transmitted torque Tk from the input torque Tin. The key portion transmitted torque Tk increases with increasing input torque Tin. The key portion 50 prevents the ring gear 20 and the differential case 30 from rotating relative to each other in the circumferential direction, i.e., from slipping. Therefore, the welded portion transmitted torque Ty gradually increases with increasing input torque Tin. In this embodiment, unlike the comparative example, the load applied to the weld 60 does not increase rapidly, and in the region where the input torque Tin is high, the weld transmission torque Ty in this embodiment is lower than that in the comparative example. As a result, in this embodiment, the weld 60 is less likely to be damaged and the transmission torque capacity Tc is less likely to be limited compared to the comparative example.

[0023] According to this embodiment, the differential gear 10 has a welded joint 60 where a ring gear 20 and a differential case 30 are welded together, and includes (a) a fitting portion 40 into which the ring gear 20 and the differential case 30 are fitted, (b) a keyway 52 provided in the fitting portion 40 so as to span both the ring gear 20 and the differential case 30, and (c) a key material 54 pressed into the inside of the keyway 52 in the circumferential direction of the ring gear 20. As a result, the differential gear 10 shares the load in torque transmission between the welded joint 60 and the keyway 52 and key material 54, i.e., the key portion 50. This prevents the load borne by the welded joint 60 from becoming excessive, thereby suppressing damage to the welded joint 60, and the differential gear 10 has a high transmission torque capacity Tc.

[0024] The above-described examples are embodiments of the present invention, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, without departing from its spirit.

[0025] In the above-described embodiment, four key portions 50 were provided, but the present invention is not limited to this and can also be applied to embodiments in which one key portion 50 is provided or multiple key portions other than four.

[0026] In the above-described embodiment, as shown in Figure 2, the circumferential position θ was 45[deg], 135[deg], 225[deg], and 315[deg], with stress F being high at intervals of 90[deg] between either the forward torque or the reverse torque, and the key portion 50 was provided at these circumferential position θ. However, the present invention is not limited to this embodiment. For example, the present invention can also be applied to an embodiment in which the key portion 50 is provided offset from the circumferential position θ where stress F is high at either the forward torque or the reverse torque.

[0027] In the above-described embodiment, the welded portion 60 was formed by welding a cylindrical portion 24 and a flange portion 34, but the present invention is not limited to this. The welded portion 60 may be formed by welding a ring gear 20 and a differential case 30. For example, in the above-described embodiment in which the cylindrical portion 24 and flange portion 34 are not provided, the fitting portion 40 may be formed by laser welding, for example, from one side in the direction of axis C to the other side (in the opposite direction to arrow b) over its entire circumference. [Explanation of Symbols]

[0028] 10: Differential gear, 20: Ring gear, 30: Differential case, 40: Mating section, 52: Keyway, 54: Key material, 60: Welded section

Claims

[Claim 1] A differential having a welded joint between a ring gear and a differential case, wherein the differential case has a partial opening for assembling a side gear, and its rigidity varies depending on the circumferential position around the axis of rotation, and the stress on the welded joint varies according to the circumferential position of the differential case, The fitting portion into which the ring gear and the differential case are fitted, The fitting portion includes a keyway that spans both the ring gear and the differential case, The ring gear comprises a key material pressed into the circumferential direction within the keyway, The keyway is provided at the circumferential position where the stress on the welded portion is locally high, and at a position opposite the circumferential position across the axis of rotation. A differential device characterized by the following features.

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