differential device

Abstract

The differential device comprises: a housing that is capable of rotating around an axis; a differential gear set that comprises: a pair of side gears that are accommodated in the housing and are capable of rotating around the axis; a pinion shaft that passes through the housing orthogonally to the axis and is fixed so as to rotate around the axis together with the housing; and a pinion gear that is rotatably supported on the pinion shaft and meshes with the side gear in a manner that allows differential movement between the side gears; a friction clutch that is interposed between the side gears and the inner surface of the housing to limit the differential; a pair of elastic bodies that apply preload to the friction clutch in the direction of the axis, respectively; and a block that contacts both sides of the elastic body and is supported in the direction of the axis, respectively, and is engaged with the pinion shaft so that the reaction force received from the friction clutch via the elastic body is borne by the pinion shaft.

Description

Technical Field

[0001] The present invention relates to a limited differential (LSD) device, and more particularly to an LSD device that always exerts a certain degree of differential limiting effect. Background Art

[0002] In a car, the left and right axles do not necessarily rotate at the same speed, so a differential between them is required. In order to allow the differential between the two axles, a differential device is used.

[0003] When both wheels have traction, the differential device can effectively transfer torque to both axles. However, if one wheel loses traction, the differential device can maintain the other wheel's differential, preventing torque from being transferred to either axle. One method to avoid this situation is the so-called limited slip differential (LSD). For example, an LSD has a friction clutch that operates by sensing torque, and the friction clutch operates by limiting the differential (torque-sensing LSD).

[0004] There are various types of torque-sensing LSDs, including a planetary gear type that uses the tooth surface resistance of a planetary gear as a pressing force on a clutch, a multi-plate clutch type that uses a multi-plate clutch as a friction clutch, and a cone clutch type that uses a cone clutch.

[0005] In any system, there is a slight time lag before differential limiting takes effect. This can lead to a loss of driving force when the vehicle starts moving, or even when traction is momentarily lost while driving. Therefore, designs are being developed to apply a pressing force to the friction clutch before the LSD senses torque, attempting to pre-transmit a certain amount of torque (initial torque).

[0006] Patent Documents 1 and 2 disclose related technologies.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 11-82682

[0010] Patent Document 2: Japanese Patent Application Publication No. 2000-283263 Summary of the Invention

[0011] The technologies disclosed in Patent Documents 1 and 2 all use strong springs to constantly apply pressure to the multi-plate clutch, which has a certain effect. However, in order to obtain a stronger elastic force, problems arise when actually manufacturing the device. That is, if you want to assemble a device such as the one disclosed in Patent Document 2, you must overcome the elastic force of the disc spring and press it into the pinion shaft, causing a press-in scratch on the pinion shaft based on the disc spring. The pinion rotates in direct contact with the press-in scratch, which does not hinder smooth rotation or increase the loss. In order to prevent the occurrence of damage, there is an assembly method in which the differential case is divided in the center and the pinion shaft is assembled, and then the divided case parts are fastened to each other using bolts, etc., but each part requires a large-diameter flange for fastening, which significantly reduces the compactness of the device. If it is limited to preventing press-in scratches, it can be a solution to reduce the elastic force, but this will naturally lead to a reduction in initial torque. The device disclosed below was created in view of this problem.

[0012] According to one aspect, the differential device comprises: a housing that is capable of rotating around an axis; a differential gear set that comprises: a pair of side gears that are accommodated in the housing and are capable of rotating around the axis; a pinion shaft that passes through the housing orthogonally to the axis and is fixed, and rotates around the axis together with the housing; and a pinion gear that is rotatably supported on the pinion shaft and meshes with the side gear in a manner that allows differential movement between the side gears; a friction clutch that is interposed between the side gears and the inner surface of the housing to limit the differential; a pair of elastic bodies that apply preload to the friction clutch in the direction of the axis, respectively; and a block that contacts both sides of the elastic body and is supported in the direction of the axis, respectively, and is engaged with the pinion shaft so that the reaction force received from the friction clutch via the elastic body is borne by the pinion shaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is an exploded perspective view of the differential device.

[0014] Figure 2 This is a cross-sectional view of the differential device, taken from Figure 1 A cross-sectional view taken along line II-II.

