JP7742250B2 - Storage battery and battery case molds - Google Patents

Description

The present invention relates to a storage battery having a battery case and a mold for the battery case.

Some storage batteries, such as lead-acid batteries, employ a battery case whose interior space is divided into multiple cell chambers by partition walls. This type of battery case is manufactured, for example, by using an injection molding machine to inject molten resin into a mold of a predetermined shape and then solidifying it.
A known structure of conventional battery cases is one in which the strength of the central portion is increased by providing multiple ribs extending in the vertical direction on the inner wall of the battery case facing the partition wall and on the partition wall, with the central ribs on the left and right sides being longer than the other ribs (see, for example, Patent Document 1).

Patent No. 4374656

One of the reasons for molding defects during injection molding is that the resin hardens before reaching every corner of the mold. For example, if the resin is supplied from a position corresponding to the bottom of the battery case, the resin may not reach the center of the left and right sides of the inner wall or partition wall of the battery case, resulting in molding defects.
According to the inventors' investigations, when the central rib among the multiple ribs is lengthened, as exemplified in Patent Document 1, although the groove in the mold corresponding to the central rib can guide the resin to the center of the left and right sides of the wall, this is still insufficient to eliminate molding defects.

The present invention therefore aims to make it easier to eliminate molding defects in battery cases.

In order to solve the above-mentioned problems, a storage battery is provided which includes a battery case whose internal space is divided into multiple cell chambers by partition walls and which has gate marks formed by injection molding at the bottom of the battery case, wherein the battery case has multiple ribs extending in the vertical direction at least on the inner wall of the battery case facing the partition wall, and the central rib on the left and right of the multiple ribs is longer in the vertical direction and wider in the horizontal direction than the remaining ribs.

In the above configuration, the multiple ribs may protrude by the same amount from the inner wall of the battery case and/or the partition wall on which they are provided.

In the above configuration, the ribs among the plurality of ribs, excluding the central rib, may be provided in equal numbers at symmetrical positions with respect to the central rib, and may have the same shape including width, vertical length, bottom end position, and top end position, and the left-right spacing of all the ribs, including the central rib, may be the same.

Furthermore, in a mold for a battery case used for injection molding to produce a battery case whose internal space is divided into multiple cell chambers by partition walls, the mold for the battery case has a gate for injecting molten resin into a position corresponding to the lower part of the battery case, and has an internal space connected to the gate and corresponding to the battery case, the internal space including a space for providing multiple ribs extending in the vertical direction at least on the inner wall of the battery case facing the partition wall, and the central rib of the multiple ribs on the left and right is longer in the vertical direction than the remaining ribs and wider in the horizontal direction.

This invention makes it easy to eliminate molding defects caused by insufficient filling of the battery case walls.

1 is a top view of a battery case of a lead-acid battery according to an embodiment of the storage battery of the present invention. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is a view taken along the arrow B in FIG. 2 . 1A to 1C are diagrams illustrating the injection molding of a battery case according to a first reference example. 10A and 10B are diagrams illustrating the injection molding of a battery case according to a second reference example. 1A to 1C are diagrams schematically illustrating injection molding of a battery case according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a top view of a battery case for a lead-acid battery according to an embodiment of the storage battery of the present invention.
The lead-acid battery includes a battery case 1 and a plate pack 3 housed in the battery case 1. The battery case 1 has an internal space divided into multiple cell chambers 4 by multiple partition walls 13, and the upper opening is covered with a lid (not shown). The battery case 1 integrally includes a pair of first walls 11 erected on a pair of long sides of a rectangular bottom plate 19 (see FIG. 2 , etc.), second walls 12 erected on a pair of short sides, and multiple partition walls 13 bridging the first walls 11. The partition walls 13 are parallel to the second walls 12 and are arranged at equal intervals. In this embodiment, five partition walls 13 are provided to divide the battery case 1 into six cell chambers 4. However, the number of partition walls 13 may be changed as appropriate. Furthermore, the partition walls 13 do not have to be parallel to the second walls 12.

