Deterioration diagnosis method, device, and non-transitory computer-readable storage medium

Abstract

The present invention relates to a deterioration diagnosis method, apparatus, and non-transitory computer-readable storage medium. A deterioration diagnosis method for an electronic control unit (1) including a power semiconductor device (17) and a circuit board (13) that supports the power semiconductor device includes the steps of: acquiring a cooling curve based on a detection result of a temperature sensor (43) provided on the power semiconductor device or the circuit board during operation of the power semiconductor device; obtaining a differential curve by time-differentiating the cooling curve; approximating the differential curve as an exponential function over a predetermined time range to obtain a corresponding exponent (b); and diagnosing the electronic control unit by comparing the obtained exponent with a predetermined reference value.

Description

Technical Field

[0001] The present invention relates to a method, apparatus, and non-transitory computer-readable storage medium for diagnosing the degradation of electronic units, particularly electronic units including power semiconductor devices. Background Technology

[0002] Methods for predicting the time before failure of electronic control devices, such as electronic control units comprising power semiconductor devices and circuit boards electrically connected to the power semiconductor devices, are known in the art (see, for example, JP2011-253971A).

[0003] The power semiconductor device disclosed in JP2011-253971A is fixed to a circuit board via a die-attachment material. The circuit board incorporates a heat-generating thermistor, which has a heat-generating layer that heats up when a voltage is applied thereto and a temperature-measuring thermistor layer.

[0004] By applying short electrical pulses to the heating layer of the thermistor, the heating layer is heated for a very short period of time, and then cooled. The history of this heating and cooling process is obtained from the temperature history (heat dissipation profile) of the thermistor layer. If cracks occur in the die-attached material due to fatigue fracture, resulting in a region of increased heat resistance in the heat dissipation path from the thermistor, the heat dissipation profile changes. Therefore, cracks in the die-attached material due to fatigue fracture can be detected at an early stage.

[0005] In recent years, electric vehicles have gained attention as part of efforts to achieve a low-carbon or decarbonized society due to their reduced CO2 emissions and improved energy efficiency. Electric vehicles consist of a battery, an electric motor, and an electronic control unit (ECU). The ECU contains an inverter that converts the direct current supplied by the battery into alternating current (AC) to drive the electric motor. The inverter is equipped with power semiconductors (power semiconductor devices) used as switching elements.

[0006] The method disclosed in JP2011-253971A can be used to detect degradation of power control units installed in electric vehicles. However, according to the method disclosed in JP2011-253971A, the initial temperature needs to be controlled when obtaining the heat dissipation profile. Furthermore, the circuit board structure becomes unnecessarily complex because heating elements need to be incorporated into the circuit board. Therefore, the method disclosed in JP2011-253971A cannot be used for degradation diagnosis of electronic control units, where ordinary power semiconductor devices are simply mounted on the circuit board. Summary of the Invention

[0007] In view of these problems in the prior art, the main objective of the present invention is to provide a method, apparatus and non-transitory computer-readable storage medium for diagnosing the degradation of electronic units, which is widely applicable and easy to implement without requiring precise control of heating conditions and the initial temperature of the cooling process.

[0008] This invention also aims to improve the convenience and safety of electric vehicles, and to improve energy efficiency.

[0009] To achieve this objective, one aspect of the present invention provides a degradation diagnosis method for an electronic control unit (power control unit 1), the electronic control unit including a power semiconductor device 17 and a circuit board 13 supporting the power semiconductor device, the degradation diagnosis method comprising the steps of: obtaining a cooling curve based on the detection results of a temperature sensor 43 disposed on the power semiconductor device or the circuit board during operation of the power semiconductor device; obtaining a differential curve by time differentiation of the cooling curve; approximating the differential curve as an exponential function within a predetermined time range to obtain a corresponding exponent b; and diagnosing the electronic control unit by comparing the obtained exponent with a predetermined reference value.

[0010] By approximating the differential curve as an exponential function within a predetermined time range, an exponent accurately representing the degradation of the electronic control unit (ECU) can be obtained, without considering heating conditions, the initial temperature of the cooling process, and the cooling temperature. Therefore, the method of this invention is applicable to a wide range of ECUs without requiring precise control of heating conditions, cooling device characteristics, and initial temperature. Consequently, the method of this invention is widely applicable and easy to implement.

[0011] Preferably, in this degradation diagnosis method, the electronic control unit is configured to control the power supplied to the vehicle electric motor 5, and to initiate the step of acquiring a cooling profile when the vehicle electric motor is turned off.

[0012] This minimizes the impact of the vehicle's electric motor's operating status on the temperature sensor's detection results.

[0013] Preferably, in this degradation diagnosis method, degradation is determined to have occurred when the obtained index is less than the reference value.

[0014] Therefore, it is easy to determine whether there is any degradation.

[0015] Preferably, in this degradation diagnosis method, degradation prediction is performed by comparing the time rate of change of the index with a predetermined threshold.

