TWI893000B - Protection element and battery pack - Google Patents

Abstract

The present invention provides a protective element that can eliminate excess adhesive between the mating protrusion and the mating recess, thereby reliably ensuring the bonding strength between the lower and upper housings. The protective element of the present invention comprises: a fusible conductor 3; and a housing 6 having a lower housing 4 and an upper housing 5, formed by joining the upper housing 5 and the lower housing 4 with an adhesive; an engaging recess 25 is formed in one of the upper housing 5 and the lower housing 4, and an engaging protrusion 26 is formed in the other of the upper housing 5 and the lower housing 4 to engage with the engaging recess 25, and a narrow groove 27 is formed. The narrow groove 27 is continuous with the engaging recess 25 and extends to the abutting surface of the upper housing 5 and the lower housing 4, allowing the adhesive 19 to flow.

Description

Protective components, battery packs

This invention relates to a protective element for interrupting a current path, and a battery pack using the same. This invention claims priority based on Japanese Patent Application No. 2019-157431, filed in Japan on August 29, 2019, which is incorporated herein by reference.

Most rechargeable and reusable secondary batteries are processed into battery packs and provided to users. Lithium-ion secondary batteries, particularly those with a high gravimetric energy density, typically incorporate several protection circuits, such as overcharge protection and over-discharge protection, to ensure the safety of users and electronic devices. These circuits can shut down the battery pack's output under specific circumstances.

Most electronic devices using lithium-ion secondary batteries utilize a FET switch built into the battery pack to turn the output on and off, protecting the battery pack from overcharge or over-discharge. However, if the FET switch short-circuits for some reason, if a lightning surge or other transient current flows, or if the output voltage drops abnormally due to the battery cell's lifespan, or if the output voltage exceeds the normal value, the battery pack and the electronic device must be protected from fire and other hazards. Therefore, in order to safely shut down the battery cell output even in any conceivable abnormal conditions, a protective device including a fuse element that has the function of shutting down the current path in response to an external signal is used.

As a protection element for the protection circuit of a lithium-ion secondary battery, etc., a structure is used in which a heating element is internally provided in the protection element, and the heat generated by the heating element melts the fusible conductor in the current path.

[Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Application Publication No. 2015-53260

The use of lithium-ion secondary batteries has expanded in recent years, with the industry exploring applications with higher currents. For example, these batteries can be used in power tools like electric screwdrivers, and in transportation equipment like hybrid vehicles, electric vehicles, and electric power-assisted bicycles. Some adoption has already begun. In these applications, particularly during startup, high currents exceeding 10A to 100A can flow. Ideally, protective components with the capacity to handle these high currents would be desirable.

In order to implement a protective element capable of handling such high currents, a proposal has been made to use a fusible conductor with an increased cross-sectional area, with an insulating substrate having a heat generating element connected to the front surface of the fusible conductor.

Figures 26, 27, 28, and 29 illustrate an example configuration of a protective element designed for high-current applications. Figure 26 is a perspective view, Figure 27 is a top view, Figure 28 is a cross-sectional view taken along line D-D' of Figure 27, and Figure 29 is a top view showing the upper housing omitted. The protective element 100 shown in Figures 26-29 comprises a fusible conductor 103 connected between first and second external connection terminals 101 and 102, which are connected to an external circuit such as a battery charge/discharge circuit. This fusible conductor 103 forms part of the external circuit. In the event of an abnormality such as an overvoltage, the fusible conductor 103 melts, blocking the current path between the first and second external connection terminals 101, 102.

The protective element 100 comprises an insulating substrate 105; first and second external connection terminals 101 and 102, which connect to external circuits; two heating elements 106 arranged on the front surface of the insulating substrate 105; an insulating layer 107 covering the heating elements 106; a front electrode 108 laminated on the insulating layer 107 and connected to the heating elements 106; and a fusible conductor 103, which is mounted via solder paste across the first external connection terminal 101, the front electrode 108, and the second external connection terminal 102.

The protective element 100 is configured with first and second external connection terminals 101 and 102 extending across the interior and exterior of the element housing. These terminals are connected to connection electrodes on the external circuit board on which the protective element 100 is mounted, such as by screws. This allows the fusible conductor 103 to be incorporated into a portion of the current path formed on the external circuit board.

The heater 106 is a conductive component with a high electrical resistance that generates heat when current is applied. It is made of, for example, nickel-chromium alloy, W, Mo, Ru, or a material containing these. The heater 106 is connected to a heater feed electrode 109 formed on the front surface of the insulating substrate 105. The heater feed electrode 109 is connected to a third external connection terminal 110 via solder paste. The protective element 100 is connected to a connection electrode on the external circuit board where the protective element 100 is mounted, via the third external connection terminal 110, thereby connecting the heater 106 to an external power source located in the external circuit. Furthermore, the power supply and heating of the heater 106 are constantly controlled by a switching element (not shown).

The heat generator 106 is covered with an insulating layer 107 made of glass or the like, and a front electrode 108 is formed on the insulating layer 107, thereby overlapping the front electrode 108 with the insulating layer 107 interposed therebetween. Furthermore, a fusible conductor 103 is connected to the front electrode 108 via solder paste, spanning between the first and second external connection terminals 101 and 102.

In this way, the heating element 106 of the protection element 100 and the fusible conductor 103 are thermally connected by overlapping. When the heating element 106 is heated by power supply, the fusible conductor 103 can be melted.

The fusible conductor 103 is formed from a low-melting-point metal such as lead-free solder, a high-melting-point metal such as Ag, Cu, or an alloy primarily composed of these, or a laminated structure of low-melting-point and high-melting-point metals. The fusible conductor 103 connects from the first external connection terminal 101 across the front electrode 108 to the second external connection terminal 102, forming part of the current path of the external circuit in which the protective element 100 is mounted. The fusible conductor 103 melts due to self-heating (Joule heating) caused by a current exceeding the rated value, or due to heat generated by the heating element 106, thereby isolating the connection between the first and second external connection terminals 101 and 102.

When the protective element 100 needs to interrupt the current path of the external circuit, it energizes the heating element 106 via the switching element. This heats the heating element 106 of the protective element 100 to a high temperature, melting the fusible conductor 103 incorporated into the current path of the external circuit. The molten conductor of the fusible conductor 103 is pulled toward the more humid front electrode 108 and the first and second external connection terminals 101 and 102, melting the fusible conductor 103. Thus, the protective element 100 fuses the connection between the first external connection terminal 101, the front electrode 108, and the second external connection terminal 102, interrupting the current path of the external circuit.

As shown in Figure 30 , the protective element 100 includes a lower housing 111 and an upper housing 112. The lower housing 111 and the upper housing 112 are joined together to form a housing 113 of the protective element 100. Figure 30 shows the housing 113, with (A) showing a bottom view of the upper housing 112, (B) a cross-sectional view of the lower housing 111 and the upper housing 112, and (C) a top view of the lower housing 111. The lower housing 111 supports the insulating substrate 105 and the first and second external connection terminals 101 and 102. The upper housing 112 has a space for accommodating the internal components of the aforementioned components.

The lower housing 111 has mating protrusions 114 formed at each corner. Furthermore, the upper housing 112 has mating recesses 115 formed at each corner that mate with the mating protrusions 114. When forming the housing 113, as shown in Figure 31, adhesive 120 is applied to the side edge of the lower housing 111, including the mating protrusions 114, and then brought into contact with the upper housing 112. This engages the mating protrusions 114 and the mating recesses 115 via the adhesive 120, joining the lower housing 111 to the upper housing 112.

To accommodate high-current applications, the protective element 100 requires a larger fusible conductor 103 and increased heat generation by the heating element 106, as described above. However, this also increases the thermal shock when the fusible conductor 103 melts, causing the air inside the housing to expand rapidly. Consequently, the housing 113 must have a bond strength strong enough to withstand this pressure. To enhance the bond strength between the lower housing 111 and the upper housing 112, increasing the amount of adhesive 120 is considered. However, increasing the amount of adhesive 120 increases the amount that flows into the mating recess 115 during mating. Furthermore, adhesive also enters the space between the mating protrusion 114 and the mating recess 115.

