DC high voltage relay and contact materials for DC high voltage relay

Abstract

The present invention pertains to a DC high voltage relay having a rated voltage of at least 48 V and having at least a pair of contact arms consisting of a movable contact and a fixed contact, wherein the contact force and / or the release force of the contact arms are at least 100 gf. In the DC high voltage relay according to the present invention, the movable contact and / or the fixed contact are made of an Ag-oxide-based contact material. Metal components in the contact material consist of at least one metal M essentially including Zn, with the remainder comprising Ag and inevitable impurities, and the content of metal M is 0.2-8 mass% with respect to the total mass of all the metal components in the contact material. In addition, the contact material has a material structure in which one or more oxides of metal M having an average particle size of 0.01-0.4 μm are dispersed in a matrix composed of Ag or an Ag alloy.

Description

[Technical Field]

[0001] The present invention relates to a DC high-voltage relay (contactor) that performs ON / OFF control of a DC high-voltage circuit. More specifically, the present invention relates to a DC high-voltage relay that has excellent arc discharge characteristics that quickly extinguish an arc discharge that occurs when the contacts are opened, and that also has low contact resistance and low heat generation characteristics during continuous current flow. The present invention also relates to a contact material that is used in this DC high-voltage relay. [Background technology]

[0002] DC high-voltage relays are used to control high-voltage circuits such as power supply circuits and charging circuits in automobiles equipped with high-voltage batteries, such as hybrid cars (HVs), plug-in hybrid cars (PHVs), and electric vehicles (EVs), and power conditioners for power storage devices in power supply systems, such as solar power generation facilities. For example, the hybrid cars mentioned above use DC high-voltage relays known as system main relays (SMRs) or main contactors. DC high-voltage relays are similar in basic configuration and function to DC low-voltage relays conventionally used in general automotive applications. However, DC high-voltage relays are devices designed for relatively new applications, such as the hybrid cars mentioned above, and they have differences related to these applications, resulting in unique challenges.

[0003] Regarding conventional DC low-voltage circuits, the rated voltage and rated current are clearly specified. For example, in automobiles, the nominal voltage of the onboard battery is 12V DC, which is the rated voltage for a typical automotive general-purpose relay. Some trucks and buses are equipped with 24V DC batteries, so some relays have a 24V DC rated voltage. For DC low-voltage relays, the rated voltage and rated current are clearly specified, making it relatively easy to predict the upper limits of the current and load. Therefore, the challenge for DC low-voltage relays is to improve the contact materials so that they can withstand the expected power and load. Furthermore, there is a trend toward smaller and lighter DC low-voltage relays for automotive applications. While the smaller and lighter components can achieve this, this increases the strain on the contact materials. Therefore, this requirement is met by improving the durability (wear resistance and welding resistance) of the contact materials.

[0004] Ag-oxide-based contact materials have been widely used as contact materials for conventional DC low-voltage relays. Ag-oxide-based contact materials are materials in which particles of metal oxides such as Sn and In (SnO2, In2O3, etc.) are dispersed in an Ag matrix or Ag alloy matrix. Ag-oxide-based contact materials improve the performance of contact materials by utilizing the dispersion strengthening effect of the metal oxide particles, thereby ensuring required properties such as wear resistance and welding resistance. For example, the present applicant has disclosed an Ag-oxide-based contact material in Patent Document 1 as a contact material applicable to in-vehicle DC low-voltage relays.

[0005] Improvements to conventional DC low-voltage relays have been achieved by increasing the oxide content of the Ag-oxide contact material that makes up the contact pair. Contact materials that utilize the dispersion strengthening effect of oxides generally improve resistance to welding and wear by increasing the concentration of oxide-forming metal components and increasing the oxide content. Specifically, Ag-oxide contact materials containing 10% or more by mass of metal components other than Ag, such as Sn and In, are widely used. If the contact material contains less than 10% by mass of metal components other than Ag, the low oxide content can lead to problems such as welding, transfer, and wear, which may result in failure to meet required characteristics. Furthermore, improvements to Ag-oxide contact materials as described above have achieved improved durability within the specified rated voltage range and ensured durability for miniaturization and weight reduction in DC low-voltage relays. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-3885 Summary of the Invention [Problem to be solved by the invention]

[0007] In contrast, there are currently no clear regulations for the rated voltage and rated current of DC high-voltage relays. In the case of DC high-voltage relays, the required specifications will be greatly influenced by future improvements in battery performance. In other words, it is difficult to predict the upper limit of the load that the contacts of DC high-voltage relays will be subjected to, and it is highly likely that this will continue to increase. This is a difference from conventional DC low-voltage relays.

[0008] It is certain that DC high-voltage relays will continue to handle higher voltages and currents in the future, as evidenced by the recent trend toward improved battery performance and higher drive motor output.

[0009] DC high-voltage relays, which are designed to handle higher voltages and currents, have been pointed out to have several issues that differ from conventional DC low-voltage relays. Specifically, issues such as heat generation and contact welding due to increased current flow, as well as how to deal with arc discharges, have been pointed out.

[0010] Regarding the issue of heat generation, since the amount of heat generated by the contacts is proportional to the square of the current and the contact resistance, it is expected that considerable heat will be generated as DC high-voltage relays continue to carry larger currents. In the worst case scenario, abnormal heat generation in a relay can lead to fatal problems such as fire or burnout. Furthermore, welding is a phenomenon in which the contact surfaces of a contact pair melt and stick together due to Joule heat when current is applied. This contact welding can hinder the opening of the contact pair, and can cause poor resetting or even failure of the entire circuit.

[0011] In DC high-voltage relays, addressing arc discharges is equally important as the issues of heat generation and welding. Arc discharges can be broadly divided into those that occur when the contacts are opened and those that are closed. In practice, the main problem is the break arc discharge. When a break arc discharge occurs, it does not break unless the arc voltage reaches the power supply voltage. The minimum arc voltage required for an arc discharge to occur is approximately 10 V for typical Ag-oxide contact materials. In DC high-voltage relays, the higher the power supply voltage, the more likely the arc discharge is to continue. If this arc discharge continues, fatal problems such as fire or burnout, as well as abnormal heat generation in the relay, may occur. In this invention, arc discharge characteristics refer to characteristics related to the strength of the arc that can occur when the contacts are opened and closed. Contacts with excellent arc discharge characteristics are contacts that generate arcs with short duration or low energy. In DC high-voltage relays, contacts with such excellent arc discharge characteristics enable arc extinction in a short time using the arc-extinguishing structures and components described below.

[0012] To address the various issues with DC high-voltage relays as described above, measures have been taken from the perspective of the structure and mechanism of DC high-voltage relays. For example, measures have been taken to strengthen the contact pressure spring of the contact pair to increase the contact force between the movable and fixed contacts, ensuring a sufficient contact area, reducing the contact resistance between the two contacts and suppressing heat generation. Increasing the contact force also contributes to preventing the relay from catching fire or exploding in the event of a short circuit in the DC high-voltage circuit.

[0013] In addition, to deal with arc discharges, many DC high-voltage relays are now being designed to extinguish arc discharges. Specifically, measures such as ensuring a sufficient contact gap, installing an arc-extinguishing magnet, and strengthening its magnetic force are being considered. In addition, relays are sealed and filled with hydrogen gas, nitrogen gas, or a mixture of these gases to quickly extinguish the arc by cooling it.

[0014] However, the structural and mechanical measures mentioned above cause the relay body to increase in size as the capacity of the required specifications increases. Therefore, these measures alone do not meet the constant market need for smaller and lighter relays. In particular, when rare earth element magnets are selected for the arc extinguishing magnet, rare earths are used, and increasing the size or strengthening the magnetic force should be suppressed from the perspective of resource depletion. Therefore, while structural and mechanical measures are important for DC high-voltage relays, it is also preferable to take measures for the contacts themselves in addition to these.

[0015] The contacts of DC high-voltage relays have often used Ag-oxide contact materials, just like conventional DC low-voltage relays. However, in order to accommodate the higher voltages and currents of DC high-voltage relays, it is expected that even Ag-oxide contact materials will have limitations in the same composition range as before. In this regard, as mentioned above, the contacts of DC low-voltage relays have an increased concentration of metal components other than Ag in the contact material, increasing the amount of oxide and improving durability. In DC high-voltage relays as well, increasing the amount of oxide in the contact material can be a countermeasure to the problem of welding due to improved durability.

[0016] However, from the perspective of contact resistance and heat generation, an increase in the amount of oxide in the contact material is not desirable. Compared to Ag, which is a highly conductive metal, metal oxides are resistors that reduce the conductivity of the entire contact material. As already mentioned, the amount of heat generated by the contacts is proportional to the square of the current and the contact resistance. In the case of DC high-voltage relays, which have higher voltages and currents, an increase in the amount of oxide in the contact material is something that should be avoided from the perspective of heat generation control.

[0017] Furthermore, increasing the amount of oxide in the contact material does not provide any solution to the problem of arc discharge. As mentioned above, when we look at the examples of research into various contact materials for DC high-voltage relays, it can be said that they are merely an extension of the research into materials for general switching contacts. And at present, there are few reports on the practical application of these materials to DC high-voltage relays.