[0016] Therefore, by using the time rate of change of the exponent, it can be determined whether degradation is accelerating, thus enabling reliable and easy degradation prediction.

[0017] To achieve this objective, another aspect of the present invention provides a non-transitory computer-readable storage medium storing a degradation diagnostic program for an electronic control unit (power control unit 1), the electronic control unit including a power semiconductor device 17 and a circuit board 13 supporting the power semiconductor device, the degradation diagnostic program including the following steps: obtaining a cooling curve based on the detection results of a temperature sensor 43 disposed on the power semiconductor device or the circuit board during operation of the power semiconductor device; obtaining a differential curve by time differentiation of the cooling curve; approximating the differential curve as an exponential function within a predetermined time range to obtain a corresponding exponent b; and diagnosing the electronic control unit by comparing the obtained exponent with a predetermined reference value.

[0018] By approximating the differential curve as an exponential function within a predetermined time range, an exponent accurately representing the degradation of the electronic control unit can be obtained. This allows the program of the present invention to be applied to a wide range of electronic control units without considering heating conditions, the starting temperature of the cooling process, or the characteristics of the cooling device, without requiring any intensive calculations. Therefore, the program of the present invention is widely applicable and easy to implement.

[0019] Preferably, in the non-transitory computer-readable storage medium, the electronic control unit is configured to control the power supplied to the on-board electric motor 5 and to begin acquiring the cooling profile when the on-board electric motor is turned off.

[0020] This minimizes the impact of the vehicle's electric motor's operating status on the temperature sensor's detection results.

[0021] Preferably, in the non-transitory computer-readable storage medium, when the obtained index is less than the reference value, it is determined that degradation has occurred.

[0022] Therefore, it is easy to determine whether there is any degradation.

[0023] To achieve this objective, another aspect of the present invention provides a degradation diagnostic apparatus for an electronic control unit (power control unit 1), the electronic control unit including a power semiconductor device 17 and a circuit board 13 supporting the power semiconductor device, the degradation diagnostic apparatus including: a temperature sensor 43 disposed on the power semiconductor device or the circuit board; and a processor configured to perform degradation diagnosis based on the detection result of the temperature sensor, wherein the processor is configured to: acquire a cooling curve based on the detection result of the temperature sensor 43 during operation of the power semiconductor device; obtain a differential curve by time differentiation of the cooling curve; approximate the differential curve as an exponential function within a predetermined time range to obtain a corresponding exponent b; and diagnose the electronic control unit by comparing the obtained exponent with a predetermined reference value.

[0024] By approximating the differential curve as an exponential function within a predetermined time range, an exponent accurately representing the degradation of the electronic control unit can be obtained. This allows the device of the present invention to be applied to a wide range of electronic control units without considering heating conditions, the starting temperature of the cooling process, or the characteristics of the cooling device, without requiring any intensive calculations. Therefore, the device of the present invention is widely applicable and easy to implement.

[0025] Preferably, in this degradation diagnostic device, the electronic control unit is a power control unit that controls the power supplied to the vehicle electric motor 5, and acquires the cooling curve when the vehicle electric motor is turned off.

[0026] This minimizes the impact of the vehicle's electric motor's operating status on the temperature sensor's detection results.

[0027] Preferably, in this degradation diagnostic device, degradation is determined to have occurred when the obtained index is less than the reference value.

[0028] Therefore, it is easy to determine whether there is any degradation.

[0029] Therefore, the present invention provides a method, apparatus and non-transitory computer-readable storage medium for diagnosing the degradation of electronic units, which are widely applicable and easy to implement without requiring precise control of heating conditions and the initial temperature of the cooling process. Attached Figure Description

[0030] Figure 1 This is a block diagram of a degradation diagnostic device according to an embodiment of the present invention and an electronic control unit to be diagnosed by the degradation diagnostic device.

[0031] Figure 2 This is a cross-sectional view of the electronic control unit to be diagnosed.

[0032] Figure 3 This is a flowchart of the degradation diagnosis process according to an embodiment of the present invention.

[0033] Figure 4 This is a graph showing the cooling curves of three electronic control units that have deteriorated to different degrees.

[0034] Figure 5 This is a flowchart illustrating the process of obtaining a predetermined time range.

[0035] Figure 6 This is an example of a cooling curve.

[0036] Figure 7 It shows from Figure 6 The cooling curve is a graph obtained within a predetermined time range.

[0037] Figure 8 Cooling profiles obtained from three electronic control units (ECUs) that degraded to the following levels at different cooling start temperatures: Figure 4 The different degrees shown.

[0038] Figure 9 It shows that by... Figure 8 The cooling curve shown is divided into three differential curves by time, and a straight line approximating the differential curve is also shown.

[0039] Figure 10 This shows how to obtain by changing the method used. Figure 4 The cooling curve shown is a graph obtained from the cooling start temperature and coolant temperature in one of the power control units.

