Grommet

Abstract

To realize a grommet which is attached between one side and the other side where a negative pressure relative to that at the one side is created to make a seal with a harness and which maintains high sealability with the harness in a reliable manner even in a state where the negative pressure is applied from the other side.SOLUTION: A grommet includes thick outer frame parts 1a, 1b and an insertion part 2 into which a harness H is inserted. The insertion part is connected to the outer frame parts and includes a thin seal part 3 in which a harness insertion opening 2a is provided at a center. A peripheral edge of the harness insertion opening is provided with a lip 4 which makes pressure contact with an outer peripheral surface of the harness to make a seal between one side and the other side. The seal part is formed having a non-linear cross section so that the lip is located at one side relative to base parts 5 each serving as a connection part connected to the outer frame part and contacts with the harness and an intermediate part between the base part and the lip is recessed relative to the other side. When a negative pressure is applied from the other side, the seal part acts so that a contact pressure of the lip applied to the harness increases.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a grommet that is mounted between an exterior side that is the outside of a case and an interior side that is the inside of the case, and that maintains a tight seal with a harness. [Background technology]

[0002] Sealing devices called grommets or bush cords have been used to provide waterproof and dustproof sealing to harnesses inserted into holes in electrical boxes, terminal boxes, etc. For example, the screw-type cord bushing of Patent Document 1, as shown in Fig. 5, includes a cylindrical insertion portion 21, a flange portion 22 formed at one end of the insertion portion 21, and an annular lip 23 formed at the other end of the insertion portion 21.

[0003] As shown in Fig. 6, the lip 23 covers the opening on the tip side of the insertion portion 21 and has a circular opening 23a in the center. The lip 23 extends from the inner peripheral surface of the tip of the insertion portion 21 toward the insertion opening 2a of the insertion portion 21, curves at a predetermined curvature from the middle, and is formed in an annular shape that curves toward the tip side. Also, in Fig. 6, an aspect in which cords (corresponding to harness H) of different diameters are inserted into the opening 23a is shown by a two-dot chain line.

[0004] The lip 23 is formed so that the thickness from the inner peripheral surface of the insertion portion 21 to the opening 23a gradually decreases, and is configured to be thinnest at the opening 23a. In other words, it is disclosed that the lip 23 has an annular groove portion with a semicircular cross section formed from the tip side toward the flange portion 22 side, so that the center protrudes toward the tip side and the flange portion 22 side is formed in a curved shape. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-224436 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with the lip of the bush cord in Patent Document 1, when an electrical box or terminal box (hereinafter referred to as the case) has an electronic circuit such as an inverter inside, if negative pressure is applied from the inside of the electronic circuit due to temperature changes caused by heat emitted from the electronic circuit, the lip of the sealing portion will bend as if pulled inward, reducing the contact pressure of the lip against the harness and impairing the sealing performance.

[0007] Therefore, the present invention aims to provide a grommet that is attached between one side of the case (inside or outside) and the other side that is under negative pressure relative to the one side, and that seals the grommet with the harness, and that reliably maintains a high level of sealing with the harness even when negative pressure is applied from the other side. [Means for solving the problem]

[0008] In order to achieve the above object, the grommet of the first invention comprises: A grommet that is attached between one side and another side that is under negative pressure relative to the one side to seal between the harness, It has a thick outer frame portion and an insertion portion through which the harness is inserted, The insertion portion is a thin-walled seal portion connected to the outer frame portion and having a harness insertion opening at the center; a lip is provided on the periphery of the harness insertion opening to press against an outer peripheral surface of the harness to seal between the one side and the other side; The sealing portion is the lip is positioned on the one side of a base portion that is a connection portion with the outer frame portion and contacts the harness, and an intermediate portion between the base and the lip is formed to have a non-linear cross section that is concave toward the other side, When negative pressure is applied from the other side, the contact pressure of the lip against the harness increases. A second invention is characterized in that, in the first invention, the lip has a contact portion with the harness formed to have an arc-shaped cross section. A third invention is characterized in that, in the first invention, a parting line of the mold is set in the vicinity of the lip and at a position away from the portion where the lip and the harness contact each other. A fourth invention is characterized in that, in any one of the first to third inventions, EPDM is used as the elastic material. [Effects of the Invention]

