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

Abstract

A temperature measurement device according to the present invention measures the temperature of a temperature measurement target and comprises: a temperature measurement element attached to the temperature measurement target; a switching unit for changing the amount of current flowing to the temperature measurement element; and a diagnosis unit for determining that an abnormality has occurred in the temperature measurement element in a case where the amount of change in temperature as measured by the temperature measurement element deviates from a normal range when the amount of current flowing to the temperature measurement element is increased by the switching unit. Said normal range is a variable range corresponding to the value measured by the temperature measurement element.

Description

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

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

[0002] Power conversion devices and drive devices convert DC power supplied from a DC power source into AC power to drive a motor. The output torque of a motor varies depending on the motor magnetic flux, and the amount of magnetic flux in the motor varies depending on the motor temperature. To keep the motor output torque constant regardless of the motor temperature, power conversion devices and drive devices sometimes correct the current flowing through the motor according to the motor temperature. In this case, if the motor temperature measurement means fails, the power conversion device and drive device may erroneously correct the current flowing through the motor, which can cause the motor output torque to fluctuate. For this reason, techniques for diagnosing failures in the temperature measurement means are known. Patent Document 1 discloses an assembled battery control device comprising: a detection means for detecting a physical quantity representing the battery state of an assembled battery consisting of a plurality of cells; a diagnosis means for diagnosing an abnormal state of the detection means; an estimation means for estimating the state of charge of the assembled battery based on the physical quantity detected by the detection means; a setting means for setting an allowable charge / discharge range representing the range of charge states within which the assembled battery can be used according to the abnormal state when an abnormality is diagnosed by the diagnosis means; and a control means for controlling the charging / discharging of the assembled battery so that the state of charge estimated by the estimation means falls within the allowable charge / discharge range.

[0003] Japanese Patent Application Publication No. 2011-041422

[0004] The invention described in Patent Document 1 leaves room for improvement in dealing with cases where the temperature of the object to be measured fluctuates greatly.

[0005] A temperature measuring device according to a first aspect of the present invention is a temperature measuring device that measures the temperature of an object to be measured, and includes a switching unit that changes the amount of current flowing through a temperature measuring element attached to the object to be measured, and a diagnostic unit that executes a diagnostic process to determine 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 being a variable range that varies depending on the value measured by the temperature measuring element.A power conversion device according to a second aspect of the present invention is a power conversion device that includes the above-mentioned temperature measuring device, and includes a power conversion circuit that supplies power to the object to be measured.A drive device according to a third aspect of the present invention is a drive device that includes the above-mentioned temperature measuring device, and includes a motor that is the object to be measured. A diagnostic method according to a fourth aspect of the present invention is a diagnostic method executed by a temperature measurement device that measures the temperature of an object to be measured, and includes a switching process that changes the amount of current flowing through a temperature measurement element attached to the object to be measured, and a diagnostic process that determines that an abnormality has occurred in the temperature measurement element if the amount of change in 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 process, wherein the normal range is a variable range that varies depending on the value measured by the temperature measurement element.

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

[0007] Configuration diagram of a vehicle equipped with a drive device Configuration diagram of the drive device Configuration diagram of the power conversion circuit and motor Configuration diagram of the motor temperature detection circuit Flowchart showing the processing of the diagnostic unit Diagram showing the concept of a normal range table Configuration diagram of the motor temperature detection circuit in the second embodiment Flowchart showing the processing of the diagnostic unit in the second embodiment Configuration diagram of a drive device in the third embodiment Flowchart showing the processing of the diagnostic unit in the third embodiment Flowchart showing the processing of the diagnostic unit in the fourth embodiment Diagram showing the state of the switch and the characteristics of voltage and temperature Flowchart showing the switch stuck-on diagnosis processing by the diagnostic unit Configuration diagram of a drive device in the fifth embodiment

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

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

[0010] 1, the drive unit 1 is installed on the front axle 902F of the vehicle 900, but the drive unit 1 may also be installed on the rear axle 902B. Also, the drive unit 1 may be installed on both the front axle 902F and the rear axle 902B, or independent drive units 1 may be installed on the left and right wheels instead of on the axles. The vehicle 900 may also be equipped with a power source other than the drive unit 1, such as an engine.

[0011] FIG. 2 is a configuration diagram of the drive device 1. A DC power supply 910, a control device 920, and a fault notification device 930 are connected to the drive device 1. The control device 920 transmits data indicating a target torque C2 and an operating mode C1 to the drive device 1. The control device 920 receives a fault notification signal C3 output by the drive device 1. Although only one control device 920 is shown in FIG. 2, multiple control devices 920 may be present. In this case, for example, the target torque C2 and the operating mode C1 may be output by different control devices 920, and the fault notification signal C3 may be received by multiple control devices 920.

