Watertight sealing lip for grommet

A watertight sealing lip for a grommet is disclosed which tightly seals a gap between a wall of a panel or the like and an electric wire extending through a hole of the wall. The lip is annular and obliquely extends from an end of a cylindrical portion of the grommet toward the wall so that the tip of the lip comes into contact with said wall. An inside surface facing the wall is provided with a plurality of watertight sealing projections which extend in the circumferential direction of the lip and whose cross sections are sequentially enlarged from the tip of said lip toward the end of the cylindrical portion.

BACKGROUND OF THE INVENTION 
The present device relates to a watertight sealing lip for enhancing the 
watertightness of a grommet by which the gap between a wall of a panel or 
the like and an electric wire extending through the hole of the wall is 
sealed in a watertight manner. 
When the electric wire 1 of a motor vehicle or the like is inserted through 
a dashboard 2, a grommet is used to seal the gap between the electric wire 
and the dashboard, as shown in FIG. 1. 
One example of a grommet is proposed in the Japanese Utility Model 
Application No. 192423/86 (filed on Dec. 16, 1986 and published on Jun. 
28, 1988) which is assigned to the present assignee and which comprises a 
soft body A and a hard resin member B as shown in FIG. 2. The body A of 
the grommet comprises a tube 4 having a plurality of lips 3, which 
elastically pinch an electric wire 1 to seal it, an annular plate 5 
extending continuously to the tube, and a cylindrical portion 6 extending 
continuously to the outer circumferential edge of the annular plate. An 
annular holding portion 7 extends inward from the end of the cylindrical 
portion 6. An annular watertight sealing lip 8 obliquely extends outward 
from the end of the cylindrical portion 6. An inner lip 9 curves from the 
end of the holding portion 7. The butt 10 of the hard resin member B of 
the grommet is fitted in an opening defined by the annular plate 5, the 
cylindrical portion 6 and the holding portion 7. An engaging portion 12 is 
provided at the end of a cylindrical portion 11 extending continuously to 
the butt 10 of the hard resin member B. Shown at 13 in FIG. 2 is a 
watertight sealing projection 13 provided on the watertight sealing lip 8. 
When the body A of the grommet is combined with the resin member B engaged 
on a wall 2 of a panel or the like, the tip of the watertight sealing lip 
8, the watertight sealing projection 13 and the tip of the inner lip 9 are 
elastically deformed into tight contact with the wall 2, the wall can be 
sealed by the grommet body A of elasticity. 
However, if there is a projecting piece such as foreign matter 14 on the 
surface of the wall 2 as shown in FIG. 3A, the projecting piece separates 
the watertight sealing projection 13 from the wall 2 creating an opening 
between the wall and the watertight sealing projection and keep the tip 8a 
of the watertight sealing lip 8 off the wall to let water come in. 
Further, if the tip 8a of the watertight sealing lip 8 is defective at the 
time of the attachment of the grommet to the wall 2, as shown in FIG. 3B, 
the watertight sealing projection 13 is separated from the wall 2 to let 
water enter thereinto. 
The present device is made in order to solve such problems. 
According to the present device, a watertight sealing lip is provided for a 
grommet which tightly seals the gap between a wall of a panel or the like 
and an electric wire extending through the wall. The watertight sealing 
lip is annular and obliquely extends from the end of the cylindrical 
portion of the grommet toward the wall so that the tip of the lip comes 
into contact with the wall. The side of the watertight sealing lip, which 
faces the wall, is provided with a plurality of watertight sealing 
projections which extend in the circumferential direction of the lip and 
whose cross sections are sequentially enlarged from the tip of the lip 
toward the end of the cylindrical portion of the grommet. 
The watertight sealing lip of a conventional grommet is more flexible at 
and near the tip of the lip than at and near the end of the cylindrical 
portion of the grommet according to the invention so that the lip is more 
easily deformed into tight contact with a wall or a projecting piece on 
the surface of the wall, at and near the tip of the lip than at and near 
the end of the cylindrical portion of the grommet. However, the pushing 
force of the watertight sealing lip to the wall is weaker in the vicinity 
of the end of the cylindrical portion of the grommet than in the vicinity 
of the tip of the lip so that the lip does not come into tight contact 
with the wall near the end of the cylindrical portion of the grommet. 
The watertight sealing lip provided in accordance with the present device 
has the plurality of watertight sealing projections which are made 
sequentially larger in size toward an end of a cylindrical portion of the 
grommet to sequentially increase the pushing forces of the watertight 
sealing projections to the wall and are disposed so that the projection of 
larger size is located on the part of the watertight sealing lip, the 
quantity of elastic deformation of which is smaller. For that reason, at 
least one of the watertight sealing projections comes into tight contact 
with the wall. The reliability of the watertight sealing function of the 
grommet is thus made high.

