Deterioration diagnosis method for electronic control device, deterioration diagnosis program for electronic control device, and deterioration diagnosis device for electronic control device

Abstract

To provide a deterioration diagnosis method for electronic controller, a deterioration diagnosis program for electronic controller, and a deterioration diagnosis device for electronic controller that do not depend upon heating conditions, a cooling start temperature, a refrigerant temperature, etc., and are flexible and easy.SOLUTION: The present invention relates to a deterioration diagnosis method for an electronic controller 1 comprising a semiconductor element 17 for electric power and a substrate 13 supporting the semiconductor element for electric power, and the deterioration diagnosis method includes the steps of: acquiring a cooling curve based upon a detection result of a temperature sensor 43 provided to the semiconductor element for electric power or the substrate during operation of the semiconductor element for electric power; acquiring a differential curve obtained by differentiating the cooling curve with time; approximating the differential curve to an exponential function within a predetermined time range to acquire a corresponding exponent; and performing diagnosis based upon whether the acquired exponent is larger / smaller than a predetermined reference value.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a degradation diagnosis method for an electronic control device, a degradation diagnosis program for an electronic control device, and a degradation diagnosis device for an electronic control device, and in particular to a degradation diagnosis method for an electronic control device equipped with a power semiconductor element, and a degradation diagnosis device for such an electronic control device. [Background technology]

[0002] BACKGROUND ART A method for predicting the remaining life of an electronic control device including an electronic control device having a power semiconductor element and a wiring board electrically connected to the power semiconductor element is known (for example, Patent Document 1).

[0003] The power semiconductor element in Patent Document 1 is fixed to a wiring board via a die attach material. Inside the wiring board, a heat-generating / thermal device is built in, which has a heat-generating layer that generates heat when a voltage is applied and a heat-sensitive layer that can measure the temperature.

[0004] A short pulse of electricity is applied to the heat-generating layer of the heat-generating thermosensitive device to heat it instantaneously, then it is allowed to cool. The heating and cooling processes are recorded as temperature change behavior (heat dissipation curve) using the heat-sensitive layer of the heat-generating thermosensitive device. If a crack due to fatigue fracture occurs inside the die attach material and a location of increased thermal resistance appears in the heat dissipation path from the heat-generating thermosensitive device, a change occurs in the heat dissipation curve. This allows for early detection of fatigue fracture-induced cracks inside the die attach material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-253971 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, electric vehicles have been attracting attention from the perspective of reducing CO2 emissions and improving energy efficiency in order to realize a low-carbon or carbon-free society. An electric vehicle is equipped with a battery, a motor, and a power control unit. The power control unit (electronic control device) includes an inverter that converts direct current supplied from the battery into alternating current for driving the motor. The inverter is equipped with power semiconductors (power semiconductor elements) that function as switching elements.

[0007] Therefore, it is conceivable to diagnose the deterioration of a power control unit mounted on an electric vehicle according to the method described in Patent Document 1. However, the method described in Patent Document 1 requires control of the heat dissipation start temperature. Also, if a heating element is installed inside the wiring board, the structure of the wiring board becomes complex. Therefore, the method described in Patent Document 1 cannot be used to diagnose the deterioration of widely used electronic control devices in which power semiconductor elements are supported on a wiring board.

[0008] In view of the above background, an object of the present invention is to provide a versatile and easy-to-use method and program for diagnosing deterioration of an electronic control device, and a degradation diagnosis device for an electronic control device, which are independent of heating conditions, cooling start temperature, refrigerant temperature, etc. This will ultimately contribute to improving the convenience and safety of electric vehicles and improving their energy efficiency. [Means for solving the problem]

[0009] In order to solve the above problem, one aspect of the present invention is a degradation diagnosis method for an electronic control device (1) equipped with a power semiconductor element (17) and a substrate (13) supporting the power semiconductor element, the method comprising the steps of: acquiring a cooling curve based on a detection result of a temperature sensor (43) provided on the power semiconductor element or the substrate during operation of the power semiconductor element; acquiring a differential curve obtained by differentiating the cooling curve with respect to time; approximating the differential curve to an exponential function over a predetermined time range to acquire a corresponding index (b); and performing a diagnosis based on the magnitude of the acquired index and a predetermined reference value.

[0010] According to this aspect, by approximating the differential curve to an exponential function within a predetermined range, an index highly relevant to the deterioration of the electronic control device can be obtained, thereby providing a versatile and easy method for diagnosing the deterioration of an electronic control device that is not dependent on heating conditions, cooling start temperature, refrigerant temperature, etc.

[0011] In the above aspect, preferably, the power semiconductor element constitutes a part of a power control unit that controls power to the on-board motor (5), and starts acquiring the cooling curve when the on-board motor stops.