Therefore, as shown in Figure 32, when the lower housing 111 and upper housing 112 are mated, there is no overflow area for the adhesive 120 to flow between the mating protrusion 114 and the mating recess 115. This hinders the close contact between the lower housing 111 and the upper housing 112. As a result, the upper housing 112 floats away from the lower housing 111. Without achieving the desired bond strength, there is a risk that the upper housing 112 may detach when the fusible conductor 103 melts, or that the specified housing height requirements may not be met.

Therefore, an object of the present invention is to provide a protective element that can eliminate excess adhesive between the mating protrusion and the mating recess, thereby reliably ensuring the bonding strength between the lower and upper housings, and a battery pack using the same.

To address the aforementioned issues, the protective element of the present invention comprises: a fusible conductor; and a housing comprising a lower housing and an upper housing, formed by bonding the upper and lower housings together with an adhesive. A fitting recess is formed in one of the upper and lower housings, and a fitting protrusion is formed in the other housing to fit into the fitting recess. Furthermore, a narrow groove is formed, continuous with the fitting recess and extending to the mating surfaces of the upper and lower housings, allowing the adhesive to flow.

To address the aforementioned issues, the protective element of the present invention comprises: a fusible conductor; and a housing comprising a lower housing and an upper housing, formed by bonding the upper and lower housings together with an adhesive. A mating recess is formed in one of the upper and lower housings, and a mating protrusion is formed in the other housing to engage with the mating recess. The mating protrusion has a narrow groove formed on its outer circumference for allowing the adhesive to flow.

To address the aforementioned issues, the protective element of the present invention comprises: a fusible conductor; and a housing comprising a lower housing and an upper housing, formed by bonding the upper and lower housings together with an adhesive. A recessed engagement portion is formed on one of the upper and lower housings, and a protrusion is formed on the other housing to engage with the recessed engagement portion. Furthermore, a narrow groove is formed therein, continuous with the recessed engagement portion and extending to the mating surfaces of the upper and lower housings to allow the adhesive to flow. The protrusion has a narrow groove formed on its outer peripheral surface to allow the adhesive to flow.

The battery pack of the present invention comprises: one or more battery cells; a protective element connected to a charge/discharge circuit of the battery cell to block the charge/discharge circuit; and a housing comprising a lower housing and an upper housing, formed by bonding the upper and lower housings together with an adhesive. A fitting recess is formed in one of the upper and lower housings, and a fitting protrusion is formed in the other housing to fit into the fitting recess. Furthermore, a narrow groove is formed therein, continuous with the fitting recess and extending to the abutting surfaces of the upper and lower housings to allow the adhesive to flow.

The battery pack of the present invention comprises: one or more battery cells; and a protective element connected to a charge/discharge circuit of the battery cell to block the charge/discharge circuit. The protective element comprises: a fusible conductor; and a housing comprising a lower housing and an upper housing, formed by bonding the upper and lower housings together with an adhesive. A fitting recess is formed on one of the upper and lower housings, and a fitting protrusion is formed on the other housing to fit into the fitting recess. The fitting protrusion has a narrow groove formed therein to allow the adhesive to flow in the protruding direction.

Furthermore, the battery pack of the present invention comprises: one or more battery cells; and a protective element connected to the charge and discharge circuit of the battery cells to block the charge and discharge circuit; and the protective element comprises: a fusible conductor; and a housing having a lower outer shell and an upper outer shell, formed by bonding the upper outer shell and the lower outer shell with an adhesive; One of the housing and the lower housing has a recessed engagement portion, and the other has a protruding engagement portion that engages with the recessed engagement portion. A narrow groove is formed therein. The narrow groove is continuous with the recessed engagement portion and extends to the mating surfaces of the upper and lower housings to allow the adhesive to flow. The protruding engagement portion has a narrow groove formed therein to allow the adhesive to flow in the protruding direction.

According to the present invention, the narrow groove allows excess adhesive filled in the mating recess to flow inward when the upper and lower housings are mated, preventing it from accumulating in the mating recess where it engages with the mating protrusion. This prevents excess adhesive accumulating in the mating recess from obstructing the close contact between the upper and lower housings.

1,50,60,100: Protective components

2,105: Insulating substrate

2a: Front

2b: Back

2c: 1st side edge

2d: Second side edge

3,103: Fusible conductor

3a: Melting conductor

4,52,111: Lower shell

5,51,112: Upper outer shell

5a: Lower end surface of side wall

6,113: Shell

7,101: 1st external connection terminal

8,102: Second external connection terminal

9,107: Insulating layer

10,106: Heat generating body

11,108: Front electrode

12: Suction hole

13:Conductive layer

14: Back electrode

15: Heating electrode

16,109: Heating element feeding electrode

17,110: Third external connection terminal

18: Fusing components

19,120: Follow-up agent

20: Bonding materials/connecting materials

23: Concave face

25,115: Fitting recess

26,114: Fitting convex part

27: Recessed slot/slot

28: Slot/convex slot

29: Charging device

31: Low melting point metal layer

32: High melting point metal layer

33:Battery pack

33a: Positive terminal

33b: Negative terminal

34:Battery cell

34a~34d: Battery cells

35: Battery stack

36: Charge and discharge control circuit

37: Detection circuit

38: Current control element

39,39a,39b: Current control element

40: Control Department

Figure 1 is a perspective view of the protective element to which the present invention is applied.

Figure 2 is a cross-sectional view of a protective element employing the present invention.

Figure 3 is a top view showing the protective element of the present invention without the upper housing.

Figure 4 is a cross-sectional view showing a state where the fusible conductor in the protection element employing the present invention has melted.

Figure 5 shows the lower side of the outer casing, (A) is a top view, and (B) is an E-E' cross-sectional view of (A).

Figure 6 shows the upper side of the outer casing, (A) is a bottom view, and (B) is a C-C' cross-sectional view of (A).

Figure 7 shows the steps of joining the lower shell and the upper shell. (A) is a top view of the lower shell showing the flow of adhesive, and (B) is a cross-sectional view taken along line G-G' of (A) showing the flow of adhesive as the lower shell, coated with adhesive, is engaged with the upper shell.

Figure 8 shows variations of the concave groove. (A) is a bottom view of the upper housing, and (B) is a cross-sectional view taken along line H-H' of (A).

Figure 9 is a top view showing a variation of the concave groove.

Figure 10 is a top view showing a variation of the concave groove.

Figure 11 shows the steps of joining the lower and upper shells. (A) is a top view of the lower shell coated with adhesive, and (B) is a cross-sectional view taken along line F-F' of (A) with the upper and lower shells facing each other.

Figure 12 shows a housing with a protruding groove provided on the lower housing. (A) is a bottom view of the upper housing, (B) is a cross-sectional view of the upper and lower housings facing each other, and (C) is a top view of the lower housing.

Figure 13 shows a mating protrusion with a protrusion groove formed therein. (A) is a top view, and (B) is a J-J' cross-sectional view of (A).

Figure 14 shows a housing with a protruding groove provided on the lower housing. (A) is a bottom view of the upper housing, (B) is a cross-sectional view with the upper and lower housings facing each other, and (C) is a top view of the lower housing.

Figure 15 shows a mating protrusion with a protrusion groove formed therein. (A) is a top view, and (B) is a J-J' cross-sectional view of (A).

Figure 16 shows the upper side of the housing with the mating protrusions. (A) is a bottom view, and (B) is a cross-sectional view taken along line L-L' of (A).

Figure 17 shows the lower side of the housing with the mating recess. (A) is a top view, and (B) is a cross-sectional view taken along line M-M' of (A).

