Vehicle power supply system and diagnostic device

Abstract

This vehicle power supply system supplies power from a battery to a plurality of loads mounted on a vehicle via a power supply cable connected to the plurality of loads, and comprises: an oscillator that outputs an AC signal at a predetermined frequency; a superimposer that superimposes the AC signal on one end side of the power supply cable; a detector that detects the voltage or current of the power supply cable when the AC signal is superimposed on the one end side of the power supply cable via the superimposer; and a diagnosis unit that diagnoses, on the basis of the voltage or current detected by the detector, whether an abnormality has occurred in the power supply cable.

Description

Vehicle power supply system and diagnostic device

[0001] This invention relates to a power supply system installed in a vehicle.

[0002] In recent years, the advancement of vehicle electrification and autonomous driving has created a demand for highly reliable (redundant) in-vehicle power networks, while simultaneously requiring a reduction in the amount of wire harnesses used for power supply and increased efficiency. Conventional in-vehicle power networks widely employ a configuration in which relay boxes and fuse boxes are placed near the battery, and power cables are laid radially to connect each vehicle sensor and actuator. In such an in-vehicle power network configuration, the number of wire harnesses is increasing due to the advancement of electrification and increased reliability of in-vehicle equipment, as well as the increase in in-vehicle equipment and the need for power supply redundancy.

[0003] A zone-based power network configuration is known as an in-vehicle power network that can reduce the number of wire harnesses. This configuration has a power network structure in which power is transmitted collectively to each zone of the vehicle via a small number of main power cables, and then distributed to nearby in-vehicle loads within each zone. As a result, power is transmitted to each zone via a small number of main power cables, the total length of power cables can be significantly reduced compared to conventional power networks.

[0004] When employing a zone-based power distribution network, the main power cables require a current capacity of 100A or more to ensure sufficient current for the in-vehicle equipment in each zone. Furthermore, a mechanism to detect short circuits or disconnections caused by damage to the main power cables is necessary, as this would render the entire power network inoperable. In conventional in-vehicle power networks as described above, fuses have generally been used to prevent smoke and fire caused by short circuits in power cables. However, when using fuses in high-capacity power cables, such as the main power cables in a zone-based power distribution network, the fuse's blowing current must be designed to be greater than the power cable's current capacity. Therefore, in the case of short circuits caused by insulation failure or water ingress, insufficient short-circuit current may flow to blow the fuse, potentially leading to a prolonged short-circuit condition and leaving the problem unaddressed.

[0005] As a background art related to short-circuit detection of a power cable, the technique described in Patent Document 1 below is known. Patent Document 1 describes a method for testing for disconnection of a cable assembly having a structure in which a plurality of coaxial cables are arranged in parallel and the shield layers at both ends of the cables are electrically short-circuited. In this method, it is determined whether there is a disconnection by determining whether it matches the resonance frequency of the cable assembly without disconnection measured in advance.

[0006] Japanese Patent Application Laid-Open No. 2008-46038

[0007] In Patent Document 1 described above, the resonance frequency of the cable assembly is measured by changing the frequency of the high-frequency signal and obtaining the point where the signal intensity becomes minimum from the results of measuring the signal intensity at each frequency. Then, it is compared with the resonance frequency measured in advance under normal conditions to determine whether the cable is disconnected. However, although this method can detect a complete disconnection or a short circuit of the cable assembly, it is difficult to accurately detect a failure state such as an intermediate short circuit or a semi-disconnection due to insulation failure or damage, and there are problems with the measurement accuracy.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a technique capable of highly accurately detecting damages such as an intermediate short circuit or a semi-disconnection in a power cable that supplies power to in-vehicle devices.

[0009] The vehicle power supply system according to the present invention supplies power from a battery to a plurality of loads mounted on a vehicle via a power cable connected to the plurality of loads, and comprises an oscillator that outputs an AC signal at a predetermined frequency, a superimulator that superimposes the AC signal on one end of the power cable, a detector that detects the voltage or current of the power cable when the AC signal is superimposed on the one end of the power cable via the superimulator, and a diagnostic unit that diagnoses whether or not an abnormality has occurred in the power cable based on the voltage or current detected by the detector. The diagnostic device according to the present invention diagnoses whether or not an abnormality has occurred in a power cable connected to a plurality of loads mounted on a vehicle, and acquires the voltage value or current value of the power cable when an AC signal at a predetermined frequency is superimposed on the one end of the power cable, and diagnoses whether or not an abnormality has occurred in the power cable based on the acquired voltage value or current value.

[0010] According to the present invention, damage such as intermediate short circuits and partial breaks in power cables that supply power to in-vehicle equipment can be detected with high precision.

[0011] Furthermore, issues, configurations, and effects other than those mentioned above will be clarified by the following description of the embodiments.

[0012] This figure shows an example configuration of a vehicle power supply system according to the first embodiment of the present invention. This figure shows the relationship between the oscillator frequency and the amplitude of the detected voltage in the first embodiment of the present invention. This figure illustrates a desirable frequency in the AC signal output by the oscillator. This figure shows how the frequency characteristics of the detected voltage change when the distance between the power cable and the body ground is partially changed. This figure shows an example configuration of a vehicle power supply system according to the second embodiment of the present invention. This figure shows the relationship between the oscillator frequency and the amplitude of the detected voltage in the second embodiment of the present invention. This figure shows an example configuration of a vehicle power supply system according to the third embodiment of the present invention. This figure shows the relationship between the oscillator frequency and the amplitude of the detected current in the third embodiment of the present invention. This figure illustrates a method for correcting the oscillator frequency in the fourth embodiment of the present invention. This flowchart shows the flow of the oscillator frequency correction process in the fourth embodiment of the present invention.