[0040] Figure 11 It is shown that... Figure 9 The graph shows the differential curve corresponding to the cooling curve shown.

[0041] Figure 12 The graph shows the rate of change of the exponent b obtained in the power cycle test, where conditions such as heating time, cooling start temperature and coolant temperature are fixed (dashed line) and where these conditions vary randomly (solid line).

[0042] Figure 13 It is a dot plot showing the relationship between the exponential rate of change and the coolant temperature, obtained by using data obtained within a predetermined time range (black dots) and by using data obtained throughout the measurement time (white dots).

[0043] Figure 14It is a dot plot showing the relationship between the exponential rate of change obtained by using data obtained within a predetermined time range (black dots) and data obtained throughout the measurement time (white dots) and the cooling start temperature - coolant temperature. Detailed Implementation

[0044] The following describes, with reference to the accompanying drawings, a method and apparatus for diagnosing the deterioration of electronic units, and a non-transitory computer-readable storage medium.

[0045] In the following description, the present invention will be described as being applied to the degradation diagnosis of an electronic control unit including a power control unit 1.

[0046] The power control unit 1 is installed on the electric vehicle to control the power supplied from the battery 3 installed on the electric vehicle to the onboard electric motor 5. For example... Figure 1 As shown, the power control unit 1 includes: an inverter 7 that converts the direct current supplied from the battery 3 into alternating current for driving the electric motor 5; a gate driver 9 that directly controls the operation of the inverter 7; and a controller 11 that sets the operating conditions of the gate driver 9 according to a control input such as accelerator downsampling. In this embodiment, the invention is applied to the degradation diagnosis of the inverter 7.

[0047] Figure 2 This is a schematic cross-sectional view showing a portion of inverter 7, which includes circuit board 13 and semiconductor chip 15 (power semiconductor device) mounted thereon.

[0048] Circuit board 13 is made of an insulating material with high thermal conductivity and high voltage resistance. Circuit board 13 may include a ceramic or aluminum nitride substrate and a thick copper layer deposited thereon, the copper layer serving as a thermal conductor and / or providing the circuit pattern. Multiple electrodes (not shown) are disposed on one side (upper surface) of circuit board 13 for mounting electronic components on circuit board 12 and for external connections. Inverter 7 can be used in various orientations, but for ease of description, it is assumed that semiconductor chip 15 is located on top (above) circuit board 13, such as... Figure 2 As shown.

[0049] Semiconductor chip 15 incorporates multiple semiconductor devices 17, which are designed to control the power supplied to electric motor 5 and are therefore power devices (power semiconductor devices). Semiconductor devices 17 may also be bipolar transistors or power MOSFETs (metal-oxide-semiconductor field-effect transistors).

[0050] The semiconductor chip 15 is bonded to the upper surface of the circuit board 13 using a bonding material. Thus, the semiconductor devices 17 disposed on the semiconductor chip 15 are supported by the circuit board 13 made of an insulator.

[0051] The bonding materials may include solder, sintered metal materials, etc. In this embodiment, the semiconductor chip 15 and the circuit board 13 are bonded by solder, thus a solder layer 19 is provided between the semiconductor chip 15 and the circuit board 13.

[0052] Semiconductor device 17 is connected to electrodes disposed on circuit board 13 via bonding wires (not shown). Electrodes disposed on circuit board 13 are connected to wiring patterns disposed on circuit board 13 or to wires separate from circuit board 13. Voltage is applied to semiconductor device 17 via wiring patterns or electrical wiring, and semiconductor device 17 serves as a switching element for configuring inverter 7.

[0053] The other side (lower surface) of the circuit board 13 is bonded to the heat sink 21 with a bonding material. The bonding material may be composed of solder, metal sintering material, etc. In this embodiment, the circuit board 13 and the heat sink 21 are joined by soldering, thus providing a solder layer 23 between the circuit board 13 and the heat sink 21.

[0054] The radiator 21 is placed on the cooling device 27 via a heat transfer layer 25 made of a thermal interface material. The thermal interface material is a material that fills the small gaps and irregularities between the radiator 21 and the cooling device 27 to effectively conduct heat from the radiator 21 to the cooling device 27. The heat transfer layer 25 can be made of, for example, a pad, paste, grease, etc., with high thermal conductivity.

[0055] The cooling device 27 may be made of metal and has internal channels 31 for circulating coolant 29 therein. The coolant 29 may be, for example, cooling water. However, the invention is not limited to this example; the cooling device 27 may be formed as heat sink fins in the radiator 21 and may also include an electric fan for moving air along the heat sink fins.

[0056] It is known that the solder layer 19 between the semiconductor chip 15 and the circuit board 13 and / or the solder layer 23 between the circuit board 13 and the heat sink 21 may exhibit cracks, which adversely affect the thermal conductivity of the solder layers 19 and 23 due to various factors such as thermal cycling. The present invention can be applied to diagnose such degradation in electronic control units. However, this is merely an example, and the present invention can be applied to diagnose degradation of other components of electronic control units and other properties that may occur within the electronic control unit.

