Abnormality detection device of fastening state of electrical connection

Abstract

To determine the fastening state of electrical connections 10, 11, and 12 of power lines with higher accuracy.SOLUTION: A device 50 for determining a fastening state of an electrical connection of a power line determines that the fastening state of the electrical connection is normal when magnitude of a temperature difference is below a threshold, the temperature difference being a difference between a temperature Ta at the electrical connection and an estimated temperature Te of the electrical connection of when the fastening state of the electrical connection is determined to be normal on the basis of the current value I flowing through the electrical connection and the ambient temperature Ts of the power line; and determines that the fastening state of the electrical connection is abnormal when the magnitude of the temperature difference exceeds the threshold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a device for inspecting the fastening state of an electrical connection in an electric power line such as a power line of an electric vehicle, and more particularly to a device for detecting an abnormality in the fastening state due to loosening of a fastener of an electric connection or wear of the contacts of the fastener. [Background technology]

[0002] At electrical connections between terminals of bus bars or wire harnesses in power lines such as the power lines of electric vehicles (e.g., electrical wiring inside a battery pack), mechanical loosening of fasteners or wear of fastener contacts can occur due to vibrations of the vehicle or other machinery to which the power lines are attached, resulting in insufficient contact between the terminals. This increases electrical resistance and heat loss at the connection points, and various technologies have been proposed for monitoring the condition of such electrical connections. For example, Patent Document 1 proposes a configuration in which a fastening member fastens a conductive connection plate that connects the electrode terminals of multiple battery cells to the electrode terminals. When a load current greater than or equal to a predetermined value flows at a fastening point, the fastening point is loosened when either thermistors attached near both terminals of each battery cell indicate a temperature higher than a predetermined temperature. The configuration also proposes a battery abnormality when a load current greater than or equal to a predetermined value does not flow, or when a load current greater than or equal to a predetermined value flows and both thermistor readings are equal to or greater than a predetermined value. Patent document 2 proposes a configuration in which both terminals of a battery are connected to both ends of a shunt resistor, and temperature sensors are provided at both terminals of the shunt resistor, and if the difference in temperature detected by the temperature sensors exceeds a predetermined value, it is determined that there is a connection abnormality at one of the connection points. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2010-282816 [Patent Document 2] Patent Publication No. 2021-135140 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, if the fastening of a power line electrical connection becomes unstable due to loosening of the fasteners or connectors or wear of the fasteners or connectors, the electrical resistance of that portion increases, causing a temperature rise due to Joule heat. Therefore, by monitoring the temperature of the electrical connection, it is possible to determine whether the fastening state of the electrical connection is normal (whether the contact between the terminals is stable). In this regard, because the Joule heat generated in the electrical connection varies depending on the magnitude of the current flowing through the electrical connection, the temperature of the electrical connection will also change with changes in the current flowing through the electrical connection, even if the fastening state of the electrical connection is normal. Therefore, when detecting the fastening state of an electrical connection using its temperature, taking into account the change in temperature due to the current through the electrical connection will enable more accurate determination of the fastening state.

[0005] Thus, the main object of the present invention is to be able to more accurately determine the fastening condition at the electrical connection portion of the power line, i.e., whether or not the fasteners have become loose or worn. [Means for solving the problem]

[0006] According to the present invention, the above problem is solved by providing an apparatus for determining the fastening state of an electrical connection portion of a power line, comprising: a first temperature detection means for detecting the temperature at the electrical connection; a current detection means for detecting a value of a current flowing through the electrical connection portion; a second temperature detection means for detecting the temperature around the power line; a temperature estimating means for estimating a temperature of the electrical connection portion when the fastening state of the electrical connection portion is normal, based on the current value detected by the current detecting means and the ambient temperature of the power line detected by the second temperature detecting means; fastening state determination means for determining that the fastening state of the electrical connection portion is normal when the magnitude of the difference between the temperature at the electrical connection portion detected by the first temperature detection means and the temperature of the electrical connection portion estimated by the temperature estimation means when the fastening state of the electrical connection portion is normal is below a threshold value, and determining that the fastening state of the electrical connection portion is abnormal when the magnitude of the difference exceeds the threshold value; This is achieved by an apparatus comprising:

[0007] In the above configuration, the "power line" may refer to any part of a power line in an electric vehicle or other machinery or equipment, specifically, a power line between an electrode terminal of a battery cell in a battery pack and an output terminal of the battery pack. The "electrical connection" may refer to a connection between terminals in a power line, such as a portion where two or more conductors are fastened to each other using fastening elements such as screws, bolts, and nuts, or a portion where they are joined by welding or soldering. The "first temperature detection means" and "second temperature detection means" may be any type of temperature sensor used in this field. The first temperature detection means may be installed at any location where the temperature of the electrical connection can be detected. On the other hand, the second temperature detection means may be located at any location where the ambient temperature of the power line can be detected, and is preferably located at a location that is substantially or almost not directly affected by the heat of the electrical connection. The "current detection means" may be any type of sensor or ammeter used in this field that can detect current and is located at any location where the value of current flowing through the electrical connection can be detected. The "temperature estimation means" and "fastening state determination means" may be implemented in a computer device operating according to a program.

[0008] The temperature of an electrical connection is determined by the ambient temperature of the electrical connection and the Joule heat generated at the electrical connection. Joule heat at an electrical connection is determined by the electrical resistance and current of the electrical connection. Therefore, the temperature when the electrical connection is in a normal fastening state can be estimated from the ambient temperature of the electrical connection, the normal electrical resistance of the electrical connection, and the current at the electrical connection. If an abnormality occurs in the fastening state of the electrical connection, such as when a fastener loosens or wears, causing the connection to become unstable, the electrical resistance of that portion increases, resulting in greater Joule heat than when the fastening state is normal. Therefore, the temperature actually detected at the electrical connection will be higher than the temperature estimated from the ambient temperature of the electrical connection, the normal electrical resistance of the electrical connection, and the current at the electrical connection. Therefore, in the present invention described above, while the actual temperature of the electrical connection is detected by the first temperature detection means, the temperature of the electrical connection when the fastening state of the electrical connection is normal is estimated based on the ambient temperature of the electrical connection and the current value of the electrical connection, and by monitoring whether the actual temperature is significantly higher than the estimated temperature, it is possible to determine whether an abnormality such as an increase in electrical resistance has occurred in the electrical connection. Note that in the above configuration, a "threshold" for the magnitude of the difference between the actual temperature ("the temperature at the electrical connection detected by the first temperature detection means") and the estimated temperature ({the temperature of the electrical connection when the fastening state of the electrical connection is normal estimated by the temperature estimation means}) may be set to a value at which the fastening state of the electrical connection is determined to be abnormal when the difference exceeds the threshold, and may be determined experimentally.

[0009] According to the above-described configuration of the present invention, instead of simply determining whether the temperature of the electrical connection is higher than a predetermined temperature as in the past, the change in temperature of the electrical connection linked to the current value at the electrical connection is taken into consideration, and it is expected that the fastening state of the electrical connection can be determined more accurately. Furthermore, the configuration of the present invention does not compare the temperatures of two or more electrical connection parts and determine that the electrical connection is abnormal if any one of them is significantly higher, but rather determines the fastening state of each electrical connection part individually, which is advantageous in that it is possible to determine the fastening state even if there are not multiple electrical connection parts placed in similar environments, and that even if the fastening states of multiple electrical connection parts become abnormal at the same time, each abnormality can be detected.

[0010] In the above configuration, when the power line is a power line between the electrode terminal of a battery cell in the battery pack and the output terminal of the battery pack, the second temperature detection means may be placed in a position to detect the temperature of any part in the battery pack, for example, a part where heat does not accumulate.

[0011] In the above configuration, if the fastening state determination means determines that the fastening state of the electrical connection is abnormal, the fastening state determination means may be configured to send a current reduction command to a power line control device that controls the current in the power line, such as a control unit of a battery pack, to reduce the amount of current flowing through the electrical connection. This is expected to prevent the electrical connection from becoming overheated. Furthermore, if the fastening state determination means still determines that the fastening state of the electrical connection is abnormal after sending the current reduction command, the fastening state determination means may be configured to send a current prohibition command to the power line control device to prohibit the flow of current through the electrical connection. This is expected to prevent the electrical connection from becoming even hotter. Furthermore, when the present invention is applied to the power line of a drive battery for an electric vehicle, the above configuration reduces the amount of current when an abnormality in the electrical connection is first detected, rather than prohibiting the flow of current, so that the vehicle can be driven within a range that ensures safety. This makes it possible to move the vehicle to a location where repairs can be made, and is safe because the supply of power to the drive unit is not suddenly prohibited while the vehicle is in motion.