[0012] The DC power supply 910 is a power supply, such as a battery, for driving the motor 3 built into the drive device 1. When the fault notification device 930 receives the fault notification signal C3 from the drive device 1, it notifies the passengers of the vehicle 900 of the occurrence of a fault. The fault notification device 930 notifies the passengers of the vehicle 900 of the occurrence of a fault by, for example, turning on a lamp, emitting a warning sound, or notifying by voice.

[0013] The drive unit 1 includes a power conversion device 2, a motor 3, and a reducer (not shown). The reducer amplifies the driving force of the motor 3 and transmits it to the axle or wheels. The motor 3 is a three-phase electric motor with three internal windings, and may be, for example, a synchronous motor using permanent magnets or an induction motor without permanent magnets. 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 this embodiment, an example will be described in which an NTC (Negative Temperature Coefficient) thermistor is used as the temperature measurement element.

[0015] The power conversion device 2 converts DC power obtained from a DC power supply 910 into AC power to drive the motor 3. The power conversion device 2 also has a function of converting the motive power of the motor 3 into DC power to charge the DC power supply 910. The power conversion device 2 internally 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. The power conversion circuit 23 receives a drive signal C5 from the driver circuit 22 to drive internal power semiconductors and control the current flowing to the motor 3. The internal configuration of the power conversion circuit 23 will be described with reference to FIG. 3 .

[0016] 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 semiconductors switch the six power semiconductors 232 on and off in response to a drive signal C5 input from the driver circuit 22, thereby converting DC power and AC power. The power semiconductors 232 are, for example, power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors).

[0017] The smoothing capacitor 231 is a capacitor that smoothes the current generated by switching the power semiconductor 232 on and off and suppresses ripples in 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). Methods for connecting the motor neutral point to the ground include a direct grounding method, a resistance grounding method, a compensation 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 as a DC voltage sensor value to the control circuit 21. 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 as an AC current sensor value to the control circuit 21. In this embodiment, three AC current sensors 25 are provided, one for each phase, but it is also possible to provide AC current sensors 25 for only two phases. Because the sum of the U-phase current, V-phase current, and W-phase current is zero, the remaining 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 phase.

[0019] The driver circuit 22 receives a PWM (Pulse Width Modulation) signal C4 output by the control circuit 21 and outputs a drive signal C5 for switching the power semiconductor 232 on and off. The motor temperature detection circuit 26 applies a voltage to a 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 an internal circuit in response to a signal output from the control circuit 21. This internal circuit is a switch SW1, which will be 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 the operation mode C1 and the 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. Furthermore, when the control circuit 21 determines that an internal fault has occurred, it outputs a fault notification signal C3 to the control device 920 and the fault notification device 930.

[0021] The control circuit 21 includes a CPU, RAM, ROM, and communication circuit (not shown). Instead of the ROM, the control circuit 21 may include an electrically erasable programmable ROM (EEPROM) or a flash ROM. 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 diagnostic unit 217. 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 diagnostic unit 217 are implemented by the CPU loading a program stored in the ROM into the RAM and executing it.

[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), etc. Furthermore, the control circuit 21 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 changes 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 transitions the operation state of the power conversion device 2 using the operation mode C1 and the fault notification signal C3 output by the diagnosis unit 217, and outputs the current operation state to the PWM signal generation unit 214. The operation state is, for example, a PWM state, a three-phase short-circuit state, a three-phase open state, etc.

[0024] The target current calculation unit 212 calculates the value of the current to be passed through the motor 3 and outputs this current value as the target current value to the current control unit 213. The target torque C2, the DC voltage sensor value, the motor speed value, and the motor temperature value are used to calculate the value of the current to be passed through the motor 3. The calculated value of the current to be passed through the motor 3 is the value of the current to be passed through the motor 3 so that the motor 3 outputs the same torque as the target torque C2. The target current value is expressed, 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 using the following equation 1. In equation 1, Pp is the number of pole pairs of the motor 3, Φ is the magnetic flux of the motor 3, Ld is the d-axis inductance of the motor 3, Lq is the q-axis inductance of the motor 3, Id is the d-axis current flowing through the motor 3, and Iq is the q-axis current flowing through the motor 3.