[0013] Embodiments of the present invention will now be described with reference to the drawings. In this specification and the drawings, identical components or components having substantially the same function are denoted by the same reference numeral, and redundant descriptions are omitted. Furthermore, if there are multiple components having the same or similar function, different subscripts (letters) may be used with the same reference numeral to describe them.

[0014] (First Embodiment) Figure 1 is a diagram showing an example of the configuration of a vehicle power supply system according to the first embodiment of the present invention. The vehicle power supply system 100 shown in Figure 1 is an example of a power supply system suitable for applying the present invention and is used when mounted on a vehicle. The vehicle power supply system 100 is composed of a battery 1, a power cable 2, a plurality of loads 3, a body ground 4, a capacitor 5, an oscillator 6, a resistor 7, a capacitor 8, an inductor 9, a diagnostic unit 10, and a relay 11.

[0015] Battery 1 is connected to load 3 via power cable 2 and supplies power to load 3. The positive terminal of battery 1 is connected to power cable 2, and the negative terminal of battery 1 is connected to body ground 4. Body ground 4 is a ground potential formed using the vehicle body, and the negative terminals of battery 1 and load 3 are connected to it in common. As battery 1, for example, an auxiliary battery mounted on a vehicle, such as a lead-acid battery or a lithium-ion battery, can be used.

[0016] Load 3 consists of various on-board equipment installed and used in the vehicle, which operates by receiving power from battery 1. For example, various auxiliary equipment in the vehicle, an ECU (Electronic Control Unit), actuators, and the power supply circuits that supply power to these components all fall under load 3 in the vehicle power supply system 100.

[0017] The power cable 2 is connected between the battery 1 and the load 3, and transmits the power supplied from the battery 1 to the load 3. In order to supply current to multiple loads 3, the size (allowable current) of the power cable 2 is determined to meet the current capacity when all loads 3 are driven simultaneously.

[0018] An oscillator 6, a resistor 7, and a capacitor 8 are connected to one end of the power cable 2 (point A in the figure). The oscillator 6 generates an AC signal at a predetermined frequency and outputs the AC signal to point A via the resistor 7 and capacitor 8. As a result, the capacitor 8 acts as a superimposer, and the AC signal from the oscillator 6 is superimposed on point A by the capacitor 8. The resistor 7 acts as a detector to detect the voltage of the power cable 2 when the AC signal is superimposed on point A via the capacitor 8 acting as a superimposer.

[0019] An inductor 9 is connected between point A and battery 1. A capacitor 5, acting as a terminator, is connected to the other end of the power cable 2 (point B in the diagram). The capacitor 8 connected to point A blocks DC current and allows AC current to pass through, while the inductor 9 connected to point A blocks AC current and allows DC current to pass through. Therefore, the injected voltage vi, injected into point A in response to the AC signal from oscillator 6, propagates from point A to the power cable 2 and reaches point B on the opposite side. Since the capacitor 5 acting as a terminator is connected to point B, point B is short-circuited in the high-frequency region. When the transmission path is short-circuited in this way, the high-frequency injected voltage vi is reflected at point B in opposite phase. This reflected voltage vr returns to point A through the power cable 2 and passes through capacitor 8. As a result, the resistor 7, acting as a detector, detects the combined voltage (detected voltage vo) of the injected voltage vi and the reflected voltage vr. Note that the termination impedance at both ends of the power cable 2 is different from the characteristic impedance of the power cable 2.

[0020] The detected voltage vo from the resistor 7 is input to the diagnostic unit 10. Based on the detected voltage vo input from the resistor 7, the diagnostic unit 10 diagnoses whether or not there is an abnormality in the power cable 2, and if it diagnoses that there is an abnormality in the power cable 2, it switches the relay 11 to the OFF position. The relay 11 is installed between the battery 1 and the power cable 2, and when switched to the OFF position by the diagnostic unit 10, it cuts off the power supply from the battery 1 to the load 3. This protects the battery 1 and the power cable 2 in the event of an abnormality in the power cable 2. The diagnostic unit 10 is configured using, for example, an ECU, and can perform processing related to the diagnosis of abnormalities in the power cable 2 based on the detected voltage vo.

[0021] In the configuration of the vehicle power supply system 100 shown in Figure 1, if a point in the power cable 2 (point C in the figure) is short-circuited to the body ground 4, the impedance at point C changes, and the injected voltage vi is reflected at point C instead of point B. As a result, the distance to the reflection point changes between when the power cable 2 is functioning normally (when the injected voltage vi is reflected at point B) and when the power cable 2 is short-circuited (when the injected voltage vi is reflected at point C). Consequently, the phase of the reflected voltage vr returning to point A changes, causing a change in the detected voltage vo, which is a combination of the injected voltage vi and the reflected voltage vr.

[0022] Figure 2 shows the relationship between the frequency of the oscillator 6 and the amplitude of the detected voltage vo in the first embodiment of the present invention. The solid curve in the figure represents the frequency characteristics of the detected voltage vo when the power cable 2 is functioning normally. In this case, since the detected voltage vo is a signal obtained by combining the injected voltage vi from the oscillator 6 and the reflected voltage vr, the amplitude of the detected voltage vo changes according to the phase difference between the injected voltage vi and the reflected voltage vr. That is, if the phases of the injected voltage vi and the reflected voltage vr at point A are in phase, the amplitude of the detected voltage vo increases, and conversely, if the phases of the injected voltage vi and the reflected voltage vr at point A are out of phase, the amplitude of the detected voltage vo decreases.