[0015] Figure 3 It is a partial cross-sectional view that specifically enlarges the side gear, disc spring, and block. DETAILED DESCRIPTION

[0016] Several exemplary embodiments are described below with reference to the accompanying drawings. In the following description and claims, unless otherwise specified, "axis" refers to the rotational axis of the differential device. Furthermore, "axial" refers to the direction parallel to the axis, and "radial" refers to the direction perpendicular thereto. In the following description, a distinction is sometimes made between "right" and "left," but this is merely for ease of explanation; embodiments in which the left and right directions are reversed are also possible.

[0017] Reference Figure 1 、 2 As an example, the differential device according to this embodiment can be used to allow torque around axis C to be differentially distributed and output to a pair of axles (typically, right and left). Alternatively, it can be used to distribute torque to front and rear drive wheels via a connecting propeller shaft. Of course, it can also be used for various other applications involving torque transmission. The following description involves an example of torque distribution to axles, but this is for ease of explanation only.

[0018] The differential device generally includes: a housing 1, which receives torque and rotates around an axis C; a differential gear set 3, which is drivingly coupled to the housing 1 to allow differential movement and transmit torque to the two axles; a pair of friction clutches 5, which are subjected to pressing force to limit differential movement; a pair of elastic bodies 7, which apply preload to the friction clutches 5 in the axial direction respectively; and a block 9, which supports the back side of the elastic body 7.

[0019] The housing 1 is roughly cylindrical and rotatably supported by protruding projections at both ends. While the housing 1 can be a single piece, it can be a two-piece design to facilitate the loading of internal components. In the illustrated example, the housing 1 can be divided into a main body that houses and supports the gear train 3 and friction clutch 5, and a cover 31 that covers one end. However, the main body is integral and cannot be divided. The cover 31 is secured to the main body, for example, along with a ring gear 33, by bolts 35, forming the housing 1. The housing 1 receives torque via the ring gear 33 and rotates about the axis C.

[0020] The housing 1 has a shaft hole 19 on the side of its body and other shaft holes 19 symmetrically arranged about the axis C. These support the pinion shaft 13, described later. Furthermore, a plurality of grooves 47 extend parallel to the axis C on the inner surface of the body and engage with tabs 45 of the outer plate 27, described later.

[0021] 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 pinion and side gears are tilted, or it can also be a face gear type (not shown). The bevel gear type or face gear type can easily achieve the following disclosure, or other forms can be adopted if possible.

[0022] The differential gear set 3 is generally housed in the housing 1 and includes a pair of side gears 11 corresponding to a pair of axles. The differential gear set 3 also includes a pinion shaft 13 fixedly supported on the housing 1 and rotatable about axis C, and a plurality of pinion gears 15 rotatably supported on the shaft 13. The pinion gears 15 mesh with the side gears 11, enabling relative rotation between the side gears 11. Furthermore, the combination of the meshing pinion gears 15 and the side gears 11 enables torque transmission, allowing the torque received by the pinion shaft 13 to be differentially transmitted to the pair of side gears 11.

[0023] Each pinion gear 15 has gear teeth on its outer periphery and meshes with the side gear 11. In addition, the center of its axis is a smooth cylindrical through-hole, and the pinion shaft 13 is passed through the through-hole so that the pinion gear 15 can rotate around the through-hole.

[0024] The pinion shaft 13 is substantially cylindrical and has a smooth surface. It radially penetrates the housing 1 from one shaft hole 19 to the other shaft hole 19, passing through the axis C and being perpendicular thereto, and is coupled thereto. For securing the pinion shaft 13 to the housing 1, a pin 21 is utilized. This pin 21 is parallel to the outer circumference of the housing 1 and is inserted perpendicularly thereto, thereby securing the pinion shaft 13 to the housing 1.

[0025] Each side gear 11 consists of a generally cylindrical hub portion 23 and a gear portion 25 extending radially outward from the hub portion 23. The inner surface of the hub portion 23 includes a structure for coupling to the axle, such as a spline, or other coupling means. The outer surface of the hub portion 23 may include, for example, a lug groove 51 for coupling with a lug 49 of the inner plate 43, described later.