Figure 18 shows the steps of joining the lower shell and the upper shell. (A) is a top view of the lower shell showing the flow of adhesive, and (B) is a cross-sectional view taken along line K-K' of (A) showing the flow of adhesive as the lower shell, coated with adhesive, is engaged with the upper shell.

Figure 19 shows the steps of joining the lower and upper shells. (A) is a top view of the lower shell coated with adhesive, and (B) is a cross-sectional view taken along line N-N' of (A) with the upper and lower shells facing each other.

Figure 20 is a perspective view of the fusible conductor.

Figure 21 is a circuit diagram showing an example of a battery pack configuration.

Figure 22 is a circuit diagram of a protective element employing the present invention.

Figure 23 is a cross-sectional view showing a variation of the protective element to which the present invention is applied.

Figure 24 is a circuit diagram of a modified protection element.

Figure 25 is a cross-sectional view showing a state where the fusible conductor in a modified embodiment of the protection element has melted.

Figure 26 shows a three-dimensional diagram of the external appearance of a protective component designed to handle high currents.

Figure 27 is a top view of the protective element shown in Figure 26.

Figure 28 is a cross-sectional view taken along line D-D' of Figure 27.

Figure 29 is a top view of the protective element shown in Figure 26, omitting the upper housing.

Figure 30 shows the housing of the protective element shown in Figure 26. (A) is a bottom view of the upper housing, (B) is a cross-sectional view showing the lower housing and the upper housing facing each other, and (C) is a top view of the lower housing.

Figure 31 shows the steps of joining the lower and upper shells. (A) is a cross-sectional view showing the lower and upper shells coated with adhesive facing each other. (B) is a top view of the lower shell coated with adhesive.

Figure 32 shows the lower housing and upper housing being joined. (A) is a bottom view of the upper housing with the mating recess filled with adhesive, and (B) is a cross-sectional view showing the lower housing and upper housing being joined.

The following describes in detail the protection element and battery pack to which the present invention is applied, with reference to the drawings. The present invention is not limited to the following embodiments and may be modified without departing from the spirit of the present invention. The drawings are schematic, and the proportions of dimensions and other aspects may differ from actual dimensions. Specific dimensions and other aspects should be determined in light of the following description. Furthermore, some drawings may have different dimensional relationships or proportions.

[First Embodiment: Fitting Recessed Slot]

Figures 1, 2, and 3 illustrate a protective element 1 to which the present invention is applied. The protective element 1 comprises an insulating substrate 2; a fusible conductor 3 mounted on the front surface of the insulating substrate 2; and a housing 6 comprising a lower housing 4 supporting the back surface of the insulating substrate 2 and an upper housing 5 covering the front surface of the insulating substrate 2. The lower housing 4 and the upper housing 5 are bonded together with an adhesive 19 to house the insulating substrate 2. Furthermore, the protective element 1 has first and second external connection terminals 7 and 8. These terminals 7 and 8 are arranged to span the interior and exterior of the housing 6 and are connected to connection electrodes provided in the external circuit in which the protective element 1 is mounted, for example, by screwing. The first and second external connection terminals 7 and 8 are supported by the lower housing 4 and connected at one end via a fusible conductor 3. Furthermore, since the protective element 1 is incorporated into an external circuit via the first and second external connection terminals 7 and 8, the fusible conductor 3 forms part of the current path of the external circuit. This current path is interrupted by heat generated by the heating element 10 (described later) or by melting due to an overcurrent exceeding the rated value.

[Insulating substrate]

The insulating substrate 2 is formed from an insulating material such as aluminum oxide, glass ceramic, mullite, or zirconium oxide. Alternatively, the insulating substrate 2 may be made of materials used for printed wiring boards, such as glass epoxy and phenolic substrates. In the insulating substrate 2 shown in Figure 3 , the two side edges extending along the fusible conductor 3, which are connected via the front electrode 11 (described later), are designated as first side edges 2c. The two side edges forming the heater electrode 15 and heater feed electrode 16 (described later) are designated as second side edges 2d.

[Heat generating body]

The heating element 10 that melts the fusible conductor 3 is a conductive component with a high electrical resistance that generates heat when current is applied. It can be made of, for example, nickel-chromium alloy, W, Mo, Ru, Cu, Ag, or alloys containing these as primary components. It can be formed by mixing powders of these alloys, compositions, or compounds with a resin binder to form a paste. This paste is then patterned on the front surface 2a of the insulating substrate 2 using screen printing techniques and then calcined.

The heating element 10 is covered by an insulating layer 9 on the front surface 2a of the insulating substrate 2. A front electrode 11, described later, is laminated on the insulating layer 9. The insulating layer 9 is provided to protect and insulate the heating element 10 and to efficiently transfer heat from the heating element 10 to the front electrode 11 and the fusible conductor 3. It may be made of, for example, a glass layer.

One end of the heater 10 is connected to a heater electrode 15 formed on the front surface 2a of the insulating substrate 2. Furthermore, the heater electrode 15 is connected to a front electrode 11 formed on the insulating layer 9. This electrically connects the heater 10 to the fusible conductor 3 mounted on the front electrode 11. Furthermore, the other end of the heater 10 is connected to a heater feed electrode 16. The heater feed electrode 16 is formed on the front surface 2a of the insulating substrate 2 and is connected to a third external connection terminal 17 via a connection material 20 such as solder paste. The third external connection terminal 17 is then connected to an external circuit. Furthermore, the protection element 1 is connected to an external circuit, and the heating element 10 is assembled into a power supply path to the heating element 10 formed in the external circuit via the third external connection terminal 17.

Furthermore, as shown in FIG3 , the heating element 10 is formed so that the direction of current flow intersects the direction of current flow of the fusible conductor 3 . The heating element electrode 15 and the heating element feeding electrode 16 are formed on the second side edge portion 2 d . This is preferably done in terms of efficient use of the area of the insulating substrate 2 .

Furthermore, a plurality of heating elements 10 may be formed on the front surface of the insulating substrate 2. In the example of the protective element 1 shown in FIG3 , two heating elements 10 are formed. One end of each heating element 10 is connected to the heating element electrode 15 and the other end is connected to the heating element feeding electrode 16 , and the two elements are electrically connected in parallel.

Alternatively, the protective element 1 may have the heater 10 formed within the insulating layer 9 laminated on the front surface 2a of the insulating substrate 2. Alternatively, the protective element 1 may have the heater 10 formed within the insulating substrate 2. Alternatively, the protective element 1 may have the heater 10 formed on the back surface 2b of the insulating substrate 2. In the case where the heater 10 is formed on the back surface 2b of the insulating substrate 2, one end of the heater 10 is connected to a back electrode formed on the back surface 2b of the insulating substrate 2, and is electrically connected to the fusible conductor 2 mounted on the front surface 11 via a conductive through-hole extending between the back electrode and the front surface 11. Furthermore, the other end of the heating element 10 is connected to the third external connection terminal 17 via a heating element feeding electrode formed on the back surface 2b of the insulating substrate 2.

[Front electrode]

A front electrode 11 is formed on the insulating layer 9. This front electrode 11 is connected to the heater 10 via the heater electrode 15 and to the fusible conductor 3. The front electrode 11 is connected to the fusible conductor 3 via a bonding material 20 such as solder paste. Furthermore, when the fusible conductor 3 melts, the front electrode 11 agglomerates the molten conductor 3a, thereby fusing the fusible conductor 3.

The front electrode 11 may also be formed with a suction hole 12. When the fusible conductor 3 melts, the suction hole 12 draws the molten conductor 3a through the capillary phenomenon, reducing the volume of the molten conductor 3a held on the front electrode 11 (see Figure 4). Even if the cross-sectional area of the fusible conductor 3 is increased for high-current applications, resulting in an increased amount of melt, the suction hole 12 can be used to reduce the volume of the molten conductor 3a. The insulating substrate 2 with this structure forms a fuse member 18. When the heating element 10 is energized and generates heat, the heat melts the fusible conductor 3, drawing the molten conductor 3a toward the suction hole 12 and blocking it.