[0023] The phase difference between the injected voltage vi and the reflected voltage vr is determined by the frequency f of the oscillator 6 and the length x of the power cable 2 (length from point A to point B). In particular, in this embodiment, the smallest frequency f0 among the frequencies at which the amplitude of the detected voltage vo is minimized (hereinafter referred to as the "null point frequency") can be found by the following equation (1). In equation (1), c represents the propagation speed of the power cable 2, and x represents the length of the power cable 2. Note that each null point frequency in the power cable 2 is expressed as an integer multiple of the smallest null point frequency f0 obtained by equation (1). f0 = c / 2x ... (1)

[0024] The dotted curve in Figure 2 represents the frequency characteristics of the amplitude of the detected voltage vo when the power cable 2 is short-circuited to the body ground 4 at point C in Figure 1. When a short circuit occurs at point C, the reflection position of the injected voltage vi in ​​the power cable 2 changes from point B to point C, causing the frequency characteristics of the detected voltage vo to change from a solid line to a dotted line. In this case, it is equivalent to x in equation (1) becoming shorter in the power cable 2, so the values ​​of each null point frequency in the frequency characteristics after the short circuit are higher than before the short circuit.

[0025] In this embodiment, for a power cable 2 having the frequency characteristics described above, the frequency f of the oscillator 6 is set to the null point frequency, and the amplitude of the detected voltage vo is monitored by the diagnostic unit 10. In this state, if a short circuit occurs in the power cable 2, the amplitude of the detected voltage vo increases as the null point frequency changes (rises) as described above. Therefore, the diagnostic unit 10 stores the amplitude of the detected voltage vo at the null point frequency when the power cable 2 is normal as an initial value, and diagnoses that there is an abnormality in the power cable 2 when the amplitude of the detected voltage vo changes by a predetermined value or more from this initial value.

[0026] Figure 3 illustrates the desirable frequency for the AC signal output by the oscillator 6. In the power cable 2, as mentioned above, null points occur at integer multiples of the minimum null point frequency f0 (hereinafter also referred to as the "first null point frequency"). Of these multiple null point frequencies, the most desirable setting value for the frequency of the AC signal output by the oscillator 6 is the first null point frequency. The reason for this will be explained below with reference to Figure 3.

[0027] For example, if a short circuit occurs in the power cable 2 at its midpoint (length x / 2), the frequency characteristics of the detected voltage vo change from the solid line to the dotted line in Figure 3. Here, if the frequency of the AC signal output by the oscillator 6 is set to the first null point frequency, the amplitude of the detected voltage vo changes as shown in Figure 3 due to the short circuit in the power cable 2. On the other hand, if the frequency of the AC signal output by the oscillator 6 is set to the second null point frequency (frequency 2f0), which is the next smallest null point frequency after the first null point frequency, then when the power cable 2 is short-circuited, the first null point frequency at the time of the short circuit coincides with the second null point frequency under normal conditions, so there is no change in the amplitude of the detected voltage vo.

[0028] Furthermore, if a short circuit occurs at a location other than the midpoint of the power cable 2, the amplitude of the detected voltage vo will change in different ways depending on the location of the short circuit. Therefore, for other null point frequencies after the second null point frequency, these null point frequencies may overlap with one of the null point frequencies at the time of the short circuit, and in that case, even if the power cable 2 is short-circuited, there will be no change in the amplitude of the detected voltage vo.

[0029] As explained above, if the frequency of the AC signal output by oscillator 6 is set to the second null point frequency or a subsequent null point frequency, there will be points where a short circuit in the power cable 2 cannot be detected. On the other hand, if the frequency of the AC signal output by oscillator 6 is set to the normal first null point frequency, such a non-detection state will not occur. Therefore, it is possible to reliably diagnose whether or not there is an abnormality in the power cable 2 at a single frequency point.

[0030] Furthermore, the propagation speed c of the power cable 2 changes depending on the surrounding environment of the power cable 2. Figure 4 shows how the frequency characteristics of the detected voltage vo change when the distance between the power cable 2 and the body ground 4 is partially changed. As shown in Figure 4(a), when the entire area of ​​the power cable 2 is routed close to the body ground 4, each null point frequency from the second null point frequency onward occurs at integer multiples of the first null point frequency. On the other hand, as shown in Figure 4(b), when half of the power cable 2 is routed overhead, the first null point frequency does not change much compared to Figure 4(a), but each null point frequency from the second null point frequency onward changes significantly. Therefore, considering that the distance between the power cable 2 and the body ground 4 can vary in various ways when the vehicle power supply system 100 is mounted on a vehicle, it is desirable to set the frequency of the oscillator 6 to the first null point frequency which occurs stably regardless of the routing state (layout environment) of the power cable 2.

[0031] As described above, in the vehicle power supply system 100 of this embodiment, the frequency of the AC signal output by the oscillator 6 is set to the null point frequency, more preferably the first null point frequency, at which the amplitude of the detected voltage vo is minimized when the power cable 2 is in a normal state without damage. The diagnostic unit 10 then monitors the amplitude of the detected voltage vo, and diagnoses that an abnormality has occurred in the power cable 2 when the amplitude of the detected voltage vo changes from the initial value to a predetermined value or more. This makes it possible to detect damage such as an intermediate short circuit or partial break in the power cable 2 with high accuracy.

[0032] According to the first embodiment of the present invention described above, the following effects are achieved.

