Temperature measuring device, power conversion device, drive device, and diagnosis method

Abstract

To correctly diagnose a failure in a temperature measuring element even in an environment in which the temperature of an object to be measured varies greatly.SOLUTION: A temperature measuring device measures the temperature of an object to be measured, and includes a temperature measuring element attached to the object to be measured, a switching unit that changes the amount of current flowing through the temperature measuring element, and a diagnostic unit that determines that an abnormality has occurred in the temperature measuring element if the amount of change in temperature measured by the temperature measuring element deviates from a normal range when the amount of current flowing through the temperature measuring element is increased by the switching unit. The normal range is a variable range that varies depending on the value measured by the temperature measuring element.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a temperature measuring device, a power conversion device, a drive device, and a diagnostic method.

Background Art

[0002] A power conversion device and a drive device convert DC power supplied from a DC power source into AC power to drive a motor. The output torque of the motor varies depending on the motor magnetic flux, and the amount of the motor magnetic flux varies depending on the motor temperature. In order to keep the output torque of the motor constant regardless of the motor temperature, the power conversion device and the drive device may correct the current flowing through the motor according to the motor temperature. In this case, if the motor temperature measuring means fails, the power conversion device and the drive device may erroneously correct the current flowing through the motor, resulting in a problem that the output torque of the motor fluctuates. Therefore, a technique for diagnosing a failure of the temperature measuring means is known. Patent Document 1 discloses a battery pack control device including: a detection means for detecting a physical quantity representing a battery state of a battery pack composed of a plurality of cells; a diagnosis means for diagnosing an abnormal state of the detection means; an estimation means for estimating a charge state of the battery pack based on the physical quantity detected by the detection means; a setting means for setting an allowable charge and discharge range representing a range of a charge state in which the battery pack can be used according to the abnormal state when diagnosed as abnormal by the diagnosis means; and a control means for controlling charge and discharge of the battery pack so that the charge state estimated by the estimation means falls within the allowable charge and discharge range.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the invention described in Patent Document 1, there is room for improvement in dealing with the case where the temperature of the temperature measurement object fluctuates greatly.

Means for Solving the Problems

[0005] A temperature measurement device according to a first aspect of the present invention is a temperature measurement device that measures the temperature of a temperature measurement object, and includes a switching unit that changes the amount of current flowing through a temperature measurement element attached to the temperature measurement object, and when the change amount of the temperature measured by the temperature measurement element deviates from the normal range when the amount of current flowing through the temperature measurement element is increased by the switching unit, a diagnosis unit that executes a diagnosis process for determining that an abnormality has occurred in the temperature measurement element, and the normal range is a variable range according to the value measured by the temperature measurement element. A power conversion device according to a second aspect of the present invention is a power conversion device including the aforementioned temperature measurement device, and includes a power conversion circuit that supplies power to the temperature measurement object. A drive device according to a third aspect of the present invention is a drive device including the aforementioned temperature measurement device, and includes a motor that is the temperature measurement object. A diagnosis method according to a fourth aspect of the present invention is a diagnosis method executed by a temperature measurement device that measures the temperature of a temperature measurement object, and includes a switching process that changes the amount of current flowing through a temperature measurement element attached to the temperature measurement object, and a diagnosis process for determining that an abnormality has occurred in the temperature measurement element when the change amount of the temperature measured by the temperature measurement element deviates from the normal range when the amount of current flowing through the temperature measurement element is increased by the switching process, and the normal range is a variable range according to the value measured by the temperature measurement element.

Advantages of the Invention

[0006] According to the present invention, it is possible to correctly diagnose a failure of a temperature measurement element even in an environment where the temperature of a temperature measurement object fluctuates greatly.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 7

Figure 8

Figure 9

Figure 10

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Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0008] —First Embodiment— Hereinafter, with reference to FIGS. 1 to 6, a first embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described.

[0009] FIG. 1 is a configuration diagram of a vehicle 900 equipped with a drive device 1. The drive device 1 includes a power conversion device 2 described later, a motor 3 described later, and a speed reducer 4 (not shown). The drive device 1 controls the power conversion device 2 and the motor 3 in response to the driver's operation of the accelerator pedal to generate a driving force, and transmits the driving force to the front wheel axle 902F via the speed reducer.

[0010] In FIG. 1, the drive device 1 is installed on the front wheel axle 902F of the vehicle 900, but the drive device 1 may be installed on the rear wheel axle 902B. Further, the drive device 1 may be installed on both the front wheel axle 902F and the rear wheel axle 902B, or independent drive devices 1 may be installed on the left and right wheels instead of the axles. Note that the vehicle 900 may be provided with a power source other than the drive device 1, for example, an engine.

[0011] FIG. 2 is a configuration diagram of the drive device 1. A DC power source 910, a control device 920, and a failure notification device 930 are connected to the drive device 1. The control device 920 transmits data indicating a target torque C2 and an operation mode C1 to the drive device 1. The control device 920 receives a failure notification signal C3 output from the drive device 1. In FIG. 2, only one control device 920 is shown, but a plurality of control devices 920 may exist. In this case, for example, different control devices 920 may output the target torque C2 and the operation mode C1, or a plurality of control devices 920 may receive the failure notification signal C3.

[0012] The DC power source 910 is a power source for driving the motor 3 built in the drive device 1, for example, a battery. When the failure notification device 930 receives a failure notification signal C3 from the drive device 1, it notifies the passengers of the vehicle 900 of the occurrence of a failure. The failure notification device 930 notifies the occurrence of a failure using, for example, a method of lighting a lamp, generating a warning sound, or notifying by voice.

[0013] The drive device 1 includes a power conversion device 2, a motor 3, and a speed reducer (not shown). The speed reducer amplifies the driving force of the motor 3 and transmits it to the axle or the wheel. The motor 3 is a three-phase motor having three windings inside, and is, for example, a synchronous motor using a permanent magnet or an induction motor not using a permanent magnet. The motor 3 includes a motor angle sensor 31 for measuring the angle of the motor 3 and a temperature measuring element 32 for measuring the temperature of the motor 3.