[0009] According to the present invention, in a grommet that is attached between one side and another side that is under negative pressure relative to the one side and that provides a seal between the grommet and the harness, a grommet can be realized that reliably maintains a high level of sealing with the harness even when negative pressure is applied from the other side. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view showing an embodiment of a grommet according to the present invention. [Figure 2] 1 before the harness is inserted into the grommet, and FIG. 2(b) is a cross-sectional view of the harness after it has been inserted into the grommet. [Figure 3] FIG. 3 is a partially enlarged view of the seal portion of FIG. 2. [Figure 4] FIG. 2 is a partial cross-sectional view showing the molding of a grommet according to the present invention. [Figure 5] FIG. 1 is a partially cutaway perspective view of a conventional cord bushing. [Figure 6] 1 is a cross-sectional view of a conventional cord bushing and a schematic diagram illustrating an example of its use. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described with reference to the drawings. 1, grommet 1 of this embodiment is configured to have thick outer frame portions 1a, 1b (the upper region is indicated by 1a and the lower region by 1b), and an insertion portion 2 having a harness insertion opening 2a in the annular central portion of the outer frame portion for inserting a harness H. The insertion portion 2 has a shape that starts from the thick outer frame portion with a large diameter and then gradually decreases in diameter to form the harness insertion opening 2a, forming a so-called funnel shape.

[0012] The grommet 1 is fitted (engaged) into a groove formed in a case such as an electrical box or a terminal box. The groove is formed to have substantially the same shape and dimensions as the grommet 1, and the grommet 1 is fitted into the case by being pushed into the groove from the lower outer frame portion 1b (not shown). For this reason, the outer frame portion is made thick to ensure a strong fit with the case. The shape of the outer frame of the grommet 1 is not limited to that shown in FIG. 1, and may be other shapes such as a circle.

[0013] The insertion portion 2 is provided with a thin plate-like seal portion 3 that is integrally connected to the outer frame portions 1a and 1b. The insertion portion 2 is covered with the seal portion 3, and a harness insertion opening 2a for inserting the harness H is formed in the center thereof. When an electric wire cable is assumed as an example of the harness H, the cross section is usually circular, and therefore, in the grommet 1 of this embodiment, the harness insertion opening 2a is formed in a circular shape corresponding to the outer circumferential surface of the harness H. The harness H is inserted through the harness insertion opening 2a of the insertion portion 2 from the inner side, which is the inside of the case, toward the outer side, which is the outside of the case, as shown in the cross-sectional view of Fig. 2. When the harness H is inserted, the lip 4 on the periphery of the harness insertion opening 2a of the seal portion 3 presses against the outer circumferential surface of the harness H, thereby sealing the outer side (one side), which is the outside of the case, and the inner side (the other side), which is the inside of the case, and making the inside of the case waterproof and dustproof. In this embodiment, the external side, which is the outside of the case, is one side, and the internal side, which is the inside of the case, is the other side, but other forms in which the internal side, which is the inside of the case, is one side and the external side, which is the outside of the case, is the other side are also conceivable, and this is not necessarily limited to this embodiment.

[0014] Fig. 2(a) is an AA cross-sectional view of the grommet 1 shown in Fig. 1, showing the state before the harness H is inserted into the harness insertion opening 2a of the insertion portion 2 of the grommet 1. Fig. 2(b) is the same AA cross-sectional view of the grommet 1 after the harness H has been inserted into the harness insertion opening 2a of the insertion portion 2.

[0015] The grommet 1 is formed so that the opening diameter of the harness insertion opening 2a is smaller than the outer diameter of the harness H, and when the harness H is inserted into the harness insertion opening 2a, the harness insertion opening 2a is pushed by the harness H and expands in diameter to the outer diameter of the harness H. As a result, the outer side and the inner side are sealed by the insertion portion 2. Here, since the grommet 1 is an elastic body, it can easily expand in diameter according to the diameter of the harness H, and thus can accommodate the sealing of harnesses H of a plurality of different diameters.

[0016] The grommet 1 is formed by integrally molding the outer frame portions 1a and 1b and the sealing portion 3 from an elastic material, preferably non-sulfur vulcanized ethylene propylene rubber (EPDM), which provides the grommet 1 with significant heat resistance, aging resistance, ozone resistance, and weather resistance, further improving its sealing performance.

[0017] In the grommet 1 of this embodiment, the seal portion 3 has a base portion 5 at the connection portion with the outer frame portions 1a, 1b. A harness insertion opening 2a provided in the center of the seal portion 3 has a circumferential edge provided with a lip 4 having a generally O-ring shape, which is positioned more outward than the base portion 5 and presses against the outer peripheral surface of the harness H. When the harness H is inserted into the harness insertion opening 2a, as shown in Fig. 2(b), the seal portion 3 of the insertion portion 2 deforms to become convex toward the outside, and the lip 4 expands in diameter to press against the outer peripheral surface of the harness H, sealing between the outside and inside. The following provides a more detailed explanation of the above-described configuration of the grommet 1. Note that this embodiment is merely an example and is not intended to be limiting.