[0012] In the above configuration, the temperature when the electrical connection is in a normal state is estimated using the temperature rise due to Joule heat, which is determined from the current value flowing through the electrical connection and the electrical resistance value when the electrical connection is in a normal state, and the temperature drop due to heat dissipation from the electrical connection to the surroundings. The temperature rise per unit time due to Joule heat is calculated as being proportional to the square of the current value, and the temperature drop due to heat dissipation is calculated as a function of the temperature of the electrical connection and the surrounding temperature. [Effects of the Invention]

[0013] Thus, in the configuration of the present invention, focusing on the fact that the temperature when the electrical connection is in a normal state can be estimated from the temperature around the electrical connection, the electrical resistance value when the electrical connection is in a normal state, and the current value at the electrical connection, it is expected that the determination of whether the fastening state of each electrical connection is normal or not can be achieved more accurately by taking into account temperature changes due to the current at the electrical connection. According to the configuration of the present invention, the fastening state of each electrical connection can be determined individually, and even when the current at the electrical connection is small, the temperature when the electrical connection is in a normal state can be estimated corresponding to that state, which is advantageous in that it makes it easy to identify the location where an abnormality has occurred. As already mentioned, the configuration of the present invention is applied when the power line is a power line between the electrode terminal of a battery cell in a battery pack and the output terminal of the battery pack, but it may also be used to monitor the fastening state of electrical connections of other power lines, and such cases also fall within the scope of the present invention.

[0014] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0015] [Figure 1] 1(A) and (B) are schematic diagrams of electrical connections in power lines. (A) shows a case where the fastening state is normal, and (B) shows a case where the fastener is loose and the fastening state is unstable, i.e., an abnormal state. [Figure 2] FIG. 2 is a block diagram illustrating the configuration of a device for determining the fastening state of an electrical connection according to this embodiment. [Figure 3] FIG. 3 is a flowchart illustrating the operation of the device for determining the fastening state of an electrical connection according to this embodiment. [Explanation of symbols]

[0016] 10, 11... terminal, 12... fastener, 20... connection temperature sensor, 21... ambient temperature sensor, 22... ammeter, 50... determination device, 51... subtractor, 52... normal temperature estimation unit, 53... determination unit, Wd... alarm BEST MODE FOR CARRYING OUT THE INVENTION

[0017] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0018] Configuration of device for determining fastening state of electrical connection As shown in Fig. 1(A), in a power line that transmits power from a battery or generator in an electric vehicle or other machinery and equipment to various devices, when terminals 10 and 11 of two conductors (such as a bus bar, a wire harness, or battery cell electrodes) are fastened together by a fastener 12, loosening or wear of fastener 12 can cause the fastening state between terminals 10 and 11 to become unstable, reducing the contact area therebetween, as shown in Fig. 1(B). This increases the electrical resistance between terminals 10 and 11, increasing Joule heat and resulting in increased loss. Therefore, it is advantageous to provide a configuration that monitors whether the fastening state of the electrical connection is normal so that any abnormality, such as loosening, can be detected. When monitoring the fastening state of such an electrical connection, if an abnormality occurs in the electrical connection, Joule heat increases as described above, causing an abnormal rise in the temperature of the electrical connection. Therefore, by detecting this rise in temperature of the electrical connection, it is possible to detect an abnormality in the fastening state of the electrical connection. However, because the temperature of the electrical connection changes depending on the increase or decrease in the current through the electrical connection, even when the fastening state is normal, simply monitoring the temperature rise of the electrical connection makes it difficult to accurately detect an abnormality in the fastening state of the electrical connection. In this regard, the temperature when the fastening state of the electrical connection is normal can be estimated from the ambient temperature of the electrical connection, the electrical resistance value when the electrical connection is normal, and the current value of the electrical connection. Therefore, in the device of this embodiment, the temperature when the fastening state of the electrical connection is normal is estimated based on the measured values ​​of the ambient temperature of the electrical connection and the current value of the electrical connection, using the electrical resistance value (constant) when the fastening state is normal. The presence or absence of an abnormality in the fastening state of the electrical connection is determined by monitoring whether the actual temperature of the electrical connection is significantly higher than the estimated temperature when the fastening state of the electrical connection is normal.