This battery case 1 is manufactured using an injection molding machine by heating and melting pellets to obtain a thermoplastic resin, which is then fed into a mold 31 (Figure 6) and then cooled and solidified. The battery case 1 is made of a material such as PE (polyethylene) or PP (polypropylene). The second wall 12 corresponds to the "inner wall of the battery case opposite the partition wall 13" in this invention.

1, the arrangement direction of the cell chambers 4 is the X direction, and the horizontal direction perpendicular to the X direction is the Y direction. In each cell chamber 4, a plate group 3 constituting a cell battery is arranged.
The electrode plate group 3 has a structure in which multiple negative and positive electrode plates are alternately stacked with separators interposed between them, with the lugs of each negative electrode plate connected by a negative electrode strap and the lugs of each positive electrode plate connected by a positive electrode strap. The negative electrode strap and the positive electrode strap are arranged at different positions in the width direction of the negative and positive electrode plates (the direction that corresponds to the Y direction when placed in the cell chamber 4). The electrode plate group 3 further has a negative electrode intermediate electrode post that protrudes upward from one end of the negative electrode strap in the X direction, and a positive electrode intermediate electrode post that protrudes upward from the other end of the positive electrode strap in the X direction.

FIG. 2 corresponds to a cross-sectional view taken along line AA in FIG. 1, and shows a part of the side cross section of the battery case 1. As shown in FIG.
3 corresponds to a view seen from the arrow B in FIG. 2, and shows a part of the second wall 12. FIG.
As shown in FIG. 2, each partition wall 13 stands vertically, and each second wall 12 facing the partition wall 13 is integrally provided with a plurality of ribs 21, 22 extending in the vertical direction.
It should be noted that ribs having the same shape as the ribs 21 and 22 provided on the second wall 12 may be provided on the partition wall 13 .

Rib 21 is a rib provided at the left-right center (corresponding to the center in the Y direction) of the second wall 12. Ribs 22 are provided on the left and right of the left-right center rib 21. The left and right ribs 22 are multiple ribs provided in equal numbers at symmetrical positions with respect to the left-right center rib 21. These ribs 22 have different lengths in the up-down direction (length L2 shown in Figure 3) and left-right direction (width W2 shown in Figure 3) compared to the left-right center rib 21.

The walls 13, 12 and the ribs 21, 22 will now be described in detail.
2, in adjacent walls 13, 12, a separation distance P1 from the ribs 21, 22 of the second wall 12 to the surface of the partition wall 13 is set to a distance corresponding to the thickness of the electrode plate pack 3. The ribs 21, 22 provided on each second wall 12 have the same protrusion amount D1 (also referred to as protrusion height) from the corresponding wall 12.
2, each partition wall 13 is formed as a vertically erected wall, whereas the second wall 12 is formed as a wall having an inclined surface that functions as a draft. For this reason, the ribs 21, 22 provided on the second wall 12 are formed so that the protrusion amount D1 decreases downward so as to keep the separation distance P1 constant across the top and bottom.

If the second wall 12 were formed as a vertically erected wall, the second wall 12 and the partition wall 13 would be completely parallel, so the protrusion amount D1 of the ribs 21, 22 on the second wall 12 would simply be set to the same value across the top and bottom.