[0026] T=Pp{ΦIq+(Ld−Lq)IdIq} (Formula 1)

[0027] Here, since the motor magnetic flux Φ decreases as the motor temperature increases, 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 in accordance with the motor temperature. The target current calculation unit 212 corrects the target current in accordance with the motor temperature.

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

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

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

[0031] The diagnostic unit 217 diagnoses a fault in the temperature measuring element 32 mounted on the motor 3 or the motor temperature detection circuit 26 inside the power conversion device 2. When the diagnostic unit 217 detects a fault, it outputs the details of the fault location as a fault notification signal C3 to the state control unit 211 and the fault notification device 930. The diagnostic unit 217 has a normal range table 2171, which will be described later, and uses it to diagnose the motor temperature detection circuit 26.

[0032] The power conversion device 2 can be called a "temperature measurement device" because it has a built-in motor temperature detection circuit 26 and a motor temperature calculation unit 216. Similarly, the drive device 1 including the power conversion device 2 can also be called a "temperature measurement device."

[0033] 4 is a diagram of the motor temperature detection circuit 26. The motor temperature detection circuit 26 includes an internal power supply 26P1, resistors R1 and R2, and a switch SW1. The state of switch SW1 is controlled by a diagnostic unit 217 in the control circuit 21. Resistor R2 has a smaller resistance value than resistor R1. When switch SW1 is in the off state, the voltage of the internal power supply 26P1 is divided by resistor R1 and the temperature measuring element 32. Normally, switch SW1 is in the off state when measuring temperature. Note that switch SW1 may also be referred to as the "switching unit" below.

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

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

[0036] In the following step S304, the diagnostic unit 217 turns off the switch SW1 built into the motor temperature detection circuit 26. In the following step S305, the diagnostic unit 217 measures the temperature of the temperature measuring element 32. Hereinafter, the temperature measured in step S305 will be referred to as the "temperature after current increase." In the following step S306, the diagnostic unit 217 identifies a normal range of 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 steady-state temperatures and normal ranges of temperature change. In FIG. 6, the horizontal axis represents steady-state temperatures, and the vertical axis represents the amount of temperature change. The vertical distance between the two solid lines shown in FIG. 6 indicates the range of normal temperature change. The dashed and dashed dotted lines will be explained later. Note that if the temperature change is greater than the normal range, it is an abnormality where the resistance of the temperature measuring element 32 is low, and if the temperature change is smaller than the normal range, it is an abnormality where the resistance of the temperature measuring element 32 is high.

[0038] Specifically, the temperature change amount when switch SW1 is turned on can be calculated in advance based on the resistance value of the temperature measurement element 32 at each temperature, and the normal temperature change amount plus a width that takes into account the measurement error is set as the normal temperature change range. The width of the measurement error may be set as a fixed 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. Also, while FIG. 6 shows the normal range table 2171 as a graph, it may also be expressed in tabular form or as a mathematical expression such as a polynomial. Returning to FIG. 5, the explanation will continue.

[0039] In the following step S307, the diagnostic unit 217 calculates the temperature change amount, which is the difference between the low normal temperature and the temperature after the current increase, and determines whether this temperature change amount is within the normal range identified in step S306. If the diagnostic unit 217 determines that the temperature change amount is within the normal temperature change range, the process proceeds to step S308. If the diagnostic unit 217 determines that the temperature change amount is not within the normal temperature change range, the process proceeds to step S309. In step S308, the diagnostic unit 217 determines that the temperature measuring element 32 is normal, i.e., no abnormality is detected, and ends the process shown in FIG. 5. In step S309, the diagnostic unit 217 outputs a fault notification signal C3 to the state control unit 211 and the fault notification device 930, indicating that the temperature measuring element 32 is faulty, and ends the process shown in FIG. 5.

[0040] The effects of this embodiment are as follows. In Figure 6, the dashed line indicates the amount of temperature change that occurs when a failure occurs in which the resistance value of the temperature measuring element 32 decreases, and the dashed line indicates the amount of temperature change that occurs when a failure occurs in which the resistance value of the temperature measuring element 32 increases. When the resistance value of the temperature measuring element 32 decreases, the current flowing through the temperature measuring element 32 increases accordingly, and the heat generated by the temperature measuring element 32 increases, so the value of the amount of temperature change also increases. Conversely, when the resistance value of the temperature measuring element 32 increases, the current flowing through the temperature measuring element 32 decreases, and the heat generated by the temperature measuring element 32 decreases, so the value of the amount of temperature change also decreases. Therefore, it is possible to detect failures in which the resistance value of the temperature measuring element 32 decreases or increases by more than a certain amount based on the amount of temperature change.

