Differential device

Abstract

To provide a differential device capable of reducing a diameter of a ring gear by eliminating the need for bolt fastening and weldment between a differential case and the ring gear, thus appropriately achieving a smaller size and lighter weight.SOLUTION: A differential device D for enabling differential rotation between a first rotary shaft 1 and a second rotary shaft 2 opposed to each other in a rotation axis AL direction, includes a differential case 3, and a ring gear 4 mounted to an outer peripheral portion of the differential case 3 so as to be rotated integrally with the differential case 3. The differential case 3 is a split structure formed by assembling sprit-in-two first and second cases 3a, 3b to each other and the ring gear 4 is fitted to an outer peripheral portion of the first case 3a. The second case 3b is assembled and joined to the first case 3a to which the ring gear 4 is fitted to integrate the differential case 3 and the ring gear 4 with each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a differential device that is mounted on a vehicle and transmits power to left and right drive shafts. [Background technology]

[0002] Patent Document 1 describes a differential gear that aims to reduce the number of welded portions between the differential case and the ring gear. The differential gear described in Patent Document 1 includes a ring gear that receives torque from a drive gear, a differential case that rotates integrally with the ring gear, and a differential mechanism housed in the body of the differential case. The ring gear has a gear portion that meshes with the drive gear and a rim portion that is integrally formed on the inner periphery of the gear portion. The rim portion of the ring gear is fitted to the outer periphery of the body of the differential case in an unwelded state. Furthermore, the rim portion of the ring gear is welded to the body of the differential case at a position axially spaced from and radially inward of the fitting portion where it engages with the body of the differential case. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-85141 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, to reduce the size and weight of a vehicle reducer (transmission) such as a transaxle, it is necessary to reduce the diameter and size of the ring gear and differential gear unit that constitute the final drive of the reducer. Generally, the ring gear is attached to the differential case of the differential by bolting. However, reducing the diameter of the ring gear makes it difficult to secure space for arranging the bolts. Therefore, a technology for forming a differential by welding the differential case and the ring gear has been developed, such as the differential described in Patent Document 1. In the differential described in Patent Document 1, the rim portion of the ring gear is fitted to the body portion of the differential case, and a portion of the rim (the fixed portion) is welded to the differential case. This eliminates the need for bolting between the differential case and the ring gear, thereby enabling the ring gear to be made smaller in diameter and the differential to be made more compact.

[0005] However, welding the differential case and ring gear together raises concerns about cracks, deformation, or distortion due to welding heat, resulting in a decline in quality. In the differential gear described in Patent Document 1, although the number of welds between the differential case and ring gear is reduced compared to conventional differential gears, the differential case and ring gear are still welded together. The differential case in a vehicle differential gear is typically formed by casting, using materials such as cast iron or ductile cast iron. Meanwhile, the ring gear is typically formed by forging, using materials such as carbon steel or chrome-molybdenum steel. Therefore, welding between the differential case and ring gear is dissimilar welding, joining dissimilar materials, and is therefore more susceptible to weld cracks and distortion than welding between similar materials. If such distortion or deformation due to welding affects the ring gear, gear tooth contact may deteriorate, resulting in increased gear noise and vibration.

[0006] This invention was devised with an eye on the above-mentioned technical problems, and aims to provide a differential device that can be appropriately made smaller and lighter by eliminating the need for bolting and welding between the differential case and the ring gear and reducing the diameter of the ring gear. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a differential device that includes a differential case and a ring gear that is attached to the outer periphery of the differential case and rotates integrally with the differential case, and that enables differential rotation between a first rotating shaft and a second rotating shaft that face each other in the direction of the rotation axis, wherein the differential case is The ring gear is fitted with a rotation-preventing mechanism. 1 case and a second case that closes the opening of the first case. 2 cases a welding projection is provided at a tip of the first case in the direction of the rotation axis, and a welding hole into which the welding projection is fitted is provided in the second case, the ring gear is fitted to an outer circumferential portion of the first case, The ring gear has a recessed portion in a portion facing the second case in the rotational axis direction, and the second case has a protruding portion in a portion facing the ring gear in the rotational axis direction, and the protruding portion of the second case is abutted against the recessed portion of the ring gear in the rotational axis direction to form a fitting portion in which they fit together, and the welding protrusion of the first case, which fits into the welding hole portion of the second case, is joined to the welding hole portion by welding. It is characterized by the following. [Effects of the Invention]

