Seal structure of joint

Abstract

To provide a seal structure of a joint having improved sealing performance by reducing the action of grease to leak by centrifugal force.SOLUTION: The seal member 8 includes a lip portion side 8a extending from a base portion side 8c fitted to the support shaft 4 toward the outer race 7 and contacting the outer surface of the outer race 7, the lip portion side 8c has a shape protruding outward in the radial direction with respect to the center axial line of the support shaft 4, and a tip portion side 8d has a shape curved from the outside toward the inside in the radial direction of the outer race 7 and contacting the outer surface of the outer race 7. Further, the inner surface of the lip portion forms a curved surface 8d in which the rotation radius from the rotation center axis of the spider gradually increases on the tip end portion 8e side in contact with the outer surface of the outer race, the curved surface 8e has a bent portion 8d on the base portion 8a side with respect to the tip end portion 8f, and the increase ratio of the rotation radius in the curved surface 8f on the tip end portion 8d side with the bent portion 8e interposed therebetween is smaller than the increase ratio of the rotation radius in the curved surface on the base portion side with the bent portion interposed therebetween. 8f 8a 8e.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a seal structure for a joint used in, for example, a propeller shaft of a vehicle. [Background technology]

[0002] Patent Document 1 describes an example of this type of seal structure. Briefly, the spider, which is the cross shaft of a universal joint, has shanks protruding in four directions (up, down, left, and right). Bearings are attached to these shanks, with cups serving as outer races. A lip seal is provided to create a liquid-tight seal between the cup and the shank. Pressure inside the lip seal increases due to factors such as temperature rise, which could lead to leakage of grease or other substances contained inside. To prevent or mitigate this, an air vent passage is provided between the lip seal and the spider to release pressure to the outside when pressure inside the cup increases. Therefore, the lip seal described in Patent Document 1 is said to be able to prevent seal deformation caused by the seal lip, which is the grease lip of the lip seal, turning over or opening due to pressure increases or decreases inside the cup. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-257406 Summary of the Invention [Problem to be solved by the invention]

[0004] The lip seal described in Patent Document 1 releases pressure inside the cup to prevent lip deformation and opening of the seal. However, this configuration has a lip shape that opens when internal pressure increases. Therefore, when centrifugal force acts on the lip, or when centrifugal force acts on the lubricant inside the lip and the lubricant tries to push the lip open, the air inside escapes to the outside, just as when internal pressure increases. Therefore, if centrifugal force is applied frequently or over a long period of time, the lubricant inside may leak out along with the air.

[0005] The present invention has been made in light of the above technical problems, and aims to provide a seal structure for a joint that reduces the tendency of grease to leak out due to centrifugal force, thereby improving sealing performance. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a seal structure for a joint having a spider on which four support shafts protruding in the radial direction with respect to a rotation center axis are arranged at equal intervals in the circumferential direction, a clevis is rotatably fitted to the support shafts via a bearing lubricated by a lubricant, and a pair of rotating shafts are connected to the clevis, thereby rotatably connecting the pair of rotating shafts via the spider, the bearing having an outer race that holds rolling elements, and a seal member is provided that makes a liquid-tight seal between the support shafts and the outer race by contacting the outer surface of the outer race when fitted to the support shafts, and the seal member extends from a base that fits to the support shafts towards the outer race. the lip portion is shaped so as to curve radially outward relative to the central axis of the support shaft and has a tip portion that curves inward in the radial direction of the outer race to contact the outer surface of the outer race, the inner surface of the lip portion is a curved surface whose radius of rotation from the central axis of rotation of the spider gradually increases toward the tip portion where the curved surface is in contact with the outer surface of the outer race, the curved surface having a bent portion closer to the base than the tip portion, and the rate of increase in the radius of rotation of the curved surface on the tip side across the bent portion is smaller than the rate of increase in the radius of rotation of the curved surface on the base side across the bent portion. [Effects of the Invention]

[0007] In the seal structure of the joint of the present invention, the rate of increase in the radius of rotation of the curved surface on the tip side of the bend is smaller than the rate of increase in the radius of rotation of the curved surface on the base side of the bend. That is, the angle of the curved surface on the tip side of the bend relative to the outer surface of the outer race, in other words, the angle relative to the direction in which the lubricant tends to flow, is larger. This reduces the component of force acting toward the tip (toward the bottom of the outer race) due to centrifugal force. In other words, the force that causes the grease to escape outward due to centrifugal force is weakened, reducing the tendency for the grease to leak out of the seal member and improving sealing performance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating the configuration of a universal joint. [Figure 2] FIG. 2 is a cross-sectional view illustrating the configuration of a spider of a universal joint, taken along a plane perpendicular to the central axis of rotation. [Figure 3] FIG. 3 is a cross-sectional view illustrating an enlarged view of part A in FIG. 2, illustrating the seal structure of the joint of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The following description of preferred embodiments of the present invention will be given with reference to the accompanying drawings. Note that the following embodiments are merely examples of the present invention and are not intended to limit the scope of the present invention.