[0041] Furthermore, by changing the normal temperature change range according to the steady-state temperature as in this embodiment, the temperature measuring element 32 can be diagnosed appropriately regardless of the temperature of the object to be measured. In this embodiment, the object to be measured is the motor 3, and the temperature of this motor 3 is affected by its previous driving conditions. For example, if the motor 3 has not been driven for a long time, the motor temperature will be approximately equal to the ambient temperature, and if the motor 3 has just been driven, the motor temperature will be high. The temperature of the temperature measuring element 32 is close to the temperature of the motor 3, which is the object to be measured, and the resistance value of the temperature measuring element 32 changes depending on the temperature of the temperature measuring element 32.

[0042] The amount of temperature change during diagnosis is affected by the resistance value of the temperature measuring element 32, and so the normal temperature change range changes depending on the temperature of the object to be measured. If the object to be measured is always at a constant temperature, a fault in the temperature measuring element 32 can be correctly diagnosed even if the normal temperature change range is fixed. However, if a fixed normal temperature change range is used when the temperature of the object to be measured varies greatly, as in this embodiment, problems may arise such as incorrectly detecting a fault in the temperature measuring element 32 when it is actually normal, or incorrectly determining that the temperature measuring element 32 is normal when it is actually faulty.

[0043] The first embodiment described above provides the following advantageous effects. (1) The power conversion device 2, which can also be called a temperature measurement device, measures the temperature of the motor 3, which is an object to be measured. The power conversion device 2 includes a switch SW1 that changes the amount of current flowing through a temperature measurement element 32 attached to the motor 3, and a diagnostic unit 217 that determines that an abnormality has occurred in the temperature measurement element 32 if the amount of change in temperature 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 ). The normal range is a variable range determined by referring to a normal range table 2171 and corresponding to the value measured by the temperature measurement element 32 (S306 in FIG. 5 ). Therefore, a failure in the temperature measurement element can be correctly diagnosed even in an environment where the temperature of the object to be measured fluctuates greatly.

[0044] (2) The power conversion device 2 includes a power conversion circuit 23 that supplies power to the motor 3, which is the object whose temperature is to be measured.

[0045] (3) The driving device 1 includes a motor 3, which is an object whose temperature is to be measured.

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

[0047] - Second embodiment - A second embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described with reference to Figures 7 and 8. In the following description, the same components as in the first embodiment are designated by the same reference numerals, and differences will be mainly described. Points that are not particularly described are the same as in the first embodiment. In this embodiment, the main difference from the first embodiment is the processing performed when the steady-state temperature is lower than a predetermined threshold value.

[0048] FIG. 7 is a configuration diagram of a motor temperature detection circuit 26A according to the second embodiment. In addition to the configuration of the motor temperature detection circuit 26 according to the first embodiment, the motor temperature detection circuit 26A further includes a second internal power supply 26P2 and a second switch SW2. 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 a diagnostic 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 diagnostic unit 217, as in the first embodiment.

[0049] 8 is a flowchart showing the processing of the diagnostic unit 217 in the second embodiment. In step S301, the diagnostic unit 217 measures the temperature of the temperature measuring element 32, i.e., the steady-state temperature. In the following step S312, the diagnostic unit 217 determines whether the steady-state temperature exceeds a second threshold value, which is a predetermined threshold value. If the diagnostic unit 217 determines that the steady-state temperature exceeds the first threshold value, it executes the processing of steps S302 to S304, as in the first embodiment.

[0050] If the diagnostic unit 217 determines that the steady-state temperature does not exceed the first threshold, the process proceeds to step S314. In steps S314 to S316, the diagnostic unit 217 turns on the second switch SW2, waits a certain period of time, and then turns off the second switch SW2. Note that the "certain period of time" in step S315 is the same length as the "certain period of time" in step S303. Upon completion of either step S304 or step S316, the diagnostic unit 217 executes the processes of steps S305 to S309, as in the first embodiment. Note that the normal range table 2171 in this embodiment differs from that in the first embodiment. When the steady-state temperature is lower than the first threshold, the second switch SW2 is turned on, causing the temperature measuring element 32 to heat up more than in the first embodiment. Therefore, the normal range table 2171 is generated taking this effect into account.

