Electromagnetic relay

An electromagnetic relay includes a housing having an accommodating space therein, a magnet coil in the accommodating space to generate electromagnetic force when energized, a moving contact disposed in the accommodating space and driven by the coil, a fixed contact in the accommodating space, the moving contact engaged with or disengaged from the fixed contact as a result of whether the moving contact is driven or not, a breathing hole formed in the housing to communicate between the accommodating space and an exterior space of the housing, and a flame propagation route along which a flame of flammable gas ignited by arc generated between the moving contact and the fixed contact propagates toward the breathing hole. The route includes a flame extinguishment clearance that is set to have such a gap size that the flame is extinguished when passing through the clearance.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2008-234438 filed on Sep. 12, 2008, and Japanese Patent Application No. 2009-021296 filed on Feb. 2, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic relay which opens and closes an electric circuit.

2. Description of Related Art

According to a conventional electromagnetic relay described in the publication JP-A-2005-203290, a fixed contact is positioned and held at a predetermined position by a fixed contact holding member, and the moving contact is engaged with or disengaged from the fixed contact by driving a moving member, on which a moving contact is attached, by electromagnetic force of a magnet coil. As a result, the conventional relay opens or closes an electric circuit. Furthermore, an accommodating space in a housing, in which components such as the magnet coil are arranged, communicates with an exterior space of the housing through a breathing hole.

However, when the conventional electromagnetic relay having the breathing hole is used under an environment in which flammable gas is generated, flammable gas flows into the accommodating space through the breathing hole, and the flammable gas which has flowed into the accommodating space is ignited by arc generated between the moving contact and the fixed contact. If the ignited flame propagates to the exterior space of the housing through the breathing hole, flammable gas that exists in the exterior space of the housing may catch fire from the flame.

SUMMARY OF THE INVENTION

The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide an electromagnetic relay configured such that a flame of flammable gas ignited by arc does not propagate to an exterior space of a housing.

To achieve the objective of the present invention, there is provided an electromagnetic relay including a housing, a magnet coil, a moving contact; a fixed contact, a breathing hole, and a flame propagation route. The housing has an accommodating space inside the housing. The magnet coil is disposed in the accommodating space and configured to generate electromagnetic force when energized. The moving contact is disposed in the accommodating space and driven by the magnet coil as a result of energization of the magnet coil. The fixed contact is disposed in the accommodating space. The moving contact is engaged with or disengaged from the fixed contact as a result of whether the moving contact is driven or not. The breathing hole is formed in the housing so as to communicate between the accommodating space and an exterior space of the housing. A flame of flammable gas ignited by arc generated between the moving contact and the fixed contact propagates toward the breathing hole along the flame propagation route. The flame propagation route includes a flame extinguishment clearance that is set to have such a gap size that the flame is extinguished when passing through the flame extinguishment clearance.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are described below with reference to the accompanying drawings. The same numerals are used in the drawings to indicate the same or equivalent parts in the following embodiments.

First Embodiment

A first embodiment of the invention is described below with reference toFIG. 1toFIG. 3.

An electromagnetic relay according to the present embodiment is used for an electric motorcar with an electric motor as a driving source of its travel. More specifically, a lithium ion battery is installed in the electric motorcar for supplying electric power to the electric motor, and the electromagnetic relay is disposed in an electric circuit, through which electric power for charging is supplied to a capacitor from the lithium ion battery.

Battery fluid of the lithium ion battery includes organic solvent (such as dimethyl carbonate (DMC) or ethyl methyl carbonate (EMC)). If temperature of the battery fluid rises due to overcharge, for example, the dimethyl carbonate or ethyl methyl carbonate gasifies. In addition, gasified dimethyl carbonate or gasified ethyl methyl carbonate is flammable gas.

The electromagnetic relay of the present embodiment may be used for an electric motorcar in which a fuel cell is installed. Hydrogen gas, which is flammable gas, is used in the fuel cell.

As shown inFIG. 1toFIG. 3, according to the electromagnetic relay of the present embodiment, a case11formed in a rectangular parallelepiped is fitted to a plate-like base10made of resin, and the case11is made of resin and has a cylindrical shape having a bottom portion. An accommodating space10ais defined inside the relay by the base10and the case11. The accommodating space10acommunicates with an exterior space of the base10and the case11through a breathing hole101formed in the base10. The base10and the case11may constitute a “housing” of the invention.