[0012] According to this aspect, the influence of the on-board motor on the detection result of the temperature sensor can be reduced.

[0013] In the above aspect, it is preferable that the deterioration is determined when the acquired index is smaller than the reference value.

[0014] According to this aspect, it is possible to easily determine whether or not there is deterioration.

[0015] In the above aspect, preferably, deterioration prediction is performed by comparing the time rate of change of the index with a predetermined threshold value.

[0016] According to this aspect, by using the time change rate of the index, it is possible to determine whether or not the deterioration is accelerating, and therefore it is possible to perform deterioration prediction well and simply.

[0017] In order to solve the above-mentioned problems, one aspect of the present invention is a degradation diagnosis program for an electronic control device (1) having a power semiconductor element (17) and a substrate (13) supporting the power semiconductor element, the program including the steps of: acquiring a cooling curve based on a detection result of a temperature sensor (43) provided on the power semiconductor element or the substrate during operation of the power semiconductor element; acquiring a differential curve obtained by differentiating the cooling curve with respect to time; approximating the differential curve to an exponential function over a predetermined time range to acquire a corresponding index (b); and performing a diagnosis based on the magnitude of the acquired index and a predetermined reference value.

[0018] According to this aspect, by approximating the differential curve to an exponential function within a predetermined range, an index highly relevant to the deterioration of the electronic control device can be obtained, thereby providing a versatile and easy method for diagnosing the deterioration of an electronic control device that is not dependent on heating conditions, cooling start temperature, refrigerant temperature, etc.

[0019] In the above aspect, preferably, the power semiconductor device constitutes part of a power control unit that controls power to an on-board motor, and starts acquiring the cooling curve when the on-board motor stops.

[0020] According to this aspect, it is possible to reduce the influence of temperature changes of the in-vehicle motor on the detection results of the temperature sensor.

[0021] In the above aspect, it is preferable that the deterioration is determined when the acquired index is smaller than the reference value.

[0022] According to this aspect, it is possible to easily determine whether or not there is deterioration.

[0023] In order to solve the above problem, one aspect of the present invention is a degradation diagnosis device (1) for an electronic control device having a power semiconductor element (17) and a substrate (13) electrically connected to the power semiconductor element, the device including a temperature sensor (43) provided on the power semiconductor element or the substrate, and a processor that performs degradation diagnosis based on the detection result of the temperature sensor, wherein the processor, during operation of the power semiconductor element, obtains a cooling curve based on the detection result of the temperature sensor, obtains a differential curve by differentiating the cooling curve with time, approximates the differential curve to an exponential function over a predetermined time range, obtains a corresponding index (b), and performs diagnosis based on the magnitude of the obtained index and a predetermined reference value.

[0024] According to this aspect, by approximating the differential curve to an exponential function within a predetermined range, an index highly relevant to the deterioration of the electronic control device can be obtained, thereby providing a versatile and easy method for diagnosing the deterioration of an electronic control device that is not dependent on thermal conditions, cooling start temperature, refrigerant temperature, etc.

[0025] In the above aspect, preferably, the power semiconductor element forms part of a power control unit that controls power to an on-board motor, and the processor starts acquiring the cooling curve when the on-board motor stops.

[0026] According to this aspect, it is possible to reduce the influence of temperature changes of the in-vehicle motor on the detection results of the temperature sensor.

[0027] In the above aspect, it is preferable that the deterioration is determined when the acquired index is smaller than the reference value.

[0028] According to this aspect, it is possible to easily determine whether or not there is deterioration. [Effects of the Invention]

[0029] According to the above configuration, it is possible to provide a degradation diagnosis method for an electronic control device, a degradation diagnosis program for an electronic control device, and a degradation diagnosis device for an electronic control device that can easily diagnose degradation of power semiconductor elements. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a block diagram of an electronic control device diagnosed by a degradation diagnosis method according to an embodiment, and a degradation diagnosis device; [Figure 2] Schematic diagram showing part of an electronic control device [Figure 3] Deterioration diagnosis process flowchart [Figure 4] Example graph showing cooling curves for three electronic control devices with different degrees of degradation [Figure 5] Flowchart showing a specific range acquisition method [Figure 6] Graph showing an example cooling curve for a test device [Figure 7] Graph for explaining a specific range obtained using the cooling curve of FIG. 6 [Figure 8] Graph showing cooling curves obtained when the cooling start temperatures are different for the three electronic control devices with different degrees of deterioration shown in Figure 4. [Figure 9] 9 is a graph showing a differential curve obtained by differentiating the cooling curve shown in FIG. 8 and a straight line approximating the differential curve. [Figure 10] Graph showing cooling curves obtained by changing the cooling start temperature and refrigerant temperature in the power control unit used to measure curves 1 to 3 in FIG. [Figure 11] Graph showing the differential curve of the cooling curve of Figure 9 [Figure 12] This graph shows the rate of change in the index b obtained in a power cycle test when conditions such as heating time, cooling start temperature, and refrigerant temperature are fixed (dashed line) and when the conditions are randomly changed (solid line). [Figure 13]A graph showing the relationship between the refrigerant temperature and the index fluctuation rate obtained using a specific range (black circles) and the relationship between the refrigerant temperature and the index fluctuation rate obtained by exponentially approximating the entire measurement time (white circles). [Figure 14] A graph showing the relationship between (cooling start temperature - refrigerant temperature) and the index fluctuation rate obtained using a specific range (black circles), and the relationship between (cooling start temperature - refrigerant temperature) and the index fluctuation rate obtained by exponentially approximating the entire measurement time (white circles). DETAILED DESCRIPTION OF THE INVENTION