This allows the protective element 1 to reduce the volume of the fusible conductor 3a held on the front electrode 11, thereby more reliably achieving insulation between the first and second external connection terminals 7 and 8. Furthermore, this reduces the scattering of the fusible conductor 3a caused by arc discharge when the fusible conductor 3 melts, preventing a decrease in insulation resistance. Furthermore, it prevents short-circuit failures caused by the fusible conductor 3 adhering to the peripheral circuitry at the mounting location.

A conductive layer 13 is formed on the inner surface of the suction hole 12. This conductive layer 13 facilitates the suction of the molten conductor 3a. The conductive layer 13 is formed from, for example, copper, silver, gold, iron, nickel, palladium, lead, or tin, or an alloy primarily composed of any of these metals. The inner surface of the suction hole 12 can be formed by known methods such as electrolytic plating or printing a conductive paste. Alternatively, the conductive layer 13 can be formed by inserting a plurality of metal wires or a collection of conductive ribbons into the suction hole 12.

Furthermore, the suction hole 12 is preferably formed as a through-hole extending through the thickness of the insulating substrate 2. This allows the suction hole 12 to draw the molten conductor 3a toward the back surface 2b of the insulating substrate 2, thereby attracting more molten conductor 3a and reducing the volume of molten conductor 3a at the melted portion. Alternatively, the suction hole 12 may be formed as a non-through-hole.

The conductive layer 13 of the suction hole 12 is continuous with the front electrode 11 formed on the front surface 2a of the insulating substrate 2. Because the front electrode 11 supports the fusible conductor 3 and allows the molten conductor 3a to condense, the continuity between the front electrode 11 and the conductive layer 13 facilitates the guidance of the molten conductor 3a into the suction hole 12.

Furthermore, the conductive layer 13 and front electrode 11, heated by the heat element 10, easily draw the molten conductor 3a of the fusible conductor 3 into the suction hole 12 and easily aggregate it on the front electrode 11. Thus, the protective element 1 promotes the attraction of the molten conductor 3a from the front electrode 11 through the conductive layer 13 into the suction hole 12, reliably melting the fusible conductor 3.

Furthermore, a back electrode 14 can be formed on the back surface 2b of the insulating substrate 2, connected to the conductive layer 13 of the attraction hole 12. Because the back electrode 14 is continuous with the conductive layer 13, when the fusible conductor 3 melts, the molten conductor 3a that moves through the attraction hole 12 coalesces (see Figure 4). This allows the protective element 1 to attract more molten conductor 3a, reducing the volume of molten conductor 3a at the melted portion.

Furthermore, the protective element 1 can form a plurality of suction holes 12 to increase the path for attracting the molten conductor 3a of the fusible conductor 3. This allows for a greater amount of molten conductor 3a to be attracted, thereby reducing the volume of the molten conductor 3a at the melted portion. In this case, the plurality of suction holes 12 can be formed across the width of the fusible conductor 3 where the front electrode 11 and the fusible conductor 3 overlap. Alternatively, the suction holes 12 can be formed in the area where the front electrode 11 and the fusible conductor 3 do not overlap, allowing the molten conductor 3a to wet and expand.

Furthermore, when two heating elements 10 are arranged in parallel, whether formed on the front surface 2a, back surface 2b, or interior of the insulating substrate 2, they are formed on both sides of the suction hole 12. This is advantageous in heating the front electrode 11 and back electrode 14, and in attracting and condensing more molten conductor 3a.

[Shell]

Next, we will describe the housing 6 of the protective element 1. Housing 6 is formed by joining the lower housing 4 and the upper housing 5 with an adhesive 19. Housing 6 can be made of insulating materials such as various engineering plastics, thermoplastics, and ceramics. Housing 6 also has sufficient internal space on the front surface 2a of the insulating substrate 2 to allow the fusible conductor 3 to expand into a spherical shape when melted and to condense onto the front electrode 11 and the first and second external connection terminals 7 and 8.

The lower shell 4 and upper shell 5 are joined using adhesive 19. Adhesive 19 is supplied between the upper end surface of the side wall of the lower shell 4, which forms the side surface of the housing 6, and the lower end surface 5a of the side wall of the upper shell 5, where it solidifies, thereby joining the lower shell 4 and upper shell 5. The adhesive 19 is not particularly limited, and thermosetting adhesives are examples. Furthermore, the adhesive 19 can be in any form as long as it exhibits fluidity during the joining process. While its phase is not limited, a liquid state is preferred for ease of workability.

Furthermore, in the protective element employing the present invention, a fitting recess 25 is formed on one of the lower housing 4 and the upper housing 5, and a fitting protrusion 26 that fits into the fitting recess 25 is formed on the other. The following description uses the case where the fitting protrusion 26 is provided on the lower housing 4 and the fitting recess 25 is provided on the upper housing 5 as an example.

[Lower shell]

Figure 5 shows the lower housing 4, with (A) being a top view and (B) being a cross-sectional view taken along line E-E' of (A). The lower housing 4 is formed into a generally square shape, with four mating projections 26 formed at each corner. While the mating projections 26 are cylindrical, any other shape is acceptable, as long as they mate with the mating recesses 25 described below. For example, the mating projections 26 may be conical, prismatic, or pyramidal.

Furthermore, the lower housing 4 has a recessed portion 23 at its approximate center, which maintains the central portion of the insulating substrate 2 hollow. The lower housing 4 supports the outer edges of the insulating substrate 2 along the sides of the recessed portion 23. The recessed portion 23 reduces the contact area between the lower housing 4 and the insulating substrate 2, preventing heat from being absorbed by the lower housing 4 from the heating element 10. Consequently, the protective element 1 efficiently transfers heat from the heating element 10 to the fusible conductor 3, enabling faster melting. In particular, by providing the concave portion 23 approximately in the center of the lower housing 4, the area directly below the heating element 10 can be made hollow, thereby suppressing the heat dissipation of the heating element 10 to the lower housing 4.

[Upper shell]

Figure 6 shows the upper housing 5, with (A) being a bottom view and (b) being a cross-sectional view taken along line C-C' of (A). Like the lower housing 4, the upper housing 5 is formed into a generally rectangular shape, with four mating recesses 25 provided at each corner for mating with the mating protrusions 26 provided on the lower housing 4. The upper housing 5 covers the fusible conductor 3 and the first and second external connection terminals 7 and 8 formed on the front surface 2a of the insulating substrate 2, and includes an internal space for the fusible conductor 3a to be condensed on the front electrode 11 and the first and second external connection terminals 7 and 8.

Furthermore, the upper housing 5 is formed with a recessed narrow groove 27. This recessed narrow groove 27 is continuous with the mating recess 25 and extends to the lower end surface 5a of the side wall of the upper housing 5, which serves as the abutting surface between the upper housing 5 and the lower housing 4, to allow the adhesive 19 to flow. As shown in FIG7 , the recessed narrow groove 27 prevents the excess adhesive 19 from being retained in the mating recess 25, which is mated with the mating protrusion 26, by allowing the excess adhesive 19 filled in the mating recess 25 to flow inside when the upper housing 5 and the lower housing 4 are mated. This prevents excess adhesive 19 remaining in the mating recess 25 from obstructing the close contact between the upper and lower housings 5 and 4. Furthermore, since only enough adhesive 19 remains in the mating recess 25 to engage the mating protrusion 26, sufficient bonding strength is ensured between the mating recess 25 and the mating protrusion 26. Furthermore, the provision of the recessed slot 27 increases the bonding area with the adhesive 19, further enhancing bonding strength.

Therefore, the protective element 1 prevents the upper housing 5 from floating from the lower housing 4, maintaining the desired bond strength. This prevents the protective element 1 from causing problems such as the upper housing 5 becoming detached when the fusible conductor 3 melts, or failing to meet the specified housing height requirements.