[0018] The present invention has been made in light of the above-mentioned background, and provides a DC high-voltage relay that can perform reliable ON / OFF control while addressing the issues of arc discharge and heat generation in contact pairs for DC high-voltage relays such as system main relays. Furthermore, to achieve this goal, it is necessary to use a contact material that exhibits stable low contact resistance for the contacts of DC high-voltage relays. The present invention also aims to provide a suitable contact material that takes into account the characteristics of DC high-voltage relays. [Means for solving the problem]

[0019] Since the above problems are caused by the contacts of DC high-voltage relays, it is believed that their solution will involve, to some extent, optimizing the Ag-oxide contact material that makes up the contacts. However, optimizing this Ag-oxide contact material should be different from the conventional approach of increasing the amount of oxide.

[0020] Therefore, before examining the composition of the contact materials, the inventors decided to focus on the characteristics of DC high-voltage relays, namely, the strength of the contact force and opening force between the fixed and movable contacts.

[0021] Generally, in relays (including contactors with equivalent functions and structures), an electromagnet or coil works in cooperation with an appropriate biasing means to control the contact and separation between the fixed and moving contacts, thereby turning the circuit on and off. Examples of appropriate biasing means include a pressure spring and a return spring in plunger-type relays, and a moving spring and a release spring in hinge-type relays. This control mechanism between the fixed and moving contacts is common to all relays, regardless of rated voltage.

[0022] However, in DC high-voltage relays such as system main relays, the contact force and opening force between the fixed and moving contacts are often set high. Specifically, while the contact force and opening force of typical DC low-voltage relays are often set at around 10 gf to 50 gf, DC high-voltage relays often set at least one of the contact force or opening force at 100 gf or more. The high contact force of DC high-voltage relays is intended to reduce contact resistance and suppress heat generation. Contact force affects the contact area between the contacts; setting a higher contact force reduces contact resistance, suppressing Joule heat generation and reducing melting and welding of the contact surfaces. On the other hand, opening force refers to the return force required to return the contacts to their separated position. In DC high-voltage relays, to ensure smooth contact opening and closing, the opening force tends to increase as the contact force increases.

[0023] Contact welding causes interruption failure in switching contacts because the fixed and moving contacts become stuck together due to welding, making it impossible to separate them with the set opening force. In conventional DC low-voltage relays, which have clearly defined ratings and specifications, there are upper limits to the contact force and opening force settings, and these settings are not particularly large. Therefore, in conventional DC low-voltage relays, priority was given to miniaturization and weight reduction, and low contact force and opening force settings made welding problems more likely to become apparent. In this case, welding is difficult to solve by changing the characteristics of the relay. Therefore, it was hoped that the problem could be addressed by changing the properties of the contact material, and contact materials have been required to have strict welding resistance.

[0024] In contrast, in a DC high-voltage relay with a high contact force and opening force, even if the fixed and moving contacts are in a state where they may be welded together, it is possible to separate them with an increased opening force. The inventors have considered that in the DC high-voltage relay, which is the subject of this invention, the welding resistance of the contact material can be set more flexibly than in conventional DC low-voltage relays. This idea of ​​allowing a certain degree of welding is unique not only in DC high-voltage relays but also in the field of switching contacts. DC high-voltage relays, such as system main relays, are devices that have begun to become widespread due to the recent development of high-voltage power supplies, and it is expected that there are many unknown configuration factors. The tolerance for welding resistance of such contacts can be considered one of these.

[0025] As described above, if we consider that welding resistance can be flexibly addressed, the two properties that should be prioritized for contact materials in DC high-voltage relays are stable low contact resistance and arc discharge characteristics.

[0026] First, when considering methods for reducing the contact resistance of Ag-oxide contact materials, reducing the amount of oxide is an effective solution. Metal oxides are resistors that reduce the conductivity of the entire contact material, so reducing them is an effective way to lower contact resistance. Reducing the amount of oxide also reduces the welding resistance of the contact material, but in DC high-voltage relays where high contact or opening forces can be set, a significant reduction in welding resistance can be tolerated. Therefore, this measure is expected to be effective.

[0027] On the other hand, it is difficult to address the arc discharge characteristics of Ag-oxide-based contact materials by determining the amount of oxide alone. Therefore, the present inventors have investigated the relationship between the type of metal oxide dispersed in the contact material and the arc discharge characteristics. As a result, they have found that Ag-oxide-based contact materials containing Zn oxide (ZnO) as the metal oxide (hereinafter sometimes referred to as Ag-ZnO-based contact materials) have favorable arc discharge characteristics. According to the present inventors, Ag-ZnO-based contact materials exhibit favorable arc discharge characteristics compared to Ag-SnO2-based contact materials containing Sn oxide, which have been considered suitable as contact materials for relays from the standpoint of welding resistance.

[0028] The reason why Ag-ZnO-based contact materials are suitable is that they tend to exhibit better arc discharge characteristics as the amount of oxide (ZnO) decreases. Since a reduction in the amount of oxide contributes to a reduction in contact resistance, the application of Ag-ZnO-based contact materials is useful for both improving arc discharge characteristics and reducing contact resistance.

[0029] From the above-mentioned investigation results, the present inventors have investigated the application of Ag-ZnO-based contact materials to the contact pairs of DC high-voltage relays, and have also investigated to find an appropriate oxide content from the viewpoints of arc discharge characteristics, contact resistance, and durability, and have arrived at the present invention.

[0030] The present invention, which solves the above-mentioned problems, is a DC high-voltage relay having a rated voltage of 48 V or more, which includes at least one contact pair consisting of a movable contact and a fixed contact, and the contact pair has a contact force and / or opening force of 100 gf or more, wherein the movable contact and / or the fixed contacts are made of an Ag-oxide contact material, and the metal components of the contact material consist of at least one metal M essentially containing Zn, with the balance being Ag and unavoidable impurity metals, the content of the metal M being 0.2 mass % or more and 8 mass % or less of the total mass of all the metal components of the contact material, and the contact material has a material structure in which one or more oxides of the metal M are dispersed in a matrix of Ag or an Ag alloy.

[0031] The DC high-voltage relay and contact material for the DC high-voltage relay according to the present invention are described in detail below. In the contact material used in the present invention, the oxide content is defined based on the content of metal M, which is a metal element other than Ag. The content of metal M is defined based on the total mass of all metal components constituting the contact material. Since the contact material used in the present invention is an Ag-oxide contact material, its constituent elements are Ag, metal M, inevitable impurity metals, oxygen, and inevitable non-metallic impurity elements. However, when interpreting metal components and inevitable impurity metals, elements known as semimetals, such as Te and Si, are also considered to be metals.

[0032] A. DC high voltage relay according to the present invention The essential conditions for the DC high-voltage relay of the present invention are that it has a rated voltage of 48 V or more and a contact force or opening force of 100 gf or more. Other configurations and characteristics are the same as those of conventional DC high-voltage relays such as system main relays. In the following explanation, we will explain these two essential conditions, as well as the configuration of a DC high-voltage relay that can be optionally provided.

[0033] A-1. Rated voltage Relays with a rated voltage of less than 48 V, such as conventional DC low-voltage relays that handle low voltages of 12 V to 24 V, cannot satisfy the characteristics required of DC high-voltage relays such as system main relays. Therefore, there is little point in applying the present invention to such conventional DC low-voltage relays. Therefore, the DC high-voltage relay of the present invention is intended for use with a rated voltage of 48 V or more. The upper limit of the rated voltage of the DC high-voltage relay of the present invention is preferably 3000 V or less. The rated current of the DC high-voltage relay of the present invention is expected to be 10 A or more and 3000 A or less.

[0034] A-2. Contact force and opening force of the DC high voltage relay according to the present invention The present invention is applied to DC high-voltage relays with a contact force or opening force of 100 gf or more. As described above, the DC high-voltage relay of the present invention and the contact materials used therein have flexibly set welding resistance based on the relationship with the contact force or opening force of the applicable DC high-voltage relay. The target DC high-voltage relay has a contact force or opening force set to 100 gf or more between the moving contact and the fixed contact. The set value of 100 gf here is assumed to be the lower limit value to meet the required characteristics of DC high-voltage relays. On the other hand, the upper limit of the contact force or opening force is assumed to be 5000 gf. The contact force or opening force will increase as the size of the components and the relay itself increases. However, from the perspective of miniaturization and weight reduction of relays, it is desirable to design a relay with as low a contact force and opening force as possible. According to the present invention, by optimizing the contact materials used for the fixed and moving contacts, a DC high-voltage relay with an appropriate contact force and opening force can be designed while suppressing heat generation and welding. The contact force and the separation force may both be 100 gf or more, and the contact force and the separation force do not need to be the same value.

[0035] The contact force or separation force can be adjusted by adjusting the capacity and dimensions of the electromagnet or coil and appropriate biasing means, which are components of the relay described below. Note that appropriate biasing means include a contact pressure spring and a return spring in a plunger-type relay, and a movable spring and a return spring in a hinge-type relay.