[0051] The advantages 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 amount of temperature change between normal and faulty conditions, making it difficult to accurately determine whether the temperature measurement element 32 is faulty. This is because the resistance of the temperature measurement element 32 is large when the temperature of the temperature measurement element 32 is low, so even if the resistance of the temperature measurement element 32 increases or decreases slightly due to a fault, there is no significant difference in the amount of temperature change. To solve this problem, in the second embodiment, when the steady-state temperature is low, the second switch SW2 is turned on to apply the second internal power supply 26P2, which has a higher voltage than the internal power supply 26P1, to the resistor R2 and the temperature measurement element 32, thereby increasing the current flowing through the temperature measurement element 32 compared to when the switch SW1 is turned on. This increases the amount of temperature change of the temperature measurement element 32 compared to when the switch SW1 is turned on, making it possible to more accurately determine whether the temperature measurement element 32 is faulty.

[0052] The second embodiment described above provides the following advantageous effects: (4) When the value measured by the temperature measuring element is smaller than the first threshold value (NO in S312 of FIG. 8), the diagnostic unit 217 increases the amount of current flowing through the temperature measuring element 32 based on the switch SW compared to when the value measured by the temperature measuring element is larger than the first threshold value (YES in S312 of FIG. 8). This makes it possible to more accurately determine whether the temperature measuring element 32 is faulty, even at low temperatures.

[0053] (Variation of the Second Embodiment) In the second embodiment described above, the second switch SW2 is turned on when the steady-state temperature is equal to or lower than the first threshold. Because the voltage of the second internal power supply 26P2 is higher than that of the internal power supply 26P1, a larger 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. In other words, the conduction time may be lengthened instead of increasing the amount of current flow.

[0054] -Third embodiment- A third embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described with reference to Figures 9 and 10. In the following description, the same components as in the first embodiment are given the same reference numerals, and differences will be mainly described. Points that are not particularly described are the same as in the first embodiment. This embodiment differs from the first embodiment mainly in that, at low temperatures, the motor is warmed up before diagnosis.

[0055] 9 is a configuration diagram of a drive device 1B according to the third embodiment. A diagnosis unit 217 according to the third embodiment outputs a motor drive request signal to a state control unit 211 and a 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 diagnosis 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 diagnosis unit 217.

[0056] 10 is a flowchart showing the processing of the diagnosis unit 217 in the third embodiment. In step S331, the diagnosis unit 217 measures the temperature of the temperature measuring element 32, i.e., the steady-state temperature. However, in this embodiment, as will be described later, this step may be executed multiple times. In this case, the last measured temperature is used as the steady-state temperature. In other words, the steady-state temperature is updated each time step S331 is executed.

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

[0058] Step S333 is described in detail below. The diagnosis 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 diagnosis unit 217, and if the current operating state is a three-phase short-circuit state or a three-phase open state, it switches the operating state to a PWM state. The target current calculation unit 212 receives the motor drive request signal from the diagnosis unit 217, and increases the total amount of target current within a range in which the amount of change in motor output torque remains within a certain value. For example, if the motor 3 is stopped and the motor output torque is 0 Nm, by passing only the d-axis current through the motor 3, the total amount of target current can be increased while the motor output torque remains 0 Nm, according to Equation 1.

[0059] Furthermore, from Equation 1, it can be seen that the q-axis current affects both the torque due to the motor magnetic flux and the torque due to inductance, while the d-axis current affects only the torque due to inductance. This shows that the output torque of a synchronous motor is significantly affected by the q-axis current, while the d-axis current has a smaller effect than the q-axis current. Therefore, when motor 3 is in a driving state and d-axis and q-axis currents flow through motor 3, the d-axis current can be increased and the q-axis current can be reduced to maintain the output torque of motor 3, thereby increasing the total amount of target current while minimizing the amount of change in output torque. Note that if changing the target current causes a large fluctuation in the output torque of motor 3, this will affect vehicle operation. Therefore, in this embodiment, the target current is changed within a range where the amount of change in motor output torque does not affect operation.

[0060] In step S334, the diagnosis unit 217 stops the application of current to the motor 3, which began in step S333, and executes the processing from step S302 onwards. The processing from step S302 onwards is the same as in the first embodiment, and therefore a description thereof will be omitted. The normal range table 2171 in this embodiment may be the same as in the first embodiment. This is because, if the temperature at the start of processing by the diagnosis unit 217 is low, the steady-state temperature is forcibly raised above the second threshold value by the processing of steps S331 to S333, and therefore it is not necessary to take into account a situation in which the steady-state temperature is low, as in the second embodiment.