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a method for diagnosing a deterioration of an electronic control device, a program for diagnosing a deterioration of an electronic control device, and a device for diagnosing a deterioration of an electronic control device according to the present invention will be described with reference to the drawings.

[0032] In the following, an example will be described in which the deterioration diagnosis method for an electronic control device is used to perform deterioration diagnosis on a power control unit 1, which is an electronic control device.

[0033] The power control unit 1 is mounted on an electric vehicle and controls the power of an on-board motor 5 driven by a battery 3. As shown in FIG. 1 , the power control unit 1 includes an inverter 7 that converts direct current from the battery 3 mounted on the electric vehicle into alternating current for driving the on-board motor 5, a gate driver 9 that controls the driving of the inverter 7, and a controller 11 that sets the driving conditions of the gate driver 9 according to the accelerator opening degree, etc. In this embodiment, the deterioration diagnosis method for an electronic control device is used particularly to perform deterioration diagnosis of the inverter 7.

[0034] 2 is a schematic diagram showing a part of the inverter 7. The inverter 7 includes a substrate 13 and a semiconductor chip 15 (power semiconductor chip).

[0035] Substrate 13 is an insulating substrate made of an insulator (insulator) that has high thermal conductivity and high voltage resistance. Substrate 13 may be, for example, a thick copper insulating substrate made of ceramics or aluminum nitride. One surface (hereinafter referred to as the upper surface) of substrate 13 is provided with a plurality of electrodes (not shown).

[0036] The semiconductor chip 15 is provided with a plurality of semiconductor elements 17. The semiconductor elements 17 are semiconductors for controlling and converting power to the in-vehicle motor 5, and are so-called power devices (semiconductor elements for power). The semiconductor elements 17 may be, for example, bipolar transistors or power MOSFETs (metal-oxide semiconductor field-effect transistors).

[0037] The semiconductor chip 15 is bonded to the upper surface of the substrate 13 by a bonding material. As a result, the semiconductor elements 17 provided on the semiconductor chip 15 are each supported by the substrate 13 made of an insulator.

[0038] The bonding material is made of solder, a metal sintered material, etc. In this embodiment, the semiconductor element 17 and the substrate 13 are bonded by solder, and a solder layer 19 is provided between the semiconductor chip 15 and the substrate 13.

[0039] The semiconductor chip 15 is connected to electrodes provided on the substrate 13 via bonding wires (not shown). The electrodes on the substrate 13 are connected to a wiring pattern provided on the substrate 13 and electrical wiring separate from the substrate 13. A voltage is applied to the semiconductor element 17 via the wiring pattern or electrical wiring, and the semiconductor element 17 functions as a switching element for configuring the inverter 7.

[0040] The other surface (hereinafter referred to as the bottom surface) of the substrate 13 is bonded to the heat sink 21 by a bonding material. The bonding material may be solder, a metal sintered material, or the like. In this embodiment, the substrate 13 and the heat sink 21 are bonded by solder, and a solder layer 23 is provided between the substrate 13 and the heat sink 21.

[0041] The heat sink 21 is connected to the cooler 27 via a heat transfer layer 25 made of a thermal interface material. The thermal interface material is a substance that fills small gaps and irregularities between the heat sink 21 and the cooler 27 and efficiently conducts heat from the heat sink 21 to the cooler 27. The heat transfer layer 25 may be made of, for example, a highly thermally conductive pad, paste, grease, or the like.

[0042] Cooler 27 is preferably a metal member, and has a flow path 31 formed therein for circulating coolant 29. Coolant 29 may be, for example, cooling water. However, without being limited to this embodiment, cooler 27 may be, for example, a heat sink 21 equipped with fins, or may be equipped with a fan.