[0033] (1) The vehicle power supply system 100 is a system that supplies power from a battery 1 to a plurality of loads 3 mounted on a vehicle via a power cable 2 connected to the loads 3. The vehicle power supply system 100 includes an oscillator 6 that outputs an AC signal at a predetermined frequency, a capacitor 8 as a superimposer that superimposes the AC signal on point A, which is one end of the power cable 2, a resistor 7 as a detector that detects the voltage of the power cable 2 when the AC signal is superimposed on point A of the power cable 2 via the capacitor 8, and a diagnostic unit 10 that diagnoses whether or not there is an abnormality in the power cable 2 based on the voltage vo detected by the resistor 7. With this configuration, damage such as intermediate short circuits and partial breaks in the power cable 2 that supplies power to the loads 3, which are onboard equipment, can be detected with high accuracy.

[0034] (2) The oscillator 6 outputs an AC signal at the null point frequency, which is the frequency at which the detected voltage vo detected by the resistor 7 becomes the minimum value when the power cable 2 is normal. The diagnostic unit 10 diagnoses that there is an abnormality in the power cable 2 when the amplitude of the detected voltage vo detected by the resistor 7 changes from the initial value to a predetermined value or more. In this way, a short circuit occurring at any point in the power cable 2 can be reliably detected.

[0035] (3) Preferably, the oscillator 6 outputs an AC signal at the first null point frequency, which is the lowest of the multiple null point frequencies. In this way, a short circuit occurring at any point in the power cable 2 can be reliably detected regardless of the wiring condition of the power cable 2.

[0036] (4) In the vehicle power supply system 100, the superimposed element is a capacitor 8 and the detector is a resistor 7. An inductor 9 is connected to point A of the power cable 2, and a capacitor 5 is connected to point B, which is the other end of the power cable 2. In this configuration, the resistor 7, which is the detector, detects the voltage of the power cable 2, and the diagnostic unit 10 diagnoses whether or not there is an abnormality in the power cable 2 based on the detected voltage vo by the resistor 7. In this way, an injection voltage vi corresponding to the AC signal from the oscillator 6 is injected into the power cable 2, generating a reflected voltage vr with a phase difference corresponding to the short circuit location, and a detected voltage vo is obtained by combining the injection voltage vi and the reflected voltage vr. Therefore, it is possible to accurately diagnose whether or not there is an abnormality in the power cable 2 from the amplitude of the detected voltage vo.

[0037] (Second Embodiment) Figure 5 is a diagram showing an example of the configuration of a vehicle power supply system according to the second embodiment of the present invention. The vehicle power supply system 100A shown in Figure 5 is an example of a power supply system suitable for applying the present invention, and is used mounted on a vehicle, similar to the vehicle power supply system 100 described in the first embodiment. In the first embodiment, a vehicle power supply system 100 was described in which a capacitor 5 as a terminator is connected to point B of the power cable 2, but in the vehicle power supply system 100A of this embodiment, an inductor 12 as a terminator is connected to point B instead of the capacitor 5.

[0038] In this embodiment, the inductors 9 and 12 connected to points A and B respectively block the AC current and allow the DC current to pass through. Therefore, the injected voltage vi, injected into point A in response to the AC signal from the oscillator 6, propagates from point A to the power cable 2 and reaches point B on the opposite side, similar to the first embodiment. Since the inductor 12 is connected to point B as a terminator, point B becomes an open termination in the high-frequency region. When the transmission path is terminated in this open manner, the injected voltage vi, which is a high-frequency voltage, is reflected at point B in phase. This reflected voltage vr returns to point A through the power cable 2 and passes through the capacitor 8. As a result, similar to the first embodiment, the resistor 7 acting as a detector detects a voltage (detected voltage vo) which is a combination of the injected voltage vi and the reflected voltage vr.

[0039] The voltage vo detected by the resistor 7 is input to the diagnostic unit 10. Similar to the first embodiment, the diagnostic unit 10 diagnoses whether or not there is an abnormality in the power cable 2 based on the voltage vo detected from the resistor 7, and if it diagnoses that there is an abnormality in the power cable 2, it switches the relay 11 to the OFF position.

[0040] In the configuration of the vehicle power supply system 100A shown in Figure 5, if a point in the middle of the power cable 2 (point C in the figure) is short-circuited to the body ground 4, the impedance at point C changes, and the injected voltage vi is reflected at point C instead of point B. As a result, similar to the first embodiment, the distance to the reflection point changes depending on whether the power cable 2 is normal (when the injected voltage vi is reflected at point B) or when the power cable 2 is short-circuited (when the injected voltage vi is reflected at point C). Consequently, the phase of the reflected voltage vr returning to point A changes, causing a change in the detected voltage vo, which is a combination of the injected voltage vi and the reflected voltage vr.

[0041] Figure 6 shows the relationship between the frequency of the oscillator 6 and the amplitude of the detected voltage vo in the second embodiment of the present invention. The solid curve in the figure represents the frequency characteristics of the detected voltage vo when the power cable 2 is functioning normally. In this case, since the detected voltage vo is a signal obtained by combining the injected voltage vi from the oscillator 6 and the reflected voltage vr, the amplitude of the detected voltage vo changes according to the phase difference between the injected voltage vi and the reflected voltage vr. That is, as in the case of Figure 2 described in the first embodiment, if the phases of the injected voltage vi and the reflected voltage vr at point A are in phase, the amplitude of the detected voltage vo increases, and conversely, if the phases of the injected voltage vi and the reflected voltage vr at point A are out of phase, the amplitude of the detected voltage vo decreases.

