Cap assembly of battery

A cap assembly of a battery includes a cap cover in which ventilation holes are formed in the center portion, a cap assembled on the upper edge of the cap cover, and ventilation rubber interposed between the cap cover and the cap for opening and closing the ventilation holes. At least two and preferably two to four ventilation holes are formed in the cap cover. Accordingly, the life span of a battery employing the cap assembly can be greatly enhanced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cap assembly of a battery, and more 
particularly, to a cap assembly of a battery having ventilation rubber in 
which pressure applied to the ventilation rubber is dispersed by improving 
the shape of a cap cover, to maintain restoring force of the ventilation 
rubber under conditions in which the battery is repeatedly charged and 
discharged. 
2. Description of the Related Art 
In general, batteries for supplying direct current voltage are divided into 
dry cells used for various electric devices, and storage batteries used 
for automobiles and uninterruptible power systems. 
FIG. 1 is a sectional view of the internal structure of a conventional 
battery. 
Referring to FIG. 1, the battery is comprised of a cylindrical case 11 and 
a roll structure in the case 11. That is, positive plates 12 and negative 
plates 13 of rectangular thin plates having a predetermined width and 
length are alternately arranged around a core (not shown) to form the roll 
structure. A separator 14 located between the positive plate 12 and 
negative plate 13 insulates the two plates 12 and 13. 
Also, upper and lower rings 15 and 16 installed on upper and lower edges of 
the roll structure fix and support the plates 12 and 13. A gasket 20, and 
a cap 18 and a cap cover 19 each supported by the gasket 20 are installed 
on the upper ring 15. Ventilation rubber 17 is interposed between the cap 
18 and the cap cover 19. 
In the above-described battery, excessive charge generates gas, which 
causes a rapid increase in the internal pressure of the battery. Here, a 
cap assembly is for preventing explosion of the case 11 due to the 
internal pressure increase. 
FIGS. 2A and 2B are respectively a vertical cross-sectional view and an end 
view of a crimped cap assembly, and FIGS. 3A and 3B are respectively a 
vertical cross-sectional view and an end view of a welded cap assembly. 
Referring to FIGS. 2A and 2B, a cap assembly 20 of a battery is comprised 
of a cap 21, a cap cover 23, and ventilation rubber 22 interposed between 
the cap 21 and the cap cover 23. The ventilation rubber 22 closes a 
ventilation hole 24 in the center of the cap cover 23. 
Referring to FIGS. 3A and 3B, a mechanism of the cap assembly for 
preventing an increase in the internal pressure of the battery will be 
described as follows. 
When internal pressure in the case increases beyond a predetermined level 
due to the gas generated during repeated charges and discharges, pressure 
is applied toward a ventilation hole 34 in the center of the cap cover 33. 
Accordingly, ventilation rubber 32 closing the ventilation hole 34 moves 
upward and departs from the cap cover 33. As a result, the ventilation 
rubber 32 opens to emit gas outward. 
However, during repeated charges and discharges, the ventilation rubber 
repeatedly contracts and expands, so that its restoring force is 
deteriorated, which causes gas and electrolyte leakage through a gap 
between the cap cover and the ventilation rubber, so that the life span of 
the battery is reduced. 
SUMMARY OF THE INVENTION 
To solve the above problems, it is an object of the present invention to 
provide a cap assembly in which pressure applied to the ventilation rubber 
during repeated charges and discharges is dispersed, to maintain the 
restoring force of the ventilation rubber. 
Accordingly, to achieve the above object, there is provided a cap assembly 
of a battery comprising a cap cover in which ventilation holes are formed 
in the center portion, a cap assembled on the upper edge of the cap cover 
and ventilation rubber interposed between the cap cover and the cap for 
opening and closing the ventilation holes, in which at least two and 
preferably two to four ventilation holes are formed in the cap cover.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 4A and 4B, a cap assembly 40 is comprised of a cap 41 
forming a positive terminal, a cap cover 43 formed under the cap 41 in 
contact with both ends of the cap 41, and ventilation rubber 42 interposed 
between the cap 41 and the cap cover 43. 
In the cap cover 43, four ventilation holes 44 are formed, the holes 44 
being equally spaced from a central point of the cap cover 43. 
According to the present invention, at least two ventilation holes 44 
formed in the cap cover 43 disperse pressure in all directions to thereby 
maintain the restoring force of the ventilation rubber 42 as compared with 
the conventional cap cover having one ventilation hole. It is preferable 
that the diameter of each ventilation hole be 2 mm or less. Accordingly, 
it is also preferable that there be at most four ventilation holes, such 
that the diameter of each ventilation hole is not too small. 
Hereinafter, in the subsequent example and comparative example, the effect 
of the present invention will be described in more detail. However, the 
invention is not limited to the example to be described. 
EXAMPLE 
100 batteries employing a cap assembly including a cap cover having four 
ventilation holes were manufactured. Each of the 100 batteries was 
repeatedly charged and discharged until the ventilation rubber began to 
harden. The number of charging and discharging cycles conducted for each 
battery was recorded. As a result, the average obtained for 100 batteries 
was 800. 
COMATIVE EXAMPLE 
100 batteries employing the cap assembly shown in FIGS. 3A and 3B including 
a cap cover having one ventilation hole were used to conduct 
charge/discharge experiment according to the same method as in the above 
example. The average number of charging and discharging cycles was 
approximately 500. 
In the above result, the life span of the battery having the cap assembly 
according to the example was longer than that of the conventional art. 
According to the cap assembly of the battery of the present invention, the 
pressure applied to the ventilation rubber is dispersed to maintain the 
restoring force of the ventilation rubber. Accordingly, the life span of a 
battery employing the above cap assembly is enhanced compared to that of a 
battery having a conventional cap assembly.