[0011] In the differential gear of the present invention, the differential case has a split structure divided into a first case and a second case. That is, the differential case is constructed by assembling and joining the first case and the second case. Meanwhile, the ring gear is attached to the outer periphery of the first case, for example, by spline fastening or press fitting. Then, the differential case is constructed by joining the first case with the ring gear attached to the second case. At the same time, the differential case and the ring gear are fixed together. Therefore, the ring gear is directly fixed to the differential case without bolting or welding. By attaching the ring gear to the differential case without using bolts, space for bolt placement is not required, allowing the ring gear to be made smaller in diameter. This allows for further miniaturization and weight reduction of the differential gear. Furthermore, by attaching the ring gear to the differential case without using welding, the effects of welding on the ring gear, such as thermal distortion or deformation or poor welding, can be eliminated. Therefore, the differential device can be configured with high precision, and gear noise and vibration can be suppressed.

[0012] In addition, in the differential device of the present invention, the second case is assembled to the first case with the ring gear fitted thereto, and the ring gear and the second case are butted together in the direction of the rotation axis, thereby fixing the differential case and the ring gear together. At this time, a fitting portion, such as a recess and a protrusion with a so-called spigot structure, is formed at the contact portion between the ring gear and the second case. Therefore, the second case is assembled to the first case and the ring gear while being positioned. Therefore, a differential case with a split structure can be easily and accurately constructed. Furthermore, the ring gear can be easily and accurately attached and fixed to the differential case.

[0013] In the differential gear of the present invention, the differential case is constructed by joining the first case and the second case by welding. The first case and the second case can be made of the same material, so they can be easily welded together. The ring gear is not directly welded. Therefore, the differential gear can be constructed while minimizing the effect of welding on the ring gear.

[0014] In the differential gear of the present invention, the differential case is constructed by joining the first case and the second case with bolts, so the differential gear can be constructed without any influence of welding on the ring gear and the differential case.

[0015] Therefore, with the differential device of this invention, bolt fastening between the differential case and the ring gear is eliminated, allowing the diameter of the ring gear to be reduced. In this case, the influence of welding on the ring gear and the differential case can be minimized or completely eliminated. This allows a differential device that is small and lightweight to be easily and appropriately constructed. Ultimately, a transaxle incorporating such a small and lightweight differential device D can be easily and appropriately reduced in size and weight. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are diagrams showing an example of a differential gear to which the present invention is applied (an example in which the first and second cases of the differential case are joined by welding), in which (a) is an acute-angle cross-sectional view (AA cross-section) of the differential gear, and (b) is a side view of the differential gear as seen from the second case side of the differential case. [Figure 2] FIG. 10 is a diagram showing another example of a differential device (an example in which a first case and a second case of the differential case are joined by bolting). DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are merely examples of specific embodiments of the present invention and are not intended to limit the scope of the present invention.

[0018] FIG. 1 shows an example of a differential D that is a target of an embodiment of the present invention. The differential D shown in FIG. 1 is mounted on a vehicle (not shown) as, for example, a final reduction gear, and enables or allows differential rotation between left and right drive shafts (not shown). The differential D includes, as its main components, a first rotating shaft 1, a second rotating shaft 2, and a differential case 3. The differential D also includes a ring gear 4 that is integrated with the differential D. In addition, the differential D includes a general differential gear mechanism that includes a differential pinion, side gears, etc., but these are not shown in FIG. 1 and FIG. 2, which will be described later. Note that the differential D in the embodiment of the present invention may be configured to receive power from a so-called longitudinally mounted engine (not shown) mounted on a FR vehicle (not shown) via a propeller shaft, etc. (not shown). Alternatively, the differential device D in an embodiment of the present invention may be configured to transmit power from a so-called horizontally mounted engine (not shown) mounted on, for example, a front-wheel drive vehicle (not shown) or a four-wheel drive vehicle (not shown) via a transaxle transmission mechanism or the like (not shown).