[0043] It is known that the solder layer 19 between the semiconductor chip 15 and the substrate 13, and the solder layer 23 between the substrate 13 and the heat sink 21, are subject to deterioration due to cracks (fissures or crevices) caused by various factors such as thermal cycles. The deterioration diagnosis method for an electronic control device according to this embodiment is used particularly to diagnose the presence or absence of deterioration in these solder layers 19, 23. However, this is merely one example, and the deterioration diagnosis method for an electronic control device according to the present invention can be applied to the deterioration diagnosis of electronic control devices that include various power semiconductor elements.

[0044] Next, a description will be given of a deterioration diagnosis device 41 for an electronic control device for implementing the deterioration diagnosis method for an electronic control device. The deterioration diagnosis device 41 is a device that performs deterioration diagnosis of the power control unit 1, specifically, deterioration diagnosis of the solder layers 19, 23 of the inverter 7, by implementing the deterioration diagnosis method for an electronic control device. As shown in Fig. 1, the deterioration diagnosis device 41 includes a temperature sensor 43 and a diagnosis device main body 45 that performs deterioration diagnosis based on the detection result of the temperature sensor 43.

[0045] The temperature sensor 43 is a sensor that detects temperature, and in this embodiment is configured as a temperature measuring diode. However, the temperature sensor 43 is not limited to this form and may be configured as, for example, a resistance temperature detector or a thermistor whose resistance value changes with temperature. Alternatively, a calibration curve of the resistance value of the semiconductor chip 15 and the temperature may be created and the temperature may be detected from the resistance value of the semiconductor chip 15.

[0046] 2, the temperature sensor 43 is provided on the back surface of the semiconductor chip 15. Therefore, the temperature detected by the temperature sensor 43 is approximately equal to the temperature of the semiconductor chip 15. However, this is not limiting, and the temperature sensor 43 may be provided on, for example, the top surface or bottom surface of the substrate 13, or on the top surface of the semiconductor chip 15. Alternatively, the temperature sensor 43 may be provided inside the substrate 13. In this embodiment, the temperature sensor 43 is formed on the back surface of the semiconductor chip 15 and is fixed to the top surface of the substrate 13 via the solder layer 19 between the semiconductor chip 15 and the substrate 13.

[0047] In this embodiment, the semiconductor chip 15, the temperature sensor 43, the substrate 13, and the heat sink 21 are integrally sealed with a molding resin to form a semiconductor package 47.

[0048] 1, diagnostic device main body 45 is configured by a computer including a processor 51 (central processing unit, CPU), memory 53 such as RAM (random access memory) or ROM (read only memory), and storage device 55 such as SSD (solid state drive) or HDD (hard disk drive). Diagnostic device main body 45 may be connected to, for example, a car navigation system 56 equipped with a monitor 56A inside the vehicle.

[0049] The diagnostic device main body 45 (specifically, the storage device 55 of the diagnostic device main body 45) stores a specific range W. The specific range W is defined by a start time t s and the end time t corresponding to the elapsed time from the start of the measurement e (See also FIG. 7.) The specific range W is stored in the storage device 55, for example, when the automobile is manufactured.

[0050] The diagnostic device main body 45 is connected to the controller 11 of the power control unit 1. The controller 11 of the power control unit 1 controls the inverter 7 via the gate driver 9, thereby controlling the driving of the on-board motor 5. The processor 51 of the diagnostic device main body 45 receives from the controller 11 a signal indicating that the on-board motor 5 has stopped driving from a driving state.

[0051] When the processor 51 receives a signal from the controller 11 indicating that the on-board motor 5 has stopped driving, the processor 51 executes a deterioration diagnosis program for the electronic control device. By executing the deterioration diagnosis program, the processor 51 performs the deterioration diagnosis process shown in the flowchart of FIG. 3, and implements a deterioration diagnosis method for the electronic control device. In this way, the processor 51 diagnoses whether or not the electronic control device has deteriorated (specifically, whether or not the solder layers 19, 23 provided on the inverter 7 of the power control unit 1 have deteriorated). The deterioration diagnosis process will be described in detail below with reference to FIG. 3.

[0052] In the first step ST1 of the deterioration diagnosis process, the processor 51 measures the time t max The detection result of the temperature sensor 43 is acquired every acquisition time Δt until the time Δt has elapsed.

[0053] At this time, the data acquired by the processor 51 is the time when the drive is stopped, which is set to time t=0, and is obtained from time t=0 to t max The data corresponds to the change over time of the temperature T acquired by the temperature sensor 43 from time t=0 to time t=0 (see, for example, FIG. 4). In this embodiment, the temperature sensor 43 acquires the temperature T of the semiconductor element 17 (device). Therefore, the data acquired by the processor 51 corresponds to the change over time of the temperature T acquired by the temperature sensor 43 from time t=0 to time t=0. max This corresponds to data (hereinafter referred to as a cooling curve) showing the change in temperature T of the semiconductor element 17 (device) over time up to the measurement time t max The acquisition time Δt may be on the order of several seconds, and the acquisition time Δt may be on the order of 10 μsec. max After the time has elapsed, the acquisition of the detection result is stopped and step ST2 is executed.