[0014] The motor angle sensor 31 outputs the measured angle as a motor angle sensor value to the power conversion device 2. The temperature measurement element 32 is, for example, a thermistor or a diode. In the present embodiment, an example in which an NTC (Negative Temperature Coefficient) thermistor is used as the temperature measurement element will be described.

[0015] The power conversion device 2 converts the DC power obtained from the DC power supply 910 into AC power to drive the motor 3. The power conversion device 2 also has a function of converting the power of the motor 3 into DC power to charge the DC power supply 910. The power conversion device 2 includes a control circuit 21, a driver circuit 22, a power conversion circuit 23, a DC voltage sensor 24, an AC current sensor 25, and a motor temperature detection circuit 26 inside. The power conversion circuit 23 receives the drive signal C5 from the driver circuit 22 and drives the internal power semiconductor to control the current flowing through the motor 3. With reference to FIG. 3, the internal configuration of the power conversion circuit 23 will be described.

[0016] FIG. 3 is a configuration diagram of the power conversion circuit 23 and the motor 3. The power conversion circuit 23 has a smoothing capacitor 231 and six power semiconductors 232. The power semiconductor switches on and off the six power semiconductors 232 according to the drive signal C5 input from the driver circuit 22 to perform the conversion between DC power and AC power. The power semiconductor 232 is, for example, a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor).

[0017] The smoothing capacitor 231 is a capacitor for smoothing the current generated by the on / off switching of the power semiconductor 232 and suppressing the ripple of the DC current supplied from the DC power supply 910 to the power conversion circuit 23. This smoothing capacitor 231 is, for example, an electrolytic capacitor or a film capacitor. In this embodiment, the motor neutral point 3C is in a floating state, but it may be connected to a ground (not shown). The methods for connecting the motor neutral point to the ground include a direct grounding method, a resistance grounding method, a compensating reactor grounding method, and an arc suppression reactor grounding method.

[0018] Returning to the description of FIG. 2. The DC voltage sensor 24 is a sensor that measures the output voltage of the DC power supply 910, and outputs the measured voltage value to the control circuit 21 as a DC voltage sensor value. The AC current sensor 25 is a sensor that measures the AC current flowing through each phase (U-phase, V-phase, W-phase) of the motor 3, and outputs the measured AC current of each phase to the control circuit 21 as an AC current sensor value. In this embodiment, three AC current sensors 25 are provided, one for each phase. However, only two AC current sensors 25 may be provided for two phases. Since the sum of the U-phase current, V-phase current, and W-phase current is zero, the remaining one current may be calculated using this relationship and the outputs of the two AC current sensors 25. In this case, the control circuit 21 calculates the AC current sensor value for the remaining one phase.

[0019] The driver circuit 22 receives the PWM (Pulse Width Modulation) signal C4 output by the control circuit 21 and outputs a drive signal C5 for switching the on / off of the power semiconductor 232. The motor temperature detection circuit 26 applies a voltage to the temperature measurement element 32 mounted on the motor 3 and outputs the voltage value to the control circuit 21. The motor temperature detection circuit 26 also switches the internal circuit according to the signal output from the control circuit 21. This internal circuit is the switch SW1 described later.

[0020] The control circuit 21 communicates with an external control device 920 and receives an operation mode C1 and a target torque C2 from the control device 920. Based on this operation mode C1 and target torque C2, the control circuit 21 controls the PWM signal so as to control the current of each phase output from the power conversion device 2 to a predetermined value, and drives the power conversion circuit 23 via the driver circuit 22. Further, when the control circuit 21 determines that a failure has occurred inside, it outputs a failure notification signal C3 to the control device 920 and the failure notification device 930.

[0021] The control circuit 21 includes a CPU, a RAM, a ROM, and a communication circuit (not shown) inside. Instead of the ROM, the control circuit 21 may include an electrically erasable programmable ROM (EEPROM) or a flash ROM that can be electrically rewritten. The control circuit 21 includes a state control unit 211, a target current calculation unit 212, a current control unit 213, a PWM signal generation unit 214, a motor speed calculation unit 215, a motor temperature calculation unit 216, and a diagnosis unit 217. By expanding the program stored in the ROM into the RAM and executing it by the CPU, the state control unit 211, the target current calculation unit 212, the current control unit 213, the PWM signal generation unit 214, the motor speed calculation unit 215, the motor temperature calculation unit 216, and the diagnosis unit 217 are realized.

[0022] The control circuit 21 may be realized by a microcomputer, a field programmable gate array (FPGA) which is a rewritable logic circuit, an application specific integrated circuit (ASIC), or the like. Further, it may be realized by a combination of two or more of a CPU, a ROM, a RAM, a microcomputer, an FPGA, and an ASIC.

[0023] The motor speed calculation unit 215 calculates the motor rotation speed from the change in the motor angle sensor value, and outputs the calculated motor speed value to the target current calculation unit 212. The motor temperature calculation unit 216 calculates the motor temperature based on the voltage value output from the motor temperature detection circuit, and outputs the calculated motor temperature value to the target current calculation unit 212 and the diagnosis unit 217. The state control unit 211 uses the operation mode C1 and the fault notification signal C3 output by the diagnosis unit 217 to transition the operation state of the power conversion device 2, and outputs the current operation state to the PWM signal generation unit 214. The operation state is, for example, the PWM state, the three-phase short-circuit state, the three-phase open state, and the like.

[0024] The target current calculation unit 212 calculates the current value to be passed through the motor 3, and outputs this current value as the target current value to the current control unit 213. In calculating the current value to be passed through the motor 3, the target torque C2, the DC voltage sensor value, the motor speed value, and the motor temperature value are used. The calculated current value to be passed through the motor 3 is the current value to be passed through the motor 3 in order for the motor 3 to output the same torque as the target torque C2. The target current value is represented, for example, in the form of a d-axis target current value and a q-axis target current value.

[0025] The output torque T of the synchronous motor can be calculated by the following mathematical formula 1. However, in mathematical formula 1, the number of pole pairs of the motor 3 is Pp, the magnetic flux of the motor 3 is Φ, the d-axis inductance of the motor 3 is Ld, the q-axis inductance of the motor 3 is Lq, the d-axis current flowing through the motor 3 is Id, and the q-axis current flowing through the motor 3 is Iq.