[0019] The first rotating shaft 1 and the second rotating shaft 2 are disposed on the same rotation axis AL and facing each other in the direction of the rotation axis AL. The first rotating shaft 1 and the second rotating shaft 2 are each rotatably supported by a differential case 3, which will be described later. The first rotating shaft 1 and the second rotating shaft 2 are each connected to the differential gear mechanism (specifically, a pair of side gears) as described above, and are configured to enable differential rotation between the first rotating shaft 1 and the second rotating shaft 2. When the differential device D is mounted on a vehicle, the first rotating shaft 1 and the second rotating shaft 2 constitute the left and right drive shafts of the vehicle, respectively, or are connected to the left and right drive shafts of the vehicle.

[0020] The differential case 3 forms the outer shell of the differential device D. As described above, the differential case 3 houses the differential gear mechanism and rotatably supports the first rotating shaft 1 and the second rotating shaft 2. A ring gear 4, which will be described later, is attached to the outer periphery of the differential case 3. The differential case 3 and the ring gear 4 rotate integrally. The differential case 3 in this embodiment of the present invention has a split structure formed by assembling at least two split cases, a first case 3a and a second case 3b. The first case 3a and the second case 3b are assembled to form the differential case 3, and the ring gear 4, which is disposed on the outer periphery of the differential case 3, is fixed and integrated. Details of the assembly of the first case 3a and the second case 3b and the ring gear 4, as well as the fixing method, will be described later.

[0021] The ring gear 4 is attached to the outer periphery of the differential case 3. In the example shown in FIG. 1 , the ring gear 4 and the differential case 3 are fitted together by splines 5 formed on the inner periphery of the ring gear 4 and the outer periphery of the differential case 3 (specifically, the outer periphery of the first case 3a, which will be described later) so that the ring gear 4 rotates integrally with the differential case 3. The ring gear 4 is meshed with, for example, a drive pinion (not shown) and receives power from the drive pinion. Therefore, the ring gear 4 receives torque transmitted from the drive pinion and rotates integrally with the differential case 3. Note that the fastening between the ring gear 4 and the first case of the differential case 3 is not limited to the spline fastening described above. For example, the ring gear 4 and the differential case 3 may be fastened integrally together by serrations (not shown) instead of the splines 5. Alternatively, the ring gear 4 and the differential case 3 may be fastened together using a rotation stopper such as a press fit or a key structure (not shown).

[0022] As described above, the differential device D in this embodiment of the present invention aims to eliminate bolting and welding between the differential case 3 and the ring gear 4, thereby reducing the diameter of the ring gear 4 and making the differential device D more compact and lightweight. To achieve this, the differential device D in this embodiment of the present invention is configured such that the ring gear 4 is fixed and integrated to the outer periphery of the differential case 3 by assembling and joining the first case 3a and second case 3b of the differential case 3, which has the above-described split structure.

[0023] 1, the first case 3a and second case 3b of the differential case 3 are joined by welding, thereby integrally fixing the ring gear 4 to the outer periphery of the differential case 3. Specifically, the first case 3a and second case 3b of the differential case 3 are provided with welded joints 6. The welded joints 6 are made up of welded protrusions 6a, welded holes 6b, and welded parts 6c.

[0024] The weld protrusion 6a is formed on the first case 3a. The ring gear 4 is fitted onto the outer periphery of the first case 3a. The first case 3a also has an opening 3c for installing the built-in differential gear mechanism. By assembling and joining the second case 3b to the first case 3a, the opening 3c is closed, and the differential case 3 is formed. The weld protrusion 6a is formed at the tip of the opening side of the first case 3a (the right side of FIG. 1(a)). The weld protrusion 6a is formed in a shape corresponding to the weld hole 6b described below, and fits into the weld hole 6b when the second case 3b is assembled to the first case 3a.

[0025] The welding hole 6b is formed in the second case 3b. As described above, the second case 3b is a circular lid-shaped member that closes the opening 3c of the first case 3a. The welding hole 6b is formed in the second case 3b, penetrating it in the thickness direction of the second case 3b (the left-right direction in FIG. 1(a)). The welding hole 6b is formed at a position corresponding to the welding protrusion 6a and in a shape corresponding to the welding protrusion 6a.