[0054] In step ST2, the processor 51 numerically differentiates the cooling curve and inverts the sign to obtain a differential curve (-dT(t) / dt). The differential curve corresponds to a curve that indicates the magnitude of the slope of the cooling curve. The method by which the processor 51 numerically differentiates the cooling curve may be based on a known method, such as numerical differentiation by approximation, such as forward difference or central difference. Once the differential curve has been obtained, the processor 51 executes step ST3.

[0055] In step ST3, the processor 51 obtains a specific range W stored in advance from the storage device 55, and approximates the differential curve to an exponential function in the specific range W to obtain the corresponding exponent b.

[0056] The exponent b here is the coefficient of time t when the temperature T(t) is expressed by the following equation (1), and corresponds to the reciprocal (b=1 / B) of the time constant B (also called the relaxation time).

[0057]

number

[0058] In equation (1), A and C are predetermined constants.

[0059] In this embodiment, the processor 51 first performs a logarithmic transformation (log e (-dT / dt)) to obtain the logarithmic transformation curve Y, where e is the base of the natural logarithm.

[0060] Next, processor 51 performs regression analysis on logarithmic transformation curve Y. Specifically, processor 51 assumes that logarithmic transformation curve Y can be expressed as a straight line within a specific range W, that is, by the approximation formula Y=-bt+b0, and obtains exponent b by a known method. Once the acquisition of exponent b is complete, processor 51 executes step ST4.

[0061] In step ST4, the processor 51 performs a deterioration determination based on the index b. In this embodiment, when the index b is equal to or greater than a predetermined abnormality determination reference value b0, the processor 51 determines that the electronic control device is not deteriorated, and when the index b is smaller than the abnormality determination reference value b0, the processor 51 determines that the electronic control device is deteriorated. When the deterioration determination is completed, the processor 51 ends the deterioration diagnosis process.

[0062] When processor 51 determines that the electronic control device has deteriorated, processor 51 may display the fact that the electronic control device has deteriorated on monitor 56A of car navigation system 56. When diagnostic device main body 45 is connectable to a mobile terminal (such as a smartphone) of the vehicle owner via a network, for example, diagnostic device main body 45 may notify the vehicle owner via the mobile terminal that the electronic control device has deteriorated.

[0063] Next, a description will be given of a method for acquiring the specific range W stored in the storage device 55 (hereinafter referred to as the specific range acquisition method). The specific range acquisition method is implemented by executing a specific range acquisition process using a test device that tests a power control unit (hereinafter referred to as the test device) having the same specifications (structure) as the power control unit 1 that is the target of evaluation in degradation diagnosis.

[0064] The test device may execute the specific range acquisition process, for example, at the design stage of the power control unit 1. The test device may also execute the specific range acquisition process for a test device that has completed initial degradation (a product that has completed 10,000 power cycle tests).

[0065] The test device has a temperature sensor that measures the temperature of a semiconductor chip provided in the test device, a processor that analyzes the detection result of the temperature sensor, and a display device such as a monitor that displays the results analyzed by the processor. The test device may have the same configuration as the degradation diagnosis device (diagnosis device main body 45 and temperature sensor 43 that measures the temperature of the test device). Furthermore, when performing the specific range acquisition method, it is assumed that a coolant 29 at a constant temperature is supplied to the power control unit 1, and the coolant temperature (hereinafter referred to as the coolant temperature) is set to a predetermined value (hereinafter referred to as the test coolant temperature).

[0066] The specific range acquisition process will be described in detail below with reference to FIG.

[0067] In the first step ST11 of the specific range acquisition method, the test apparatus heats the semiconductor chip included in the test device, stops the heating, and waits a predetermined time (hereinafter, test measurement time t max The temperature T'(t) of the semiconductor chip is acquired until the test measurement time t max ´ is the measurement time t max It may be the same as or different from.

[0068] At this time, the data acquired by the test device is, as shown in FIG. 6, the time when heating is stopped being set as time t=0, and the data is collected from time t=0 to t max The test equipment corresponds to the data showing the time change of the temperature T'(t) until the test measurement time t max When the time ' has elapsed, the temperature acquisition is stopped and step ST12 is executed.

[0069] In step ST12, the test device calculates a difference temperature ΔT'(t) by subtracting the test refrigerant temperature from the temperature T'(t), and then calculates 1 / e (e is the base of the natural logarithm) of the difference temperature ΔT'(t) at time t = 0.