Two fixed contact holding members12,13made of conductive metal are fixed to the base10. The two fixed contact holding members12,13penetrate through the base10, and their one end side is located in the accommodating space10a, whereas the other end side is located in an exterior space.

Fixed contacts14,15made of conductive metal are calked and fixed respectively on end portions of the two fixed contact holding members12,13on the accommodating space10aside. The two fixed contacts14,15are positioned and held at predetermined positions by the two fixed contact holding members12,13.

Load circuit terminals121,131connected to an external harness (not shown) are formed respectively on the exterior space sides of the two fixed contact holding members12,13. The load circuit terminal121of the first fixed contact holding member12is connected to the lithium ion battery (not shown) via the external harness, and the load circuit terminal131of the second fixed contact holding member13is connected to the capacitor (not shown) via the external harness.

Two coil terminals17(only one of them is shown) connected to a magnet coil16and made of conductive metal, are fixed respectively to the base10by press fitting, for example. More specifically, a coil terminal insertion hole103which communicates between the accommodating space10aand the exterior space and in which the coil terminal17is inserted is formed in the base10. The coil terminal insertion hole103and the breathing hole101are formed adjacently in a communicating state. The coil terminal17is inserted in the coil terminal insertion hole103. One end side of the coil terminal17is located in the accommodating space10a, and the other end side of the coil terminal17is located in the exterior space.

The magnet coil16includes a bobbin161made of resin and a coil wire162which is wound around a cylindrical portion (not shown) of the bobbin161and an end portion of which is connected to the coil terminal17. The magnet coil16generates electromagnetic force when energized. The bobbin161includes a first flanged portion161alocated on an armature20side and a second flanged portion161blocated on an opposite side of the magnet coil16from the armature20. The armature20is described in greater detail hereinafter. A fixed core19made of a magnetic metallic material is disposed in the cylindrical portion of the bobbin161.

The yoke18is made of a magnetic metallic material, and bent in a U-shaped manner. The yoke18constitutes a magnetic path of magnetic flux induced by the magnet coil16. The yoke18is fixed to the base10by press-fitting, for example, and the magnet coil16is fixed to the yoke18.

An armature20made of magnetic metal is disposed in a position opposed to the fixed core19, and the armature20is attracted to the fixed core19side upon energization of the magnet coil16. The armature20is connected to the yoke18via a connecting plate21made of metal and bent in a generally L-shape. The connecting plate21applies elastic force, which is in a direction in which the armature20disengages from the fixed core19, to the armature20when the magnet coil16is not energized.

A U-shaped flat spring23made of conductive metal is connected to the armature20via a connecting member22made of resin. Moving contacts24,25made of conductive metal are calked and fixed on both ends of the flat spring23, and the first moving contact24is opposed to the first fixed contact14, whereas the second moving contact25is opposed to the second fixed contact15.

A first permanent magnet26for applying Lorentz force to arc that is generated when the first moving contact24disengages from the first fixed contact14is disposed on a lateral side of the first fixed contact14and the first moving contact24. A second permanent magnet27for applying Lorentz force to arc that is generated when the second moving contact25disengages from the second fixed contact15is disposed on a lateral side of the second fixed contact15and the second moving contact25. These permanent magnets26,27, which are formed in a cylindrical shape, are inserted respectively in recesses formed on the side wall of the case11.

The first fixed contact holding member12and the flat spring23extend parallel to each other and in a direction away from the first permanent magnet26. The second fixed contact holding member13and the flat spring23extend parallel to each other and in a direction away from the second permanent magnet27.

A partition wall102projecting into the accommodating space10ais formed on the base10. With this partition wall102, a space in which the first fixed contact14and the first moving contact24are disposed is divided off from a space in which the second fixed contact15and the second moving contact25are disposed.

A recessed or grooved first guide part111is formed on an inner wall part of the case11on an opposite side of the first fixed contact14and the first moving contact24from the partition wall102. The first guide part111extends in a direction parallel to an alignment direction of the first fixed contact14and the first moving contact24and thereby guides arc, which has collided with the first guide part111, in a direction generally parallel to the alignment direction.