The recessed narrow groove 27 is preferably formed along the lower end surface 5a of the side wall of the upper housing 5, where the adhesive 19 is supplied. The length of the recessed narrow groove 27 is not particularly limited. The width of the recessed narrow groove 27 is not particularly limited, but is preferably less than the diameter of the mating recess 25 when viewed from above. The depth of the recessed narrow groove 27 is not particularly limited, but is preferably the same as or shallower than the depth of the mating recess 25.

Furthermore, as shown in Figure 6(B), the recessed narrow groove 27 is preferably formed into a tapered shape that gradually becomes shallower from the bottom surface of the engaging recess 25 to the upper front surface of the engaging recess 25 as it separates from the engaging recess 25. This allows the excess adhesive 19 that flows into the recessed narrow groove 27 to be directed to the lower end surface 5a of the side wall of the upper shell 5, which serves as the abutment between the upper shell 5 and the lower shell 4, thereby providing for the joining of the upper shell 5 and the lower shell 4. Furthermore, by increasing the amount of adhesive supplied toward the corners of the housing 6, the bond strength can be enhanced.

Furthermore, as shown in FIG8 , the recessed narrow groove 27 is formed so as to gradually widen as it separates from the fitting recess 25. This facilitates the flow of excess adhesive 19 from the fitting recess 25 toward the front end of the narrow groove.

Alternatively, as shown in Figure 9, multiple recessed slots 27 may extend from a single engagement recess 25. This allows a greater amount of excess adhesive 19 to flow out of the engagement recess 25. Furthermore, the shapes (width, length, depth, inclination, etc.) of the multiple recessed slots 27 may be identical or different, allowing the amount of adhesive 19 flowing to vary depending on the direction.

Furthermore, as shown in Figure 9, recessed narrow grooves 27 are preferably formed along two adjacent side walls from one of the interlocking recesses 25 formed at each corner of the upper housing 5. This allows more of the excess adhesive 19 to flow out of the interlocking recesses 25. Furthermore, this excess adhesive 19 is directed to the lower end surface 5a of the side wall of the upper housing 5, which serves as the interface with the lower housing 4, allowing the upper and lower housings 5 and 4 to be joined.

Furthermore, the recessed groove 27 is preferably formed in the fully fitting recessed portion 25, but it does not necessarily need to be formed in the fully fitting recessed portion 25.

Furthermore, as shown in Figure 10, the recessed narrow grooves 27 extending from adjacent mating recesses 25 can be formed continuously. This allows excess adhesive 19 filling the mating recesses 25 to be directed toward the recessed narrow grooves 27. Excess adhesive 19 supplied to the mating surfaces of the upper and lower housings 5 and 4 is absorbed within the recessed narrow grooves 27, preventing excess adhesive 19 from obstructing the tight fit. Furthermore, the provision of the recessed narrow grooves 27 increases the contact area with the adhesive 19, thereby enhancing bond strength.

Furthermore, the upper housing 5 has a recessed portion formed on the lower end surface 5a of the side wall that abuts the lower housing 4. This recess allows the first and second external connection terminals 7, 8, and the third external connection terminal 17, supported by the lower housing 4, to be arranged across the interior and exterior of the housing 6. The recessed portion is formed at a position corresponding to the placement of the first, second, and third external connection terminals 7, 8, and 17, and has a shape that corresponds to the shapes of the first, second, and third external connection terminals 7, 8, and 17. Thus, the housing 6 allows the lower housing 4 and the upper housing 5 to abut and join without a gap, while also allowing the first, second, and third external connection terminals 7, 8, and 17 to be guided outside the housing.

When forming the housing 6, as shown in Figure 11, adhesive 19 is applied to the side edge of the lower housing 4, including the mating protrusion 26, and then brought into contact with the upper housing 5. This engages the mating protrusion 26 with the mating recess 25 via the adhesive 19, joining the lower housing 4 to the upper housing 5.

[Variation 1]

Next, a modified example of the protective element incorporating the present invention will be described. The protective element incorporating the present invention can replace the recessed slot 27 continuous with the mating recessed portion 25, or alternatively, form a raised slot 28 in the mating protrusion 26 in addition to the recessed slot 27 continuous with the mating recessed portion 25. The raised slot 28 is provided on the circumference of the mating protrusion 26 to allow excess adhesive 19 to flow, thereby preventing it from obstructing the close contact between the lower housing 4 and the upper housing 5.

The protrusion slot 28 is formed on the outer circumference of the mating protrusion 26. For example, as shown in Figures 12 and 13, the protrusion slot 28 can be formed as a straight line along the protruding direction of the mating protrusion 26. Figure 12 shows the housing 6 with the protrusion slot 28 provided in the lower housing 4. (A) is a bottom view of the upper housing 5, (B) is a cross-sectional view with the upper housing 5 and the lower housing 4 facing each other, and (C) is a top view of the lower housing 4. Figure 13 shows the mating protrusion 26 with the protrusion slot 28 formed. (A) is a top view, and (B) is a J-J' cross-sectional view taken along (A).

Furthermore, the shape of the protrusion slit 28 is not limited to a straight line; it can also be a wavy, rectangular, or sawtooth shape. Furthermore, the protrusion slit 28 can be formed not only in the protruding direction of the mating protrusion 26 but also in a direction surrounding the outer circumference. Furthermore, the protrusion slit 28 can be formed in a spiral shape on the outer circumference of the mating protrusion 26. Furthermore, the protrusion slit 28 can be formed continuously or intermittently.

While the orientation of the protruding narrow groove 28 is not particularly limited, it is preferably formed toward the abutting surface between the lower housing 4 and the upper housing 5, where the adhesive 19 is supplied. For example, in the configuration shown in Figure 12 , the protruding narrow groove 28 is preferably formed along the sidewall of the lower housing 4 . This allows excess adhesive 19 to flow to the abutting surface between the lower housing 4 and the upper housing 5, where the adhesive 19 is supplied, for bonding. Furthermore, when providing the recessed narrow groove 27 continuous with the aforementioned engaging recess 25 , it is preferably formed in the same orientation as the recessed narrow groove 27 .

Furthermore, the convex narrow groove 28 is preferably formed from the base of the mating convex portion 26. Since the base of the mating convex portion 26 serves as the abutment surface between the lower housing 4 and the upper housing 5, it actively absorbs excess adhesive 19, promoting close contact. Furthermore, the convex narrow groove 28 is preferably formed across the top of the mating convex portion 28. This facilitates the introduction of excess adhesive 19 remaining in the mating recess 25 into the convex narrow groove 28, increasing the amount of adhesive 19 absorbed.

Alternatively, multiple protrusion narrow grooves 28 may be formed on a single mating protrusion 26. This allows a greater amount of excess adhesive 19 to be absorbed within the protrusion narrow grooves 28. Furthermore, as shown in Figure 12, the protrusion narrow grooves 28 are preferably formed along the two adjacent side walls of the mating protrusion 26 formed at the corner of the lower housing 4. This allows excess adhesive 19 to flow to the mating surface between the lower housing 4 and the upper housing 5, where the adhesive 19 is supplied, and to be used for bonding. Furthermore, if a concave narrow groove 27 is provided that continues with the mating recess 25 described above, it is preferably formed in the same orientation as the concave narrow groove 27.

Furthermore, as shown in Figures 14 and 15 , the protrusion groove 28 can be formed into a tapered shape, with its width gradually decreasing from the periphery of the mating protrusion 26 toward the center, when viewed from above. This allows the capillary phenomenon to take effect, allowing the adhesive 19 to flow into the protrusion groove 28 and increasing the amount of inflow.

Furthermore, the protrusion groove 28 can be formed into a tapered shape, gradually widening from the top to the base of the mating protrusion 26, as seen in cross-section. This allows the capillary effect to occur, allowing excess adhesive 19 remaining on the mating surface between the lower housing 4 and the upper housing 5 to flow into the protrusion groove 28, thereby increasing the amount of adhesive flowing in.