[0026] T = Pp{ΦIq+(Ld - Lq)IdIq} ···(Mathematical formula 1)

[0027] Here, since the motor magnetic flux Φ decreases as the motor temperature rises, in order to keep the output torque T constant regardless of the motor temperature, it is necessary to increase or decrease the values of the d-axis target current and the q-axis target current according to the motor temperature. The target current calculation unit 212 corrects the target current according to the motor temperature.

[0028] The current control unit 213 performs feedback control so that the alternating current flowing through the motor follows the target current value, and calculates the duty values for three phases. Then, the current control unit 213 outputs the duty values to the PWM signal generation unit 214. The above-mentioned feedback control by the current control unit 213 uses the target current value, the alternating current sensor value, the motor angle sensor value, and the DC voltage sensor value.

[0029] The PWM signal generation unit 214 switches the signal output to the driver circuit 22 according to the operating state output from the state control unit 211. The PWM signal generation unit 214 has a timer (not shown) inside. When the operating state is the PWM state, the PWM signal generation unit 214 generates the PWM signal C4 using this timer value and the duty of each phase output by the current control unit 213. When the operating state is the three-phase open state, the PWM signal generation unit 214 generates the PWM signal C4 that turns off all six power semiconductors built in the power conversion circuit 23.

[0030] When the operating state is the three-phase short-circuit state, the PWM signal generation unit 214 generates the PWM signal C4 that turns off all the upper arms and turns on all the lower arms, or the PWM signal C4 that turns on all the upper arms and turns off all the lower arms, among the six power semiconductors built in the power conversion circuit 23. The PWM signal generation unit 214 outputs the generated PWM signal C4 to the driver circuit 22.

[0031] The diagnosis unit 217 diagnoses the failure of the temperature measurement element 32 mounted on the motor 3 or the motor temperature detection circuit 26 inside the power conversion device 2. When the diagnosis unit 217 detects a failure, it outputs the content of the failure location as a failure notification signal C3 to the state control unit 211 and the failure notification device 930. The diagnosis unit 217 includes a normal range table 2171 described later and is used for the diagnosis of the motor temperature detection circuit 26.

[0032] Since the power conversion device 2 incorporates a motor temperature detection circuit 26 and a motor temperature calculation unit 216, it can be called a "temperature measurement device". Similarly, the drive device 1 including the power conversion device 2 can also be called a "temperature measurement device".

[0033] Figure 4 is a configuration diagram of the motor temperature detection circuit 26. The motor temperature detection circuit 26 includes an internal power supply 26P1, a resistor R1, a resistor R2, and a switch SW1 inside. The state of the switch SW1 is controlled by a diagnosis unit 217 within the control circuit 21. The resistance value of the resistor R2 is smaller than that of the resistor R1. When the switch SW1 is in the off state, the voltage of the internal power supply 26P1 is divided by the resistor R1 and the temperature measurement element 32. Usually, when measuring temperature, the switch SW1 is in the off state. Hereinafter, the switch SW1 may also be referred to as a "switching unit".

[0034] When the switch SW1 is in the on state, the voltage of the internal power supply 26P1 is divided by the parallel combined resistance of the resistor R1 and the resistor R2 and the temperature measurement element 32. Since the resistance value of the parallel combined resistance of the resistor R1 and the resistor R2 is smaller than the resistance value of the resistor R1, when the switch SW1 is in the on state, a larger current flows through the temperature measurement element 32 than when the switch SW1 is in the off state, and the heat generation of the temperature measurement element 32 increases due to this current.

[0035] Figure 5 is a flowchart showing the diagnostic process by the diagnosis unit 217. This diagnostic process is performed by the diagnosis unit 217 at least in one of when the power conversion device 2 is started up and at a certain time period after the power conversion device 2 is started up. In step S301, the diagnosis unit 217 measures the temperature of the temperature measurement element 32. Hereinafter, the temperature measured in this step will be referred to as the "steady-state temperature". In the subsequent step S302, the diagnosis unit 217 turns on the switch SW1 built in the motor temperature detection circuit 26. In the subsequent step S303, the diagnosis unit 217 waits for a certain time. This certain time is a predetermined time.

[0036] In the subsequent step S304, the diagnostic unit 217 turns off the switch SW1 incorporated in the motor temperature detection circuit 26. In the subsequent step S305, the diagnostic unit 217 measures the temperature of the temperature measurement element 32. Hereinafter, the temperature measured in step S305 is referred to as the "temperature after current increase". In the subsequent step S306, the diagnostic unit 217 specifies the normal range of the temperature change corresponding to the steady-state temperature.

[0037] FIG. 6 is a diagram showing the concept of the normal range table 2171. The normal range table 2171 is created in advance. The normal range table 2171 is data showing the correspondence between the steady-state temperature and the normal range of the temperature change. In FIG. 6, the horizontal axis represents the steady-state temperature, and the vertical axis represents the amount of temperature change. The vertical distance between the two solid lines shown in FIG. 6 indicates the normal range of temperature change. The broken line and the dashed-dotted line will be described later. When the temperature change is larger than the normal range, it is an abnormality that the resistance of the temperature measurement element 32 is small. When the temperature change is smaller than the normal range, it is an abnormality that the resistance of the temperature measurement element 32 is large.

[0038] Specifically, based on the resistance value of the temperature measurement element 32 at each temperature, the amount of temperature change when the switch SW1 is turned on can be calculated in advance. The range obtained by adding the measurement error to the normal temperature change amount is set as the normal temperature change range. The width of the measurement error may be set as a certain percentage of the normal temperature change amount, for example, 5% or 10%, or may be set as a fixed value such as 1 ° C or 3 ° C regardless of the value of the normal temperature change amount. Although the normal range table 2171 is shown as a graph in FIG. 6, it may be represented in a table format or by a mathematical formula such as a polynomial. Returning to FIG. 5, the description will be continued.

[0039] In the subsequent step S307, the diagnosis unit 217 calculates the temperature change amount, which is the difference between the abnormal temperature and the temperature after the current increase, and determines whether this temperature change amount falls within the normal range specified in step S306. If the diagnosis unit 217 determines that the temperature change amount is within the normal temperature change range, it proceeds to step S308; if it determines that the temperature change amount is not within the normal temperature change range, it proceeds to step S309. In step S308, the diagnosis unit 217 determines that the temperature measurement element 32 is normal, that is, no abnormality is detected, and ends the process shown in FIG. 5. In step S309, the diagnosis unit 217 outputs a signal indicating that the temperature measurement element 32 has failed as a failure notification signal C3 to the state control unit 211 and the failure notification device 930, and ends the process shown in FIG. 5.