PREFERRED EMBODIMENTS OF THE INVENTION 
Embodiments of the present device are hereafter described with reference to 
the drawings attached hereto. The mutually corresponding portions shown in 
the drawings are denoted by the same reference symbols therein. 
FIG. 4 shows an annular watertight sealing lip 8 which is one of the 
embodiments and provided with two watertight sealing projections 13A and 
13B. As shown in FIGS. 6A to 6C, the watertight sealing lip 8 obliquely 
extends from the end of a cylindrical portion 6 toward a wall 2 so that 
the tip 8a of the watertight sealing lip comes into contact with the wall. 
The watertight sealing projections 13A and 13B are located on the side of 
the watertight sealing lip 8, which faces the wall 2. As shown in FIG. 5, 
the size of the watertight sealing projection 13B near the end of the 
cylindrical portion 6 is larger than that of the other watertight sealing 
projection 13A near the tip 8a of the watertight sealing lip 8. The size 
of each of the watertight sealing projections 13A and 13B is made 
inversely proportional to the distance between the watertight sealing 
projection and the cylindrical portion 6, as shown by one-dot chain lines 
in FIG. 5. Since the cross section of the watertight sealing projection 
13B is made larger, the pushing force of the projection to the wall 2 is 
stronger. For that reason, even if the position of the wall 2 is changed 
or there is a projecting piece between the watertight sealing lip 8 and 
the wall, the pushing force of the lip to the wall is made strong enough 
to render the watertightness of the lip to the wall high. 
The quantity of elastic deformation of the watertight sealing lip 8 
increases toward the tip 8a thereof so that the watertightness of the lip 
to the wall 2 is high at or near the tip of the lip. On the contrary, the 
quantity of elastic deformation of the watertight sealing lip 8 decreases 
toward the cylindrical portion 6 so that the watertightness of the lip to 
the wall 2 is not high at and near the cylindrical portion. However, since 
the watertight sealing projection 13B of larger cross section is provided 
near the cylindrical portion 6, one of the watertight sealing projections 
13A and 13B seals the wall 2 in a watertight manner if the other 
watertight sealing projection does not seal it in a watertight manner. 
FIG. 6A shows that the watertight sealing projections 13A and 13B are both 
in tight contact with the wall 2. FIG. 6B shows that the watertight 
sealing projection 13B is not in contact with the wall 2 but the other 
watertight sealing projection 13A is in tight contact therewith. FIG. 6C 
shows that the tip 8a of the watertight sealing lip 8 is involved on the 
wall 2 to keep the watertight sealing projection 13A off the wall but the 
other watertight sealing projection 13B is in tight contact with the wall 
to prevent water from coming in. 
FIG. 7 shows a watertight sealing lip which is the other one of the 
embodiments and provided with watertight sealing projections 13A, 13B, 13C 
and 13D which function to seal a wall 2 in a watertight manner. 
According to the present device, a watertight sealing lip is provided with 
a plurality of watertight sealing projections whose cross sections are 
sequentially enlarged toward the end of a cylindrical portion and which 
function to perform watertight sealing. The number of the sealing layers 
of a grommet is thus increased to enhance the reliability of the 
watertight sealing function thereof.