Furthermore, in the protective element 1 shown in Figures 12 and 14 , while a convex narrow groove 28 is provided in the mating protrusion 26 formed on the lower housing 4 to engage with the mating recess 25 formed on the upper housing 5 , a concave narrow groove 27 continuous with the mating recess 25 may also be formed in the upper housing 5 . By forming the convex narrow groove 28 continuous with the mating protrusion 26 and the concave narrow groove 27 continuous with the mating recess 25 , more excess adhesive 19 can be absorbed, preventing it from obstructing the close contact between the lower housing 4 and the upper housing 5 .

[Variation 2]

In the above embodiment, the upper housing 5 is described as having a fitting recess 25 and recessed slot 27, and the lower housing 4 as having a fitting protrusion 26 and protrusion slot 28. However, a protective element employing the present invention can also have the fitting protrusion 26 formed on the upper housing 51 and the fitting recess 25 and recessed slot 27 formed on the lower housing 52, as shown in Figures 16 and 17. In the following description, components identical to those of the protective element 1 described above are designated by the same reference numerals, and details are omitted.

Figure 18 shows the step of joining the upper housing 51 and the lower housing 52 to form the protective element 50. Figure 16 shows the upper housing 51 provided with the mating protrusion 26, (A) a bottom view, and (B) a cross-sectional view taken along the line L-L' of (A). Figure 17 shows the lower housing 52 provided with the mating recess 25, (A) a top view, and (B) a cross-sectional view taken along the line M-M' of (A). As shown in Figure 17, the protective element 50 has the aforementioned mating recess 25 and recessed slot 27 formed in the lower housing 52.

The steps for joining the lower housing 52 and the upper housing 51 are the same as those for the aforementioned protective element 1. Specifically, as shown in Figures 19(A) and 19(B), adhesive 19 is applied along the mating surfaces of the lower housing 52 and the upper housing 51. At this point, adhesive 19 is applied to the fitting recesses 25 and recess grooves 27 formed at each corner of the lower housing 52. Furthermore, as shown in Figure 18, when the mating protrusion 26 formed on the upper housing 51 is inserted into the mating recess 25 and the lower housing 52 is brought into contact with the upper housing 51, the excess adhesive 19 filling the mating recess 25 flows out into the recess groove 27, preventing it from being retained in the mating recess 25. This prevents the excess adhesive 19 retained in the mating recess 25 from impeding the close contact between the upper and lower housings 51 and 52. Furthermore, the provision of the recess groove 27 increases the contact area with the adhesive 19, thereby enhancing the bond strength.

[Variation 3]

Similarly, in the protective element 50, the aforementioned convex slit 28 can be formed on the convex fitting portion 26 formed on the upper housing 51, instead of or in addition to the concave slit 27 continuous with the fitting concave portion 25 formed on the lower housing 52. Since the configuration of these concave slit 27 and convex slit 28 has already been described in detail in the protective element 1, the details are omitted here. Furthermore, in the protective element 50, as in the protective element 1, the configuration of the concave slit 27 and convex slit 28 can be modified in various ways.

[Fusible conductor]

Next, let's explain the fusible conductor 3. It's installed between the first and second external connection terminals 7 and 8. It melts due to heat generated by the heating element 10 or self-heating (Joule heat) caused by the flow of current exceeding the rated value, thus shutting off the current path between the first and second external connection terminals 7 and 8.

The fusible conductor 3 can be any conductive material that melts due to the heat generated by the heating element 10 or due to an overcurrent condition. For example, in addition to SnAgCu-based Pb-free solder, BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, etc. can also be used.

Alternatively, the fusible conductor 3 may be a structure containing both a high-melting-point metal and a low-melting-point metal. For example, as shown in Figure 20 , the fusible conductor 3 comprises a laminated structure including an inner layer and an outer layer, with a low-melting-point metal layer 31 serving as the inner layer and a high-melting-point metal layer 32 serving as the outer layer laminated on the low-melting-point metal layer 31. The fusible conductor 3 is connected to the first and second external connection terminals 7 and 8 and the front electrode 11 via a bonding material 20 such as solder paste.

The low-melting-point metal layer 31 is preferably solder or a metal primarily composed of Sn, a material commonly referred to as "Pb-free solder." The melting point of the low-melting-point metal layer 31 does not necessarily need to be higher than the reflow furnace temperature and can melt at around 200°C. The high-melting-point metal layer 32 is a metal layer laminated on the front surface of the low-melting-point metal layer 31. For example, it can be made of Ag, Cu, or a metal primarily composed of either of these. It has a relatively high melting point and does not melt even during reflow to connect the first and second external connection terminals 7 and 8 and the front electrode 11 to the fusible conductor 3.

This fusible conductor 3 can be formed by depositing a high-melting-point metal layer on a low-melting-point metal foil using a plating technique, or it can be formed using other well-known lamination or film-forming techniques. In this case, the fusible conductor 3 can have a structure in which the low-melting-point metal layer 31 is entirely covered by the high-melting-point metal layer 32, or it can have a structure in which all but one pair of opposing side surfaces are covered. Furthermore, the fusible conductor 3 can have a high-melting-point metal layer 32 as the inner layer and the low-melting-point metal layer 31 as the outer layer, or it can have a multi-layer structure consisting of three or more layers alternately laminated with low-melting-point and high-melting-point metal layers, with an opening provided in one portion of the outer layer to expose a portion of the inner layer.

By laminating a high-melting-point metal layer 32 as the outer layer on a low-melting-point metal layer 31, the fusible conductor 3 maintains its shape and prevents melting even when the reflow temperature exceeds the melting temperature of the low-melting-point metal layer 31. Consequently, the protective element 1 can efficiently connect the first and second external connection terminals 7 and 8 and the front electrode 11 to the fusible conductor 3 during reflow. Furthermore, reflow prevents variations in the protective element 1's melting characteristics, such as failure to melt at a specified temperature or melting below the specified temperature, due to localized increases or decreases in resistance associated with deformation of the fusible conductor 3.

Furthermore, the fusible conductor 3 will not melt due to self-heating even when a specific rated current is flowing. However, when a current exceeding the rated value is flowing, the fusible conductor 3 melts due to self-heating, blocking the current path between the first and second external connection terminals 7 and 8. Furthermore, the fusible conductor 3 is energized by the heating element 10, generating heat and melting, thereby blocking the current path between the first and second external connection terminals 7 and 8.

At this point, the fusible conductor 3 erodes the high-melting-point metal layer 32 (solder etching) through the molten low-melting-point metal layer 31, causing the high-melting-point metal layer 32 to melt at a temperature lower than its melting point. Consequently, the fusible conductor 3 is quickly melted by the erosion of the high-melting-point metal layer 32 by the low-melting-point metal layer 31. Furthermore, the molten conductor 3a of the fusible conductor 3 is physically pulled apart by the front electrode 11 and the first and second external connection terminals 7 and 8, quickly and reliably interrupting the current path between the first and second external connection terminals 7 and 8 (Figure 4).

Furthermore, the fusible conductor 3 is preferably formed so that the volume of the low-melting-point metal layer 31 is larger than the volume of the high-melting-point metal layer 32. The fusible conductor 3 is heated by self-heating due to overcurrent or by heating of the heating element 10. The low-melting-point metal melts, corroding the high-melting-point metal, thereby rapidly melting and fusing. Therefore, by forming the fusible conductor 3 with the low-melting-point metal layer 31 larger than the high-melting-point metal layer 32, this erosion is accelerated, allowing for rapid isolation between the first and second external connection terminals 7 and 8.

Furthermore, because the fusible conductor 3 is constructed by laminating a high-melting-point metal layer 32 onto an inner low-melting-point metal layer 31, its melting temperature is significantly lower than that of conventional chip fuses containing high-melting-point metals. Consequently, the fusible conductor 3 can have a larger cross-sectional area and significantly higher current rating than conventional chip fuses of the same size. Furthermore, this allows for a more compact and thinner design than conventional chip fuses with the same current rating, while maintaining superior quick-blow characteristics.