[0040] The effects of this embodiment are as follows. In FIG. 6, the temperature change amount when a failure occurs in which the resistance value of the temperature measurement element 32 becomes small is indicated by a broken line, and the temperature change amount when a failure occurs in which the resistance value of the temperature measurement element 32 becomes large is indicated by a one-dot chain line. When the resistance value of the temperature measurement element 32 becomes small, the current flowing through the temperature measurement element 32 increases accordingly, and the heat generation of the temperature measurement element 32 increases, so the value of the temperature change amount also increases. Conversely, when the resistance value of the temperature measurement element 32 becomes large, the current flowing through the temperature measurement element 32 decreases, and the heat generation of the temperature measurement element 32 decreases, so the value of the temperature change amount also decreases. Therefore, it is possible to detect a failure in which the resistance value of the temperature measurement element 32 becomes smaller than a certain value or larger than a certain value based on the temperature change amount.

[0041] Also, by changing the normal temperature change range according to the steady-state temperature as in this embodiment, the temperature measurement element 32 can be appropriately diagnosed regardless of the temperature of the temperature measurement object. In this embodiment, the temperature measurement object is the motor 3, and the temperature of this motor 3 depends on the previous driving situation. For example, when the motor 3 has not been driven for a long time, the motor temperature becomes almost equal to the ambient temperature, and when it is immediately after the motor 3 has been driven, the motor temperature is in a high-temperature state. The temperature of the temperature measurement element 32 is close to the temperature of the motor 3, which is the temperature measurement object, and the resistance value of the temperature measurement element 32 changes according to the temperature of the temperature measurement element 32.

[0042] And since the amount of temperature change at the time of diagnosis is affected by the resistance value of the temperature measurement element 32, the normal temperature change range varies depending on the temperature of the temperature measurement target. When the temperature measurement target is always at a constant temperature, even if the normal temperature change range is fixed, the failure of the temperature measurement element 32 can be correctly diagnosed. However, when the temperature of the temperature measurement target changes greatly as in this embodiment, if a fixed normal temperature change range is used, problems such as misdetection that the temperature measurement element 32 is faulty even though it is normal, and misjudgment that the temperature measurement element 32 is normal even though it is faulty may occur.

[0043] According to the first embodiment described above, the following operational effects can be obtained. (1) The power conversion device 2, which can also be called a temperature measurement device, measures the temperature of the motor 3 that is the temperature measurement target. A switch SW1 that changes the amount of current flowing through the temperature measurement element 32 attached to the motor 3, and when the amount of temperature change measured by the temperature measurement element 32 deviates from the normal range when the amount of current flowing through the temperature measurement element 32 is increased by the switch SW1 (S307: NO in FIG. 5), it includes a diagnosis unit 217 that determines that an abnormality has occurred in the temperature measurement element 32. The normal range is a variable range (S306 in FIG. 5) corresponding to the value measured by the temperature measurement element 32, which is determined by referring to the normal range table 2171. Therefore, even in an environment where the temperature of the temperature measurement target fluctuates greatly, the failure of the temperature measurement element can be correctly diagnosed.

[0044] (2) The power conversion device 2 includes a power conversion circuit 23 that supplies power to the motor 3 that is the temperature measurement target.

[0045] (3) The drive device 1 includes the motor 3 that is the temperature measurement target.

[0046] (Modification 1) In this embodiment, the diagnosis of the temperature measurement element 32 for measuring the motor temperature has been described, but the temperature measurement target is not limited to the motor 3. For example, when a temperature detection circuit and a temperature measurement element 32 similar to those in this embodiment are used as a circuit for measuring the temperature of a power semiconductor or the control circuit 21, the failure of the temperature measurement element 32 can be detected using the method described in this embodiment.

[0047] - Second Embodiment - Referring to FIGS. 7 to 8, a second embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described. In the following description, the same reference numerals are given to the same components as in the first embodiment, and the differences will be mainly described. For points not particularly described, they are the same as in the first embodiment. In this embodiment, mainly, the processing when the steady-state temperature is lower than a predetermined threshold value is different from that in the first embodiment.

[0048] FIG. 7 is a configuration diagram of the motor temperature detection circuit 26A in the second embodiment. The motor temperature detection circuit 26A further includes a second internal power supply 26P2 and a second switch SW2 in addition to the configuration of the motor temperature detection circuit 26 in the first embodiment. The voltage of the second internal power supply 26P2 is higher than that of the internal power supply 26P1. The state of the second switch SW2 is controlled by the diagnosis unit 217 in the control circuit 21. In this embodiment, both the switch SW1 and the second switch SW2 are referred to as a "switching unit". The operation of the switching unit is controlled by the diagnosis unit 217 in the same manner as in the first embodiment.

[0049] FIG. 8 is a flowchart showing the processing of the diagnosis unit 217 in the second embodiment. In step S301, the diagnosis unit 217 measures the temperature of the temperature measurement element 32, that is, the steady-state temperature. In the subsequent step S312, the diagnosis unit 217 determines whether the steady-state temperature exceeds a second threshold value, which is a predetermined threshold value. When the diagnosis unit 217 determines that the steady-state temperature exceeds the first threshold value, it executes the processing of steps S302 to S304 in the same manner as in the first embodiment.

[0050] When the diagnostic unit 217 determines that the steady-state temperature does not exceed the first threshold value, it proceeds to step S314. In steps S314 to S316, the diagnostic unit 217 turns on the second switch SW2, waits for a certain period of time, and then turns off the second switch SW2. The "certain period of time" in step S315 is the same length as the "certain period of time" in step S303. When either step S304 or step S316 is completed, the diagnostic unit 217 executes the processes of steps S305 to S309 in the same manner as in the first embodiment. Note that the normal range table 2171 in this embodiment is different from that in the first embodiment. When the steady-state temperature is lower than the first threshold value, since the second switch SW2 is turned on and the temperature measurement element 32 is heated more than in the first embodiment, the normal range table 2171 is generated taking this influence into account.