As shown in Figures 2 and 3, the left and right ribs 22 provided on the second wall 12 have the same shape in each part, including the lower end position, upper end position, and protrusion amount D1, and further have the same lower end position as the rib 21.
2 shows an example in which the upper portions of the ribs 21, 22 are formed in an inclined shape in which the protrusion amount D1 gradually decreases toward the top. This inclined shape makes it easier to smoothly insert the electrode plate group 3 between the cell chambers 4 at both left and right ends, with the separation distance P1. However, this inclined shape is not necessary.
At least one of the cell chambers 4 at both left and right ends is often located in the engine compartment, close to a heat source such as an engine. It is generally known that lead-acid batteries deteriorate more rapidly at higher operating temperatures. Furthermore, the greater the contact area between the electrode plates and the electrolyte, the more rapidly the battery deteriorates, and therefore, worn electrode plates deteriorate more rapidly. When inserting the electrode plate pack 3 into the cell chamber 4, if a large force is applied to the electrode plate pack 3 due to factors such as a small separation distance P1, the electrode plate surfaces may be damaged by protrusions such as the ribs 21 and 22. Forming the inclined shape shown in Figure 2 can suppress such wear and is expected to extend the life of the lead-acid battery.

As shown in Figure 3, a single rib 21 is provided in the center of the left and right sides, and is longer in the vertical direction and wider in the horizontal direction (corresponding to the Y direction) than the ribs 22 located on either side of this rib 21. The left and right ribs 22 are arranged at equal intervals on the left and right. In the following description, when the ribs 21 and 22 are to be particularly distinguished, they will be referred to as the first rib 21 and the second rib 22, respectively.

In Figure 3, the height of the second wall 12 (the same as the height of the partition wall 13 and the height of the battery case 1) is indicated by the symbol L0, the length of the first rib 21 (also referred to as rib length) is indicated by the symbol L1, and the length of the second rib 22 (also referred to as rib length) is indicated by the symbol L2. The width of the first rib 21 is indicated by the symbol W1, and the width of the second rib 22 is indicated by the symbol W2. The height L0 of the second wall 12 > the length L1 of the first rib 21 > the length L2 of the second rib 22. The symbol LC in Figure 3 indicates the left-right center of the second wall 12 (the same as the left-right center of the partition wall 13).

The second ribs 22 are positioned so that they contact the electrode plate located at one end of the electrode plate pack 3. Each second rib 22 extends linearly upward from the bottom plate 19, with its upper end set at a predetermined distance Z2 from the upper end of the second wall 12. For example, the upper end of the second rib 22 is set at a position that allows the second rib 22 to contact both the top and bottom of the electrode plate located at one end of the electrode plate pack 3. For example, the value Z2 is set in the range of 25% to 35% of the height L0 of the second wall 12; in other words, the length L2 of the second rib 22 is set in the range of 65% to 75% of the height L0 of the second wall 12.

The width W2 of the second ribs 22 and the spacing (also referred to as pitch) between the second ribs 22 are set to values that ensure a sufficient contact area with the electrode plate pack 3 while ensuring gaps that allow sufficient passage of air and reactive gases between the second ribs 22 and between the second ribs 22 and the first rib 21. This allows the second ribs 22 to suppress changes in the distance between the electrode plates of the electrode plate pack 3 and makes it easier to suppress temperature increases in the electrode plate pack 3.
For example, the width W2 of the second rib 22 is preferably 2.0 mm or more and 5.0 mm or less, and in the range of 40 to 80% of the width W1 of the first rib 21, and the spacing between the second ribs 22 is preferably in the range of 8 to 30% of the left-right width of the second wall 12.

The first rib 21 extends linearly upward from the bottom plate 19 and extends to the vicinity of the upper end of the second wall 12, thereby extending higher than the second rib 22. In this embodiment, the upper end of the first rib 21 is set at a position that is a predetermined value Z1 away from the upper end position of the second wall 12.
The value Z1 is smaller than the value Z2. For example, the value Z1 is preferably in the range of 3 to 20% of the height L0 of the second wall 12. In other words, the length L1 of the first rib 21 is preferably in the range of 80 to 97% of the height L0 of the second wall 12. The first rib 21 can suppress expansion of the left-right center of the electrode plate pack 3 in the cell chamber 4, which is disposed at the farthest end and is most likely to be closest to a heat source in the engine compartment. The width W1 of the first rib 21 is larger than the width W2 of the second rib 22, so expansion of the left-right center of the electrode plate pack 3 can be more effectively suppressed. These ribs 21, 22 also function as reinforcing ribs that reinforce the second wall 12.