[0061] The effects of this embodiment are as follows. As described in the second embodiment, with the method of the first embodiment, if the temperature of the temperature measuring element 32 is low when the operation of the diagnostic unit 217 is started, it is difficult to correctly determine whether there is a failure in the temperature measuring element 32. To solve this problem, in the third embodiment, if the steady-state temperature is low, the current flowing through the motor 3 is increased to cause the motor 3 to generate heat, and a diagnosis is performed after the steady-state temperature exceeds the second threshold, thereby making it possible to more accurately determine whether there is a failure in the temperature measuring element 32.

[0062] The third embodiment described above provides the following advantageous effects. (5) The object of temperature measurement by the motor temperature detection circuit 26 is the motor 3. If 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 passes current through the motor 3 (S333), and after the value measured by the temperature measurement element 32 exceeds the second threshold value (S332: YES), performs an abnormality determination of the temperature measurement element 32 (S302 to S309). This makes it possible to more accurately determine a failure of the temperature measurement element 32 even at low temperatures.

[0063] (6) The diagnosis unit 217 controls the current so that the current flowing through the motor 3 is maximized while keeping the torque output by the motor 3 within a certain range from the target value (S333).

[0064] Fourth Embodiment A fourth embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described with reference to Figures 11 to 13. In the following description, the same components as in the first embodiment are designated by the same reference numerals, and differences will be mainly described. Points that are not specifically described are the same as in the first embodiment. This embodiment differs from the first embodiment mainly in that it detects the sticking of a switch built into the motor temperature detection circuit 26.

[0065] In the first embodiment, a fault in the temperature measuring element 32 is determined by switching the switch SW1 built into the motor temperature detection circuit 26. However, if this switch SW1 fails, it becomes impossible to perform accurate temperature measurement and fault determination. For example, if a fault occurs in which the switch SW1 is turned off while being controlled to be on (a stuck-off fault), the current flowing through the temperature measuring element 32 does not increase, and the temperature measuring element 32 is unable to generate heat. As a result, there is no difference between the current increase temperature and the steady-state temperature, and in diagnosing the temperature measuring element 32, it may be erroneously determined that the temperature measuring element 32 is faulty even though it is not.

[0066] Furthermore, if a fault (a stuck-on fault) occurs in which switch SW1 is turned on while being controlled to be off, it is not possible to measure the temperature when switch SW1 is off. As a result, when diagnosing the temperature measuring element 32, it may be erroneously determined that the temperature measuring element 32 is faulty even though it is not. For this reason, it is necessary to distinguish between a stuck-off fault and a stuck-on fault of switch SW1.

[0067] Fig. 11 is a flowchart showing the processing of the diagnosis unit 217 in the fourth embodiment. Fig. 11 is a flowchart showing the processing of Fig. 5 in the first embodiment with the addition of a stuck-off fault diagnosis of the switch SW1, and a description of the same processing as in Fig. 5 will be 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 the switch SW1 is turned on, the diagnosis unit 217 measures the temperature again in step S351.

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

[0069] If a stuck-off failure of the switch SW1 occurs, it is not possible to correctly diagnose the temperature measuring element 32. Therefore, after a stuck-off failure of the switch SW1 is detected, the diagnosis process for the temperature measuring element 32 is not performed.

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

[0071] For example, when the currently measured temperature is Ta, the measured voltage in the off state is Va, and when the switch SW1 is controlled to the on state, the measured voltage changes to Vb. If the motor temperature calculation unit 216 converts the measured voltage to temperature using the voltage-temperature characteristics when the switch SW1 is off, the measured temperature when the measured voltage is Vb is Tb, so when the switch SW1 changes from the off state to the on state, the measured temperature changes from Ta to Tb.

[0072] If a stuck-off fault occurs in switch SW1, switch SW1 will remain off even if diagnostic unit 217 controls switch SW1 to be on. In this case, the voltage measured by diagnostic unit 217 remains at Va, and the measured temperature also remains at Ta. Therefore, if the difference between the measured temperature when switch SW1 is off and the measured temperature when switch SW1 is on is less than the third threshold, it can be determined that switch SW1 has a stuck-off fault.

[0073] 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 used as the third threshold value based on the currently measured temperature. Alternatively, the minimum value of the previously calculated amount of temperature change for each measured temperature when the switch SW1 is switched may be used as the third threshold value. While the present embodiment uses the difference in measured temperatures to determine whether the switch SW1 is stuck-off, a similar fault determination can also be made using the difference in measured voltage.