[0019] 2, in the configuration of the determination device 50 of this embodiment, a temperature sensor 20 that measures the actual temperature Ta of the electrical connection 12 is disposed near the electrical connection 12 where the terminals 10 and 11 are connected to each other, a temperature sensor 21 that measures the ambient temperature Ts of the electrical connection is disposed in a portion around the electrical connection 12 that is substantially not affected by the heat generated by the electrical connection 12 (a portion where heat is less likely to build up), and an ammeter or current sensor 22 that measures the current value I flowing through the electrical connection 12 is disposed on any power line connected to the electrical connection. Of these, the ambient temperature Ts detected by the temperature sensor 21 and the current value I detected by the ammeter or current sensor 22 are input to a normal-state temperature estimation unit 52 in the determination device 50, and an estimated temperature Te when the fastening state of the electrical connection is normal is estimated therein using the electrical resistance value when the fastening state of the electrical connection is normal. The actual temperature Ta of the electrical connection 12 detected by the temperature sensor 20 and the estimated temperature Te when the fastening state of the electrical connection is normal are input to a subtractor 51, and the temperature difference ΔT is input to a determination unit 53, which determines whether ΔT exceeds an appropriately set threshold value ΔTo. If ΔT exceeds the threshold value ΔTo, it is determined that there is an abnormality in the fastening state of the electrical connection, and an alarm Wd is issued, and a control command to adjust the output may be sent to a control device (such as a power control unit PCU) that controls the current in the power line.

[0020] In the device of this embodiment, the temperature sensor 20, the temperature sensor 21, and the ammeter or current sensor 22 may each be a normal sensor or measuring instrument used in this field. The determination device 50 may be a computer device, and the subtractor 51, the normal temperature estimation unit 52, and the determination unit 53 are each realized by the operation of the computer device in accordance with a program.

[0021] More specifically, the estimated temperature Te when the fastening state of the electrical connection part is normal in the normal temperature estimation unit 52 is Estimated temperature Te = initial temperature + temperature rise - temperature drop ... (1) The initial temperature is the temperature of the electrical connection before current is passed through it, and the ambient temperature Ts of the electrical connection may be used. The temperature rise is due to Joule heat and is calculated using the current value detected by the ammeter 22 and the electrical resistance value when the electrical connection is properly fastened. The current in the power line is adjusted by controlling the power transmitted from the battery or generator in the electric vehicle or other machinery to various devices through the power line, so it does not substantially fluctuate with increases or decreases in the electrical resistance of the electrical connection. The temperature drop in equation (1) above is due to heat dissipation through thermal conduction, thermal convection, and thermal radiation at the electrical connection, and can be calculated sequentially or recursively using the ambient temperature Ts and the estimated temperature Te. The actual estimated temperature Te may be calculated using a map or the like experimentally obtained using the current value I and the ambient temperature Ts as variables.

[0022] The electrical connection portion to which the device of this embodiment is applied may be not only a connection portion between terminals fastened by a fastener as shown in the figure, but also a connection portion between terminals fastened by joining by welding, adhesive, etc.

[0023] Operation of the device The monitoring of the fastening state of the electrical connection by the device of this embodiment illustrated in FIG. 2 may be performed continuously while the power line is in use. The operation of the device may be performed according to the flowchart illustrated in FIG. 3. Referring to FIG. 3, prior to determining the fastening state, the actual temperature Ta of the electrical connection, the ambient temperature Ts, and the current value I are each measured (step 1). As described above, the normal temperature Te of the electrical connection is estimated using the ambient temperature Ts and the current value I (step 2). It is then determined whether the temperature difference ΔT = Ta - Ts exceeds the threshold value ΔT (step 3). The threshold value ΔT is a temperature difference that, when ΔT exceeds ΔT, indicates that there is an abnormality in the fastening state of the electrical connection. This threshold value may be determined experimentally (ΔT may vary depending on the current value I and the ambient temperature Ts). If ΔT<ΔT (determination N in S3), the fastening state of the electrical connection is determined to be normal, and monitoring continues (R: return).