Here, if the width W1 and rib length L1 of the first rib 21 are made larger than those of the second rib 22, when the battery case 1 is manufactured by injection molding, it becomes easier to flow molten resin into the space corresponding to the left-right center of the second wall 12 in a mold 31 (Figure 6) having an internal space corresponding to the battery case 1.Therefore, by setting the width W1 and length L1 of the first rib 21 so that the resin reaches the left-right center of the second wall 12, it becomes easier to eliminate molding defects in the battery case 1.
Furthermore, increasing the width W1 and length L1 of the first rib 21 is effective from the viewpoint of obtaining the strength to suppress expansion of the left and right central portions of the electrode plate pack 3 and from the viewpoint of reinforcing the second wall 12 .

FIG. 4 is a diagram showing a schematic view of injection molding of a battery case 1A according to the first reference example.
In FIG. 4, reference numeral 31A denotes a mold having an internal space corresponding to the battery case 1A (the female mold forming the internal space is also called a cavity, and the corresponding male mold is also called a core).
The battery case 1A of the first reference example differs from the battery case 1 of this embodiment in that the length L1 and width W1 of the first rib 21 are the same as the length L2 and width W2 of the second rib 22.
In injection molding, a gate G for injecting thermoplastic resin (hereinafter referred to as molten resin SM) into the mold 31A is provided at a position corresponding to the lower part of the battery case 1A. The location of the gate G is not limited to one position corresponding to the lower part of the battery case 1A, but may be two or more positions corresponding to the lower part of the battery case 1A.
4, the symbol SP schematically indicates the internal space of the mold 31A, which is also the internal space that forms the battery case 1A. In this internal space SP, locations corresponding to the various components of the battery case 1A (ribs 21, 22, second wall 12, first wall 11, and bottom plate 19) are indicated by the reference symbols of the various components.

As shown in Figure 4, the molten resin SM flowing in from the gate G is supplied into the mold 31A from the space corresponding to the bottom plate 19 of the battery case 1A, through the grooves corresponding to the ribs 21 and 22, the space corresponding to the second wall 12, and the space corresponding to the first wall 11.
In the first reference example, although a portion of the molten resin SM can be guided to the space corresponding to the upper end of the second wall 12 by the grooves corresponding to the ribs 21, 22, as shown in Fig. 4, the amount of resin supplied to the space corresponding to the left-right center of the second wall 12 may be relatively smaller than the amount of resin supplied to the spaces corresponding to both left and right sides of the second wall 12. For this reason, the molten resin SM may solidify before reaching the left-right center of the second wall 12, which may result in molding defects as shown in the bottom row of Fig. 4.

FIG. 5 is a diagram schematically showing injection molding of a battery case 1B according to a second reference example.
In FIG. 5, reference numeral 31B denotes a mold having an internal space SP corresponding to the battery container 1B.
The battery case 1B according to the second reference example differs from the battery case 1 of this embodiment in that the width W1 of the first rib 21 is the same as the width W2 of the second rib 22.
In the second reference example, the first rib 21 in the left and right center is longer than the second ribs 22 on the left and right, so that, compared to the second reference example, more of the molten resin SM can be guided into the space corresponding to the left and right center of the second wall 12 during injection molding.
However, as shown in Figure 5, even in the second reference example, the amount of resin supplied to the space corresponding to the center of the second wall 12 is relatively less than the amount of resin supplied to the spaces corresponding to both the left and right sides of the second wall 12, which may result in molding defects such as those shown in the bottom row of Figure 5.