[0042] The phase difference between the injected voltage vi and the reflected voltage vr is determined by the frequency f of the oscillator 6 and the length x of the power cable 2 (length from point A to point B). In particular, in this embodiment, the smallest null point frequency f0, i.e., the first null point frequency, which is the null point frequency at which the amplitude of the detected voltage vo is minimized, can be found by the following equation (2). In equation (2), as in equation (1) above, c represents the propagation speed of the power cable 2 and x represents the length of the power cable 2. f0 = c / 4x ... (2)

[0043] The dotted curve in Figure 6 represents the frequency characteristics of the amplitude of the detected voltage vo when the power cable 2 is short-circuited to the body ground 4 at point C in Figure 5. When a short circuit occurs at point C, the reflection position of the injected voltage vi in ​​the power cable 2 changes from point B to point C, causing the frequency characteristics of the detected voltage vo to change from a solid line to a dotted line. In this case, it is equivalent to x in equation (2) becoming shorter in the power cable 2, and furthermore, the termination changes from open to short. Therefore, similar to Figure 2 explained in the first embodiment, the values ​​of each null point frequency in the frequency characteristics after the short circuit are higher than before the short circuit.

[0044] In this embodiment, for the power cable 2 having the above frequency characteristics, the frequency f of the oscillator 6 is set to the null point frequency, and the diagnostic unit 10 monitors the amplitude of the detected voltage vo. In this state, when a short circuit occurs in the power cable 2, the null point frequency changes (increases) as described above, so that the amplitude of the detected voltage vo increases. Therefore, the diagnostic unit 10 stores in advance, as an initial value, the amplitude of the detected voltage vo at the null point frequency when the power cable 2 is normal, and diagnoses that an abnormality has occurred in the power cable 2 when the amplitude of the detected voltage vo changes from this initial value by a predetermined value or more.

[0045] In this embodiment, each null point frequency occurring in the power cable 2 is represented by an odd multiple (2n + 1 times) of the first null point frequency obtained by the formula (2). Among these plural null point frequencies, the most desirable as the set value of the frequency of the AC signal output from the oscillator 6 is the first null point frequency. The reason is that, as shown in FIG. 3 in the first embodiment, by setting the frequency of the AC signal output from the oscillator 6 to the first null point frequency in the normal state, it is possible to avoid the occurrence of a point where a short circuit in the middle of the power cable 2 cannot be detected, and as shown in FIG. 4 in the first embodiment, it is possible to reduce the influence due to the wiring state (laying environment) of the power cable 2.

[0046] As described above, the vehicle power supply system 100A of this embodiment shows a configuration in which the inductor 12 is used as the terminator of the power cable 2. Thereby, as shown in FIG. 6, an effect is obtained in which the difference in the detected voltage vo between the normal state and the short circuit (ground fault) state becomes clearer at the first null point frequency. Therefore, the detection accuracy for the short circuit of the power cable 2 can be further improved.

[0047] (Third Embodiment) FIG. 7 is a diagram showing a configuration example of a vehicle power supply system according to the third embodiment of the present invention. The vehicle power supply system 100B shown in FIG. 7 is an example of a power supply system suitable for applying the present invention, and is mounted on a vehicle and used in the same manner as the vehicle power supply systems 100 and 100A described in the first and second embodiments respectively. In the first and second embodiments, the injection voltage vi, which is a high-frequency voltage corresponding to the AC signal output from the oscillator 6, is injected into the power cable 2 from point A of the power cable 2 through the capacitor 8 as a superimposer. However, in the vehicle power supply system 100B of the present embodiment, by using the inductor 13 as a superimposer instead of the capacitor 8, a high-frequency current corresponding to the AC signal output from the oscillator 6 is injected into the power cable 2.

[0048] The vehicle power supply system 100B shown in FIG. 7 includes a battery 1, a power cable 2, a plurality of loads 3, a body ground 4, a capacitor 5, an oscillator 6, a diagnostic unit 10B, a relay 11, an inductor 13, a current sensor 14, and a capacitor 15. Note that the battery 1, the power cable 2, the load 3, the body ground 4, the capacitor 5, the oscillator 6, and the relay 11 are the same as those of the vehicle power supply systems 100 and 100A described in the first and second embodiments respectively.

[0049] An oscillator 6, an inductor 13, and a current sensor 14 are connected to one end side (point A in the figure) of the power cable 2. The oscillator 6 generates an AC signal at a predetermined frequency and outputs the AC signal to point A through the inductor 13. As a result, the inductor 13 acts as a superimposer, and the AC signal from the oscillator 6 is superimposed on point A by the inductor 13. The current sensor 14 acts as a detector that detects the current of the power cable 2 when an AC signal is superimposed on point A through the inductor 13 as a superimposer.

[0050] A capacitor 15 is connected between point A and battery 1. Additionally, a capacitor 5, acting as a terminator, is connected to the other end of power cable 2 (point B in the diagram). When the AC signal from oscillator 6 is superimposed on point A by inductor 13, a high-frequency current, injection current ii, is generated in the current flowing from battery 1 to power cable 2. This injection current ii propagates from point A to power cable 2 and reaches point B on the opposite side. Because capacitor 5, acting as a terminator, is connected to point B, point B becomes a short-circuit termination in the high-frequency region. When the transmission path is short-circuited in this way, the high-frequency injection current ii is reflected at point B. This reflected current ir returns to point A through power cable 2. As a result, the current sensor 14, acting as a detector, detects a current (detected current io) which is a combination of the injection current ii and the reflected current ir.