[0051] The effects of this embodiment are as follows. In the example of FIG. 6 in the first embodiment, when the steady-state temperature is low, there is no significant difference in the temperature change amount between normal and faulty conditions, and it is difficult to correctly determine the failure of the temperature measurement element 32. This is because when the temperature of the temperature measurement element 32 is low, the resistance value of the temperature measurement element 32 is large, so even if the resistance value of the temperature measurement element 32 increases or decreases somewhat due to a failure, there is no significant difference in the temperature change amount. To solve this problem, in the second embodiment, when the steady-state temperature is low, by turning on the second switch SW2, the second internal power supply 26P2 with a higher voltage than the internal power supply 26P1 is applied to the resistor R2 and the temperature measurement element 32, and the current flowing through the temperature measurement element 32 is made larger than when the switch SW1 is turned on. As a result, since the temperature change amount of the temperature measurement element 32 becomes larger than when the switch SW1 is turned on, the failure of the temperature measurement element 32 can be determined more accurately.

[0052] According to the second embodiment described above, the following operational effects can be obtained. (4) When the value measured by the temperature measurement element is less than the first threshold (S312: NO in FIG. 8), the diagnostic unit 217 increases the energization current amount of the temperature measurement element 32 based on the switch SW compared to the case where the value measured by the temperature measurement element is greater than the first threshold (S312: YES in FIG. 8). Therefore, even at low temperatures, the failure of the temperature measurement element 32 can be determined more accurately.

[0053] (Modification of the Second Embodiment) In the above-described second embodiment, the second switch SW2 is turned on when the steady-state temperature is equal to or lower than the first threshold. Since the voltage of the second internal power supply 26P2 is higher than that of the internal power supply 26P1, more current flows per unit time when the second switch SW2 is turned on than when the switch SW1 is turned on. However, the application time may be changed without changing the current per unit time. That is, instead of increasing the energization current amount, the energization time may be lengthened.

[0054] - Third Embodiment - Referring to FIGS. 9 to 10, a third embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the differences will be mainly described. For points not particularly described, they are the same as those in the first embodiment. In this embodiment, it is mainly different from the first embodiment in that the motor is warmed up before diagnosis at low temperatures.

[0055] FIG. 9 is a configuration diagram of the drive device 1B in the third embodiment. The diagnostic unit 217 in the third embodiment outputs a motor drive request signal to the state control unit 211 and the target current calculation unit 212. The state control unit 211 changes the current operating state in response to the motor drive request signal from the diagnostic unit 217. The target current calculation unit 212 changes the value of the target current in response to the motor drive request signal from the diagnostic unit 217.

[0056] FIG. 10 is a flowchart showing the processing of the diagnostic unit 217 in the third embodiment. In step S331, the diagnostic unit 217 measures the temperature of the temperature measurement element 32, that is, the steady-state temperature. However, in this embodiment, as will be described later, this step may be executed multiple times. In this case, the temperature measured last is taken as the steady-state temperature. In other words, the steady-state temperature is updated every time step S331 is executed.

[0057] In the subsequent step S332, the diagnostic unit 217 determines whether the temperature measured in step S331 is greater than the second threshold value. If the diagnostic unit 217 determines that the temperature measured in step S331 is greater than the second threshold value, it proceeds to step S334. If it determines that the temperature measured in step S331 is less than or equal to the second threshold value, it proceeds to step S333. In step S333, the diagnostic unit 217 applies current to the motor 3 and returns to step S331. When returning from step S333 to step S331, the application of current to the motor is continued until the measured temperature exceeds the second threshold value. Note that the second threshold value may be the same as or different from the first threshold value in the second embodiment.

[0058] The details of step S333 are as follows. The diagnostic unit 217 outputs a motor drive request signal to the state control unit 211 and the target current calculation unit 212. The state control unit 211 receives the motor drive request signal from the diagnostic unit 217 and switches the operating state to the PWM state if the current operating state is a three-phase short-circuit state or a three-phase open state. The target current calculation unit 212 receives the motor drive request signal from the diagnostic unit 217 and increases the total amount of the target current within a range where the change amount of the motor output torque remains within a certain value. For example, when the motor 3 is in a stopped state and the motor output torque is 0 Nm, if only the d-axis current flows through the motor 3, from Equation 1, the motor output torque remains 0 Nm and the total amount of the target current can be increased.

[0059] Also, from Equation 1, it can be seen that the q-axis current affects both the torque due to the motor flux and the torque due to the inductance, while the d-axis current affects only the torque due to the inductance. From this, it can be understood that the output torque of the synchronous motor is greatly affected by the q-axis current, and the influence of the d-axis current is smaller than that of the q-axis current. Therefore, when the motor 3 is in the driving state and the d-axis current and the q-axis current are flowing through the motor 3, by increasing the d-axis current and decreasing the q-axis current so as to maintain the output torque of the motor 3, the total amount of the target current can be increased while reducing the change amount of the output torque. Note that if the output torque of the motor 3 fluctuates greatly by changing the target current, it will affect the operation of the vehicle. Therefore, in this embodiment, the target current is changed within a range where the change amount of the motor output torque does not affect the operation.

[0060] In step S334, the diagnostic unit 217 stops the application of current to the motor 3 started in step S333 and executes the processes after step S302. Since the processes after step S302 are the same as those in the first embodiment, the description thereof is omitted. The normal range table 2171 in this embodiment may be the same as that in the first embodiment. When the temperature at the start of the process of the diagnostic unit 217 is low, the steady-state temperature is forcibly increased above the second threshold by the processes of steps S331 to S333. Therefore, it is not necessary to consider the situation where the steady-state temperature is low as in the second embodiment.

[0061] The effects in this embodiment are as follows. As described in the second embodiment, in the method of the first embodiment, when the temperature of the temperature measurement element 32 is low when the operation of the diagnostic unit 217 is started, it is difficult to correctly determine the failure of the temperature measurement element 32. As a method for solving this problem, in the third embodiment, when the steady-state temperature is low, the current flowing through the motor 3 is increased to heat the motor 3, and the diagnosis is performed after the steady-state temperature exceeds the second threshold, so that the failure of the temperature measurement element 32 can be determined more accurately.