[0036] The contact force or separation force can be set and measured based on the spring constants of the contact pressure spring and return spring. When measuring the contact force or separation force, the force applied to all contact pairs is calculated from the spring displacement and the spring constant when the contacts make and break. The force applied to all contact pairs follows Hooke's law (F = kx (k: spring constant, x: displacement)). The contact force or separation force can then be calculated by dividing the calculated force by the number of contact pairs. For example, a DC high-voltage relay with a double-break structure has two contact pairs, so the contact force and separation force for each contact pair can be calculated by dividing the force calculated above by 2.

[0037] A-3. Structure of the DC high voltage relay according to the present invention The DC high-voltage relay according to the present invention can be characterized by the above-mentioned rated voltage, contact force, and opening force. Furthermore, functions, configurations, and mechanisms other than the rated voltage, contact force, and opening force can be the same as those of conventional DC high-voltage relays. The structure of the DC high-voltage relay according to the present invention will be described below.

[0038] A-3-1. Overall structure and components of DC high voltage relay A DC high-voltage relay is broadly composed of a drive section that generates and transmits the driving force to move the movable contact, and a contact section that opens and closes the DC high-voltage circuit. The drive section includes an electromagnet or coil that generates the driving force, a transmission means (a plunger or armature, described below) that transmits the driving force to the contact section, and a biasing means (springs such as a contact pressure spring, return spring, movable spring, and recovery spring) that biases the transmission means to bring the contact pair into contact or separate it. The contact section includes a contact pair consisting of a movable contact and a fixed contact that are moved by the transmission means of the drive section, a movable terminal that joins the movable contact, and a fixed terminal that joins the fixed contact. DC high-voltage relays are roughly classified into plunger type and hinge type based on the difference in the physical configuration of the contact pair.

[0039] FIG. 1 shows an example of the structure of a plunger-type DC high-voltage relay. A plunger-type relay uses a plunger-type electromagnet to drive a contact section and open or close a contact pair. The contact section of a plunger-type relay is composed of a movable contact, a fixed contact, a movable terminal, and a fixed terminal. The drive section of a plunger-type relay is composed of an electromagnet, a movable core, a fixed core, a plunger as a transmission means, and a pressure spring and a return spring as a biasing means. Springs such as the pressure spring and return spring are selected as either compression springs or tension springs depending on the relay structure. The plunger as a transmission means is sometimes referred to as a movable core or shaft. In addition to the above components, a DC high-voltage relay may also include additional components such as an electromagnetic repulsion suppression yoke, an arc-extinguishing magnet (permanent magnet), a terminal cover, electrodes, and a buffer spring (buffer rubber). Furthermore, a DC high-voltage relay includes wiring connected to the circuit and wiring for controlling the electromagnet.

[0040] FIG. 2 shows an example of the structure of a hinge-type DC high-voltage relay. A hinge-type relay is a relay in which the armature of an electromagnet rotates around a fulcrum, directly or indirectly driving a movable contact to open or close a pair of contacts. The contact section of a hinge-type relay is composed of the following components: a movable contact, a fixed contact, a movable spring (movable terminal), and a fixed terminal (fixed spring). The drive section of a hinge-type relay is composed of a coil, an iron core, a yoke, an armature as a transmission means, and a return spring as a biasing means. Springs such as the return spring are selected as either compression springs or tension springs depending on the relay structure. Some hinge-type relays, such as the one shown in FIG. 2, are equipped with a contact drive card as a transmission means, which drives the contacts. In addition to the above components, additional components such as an arc-extinguishing magnet (permanent magnet), a terminal cover, and electrodes may also be included. Furthermore, a DC high-voltage relay includes wiring connected to the circuit, and terminals and wiring for controlling the electromagnet.

[0041] In DC high-voltage relays, arc-extinguishing magnets are installed near the contact pairs in the contact section as needed. The arc-extinguishing magnets use Lorentz force to stretch the arc discharge that occurs between the moving contact and the fixed contact when they separate, thereby quickly extinguishing the arc. The arc-extinguishing magnet is not involved in the opening and closing of the contact pairs, so it is not an essential component. However, arc-extinguishing magnets can exhibit a significant arc-extinguishing effect in DC high-voltage relays, so they are used in many products. The higher the magnetic flux density of the arc-extinguishing magnet, the shorter the time it takes to completely extinguish the arc. The type of arc-extinguishing magnet is selected from either a ferrite magnet or a rare-earth magnet, taking into account the balance between manufacturing cost and operational design.

[0042] The various components described above are housed in a case, body, or the like that forms the entire device. The case or body has an airtight structure that protects the relay structure from external forces and prevents the intrusion of dirt and dust, as well as preventing the intrusion of outside air and gas. Known airtight structures for DC high-voltage relays include an open-air type in which gaps in the terminals and fittings of the case are left untreated, and a resin-sealed type in which gaps are sealed with a sealing material such as resin. Also known is a cooling gas-filled type in which a cooling gas such as hydrogen gas or nitrogen gas is filled in a sealed case with a sealed structure in which gaps are sealed. The DC high-voltage relay of the present invention can employ either of these airtight structures.

[0043] A-3-2. Number of contact pairs The DC high-voltage relay of the present invention, like a general relay, has at least one contact pair consisting of a movable contact and a fixed contact. The number of contact pairs can be one. However, many DC high-voltage relays, such as system main relays, employ a double-break structure with two contact pairs. The DC high-voltage relay illustrated in FIG. 1 shows an example of the structure of a DC high-voltage relay with a double-break structure. By employing a double-break structure, the voltage is divided among two contact pairs, achieving rapid arc extinction. Therefore, the more contact pairs there are, the greater the arc extinction effect. However, if there are too many contact pairs, control becomes difficult. Furthermore, providing a large number of contact pairs requires a large amount of space. Therefore, considering requirements such as miniaturization, a DC high-voltage relay with a double-break structure is preferred.

[0044] A-3-3.Contact structure In the DC high-voltage relay according to the present invention, the contact material described below is used for at least one of the movable contact and the fixed contact. At least one of the movable contact and the fixed contact is joined to a movable terminal and a fixed terminal. As a specific embodiment, both the movable contact and the fixed contact are made of the contact material described below and joined to the respective terminals, or one of the movable contact or the fixed contact can be made of the contact material described below and the other can be made of another contact material and joined to the respective terminals. Furthermore, while the movable contact (or the fixed contact) is made of the contact material described below, the other fixed contact (or the movable contact) can use the fixed terminal (or the movable terminal) as is without joining any contact material. In this embodiment where one of the contacts is made of only a terminal, that contact acts as either the movable contact or the fixed contact and forms a contact pair.

[0045] There are no particular limitations on the shape and dimensions of the movable contact and fixed contact. Possible shapes of the movable contact or fixed contact include rivet contacts, chip contacts, button contacts, and disk contacts. The movable contact and fixed contact may be solid materials made of the contact material described below, or may be clad with other materials. For example, the movable contact and fixed contact may be made by cladding a base material made of Cu, a Cu alloy, an Fe-based alloy, or the like with the contact material described below. There are also no limitations on the shape of the clad material, and various shapes such as tape-shaped contacts (clad tape), crossbar contacts, rivet contacts, chip contacts, button contacts, and disk contacts can be used.

[0046] The movable terminal and the fixed terminal are made of Cu, Cu alloy, or Fe-based alloy, and may be subjected to surface treatment such as Sn plating, Ni plating, Ag plating, Cu plating, Cr plating, Zn plating, Pt plating, Au plating, Pd plating, Rh plating, Ru plating, or Ir plating, as required.

[0047] The movable contact and fixed contact can be joined to the respective terminals by processing means such as crimping, brazing, welding, etc. Alternatively, the movable contact and fixed contact may be formed by coating part or all of the surface of the movable terminal and / or fixed terminal with a contact material having the composition described below by surface treatment such as sputtering.

[0048] B. Materials for the movable and fixed contacts (contact materials according to the present invention) The DC high voltage relay according to the present invention is characterized by the use of a predetermined contact material as a suitable constituent material for the movable contact and the fixed contact, in consideration of the need for a high contact force and opening force.

[0049] That is, the contact material of the present invention is an Ag-oxide-based contact material for constituting at least the surfaces of the movable and / or fixed contacts of a DC high-voltage relay having a rated voltage of 48 V or more and a contact force and / or opening force of a contact pair of 100 gf or more, wherein the metal components of the contact material consist of at least one metal M containing Zn as an essential component, with the remainder being Ag and unavoidable impurity metals, the content of the metal M being 0.2% by mass or more and 8% by mass or less of the total mass of all the metal components of the contact material, and the contact material has a material structure in which one or more oxides of the metal M are dispersed in a matrix of Ag or an Ag alloy. The composition, material structure, and production method of the contact material applied in this invention will be described below.

