differential gear

Abstract

To provide a differential gear device capable of preventing or suppressing action of excessive torque by a torque limiting function and being miniaturized.SOLUTION: A differential mechanism 3 is housed inside of a casing 2, a ring gear 4 for transmitting torque from the external is retained by the casing 2, and the ring gear 4 is mounted on the casing 2 rotatably to the casing 2 and movably in a direction of a rotation center axis. A frictional portion 13 generating frictional force to inhibit relative rotation of the ring gear 4 and the casing 2 is disposed between the ring gear 4 and the casing 2, an elastic member 12 is disposed to press the ring gear 4 in a direction to increase the frictional force at the frictional portion 13, and the torque transmittable between the ring gear 4 and the casing 2 is determined to be the torque based on the pressing force by the elastic member 12 and the frictional force of the frictional portion 13.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a differential gear device configured such that a casing serves as an input element, a differential mechanism is housed inside the casing, and output is provided from the differential mechanism. [Background technology]

[0002] This type of differential gear device is widely used, for example, as a final reduction gear that transmits torque to the left and right drive wheels of a vehicle while allowing differential movement between them. Patent Document 1 describes an example of such a differential structure. The differential gear device described in Patent Document 1 uses a differential case as an input element, and the differential case is provided with flanges extending outward. A ring gear (differential drive gear) attached to the differential case is provided with flanges extending inward and facing and contacting the flanges of the differential case. These flanges are brought into surface contact with each other and are fastened together with bolts that pass through the flanges, thereby fixing the ring gear to the differential case. In the structure described in Patent Document 1, the contact surface between the ring gear and the differential case is tapered to prevent the bolts from loosening. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-91449 Summary of the Invention [Problem to be solved by the invention]

[0004] The differential gear device described in Patent Document 1 is sometimes used as a final reduction gear in a vehicle. In this case, large torque and vibration may act between the ring gear and the differential case. Therefore, as described in Patent Document 1, it is desirable to adopt a configuration that suppresses bolt loosening, and it is also desirable to ensure sufficient strength. In particular, in electric vehicles (EVs) and hybrid vehicles (HEVs, PHEVs) that use electric motors as their driving power sources, the maximum torque that acts instantaneously, including inertia torque, is large, so it is necessary to maintain strength that can withstand this. However, providing a sufficient strength to withstand the maximum torque would result in an increase in size, which could reduce on-board compatibility when used in a vehicle, for example. On the other hand, adding a torque limiter to prevent the application of temporary excessive torque could be considered, but even if such a configuration could reduce the need for increased strength, the added torque limiter could result in an increase in the size of the differential gear device. When a differential gear unit is used as a final reduction gear in a vehicle, it may be integrated with a transmission mechanism and the like to form a transaxle. In such cases, there is an even greater demand for compactness and lighter weight, and there is considerable room for the development of new technologies for compactness without compromising durability.

[0005] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a differential gear device that can avoid or suppress the application of excessive torque and that can be made compact. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a differential gear device in which a differential mechanism is housed inside a casing, and a ring gear that transmits torque from outside is held by the casing, wherein the ring gear is attached to the casing so as to be rotatable relative to the casing and movable in the direction of a rotation center axis, a friction portion is provided between the ring gear and the casing to generate a friction force that prevents relative rotation between the ring gear and the casing, and an elastic member is provided to press the ring gear in a direction that increases the friction force at the friction portion, and the torque that can be transmitted between the ring gear and the casing is set to a torque based on the pressing force of the elastic member and the friction force of the friction portion The ring gear is a helical gear that generates a thrust force in a direction that compresses the elastic member and reduces the contact pressure at the friction portion based on torque transmitted from an external source. It is characterized by the following.

[0008] In the present invention, the friction portion may include a first tapered surface and a second tapered surface that come into surface contact with each other to generate the friction force.

[0009] In this invention, an annular member that rotates integrally with the casing may be disposed adjacent to the ring gear on the same axis as the ring gear, the first tapered surface being formed on the ring gear, and the second tapered surface being formed on the annular member. 。 The present invention also provides a differential gear device in which a differential mechanism is housed inside a casing and a ring gear that transmits torque from the outside is held by the casing, wherein the ring gear is attached to the casing so as to be rotatable relative to the casing and movable in the direction of the rotation center axis, a friction portion is provided between the ring gear and the casing to generate a friction force that prevents relative rotation between the ring gear and the casing, an elastic member is provided to press the ring gear in a direction that increases the friction force at the friction portion, the torque that can be transmitted between the ring gear and the casing is set to a torque based on the pressing force of the elastic member and the friction force of the friction portion, the friction portion has a first tapered surface and a second tapered surface that come into surface contact with each other to generate the friction force, an annular member that rotates integrally with the casing is arranged adjacent to the ring gear and on the same axis, the first tapered surface is formed on the ring gear, and the second tapered surface is formed on the annular member.