[0057] Next, the degradation diagnosis device 41 for the electronic control unit, configured to implement the degradation diagnosis method for the electronic control unit according to an embodiment of the present invention, will be described. The degradation diagnosis device 41 is designed to diagnose degradation of the power control unit 1, particularly degradation of the solder layers 19 and 23 of the inverter 7, by executing the degradation diagnosis method for the electronic control unit. Figure 1As shown, the degradation diagnosis device 41 includes a temperature sensor 43 and a diagnostic device body 45 that performs degradation diagnosis based on the detection results of the temperature sensor 43.

[0058] In this embodiment, the temperature sensor 43 includes a temperature-measuring diode. However, the temperature sensor 43 is not limited to this embodiment and can be made of, for example, a resistance thermometer or a thermistor whose resistance changes with temperature. Alternatively, a calibration curve relating the resistance value of the semiconductor chip 15 to temperature can be prepared in advance to detect temperature based on the resistance value of the semiconductor chip 15.

[0059] like Figure 2 As shown, temperature sensor 43 is disposed on the lower surface of semiconductor chip 15. Therefore, the temperature detected by temperature sensor 43 is approximately equal to the temperature of semiconductor chip 15. However, the positioning of temperature sensor 43 is not limited to this example, and temperature sensor 43 may also be disposed on the upper or lower surface of circuit board 13 or on the upper surface of semiconductor chip 15. Alternatively, temperature sensor 43 may be disposed within circuit board 13. In this embodiment, temperature sensor 43 is formed on the lower surface of semiconductor chip 15 and fixed to the upper surface of circuit board 13 via solder layer 19 present between semiconductor chip 15 and circuit board 13.

[0060] In this embodiment, the semiconductor chip 15, temperature sensor 43, circuit board 13 and heat sink 21 are integrally sealed with molding resin to form a semiconductor package 47.

[0061] like Figure 1 As shown, the diagnostic device body 45 includes a processor 51 (central processing unit, CPU), a memory 53 such as RAM (random access memory) and ROM (read-only memory), and a storage device 55 such as HDD (hard disk drive) and SSD (solid-state drive). The diagnostic device body 45 can be connected to, for example, a car navigation system 56 with a monitor 56A in a vehicle.

[0062] The diagnostic device body 45 (more specifically, the storage device 55 of the diagnostic device body 45) stores a predetermined range W, which is defined as the range at start time t. s Or at the start of the measurement t s The scheduled time period t s Time point and end time t e Or the time interval between two predetermined time periods W after the start time (see...) Figure 7 The predetermined range W is stored in the storage device 55. When the degradation diagnostic device is installed in a vehicle as an on-board device, the predetermined range W can also be stored in the storage device 55 before the vehicle leaves the factory.

[0063] The diagnostic device 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 operation of the electric motor 5 by controlling the inverter 7 via the gate driver 9. The processor 51 of the diagnostic device body 45 receives a signal from the controller 11 indicating that the electric motor 5 has stopped operating from the operating state.

[0064] When processor 51 receives a signal from controller 11 indicating that electric motor 5 has stopped operating from the operating state, processor 51 executes the degradation diagnosis program of power control unit 1. By executing the degradation diagnosis program, processor 51 performs... Figure 3 The degradation diagnosis process outlined in the flowchart shown is implemented as a degradation diagnosis method for the power control unit 1. Thus, the processor 51 diagnoses whether degradation exists in the power control unit 1 (specifically, whether degradation exists in the solder layers 19 and 23 provided in the inverter 7 of the power control unit 1). The following will refer to... Figure 3 The flowchart describes the details of the degradation diagnosis and treatment process.

[0065] In the first step of the degradation diagnosis process, or in step ST1, the processor 51 measures the time elapsed from the point when the electric motor 5 stops (t=0) to the point when the electric motor 5 stops (hereinafter referred to as the measurement time t). max The detection results of temperature sensor 43 are obtained at regular time intervals Δt up to ) .

[0066] Therefore, the data acquired by processor 51 represents the data obtained by temperature sensor 43 from time t = 0 to t max The time history of temperature T is obtained, where time t = 0 corresponds to the point in time when electric motor 5 stops (for example, see...). Figure 4 In this embodiment, temperature sensor 43 acquires the temperature T of semiconductor device 17 (device), such that the data acquired by processor 51 is from time t = 0 to t max The temperature T of the semiconductor device 17. In this embodiment, since the temperature sensor 43 acquires the temperature T of the semiconductor device 17, the data acquired by the processor 51 is the temperature T (cooling curve) of the semiconductor device 17 from t=0 to t0. max Variation over a time range. Measurement time t max It can be on the order of a few seconds, and the time interval Δt can be on the order of approximately 10 μs. After the measurement time t... max At that time, processor 51 stops acquiring detection results and executes step ST2.