[0050] B-1. Composition of contact materials used in this invention The contact material used in the DC high-voltage relay of the present invention is an Ag-oxide-based contact material whose metallic components are Ag, metal M, and unavoidable impurity metals. Metal M, the metallic component, exists as a constituent element of an oxide dispersed in a matrix. This metal oxide is dispersed to ensure the mechanical strength and adhesion resistance of the contact material. As described above, for the DC high-voltage relay that is the subject of the present invention, the adhesion resistance of the contact material is interpreted flexibly. That is, if the contact force and / or opening force of the DC high-voltage relay are set high, a decrease in the adhesion resistance of the contact material itself is acceptable. However, this does not mean that adhesion resistance is completely unnecessary. In the present invention, adhesion resistance is still necessary to a certain extent, so an oxide is formed and dispersed. Therefore, metal M is an essential metallic element in the contact material used in the present invention.

[0051] In the present invention, the content of metal M is set to 0.2% by mass or more and 8% by mass or less based on the total mass of all metal components of the contact material. As described above, the Ag-ZnO-based contact material used in the present invention improves arc discharge characteristics and lowers contact resistance as the oxide content (content of metal M) decreases. From this perspective, a lower content of metal M is preferable. However, if the content of metal M is less than 0.2% by mass, there are concerns about insufficient welding resistance and reduced mechanical strength. The reduced mechanical strength may cause contact transfer with the number of contact opening and closing cycles, leading to the risk of contact wear and deformation, poor contact, and locking. Taking this into consideration, the lower limit of the metal M content is set to 0.2% by mass.

[0052] On the other hand, contact materials containing more than 8% by mass of metal M have high contact resistance, making it difficult to resolve the problem of heat generation in DC high-voltage relays. Furthermore, the arc discharge characteristics are also poor. In the present invention, the contents of Ag, metal M, and unavoidable impurity metals are defined as their mass concentrations relative to the total mass of all metal components. The total mass of all metal components is the mass of the entire contact material minus the mass of components other than metal components, such as oxygen and other gas components.

[0053] Furthermore, if a sufficiently high contact force or opening force is set for the DC high-voltage relay, a corresponding decrease in welding resistance can be tolerated. In such cases, the content of metal M can be set lower within the above range. Specifically, to optimize the contact resistance, it is preferable to set the content of metal M to 0.2% by mass or more and 3% by mass or less. On the other hand, if there are design limitations on the contact force or opening force of the DC high-voltage relay from the perspective of reducing size and weight, it is necessary to give greater consideration to the balance between welding resistance and contact resistance. In such cases, the content of metal M is preferably 3% by mass or more and 6% by mass or less.

[0054] The content of the additive metal (metal M) in the contact material of the DC high-voltage relay of the present invention described above is intentionally reduced compared to the content of the additive metal in contact materials of conventional general in-vehicle relays, etc. In contact materials (Ag-oxide-based contact materials) used in general in-vehicle relays, etc., the content of metal components other than Ag (metal M of the present invention) generally exceeds 10 mass %.

[0055] The Ag-oxide-based contact material used in the present invention essentially contains Zn as the metal M. Zn is dispersed as an oxide of zinc alone (ZnO). As described above, the Ag-ZnO-based contact material has excellent arc discharge characteristics and is a means of fundamentally resolving the problems of the present invention. In the present invention, Zn is an essential metal component. In the present invention, Zn may be the only metal M. When Zn is the only metal M, the contact material of the present invention contains Zn in a range of 0.2 to 8 mass %. As described above, when there is leeway or limitation in the design of the contact force or separation force, the Zn content may be set to 0.2 to 3 mass %, or 3 to 6 mass %.

[0056] The Ag-oxide-based contact material used in the present invention requires Zn but can also contain other metals as the metal M. Specifically, it can contain at least one of Sn, In, Ni, Te, Bi, and Cu. These metals tend to adjust the mechanical strength, such as hardness, and welding resistance of the Ag-ZnO-based contact material when dispersed as oxides. Furthermore, these metals do not impair the arc duration shortening effect of Zn. When the contact material contains at least one of Sn, In, Ni, Te, Bi, and Cu in addition to Zn as the metal M, the content of the metal M (the total content of Zn and Sn, In, Ni, Te, Bi, and Cu) is preferably 0.2% by mass or more and 8.0% by mass or less based on the total mass of all metal components of the contact material. A content exceeding 8% by mass can cause problems such as contact resistance. As the metal M other than Zn, any element other than Sn, In, Ni, Te, Bi, or Cu can be added as long as it does not impair the above-mentioned properties of the contact material or can contribute to improving the properties.

[0057] In addition, when the contact material contains at least one of Sn, In, Ni, Te, Bi, and Cu in addition to Zn, the content of Zn relative to the total mass of all metal components of the contact material (S Zn ) and the total content of the above metals other than Zn relative to the total mass of all metal components of the contact material (So The ratio (S Zn / S o ) can be calculated. Zn / S o The larger the value of Zn, the better the arc discharge characteristics of the contacts tend to be. Zn is effective in improving arc discharge characteristics. Sn and other elements contribute to improving the welding resistance of the contact material, but do not contribute to improving the discharge arc characteristics.

[0058] The metal components of the contact material according to the present invention consist of the metal M, which is essentially Zn as described above, with the remainder being Ag and unavoidable impurity metals. Examples of unavoidable impurity metals include Ca, Pb, Pd, Al, Mo, Mg, La, Mg, Li, Ge, W, Na, Zr, Nb, Y, Ta, Mn, Ti, Co, Cr, Cd, K, and Si. The content of these unavoidable impurity metals is preferably 0% by mass or more, for example 1% by mass or less, based on the total mass of all metal components of the contact material, within a range that does not impair the properties. The content of unavoidable impurities is more preferably 0.8% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.2% by mass or less.

[0059] As mentioned above, the contact material used in the present invention is an Ag-oxide contact material, which contains oxygen and unavoidable non-metallic impurities in addition to the above metal components. The oxygen content in the contact material of the present invention is 0.025% by mass or more and 2% by mass or less, based on the mass of the entire contact material. Examples of unavoidable non-metallic impurities include C, S, and P. The content of each of these unavoidable impurity elements is preferably 0% by mass or more and 0.1% by mass or less, based on the mass of the entire contact material. Furthermore, the unavoidable impurity metals and the unavoidable non-metallic impurity elements may form intermetallic compounds. Examples of such intermetallic compounds include WC and TiC. The content of each of these intermetallic compounds is preferably 0% by mass or more and 1% by mass or less, based on the mass of the entire contact material.

[0060] B-2. Material structure of the contact material used in this invention The contact material used in the DC high-voltage relay of the present invention is an Ag-oxide-based contact material. Its structure is essentially the same as that of conventional Ag-oxide-based contact materials. That is, it has a material structure in which at least one oxide of the metal M is dispersed in a matrix of Ag and / or Ag alloy. This matrix is ​​composed of Ag (pure Ag), an Ag alloy, or a combination of Ag and an Ag alloy. An Ag alloy is an alloy of Ag with an additive metal M or unavoidable impurity metal. However, it is not limited to a single-phase Ag alloy with a single composition. It may also be composed of multiple Ag alloys with different amounts of solid solution of the metal M. This indicates that when the contact material is produced by internal oxidation of an alloy of Ag and a metal M, the composition and structure of the Ag alloy can change depending on the degree of oxidation. Therefore, the matrix may contain a metal M. The concentration (average concentration) of the metal M in the matrix is ​​preferably 4% by mass or less, but even an upper limit of less than 8% by mass, e.g., 7% by mass or less, can still function as a matrix for the contact material. On the other hand, the oxide particles dispersed in the matrix are composed of at least one oxide such as ZnO or SnO2, depending on the range of the metal M.

[0061] As described above, in the present invention, the dispersed oxide is Zn oxide or the like, and its content (content of metal M) is intentionally reduced compared to conventional Ag-oxide-based contact materials, thereby achieving good arc discharge characteristics and stable low contact resistance. However, even in the present invention, it is not intended to ignore welding resistance and mechanical strength. Therefore, in the present invention, while suppressing the amount of oxide, by miniaturizing the oxide particles, the number of oxides is increased, shortening the interparticle distance, and improving the dispersion effect. This ensures the minimum material strength required for a DC high-voltage relay.

[0062] The contact material used in the present invention has an average particle size of the oxide dispersed in the matrix of 0.01 μm or more and 0.4 μm or less. As described above, the oxide content is reduced in the present invention. Therefore, if the average particle size of the oxide exceeds 0.4 μm and becomes coarse, the interparticle distance increases, suppressing the dispersion effect. The average particle size of this oxide is more preferably 0.3 μm or less. Although a smaller average particle size of the oxide is preferable, it is difficult to make it less than 0.01 μm, so the lower limit is set to 0.01 μm. In the present invention, the particle size of the oxide particle is the circle-equivalent diameter (area-equivalent circle diameter), which is the diameter of a perfect circle having an area equivalent to the area of ​​the particle.

[0063] In the contact material used in the present invention, it is preferable that the particle size of the dispersed oxide particles is uniform. The standard for this is the particle size (D) at which the cumulative number of particles becomes 90% when the particle size distribution of all oxide particles is measured by observing an arbitrary cross section. 90 ) is preferably 0.8 μm or less.