A recessed or grooved second guide part112is formed on an inner wall part of the case11on an opposite side of the second fixed contact15and the second moving contact25from the partition wall102. The second guide part112extends in a direction parallel to an alignment direction of the second fixed contact15and the second moving contact25and thereby guides arc, which has collided with the second guide part112, in a direction generally parallel to the alignment direction.

As described above, the electromagnetic relay of the present embodiment is used under an environment in which flammable gas may be generated. If flammable gas is generated, the flammable gas flows into the accommodating space10athrough the breathing hole101, and the flammable gas which has flowed into the accommodating space10ais ignited by the arc generated between the fixed contacts14,15and the moving contacts24,25respectively.

Accordingly, in the present embodiment, by forming flame extinguishment clearances C1to C11that is set to have such a gap size S that they can extinguish the flame in a flame propagation route along which a flame of flammable gas ignited by the arc propagates toward the breathing hole101, the propagation of flame to the exterior space is prevented. Furthermore, by setting a gap size S′ of the breathing hole101at such a size that it can extinguish the flame, the propagation of flame to the exterior space is prevented more reliably.

The flame extinguishment clearances C1to C11are formed at eleven places respectively as described below. Specifically, a first flame extinguishment clearance C1(seeFIG. 1andFIG. 3) is formed between a region of the yoke18on its opposite side from the base10(i.e., on the second flanged portion161bside of the bobbin161) and the case11; a second flame extinguishment clearance C2and a third flame extinguishment clearance C3are formed (seeFIG. 2) between side surfaces of the second flanged portion161band the case11; and a fourth flame extinguishment clearance C4and a fifth flame extinguishment clearance C5are formed (seeFIG. 2) between an outer circumferential surface of the coil wire162and the case11.

A sixth flame extinguishment clearance C6(seeFIG. 1andFIG. 2) is formed between an end face122of the first fixed contact holding member12on its one end side, on which the first fixed contact14is attached, and the case11; a seventh flame extinguishment clearance C7(seeFIG. 2andFIG. 3) is formed between the partition wall102and the first fixed contact holding member12; and a eighth flame extinguishment clearance C8(seeFIG. 1andFIG. 3) is formed between the first fixed contact holding member12and the flat spring23.

A ninth flame extinguishment clearance C9(seeFIG. 2) is formed between an end face132of one end side of the second fixed contact holding member13, on which the second fixed contact15is attached, and the case11; a tenth flame extinguishment clearance C10(seeFIG. 2andFIG. 3) is form ed between the partition wall102and the second fixed contact holding member13; and an eleventh flame extinguishment clearance C11(seeFIG. 3) is formed between the second fixed contact holding member13and the flat spring23.

Additionally, when the flammable gas is gasified dimethyl carbonate or gasified ethyl methyl carbonate, the flame is reliably extinguished by setting the gap sizes S, S′ at 2 mm or less. When the flammable gas is hydrogen gas, the flame is reliably extinguished by setting the gap sizes S, S′ at 0.6 mm or less.

Next, workings of the electromagnetic relay according to the present embodiment are explained. First, when the magnet coil16is energized, the armature20is attracted toward the fixed core19by electromagnetic force generated as a result of the energization. Then, the first moving contact24is brought into contact with the first fixed contact14and the second moving contact25is brought into contact with the second fixed contact15. Accordingly, the two fixed contacts14,15are connected by the flat spring23so as to close an electric circuit. On the other hand, when the energization of the magnet coil16is stopped, the moving contacts24,25are disengaged respectively from the fixed contacts14,15by the elastic force of the connecting plate21so as to open the electric circuit.

An arrow of a short dashed line inFIG. 1toFIG. 3indicates a flame propagation route along which the flame ignited by the arc propagates toward the breathing hole101. An arrow of a continuous line inFIG. 1toFIG. 3indicates a generally illustrated region in which the flame is extinguished.

When the flammable gas which has flowed into the accommodating space10acatches fire from the arc generated between the fixed contacts14,15and the moving contacts24,25respectively, the flame caused by this ignition is extinguished as follows.

Workings for extinguishing the flame of the flammable gas which catches fire from the arc generated between the first fixed contact14and the first moving contact24are described below.

Heat is conducted away from a flame propagating along a first flame propagation route D1(seeFIG. 1toFIG. 3), which leads to the opposite side from the base10through the first guide part111, by the members (i.e., the yoke18and the case11) that constitute the first flame extinguishment clearance C1while the flame is passing through the clearance C1. Accordingly, the flame is not maintained to be extinguished.