[0010] The present invention relates to a seal structure in a joint that connects rotating shafts, and one example of such a joint is a universal joint that uses a spider, as shown in Figure 1. The universal joint (hereinafter sometimes simply referred to as a joint) 1 shown in Figure 1 has a conventionally known structure, and is configured by connecting a pair of double knuckles (or clevises) 2 with a common spider 3. A rotating shaft S is connected to each knuckle 2, and each knuckle 2 can rotate relative to the spider 3, so that each rotating shaft S is connected in a bent state at the spider 3, and torque can be transmitted between them in this bent state.

[0011] As is well known, the spider 3 is a cross-shaped member in a front view, with support shafts 4 that protrude at equal intervals around the center in four mutually perpendicular directions, up and down and left and right. A partial cross-sectional view is shown in Figure 2. In the spider, one knuckle 2 is rotatably fitted to a pair of upper and lower support shafts 4, and the other knuckle 2 is rotatably fitted to a pair of left and right support shafts 4. Therefore, one knuckle 2 can rotate about the pair of upper and lower support shafts 4, and the other knuckle 2 can rotate about the pair of left and right support shafts 4, so that the rotation axis S is bent relatively at a predetermined angle and rotatably connected.

[0012] The connection structure between each support shaft 4 and the knuckle 2 will now be described. Figure 2 shows a cross-sectional view of the fitting portion. There are four fitting portions between the support shafts 4 and the knuckle 2, the same number as the number of support shafts 4. However, since all of them have the same configuration, the same reference numerals will be used for parts or components with the same names.

[0013] A bearing 5 is provided between the support shaft 4 and the knuckle 2 so that they can rotate relative to each other. The bearing 5 may be any conventional bearing, such as a sliding bearing or a rotary bearing. In the example shown in FIG. 2, a roller bearing is used as the bearing 5. That is, the bearing 5 is a rotary bearing whose rolling elements are multiple rollers (or rolling pins) 6 arranged along the outer circumferential surface of the support shaft 4. The rollers 6 are arranged along the inner circumferential surface of a cap 7 with their central axes of rotation parallel to the central axis of the support shaft 4. The rollers 6 are held by the cap 7 in close contact with the outer circumferential surface of the support shaft 4. Therefore, the outer circumferential surface of the support shaft 4 forms the inner case of the bearing 5, and the inner circumferential surface of the cap 7 forms the outer race of the bearing 5.

[0014] As shown in Fig. 2, cap 7 is a cylindrical metal member with a bottom that covers the entire tip of support shaft 4. Therefore, the tip sides of support shaft 4 and bearing 5 (the radially outer side of spider 3) are covered by the bottom of cap 7 and shielded from the outside, preventing the intrusion of dust and moisture and the leakage of lubricant. In contrast, a sealing member 8 made of an elastic material such as rubber is provided at the base of support shaft 4, in other words, at the open end side of cap 7.

[0015] The seal member 8 is provided to prevent dust, muddy water, and the like from entering the bearing 5 from the base side of the support shaft 4 and to prevent lubricants such as grease from leaking. The seal member 8 is formed in an annular shape as a whole, as shown in Figure 2. Meanwhile, a boss portion 9 with a diameter slightly larger than the outer diameter of the support shaft 4 (the outer diameter of the portion in contact with the roller 6) is formed at the base of the support shaft 4. The seal member 8 fits into this boss portion 9 in a liquid-tight manner.

[0016] The cross-sectional shape of the sealing member 8 is shown enlarged in Fig. 3. Here, the cross section is a cross section obtained by cutting along a plane perpendicular to the central axis of rotation of the spider 3, as shown in Fig. 2 and Fig. 3, or a cross section obtained by cutting along a plane including the central axis of the sealing member 8 (or the central axis of the support shaft 4 and the cap 7 attached thereto).

[0017] The seal member 8 has a thick base 8a that fits into the boss 9, and two lip portions 8b, 8c that extend from the base 8a toward the open end of the cap 7. One of the lip portions, 8b, is a thin annular piece that extends axially (toward the open end of the cap 7) from the inner circumferential portion of the side surface of the base 8a, and will be referred to hereinafter as the grease lip portion 8b. The other lip portion 8c is a thin annular piece that extends axially (toward the open end of the cap 7) from the outer circumferential portion of the side surface of the base 8a, and will be referred to hereinafter as the dust lip portion 8c.

[0018] The grease lip portion 8b has a smaller diameter than the dust lip portion 8c and protrudes less in the axial direction. This grease lip portion 8b contacts the side surface of the tip side of the cap 7 (the base side of the support shaft 4), with its lip tip facing outward in the radial direction of the support shaft 4. In contrast, the dust lip portion 8c is an annular piece with a diameter roughly equal to the outer diameter of the cap 7, and its length in the axial direction is longer than that of the grease lip portion 8b. The tip portion 8d of the dust lip portion 8c almost reaches the outer peripheral surface of the cap 7 and contacts the outer surface of the cap 7. Therefore, the inner peripheral portion of the cap 7 is shielded from the outside by these lips 8b and 8c, preventing or suppressing dust and leakage of lubricant.