[0064] Furthermore, since the contact material used in the present invention has a reduced oxide content, the area of ​​oxide is relatively small when the material structure is observed. Specifically, when an arbitrary cross section is observed, the area ratio of oxide in the cross section is 0.1% or more and 20% or less. This area ratio can be measured by observing a cross section of the contact material cut in an arbitrary direction with a microscope (preferably an electron microscope) at 1000 to 10000 magnifications. The area of ​​the observed field of view can be taken as the total area of ​​the contact material, and the ratio of the total area occupied by oxide particles in the field of view can be calculated. The above-mentioned average particle size can also be calculated from this observation. Image processing software can also be used as appropriate.

[0065] The material strength of the contact material used in the present invention is preferably 40 Hv or more and 300 Hv or less in Vickers hardness. If the material strength is less than 40 Hv, the strength is too low and excessive wear or deformation may occur when the contact pair is opened and closed. On the other hand, if the material is hard and exceeds 300 Hv, the contact resistance may become high. The Vickers hardness of the contact material is more preferably 50 Hv or more and 200 Hv or less.

[0066] B-3. ​​Manufacturing method of contact material applied in the present invention Next, we will explain the manufacturing method and conditions for the Ag-oxide contact material used in the DC high-voltage relay of the present invention. Although there are no particular limitations on the manufacturing method and conditions for the contact material of the present invention, it can be manufactured preferably by the internal oxidation method, the powder metallurgy method, or a combination of the internal oxidation method and the powder metallurgy method.

[0067] B-3-1. Internal oxidation method In the internal oxidation method, an alloy of Ag and metal M (Ag-M alloy) is produced and then subjected to internal oxidation treatment to produce a contact material. Specifically, the alloy produced here includes Ag-Zn alloys, and when Sn or the like is included as metal M, the alloy is produced from Ag-Zn-Sn alloys, Ag-Zn-In alloys, Ag-Zn-Ni alloys, Ag-Zn-Te alloys, Ag-Zn-Bi alloys, Ag-Zn-Cu alloys, etc. The total concentration of metal M (Zn, Sn, In, Ni, Te, Bi, Cu) is 0.2 to 8 mass%, with the remainder being Ag. These alloys can be produced by known melting and casting methods. A molten alloy adjusted to the desired composition is produced and cast to obtain the alloy.

[0068] The Ag-M alloy is then internally oxidized to convert the metal M into an oxide, which serves as a contact material. The conditions for the internal oxidation of the Ag-M alloy are preferably an oxygen partial pressure of atmospheric pressure or higher but not higher than 0.9 MPa and a temperature of 300°C or higher but not higher than 900°C. At temperatures below 300°C, it is difficult to promote internal oxidation, and there is a concern that oxide particles may not be sufficiently dispersed within the alloy. On the other hand, if the oxygen partial pressure is higher than 0.9 MPa, the oxides may be excessively finely dispersed, resulting in a deterioration in workability. Furthermore, if the temperature is higher than 900°C, depending on the alloy composition, some or all of the alloy may melt before being internally oxidized. To optimize the particle size and dispersion of the oxide particles, the oxygen partial pressure and heating temperature can be appropriately adjusted within the above-mentioned ranges, taking into account the type and content of the added metal M. The internal oxidation treatment time is preferably 24 hours or longer.

[0069] In the manufacture of contact materials by the internal oxidation method, an alloy ingot can be appropriately shaped and processed, then subjected to internal oxidation and appropriately shaped again to produce contact material. Alternatively, the alloy ingot can be crushed, cut, or otherwise made into solid pieces (small pieces, chips), and these solid pieces can be subjected to internal oxidation under the above conditions, collected, and compression-molded into billets for processing. The manufactured billets can be appropriately processed, such as by extrusion and wire drawing, to produce contact materials of the desired shape and dimensions.

[0070] B-3-2. Powder metallurgy method In powder metallurgy, contact materials are manufactured by mixing Ag powder and powder of an oxide of metal M (ZnO powder, SnO powder, etc.), compressing the mixture, and then sintering it. The Ag powder and oxide powder preferably have an average particle size of 0.5 μm or more and 100 μm or less. The sintering temperature for sintering the powder is preferably 700°C or more and 850°C or less.

[0071] In the production of contact materials by powder metallurgy, it is preferable to prevent the coarsening of oxides due to excessive sintering in the sintering step. To achieve this, in addition to adjusting the sintering temperature, it is preferable to perform sintering multiple times in a relatively short time (6 hours or less) and then perform compression after sintering. Cold compression is preferable as the compression. In this case, cold compression and hot compression can be combined. The load for each compression can be adjusted for each compression. For example, if sintering and cold compression are performed multiple times, the load for the cold compression can be set to about 2 to 3 times the load for the cold compression after the previous sintering. By performing such a sintering step, it is possible to obtain a contact material in which oxides of an appropriate particle size are dispersed.

[0072] The contact material used in the present invention is basically produced by the internal oxidation method or powder metallurgy method described above, but the internal oxidation method and powder metallurgy method can also be combined. In this case, a powder consisting of an alloy of Ag and metal M (Ag-M alloy powder) is produced, and this alloy powder is subjected to internal oxidation treatment, compressed, and sintered to produce the contact material. In this production method, the Ag-M alloy powder is a powder consisting of an Ag alloy having the same composition as described above (Ag-Zn alloy, Ag-Zn-Sn alloy, Ag-Zn-In alloy, Ag-Zn-Ni alloy, Ag-Zn-Te alloy, Ag-Zn-Bi alloy, Ag-Zn-Cu alloy, etc.). This alloy powder preferably has an average particle size of 100 μm to 3.0 mm. The conditions for internal oxidation of the Ag alloy powder are preferably the same as those described above. The sintering temperature for the Ag alloy powder is preferably 700°C to 900°C. [Effects of the Invention]

[0073] As described above, the DC high-voltage relay according to the present invention can perform reliable ON / OFF control while addressing the issues of arc discharge and heat generation in the contact pairs. This effect is due to the use of an Ag-Zn-based contact material containing Zn as an essential additive metal (metal M) for the contact material constituting the movable contact and / or fixed contact, taking into consideration the high contact force and opening force set for the DC high-voltage relay.

[0074] The Ag-Zn contact material used in the DC high-voltage relay of the present invention intentionally reduces the content of dispersed oxides. This achieves good arc discharge characteristics while exhibiting stable low contact resistance characteristics, eliminating the problem of heat generation in DC high-voltage relays. In this invention, by utilizing the contact force and opening force of the DC high-voltage relay and setting the minimum amount of oxides, a contact pair is formed that does not fail to break due to welding.

[0075] According to the present invention, by incorporating a contact material exhibiting excellent arc discharge characteristics, it is expected that arc-extinguishing performance equivalent to that of conventional designs can be maintained even when magnets with weaker magnetic force are used. Specifically, this suggests the possibility of replacing rare-earth element magnets, such as neodymium magnets, with ferrite magnets, which have weaker magnetic force. Ferrite magnets have a characteristic of inferior magnetic force compared to rare-earth element magnets, but they do not contain rare earth elements and are primarily composed of inexpensive and easily procured iron oxide, and they also have superior heat resistance compared to rare-earth element magnets. Therefore, replacing rare-earth element magnets with ferrite magnets based on the present invention has significant benefits in terms of reducing the cost of DC high-voltage relays and avoiding rare-earth element procurement risks. Furthermore, because the present invention is expected to maintain equivalent arc-extinguishing performance with weaker magnetic force than conventional relays, it is possible to reduce the relay size without changing the type of magnet. Eliminating the need for extra magnet space allows for a smaller relay.

[0076] The present invention, which has the effects described above, is expected to have a significant impact on industries, including the automotive industry. For example, the global market for HVs, PHVs, and EVs equipped with high-voltage batteries is expected to expand at an accelerated pace in the future. Specifically, research reports predict that the total annual sales volume of HVs, PHVs, and EVs will increase significantly to over 27 million units by 2035, compared to approximately 3.24 million units in 2017. The present invention, which brings about the effects of reducing the cost and size of DC high-voltage relays installed in these rapidly expanding automotive products, will contribute to the development of these industries.

[0077] The present invention is also useful from the perspective of reducing the amount of rare earth elements used and preserving resources. Rare earths are essential for the manufacture of a wide range of industrial products in recent high-tech industries, such as rare earth magnets, glass substrates for hard disks, abrasives for liquid crystal panel displays, and automotive catalysts. Neodymium, in particular, is used in many applications, including neodymium magnets (neodymium magnets contain approximately 28% neodymium), FCC catalysts, glass additives, nickel-metal hydride batteries, and ceramic capacitors. Demand for rare earths is expected to continue to expand, and rare earth depletion is becoming a global issue.