Heat is drawn from a flame propagating along a second flame propagation route D2(seeFIG. 2), which leads to a side surface of the second flanged portion161bor an outer circumferential surface of the coil wire162, by the members (i.e., the second flanged portion161band the case11) that constitute the second flame extinguishment clearance C2or by the members (i.e., the coil wire162and the case11) that constitute the fourth flame extinguishment clearance C4, while the flame is, passing through the second flame extinguishment clearance C2or the fourth flame extinguishment clearance C4. As a result, the flame is extinguished.

The members (i.e., the first fixed contact holding member12and the case11) that constitute the sixth flame extinguishment clearance C6provide heat removal from a flame, propagating along a third flame propagation route D3(seeFIG. 1andFIG. 2), which passes between the end face122of the first fixed contact holding member12and the case11, while the flame is passing through the sixth flame extinguishment clearance C6. Accordingly, the flame is extinguished.

The members (i.e., the first fixed contact holding member12and the partition wall102) that constitute the seventh flame extinguishment clearance C7conduct heat away from a flame propagating along a fourth flame propagation route D4(seeFIG. 3), which passes between the partition wall102and the first fixed contact holding member12, while the flame is passing through the seventh flame extinguishment clearance C7. As a result, the flame.

The members (i.e., the first fixed contact holding member12and the flat spring23) that constitute the eighth flame extinguishment clearance C8draw heat from a flame propagating along a fifth flame propagation route D5(seeFIG. 1), which passes between the first fixed contact holding member12and the flat spring23, while the flame is passing through the eighth flame extinguishment clearance C8. Accordingly, the flame is extinguished.

In the above-described manner, the flame of the flammable gas which catches fire from the arc generated between the first fixed contact14and the first moving contact24is extinguished.

Next, workings for extinguishing the flame of the flammable gas which catches fire from the arc generated between the second fixed contact15and the second moving contact25are described below.

Heat is conducted away from a flame propagating along a sixth flame propagation route D6(seeFIG. 2toFIG. 3), which leads to the opposite side from the base10through the second guide part112, by the members (i.e., the yoke18and the case11) that constitute the first flame extinguishment clearance C1while the flame is passing through the clearance C1. Accordingly, the flame is not maintained to be extinguished.

Heat is drawn from a flame propagating along a seventh flame propagation route D7(seeFIG. 2), which leads to a side surface of the second flanged portion161bor an outer circumferential surface of the coil wire162, by the members (i.e., the second flanged portion161band the case11) that constitute the third flame extinguishment clearance C3or by the members (i.e., the coil wire162and the case11) that constitute the fifth flame extinguishment clearance C5, while the flame is passing through the third flame extinguishment clearance C3or the fifth flame extinguishment clearance C5. As a result, the flame is extinguished.

The members (i.e., the second fixed contact holding member13and the case11) that constitute the ninth flame extinguishment clearance C9provide heat removal from a flame propagating along an eighth flame propagation route D8(seeFIG. 2), which passes between the end face132of the second fixed contact holding member13and the case11, while the flame is passing through the ninth flame extinguishment clearance C9. Accordingly, the flame is extinguished.

The members (i.e., the second fixed contact holding member13and the partition wall102) that constitute the tenth flame extinguishment clearance C10conduct heat away from a flame propagating along a ninth flame propagation route D9(seeFIG. 3), which passes between the partition wall102and the second fixed contact holding member13, while the flame is passing through the tenth flame extinguishment clearance C10. As a result, the flame is extinguished.

Heat is drawn by the members (i.e., the second fixed contact holding member13and the flat spring23), which constitute the eleventh flame extinguishment clearance C11, from a flame propagating along a tenth flame propagation route (not shown), which passes between the second fixed contact holding member13and the flat spring23, while the flame is passing through the eleventh flame extinguishment clearance C11. Accordingly, the flame is extinguished.

In the above-described manner, the flame of the flammable gas which catches fire from the arc generated between the second fixed contact15and the second moving contact25is extinguished.