[0067] In step ST2, processor 51 obtains a differential curve (-dT(t) / dt) by performing time differentiation on the cooling curve and reversing the sign. The differential curve corresponds to a curve indicating the magnitude of the slope of the cooling curve. The time differentiation of the cooling curve can be performed using numerical differentiation processing known per se, which can be based on forward difference, central difference, etc. Once the differential curve is obtained, processor 51 executes step ST3.

[0068] In step ST3, the processor 51 obtains a predetermined range W from the storage device 55, approximates the differential curve as an exponential function within the predetermined range W, and obtains the corresponding exponent b.

[0069] The exponent b here is the coefficient of time t when the temperature T(t) is expressed by the following equation (1), and is the reciprocal of the time constant B (which can also be called the relaxation time) (b = 1 / B).

[0070]

[0071] Where A and C are predetermined constants.

[0072] In this embodiment, the processor 51 first obtains the logarithmic transformation curve Y, which is obtained by using the base e (or log...). e (-dT / dt) is obtained by performing a logarithmic transformation on the differential curve (-dT(t) / dt), where e represents the base of the natural logarithm.

[0073] Next, processor 51 performs regression analysis on the logarithmic transformation curve Y. More specifically, processor 51 assumes that the logarithmic transformation curve Y can be represented by a straight line or an approximate expression Y = -bt + b0 within a predetermined range W, and obtains the exponent b through a method known per se. After obtaining the exponent b, processor 51 executes step ST4.

[0074] In step ST4, the processor 51 determines the progress of degradation based on an index b. In this embodiment, when the index b is equal to or greater than a predetermined anomaly determination reference value b0, the processor 51 determines that the power control unit 1 is not severely degraded, and when the index b is less than the anomaly determination reference value b0, it determines that the power control unit has been severely degraded. When the degradation determination is complete, the processor 51 terminates the degradation diagnosis process.

[0075] When the processor 51 determines that the power control unit 1 has deteriorated, the processor 51 can cause the monitor 56A of the vehicle navigation system 56 to display that the power control unit 1 has been severely deteriorated. For example, if the diagnostic device body 45 is configured to connect to the vehicle owner's mobile terminal (smartphone, etc.) via a network, the diagnostic device body 45 can detect the deterioration of the power control unit 1 and notify the vehicle owner via the mobile terminal.

[0076] The method for obtaining the predetermined range W to be stored in the storage device 55 (hereinafter referred to as the predetermined range acquisition method) will then be described below. The predetermined range acquisition method is performed by performing a predetermined range acquisition process using a test device (deterioration diagnostic device 41) that tests a reference unit or power control unit 1 having the same specifications (structure) as the power control unit 1 actually installed in the vehicle.

[0077] The testing apparatus can perform a predetermined range acquisition process during the design phase of the power control unit 1. Furthermore, the testing apparatus can perform the predetermined range acquisition process on a reference unit that has already undergone initial stress treatment (which subject the product to 10,000 electrical cycle tests).

[0078] The testing apparatus includes a temperature sensor for measuring the temperature of a semiconductor chip placed in a reference unit, a processor for analyzing the detection results of the temperature sensor, and a display unit such as a monitor for displaying the results analyzed by the processor. The testing apparatus may have the same configuration as a degradation diagnostic apparatus (diagnostic apparatus body 45 and temperature sensor 43 for measuring the temperature of power control unit 1). Furthermore, when performing a predetermined range acquisition process, a constant-temperature coolant 29 is supplied to the power control unit 1, and the temperature of the coolant (hereinafter referred to as coolant temperature) is set to a predetermined value (hereinafter referred to as test coolant temperature).

[0079] The following will refer to Figure 5 Describe the details of the predefined range acquisition process.

[0080] In the first step or step ST11 of the predetermined range acquisition method, the test apparatus heats the semiconductor chip included in the reference cell for a certain period of time, and when heating stops, acquires the temperature of the semiconductor chip (chip temperature T'(t)) until a predetermined time (hereinafter referred to as the test measurement time t) has elapsed. max '). Test measurement time t max 'Can be used with measurement time t max Same or different.

[0081] At this point, the data acquired by the testing device corresponds to the temperature T'(t) from time t=0 or the time point when heating stops to t=t. max '(Test measurement time) time history (test cooling curve), such as Figure 6 As shown. When the test measurement time t max 'The past tense has been reached. The testing device stops acquiring temperature and proceeds to step ST12.'

[0082] In step ST12, the testing device calculates the temperature difference ΔT'(t) by subtracting the test coolant temperature from the temperature T'(t). Then, the testing device calculates the value of 1 / e (where e is the base of the natural logarithm) multiplied by the temperature difference ΔT'(t) at time t = 0.