[0070] The test device then obtains the time when the differential temperature ΔT'(t) becomes 1 / e of the value of the differential temperature at t=0 (i.e., the time when the temperature T'(t) becomes lower than (cooling start temperature - refrigerant temperature) / e + refrigerant temperature, where the cooling start temperature is the temperature when heating is stopped) as the provisional time constant τ (see Figure 6).The test device then sets a time period of a predetermined width that includes the provisional time constant τ as the specific range W.

[0071] In this embodiment, the test device calculates the differential value (-dT'(t) / dt) of the temperature T'(t) and plots it on a semi-logarithmic graph (see FIG. 7). Then, the test device selects a specific range W that includes the tentative time constant τ and has a contribution ratio (R2) of approximately 0.99 over as wide a range as possible. The contribution ratio R2 here is the logarithm (log e Assuming that (-dT'(t) / dt)) can be expressed as a straight line within a specific range W, R2 is the quantity that indicates the degree of deviation between the logarithm of the differential value of temperature T'(t) and that line, and is also called the R-squared value or coefficient of determination. Alternatively, the test device may change the specific range W by receiving input from the operator conducting the test. However, when changing the specific range W, it is important to consider that widening the range will decrease R2, and narrowing the range will decrease the opposite.

[0072] When the setting of the specific range W is completed, the test device displays the specific range W on the display device, and the specific range acquisition process is completed.

[0073] The specific range W may be stored in the storage device 55 by an operator who performs testing using a test device, or an operator who assembles or maintains an automobile, or the like, who performs input work as appropriate.

[0074] Next, the effects of the degradation diagnostic method and degradation diagnostic device 41 configured as described above will be described with reference to the drawings.

[0075] Figure 4 shows an example of a cooling curve, plotting time t on the horizontal axis and temperature T on the vertical axis.

[0076] The faster the rate at which heat dissipates from the semiconductor chip 15 to the cooler 27, the faster the temperature of the semiconductor chip 15 cools. If cracks (fissures or fissures) occur in the solder layers 19 and 23, it becomes more difficult for heat to dissipate from the semiconductor chip 15 to the cooler 27, and the cooling of the semiconductor chip 15 slows down. For example, it can be seen that compared to curve 1 shown in FIG. 4, curves 2 and 3 show that the cooling of the semiconductor chip 15 is slower and heat dissipation is more difficult. In this way, by evaluating the cooling rate, it is possible to determine whether the solder layers 19 and 23 have deteriorated.

[0077] However, the cooling start temperature (the temperature of the semiconductor chip 15 when cooling starts) and the coolant temperature can change depending on the vehicle's driving conditions and driving environment, so they cannot be generally compared.

[0078] Figure 8 shows cooling curves obtained by changing the cooling start temperature and refrigerant temperature in the power control unit 1 corresponding to curves 1 to 3 in Figure 4. It is difficult to determine the cooling rate, or the state of deterioration, from this graph.

[0079] Therefore, after extensive research, the inventors discovered that when the cooling curve is differentiated with time and plotted on a semi-logarithmic graph with the y-axis (temperature) as the target (see FIG. 9), there is a section within a predetermined specific range W where the slope remains constant even when the cooling start temperature or refrigerant temperature changes. In other words, the inventors discovered that the value obtained by differentiating the cooling curve with time can be approximated by an exponential function within the specific range W, and when plotted on a semi-logarithmic graph, the slope remains constant even when the cooling start temperature or refrigerant temperature changes. For example, as shown in FIG. 9, the slopes of curves 1, 2, and 3 become steeper in this order, making it easier to determine the state of deterioration.

[0080] Fig. 10 shows cooling curves obtained by changing the cooling start temperature and the refrigerant temperature in the power control unit 1 used to measure the curves 1 to 3 shown in Fig. 4, Fig. 8, and Fig. 9. Fig. 11 shows differential curves obtained by differentiating the cooling curves shown in Fig. 10.

[0081] Table 1 below shows the results of obtaining the slope (index b) for each of the curves shown in FIG.

[0082] [Table 1]

[0083] From Table 1, it can be seen that even if the cooling start temperature or refrigerant temperature changes, index b remains almost constant, and if the degree of deterioration is the same, index b will be the same.

[0084] However, the cooling curve of the semiconductor element 17 mounted on the power control unit 1 is theoretically expressed by the following equation (2).

[0085]

number

[0086] In equation (2), C, Ai, and bi (i = 1 to N) are each predetermined constants that do not depend on time t, and N is a predetermined positive integer equal to or greater than 1. Since equation (2) does not become an exponential function when differentiated, it contradicts the result that the slope is constant when plotted on a semi-logarithmic graph (see Figure 6).

[0087] Equation (2) can also be expressed as equation (3).