[0026] Welded portion 6c is a portion where welding protrusion 6a of first case 3a and welding hole 6b of second case 3b are welded together. With welding protrusion 6a fitted into welding protrusion 6a, the welded joint 6 is formed as welding portion 6c. Therefore, welding protrusion 6a, welding hole 6b, and welding portion 6c form welded joint 6.

[0027] Furthermore, the first case 3a and the second case 3b are formed with mating portions 7 that fit together when the first case 3a and the second case 3b are butted together in the direction of the rotation axis. As described above, the first case 3a and the second case 3b are assembled by butting the second case 3b against the ring gear 4 in the direction of the rotation axis AL with the first case 3a fitted with the ring gear 4. The mating portions 7 are made up of a protrusion 7a formed in a portion of the second case 3b facing the ring gear 4 in the direction of the rotation axis AL, and a recess 7b formed in a portion of the ring gear 4 facing the second case 3b in the direction of the rotation axis AL.

[0028] Specifically, a protrusion 7a that protrudes in the direction of the rotation axis AL is formed on a side surface 3d of the second case 3b facing the ring gear 4 (the left side of (a) of FIG. 1). In the example shown in FIG. 1, the protrusion 7a is formed so as to protrude in a cylindrical shape from the side surface 3d. The protrusion 7a is molded with a shape and outer diameter that correspond to a recess 7b of the ring gear 4, which will be described later.

[0029] Meanwhile, recesses 7b that fit with the protrusions 7a of the second case 3b are formed on the end face 4a of the ring gear 4 on the side facing the second case 3b (the left side of (a) of FIG. 1). In the example shown in FIG. 1, the inner peripheral portion of the end face 4a of the ring gear 4 forms the recesses 7b. The recesses 7b are formed with a shape and inner diameter that correspond to the protrusions 7. The protrusions 7a and the recesses 7b are formed, for example, in a loose fit between the protrusions 7a and the recesses 7b. Well then Therefore, the protrusion 7a of the second case 3b and the recess 7b of the ring gear 4 have a so-called spigot structure, and the fitting of the protrusion 7a and the recess 7b positions the second case 3b and the ring gear 4, and the second case 3b and the ring gear 4 are assembled with high precision. In other words, the first case 3a and the second case 3b are assembled with high precision, and the differential case 3 is constructed with high precision.

[0030] Furthermore, the fitting portions 7, i.e., the convex portion 7a of the second case 3b and the concave portion 7b of the ring gear 4, are formed so that when the second case 3b is butted against the ring gear 4 in the direction of the rotation axis AL with respect to the first case 3a into which the ring gear 4 is fitted, the ring gear 4 and the second case 3b come into contact before the first case 3a and the second case 3b come into contact. Therefore, when the second case 3b is assembled to the first case 3a, the convex portion 7a of the second case 3b fits into the concave portion 7b of the ring gear 4. At the same time, the end face 4a of the ring gear 4 comes into contact with the side surface 3d of the second case 3b, restricting movement or slippage of the ring gear 4 in the direction of the rotation axis AL.

[0031] figure In the example shown in Fig. 2, the first case 3a and second case 3b of the differential case 3 are joined by bolting, so that the ring gear 4 is fixed integrally to the outer periphery of the differential case 3. Note that, with regard to the configuration of each part of the differential device D shown in Fig. 2, parts that are the same as those shown in Fig. 1 above are given the same reference numerals as in Fig. 1.

[0032] Specifically, bolt fastening portions 8 are provided on the first case 3a and the second case 3b of the differential case 3 to butt and join the first case 3a and the second case 3b in the direction of the rotation axis. The bolt fastening portions 8 are made up of bolt holes 8a, threaded holes 8b, and bolts 8c.

[0033] The bolt hole 8a is formed in a portion of the second case 3b facing the ring gear 4 in the direction of the rotation axis AL and in a portion close to the outer periphery of the second case 3b. The bolt hole 8a is a through-hole that penetrates the second case 3b in the thickness direction (the left-right direction in FIG. 2), and a bolt 8c (described later) is inserted into the bolt hole 8a.