In addition, in case the flame is not extinguished in any of the first flame extinguishment clearance C1to the eleventh flame extinguishment clearance C11, the base10or the coil terminal17draws heat from the flame while the flame is passing through the breathing hole101, so that the flame is extinguished. Since the coil terminal17is made of metal, a large amount of heat of the flame is conducted away by the coil terminal17, and thereby the flame is reliably extinguished.

As described above, in the present embodiment, the flame of flammable gas ignited by the arc is extinguished in the flame extinguishment clearances C1to C11, and consequently the propagation of flame to the exterior space is prevented. Consequently, the ignition of flammable gas that exists in the exterior space of the base10and the case11is prevented.

In case the flame is not extinguished in the flame extinguishment clearances C1to C11, the flame is extinguished through the breathing hole101. In other words, because the electromagnetic relay has a dual explosion-proof structure (flame extinguishment structure) that carries out the extinguishment of flame by the flame extinguishment clearances C1to C11and the breathing hole101, the flame of flammable gas ignited by the arc is extinguished even more reliably.

The breathing hole101may be set to have such a gap size S′ that extinguishes a flame.

Accordingly, since the flame of flammable gas ignited by the arc propagates toward the breathing hole101after passing through the flame extinguishment clearances C1to C11, the flame is extinguished at the flame extinguishment clearances C1to C11first, and in case the flame is not extinguished at the clearances C1to C11, the unextinguished flame is put out while passing through the breathing hole101. Therefore, the electromagnetic relay has a dual explosion-proof structure (flame extinguishment structure) that carries out the extinguishment of flame with the flame extinguishment clearances C1to C11and the breathing hole101. As a result, the flame of flammable gas ignited by the arc is extinguished even more reliably.

Moreover, gas, which is ignited by the arc so as to burn, is only the gas in a space of the accommodating space10aon an upstream side of the flame extinguishment clearances C1to C11along the flame propagation route. Thus, heat is more easily drawn from the combustion gas by the base10or the case11than when the entire gas in the accommodating space10acombusts. Accordingly, pressure increase in the accommodating space10abecomes small, so that it becomes difficult to cause damage to the base10or the case11.

By appropriately setting the gap size S of the flame extinguishment clearances C1to C11in accordance with types of flammable gas (e.g., organic solvent, gasified dimethyl carbonate, gasified ethyl methyl carbonate, and hydrogen gas), a flame of flammable gas ignited by the arc may be securely extinguished.

Second Embodiment

A second embodiment of the invention is explained below with reference toFIG. 4toFIG. 7. The present embodiment is different from the first embodiment in the constitution of a coil terminal17. Since the second embodiment is similar to the first embodiment in the other constitutions, only a different part from the first embodiment is explained below.

As shown inFIG. 4toFIG. 7, the coil terminal17is formed in a predetermined shape after a plate material made of conductive metal is stamped and then bent at two or more positions. The coil terminal17includes a connecting terminal plate portion171projecting into an exterior space and connected to an external harness (not shown), and an insertion plate portion172joined to the connecting terminal plate portion171and located in a coil terminal insertion hole103.

The coil terminal17is bent over on the opposite side of the insertion plate portion172from the connecting terminal plate portion171, in other words, it is bent over at a boundary part between the coil terminal insertion hole103and an accommodating space10a, so as to be formed into a covering plate portion173. The covering plate portion173covers an opening of a breathing hole101on the accommodating space10aside, and extends generally parallel to a surface of a base10on the accommodating space10aside.

The coil terminal17is bent over on the opposite side of the covering plate portion173from the insertion plate portion172so as to be formed into a wire connecting plate portion174. A coil wire162is connected to an end portion of this wire connecting plate portion174.

Additionally, when foreign substances such as resin which have entered into the accommodating space10ain the manufacturing process are heated by the arc, and the foreign substance pass through the breathing hole101with a gas stream, flammable gas that exists in the exterior space may take fire due to a spark in the foreign substance.

In the present embodiment, because the opening of a breathing hole101on the accommodating space10aside is covered with the covering plate portion173, it is difficult for the foreign substances to pass through the breathing hole101. Therefore, the ignition of the flammable gas that exists in the exterior space by the spark in the foreign substance is prevented.

Furthermore, when the flame passes between the covering plate portion173and the surface of the base10opposed to the covering plate portion173as well, the covering plate portion173and the base10conduct heat away from the flame. Accordingly, the flame is extinguished even more reliably.