[0026] The gear portion 25 has gear teeth for meshing with the pinion 15 on the side facing the pinion 15, and a generally flat clutch surface 27 on the back side. The clutch surface 27 is an element related to the friction clutch 5 described above. As described later, when the friction clutch 5 is a multi-plate clutch, it is the surface that presses the clutch plates.

[0027] The hub portion 23 also includes a pivot portion 23P at its end opposite the gear portion 25, and the housing 1 includes a corresponding bearing portion 1B. The pivot portion 23P is dimensioned to rotatably engage with the bearing portion 1B, and this engagement of the two positions each side gear 11 relative to the axis C. Each side gear 11 contacts the housing 1 only at the pivot portion 23P, and is positioned through support by the friction clutch 5 and indirect support by the pinion shaft 13, eliminating the need for additional positioning means.

[0028] The inner surface 17 of the housing 1, which faces the clutch surface 27, is also flat and is an element associated with the friction clutch 5. The friction clutch 5 can be formed by direct contact between the inner surface 17 and the clutch surface 27 or indirectly via appropriate friction plates, but the friction clutch 5 is preferably a multi-plate clutch interposed between the side gear 11 and the inner surface 17 of the housing 1.

[0029] The multi-plate clutch comprises outer plates 41 and inner plates 43 that are alternately stacked, each of which is a flat circular plate perpendicular to the axis C. Both plates are made of a wear-resistant material such as low-carbon steel, but a friction material such as carbon fiber may be bonded to one or more of their surfaces.

[0030] The outer plate 41 includes, for example, a plurality of radially outwardly projecting tabs 45. These tabs 45 engage with grooves 47 in the housing 1, thereby preventing the outer plate 41 from rotating relative to the housing 1. The inner plate 43 includes, for example, a plurality of radially inwardly projecting lugs 49. The lugs 49 engage with lug grooves 51, preventing the inner plate 43 from rotating relative to the side gears 11. Therefore, when axial pressure is applied to the friction clutch 5, the side gears 11 are braked relative to the housing 1, thereby limiting the differential motion between the side gears 11.

[0031] The elastic body 7 can be interposed between the block 9 and the side gear 11, and can press the side gear 11 toward the friction clutch 5 by its elastic force. In addition, the block 9 supports the back surface of the elastic body 7, so that the block 9 bears the reaction force.

[0032] The elastomer 7 can also be applied to any element that generates sufficient elastic force, but one example is a so-called disc spring made of an elastic material such as spring steel, which is a circular ring and slightly protrudes toward its center. Multiple disc springs can be stacked, or they can also be springs of other forms. In the case of disc springs, they can be oriented in a conical shape toward the side gear 11. In this orientation, the inner periphery of the elastomer 7 is in contact with the side gear 11, and the outer periphery is in contact with the block 9. Therefore, when the side gear 11 rotates relative to the block 9, the elastomer 7 stays on the block 9 and does not rotate with the side gear 11. Since the elastomer 7 does not rub the block 9 strongly, it can prevent its wear even when the block 9 is made of a relatively soft material.

[0033] Block 9 is not essential; it can be, for example, a cylinder circumferentially around axis C, with a through-hole through which pinion shaft 13 passes. Block 9 contacts elastic body 7 at both ends, absorbing its reaction force. The through-hole and pinion shaft 13 are dimensioned to ensure close contact. Therefore, the reaction force from friction clutch 5 is ultimately borne by pinion shaft 13. The contact between the two is sufficient for pinion shaft 13 to absorb the reaction force, but allows for sufficient play to ensure smooth insertion of pinion shaft 13 into the through-hole.

[0034] The above differential device can be assembled as follows. Figure 1 First, the right friction clutch 5 and the right gear 11 are housed in the housing 1. Next, the right elastic body 7 and the block 9 are housed, and the pinion 15 is meshed with the right gear 11. At this moment, it should be noted that the pinion shaft 13 has not yet been assembled.

[0035] Combine Figure 1 , refer to Figure 2 Using an appropriate fixture, block 9 is pressed toward right-hand gear 11 against the elastic force generated by elastic body 7. This aligns axial hole 19 in housing 1, the through-hole of pinion 15, and the through-hole of block 9, allowing pinion shaft 13 to be inserted into these holes. The elastic force applied to block 9 is offset by the fixture, and as mentioned above, some play is allowed between the through-hole and pinion shaft 13, eliminating the need for pressure during insertion. Consequently, indentations on the surface of pinion shaft 13 are prevented.