[0010] In this invention, the differential mechanism may have a pair of side gears arranged opposite each other on the same axis inside the casing, a pinion gear arranged between the side gears and meshing with the side gears to rotate on its own axis and revolve around the axis, and a pinion shaft that holds the pinion gear rotatably and is attached to the casing, and the annular member may be connected to the pinion shaft. [Effects of the Invention]

[0011] In this invention, the ring gear, which serves as the input element, is attached or connected to the casing by a friction portion. Therefore, conventional fastening means such as set bolts are not required, allowing for a smaller, lighter differential gear unit. This also reduces manufacturing steps and improves manufacturability. The friction portion transmits torque according to the contact pressure applied by the elastic member, and slips when torque exceeding this pressure acts. In other words, it functions as a torque limiter. Therefore, in this invention, the friction portion serves both as a means for holding the ring gear to the casing and as a function for limiting the transmitted torque. This prevents or suppresses the application of excessive torque, and eliminates the need for high strength to accommodate excessive torque, allowing for a smaller, lighter differential gear unit.

[0012] Furthermore, if the ring gear is configured as a helical gear so that a thrust force corresponding to the torque input to the ring gear acts on the friction portion or the elastic member, excessive torque will appear as a thrust force or a force that compresses the elastic member and reduces the contact pressure at the friction portion, so that excessive torque can be reliably blocked.

[0013] If the friction portion is configured with a tapered surface or if the second tapered surface is formed on the annular member, the elastic force of the elastic member required to generate a necessary and sufficient friction force can be reduced, which also makes it possible to make the differential gear device smaller and lighter.

[0014] If the annular member that constitutes the friction portion is connected to the pinion shaft, the torque from the ring gear can be transmitted to the differential mechanism without going through the casing, thereby reducing the number of components, simplifying the overall configuration, and making it smaller and lighter. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing an embodiment of the present invention. [Figure 2] FIG. 2 is a partially cutaway side view illustrating the configuration of the ring gear. [Figure 3] FIG. 4 is a partial view showing a connection state between the annular member and the pinion shaft. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is merely an example of how the present invention can be implemented, and is not intended to limit the present invention.

[0017] Figure 1 shows a cross-sectional view of a differential gear device 1 according to an embodiment of the present invention. The differential gear device 1 shown here houses a differential mechanism 3 inside a casing (hereinafter referred to as a differential case) 2, holds a ring gear 4 that transmits torque from the outside in the differential case 2, and is configured to output torque in two directions from the differential mechanism 3, making it similar to conventionally known differential gear devices in these respects. That is, the differential case 2 is a hollow member with a so-called frame-like (frame structure) shape formed with openings for assembly and for the inflow and outflow of lubricating oil, and has a cylindrical boss portion 5 formed in the left-right direction of Figure 1 that protrudes on the same axis.

[0018] Describing the differential mechanism 3 disposed inside this differential case 2, left and right side gears 6 are disposed with their central axes aligned with the boss portion 5. These side gears 6 are bevel gears, and in a vehicle, are connected to a drive shaft (not shown) to output driving torque to the drive shaft. In other words, the side gears 6 serve as so-called output elements. A pair of pinion gears 7 meshing with these side gears 6 are disposed symmetrically about the central axis of the boss portion 5 (the central axis of the side gears 6). These pinion gears 7 are bevel gears like the side gears 6, and are rotatably held by pinion shafts 8 that pass through along their respective central rotation axes.

[0019] The pinion shaft 8 passes through the differential case 2 and is fixed to the differential case 2 by a pinion pin 9. The pinion pin 9 is inserted into a pin hole formed by passing through the pinion shaft 8 in the diameter direction at the portion of the pinion shaft 8 that is inserted into the differential case 2, and is fitted into both the differential case 2 and the pinion shaft 8. Therefore, the pinion gear 7 can rotate about the pinion shaft 8 and revolve together with the differential case 2. As such, the basic configuration of the differential mechanism 3 described above is similar to the configuration of a conventionally known general differential mechanism. Although not specifically described, bearing members are arranged in sliding portions, such as between each of the gears 6, 7 and the differential case 2.