[0018] 2(a) and 2(b), the insertion portion 2 has a thin seal portion 3 compared to the thick outer frame portions 1a and 1b. The seal portion 3 rises from the end faces of the outer frame portions 1a and 1b from the base portion 5 toward the axial center of the harness insertion opening 2a, and has a non-linear cross section that is gently curved with a predetermined curvature and has a substantially uniform predetermined thickness W1.

[0019] Specifically, the seal portion 3 is formed with a curved cross section such that the intermediate portion 3a between the base portion 5 and the lip 4 is concave toward the other side. Here, the curvature Ra of the portion of the intermediate portion 3a closer to the base portion 5 is slightly different from the curvature Rb of the portion closer to the lip 4, that is, the curvature Rb of the portion closer to the lip 4 is slightly smaller (the curve is gentler) than the curvature Ra of the portion closer to the base portion 5. As shown in Figure 3, the convex side of the sealing portion 3 facing the outside is formed to be located at a position approximately half the thickness d1 of the outer frame portion 1b, i.e., a distance d2 toward the outside from the end face of the outer frame portion 1b of the base 5.

[0020] In the seal portion 3, the lip 4 protrudes inward from the harness insertion opening 2a and is formed into a rounded (circular) cross-sectional shape with a cross-sectional radius Rc. The lip 4 is recessed by a distance d3 between the arc-shaped outer peripheral surface of the lip 4 and the end face of the outer frame portion 1b of the base portion 5 (FIG. 3 shows that the lip 4 is located the distance d3 outward from the end face of the outer frame portion 1b of the base 5).

[0021] This lip 4 is molded integrally with the seal portion 3 as the grommet 1 by injection molding. Figure 4 shows a schematic diagram of the molding die. Here, one side S1 of the die S and the other side S2 are fitted together, and an elastic material is injected into the cavity between them to vulcanize and mold the grommet. The line where one side S1 of the die S and the other side S2 are fitted together is the parting line P.

[0022] This parting line P is set in a position near the lip 4 that is away from the portion where the lip 4 and the harness H contact each other. Specifically, the parting line P near the lip 4 is set in a position shifted outward from the lip 4. In other words, this parting line P is set in a position that is away from the portion where the lip 4 contacts the harness H and on a step Q on the opposite side (outer side) from the side where the harness H is inserted (inner side) (see FIG. 3). The parting line P on the step Q in this position allows the harness H to be smoothly inserted into the harness insertion opening 2a in the center of the insertion portion 2 and does not hinder smooth insertion of the harness H.

[0023] After the grommet 1 has been injection molded, it is removed from the mold S by a so-called forced removal method that utilizes deformation due to compression or bending that is allowable within the elastic limit when pulling the arc-shaped lip 4 out of the mold S. In other words, the grommet 1 can be removed without any problems because it is made of an elastic material.

[0024] Additionally, grommet 1 has cavity 6 in the spatial region outside seal portion 3 inside outer frame portions 1a and 1b.

[0025] In this embodiment, when the external side and the internal side are sealed and an electronic circuit such as an inverter is provided on the internal side, the temperature change of the heat generated from the electronic circuit may cause the pressure of the electronic circuit to increase relative to the atmospheric pressure on the external side. but In other words, grommet 1 is installed between the outside, which is at atmospheric pressure, and the inside, which is at negative pressure relative to the outside.

[0026] The grommet 1 of this embodiment has thick outer frame portions 1a, 1b and an insertion portion 2 through which the harness H is inserted, and the insertion portion 2 is connected to the outer frame portions 1a, 1b and has a thin seal portion 3 with a harness insertion opening 2a in the center, and a lip 4 is provided on the periphery of the harness insertion opening 2a, which is located on one side of the base and is pressed against the outer surface of the harness H to seal between one side and the other side, and the seal portion 3 is located on one side of the base 5, which is the connection portion with the outer frame portions 1a, 1b, so that the lip 4 contacts the harness H, and the intermediate portion 3a between the base 5 and the lip 4 is formed with a curved (non-linear) cross section so that it is concave toward the other side.