[0051] The current io detected by the current sensor 14 is input to the diagnostic unit 10B. Based on the current io detected from the current sensor 14, the diagnostic unit 10B diagnoses whether or not there is an abnormality in the power cable 2. If it diagnoses that there is an abnormality in the power cable 2, it switches the relay 11 to the OFF position, similar to the first and second embodiments. This protects the battery 1 and the power cable 2 in the event of an abnormality in the power cable 2. The diagnostic unit 10B is configured, for example, using an ECU, similar to the diagnostic unit 10 described in the first embodiment, and can perform processing related to the diagnosis of abnormalities in the power cable 2 based on the detected current io.

[0052] In the configuration of the vehicle power supply system 100B shown in Figure 7, if a point in the middle of the power cable 2 (point C in the figure) is short-circuited to the body ground 4, the impedance at point C changes, and the injected current ii is reflected at point C instead of point B. As a result, the distance to the reflection point changes between when the power cable 2 is normal (when the injected current ii is reflected at point B) and when the power cable 2 is short-circuited (when the injected current ii is reflected at point C). Consequently, the phase of the reflected current ir returning to point A changes, causing a change in the detected current io, which is the sum of the injected current ii and the reflected current ir.

[0053] Figure 8 shows the relationship between the frequency of the oscillator 6 and the amplitude of the detected current io in the third embodiment of the present invention. The solid curve in the figure represents the frequency characteristics of the detected current io when the power cable 2 is functioning normally. In this case, since the detected current io is a signal that is a combination of the injected current ii and the reflected current ir from the oscillator 6, the amplitude of the detected current io changes according to the phase difference between the injected current ii and the reflected current ir. That is, as with Figures 2 and 6 described in the first and second embodiments, respectively, if the phases of the injected current ii and the reflected current ir at point A are in phase, the amplitude of the detected current io increases, and conversely, if the phases of the injected current ii and the reflected current ir at point A are out of phase, the amplitude of the detected current io decreases.

[0054] The phase difference between the injected current ii and the reflected current ir is determined by the frequency f of the oscillator 6 and the length x of the power cable 2 (length from point A to point B). In particular, the minimum frequency f0 of the null point frequencies at which the amplitude of the detected current io is maximum in this embodiment can be found by the following equation (3). In equation (3), as in equations (1) and (2) above, c represents the propagation speed of the power cable 2 and x represents the length of the power cable 2. f0 = c / 2x ... (3)

[0055] The dotted curve in Figure 8 represents the frequency characteristics of the amplitude of the detected current io when the power cable 2 is short-circuited to the body ground 4 at point C in Figure 7. When a short circuit occurs at point C, the reflection position of the injected current ii in the power cable 2 changes from point B to point C, causing the frequency characteristics of the detected current io to change from a solid line to a dotted line. In this case, it is equivalent to the x in equation (3) becoming shorter in the power cable 2, so, as with Figure 2 explained in the first embodiment and Figure 6 explained in the second embodiment, the values ​​of each null point frequency in the frequency characteristics after the short circuit are higher than before the short circuit.

[0056] In this embodiment, for a power cable 2 having the frequency characteristics described above, the frequency f of the oscillator 6 is set to the null point frequency, and the amplitude of the detected current io is monitored by the diagnostic unit 10B. In this state, if a short circuit occurs in the power cable 2, the amplitude of the detected current io decreases as the null point frequency changes (increases) as described above. Therefore, the diagnostic unit 10B stores the amplitude of the detected current io at the null point frequency when the power cable 2 is normal as an initial value, and diagnoses that there is an abnormality in the power cable 2 when the amplitude of the detected current io changes by a predetermined value or more from this initial value.

[0057] In this embodiment, each null point frequency occurring in the power cable 2 is expressed as an integer multiple of the minimum null point frequency f0 obtained by equation (3). Of these multiple null point frequencies, the most desirable setting value for the frequency of the AC signal output by the oscillator 6 is the first null point frequency, as in the first and second embodiments. The reason for this is that, as shown in Figure 3 in the first embodiment, by setting the frequency of the AC signal output by the oscillator 6 to the normal first null point frequency, it is possible to avoid the occurrence of points in the power cable 2 where a short circuit cannot be detected, and, as shown in Figure 4 in the first embodiment, it is possible to reduce the influence of the wiring condition (layout environment) of the power cable 2.

[0058] As described above, in the vehicle power supply system 100B of this embodiment, the inductor 13 is used as a superimposing device to inject an injection current ii, which is a high-frequency current, into point A of the power cable 2. At this time, the current flowing through the power cable 2 is detected by the current sensor 14, and based on the detected current io obtained, the diagnostic unit 10B diagnoses whether or not there is an abnormality in the power cable 2. As a result, unlike the voltage superimposing method described in the first and second embodiments, it is not necessary to provide an inductor 9 in the power line between the battery 1 and the power cable 2, and the inductance component of the power line can be reduced. Therefore, fluctuations in the power supply voltage due to sudden changes in current, etc., are suppressed, and the power supply voltage can be stabilized.

[0059] (Fourth Embodiment) Next, a vehicle power supply system according to the fourth embodiment of the present invention will be described. The vehicle power supply system of this embodiment is an example of a power supply system suitable for applying the present invention, and can be realized with the same configuration as any of the vehicle power supply systems 100, 100A, and 100B described in the first to third embodiments, respectively. In the following, the vehicle power supply system of this embodiment will be described using the configuration of the vehicle power supply system 100 shown in Figure 1, which was described in the first embodiment, but it is also possible to apply the configurations of other embodiments.