[0020] The mechanism for transmitting torque from an external source to the differential case 2 is unique to this embodiment of the present invention. Specifically, the differential case 2 includes a ring gear 4 as a member for transmitting torque. The ring gear 4 is a so-called external gear with teeth 4a formed on its outer circumferential surface. A cylindrical mounting seat 10 with an outer diameter equal to the inner diameter of the ring gear 4 is formed on the outer periphery of the differential case 2, at a location offset from the extension of the pinion shaft 8 toward the central axis of the side gear 6. A flange portion 11 extending outward from the outer periphery of the mounting seat 10 is formed on the side opposite the pinion shaft 8. The ring gear 4 is mounted on the mounting seat 10 rotatably and axially movable. An elastic member 12 is disposed between the flange portion 11 and the ring gear 4 to press the ring gear 4 toward the pinion shaft 8. The elastic member 12 may be a spring such as a coil spring or a diaphragm spring, or a so-called volume elastic body whose volume changes elastically.

[0021] 2, the ring gear 4 is a helical gear whose teeth 4a are twisted relative to the central axis of rotation, and therefore, when torque is transmitted between the ring gear 4 and another gear (not shown) meshing with it, a force (thrust force) acts on the ring gear 4 in the axial direction. In the embodiment shown in FIG. 1, when torque is input in a direction that rotates the ring gear 4 forward (a direction that moves the vehicle forward), a thrust force is generated in a direction that compresses the elastic member 12.

[0022] As described above, the ring gear 4 is not directly fixed to the differential case 2. In other words, there are no set bolts or other components for fixing the ring gear 4 to the differential case 2, which reduces the overall configuration and manufacturing man-hours. A mechanism that functions as a torque limiter to limit the transmitted torque is used as the mechanism for transmitting torque from the ring gear 4 to the differential case 2.

[0023] As shown in FIGS. 1 and 2, a tapered surface 13a that functions as a friction surface is formed on the inner periphery of the ring gear 4, on the side opposite the elastic member 12. The tapered surface 13a has a small inner diameter toward the center in the width direction of the ring gear 4 and gradually increases toward the side opposite the elastic member 12. An annular member 14, on which a tapered surface 13b that pairs with the tapered surface 13a is formed, is fitted into the differential case 2 at a position where the pinion shaft 8 extends. Both ends of the pinion shaft 8 are inserted into the annular member 14, forming a single unit (see FIG. 3). Therefore, the ring gear 4 is connected to the differential case 2 via the tapered surfaces 13a and 13b, the annular member 14, and the pinion shaft 8.

[0024] 1 by the elastic member 12, while the annular member 14 is fixed to the differential case 2 via the pinion shaft 8, so that the tapered surface 13a of the ring gear 4 and the tapered surface 13b of the annular member 14 are in frictional contact. Torque corresponding to this contact pressure (frictional force) is transmitted between the ring gear 4 and the annular member 14 (or the differential case 2), and therefore these tapered surfaces 13a and 13b serve as friction portions 13 for torque transmission.

[0025] The torque that can be transmitted by the friction portion 13 is a torque corresponding to the friction force between the tapered surfaces 13a, 13b, and this friction force is determined by the elastic force (pressing force) of the elastic member 12 and the thrust force (thrust force in the direction that reduces the contact pressure) that accompanies the torque transmission by the ring gear 4. In other words, the torque that can be transmitted by the friction portion 13 is appropriately determined by adjusting the elastic force (pressing force) of the elastic member 12. When torque that exceeds the torque that can be transmitted by the friction portion 13 determined in this manner is input to the ring gear 4, slippage occurs at the friction portion 13, and the transmission of the torque is limited. In this way, the friction portion 13 functions as a torque limiter in addition to connecting the ring gear 4 to the differential case 2.

[0026] In the differential gear device 1 according to the embodiment of the present invention described above, when torque is input to the ring gear 4 from the outside, the torque is transmitted to the annular member 14 via the friction portion 13 between the ring gear 4 and the annular member 14. The annular member 14 is connected to the pinion shaft 8, which is inserted into the differential case 2 and fixed to the differential case 2 by the pinion pin 9. Therefore, the torque input to the ring gear 4 is transmitted to the differential case 2. In other words, the differential case 2 rotates integrally with the ring gear 4. The pinion gear 7 provided inside the differential case 2 revolves together with the differential case 2, and torque is transmitted from the pinion gear 7 to the left and right side gears 6, thereby rotating the side gears 6 and the rotation shafts, such as drive shafts (not shown) connected to the side gears 6. In this case, the pinion gear 7 rotates about the pinion shaft 8, causing the left and right side gears 6 to rotate differentially.