[0083] Subsequently, the time interval required for the temperature difference ΔT'(t) to become 1 / e times the value of the temperature difference at t=0 (in other words, the time required for the temperature T'(t) to become lower than (cooling start temperature - coolant temperature) / e + coolant temperature) was determined as the temporary time constant τ (see [link to relevant documentation]). Figure 6 Then, the testing device sets the predetermined range W to a time period with a predetermined width including a temporary time constant τ.

[0084] In this embodiment, the testing device plots the differential value of temperature T'(t) (-dT'(t) / dt) on a semi-logarithmic graph (see...). Figure 7 The testing apparatus is then selected to include a predetermined range W containing the temporary time constant τ, and exhibits a contribution rate (R²) of approximately 0.99 over the widest possible range. The contribution rate R² referred to here is the degree of deviation of the logarithm of the differential of temperature T'(t) (log(-dT'(t) / dt)) from the straight line within the predetermined range W, assuming that the logarithm of the differential of temperature T'(t) can be approximated by a straight line. The contribution rate R² can also be referred to as the R-squared value or the coefficient of determination. Optionally, the testing apparatus can be configured such that the predetermined range W can be changed by operator input. In doing so, it should be noted that the narrower the predetermined range W, the smaller the value of the contribution rate R² becomes, and the wider the predetermined range W, the larger the value of the contribution rate R² becomes.

[0085] When the predetermined range W is set, the testing device displays the predetermined range W on the display unit and completes the predetermined range acquisition process.

[0086] Workers who use this testing device to perform testing work, workers who assemble and maintain automobiles, etc., can appropriately perform input work and store the predetermined range W in the storage device 55.

[0087] The features and advantages of the degradation diagnosis method and degradation diagnosis device 41 configured in this manner will then be described with reference to the accompanying drawings.

[0088] Figure 4 An example of a cooling curve is shown, where the horizontal axis represents time t and the vertical axis represents temperature T.

[0089] The more active the heat transfer from semiconductor chip 15 to cooling device 27, the faster the temperature of semiconductor chip 15 drops. If cracks (fissures or fissures) occur in solder layers 19 or 23, the heat resistance for transferring heat from semiconductor chip 15 to cooling device 27 increases, resulting in a decrease in the cooling rate of semiconductor chip 15. For example, Figure 4 The cooling rate of semiconductor chip 15, as shown by curves 2 and 3, is less than that shown by curves 2 and 3. Figure 4 Curve 1 in the figure represents the cooling rate. By evaluating the cooling rate in this way, it can be determined whether either of solder layers 19 and 23 has deteriorated.

[0090] However, since the cooling start temperature (the temperature of the semiconductor chip 15 when cooling begins) and the coolant temperature can vary depending on the vehicle's driving conditions and environment, a general comparison cannot be made.

[0091] Figure 8 It shows how to correspond to respectively Figure 4 Curves 1 to 3 are cooling curves obtained by changing the cooling start temperature and coolant temperature in power control unit 1. It is difficult to determine the cooling rate or the degradation process of power control unit 1 from these curves.

[0092] To overcome this problem, the inventors have discovered that when the cooling curve is time-differential and plotted on a semi-logarithmic graph, where the y-axis (logarithmic scale) represents the temperature at the time derivative and the x-axis (linear scale) represents time (see...), the cooling curve becomes more efficient. Figure 9 When the time derivative of the cooling curve is approximately constant within a certain range (a predetermined range W), the slope of the temperature gradient remains essentially constant, independent of the cooling start temperature or the coolant temperature. In other words, the time derivative of the cooling curve can be approximated by an exponential function within the predetermined range W, such that when plotted on a semi-logarithmic graph, the slope remains constant even if the cooling start temperature or the coolant temperature changes. For example, according to... Figure 9 The curve shown simplifies the assessment of degradation progress because the slope of the line can be used to determine the degradation progress.

[0093] Figure 10 It shows how to obtain by changing the method used Figure 4 , Figure 8 and Figure 9 The cooling curves shown in curves 1 to 3 are obtained by measuring the cooling start temperature and coolant temperature in one of the power control units 1. Figure 11 It shows that by... Figure 10 The differential curve is obtained by taking the differential of the cooling curve shown.

[0094] Table 1 below shows the data from... Figure 11 The slope (exponent b) of the curve shown.

[0095] Table 1

[0096] 44 25 2.12 52 25 2.13 62 25 2.15 72 25 2.12 59 40 2.14 67 40 2.13 76 40 2.15 87 40 2.14

[0097] Table 1 shows that the index b is essentially the same and is independent of changes in cooling start temperature and / or coolant temperature, and that the index b will be the same if the degree of degradation is the same.

[0098] The cooling curve of the semiconductor device 17 installed on the power control unit 1 is theoretically represented by the following formula (2).

[0099]

[0100] In equation (2), C, Ai, and bi (i = 1 to N) are predetermined constants independent of time t, and N is a predetermined positive integer of 1 or greater. Since equation (2) is not a single exponential function, and does not produce a single exponential function even at the time of differentiation, it is inconsistent with the fact that the slope is constant when plotted on a semi-logarithmic graph (see...). Figure 6 ).