[0062] According to the above-described third embodiment, the following operational effects can be obtained. (5) The object of temperature measurement by the motor temperature detection circuit 26 is the motor 3. When the value measured by the temperature measurement element 32 is smaller than the second threshold value (S332: NO in FIG. 10), the diagnosis unit 217 supplies current to the motor 3 (S333), and after the value measured by the temperature measurement element 32 exceeds the second threshold value (S332: YES), it determines whether the temperature measurement element 32 is abnormal (S302 to S309). Therefore, even at low temperatures, it is possible to more accurately determine the failure of the temperature measurement element 32.

[0063] (6) The diagnosis unit 217 controls the current so that the current flowing through the motor becomes maximum within a range where the torque output by the motor 3 falls within a certain range from the target value (S333).

[0064] - Fourth Embodiment - With reference to FIGS. 11 to 13, a fourth embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the differences will be mainly described. Points not particularly described are the same as those in the first embodiment. In this embodiment, it is mainly different from the first embodiment in that it detects the sticking of a switch built in the motor temperature detection circuit 26.

[0065] In the first embodiment, the failure of the temperature measurement element 32 is determined by switching the switch SW1 built in the motor temperature detection circuit 26. However, if this switch SW1 fails, correct temperature measurement and failure determination cannot be performed. For example, if a failure (off-sticking failure) occurs in which the switch SW1 turns off while it is being controlled to be in the on state, the current flowing through the temperature measurement element 32 does not increase, and the temperature measurement element 32 cannot generate heat. As a result, the temperature difference between the current increase temperature and the steady-state temperature disappears, and in the diagnosis of the temperature measurement element 32, there is a possibility of erroneously determining that the temperature measurement element 32 has failed when it has not actually failed.

[0066] Also, if a failure (ON-stuck failure) occurs in which switch SW1 turns on while it is being controlled to the off state, the temperature of switch SW1 in the off state cannot be measured. As a result, when diagnosing temperature measurement element 32, there is a possibility of erroneously determining that temperature measurement element 32 is faulty when it is not. Therefore, it is necessary to determine the off-stuck failure and on-stuck failure of switch SW1.

[0067] FIG. 11 is a flowchart showing the processing of diagnosis unit 217 in the fourth embodiment. FIG. 11 is obtained by adding the off-stuck failure diagnosis of switch SW1 to FIG. 5 in the first embodiment, and the description of the same processing as in FIG. 5 is omitted. In the processing shown in FIG. 11, steps S301 and S302 are executed in the same manner as in the first embodiment. Then, immediately after turning on switch SW1, diagnosis unit 217 measures the temperature again in step S351.

[0068] In the subsequent step S352, diagnosis unit 217 calculates the temperature change amount, which is the difference between the steady-state temperature and the temperature in step S351, and determines whether the temperature change amount is equal to or greater than the third threshold value. When diagnosis unit 217 determines that the temperature change amount is equal to or greater than the third threshold value, it executes the same processing as in the first embodiment after step S303. When diagnosis unit 217 determines that the temperature change amount is less than the third threshold value, it proceeds to step S353, outputs a signal indicating that an off-stuck of switch SW1 has occurred as a failure notification signal C3 to state control unit 211 and failure notification device 930, and ends the processing shown in FIG. 5.

[0069] Note that if an off-stuck failure of switch SW1 has occurred, temperature measurement element 32 cannot be correctly diagnosed. Therefore, after detecting an off-stuck failure of switch SW1, the diagnosis process of temperature measurement element 32 is not performed.

[0070] FIG. 12 is a diagram showing the voltage and temperature characteristics in the state where switch SW1 is off (hereinafter referred to as the "off state") and in the state where switch SW1 is on (hereinafter referred to as the "on state"). In FIG. 12, the on state is shown by a solid line and the off state is shown by a broken line. Since the resistance value of resistor R2 is smaller than that of resistor R1, when switch SW1 changes from off to on, resistors R1 and R2 are in parallel, and the resistance value becomes smaller compared to only resistor R1. As a result, the voltage measured by diagnostic unit 217 increases when switch SW1 changes from off to on.

[0071] For example, when the current measured temperature is Ta, the measured voltage in the off state is Va, and when controlled to the on state, the measured voltage changes to Vb. When motor temperature calculation unit 216 converts the measured voltage to temperature based on the voltage-temperature characteristics in the state where switch SW1 is off, since the measured temperature when the measured voltage is Vb is Tb, when switch SW1 changes from the off state to the on state, the measured temperature changes from Ta to Tb.

[0072] If an off-stuck fault has occurred in switch SW1, switch SW1 remains off even when diagnostic unit 217 controls switch SW1 to be on. In this case, the voltage measured by diagnostic unit 217 does not change from Va, and the measured temperature also does not change from Ta. Therefore, if the difference between the measured temperature in the off state of switch SW1 and the measured temperature in the on state of switch SW1 is less than the third threshold value, it can be determined that switch SW1 has an off-stuck fault.

[0073] As this third threshold value, for example, the temperature change amount when switching switch SW1 from off to on may be calculated in advance for each measured temperature and used in accordance with the current measured temperature. Also, as the third threshold value, for example, the minimum value among the temperature change amounts for each measured temperature when switching switch SW1 calculated in advance as described above may be used. Note that in this embodiment, an off-stuck fault of switch SW1 is determined using the difference in measured temperature, but a similar fault determination is also possible using the difference in measured voltage.

[0074] FIG. 13 is a flowchart showing the on-stuck diagnosis process of switch SW1 by the diagnosis unit 217. This process is performed by the diagnosis unit 217 at regular time intervals after the power conversion device 2 is started. First, in step S371, the diagnosis unit 217 measures the temperature of the temperature measurement element 32. In the following step S372, the diagnosis unit 217 calculates the temperature difference between the temperature measured in step S371 and the previously measured temperature, and determines whether the temperature difference is equal to or greater than the fourth threshold value. However, when step S372 is executed for the first time after the power conversion device 2 is started, since there is no previous measured temperature, the process proceeds from step S371 to step S375 and the process shown in FIG. 13 ends.