[0027] For example, when the differential gear device 1 is incorporated into a transaxle (not shown) and used as a drive device for a vehicle, the input torque to the differential gear device 1 may increase instantaneously when the accelerator pedal is suddenly depressed or when a spinning drive wheel regains its grip. In this case, if the torque input to the differential gear device 1 via the ring gear 4 exceeds the torque that can be transmitted by the friction portion 13, slippage occurs between the tapered surfaces 13a, 13b of the friction portion 13, restricting the transmission of torque.

[0028] According to the differential gear device 1 of the embodiment of the present invention, as described above, excessive torque exceeding a torque corresponding to a preset strength is not applied to the differential case 2 or the differential mechanism 3 therein, so that damage to the differential gear device 1 can be prevented in advance, and situations such as increasing the size in order to increase the strength can be avoided, thereby making the differential gear device 1 smaller and lighter.

[0029] In the above-described embodiment, the annular member 14 is integrated with the differential case 2 by connecting the annular member 14 to the pinion shaft 8. However, in the present invention, the annular member may be fixed to the differential case. Also, one of the tapered surfaces constituting the friction portion may be formed on the differential case instead of on the annular member, in which case the annular member can be omitted. Furthermore, the friction portion in the present invention may be formed by a pair of friction surfaces having a shape other than a pair of tapered surfaces. [Explanation of symbols]

[0030] 1 Differential gear unit 2 Casing (differential case) 3 Differential mechanism 4 ring gear 5 Boss section 6 Side Gear 7 Pinion gear 8 Pinion shaft 9 Pinion pin 10 Mounting seat 11 Flange 12 Elastic member 13 Friction part 13a, 13b Tapered surface 14 Annular member

Claims

1. A differential gear device in which a differential mechanism is housed inside a casing and a ring gear that transmits torque from an outside is held by the casing, the ring gear is attached to the casing so as to be rotatable relative to the casing and movable in the direction of the rotation center axis, a friction portion is provided between the ring gear and the casing to generate a friction force that prevents relative rotation between the ring gear and the casing, an elastic member is provided that presses the ring gear in a direction that increases the friction force at the friction portion; a torque that can be transmitted between the ring gear and the casing is set to a torque based on the pressing force of the elastic member and the friction force of the friction portion, The ring gear is a helical gear that generates a thrust force in a direction that compresses the elastic member and reduces the contact pressure at the friction portion based on torque transmitted from an external source. A differential gear device characterized by:

2. 2. The differential gear device according to claim 1, The friction portion includes a first tapered surface and a second tapered surface that are in surface contact with each other to generate the friction force. A differential gear device characterized by:

3. 3. The differential gear device according to claim 2, an annular member that rotates integrally with the casing is disposed adjacent to the ring gear on the same axis as the ring gear; the first tapered surface is formed on the ring gear, The second tapered surface is formed on the annular member. A differential gear device characterized by:

4. A differential gear device in which a differential mechanism is housed inside a casing and a ring gear that transmits torque from the outside is held by the casing, the ring gear is attached to the casing so as to be rotatable relative to the casing and movable in the direction of the rotation center axis, a friction portion is provided between the ring gear and the casing to generate a friction force that prevents relative rotation between the ring gear and the casing, an elastic member is provided that presses the ring gear in a direction that increases the friction force at the friction portion; a torque that can be transmitted between the ring gear and the casing is set to a torque based on the pressing force of the elastic member and the friction force of the friction portion, the friction portion includes a first tapered surface and a second tapered surface that are in surface contact with each other to generate the friction force, an annular member that rotates integrally with the casing is disposed adjacent to the ring gear on the same axis as the ring gear; the first tapered surface is formed on the ring gear, The second tapered surface is formed on the annular member. A differential gear device characterized by:

5. 5. A differential gear device according to claim 3 or 4, the differential mechanism includes a pair of side gears arranged opposite to each other on the same axis inside the casing, a pinion gear arranged between the side gears and meshing with the side gears to rotate on its own axis and revolve around the axis, and a pinion shaft that rotatably holds the pinion gear and is attached to the casing, The annular member is connected to the pinion shaft. A differential gear device characterized by:

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