[0034] The threaded hole portion 8b is formed in a portion and position facing the bolt hole portion 8a in the direction of the rotation axis AL of the ring gear 4. The threaded hole portion 8b is a bolt hole into which a bolt 8c, which will be described later, is screwed, and is formed with a female thread that corresponds to the male thread of the bolt 8c.

[0035] Bolt 8c is a fastening bolt that joins first case 3a and second case 3b. As shown in Fig. 2, with first case 3a, ring gear 4, and second case 3b assembled, bolt 8c is inserted into bolt hole 8a and screwed into threaded hole 8b to fasten first case 3a and second case 3b together, thereby forming differential case 3. At the same time, differential case 3 and ring gear 4 are fixed together. In other words, differential device D is formed.

[0036] As described above, in the differential device D according to the embodiment of the present invention, the differential case 3 and the ring gear 4 are fixed together by assembling the second case 3b to the first case 3a, into which the ring gear 4 is fitted, and then butting the ring gear 4 and the second case 3b in the direction of the rotation axis AL. At this time, fitting portions 7, such as recesses 7b and protrusions 7a with a so-called spigot structure, are formed at the contact portions between the ring gear 4 and the second case 3b. Therefore, the second case 3b is assembled to the first case 3a and the ring gear 4 while being positioned. Therefore, the split-structure differential case 3 can be easily and accurately constructed. Furthermore, the ring gear 4 can be easily and accurately attached and fixed to the differential case.

[0037] In the example shown in FIG. 1, the differential case 3 is constructed by joining the first case 3a and the second case 3b by welding. The first case 3a and the second case 3b can be made of the same type of material (for example, cast iron or ductile cast iron), so the first case 3a and the second case 3b can be easily welded together. The ring gear 4 is not directly welded. Therefore, the differential D can be constructed while minimizing the effect of welding on the ring gear 4.

[0038] 2, the differential case 3 is constructed by joining the first case 3a and the second case 3b with bolts. Therefore, the differential device D can be constructed without any influence of welding on the ring gear 4 and the differential case 3.

[0039] Therefore, according to the differential device D of the embodiment of the present invention, bolt fastening between the differential case 3 and the ring gear 4 is eliminated, and the diameter of the ring gear 4 can be reduced. Also, direct welding between the differential case 3 and the ring gear 4 is eliminated, and the influence of welding on the ring gear 4 and the differential case 3 can be minimized or completely eliminated. Therefore, a differential device D that is small and lightweight can be easily and appropriately configured. And by constructing a transaxle by incorporating such a small and lightweight differential device D, it is possible to easily and appropriately achieve a small and lightweight transaxle. [Explanation of symbols]

[0040] 1 First rotation axis 2. Third rotation axis 3 Differential case 3a Case 1 3b Second Case 3c Opening (of the first case) 3D (2nd case) side 4 ring gear 4a End face 5 Splines 6 Welded joints 6a Welding protrusion 6b Welding hole 6c Welded section 7 Fitting 7a Convex part 7b Recess 8 Bolt fastening section 8a Bolt hole 8b Screw hole 8c bolt D Differential AL rotation axis

Claims

[Claim 1] A differential device comprising: a differential case; and a ring gear attached to an outer periphery of the differential case and rotating integrally with the differential case, the differential device enabling differential rotation between a first rotating shaft and a second rotating shaft that face each other in a rotation axis direction, the differential case comprises a first case into which the ring gear is fitted in a rotation-preventing manner, and a second case that closes an opening of the first case, a welding projection is provided at a tip of the first case in the direction of the rotation axis, and a welding hole into which the welding projection is fitted is provided in the second case; the ring gear is fitted to an outer circumferential portion of the first case, the ring gear has a recess in a portion facing the second case in the direction of the rotation axis, the second case has a protrusion at a portion facing the ring gear in the direction of the rotation axis, a fitting portion is formed by abutting the protrusion of the second case against the recess of the ring gear in the rotation axis direction with respect to the first case, and the fitting portions are fitted together; and The welding projection of the first case, which is fitted into the welding hole of the second case, is joined to the welding hole by welding. A differential device characterized by:

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