Furthermore, the fusible conductor 3 improves its resistance to surges (pulse resistance) caused by the momentary application of abnormally high voltages to the electrical system in which the protective element 1 is installed. That is, the fusible conductor 3 will not melt even when a current of, for example, 100A flows for a few milliseconds. This is due to the skin effect, in which large currents flowing for extremely short periods of time flow through the surface of the conductor. The fusible conductor 3 is coated with a high-melting-point metal layer 32, such as Ag, with a relatively low resistance, as an outer layer. This facilitates the flow of current applied by surges, preventing melting due to self-heating. Consequently, the fusible conductor 3 significantly improves its resistance to surges compared to conventional fuses containing solder alloys.

In addition, the fusible conductor 3 may be coated with a flux (not shown) to prevent oxidation and improve wettability during melting.

[Circuit Configuration Example]

As shown in FIG21 , this protection element 1 is used by being incorporated into a circuit within a battery pack 33 of lithium-ion secondary batteries. The battery pack 33 includes, for example, a battery stack 35 containing a total of four lithium-ion secondary battery cells 34a to 34d.

The battery pack 33 includes: a battery stack 35; a charge/discharge control circuit 36 that controls the charging and discharging of the battery stack 35; a protective element 1 according to the present invention that interrupts the charge/discharge circuit when an abnormality occurs in the battery stack 35; a detection circuit 37 that detects the voltage of each battery cell 34a-34d; and a current control element 38 that functions as a switch element to control the operation of the protective element 1 in response to the detection result of the detection circuit 37.

The battery stack 35 is composed of battery cells 34a-34d connected in series to protect against overcharge and over-discharge conditions. The battery pack 33 is removably connected to the charging device 29 via its positive and negative terminals 33a and 33b, applying a charging voltage from the charging device 29. By connecting the positive and negative terminals 33a and 33b of the battery pack 33, after being charged by the charging device 29, to an electronic device that operates using the battery, the device can be operated.

The charge-discharge control circuit 36 includes two current control elements 39a and 39b connected in series in the current path between the battery stack 35 and the charging device 29, and a control unit 40 that controls the operation of these current control elements 39a and 39b. The current control elements 39a and 39b are composed of, for example, field-effect transistors (FETs). The control unit 40 controls the gate voltage to enable and disable the current path to the battery stack 35 in the charging and/or discharging directions. The control unit 40 operates by receiving power from the charging device 29. In response to the detection results of the detection circuit 37, the control unit 40 controls the operation of the current control elements 39a and 39b by blocking the current path when the battery stack 35 is over-discharged or over-charged.

The protection element 1 is connected to the charge and discharge current path between the battery stack 35 and the charge and discharge control circuit 36, for example, and its operation is controlled by the current control element 38.

Detection circuit 37 is connected to each battery cell 34a-34d, detects the voltage value of each battery cell 34a-34d, and supplies each voltage value to control unit 40 of charge and discharge control circuit 36. Furthermore, when any battery cell 34a-34d reaches an overcharge voltage or an overdischarge voltage, detection circuit 37 outputs a control signal to control current control element 38.

The current control element 38 is composed of, for example, an FET. Based on the detection signal output from the detection circuit 37, when the voltage of the battery cells 34a-34d exceeds a specific over-discharge or over-charge voltage, the protection element 1 is activated, controlling the battery stack 35 by blocking the charge and discharge current path without relying on the switching operation of the current control elements 39a and 39b.

The protective element 1 according to the present invention, used with the battery pack 33 having the above-described configuration, has the circuit configuration shown in FIG22 . Specifically, the protective element 1 connects the first external connection terminal 7 to the battery stack 35 side, and the second external connection terminal 8 to the positive terminal 33a side, thereby connecting the fusible conductor 3 in series with the charge and discharge path of the battery stack 35. Furthermore, the protective element 1 connects the heater 10 to the current control element 38 via the heater feed electrode 16 and the third external connection terminal 17, and also connects the heater 10 to the open end of the battery stack 35. Thus, one end of the heating element 10 is connected to the open end of either the fusible conductor 3 or the battery stack 35 via the front electrode 11, and the other end is connected to the current control element 38 and the other open end of the battery stack 35 via the third external connection terminal 17. This forms a feed path to the heating element 10, whose current flow is controlled by the current control element 38.

[Protection element operation]

If the detection circuit 37 detects an abnormal voltage in any of the battery cells 34a-34d, it outputs a shutoff signal to the current control element 38. This controls the current flow by energizing the heating element 10. The protective element 1 then flows a current from the battery stack 35 to the heating element 10, causing the heating element 10 to begin heating. The heat generated by the heating element 10 causes the protective element 1 to melt the fusible conductor 3, interrupting the charge and discharge path of the battery stack 35. Furthermore, the protective element 1 is formed by making the fusible conductor 3 contain a high-melting-point metal and a low-melting-point metal. Before the high-melting-point metal melts, the low-melting-point metal melts. The molten low-melting-point metal corrodes the high-melting-point metal, quickly dissolving the fusible conductor 3.

Since the protective element 1 melts due to the fusible conductor 3, the power supply path to the heating element 10 is also cut off, thus stopping the heating element 10 from generating heat.

Furthermore, when an overcurrent exceeding the rated value flows through the battery pack 33, the protective element 1 will melt the fusible conductor 3 through self-heating, thereby blocking the charge and discharge path of the battery pack 33.

Here, the protective element 1 securely bonds the lower shell 4 and upper shell 5 of the housing 6, achieving the desired bond strength. Consequently, the protective element 1 prevents the upper shell 5 from detaching when the fusible conductor 3 melts. Furthermore, by securely bonding the lower shell 4 and upper shell 5 of the housing 6, the protective element 1 can meet specific housing height requirements.

In this manner, the protective element 1 melts the fusible conductor 3 by heating caused by the passage of current to the heater 10 or by self-heating of the fusible conductor 3 due to overcurrent. Even when the fusible conductor 3 is exposed to high-temperature environments, such as during reflow mounting to the first and second external connection terminals 7 and 8 and the front electrode 11, the protective element 1, with its structure of a low-melting-point metal covered by a high-melting-point metal, suppresses deformation of the fusible conductor 3. This prevents changes in the melting characteristics caused by changes in the resistance value due to deformation of the fusible conductor 3, enabling rapid melting by a specific overcurrent or heating of the heater 10.

The protection element 1 of the present invention is not limited to use in lithium-ion secondary battery packs. It can also be used in various applications requiring interruption of current paths mediated by electrical signals.

[Variation 4]

Next, another variation of the protective element to which the present invention is applied will be described. In the following description, components identical to those of the aforementioned protective elements 1 and 50 are sometimes designated with the same reference numerals, and details are omitted. A variation of the protective element 60, as shown in FIG23 , can have multiple fuse members 18 sandwiching the fusible conductor 3. The protective element 60 shown in FIG23 has the fuse members 18 disposed on one and the other surfaces of the fusible conductor 3. FIG24 is a circuit diagram of the protective element 60. Each fuse member 18 disposed on the front and back surfaces of the fusible conductor 3 connects one end of the heating element 10 to the fusible conductor 3 via the heating element electrode 15 and the front electrode 11 formed on each insulating substrate 2, and connects the other end of the heating element 10 to a power source for generating heat for the heating element 10 via the heating element feeding electrode 16 and the third external connection terminal 17 formed on each insulating substrate 2.

Furthermore, as shown in Figure 25 , when the protective element 60 melts the fusible conductor 3 by heating the heating element 10, the heating elements 10 connected to the respective fuse members 18, 18 on both sides of the fusible conductor 3 generate heat, heating the fusible conductor 3 from both sides. Therefore, even when the cross-sectional area of the fusible conductor 3 is increased to accommodate high current applications, the protective element 60 can still quickly heat and melt the fusible conductor 3.