[0075] In step S372, when the diagnosis unit 217 determines that the temperature difference is equal to or greater than the fourth threshold value, the process proceeds to step S373. When it determines that the temperature difference is less than the fourth threshold value, the process proceeds to step S374. In step S373, the diagnosis unit 217 outputs a message indicating that switch SW1 has an on-stuck fault as a fault notification signal C3 to the state control unit 211 and the fault notification device 930, and then proceeds to step S375. In step S374, the diagnosis unit 217 determines that it is normal, that is, no on-stuck has occurred in switch SW1, and then proceeds to step S375. In step S375, the diagnosis unit 217 saves the temperature measured in step S371 for use in the next diagnosis and ends the process shown in FIG. 13.

[0076] When an on-stuck fault of switch SW1 is detected, since the temperature when switch SW1 is turned off cannot be measured, the diagnosis of the temperature measurement element 32 cannot be correctly performed. Therefore, after an on-stuck fault of switch SW1 is detected, the diagnosis process of the temperature measurement element 32 is not performed. In other words, in this embodiment, the diagnosis process of the temperature measurement element 32 is performed only when neither an on-stuck fault nor an off-stuck fault of switch SW1 is detected.

[0077] Since the thermal time constant of the motor 3, which is the temperature measurement target in this embodiment, is large, a large temperature change does not occur in a short time. On the other hand, as described in the explanation of FIG. 12, when the switch SW1 changes from off to on, the measured temperature changes greatly. By utilizing this fact and executing the on-stuck diagnosis process shown in FIG. 13 at a short cycle, a large temperature change occurs only when the switch SW1 has an on-stuck fault, so the on-stuck fault can be detected.

[0078] As this fourth threshold value, for example, the amount of temperature change when the switch SW1 is switched from off to on may be calculated in advance for each measured temperature and switched and used according to the current measured temperature. Also, as the fourth threshold value, for example, the minimum value among the amounts of temperature change for each measured temperature when the switch SW1 described above is switched, which is calculated in advance, may always be used. Note that in this embodiment, the on-stuck fault of the switch SW1 is determined using the difference in measured temperature, but the same fault determination is possible using the difference in measured voltage.

[0079] The effects of this embodiment are as follows. As described above, when an off-stuck fault or an on-stuck fault occurs in the switch SW1, there is a possibility of misjudging that the temperature measurement element 32 is faulty when it is not. In this embodiment, the presence or absence of an off-stuck fault and an on-stuck fault of the switch SW1 is diagnosed, and when either fault is detected, the diagnosis of the temperature measurement element 32 is terminated thereafter, thereby preventing misjudgment of the fault of the temperature measurement element 32.

[0080] According to the fourth embodiment described above, the following operational effects can be obtained. (7) When the temperature difference before and after the current amount is switched by the switching unit is smaller than the third threshold value (S352: NO in FIG. 11), the diagnosis unit 217 determines that an off-stuck abnormality has occurred in the switch SW1. Therefore, the off-stuck abnormality of the switch SW1 can be detected.

[0081] (8) When the measured temperature difference within a certain period is equal to or greater than the fourth threshold value (S372 in FIG. 13: YES), the diagnostic unit 217 determines that an abnormal stuck-on state has occurred in the switch SW1. Therefore, it is possible to detect the abnormal stuck-on state of the switch SW1.

[0082] (9) The diagnostic unit 217 performs the abnormal determination process (S302 to S309) of the temperature measurement element 32 only when it determines that no abnormality has occurred in the switching unit. Therefore, it is possible to detect an abnormality of the temperature measurement element 32 after confirming that no abnormal stuck-off state or abnormal stuck-on state has occurred in the switch SW1.

[0083] (Modification of the Fourth Embodiment) In the above-described fourth embodiment, the diagnostic unit 217 detected both the abnormal stuck-off state and the abnormal stuck-on state of the switch SW1. However, the diagnostic unit 217 may detect only one of the abnormal stuck-off state and the abnormal stuck-on state of the switch SW1. In this case, the diagnostic unit 217 performs the abnormal determination process (S302 to S309) of the temperature measurement element 32 only when no abnormality is detected in the detection of the abnormal stuck-off state or the abnormal stuck-on state to be executed.

[0084] - Fifth Embodiment - Referring to FIG. 14, a fifth embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the differences will be mainly described. Regarding points not particularly described, they are the same as those in the first embodiment. In this embodiment, it is different from the first embodiment mainly in that the temperature is corrected during the diagnosis of the temperature measurement element 32.

[0085] FIG. 14 is a configuration diagram of the drive device 1 in the fifth embodiment. In this embodiment, a diagnosis execution signal is further input to the motor temperature calculation unit 216 from the diagnosis unit 217, a target current is input from the target current calculation unit 212, and a motor speed is input from the motor speed calculation unit 215. The motor temperature calculation unit 216 corrects the motor temperature using the diagnosis execution signal, the target current, and the motor speed. The diagnosis unit 217 in this embodiment outputs the diagnosis execution signal to the motor temperature calculation unit 216 during the diagnosis of the temperature measurement element 32.

[0086] When the diagnosis unit 217 is not diagnosing the temperature measurement element 32, that is, when the diagnosis execution signal is not received, the motor temperature calculation unit 216 outputs the measured temperature as it is. When the diagnosis unit 217 is diagnosing the temperature measurement element 32, that is, when the diagnosis execution signal is received, the motor temperature calculation unit 216 adds a temperature correction value to the motor temperature measured last before the start of diagnosis and outputs it. The motor temperature calculation unit 216 calculates the motor loss using the current target current and the motor speed, and calculates the temperature correction value based on the motor loss.

[0087] The loss of the motor 3 is divided into copper loss and iron loss. The copper loss can be calculated from the winding resistance in the motor 3 and the current value flowing through the motor 3. Also, the iron loss changes according to the current value flowing through the motor 3 and the motor speed. Since the current value flowing through the motor 3 follows the target current, the motor temperature calculation unit 216 calculates the copper loss of the motor 3 from the winding resistance value of the motor 3 recorded in advance and the target current. Also, for the iron loss, information on the iron loss corresponding to the current flowing through the motor 3 and the motor speed is recorded in advance, and the motor temperature calculation unit 216 calculates the iron loss of the motor 3 from the iron loss information, the current target current, and the current motor speed. Then, the motor speed calculation unit 215 calculates the temperature rise amount of the motor 3 due to the current motor operating condition from the copper loss of the motor 3, the iron loss of the motor 3, and the thermal time constant of the motor 3 recorded in advance, and uses it as the temperature correction value. Note that, although an example using the target current as the current value flowing through the motor 3 is shown this time, an AC current sensor value may be used as the current value flowing through the motor 3.