Here, the degree of insufficiency in the amount of resin supplied to the space corresponding to the center of the second wall 12 is affected by various parameters related to the gate G, the pressure and temperature of the molten resin SM, in addition to parameters related to the shape of the battery container, such as the surface shape and thickness distribution of the second wall 12. According to the studies of the inventors, there is a limit to the adjustment range when only adjusting the length of the first rib 21, and it may not be possible to sufficiently suppress molding defects, or it may become necessary to review the above multiple parameters in order to sufficiently suppress molding defects.
Furthermore, the lower the height of the second wall 12, or the higher the ratio of the length L2 of the second rib 22 to the height of the second wall 12, the smaller the effect of suppressing molding defects by adjusting the length of the first rib 21. For example, if the height of the second wall 12 is less than 180 mm or the ratio of the length L2 of the second rib 22 to the height of the second wall 12 exceeds 75%, it becomes more difficult to suppress molding defects as described above.

FIG. 6 is a diagram schematically showing injection molding of the battery case 1 according to this embodiment.
In Fig. 6, reference numeral 31 denotes a mold having an internal space SP corresponding to the battery case 1. This mold 31 corresponds to the "battery case mold" in this invention.
In this battery case 1, the first rib 21 is longer in the up-down direction and wider in the left-right direction than the second rib 22, so the fluidity of the molten resin SM is improved compared to the first and second reference examples. As a result, as shown in Fig. 6, more of the molten resin SM can be guided to the space corresponding to the left-right center of the second wall 12, allowing the molten resin SM to spread throughout the entire space corresponding to the second wall 12, making it easier to prevent molding defects in the second wall 12.
If the ribs 21, 22 are provided on the partition wall 13 (see FIG. 2), the first rib 21 can be made longer in the vertical direction and wider in the horizontal direction than the second rib 22 in the partition wall 13, thereby improving the fluidity of the molten resin SM in the partition wall 13. This allows more of the molten resin SM to be guided to the space corresponding to the center of the left and right of the partition wall 13, allowing the molten resin SM to spread throughout the entire space corresponding to the partition wall 13, making it easier to suppress molding defects in the partition wall 13.

Furthermore, even if the shape of the battery case 1 is different, by combining length and width adjustment of the first rib 21 provided on the second wall 12, it becomes easier to eliminate molding defects caused by insufficient filling at the center of the left and right sides of the second wall 12. Therefore, when the design of the battery case 1 is changed, simply adjusting the length and width of the first rib 21 makes it easier to eliminate molding defects in the second wall 12. As a result, it is also expected that the labor required to adjust various parameters of the injection molding machine will be reduced.

In the above description, the length and width of the first rib 21 of each wall 12 are made larger than the second rib 22 to eliminate molding defects in the second wall 12 only, but this is not limiting. For example, if manufacturing conditions are such that molding defects are likely to occur in both walls 13, 12, and adjusting the length and width of the first rib 21 on each wall 13, 12 can sufficiently suppress molding defects, the length and width of the first rib 21 on the other wall 13, 12 may be adjusted to be larger than the second rib 22.

As explained above, in the battery container 1 manufactured by supplying molten resin SM into a mold having an internal space SP corresponding to the shape of the battery container 1 from a position corresponding to the bottom of the battery container 1, at least the second wall 12 of the walls 13, 12 of the battery container 1 is provided with multiple ribs 21, 22 extending in the vertical direction, with the central rib 21 on the left and right being longer in the vertical direction and wider in the horizontal direction than the remaining ribs 22. This improves the fluidity of the molten resin SM in the wall 12, making it easier to eliminate molding defects caused by insufficient filling of the wall 12 during injection molding.

Furthermore, the multiple ribs 21, 22 are formed so that the protrusion amount D1 from any of the second walls 12 on which these ribs are provided is the same if the height between each rib is the same in the vertical direction. This aligns the protruding surfaces of the ribs 21, 22 provided on the second wall 12 in the same plane, making it easier to evenly press down on the electrode plate group 3 placed in the cell chamber 4.