[0101] Equation (2) can also be expressed as Equation (3).

[0102] T(t)=C-A1exp(-b1t)-A2exp(-b2t)-A3exp(-b3t)…(3)

[0103] The inventors of this application have discovered that in equation (2) (or equation (3)), there exists a range (a predetermined range W) in which a certain term, for example, n terms (-A) n exp(-bnt)) is so dominant that other terms change very little over time (or can be approximated by constants) or deviate from this assumption only at the beginning of the cooling curve. In other words, the inventors of this application have discovered that, within a predetermined range W, equation (3) can be approximated by equation (4) given below.

[0104]

[0105] Figure 12 The figure shows the exponent b obtained in power cycle tests when the heating time, cooling start temperature, and coolant temperature are fixed (dashed line) and when these values ​​are randomly changed based on this consideration (solid line). Figure 12 As can be seen, according to the degradation diagnosis method of this embodiment, even if the heating time, cooling start temperature and coolant temperature change, the degradation state of the power control unit 1 can be detected from the value of index b.

[0106] Furthermore, the relationship between coolant temperature and the rate of change of the exponent b is... Figure 13 The figure is represented by black dots, and the relationship between (cooling start temperature - coolant temperature) and the rate of change of the exponent b is shown in [the figure]. Figure 14 The value is indicated by black dots. For comparison, when the entire cooling curve is assumed to be an exponential function without using this method, the value of the exponent b is also determined by... Figure 13 and Figure 14 The white dots in the text represent...

[0107] from Figure 13 It can be seen that the degradation diagnosis method of this embodiment can obtain an index b representing the degradation state, unaffected by the cooling start temperature and coolant temperature. From Figure 13 and Figure 14 As can be seen from the black and white dots, when the degradation state is calculated from the entire cooling curve instead of using the degradation diagnosis method of the present invention, the value of the index b is greatly affected by the cooling start temperature and the coolant temperature. Therefore, it can be seen that the method of calculating the degradation state from the entire cooling curve without using the degradation diagnosis method according to the present invention cannot accurately diagnose the degradation state.

[0108] As described above, the present invention provides a method for diagnosing the degradation of electronic units. This method is widely applicable and easy to implement regardless of heating conditions, cooling start temperature, coolant temperature, etc. As a result, the convenience and safety of electric vehicles are improved, and therefore, it is expected that the present invention will contribute to improving energy efficiency.

[0109] In step ST4, when the index b is less than the anomaly determination reference value b0, the processor 51 determines that the power control unit 1 has deteriorated. Thus, the deterioration state can be determined by comparing the index b with the anomaly determination reference value b0, thereby easily and accurately detecting unacceptable levels of deterioration.

[0110] When the processor 51 receives a signal indicating that the electric motor 5 has transitioned from an active state to a deactivated state, the processor 51 performs degradation diagnostic processing and begins acquiring a cooling profile. Due to this arrangement, compared to acquiring a cooling profile while the electric motor 5 is still operating, the influence of the onboard electric motor 5 on the detection results of the temperature sensor 43, such as electromagnetic noise, can be reduced.

[0111] As a modification example, the processor 51 can be configured to store the index b in the storage device 55 along with the time of performing the degradation diagnosis process in step ST4, and evaluate the change of the index b accumulated in the storage device 55 over time. This enables good degradation prediction. It is also conceivable to perform degradation prediction by evaluating the change of the index b over a unit time interval or the range of time variation of the index b.

[0112] For example, in step ST4, in order to obtain the time rate of change of the exponent b, the processor 51 may first retrieve the time s from the storage device 55 for the previous degradation diagnosis process. aAnd the index b(s) obtained in the previous degradation diagnosis process a Then, processor 51 calculates the exponent b(s). a ) and the newly acquired exponent b(s) in step ST3 b The absolute value of the difference between (Δb=|b(s)) b )-b(s a Furthermore, processor 51 obtains the time s from performing the previous degradation diagnostic process. a Time s until execution of step ST1 b The elapsed time Δs (=s) b -s a The processor 51 divides the absolute value Δb of the difference between the exponents b by the elapsed time Δs to obtain a value (Δb / Δs) that can be considered the time rate of change of the exponent b. When the time rate of change of the exponent b is equal to or greater than a predetermined threshold, the processor 51 can determine that a critical deterioration state is approaching.

[0113] This completes the description of the specific implementation, but the invention can be extensively modified and is not limited to the above-described implementation.

[0114] According to the above embodiment, in step ST4 of the degradation diagnosis process, the processor 51 performs a logarithmic transformation on the differential curve with base e, performs regression analysis, and obtains the exponent b. However, the present invention is not limited to this embodiment. In step ST4 of the degradation diagnosis process, the processor 51 may also perform a logarithmic transformation on the differential curve with base 10 or any other number, perform regression analysis, and obtain the exponent b.