[0036] The pinion shaft 13 is fixed relative to the housing 1 by the insertion pin 21. At this time, since the block 9 is in close contact with the pinion shaft 13 and resists the elastic force generated by the elastic body 7, the components will not fall off from the housing 1 even if the clamp is removed.

[0037] Next, the left elastic body 7 is placed on the block 9, and the left gear 11 is housed in the housing 1 along with the friction clutch 5. The cover 31 is pressed against the elastic force and fastened to the main body of the housing 1 along with the ring gear 33, thereby assembling the differential device. When the cover 31 is pressed, the block 9 also resists the pressure, so the pressing force does not affect the internal components.

[0038] Reference Figure 3 The differential device according to this embodiment operates as follows.

[0039] When there is no rotational speed difference between the left and right axles, the housing 1, the side gears 11, and the pinion shaft 13 rotate or stop integrally about the axis C. At this point, the elastic body 7 applies a preload f1 to the side gears 11, which acts on the friction clutch 5, thereby generating a pre-existing differential limiting force. At this point, the left and right reaction forces f1R applied to the block 9 are balanced, allowing the components to maintain stable positions even when the pinion shaft 13 is not supporting the block 9.

[0040] When a speed difference occurs between the left and right axles, the side gear 11 rotates while meshing with the pinion 15, generating a meshing reaction force f2. This meshing reaction force f2 presses the side gear 11 outward toward the axis C. The combined force of this force and the preload f1 acts on the friction clutch 5, increasing the differential limiting force.

[0041] Meanwhile, the friction clutch 5 generates a reaction force FR, with the pinion 15 bearing a portion f2R and the block 9 bearing the remaining portion f1R via the elastic body 7. Both are supported by the pinion shaft 13 and ultimately by the housing 1. It should be noted that the pressing force and reaction force are balanced on the right side of the housing 1 and also on the left side, with neither affecting the other. While the reaction force may differ on the right and left sides depending on the speed difference and traction difference between the left and right wheels, this does not adversely affect either side.

[0042] Since force is applied only in the direction along the axis C to the side gear 11 and the friction clutch 5 is perpendicular to the axis C and supports the side gear 11, the side gear 11 is not eccentric with respect to the axis C. The side gear 11 is stabilized in its original position by positioning only by the bearing portion 1B, and there is no need to support the side gear 11 on the outer periphery, for example.

[0043] Several embodiments have been described, but corrections or modifications can be made to the embodiments based on the above disclosure.

Claims

1. A differential device comprising: a housing capable of rotating about an axis; The differential gear set includes: a pair of side gears housed in the housing and rotatable about the shaft; a pinion shaft perpendicular to the shaft and passing through the housing and fixed so as to rotate about the shaft together with the housing; and a pinion gear rotatably supported on the pinion shaft and meshing with the side gears to allow differential motion between the side gears; a friction clutch interposed between the side gear and the inner surface of the housing to limit the differential; a pair of elastic bodies, each applying pre-compression to the friction clutch in the direction of the shaft; as well as a block which contacts both sides of the elastic body and supports the elastic body in the direction of the axis, and is engaged with the pinion shaft so that the reaction force received from the friction clutch via the elastic body is borne by the pinion shaft, The differential device is characterized in that: The elastic bodies are respectively interposed between the blocks and the side gears. The inner peripheries of the elastic bodies are in contact with the side gears, and the outer peripheries of the elastic bodies are in contact with the blocks.

2. The differential device according to claim 1, characterized in that: Each of the side gears includes a boss portion rotatably fitted to the housing and a gear portion meshing with the pinion gear. Each of the side gears is positioned only when the boss portion contacts the housing.

3. The differential device according to claim 2, characterized in that: The friction clutch is interposed between the rear surface of the gear portion and the inner surface of the housing.

4. The differential device according to claim 1, wherein: The friction clutches are respectively multi-plate clutches.

5. The differential device according to claim 1, wherein: The elastic bodies are respectively disc springs tapered toward the side gears.

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