Furthermore, the ribs 22, excluding the central rib 21, are provided in equal numbers at symmetrical positions relative to the central rib 21, and are formed with the same shape, including the width W2, vertical length L2, bottom end position, and top end position. This makes it easier for the ribs 21, 22 to feed resin evenly to the left and right. With this configuration, adjusting the width W1 and length L1 of the central rib 21 to compensate for insufficient filling at the center makes it easier to eliminate molding defects throughout the second wall 12.

As shown in Figure 6, the mold 31 used to produce the battery case 1 by injection molding has a gate G for introducing molten resin SM at a position corresponding to the bottom of the battery case 1, and an internal space SP connected to the gate G and corresponding to the battery case 1. The internal space SP includes a space in at least the second wall 12 where multiple ribs 21, 22 extending in the vertical direction are provided, and the central rib 21 of the multiple ribs 21, 22 is formed to be longer in the vertical direction and wider in the horizontal direction than the remaining ribs 22. This improves the fluidity of the molten resin SM in the area corresponding to the second wall 12, making it easier to eliminate molding defects caused by insufficient filling of the second wall during injection molding.

The present invention is not limited to the above-described embodiment, and various modifications and changes are possible based on the technical concept of the present invention.
For example, although the case has been described where the protrusion amounts D1 of the ribs 21, 22 from the second walls 12, 13 are the same, a configuration where the protrusion amounts D1 are not the same may be adopted as long as there is no problem in supporting the electrode plate pack 3. Furthermore, although the case has been described where the ribs 22, excluding the rib 21 at the center of the left and right, are provided in equal numbers at positions symmetrical to the center rib 21 at the center of the left and right, and have the same shape including the width W2, the length L2 in the vertical direction, the lower end position, and the upper end position, any of the dimensions may be different.
Furthermore, although the present invention has been exemplified as being applied to the battery case 1 for a lead-acid battery and the mold 31 used for injection molding the battery case 1, the present invention may also be applied to battery cases other than lead-acid batteries and molds used for injection molding battery cases other than lead-acid batteries.

1 Battery case 1A, 1B Battery case according to reference example 3 Plate group 4 Cell chamber 11 First wall 12 Second wall (inner wall of battery case facing partition wall 13)
13 Partition wall 21 Rib at the center of the left and right (first rib)
22 Left and right ribs (second ribs)
31 Mold (mold for battery case)
31A, 31B Mold according to the reference example L0 Height of partition wall (height of battery case)
L1: Length of the rib at the center of the left and right L2: Length of the ribs on the left and right W1: Width of the rib at the center of the left and right W2: Width of the ribs on the left and right SM: Molten resin SP: Internal space of the mold

Claims (4)

A storage battery comprising a battery case whose internal space is divided into a plurality of cell chambers by partition walls , and a gate mark formed by injection molding at the bottom of the battery case,
The battery case has a plurality of ribs extending in the vertical direction at least on an inner wall of the battery case facing the partition wall,
A storage battery characterized in that the central rib of the plurality of ribs is longer in the vertical direction and wider in the horizontal direction than the remaining ribs. The storage battery described in claim 1, characterized in that the multiple ribs protrude by the same amount from the inner wall of the battery case on which they are provided. Among the plurality of ribs, the ribs other than the left-right central rib are provided in equal numbers at symmetrical positions with respect to the left-right central rib, and have the same shape including width, vertical length, lower end position, and upper end position,
The storage battery according to claim 1 or 2, wherein the left and right arrangement intervals of all the ribs, including the left and right central ribs, are the same. A mold for a battery case is used to manufacture, by injection molding, a battery case whose internal space is divided into a plurality of cell chambers by partition walls,
The mold for the battery case has a gate for injecting molten resin at a position corresponding to the lower part of the battery case, and has an internal space connected to the gate and corresponding to the battery case,
the internal space includes a space in which a plurality of ribs extending in the vertical direction are provided on at least an inner wall of the battery case facing the partition wall,
A mold for a battery container, wherein the rib at the center of the left and right sides of the plurality of ribs is longer in the vertical direction and wider in the horizontal direction than the remaining ribs.