[0078] A certain country contains 36% of the world's rare earth reserves. Furthermore, approximately 80% (105,000 tons) of the world's total ore production (130,000 tons: 2017) is produced in that country. Domestic demand for rare earths is expanding in that country, and since 2004, domestic demand in that country has accounted for the majority of total global consumption. Research reports have indicated that if that country continues to develop its deposits at the current pace, resources could be depleted within the next 15 to 20 years.

[0079] Meanwhile, domestic demand for rare earths in Japan is approximately 18,000 tons, of which demand for didymium (a mixture of neodymium and praseodymium) and neodymium was 4,400 tons (2017), due in part to growth in automotive magnets. Domestic industry relies heavily on imports for rare earths, with approximately 60% of those imports coming from the country. In recent years, the country has tightened its regulations on rare earths, resulting in a decrease in supply and a rise in international prices.

[0080] Furthermore, serious environmental problems have arisen in rare earth production areas, including water and soil contamination caused by contamination from strong acids (ammonium sulfate) during the rare earth mining and refining process, and the leakage of radioactive materials accompanying rare earths.

[0081] As such, the issues surrounding rare earths include resource depletion, increasing quantitative and cost risks to domestic industries in procuring rare metal raw materials, and environmental issues in rare metal producing areas. Therefore, reducing the amount of rare metals used is an urgent and important issue.

[0082] Against this background, private companies in Japan, including automobile manufacturers and materials manufacturers, are engaged in various developments aimed at reducing rare metal use. For example, there are magnets for EV drive motors that can reduce neodymium usage by up to 50%, and EV drive motors that use neodymium magnets that are free of heavy rare earth elements such as dysprosium. Some of these are aimed for practical use within 10 years, while others have already been released to the market. Many domestic industries are promoting development, regarding the reduction of rare metal usage as an urgent and important theme, and this invention, like these efforts, is an important invention that is expected to contribute to reducing rare metal usage. [Brief explanation of the drawings]

[0083] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a plunger-type DC high-voltage relay (double-break structure). [Figure 2] FIG. 1 is a diagram showing an example of the configuration of a hinge-type DC high-voltage relay. [Figure 3] FIG. 10 is a diagram showing a circuit used in a capacitor load durability test of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0084] Hereinafter, an embodiment of the present invention will be described. In this embodiment, an Ag-ZnO-based contact material containing only Zn as the metal M, as well as an Ag-ZnO-based contact material containing Sn added together with Zn, were manufactured, and their structure was observed and their hardness was measured. The manufactured Ag-oxide-based contact materials were then incorporated into DC high-voltage relays, and their characteristics were evaluated. As a comparative example, an Ag-oxide-based contact material containing no Zn but containing Sn or other additives was also manufactured and evaluated.

[0085] First embodiment In this embodiment, various Ag-oxide contact materials were manufactured by the internal oxidation method and the powder metallurgy method, and the material properties were examined. Then, a DC high-voltage relay (contact force / opening force: 75 gf / 125 gf) was manufactured, and its operation (interruption durability) was confirmed, and the arc discharge characteristics and contact resistance were measured.

[0086] In manufacturing contact materials using the internal oxidation method, first, Ag alloy ingots of each composition were melted and cast in a high-frequency melting furnace. After melting and casting, the ingots were cut into solid pieces of 3 mm or less, which were then subjected to internal oxidation treatment. For the internal oxidation treatment, the oxygen partial pressure and heating temperature were adjusted within the range of 0.2 to 0.9 MPa and 500 to 900°C. Next, the solid pieces after the internal oxidation treatment were collected and compression molded into billets with a diameter of 50 mm. These billets were hot extruded and then drawn into wire rods with a diameter of 2.3 mm, and rivet-type contact materials were manufactured using a header machine.

[0087] In the production of the contact material by powder metallurgy, Ag powder and oxide powder (both with an average particle size of 0.5 to 100 μm) were mixed and compression molded to form a billet with a diameter of 50 mm.

[0088] After sintering this billet, it underwent two cold compression processes and two sintering processes, followed by hot compression to obtain a sintered body. In the multiple sintering processes, the heating temperature was set to 800°C to 850°C, and the material was heated and sintered within this range. Furthermore, for the cold compression process after sintering, the load for the second process was set to be twice that of the first process. The sintered body was then hot extruded, and subsequently drawn into a wire rod with a diameter of 2.3 mm, which was then used in a header machine to produce rivet-type contact materials.

[0089] In this embodiment, two types of rivet-type contact materials were manufactured for the movable contact and the fixed contact. The dimensions of the head of the movable contact were 3.15 mm in diameter and 0.75 mm in height, and the dimensions of the head of the fixed contact were 3.3 mm in diameter and 1.0 mm in height.

[0090] [Hardness measurement of contact materials] In the manufacturing process of the contact material described above, wire samples were cut from the wire that had been drawn and annealed (at 700°C) and the hardness was measured. The hardness was measured by embedding the sample in resin, polishing it to expose the cross section (cross section in the short direction), and measuring it with a Vickers hardness tester (HMV-G21ST, manufactured by Shimadzu Corporation). The measurement was performed at five locations with a load of 200 gf, and the average value was used as the hardness value.

[0091] The compositions and hardness values ​​of contact materials of Examples (Examples 1 to 49) and Comparative Examples (Comparative Examples 1 to 23) manufactured in this embodiment are shown in Tables 1 and 2. In this embodiment, a contact material made of pure Ag without oxide particles was also manufactured and evaluated (Comparative Example 23). This Ag contact was manufactured by hot extrusion of a melted and cast billet. To measure the hardness of the Ag contact, an Ag wire was annealed (at 700°C), then wiredrawn at a processing rate of 4.2%, and samples were cut out and measured.

[0092] [Observation of the structure of contact materials] Next, the structure of each contact material was observed. As in the case of hardness measurement, the cross section of the resin-embedded sample was observed under an electron microscope (SEM) (magnification 5000x). The SEM images were then processed using particle analysis software. In the image processing, the total area of ​​the oxide (area ratio to the field of view area), average particle diameter, and particle size distribution were measured and analyzed to determine the dispersion state of the oxide in the contact material. For this analysis, the particle analysis system AZtecFeature manufactured by Oxford Instruments Ltd. was used. The particle size was also calculated as the circle equivalent diameter (area-equivalent circle diameter). Based on the area f of each oxide particle, the circle equivalent diameter was calculated using the formula ((4f / π) 1 / 2 ) and calculated the particle size of the oxide particles, and then calculated the average and standard deviation σ.

[0093] The compositions and hardness values ​​of the contact materials of Examples (Examples 1 to 49) and Comparative Examples (Comparative Examples 1 to 23) produced according to this embodiment, as well as the measurement results of the dispersion state of oxide particles, are shown in Tables 1 and 2. These tables confirm that fine oxide particles are dispersed in the Ag matrix in the contact materials of each Example.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Evaluation of DC high voltage relay interruption durability] DC high-voltage relays incorporating the contact materials of each example and comparative example were manufactured, and their interruption durability was confirmed. Here, a relay with the same double-break structure as in Figure 1 was prepared, and rivet-type contacts made of each contact material were joined to the movable terminal and fixed terminal (a total of four contact points formed two pairs of contacts). The dimensions of the contacts (rivet head dimensions) were: diameter 3.15 mm x thickness 0.75 mm for the movable contact (the area of ​​the contact surface when the head is observed from above is 7.79 mm 2 ), the fixed contact has a diameter of 3.3 mm and a thickness of 1.0 mm (the area of ​​the contact surface when observing the head from above is 8.55 mm 2 ) In addition, arc-extinguishing magnets (two neodymium magnets containing neodymium, a rare earth element, with a magnetic flux density of 200 mT) were placed around the moving and fixed contacts. Measurements using a gauss meter showed that the magnetic flux density at the center of the contacts was 26 mT.

[0097] In this embodiment, the operating conditions for the DC high-voltage relay were voltage and current: DC 360V and 400A, and contact force / opening force of the moving contact: 75gf / 125gf. The contact force was set by adjusting the strength of the pressure spring, and the opening force was set by adjusting the strength of the return spring. Because the DC high-voltage relay used in this evaluation test has a double-break structure, the force applied to each contact pair was set to half the force applied by the pressure spring and return spring, respectively, as the contact force and opening force.

[0098] The DC high-voltage relay of this embodiment was evaluated for interruption durability by performing 10 contact opening and closing operations and checking for contact welding after each opening and closing operation. Relays that did not experience contact welding after 10 contact opening and closing operations were evaluated as passing (◯), and relays that experienced contact welding within 10 operations were evaluated as failing (×).

[0099] [Evaluation of Arc Discharge Characteristics in DC High-Voltage Relays] Next, DC high-voltage relays incorporating the contact materials of each example and comparative example were manufactured, and tests were conducted to evaluate the arc discharge characteristics of the contacts. A relay with the same double-break structure as above was prepared, and rivet-type contacts made of each contact material were joined to its movable terminal and fixed terminal. The dimensions of the contacts and the magnetic flux density of the arc-extinguishing magnet were the same as above.