[0019] The shape of the dust lip 8c will be described in more detail. The dust lip 8c has a shape that curves from the outside to the inside in the radial direction of the cap 7 and contacts the outer peripheral surface of the tip side of the cap 7, or the outer surface of the corner portion extending from the outer peripheral surface to the side. Furthermore, as shown enlarged in Figure 3, the inner surface of the dust lip 8c has a convex arc-shaped cross section, forming a curved surface 8e where the radius of rotation from the rotation center axis of the spider 3 gradually increases toward the tip portion 8d that contacts the outer surface of the cap 7.

[0020] The curved surface 8e has a bent portion 8f closer to the base 8a than the tip 8d, and the rate of increase in the radius of rotation of the curved surface 8e on the tip 8d side of the bent portion 8f is smaller than the rate of increase in the radius of rotation of the curved surface 8e on the base 8a side of the bent portion 8f. Here, the rate of increase in the radius of rotation is the amount of increase in the distance (radius of rotation) between the curved surface 8e and the center of rotation of the spider 3 per unit amount of central angle at the center of rotation.

[0021] Grease 10 used as a lubricant for bearing 5 is stored in a space 11 surrounded by the tip side of cap 7 (the base side of support shaft 4) or the inner side of cap 7 and the radially inner side of support shaft 4 of grease lip portion 8b.

[0022] Next, the operation and effect of the seal structure of the joint of the present invention will be described. When the spider 3 rotates, a centrifugal force F is generated in the radial direction of the rotation axis, as shown in Figures 2 and 3. The centrifugal force F also acts on the grease 10 inside the seal member 8, and inside the dust lip 8c, the grease 10 is pressed against the curved surface 8e, which is the inner circumferential surface of the dust lip 8c. As described above, the curved surface 8e is curved so that the radius of rotation (the radius from the rotation center of the spider 3) gradually increases toward the tip of the dust lip 8c. Therefore, the grease 10 pressed against the curved surface 8e is pushed toward the tip of the dust lip 8c along the curved surface 8e. The force pushing the grease 10 along the curved surface 8e increases as the angle between the direction of action of the centrifugal force F and the tangent to the curved surface 8e decreases, as explained using the cross-sectional view of Figure 3. In other words, when the centrifugal force F is decomposed into a normal component Fa at a predetermined point on the curved surface 8e and a tangential component Fb in a direction along the curved surface 8e, the tangential component Fb becomes the force that pushes the grease 10 in a direction along the curved surface 8e.

[0023] As described above, the curved surface 8e has a bent portion 8f, and the rate of increase in the radius of gyration of the curved surface 8e on the side of the tip 8d across the bent portion 8f is smaller than the rate of increase in the radius of gyration of the curved surface 8e on the side of the base 8a across the bent portion 8f. Therefore, the angle between the direction in which the centrifugal force F acts and the tangent to the curved surface 8e is smaller on the side of the base 8a across the bent portion 8f and larger on the side of the tip 8d across the bent portion 8f. Explaining this in terms of the component force Fb acting along the curved surface 8e, the component force Fb is larger on the side of the base 8a across the bent portion 8f and smaller on the side of the tip 8d across the bent portion 8f. The force or action that pushes the grease 10 along the curved surface 8e is the force or action that pushes the grease 10 out of the sealing member 8, so in the above-described embodiment, the force (component force Fb) becomes smaller on the tip 8d side of the dust lip portion 8c, thereby reducing the action that causes the grease 10 to leak out of the sealing member 8 and improving sealing performance. [Explanation of symbols]

[0024] 1 Universal Joint 2 Knuckles 3. Spider 4 Support shaft 5. Bearings 6. Laura 7 Cap 8 Sealing material 8a base 8b Grease lip 8c Dust Lip 8d Tip 8e Curved surface 8f bent part 9 Boss section 10 Grease 11 Space F centrifugal force S rotation axis

Claims

[Claim 1] A seal structure for a joint in which four support shafts protruding in the radial direction relative to a central axis of rotation have spiders arranged at equal intervals in the circumferential direction, a clevis is rotatably fitted to the support shafts via a bearing lubricated by a lubricant, and a pair of rotating shafts are connected to the clevis, thereby rotatably connecting the pair of rotating shafts via the spiders, The bearing has an outer race that holds the rolling elements, a seal member that contacts an outer surface of the outer race when fitted onto the support shaft to provide a liquid-tight seal between the support shaft and the outer race; the seal member includes a lip portion that extends from a base portion that fits onto the support shaft toward the outer race and contacts an outer surface of the outer race, the lip portion is shaped to be convex outward in a radial direction relative to a central axis of the support shaft, and a tip portion thereof is curved from the outside toward the inside in the radial direction of the outer race to contact the outer surface of the outer race, Furthermore, the inner surface of the lip portion is a curved surface whose radius of rotation gradually increases from the rotation center axis of the spider toward the tip end portion where the tip end contacts the outer surface of the outer race, the curved surface has a bent portion closer to the base portion than the tip portion, The rate of increase of the radius of rotation on the curved surface on the distal end side across the bent portion is smaller than the rate of increase of the radius of rotation on the curved surface on the proximal side across the bent portion. A seal structure for a joint characterized by:

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