[0060] In the first to third embodiments, the frequency of the oscillator 6 is fixed and set to a predetermined frequency, for example, the first null point frequency. However, since the null point frequency can fluctuate depending on environmental conditions, a discrepancy may occur between the frequency set in the oscillator 6 and the null point frequency. Therefore, in this embodiment, the frequency of the oscillator 6 is made up to track the null point frequency, so that even if the frequency of the oscillator 6 deviates from the null point frequency during operation of the vehicle power supply system, a short circuit in the power cable 2 can be detected with high accuracy.

[0061] Figure 9 illustrates a method for correcting the frequency of the oscillator 6 in a fourth embodiment of the present invention. When the initial setting value of the oscillator 6's frequency is the aforementioned first null point frequency (frequency f0), first, a predetermined fluctuation value Δf is added to this initial setting frequency f0 to change the frequency of the AC signal output by the oscillator 6. If, at this changed frequency, the amplitude of the detected voltage vo by the resistor 7 decreases compared to the amplitude at the initial setting frequency f0, the frequency of the AC signal output by the oscillator 6 is updated with the changed frequency. Then, the updated frequency is used as the setting value fs for the oscillator 6's frequency thereafter.

[0062] On the other hand, if, at the frequency after the above-mentioned fluctuation, the amplitude of the voltage vo detected by the resistor 7 increases compared to the amplitude at the initial setting frequency f0, the frequency of the AC signal output by the oscillator 6 is then changed by subtracting the fluctuation value Δf from the initial setting frequency f0. If, at this newly changed frequency, the amplitude of the voltage vo detected by the resistor 7 decreases compared to the amplitude at the initial setting frequency f0, the frequency of the AC signal output by the oscillator 6 is updated according to the newly changed frequency. The updated frequency is then used as the setting value fs for the frequency of the oscillator 6 thereafter.

[0063] In the example shown in Figure 9, when the fluctuation value Δf is added to the initial frequency f0, the amplitude of the detected voltage vo increases compared to the amplitude at the initial frequency f0. On the other hand, when the fluctuation value Δf is added to the initial frequency f0, the amplitude of the detected voltage vo decreases compared to the amplitude at the initial frequency f0. Therefore, the set value fs of the oscillator 6 frequency is updated to f0 - Δf.

[0064] In addition, in both cases—when the fluctuation value Δf is added to the initial setting frequency f0, and when the fluctuation value Δf is subtracted from the initial setting frequency f0—if the amplitude of the voltage vo detected by the resistor 7 increases compared to the amplitude at the initial setting frequency f0, it is preferable not to update the frequency of the AC signal output by the oscillator 6, keeping it at the original initial setting frequency f0.

[0065] Figure 10 is a flowchart showing the flow of the frequency correction process for the oscillator 6 in the fourth embodiment of the present invention. The correction process shown in this flowchart is performed, for example, at predetermined intervals in the diagnostic unit 10.

[0066] In step S10, the oscillator 6 outputs an AC signal at the current frequency setting value fs. This AC signal is superimposed at point A by the capacitor 8 and propagates through the power cable 2 as an injected voltage vi. When the correction process in Figure 10 is performed for the first time, the oscillator 6 outputs an AC signal with the initial setting frequency (e.g., the first null point frequency) f0 as the current frequency setting value fs.

[0067] In step S20, the value of the detected voltage vo when the AC signal was output in step S10 is obtained from the resistor 7.

[0068] In step S30, the oscillator 6 outputs an AC signal at a frequency fs + Δf, which is obtained by adding a predetermined variation value Δf to the current frequency setting value fs from which the AC signal was output in step S10. This causes the frequency of the AC signal output from the oscillator 6 to vary.

[0069] In step S40, the value of the detected voltage vo when the AC signal was output in step S30 is obtained from the resistor 7. This allows obtaining the value of the detected voltage vo when the frequency of the AC signal output from the oscillator 6 is varied.

[0070] In step S50, the value of the detected voltage vo at the frequency before the change, obtained in step S20, is compared with the value of the detected voltage vo at the frequency after the change, obtained in step S40, to determine whether the amplitude of the detected voltage vo has decreased by changing the frequency of the AC signal upwards. If the amplitude of the detected voltage vo has decreased due to the frequency change, that is, if the value of the detected voltage vo obtained in step S40 is smaller than the value of the detected voltage vo obtained in step S20, the process proceeds to step S60; otherwise, the process proceeds to step S70.

[0071] In step S60, the frequency of the AC signal output from the oscillator 6 is updated to the frequency fs + Δf set in step S30. This corrects the frequency of the oscillator 6 so that, in subsequent abnormality diagnosis of the power cable 2, the oscillator 6 outputs an AC signal with frequency fs + Δf. After the process in step S60 is completed, the frequency correction process shown in the flowchart of Figure 10 is terminated.

[0072] In step S70, the oscillator 6 outputs an AC signal at a frequency fs-Δf, which is obtained by subtracting a predetermined variation value Δf from the current frequency setting value fs from which the AC signal was output in step S10. This causes the frequency of the AC signal output from the oscillator 6 to vary.

[0073] In step S80, the value of the detected voltage vo when the AC signal was output in step S70 is obtained from the resistor 7. This allows obtaining the value of the detected voltage vo when the frequency of the AC signal output from the oscillator 6 is varied.