[0024] On the other hand, if ΔT>ΔTo, it is determined that the fastening state of the electrical connection is abnormal, and a notification to that effect (abnormality notification) is issued (step 4). Then, when an abnormality in the fastening state of the electrical connection is first detected (determination of N in S5), a request is made to the control device that controls the current in the power line to impose an output limit to reduce the current flowing through the power line (step 6), and monitoring may continue as is (R: Return).

[0025] When the above output restriction is implemented, the current value is reduced, so that the actual temperature Ta of the electrical connection is expected to decrease (the estimated temperature is also reduced). However, if the temperature difference ΔT in step 3 still exceeds the threshold value ΔTo (Y judgment in S3, Y judgment in S5), the output is prohibited (step 7) to prohibit the passage of electricity to the electrical connection, and monitoring ends (E: End).

[0026] As described above, when an abnormality in the fastening state of the electrical connection is first detected, output is not immediately prohibited but temporarily reduced. This allows the electrical equipment, such as an electric vehicle, to remain in an operational state within a range that ensures safety depending on the severity of the abnormality, allowing the electrical equipment to be moved to a location where it can be repaired and preventing malfunctions due to a sudden shutdown. Furthermore, by continuing to monitor the electrical equipment even after the restriction, it is possible to stop the transmission of power before the fastening state of the electrical connection becomes more serious.

[0027] In the configuration of the device of this embodiment, the fastening state of each electrical connection can be monitored individually, so monitoring is possible even if there are no two or more parts with similar conditions. Furthermore, since abnormality determination is performed taking into account changes in the current flow state, it is advantageous in that it can also determine abnormalities in heat generation that cannot be determined based on absolute temperature values.

[0028] The configuration of the device of this embodiment is advantageously used to monitor the fastening state of each electrical connection part in a wire harness or bus bar in a battery stack, from the output terminal in a battery pack to a junction block (relay, etc.), but is not limited to these.

[0029] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. A device for determining the fastening state of an electrical connection portion of a power line, comprising: a first temperature detection means for detecting the temperature at the electrical connection; a current detection means for detecting a value of a current flowing through the electrical connection portion; a second temperature detection means for detecting the temperature around the power line; a temperature estimating means for estimating a temperature of the electrical connection portion when the fastening state of the electrical connection portion is normal, based on the current value detected by the current detecting means and the ambient temperature of the power line detected by the second temperature detecting means; fastening state determination means for determining that the fastening state of the electrical connection portion is normal when the magnitude of the difference between the temperature at the electrical connection portion detected by the first temperature detection means and the temperature of the electrical connection portion estimated by the temperature estimation means when the fastening state of the electrical connection portion is normal is below a threshold value, and determining that the fastening state of the electrical connection portion is abnormal when the magnitude of the difference exceeds the threshold value; An apparatus comprising:

2. 2. The device of claim 1, wherein the power line is a power line between an electrode terminal of a battery cell in a battery pack and an output terminal of the battery pack, and the second temperature detection means is placed at a position where it can detect the temperature of any location within the battery pack.

3. 2. The device according to claim 1, wherein when the fastening state determination means determines that the fastening state of the electrical connection portion is abnormal, the device transmits a current reduction command to a power line control device that controls the current in the power line, the current reduction command reducing the amount of current flowing through the electrical connection portion.

4. 4. The device according to claim 3, wherein if the fastening state determination means determines that the fastening state of the electrical connection is abnormal after the fastening state determination means has sent the current reduction command, the device is configured to send a current prohibition command to the power line control device to prohibit current from flowing through the electrical connection.

5. 2. The device of claim 1, wherein the temperature estimation means is configured to estimate the temperature of the electrical connection portion when the fastening state of the electrical connection portion is normal, using a temperature increase due to Joule heat determined based on the current value and the electrical resistance value when the fastening state of the electrical connection portion is normal, and a temperature decrease due to heat radiation from the electrical connection portion.

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