[0027] With this configuration, when negative pressure is applied from the inside with the lip 4 of the seal portion 3 pressed against the outer surface of the harness H to seal the inside from the outside, the contact pressure of the lip 4 with the harness H increases. That is, when negative pressure is applied from the inside, a force pulling the seal portion 3 toward the inside, which is the negative pressure side, acts on the seal portion 3. However, since the lip 4 of the seal portion 3 contacts the harness H on the outside side of the base 5 and the intermediate portion 3a between the base 5 and the lip 4 has a curved cross section that is concave toward the inside, which is the negative pressure side, the lip 4 is pressed strongly against the outer surface of the harness H without being inverted toward the inside, and a force that increases the contact pressure acts on the lip 4. This allows the grommet 1 of this embodiment to maintain high sealing performance. In this embodiment, the intermediate portion of the seal portion 3 is formed to have a curved cross section, but it may have another non-linear cross section, for example, a non-linear cross section bent in a V-shape.

[0028] In contrast to the grommet of this embodiment, the lip 23 of the bush cord shown in Figure 5 of the prior art (Patent Document 1) is formed so that its thickness gradually decreases from the inner circumferential surface of the insertion portion 21 to the opening 23a, and is formed so that it is thinnest at the opening. If the lip 23 gradually becomes thinner toward the insertion portion 21, when negative pressure is applied from the inside, the lip 23 is pulled inward, causing the thin portion of the lip 23 to bend, which may result in an inability to maintain a tight seal. In contrast, in the grommet of this embodiment, as shown in Figure 3, the seal portion 3 has a substantially uniform thickness, and the intermediate portion 3a between the base 5 and the lip 4 is formed with a non-linear cross section that is concave toward the inside, and the lip 4 of the seal portion 3 is formed with a rounded arc-shaped cross section, and is positioned outside the base 5 so that the lip 4 is in pressure contact with the outer circumferential surface of the harness H, sealing between the outside and the inside.

[0029] That is, in the seal portion 3 of the grommet 1 of this embodiment, the portion of the lip 4 that contacts the harness H is formed in an arc-shaped cross section (approximately O-ring shape), the lip 4 is located more outer than the base 5 and contacts the harness H, and the intermediate portion 3a between the base 5 and the lip 4 is formed with an arc-shaped cross section that is concave toward the inside, so that when negative pressure is applied from the inside, the contact pressure of the lip 4 with the harness H increases, and the arc-shaped surface of the lip 4 always contacts even harnesses H of different diameters, ensuring a reliable seal. Also, as described above, by setting the parting line P of the mold S at a position away from the portion of the lip 4 that contacts the harness H, and by the shape of the lip 4 having a rounded cross section with an arc-shaped portion in contact with the harness H, the harness H can be smoothly inserted.

[0030] The lip 23 shown in Figure 5 of the prior art (Patent Document 1) contacts the harness on the inner side of its base, whereas the seal portion 3 in this embodiment differs in that the lip 4 contacts the harness H on the outer side of its base 5.

[0031] As explained above, according to the present invention, in a grommet that is attached between one side and the other side that is under negative pressure relative to the one side and that seals with the harness, when negative pressure is applied from the other side, the contact pressure of the lip 4 against the harness H acts to increase, thereby realizing a grommet that reliably has a high sealing performance with the harness H compared to the bush cord shown in the prior art. [Industrial Applicability]

[0032] The grommet of the present invention can be widely applied as a waterproof and dustproof sealing device to seal between harnesses in various cases, not limited to electrical boxes and terminal boxes. [Explanation of symbols]

[0033] 1 grommet 1a, 1b Outer frame 2 Insertion section 2a Harness insertion opening 3 Seal part 3a middle part 4 Lip 5 base 6 cavities H harness P parting line S mold

Claims

1. A grommet that is attached between one side and another side that is under negative pressure relative to the one side to seal between the harness, It has a thick outer frame portion and an insertion portion through which the harness is inserted, The insertion portion is a thin-walled seal portion connected to the outer frame portion and having a harness insertion opening at the center; a lip is provided on the periphery of the harness insertion opening to press against an outer peripheral surface of the harness to seal between the one side and the other side; The sealing portion is the lip is positioned on the one side of a base portion that is a connection portion with the outer frame portion and contacts the harness, and an intermediate portion between the base and the lip is formed to have a non-linear cross section that is concave toward the other side, A grommet characterized in that when negative pressure is applied from the other side, the contact pressure of the lip against the harness increases.

2. 2. The grommet according to claim 1, wherein the lip has a contact portion with the harness that is formed to have an arc-shaped cross section.

3. 2. The grommet according to claim 1, wherein a parting line of the mold is set in the vicinity of the lip and at a position away from a portion where the lip contacts the harness.

4. 4. The grommet according to claim 1, wherein the elastic material is EPDM.

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