[0074] In step S90, the value of the detected voltage vo at the frequency before the change, obtained in step S20, is compared with the value of the detected voltage vo at the frequency after the change, obtained in step S80, to determine whether the amplitude of the detected voltage vo has decreased by changing the frequency of the AC signal downwards. If the amplitude of the detected voltage vo decreases due to the frequency change, that is, if the value of the detected voltage vo obtained in step S80 is smaller than the value of the detected voltage vo obtained in step S20, the process proceeds to step S100. On the other hand, if the amplitude of the detected voltage vo does not decrease due to the frequency change, the frequency correction process shown in the flowchart of Figure 10 is terminated. In this case, the frequency of the AC signal output by the oscillator 6 is not updated.

[0075] In step S100, the frequency of the AC signal output from the oscillator 6 is updated to the frequency fs-Δf set in step S70. This corrects the frequency of the oscillator 6 so that, in subsequent abnormality diagnosis of the power cable 2, the oscillator 6 outputs an AC signal with frequency fs-Δf. After the process in step S100 is completed, the frequency correction process shown in the flowchart of Figure 10 is terminated.

[0076] In the vehicle power supply system of this embodiment, by periodically performing the frequency correction process described above, the frequency of the oscillator 6 can be corrected so that it matches the null point frequency even if the null point frequency and the frequency of the oscillator 6 are out of sync. Therefore, false detection due to fluctuations in the null point frequency can be prevented.

[0077] In the above, an example was described in which the frequency of the oscillator 6 is corrected based on the detected voltage vo when the injected voltage vi is superimposed, similar to the first and second embodiments. However, as in the third embodiment, it is also possible to obtain the detected current io when the injected current ii is superimposed and correct the frequency of the oscillator 6 based on this. In this case, in steps S20, S40, and S80 of Figure 10, the value of the detected current io should be obtained from the current sensor 14 instead of the detected voltage vo. Also, in steps S50 and S90 of Figure 10, it is determined whether the amplitude of the detected current io has increased by changing the frequency of the AC signal. If the amplitude of the detected current io has increased due to the frequency change, that is, if the value of the detected current io obtained in step S40 or step S80 is greater than the value of the detected current io obtained in step S20, the process proceeds to step S60 or step S100 to update the frequency of the AC signal output by the oscillator 6.

[0078] According to the embodiments of the present invention described above, damage such as an intermediate short circuit or partial break in the power cable 2 can be detected with high accuracy. Furthermore, by continuously outputting an AC signal from the oscillator 6 and superimposing it on point A, it is possible to immediately detect any abnormality in the power cable 2 while continuing to supply power from the battery 1 to the load 3 via the power cable 2. Moreover, regardless of the wiring condition (layout environment) of the power cable 2, any abnormality in the power cable 2 can be reliably detected. As a result, it is possible to detect abnormalities before the power cable 2 completely fails and take measures such as switching to power supply from an alternative route, thereby increasing the reliability of power supply to the load 3 mounted on the vehicle. Therefore, for example, a suitable vehicle power supply system can be realized in a zone-distribution type power network.

[0079] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0080] 1...Battery 2...Power cable 3...Load 4...Body ground 5...Capacitor 6...Oscillator 7...Resistor 8...Capacitor 9...Inductor 10, 10B...Diagnostic unit 11...Relay 12...Inductor 13...Inductor 14...Current sensor 15...Capacitor 100, 100A, 100B...Vehicle power supply system

Claims

1. A vehicle power supply system that supplies power from a battery to a plurality of loads mounted on a vehicle via power cables connected to the plurality of loads, comprising: an oscillator that outputs an AC signal at a predetermined frequency; a superimposing device that superimposes the AC signal on one end of the power cable; a detector that detects the voltage or current of the power cable when the AC signal is superimposed on the one end of the power cable via the superimposing device; and a diagnostic unit that diagnoses whether or not an abnormality has occurred in the power cable based on the voltage or current detected by the detector.

2. A vehicle power supply system according to claim 1, wherein the oscillator outputs the AC signal at the null point frequency, with the null point frequency being the frequency at which the voltage detected by the detector is at its minimum or the current is at its maximum when the power cable is functioning normally, and the diagnostic unit diagnoses that there is an abnormality in the power cable when the amplitude of the voltage or current detected by the detector changes from an initial value to a predetermined value or more.

3. A vehicle power supply system according to claim 2, wherein the oscillator outputs the AC signal at a first null point frequency which has the lowest frequency among a plurality of null point frequencies.

4. A vehicle power supply system according to claim 1, wherein the superimposed element is a capacitor, the detector is a resistor, an inductor is connected to one end of the power cable, a capacitor or inductor is connected to the other end of the power cable, the detector detects the voltage of the power cable, and the diagnostic unit diagnoses whether or not there is an abnormality in the power cable based on the voltage detected by the detector.

5. A vehicle power supply system according to claim 1, wherein the superimposed element is an inductor, the detector is a current sensor, capacitors are connected to one end and the other end of the power cable, the detector detects the current of the power cable, and the diagnostic unit diagnoses whether or not there is an abnormality in the power cable based on the current detected by the detector.

6. A vehicle power supply system according to claim 1, wherein the oscillator is capable of varying the frequency of the AC signal, and the frequency of the AC signal output by the oscillator is updated when the amplitude of the voltage or current when the oscillator outputs the AC signal at the varied frequency is smaller than the amplitude of the voltage at the frequency before variation, or larger than the amplitude of the current at the frequency before variation.

7. A diagnostic device for diagnosing whether or not there is an abnormality in a power cable connected to multiple loads mounted on a vehicle, the device which acquires the voltage value or current value of the power cable when an AC signal of a predetermined frequency is superimposed on one end of the power cable, and diagnoses whether or not there is an abnormality in the power cable based on the acquired voltage value or current value.

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