[0115] In the above embodiment, when the exponent b becomes less than the anomaly determination reference value b0 in step ST4, the processor 51 determines that the power control unit 1 has deteriorated. However, the present invention is not limited to this embodiment. In step ST3, the processor 51 can obtain the reciprocal of b (1 / b, also known as the time constant B), and when the time constant B is greater than the anomaly determination reference value B0, it can determine that the electronic control unit (power control unit 1) has severely deteriorated.

[0116] In the above embodiment, in step ST3, the processor 51 can assume that the differential curve is represented by the sum of multiple exponential functions, and fit the differential curve using known techniques to obtain the exponent b corresponding to each exponential function. In this case, in step ST4, the processor 51 can determine the occurrence of critical degradation based on the difference between the minimum exponent b (or the maximum time constant B) and the corresponding anomaly determination reference value b0 (or anomaly determination reference time constant B0). Specifically, when the minimum exponent b is less than the anomaly determination reference value b0 (or when the maximum time constant B is greater than the anomaly determination reference time constant B0), the processor 51 can determine that the power control unit 1 has severely degraded. Since the smaller the exponent b, the less active the heat dissipation, by selecting the minimum exponent, the degradation process of the part where heat dissipation is hindered by cracks can be effectively detected.

[0117] Alternatively, the processor 51 may, based on the differential curve obtained in ST2, select a predetermined range W of time points (e.g., the center of the surrounding area) where the initial value of the differential curve is 1 / e (e is the base of the natural logarithm) during each degradation diagnosis process.

[0118] In the above embodiments, instead of processor 51, analog circuits known per se, such as differentiating circuits and / or logarithmic conversion circuits, can be used.

[0119] Furthermore, not all components shown in the above embodiments are essential to the broad concept of the present invention, and they may be appropriately selected, omitted, and substituted without departing from the spirit of the invention. The contents of any references cited in this disclosure are incorporated herein by reference.

Claims

1. A degradation diagnosis method for an electronic control unit, the electronic control unit including a power semiconductor device and a circuit board supporting the power semiconductor device, the degradation diagnosis method comprising the following steps: The cooling profile is obtained based on the detection results of a temperature sensor disposed on the power semiconductor device or the circuit board during the operation of the power semiconductor device. A differential curve is obtained by differentiating the cooling curve over time. Within a predetermined time range, the differential curve is approximated as an exponential function to obtain the corresponding exponent; and The electronic control unit is diagnosed by comparing the obtained index with a predetermined reference value, wherein The electronic control unit is configured to control the power supplied to the vehicle's electric motor, and The step of obtaining the cooling curve is initiated when the vehicle-mounted electric motor is turned off.

2. The degradation diagnosis method according to claim 1, wherein, When the obtained index is less than the reference value, it is determined that degradation has occurred.

3. The degradation diagnosis method according to claim 1, wherein, Degradation prediction is performed by comparing the time rate of change of the index with a predetermined threshold.

4. A non-transitory computer-readable storage medium storing a degradation diagnostic program for an electronic control unit, the electronic control unit including a power semiconductor device and a circuit board supporting the power semiconductor device, the degradation diagnostic program including the following steps: The cooling profile is obtained based on the detection results of a temperature sensor disposed on the power semiconductor device or the circuit board during the operation of the power semiconductor device. A differential curve is obtained by differentiating the cooling curve over time. Within a predetermined time range, the differential curve is approximated as an exponential function to obtain the corresponding exponent; and The electronic control unit is diagnosed by comparing the obtained index with a predetermined reference value, wherein The electronic control unit is configured to control the power supplied to the vehicle's electric motor, and The cooling profile is acquired when the vehicle-mounted electric motor is turned off.

5. The non-transitory computer-readable storage medium according to claim 4, wherein, When the obtained index is less than the reference value, it is determined that degradation has occurred.

6. A degradation diagnostic device for an electronic control unit, the electronic control unit including a power semiconductor device and a circuit board supporting the power semiconductor device, the degradation diagnostic device comprising: A temperature sensor, wherein the temperature sensor is disposed on the power semiconductor device or the circuit board; as well as A processor configured to perform degradation diagnosis based on the detection results of the temperature sensor. The processor is configured as follows: A cooling profile is obtained based on the detection results of the temperature sensor during the operation of the power semiconductor device; A differential curve is obtained by differentiating the cooling curve over time. Within a predetermined time range, the differential curve is approximated as an exponential function to obtain the corresponding exponent; and The electronic control unit is diagnosed by comparing the obtained index with a predetermined reference value, wherein The electronic control unit is a power control unit that controls the power supplied to the vehicle's electric motor, and The cooling curve is obtained when the vehicle-mounted electric motor is turned off.

7. The degradation diagnostic device according to claim 6, wherein, When the obtained index is less than the reference value, it is determined that degradation has occurred.

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