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

[0075] If the diagnostic unit 217 determines in step S372 that the temperature difference is equal to or greater than the fourth threshold, the process proceeds to step S373. If the diagnostic unit 217 determines that the temperature difference is less than the fourth threshold, the process proceeds to step S374. In step S373, the diagnostic unit 217 outputs a fault notification signal C3 to the state control unit 211 and the fault notification device 930, indicating that switch SW1 has a stuck-on fault, and the process proceeds to step S375. In step S374, the diagnostic unit 217 determines that switch SW1 is normal, i.e., that a stuck-on fault has not occurred in switch SW1, and the process proceeds to step S375. In step S375, the diagnostic unit 217 saves the temperature measured in step S371 for use in the next diagnosis, and the process shown in FIG. 13 ends.

[0076] If a stuck-on failure of the switch SW1 is detected, the temperature when the switch SW1 is turned off cannot be measured, and therefore the diagnosis of the temperature measuring element 32 cannot be performed correctly. Therefore, after a stuck-on failure of the switch SW1 is detected, the diagnosis process of the temperature measuring element 32 is not performed. In other words, in this embodiment, the diagnosis process of the temperature measuring element 32 is performed only when a stuck-on failure of the switch SW1 is not detected and a stuck-off failure of the switch SW1 is not detected.

[0077] The motor 3, which is the temperature measurement target in this embodiment, has a large thermal time constant, so a large temperature change does not occur in a short period of time. On the other hand, as described in the explanation of FIG. 12, the measured temperature changes significantly when the switch SW1 changes from off to on. By utilizing this fact and executing the stuck-on diagnostic process shown in FIG. 13 at short intervals, a large change in temperature occurs only when the switch SW1 experiences a stuck-on fault, making it possible to detect a stuck-on fault.

[0078] For example, the fourth threshold value may be calculated in advance for each measured temperature by calculating the amount of temperature change when switch SW1 is switched from off to on, and may be switched to match the currently measured temperature. Alternatively, the fourth threshold value may always be the minimum value among the previously calculated amounts of temperature change for each measured temperature when switch SW1 is switched. While this embodiment uses the difference in measured temperatures to determine whether switch SW1 is stuck on, a similar fault can also be determined using the difference in measured voltage.

[0079] The effects of this embodiment are as follows. As described above, if a stuck-off failure or a stuck-on failure occurs in the switch SW1, there is a possibility that the temperature measurement element 32 will be erroneously determined to be faulty even though it is not. In this embodiment, the presence or absence of a stuck-off failure or a stuck-on failure of the switch SW1 is diagnosed, and if either failure is detected, the diagnosis of the temperature measurement element 32 is stopped thereafter, thereby preventing erroneous determination of a failure in the temperature measurement element 32.

[0080] The fourth embodiment described above provides the following advantageous effects: (7) If the difference in the measured temperatures before and after the switching unit switches the amount of current is smaller than the third threshold (NO in S352 of FIG. 11 ), the diagnosis unit 217 determines that the switch SW1 is stuck-off abnormal. Therefore, the switch SW1 can be detected as being stuck-off abnormal.

[0081] (8) If the temperature difference measured within a certain period of time is equal to or greater than the fourth threshold (YES in S372 of FIG. 13), the diagnosis unit 217 determines that the switch SW1 is stuck on. Therefore, the switch SW1 is detected as being stuck on.

[0082] (9) Only when it is determined that no abnormality has occurred in the switching unit, the diagnostic unit 217 performs the abnormality determination process (S302 to S309) for the temperature measuring element 32. Therefore, it is possible to detect an abnormality in the temperature measuring element 32 after confirming that the switch SW1 is not stuck off or stuck on.

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

[0084] Fifth Embodiment A fifth embodiment of a power conversion device and a drive device, which can also be called a temperature measurement device, will be described with reference to Fig. 14. In the following description, the same components as those in the first embodiment are designated by the same reference numerals, and differences will be mainly described. Points that are not particularly described are the same as those in the first embodiment. This embodiment differs from the first embodiment mainly in that the temperature is corrected during diagnosis of the temperature measurement element 32.

[0085] 14 is a configuration diagram of a drive device 1 according to a fifth embodiment. In this embodiment, a diagnosis execution signal is input to a motor temperature calculation unit 216 from a diagnosis unit 217, a target current is input from a target current calculation unit 212, and a motor speed is input from a 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 according to this embodiment outputs a diagnosis execution signal to the motor temperature calculation unit 216 while diagnosing the temperature measuring element 32.