[0100] In an evaluation test of the arc discharge characteristics of the DC high-voltage relay of this embodiment, the contacts were opened and closed under the conditions of a voltage and current of DC 360 V and 400 A, and a contact force / opening force of the movable contact of 75 gf / 125 gf, and the characteristics of the arc discharge that occurred when the contacts were opened were measured. To measure the arc discharge characteristics, an oscilloscope (Teledyne LeCroy WAVESURFER454VL) was used to measure the arc current waveform and arc voltage waveform when the contacts were opened. An arc power waveform was then created from the product of the arc current waveform and the arc voltage waveform. The time during which the arc discharge continued was defined as the arc duration (msec), and the integral value of the arc power waveform over the arc duration was calculated as the arc energy (J). The arc discharge characteristics were evaluated based on the length of the arc duration and the magnitude of the arc energy. In this arc discharge characteristic evaluation, the number of measurements (n) was 1 to 15, and the average was used as the characteristic value.

[0101] [Contact resistance and heat generation measurement for DC high voltage relays] Furthermore, the contact resistance was measured for contacts made of the contact materials of each example and comparative example. Each contact material was incorporated into the same relay as in the arc discharge characteristic evaluation test described above, and the contact resistance was measured after one switching operation under the same conditions. The contact resistance was measured by connecting the DC high-voltage relay to a resistance measurement circuit (DC 5V 30A) prepared separately from the interrupter circuit after the switching operation. In measuring the contact resistance using this resistance measurement circuit, the voltage drop between the terminals was measured after 30 minutes of continuous current (30A) flow through the circuit. The measured voltage drop (mV) was then divided by the current (30A) to obtain the contact resistance (mΩ).

[0102] During this contact resistance measurement, the temperature rise due to heat generation at the contacts was also measured. Heat generation was measured by measuring the temperature rise at the terminals that connect the relay incorporating the contact material to the resistance measurement circuit. In this measurement, the temperatures of the two terminals, the anode terminal and the cathode terminal, were measured 30 minutes after the start of continuous current flow for the contact resistance measurement described above, and the average value of the temperature difference from room temperature was evaluated as the temperature rise (°C). Note that the number of measurements, n = 1, was used to measure and evaluate the contact resistance of this DC high-voltage relay.

[0103] Tables 3 and 4 show the evaluation results of the interruption durability, arc discharge characteristics, contact resistance, and heat generation measurements of the DC high-voltage relay of this embodiment.

[0104] [Table 3]

[0105] [Table 4]

[0106] The evaluation results shown in Table 4 confirm that pure Ag is unsuitable as a contact material for DC high-voltage relays. In the DC high-voltage relay (Comparative Example 23) in which pure Ag was used for the contacts, welding occurred after less than 10 interruptions. Although the interruption test of the relay conducted in this embodiment was conducted under relatively severe conditions, it is still not desirable for welding to occur after less than 10 switching operations.

[0107] On the other hand, it can be said that the DC high voltage relays (Examples 1 to 49) having contact materials essentially containing Zn as the metal M have interruption durability. Furthermore, it can be seen that these Examples have excellent arc discharge characteristics, with shortened arc duration and reduced arc energy.

[0108] In this embodiment, DC high-voltage relays were also evaluated using a contact material (Comparative Example 4) containing approximately 10% by mass of metal M, including Sn, In, and other elements, as contact materials for general relays. Also, contact materials (Comparative Examples 1 to 3, 15 to 21) containing no Zn and relatively low amounts of Sn, In, and other elements were evaluated. The results confirmed that the arc discharge characteristics of both contact materials were inferior to those of the Examples. This result indicates that the arc discharge characteristics can be improved by including Zn as an essential component in the contact material. However, when the Zn content exceeds 8% by mass, the arc discharge characteristics become comparable to those of conventional contact materials (Comparative Examples 5 and 8). Therefore, it is necessary to set the upper limit of the content of metal M, including Zn, to approximately 8% by mass. Furthermore, considering the average particle size of the oxide particles in the contact material, Comparative Examples 10 to 14 showed poor interruption durability, suggesting that the average particle size of the oxide particles should be 0.4 μm or less.

[0109] Furthermore, with regard to the issues of contact resistance and heat generation, the superiority of the contact materials of Examples 1 to 49 can be seen from the measurement results when they are actually incorporated into a relay. The temperature rise value of the contact materials of each Example is lower than that of the Comparative Example. The amount of heat generated by the contact is proportional to the square of the current and the contact resistance value. Although the current flowing in the measurement test of this embodiment was relatively low at 30 A, if the current flowing is increased when the material is applied to an actual DC high-voltage relay, the temperature rise will be even greater.

[0110] The metal M of the contact material used in the present invention is essentially Zn, but may also contain metals other than Zn (Sn). Comparison with comparative examples shows that the addition of other metals to Zn also results in excellent arc discharge characteristics and contact resistance (Examples 8-10, 13-48). In Ag-oxide-based contact materials, Sn oxide (SnO2) and the like have the effect of improving welding resistance. Therefore, by using an Ag-oxide-based contact material containing Sn in addition to Zn, both the arc discharge characteristics and welding resistance can be adjusted. However, since additional metals other than Zn do not have a significant effect on the arc discharge characteristics, their addition is not essential.

[0111] Second embodiment In this embodiment, a DC high-voltage relay similar to that of the first embodiment was manufactured in which the magnetic force of the arc-extinguishing magnet was set to be low, and the arc discharge characteristics were evaluated when the contact materials of each of the examples and comparative examples were incorporated.

[0112] In this embodiment, a DC high-voltage relay with a double-break structure similar to that of the first embodiment was prepared, and rivet-type contacts made of each contact material were joined to its movable and fixed terminals. The dimensions of each contact were the same as in the first embodiment. A neodymium magnet with a magnetic flux density of 200 mT was placed around the movable and fixed contacts as an arc-extinguishing magnet, reducing the amount of neodymium used, a rare earth element, compared to the first embodiment. Measurement with a gauss meter revealed that the magnetic flux density at the center of the contacts was 13 mT.

[0113] The evaluation test of the arc discharge characteristics of the DC high-voltage relay of this embodiment was the same as that of the first embodiment, with the voltage and current being DC 360V and 400A, and the contact force / opening force of the movable contact being 75gf / 125gf, and the contact was opened and closed, and the arc discharge characteristics were evaluated each time. Then, as in the first embodiment, the arc discharge characteristics were used as measurement indices. In this evaluation of the arc discharge characteristics, the number of measurements n was 1 to 15, and the average value was used. The measurement results are shown in Tables 5 and 6.

[0114] [Table 5]

[0115] [Table 6]

[0116] This embodiment is a DC high-voltage relay in which the magnetic force of the arc-extinguishing magnet is set to half that of the first embodiment. The reduction in magnetic force due to the reduction in rare earth elements increases the arc duration and arc energy. Even under such circumstances, the contact materials of each example containing Zn suppress the arc duration and arc energy. The results of this embodiment support the use of reduced rare earth elements by reducing the magnetic force of the arc-extinguishing magnet in DC high-voltage relays.

[0117] Third embodiment In the first and second embodiments, a double-break DC high-voltage relay (Fig. 1) incorporating various contact materials was manufactured, and an interruption durability test was conducted to simulate the interruption operation during an abnormality. In this embodiment, this DC high-voltage relay was installed as a system main relay for a hybrid car or the like, and durability and contact resistance were evaluated when simulating the opening and closing operation during normal use. Normal use refers to conditions under which the relay is subjected to loads caused by the normal ON / OFF operation of the power supply to the circuit.

[0118] The normal operating conditions of the DC high-voltage relay assumed in this invention will now be specifically described. In DC circuits such as those in hybrid cars, a pre-charge relay suitable for inrush current is installed to prevent damage to the contacts of the system main relay caused by the high inrush current that occurs when the power is turned on. The system main relay is then powered on after the pre-charge relay has absorbed the high inrush current.

[0119] In this embodiment, a DC high-voltage relay having the same structure as the first embodiment incorporating the contact material of each example was installed in a test circuit such as that shown in FIG. 3 , and a capacitor load endurance test was conducted to evaluate durability by simulating the contact switching operation due to the inrush current mitigated as described above. The test conditions for the capacitor load endurance test of this embodiment were a voltage of 20 V DC, a load current of 80 A (inrush) and 1 A (breaking), and an open / close cycle of 1 second (ON) and 9 seconds (OFF). The contact force / opening force of the moving contact was 75 gf / 125 gf. In this capacitor load endurance test, the number of actuations was set at 10,000, which was the pass criterion for durability. A relay that did not experience contact welding within 10,000 actuations was evaluated as passing (◯), and a relay that experienced contact welding or other operational malfunctions within 10,000 actuations was evaluated as failing (×).

[0120] In this embodiment, as in the first embodiment, the contact resistance and temperature rise (amount of heat generation) were measured. After the capacitor load endurance test, the contact resistance was measured by switching the connection of the relay to a resistance measurement circuit (DC 5V 30A) separate from the circuit used for the capacitor load endurance test. The measurement method was the same as in the first embodiment. When measuring the contact resistance, the temperature rise due to heat generation at the contacts was also measured.