[0088]

number

[0089] The inventors of the present application have found that a certain term in formula (2) (or formula (3)), for example, the nth term -A n exp(-b n The inventors considered that there exists a specific range W in which the term t becomes dominant and can be approximated as a constant with almost no change in other terms. In other words, the inventors considered that within the specific range W, formula (3) can be approximated by the following formula (4).

[0090]

number

[0091] Based on this consideration, the values ​​of index b obtained in a power cycle test are shown in Figure 12, where the heating time, cooling start temperature, and refrigerant temperature are constant (dashed line) and where they are randomly changed (solid line). Figure 12 shows that the deterioration diagnosis method of the present invention can detect the deterioration state of the power control unit 1 from the value of index b, even if the heating time, cooling start temperature, and refrigerant temperature are changed.

[0092] The relationship between the refrigerant temperature and the rate of change of index b is shown by black circles in Figure 13, and the relationship between the (cooling start temperature - refrigerant temperature) and the rate of change of index b is shown by black circles in Figure 14. For comparison, the value of index b when the entire cooling curve is assumed to be an exponential function without using this method is also shown by white circles.

[0093] It can be seen from Figure 13 that the deterioration diagnosis method of the present invention makes it possible to obtain index b, which represents deterioration, without being affected by the cooling start temperature or refrigerant temperature. That is, from the black and white circles in Figures 13 and 14, it can be seen that if the value of index b is calculated from the entire cooling curve without using the deterioration diagnosis method of the present invention, the value is greatly affected by the cooling start temperature and refrigerant temperature. Therefore, it can be seen that a method of calculation from the entire cooling curve without using the deterioration diagnosis method of the present invention cannot be used for deterioration diagnosis.

[0094] In this way, the present invention provides a versatile and easy deterioration diagnosis method for the power control unit 1, which is independent of heating conditions, cooling start temperature, refrigerant temperature, etc. This increases the convenience and safety of electric vehicles, and the present invention is expected to contribute to improving energy efficiency.

[0095] In step ST4, when the index b is smaller than the abnormality determination reference value b0, the processor 51 determines that the electronic control device is deteriorated. In this way, since the deterioration determination can be performed by comparing the index b with the abnormality determination reference value b0, it is possible to easily determine whether or not the electronic control device is deteriorated.

[0096] When processor 51 receives a signal indicating that on-board motor 5 has stopped driving, it executes a deterioration diagnosis process and starts acquiring a cooling curve. This configuration makes it possible to reduce the influence of on-board motor 5 on the detection results of temperature sensor 43 (for example, the influence of electromagnetic noise caused by driving on-board motor 5) compared to when acquisition of a cooling curve is started while on-board motor 5 is driving.

[0097] As a modified embodiment, the processor 51 may store the index b in the storage device 55 together with the time when the deterioration diagnosis process was performed in step ST4, and may perform deterioration prediction by evaluating the change over time of the index b already stored in the storage device 55. For deterioration prediction, for example, the amount of change in the index b per unit time, i.e., the time change rate of the index b, may be used as a value indicating the change over time of the index b.

[0098] In order to obtain the time rate of change of the index b, for example, in step ST4, the processor 51 first obtains from the storage device 55 the time s when the deterioration diagnosis process was last executed. a and the index b(s a ) is obtained. Then, the processor 51 obtains the exponent b(s a ) and the newly obtained exponent b(s b ) and the absolute value of the difference Δb = |b(s b )-b(s a Furthermore, the processor 51 calculates the time s at which the previous degradation diagnosis process was performed. a From the time s when step ST1 was executed b The elapsed time Δs (=s b -s b ), and calculate the absolute value Δb of the difference between the indexes b divided by the elapsed time Δs (Δb / Δs), and obtain the calculated value as the time rate of change of the index b. The processor 51 may determine that the index is approaching a deteriorated state when the time rate of change of the index b is equal to or greater than a predetermined threshold.

[0099] Although the description of the specific embodiment has been completed above, the present invention is not limited to the above embodiment and can be widely modified and implemented.

[0100] In the above embodiment, in step ST4 of the degradation diagnosis processing, processor 51 performs logarithmic transformation with base e on the differential curve and performs regression analysis to obtain index b, but this is not limited to this. In step ST4 of the degradation diagnosis processing, processor 51 may perform logarithmic transformation with base 10 on the differential curve and perform regression analysis to obtain index b.

[0101] In the above embodiment, the processor 51 determines in step ST4 that the electronic control device has deteriorated when the index b is smaller than the abnormality determination reference value b0, but this is not limited to this. The processor 51 may obtain the reciprocal of b (1 / b, also referred to as time constant B) in step ST3, and determine that the electronic control device (power control unit 1) has deteriorated when the time constant B is larger than the abnormality determination reference value B0.