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

[0087] Losses in the motor 3 can be divided into copper loss and iron loss. Copper loss can be calculated from the winding resistance within the motor 3 and the value of the current flowing through the motor 3. Iron loss also varies depending on the value of the current flowing through the motor 3 and the motor speed. Because the value of the current 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 pre-recorded winding resistance value of the motor 3 and the target current. Iron loss information corresponding to the current flowing through the motor 3 and the motor speed is also pre-recorded, 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. The motor speed calculation unit 215 then calculates the temperature rise of the motor 3 due to the current motor operating conditions from the copper loss of the motor 3, the iron loss of the motor 3, and the pre-recorded thermal time constant of the motor 3, and sets this as a temperature correction value. Note that while an example is shown in which the target current is used as the value of the current flowing through the motor 3, an AC current sensor value may also be used as the value of the current flowing through the motor 3.

[0088] The effects of this embodiment are as follows: In the first embodiment, while diagnosing the temperature measuring element 32, a current is passed through the temperature measuring element 32 to generate heat, making it impossible to accurately measure the temperature of the motor 3, which is the object of temperature measurement. In this embodiment, while diagnosing the temperature measuring element 32, a value obtained by adding a temperature correction value according to the current operating status of the motor to the temperature measured immediately before the diagnosis is output as the measured temperature, so the temperature of the motor 3 can be measured more accurately even during diagnosis.

[0089] According to the fifth embodiment described above, the following advantageous 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 value of the current 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 while the diagnosis unit 217 is performing a diagnosis, and outputs a value obtained by adding the temperature correction value to the temperature measured immediately before the diagnosis unit 217 starts the diagnosis as the measured temperature. Therefore, the temperature of the motor 3 can be measured more accurately even during the diagnosis.

[0090] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0091] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented in software, with a processor interpreting and executing a program that implements each function. Information such as the programs, tables, and files that implement each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0092] In the above-described embodiments and modifications, the functional block configurations are merely examples. Some functional configurations shown as separate functional blocks may be integrated, or a configuration shown in a single functional block diagram may be divided into two or more functions. Furthermore, some of the functions of each functional block may be provided by 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. Other embodiments conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention.

[0094] 1: Drive 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 measuring device that measures the temperature of an object to be measured, comprising: a switching unit that changes an amount of current flowing through a temperature measuring element attached to the object to be measured; and a diagnostic unit that executes a diagnostic process to determine 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, wherein the normal range is a variable range that varies depending on the value measured by the temperature measuring element.

2. A temperature measuring device as described in claim 1, wherein the diagnostic unit controls the switching unit so that when the value measured by the temperature measuring element is smaller than a first threshold value, the amount of current flowing through the temperature measuring element or the time for which current is flowing is larger than when the value measured by the temperature measuring element is larger than the first threshold value.

3. A temperature measuring device as described in claim 1, wherein the object to be measured is a motor, and the diagnostic unit causes a current to flow through the motor when the value measured by the temperature measuring element is smaller than a second threshold value, and determines whether the temperature measuring element is abnormal after the value measured by the temperature measuring element exceeds the second threshold value.

4. A temperature measuring device as claimed in claim 3, wherein the diagnostic unit controls the current flowing through the motor so that the current is maximized while the torque output by the motor falls within a certain range from a target value.

5. A temperature measuring device as described in claim 1, wherein the diagnostic unit determines that an abnormality has occurred in the switching unit if the difference between the values ​​measured by the temperature measuring element before and after the switching unit changes the amount of current flowing through the temperature measuring element is smaller than a third threshold value.

6. A temperature measuring device as claimed in claim 1, wherein the diagnostic unit determines that an abnormality has occurred in the switching unit if the difference in measured temperature within a certain period of time is equal to or greater than a fourth threshold value.

7. A temperature measuring device as claimed in claim 5, wherein the diagnostic section performs the diagnostic process only when it is determined that no abnormality has occurred in the switching section.

8. A temperature measuring device according to claim 6, wherein the diagnostic section performs the diagnostic process only when it is determined that no abnormality has occurred in the switching section.

9. A temperature measuring device as described in claim 1, wherein the object to be measured is a motor, and further comprising: means for acquiring the rotation speed of the motor and the value of the current flowing through the motor; and temperature calculation means for calculating a temperature correction value using the rotation 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.

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

11. A drive device including the temperature measuring device according to claim 1, the drive device including a motor as the object of temperature measurement.

12. A diagnostic method executed by a temperature measuring device that measures the temperature of an object to be measured, comprising: a switching process for changing an amount of current flowing through a temperature measuring element attached to the object to be measured; and a diagnostic process for determining 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 process, wherein the normal range is a variable range that varies depending on the value measured by the temperature measuring element.

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