[0121] The measurements and evaluations in the capacitor load durability test of this embodiment were performed using the average value with the number of measurements n=1 to 3. Table 7 shows the durability evaluation results and the measurement results of contact resistance and temperature rise in this embodiment.

[0122] [Table 7]

[0123] As can be seen from Table 7, the DC high-voltage relays of each Example passed the durability test (10,000 operations) under the load of normal use. Furthermore, the contact resistance and heat generation were both low values ​​comparable to those of the Examples of other embodiments. The evaluation results of this Example confirmed that the DC high-voltage relays of each Example, which use contact materials containing Zn as an essential metal but with a reduced amount of oxide, can function effectively even when considering the actual usage conditions of hybrid cars, etc.

[0124] From the results of the first to third embodiments, it was confirmed that the DC high-voltage relay according to the present invention operates favorably as a DC high-voltage relay by using suitable contact material configurations for the movable contact and the fixed contact. The DC high-voltage relay according to the present invention can operate effectively even when a circuit is interrupted due to an abnormal operation, and can operate stably even in normal use.

[0125] Fourth embodiment In this embodiment, a DC high-voltage relay was manufactured in which the magnetic force of the arc-extinguishing magnet was set between that of the first embodiment (26 mT) and the second embodiment (13 mT), and the arc discharge characteristics were evaluated when the contact materials of the example and comparative example were incorporated. A DC high-voltage relay with a double-break structure similar to that of the first embodiment was prepared, and one neodymium magnet with a magnetic flux density of 200 mT and one ferrite magnet with a magnetic flux density of 54 mT were arranged as arc-extinguishing magnets around the movable contact and fixed contact. The number of magnets was the same as in the first embodiment, but the amount of rare earth element used was reduced by using a ferrite magnet that does not contain neodymium, a rare earth element. Measurement with a gauss meter revealed that the magnetic flux density at the center position when the contacts were in contact was 18 mT.

[0126] As in the first and second embodiments, the contacts were opened and closed at a voltage and current of DC 360V and 400A, and the contact force and opening force of the movable contact were 75gf and 125gf, respectively, and the arc discharge characteristics were evaluated for each operation. Measurements were made for n=1 to 15, and the average values ​​were used. The measurement results are shown in Table 8. Note that for this embodiment, the contact materials of Examples 1, 2, 5, 7, 12, 25, 35, 38, 42, 44 to 46, and 48 and Comparative Examples 2, 3, 5, 9, 15 to 18, 20, 21, and 23 were used.

[0127] [Table 8]

[0128] From Table 8, it can be seen that in this embodiment as well, the DC high voltage relays equipped with the contact materials of each example containing Zn are able to suppress the arc duration and arc energy. This is the same as in the second embodiment. From this embodiment, it can be confirmed that magnets other than rare earth magnets (neodymium magnets) can be used as arc-extinguishing magnets in DC high voltage relays. This embodiment can also be said to support the reduction in the amount of rare earth elements used.

[0129] Fifth embodiment In this embodiment, a DC high-voltage relay was manufactured in which the contact force was increased while the opening force was reduced compared to the DC high-voltage relays of the first to fourth embodiments. In this embodiment, the arc discharge characteristics of a DC high-voltage relay with a double-break structure in which the contact force / opening force was 100 gf / 90 gf were evaluated. The other evaluation conditions were the same as those of the first embodiment. Note that for this embodiment, the contact materials of Examples 1, 2, 5, 7, 12, 25, 35, 38, 42, 44-46, and 48 and Comparative Examples 2, 3, 5, 9, 15-18, 20, and 21 were used.

[0130] In this embodiment, a DC high-voltage relay in which both the contact force and the opening force are less than 100 gf was also evaluated as a reference example. Using the contact materials of Examples 1 and 2, a DC high-voltage relay with a double-break structure in which the strength of the contact pressure spring and return spring are smaller than those of the first to fourth embodiments was manufactured (Reference Examples 1 and 2). The contacts were then opened and closed in the same manner, and the arc discharge characteristics were evaluated for each operation. The results are shown in Table 9.

[0131] [Table 9]

[0132] Table 9 shows that even in DC high-voltage relays in which the contact force is increased and the opening force is decreased compared to the first embodiment, etc., DC high-voltage relays equipped with the contact materials of each Example have good interruption durability and suppress the arc duration and arc energy. Furthermore, referring to the results of Reference Examples 1 and 2, when the contact force and opening force of a DC high-voltage relay are less than 100 gf, the interruption durability performance is poor even when the contact material of Examples 1 and 2 is used. This is partly due to the content of metal M, but is also thought to be due to the contact force or opening force being too low (less than 100 gf).

[0133] Sixth embodiment In this embodiment, a DC high-voltage relay was manufactured that had the same structure as the first embodiment, but with a voltage and current of DC 200 V and 200 A. Furthermore, a DC high-voltage relay was manufactured with a contact force and opening force set greater than those of the first to fifth embodiments, and the arc discharge characteristics were evaluated when the contact materials of the example and comparative example were incorporated. To adjust the contact force and opening force, a DC high-voltage relay with a double-break structure similar to that of the first embodiment was prepared, and a relay with a stronger contact pressure spring and return spring was used. In this embodiment, two types of DC high-voltage relay were manufactured: one with a contact force / opening force of 250 gf / 600 gf and the other with a contact force / opening force of 500 gf / 1250 gf. The contacts were opened and closed for each relay, and the arc discharge characteristics were evaluated for each cycle. Other evaluation conditions were the same as those of the first embodiment. For this embodiment, the contact materials used were Examples 1, 2, 5, 7, 12, 25, 35, 38, 42, 44 to 46, and 48 and Comparative Examples 2, 3, 5, 9, 15 to 18, 20, and 21. Tables 10 and 11 show the evaluation results.

[0134] [Table 10]

[0135] [Table 11]

[0136] Referring to Tables 10 and 11, it can be seen that increasing the contact force and opening force results in a DC high-voltage relay with good arc characteristics, and that the arc duration and arc energy tend to decrease. This tendency is not limited to the contact materials of each example, but is also seen in contact materials that do not contain Zn (Comparative Examples 2, 3, 15-18, 20, and 21) and contact materials with a high concentration of metal M (Comparative Examples 5 and 9). However, when comparing examples and comparative examples with similar contents (oxide amounts) of metal M (for example, Example 5 and Comparative Example 18), it is found that DC high-voltage relays using contact materials containing Zn have a suppression effect of 10% or more in arc duration and 5% or more in arc energy.

[0137] Furthermore, the arc duration and arc energy are greater than those of the respective examples for DC high-voltage relays using contact materials with a high content of metal M. In fact, for DC high-voltage relays using contact materials with a high content of metal M, even if improvements in arc characteristics are seen due to increased contact force and opening force, the problem of heat generation due to the contact resistance of the contact material is not resolved. [Industrial Applicability]

[0138] The Ag-oxide-based contact material used in the DC high-voltage relay of the present invention exhibits excellent arc discharge characteristics, and in addition, is a contact material with low contact resistance and low heat generation. The DC high-voltage relay of the present invention solves the problems of arc discharge and heat generation in the contact pairs and can perform reliable ON / OFF control. The present invention is suitably applied to system main relays in power supply circuits of high-voltage batteries such as hybrid cars, and power conditioners in power supply systems such as solar power generation facilities.

Claims

1. A DC high voltage relay having at least one contact pair consisting of a movable contact and a fixed contact and having a rated voltage of 48V or more, a drive section that generates and transmits a drive force for moving the movable contact, and a contact section that opens and closes a DC high voltage circuit; the drive section includes an electromagnet or a coil that generates a drive force, a transmission means that transmits the drive force to the contact section, and a biasing means that biases the transmission means to bring the contact pairs into contact with or separate the contact pairs; the contact section includes at least one contact pair consisting of a movable contact and a fixed contact that are moved by the transmission means of the drive section, at least one movable terminal that joins the movable contact, and at least one fixed terminal that joins the fixed contact; a contact force and / or a separation force adjusted by the capacity and size of the electromagnet or the coil of the driving section and the capacity and size of the biasing means is 100 gf or more; the movable contact and / or the fixed contact are made of an Ag-oxide-based contact material, the metal component of the contact material comprises at least one metal M essentially containing Zn, with the remainder being Ag and unavoidable impurity metals; the content of the metal M is 0.2% by mass or more and 6% by mass or less relative to the total mass of all metal components of the contact material, the contact material has a material structure in which one or more oxides of the metal M are dispersed in a matrix made of Ag or an Ag alloy, The average particle size of the oxide is 0.01 μm or more and 0.4 μm or less.

2. The contact material further contains, as the metal M, at least one of Sn, In, Ni, Te, Bi, and Cu; 2. The DC high-voltage relay according to claim 1, wherein the content of the metal M relative to the total mass of all metal components of the contact material is 0.2 mass % or more and 6 mass % or less.

3. 3. A DC high-voltage relay according to claim 1, wherein the area ratio of oxide in any cross section of the contact material is 0.1% to 20%.

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