[0102] In the above embodiment, in step ST3, the processor 51 may assume that the differential curve is represented by the sum of multiple exponential functions and may acquire the exponent b corresponding to each exponential function by fitting the differential curve based on a known method. In this case, in step ST4, the processor 51 may determine degradation based on the relationship between the smallest exponent b (or the largest time constant B) and the abnormality determination reference value b0. Specifically, the processor 51 may determine that the electronic control device (power control unit 1) has deteriorated when the smallest exponent b becomes smaller than the abnormality determination reference value b0 (or the largest time constant B becomes larger than the abnormality determination reference value B0). A smaller exponent b (larger time constant B) indicates that heat is less likely to escape. Therefore, by using the smallest exponent b (largest time constant B), it is possible to effectively identify degradation in a location where heat is less likely to escape due to a crack.

[0103] Furthermore, each time processor 51 performs degradation diagnosis processing based on the differential curve acquired in ST2, processor 51 may set specific range W so that it includes the time when the initial value of the differential curve becomes 1 / e (e is the base of the natural logarithm) (for example, a range of a predetermined time width centered on that time).

[0104] In the above embodiment, a known analog circuit such as a differentiation circuit or a logarithmic conversion circuit may be used instead of the processor 51, or a combination of a known analog circuit and a known digital circuit may be used. [Explanation of symbols]

[0105] 1: Power control unit (electronic control device) 5: In-vehicle motor 13: Substrate 17: Semiconductor elements (power semiconductor elements) 41: Deterioration diagnosis device 43: Temperature sensor b: index

Claims

1. A degradation diagnosis method for an electronic control device including a power semiconductor device and a substrate supporting the power semiconductor device, comprising: obtaining a cooling curve based on a detection result of a temperature sensor provided on the power semiconductor device or the substrate during operation of the power semiconductor device; obtaining a differential curve by differentiating the cooling curve with respect to time; fitting the differential curve to an exponential function over a predetermined time range to obtain a corresponding exponent; A deterioration diagnosis method for an electronic control device, comprising the step of making a diagnosis based on whether the acquired index is larger or smaller than a predetermined reference value.

2. the power semiconductor device constitutes a part of a power control unit that controls power to an on-vehicle motor, 2. The deterioration diagnosis method for an electronic control device according to claim 1, wherein acquisition of the cooling curve is started when the on-board motor is stopped.

3. 3. The deterioration diagnosis method for an electronic control device according to claim 1, wherein the electronic control device is judged to be deteriorated when the acquired index is smaller than the reference value.

4. 4. The deterioration diagnosis method for an electronic control device according to claim 1, wherein deterioration is predicted by comparing the time rate of change of the index with a predetermined threshold value.

5. 1. A degradation diagnosis program for an electronic control device including a power semiconductor device and a substrate supporting the power semiconductor device, obtaining a cooling curve based on a detection result of a temperature sensor provided on the power semiconductor device or the substrate during operation of the power semiconductor device; obtaining a differential curve by differentiating the cooling curve with respect to time; fitting the differential curve to an exponential function over a predetermined time range to obtain a corresponding exponent; A deterioration diagnosis program for an electronic control device, comprising a step of making a diagnosis based on whether the acquired index is larger or smaller than a predetermined reference value.

6. the power semiconductor device constitutes a part of a power control unit that controls power to an on-vehicle motor, 6. The deterioration diagnosis program for an electronic control device according to claim 5, wherein acquisition of the cooling curve starts when the on-board motor stops.

7. 7. The deterioration diagnosis program for an electronic control device according to claim 5, wherein it is determined that the electronic control device has deteriorated when the acquired index is smaller than the reference value.

8. A degradation diagnosis device for an electronic control device including a power semiconductor element and a substrate electrically connected to the power semiconductor element, a temperature sensor provided on the power semiconductor element or the substrate, and a processor that performs a deterioration diagnosis based on a detection result of the temperature sensor; The processor: obtaining a cooling curve based on the detection result of the temperature sensor during operation of the power semiconductor device; A differential curve is obtained by differentiating the cooling curve with respect to time; Fitting the differential curve to an exponential function over a predetermined time range to obtain a corresponding exponent; A deterioration diagnosis device for an electronic control device that performs diagnosis based on whether the acquired index is larger or smaller than a predetermined reference value.

9. the power semiconductor device constitutes a part of a power control unit that controls power to an on-vehicle motor, 9. The deterioration diagnosis device for an electronic control device according to claim 8, wherein the processor starts acquiring the cooling curve when the on-board motor stops.

10. 10. The deterioration diagnosis device for an electronic control device according to claim 8, wherein the deterioration is determined to occur when the acquired index is smaller than the reference value.

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