The protective element 60 also has a housing 6 similar to the protective elements 1 and 50 described above, with a fitting recess 25 and recessed slot 27, or a fitting protrusion 26 and protrusion slot 28 formed on the lower outer shell 4 or upper outer shell 5.

Furthermore, the protective element 60 draws the fusible conductor 3a from both sides of the fusible conductor 3 into the respective draw holes 12 formed in the insulating substrate 2 within the respective fuse members 18. Therefore, even if the cross-sectional area of the fusible conductor 3 is increased to accommodate high-current applications and a large amount of fusible conductor 3a is generated, the protective element 60 can reliably melt the fusible conductor 3 by drawing the fusible conductor 3a through the multiple fuse members 18. Furthermore, by utilizing the multiple fuse members 18 to draw the fusible conductor 3a, the protective element 60 can melt the fusible conductor 3 more quickly.

Even when the protective element 60 uses a low-melting-point metal coating as the fusible conductor 3, the fusible conductor 3 can be quickly melted. Specifically, even when the heating element 10 is energized, a fusible conductor 3 coated with a high-melting-point metal takes time to heat to a temperature at which the outer high-melting-point metal melts. By including multiple fuse members 18 and simultaneously energizing each heating element 10, the protective element 60 can quickly heat the outer high-melting-point metal to a melting point. Consequently, the protective element 60 can increase the thickness of the outer high-melting-point metal layer, achieving a higher rating while maintaining fast-blowing characteristics.

Furthermore, as shown in Figure 23, the protective element 60 preferably has a pair of fuse members 18, 18 connected to the fusible conductor 3 in opposing directions. This allows the protective element 60 to simultaneously heat the same portion of the fusible conductor 3 from both sides, while also attracting the molten conductor 3a, allowing for faster heating and melting of the fusible conductor 3.

Furthermore, the protective element 60 is preferably formed on the front electrodes 11 of the insulating substrate 2 of a pair of fuse members 18, 18, facing each other with the fusible conductor 3 interposed therebetween. This symmetrical connection of the pair of fuse members 18, 18 prevents unbalanced load application to the fusible conductor 3 during reflow assembly, thereby improving resistance to deformation.

Furthermore, the heating element 10, whether formed on the front surface 2a or the back surface 2b of the insulating substrate 2, is formed on both sides of the suction hole 12. This is advantageous in heating the front electrode 11 and the back electrode 14, and in converging and sucking more of the molten conductor 3a.

1: Protective components

4: Lower shell

5: Upper shell

5a: Lower end surface of the side wall

19: Follow-up agent

25: Fitting recess

26: Fitting convex part

27: Recessed slot/slot

Claims (18)

A protective element comprises: a fusible conductor; and a housing having a lower housing and an upper housing, the housing being formed by bonding the upper and lower housings together with an adhesive. A fitting recess is formed in one of the upper and lower housings, and a fitting protrusion is formed in the other housing to fit into the fitting recess. Furthermore, a narrow groove is formed therein, continuous with the fitting recess and extending to the mating surfaces of the upper and lower housings, and allows the adhesive to flow when the upper and lower housings are mated. The protective element of claim 1, wherein the narrow groove is formed into a tapered shape that gradually becomes shallower from the bottom surface of the fitting recess to the upper front surface of the fitting recess as it separates from the fitting recess. The protective element of claim 1 or 2, wherein the narrow groove gradually widens as it separates from the engaging recess. The protective element of claim 1 or 2, wherein a plurality of the narrow grooves extend from one of the above-mentioned recesses. The protective element of claim 4, wherein the engagement recess is formed at a corner of the upper or lower housing; and the narrow groove is formed from one of the engagement recesses along two adjacent side walls of the housing. The protective element of claim 1 or 2, wherein the engaging recess is formed at all corners of the upper outer shell or the lower outer shell. In the protective element of claim 1 or 2, the width of the narrow groove is less than the diameter of the engaging recess when viewed from above. A protective element as claimed in claim 1 or 2, wherein the narrow grooves extending from adjacent engaging recesses are continuous with each other. A protective element comprises: a fusible conductor; and a housing having a lower housing and an upper housing, the housing being formed by bonding the upper and lower housings together with an adhesive. A fitting recess is formed in one of the upper and lower housings, and a fitting protrusion is formed in the other housing to fit into the fitting recess. The fitting protrusion has a narrow groove formed on its outer circumference for allowing the adhesive to flow when the upper and lower housings are brought into contact. The protective element of claim 9, wherein the narrow groove is formed in a plurality of the above-mentioned engaging protrusions. The protective element of claim 9 or 10, wherein the narrow groove is formed on the peripheral surface of the engaging protrusion in a direction along the side wall of the housing. The protective element of claim 11, wherein the engaging protrusion is formed at a corner of the upper outer shell or the lower outer shell; and the narrow groove is formed along two adjacent side walls of the shell. The protective element of claim 9 or 10, wherein the narrow groove is formed into a tapered shape in a plan view, the width of which gradually decreases from the peripheral surface of the engaging protrusion toward the center. The protective element of claim 9 or 10, wherein the narrow groove is formed into a tapered shape that gradually widens from the top to the base of the engaging protrusion in a plan view. A protective element comprises: a fusible conductor; and a housing having a lower housing and an upper housing, formed by bonding the upper housing and the lower housing with an adhesive; and a fitting recess is formed on one of the upper housing and the lower housing, and a fitting protrusion is formed on the other of the upper housing and the lower housing to fit into the fitting recess, and A narrow groove is formed on the outer peripheral surface of the mating protrusion, which is continuous with the mating recess and extends to the mating surfaces of the upper and lower housings, allowing the adhesive to flow when the upper and lower housings are mated. The mating protrusion has a narrow groove formed on its outer peripheral surface, which allows the adhesive to flow when the upper and lower housings are mated. A battery pack comprises: one or more battery cells; and a protective element connected to the charge and discharge circuit of the battery cells to block the charge and discharge circuit; and the protective element comprises: a fusible conductor; and a housing having a lower housing and an upper housing, formed by bonding the upper housing and the lower housing with an adhesive; and One of the upper and lower housings has a recessed engagement portion, while the other has a protruding engagement portion that engages with the recessed engagement portion. Furthermore, a narrow groove is formed therein. The narrow groove is continuous with the recessed engagement portion and extends along the mating surfaces of the upper and lower housings, allowing the adhesive to flow when the upper and lower housings are mated. A battery pack comprises: one or more battery cells; and a protective element connected to a charge/discharge circuit of the battery cell to block the charge/discharge circuit; the protective element comprising: a fusible conductor; and a housing comprising a lower housing and an upper housing, the housing being formed by bonding the upper and lower housings together with an adhesive; wherein one of the upper and lower housings has a mating recess, and the other has a mating projection that engages with the mating recess; the mating projection has a narrow groove that allows the adhesive to flow in a protruding direction when the upper and lower housings are mated. A battery pack comprising: one or more battery cells; a protective element connected to a charge/discharge circuit of the battery cells to block the charge/discharge circuit; the protective element comprising: a fusible conductor; and a housing comprising a lower housing and an upper housing, the housing being formed by bonding the upper housing and the lower housing with an adhesive; and a fitting recess being formed in either the upper housing or the lower housing. A fitting protrusion is formed on either of the other ones and is fitted into the above-mentioned fitting recess, and a narrow groove is formed. The narrow groove is continuous with the above-mentioned fitting recess and extends to the mating surface of the above-mentioned upper shell and the above-mentioned lower shell, so that the above-mentioned adhesive flows when the above-mentioned upper shell and the above-mentioned lower shell are mated; the above-mentioned fitting protrusion is formed with a narrow groove that causes the above-mentioned adhesive to flow along the protruding direction when the above-mentioned upper shell and the above-mentioned lower shell are mated.