[0088] The effects of the present embodiment are as follows. In the first embodiment, since a current is passed through the temperature measurement element 32 to generate heat during the diagnosis of the temperature measurement element 32, the temperature of the motor 3, which is the temperature measurement target, cannot be accurately measured. In the present embodiment, during the diagnosis of the temperature measurement element 32, since a value obtained by adding a temperature correction value corresponding to the current motor operation state to the temperature measured immediately before the diagnosis is output as the measured temperature, the temperature of the motor 3 can be measured more accurately even during the diagnosis.

[0089] According to the fifth embodiment described above, the following operational effects can be obtained. (10) The power conversion device 2 includes a target current calculation unit 212 and a motor speed calculation unit 215 that acquire the rotation speed of the motor 3 and the current value flowing through the motor 3, and a motor temperature calculation unit 216 that calculates a temperature correction value using the rotation speed and the current value and outputs, as the measured temperature, a value obtained by adding the temperature correction value to the measured temperature immediately before the diagnosis unit 217 starts the diagnosis. Therefore, the temperature of the motor 3 can be measured more accurately even during the diagnosis.

[0090] Note that the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for a part of the configuration of each embodiment, addition, deletion, or replacement with other configurations can be made.

[0091] In addition, each of the above-described configurations, functions, processing units, processing means, etc. may be realized in hardware by designing a part or all of them, for example, by using an integrated circuit. Further, each of the above-described configurations, functions, etc. may be realized in software by a processor interpreting and executing a program for realizing each function. Information such as a program, a table, and a file for realizing each function can be stored in a memory, a recording device such as a hard disk or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

[0092] In each of the above-described embodiments and modifications, the configuration of the functional blocks is merely an example. Some of the functional configurations shown as separate functional blocks may be integrally configured, or the configuration represented by one functional block diagram may be divided into two or more functions. Further, a part of the functions of each functional block may be configured to be provided in other functional blocks.

[0093] The above-described embodiments and modifications may be combined with each other. Although various embodiments and modifications have been described above, the present invention is not limited to these contents. Other aspects conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

Explanation of Reference Numerals

[0094] 1: Driving device 2: Power conversion device 3: Motor 21: Control circuit 22: Driver circuit 23: Power conversion circuit 26: Motor temperature detection circuit 31: Motor angle sensor 32: Temperature measurement element 212: Target current calculation unit 216: Motor temperature calculation unit 217: Diagnosis unit 2171: Normal range table

Claims

1. A temperature measurement device for measuring the temperature of an object to be temperature-measured, comprising: a switching unit that changes the amount of current flowing through a temperature measurement element attached to the object to be temperature-measured; a diagnosis unit that executes a diagnosis process for determining that an abnormality has occurred in the temperature measurement element when a change amount of the temperature measured by the temperature measurement element deviates from a normal range when the amount of current flowing through the temperature measurement element is increased by the switching unit; The temperature measurement device, wherein the normal range is a variable range according to the value measured by the temperature measurement element.

2. The temperature measurement device according to claim 1, wherein when the value measured by the temperature measurement element is smaller than a first threshold value, the diagnosis unit controls the switching unit so that the energization current amount or energization time of the temperature measurement element becomes larger than when the value measured by the temperature measurement element is larger than the first threshold value.

3. The temperature measurement device according to claim 1, wherein the object to be temperature-measured is a motor, when the value measured by the temperature measurement element is smaller than a second threshold value, the diagnosis unit supplies current to the motor, and after the value measured by the temperature measurement element exceeds the second threshold value, determines an abnormality of the temperature measurement element.

4. The temperature measurement device according to claim 3, wherein the diagnosis unit controls the current so that the current flowing through the motor becomes maximum within a range where the torque output by the motor falls within a certain range from a target value.

5. The temperature measurement device according to claim 1, wherein when a difference between values measured by the temperature measurement element before and after the switching unit changes the amount of current flowing through the temperature measurement element is smaller than a third threshold value, the diagnosis unit determines that an abnormality has occurred in the switching unit.

6. The temperature measurement device according to claim 1, wherein when a measured temperature difference within a certain time is equal to or greater than a fourth threshold value, the diagnosis unit determines that an abnormality has occurred in the switching unit.

7. The temperature measurement device according to claim 5, wherein the diagnosis unit performs the diagnosis process only when it is determined that no abnormality has occurred in the switching unit.

8. The temperature measurement device according to claim 6, wherein the diagnosis unit performs the diagnosis process only when it is determined that no abnormality has occurred in the switching unit.

9. The temperature measurement device according to claim 1, wherein The object to be temperature-measured is a motor, means for obtaining the rotational speed of the motor and the value of the current flowing through the motor; temperature calculation means for calculating a temperature correction value using the rotational speed and the current value while the diagnostic unit is executing the diagnostic process, and outputting, as the measured temperature, a value obtained by adding the temperature correction value to the measured temperature immediately before the diagnostic unit starts the diagnostic process. A temperature measuring device further comprising:

10. A power conversion device including the temperature measuring device according to claim 1, A power conversion device comprising a power conversion circuit for supplying power to the object to be temperature-measured.

11. A drive device including the temperature measuring device according to claim 1, A drive device including the motor that is the object to be temperature-measured.

12. A diagnostic method executed by a temperature measuring device for measuring the temperature of an object to be temperature-measured, a switching process for changing the amount of current flowing through a temperature measuring element attached to the object to be temperature-measured; a diagnostic process for determining that an abnormality has occurred in the temperature measuring element when the amount of change in the temperature measured by the temperature measuring element deviates from the normal range when the amount of current flowing through the temperature measuring element is increased by the switching process, The normal range is a variable range according to the value measured by the temperature measuring element. A diagnostic method.

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