JP6205208B2 - Overheat prevention device, overheat prevention method, and overheat prevention program - Google Patents

Description

  The present invention relates to an overheating prevention device, an overheating prevention method, and an overheating prevention program for preventing overheating of a driving device such as a motor.

  Conventionally, when there is a possibility that the motor is overheated due to overload or the like, a method for preventing overheating in advance by attaching a temperature sensor directly to the motor and measuring the temperature of the motor is known. However, with such a method, the cost of the temperature sensor itself, the wiring cost, the cost of the temperature sensor input circuit of the controller that controls the motor, and the like will increase greatly.

  On the other hand, there is a technique for reducing costs by preventing motor overheating by software processing. For example, when a state where a certain duty (for example, 40%) or more continues for a certain time (for example, about 5 seconds), fail control is performed to stop the motor drive. However, with such a method, there is a problem that motor overheating cannot be detected with a duty equal to or lower than a certain duty. Further, if the above-described constant duty is set to a small value, the fail control is performed even if the motor temperature is below the limit of the motor temperature for a certain time or more, and the performance of the motor is remarkably deteriorated.

  In order to compensate for the above-described drawbacks, there is a method of estimating the motor temperature from the motor duty or current value. For example, the motor drive duty or drive current is integrated to calculate the thermal energy input to the motor, the heat dissipation energy from the motor is calculated from the estimated motor temperature, and the input energy related to the temperature rise is calculated from the difference between the two To do. By such a method, it becomes possible to estimate the temperature of the motor without a temperature sensor, and the above disadvantage can be compensated by controlling the driving of the motor using the estimated temperature.

  As a related technique, in a motor control device having an electronic thermal function, a technique is known that enables quick restart after a motor stop while reliably performing overheat protection of the motor (see, for example, Patent Document 1). ).

Japanese Patent No. 4526418

  However, if the motor drive return timing is too early after the motor overheat is detected and the fail control is performed, that is, if the motor is started without passing through the cooling period, the motor temperature has decreased sufficiently. Absent. When such a case is repeated, the difference between the estimated temperature of the motor and the actual temperature increases, the actual temperature of the motor continues to rise, and the preset upper limit temperature of the motor is exceeded. Arise. If the actual temperature of the motor exceeds the upper limit temperature of the motor, various parts such as coils, wiring, and bearings constituting the motor and peripheral members of the motor may be damaged.

  The present invention has been made to solve the above-described problems, and an overheat prevention device, an overheat prevention method, and an overheat prevention that can prevent overheating of the drive device even when the drive return timing of the drive device is early. The purpose is to provide a program.

  In order to solve the above-described problem, according to one aspect of the present invention, the heat dissipation energy is calculated based on the heat dissipation coefficient of the drive device corrected by a correction value for increasing the estimated temperature of the drive device. A calculation unit that calculates input heat energy input to the drive device based on a drive duty or a drive current for driving, and calculates the estimated temperature based on the heat radiation energy and the input heat energy; and the estimation A determination unit that determines whether or not the temperature exceeds a preset upper limit temperature, and a control unit that performs fail control on the drive device when it is determined that the estimated temperature exceeds the upper limit temperature.

  According to another aspect of the present invention, the overheat prevention device calculates heat radiation energy based on a heat radiation coefficient of the drive device corrected by a correction value for increasing the estimated temperature of the drive device, and drives the drive device. The input heat energy input to the drive device is calculated based on the drive duty for causing the estimated temperature to be calculated based on the heat radiation energy and the input heat energy, and the estimated temperature is set to a preset upper limit. It is determined whether or not the temperature is exceeded, and when it is determined that the estimated temperature exceeds the upper limit temperature, the drive device is subjected to fail control.

  In one embodiment of the present invention, a computer calculates heat radiation energy based on a heat radiation coefficient of the driving device corrected by a correction value for increasing the estimated temperature of the driving device, and drives the driving device. The input heat energy input to the drive device is calculated based on the drive duty, and the estimated temperature is calculated based on the heat radiation energy and the input heat energy, and the estimated temperature is preset. A determination unit that determines whether or not the upper limit temperature is exceeded, and if it is determined that the estimated temperature exceeds the upper limit temperature, the drive device is caused to function as a control unit that performs fail control.

  According to the present invention, overheating of the drive device can be prevented even when the drive return timing of the drive device is early.

It is a block diagram which shows TVC concerning this Embodiment, and the hardware constitutions of an electronic control valve. It is a figure which shows the coil temperature correction table showing the relationship between coil fall temperature and IPD fall temperature. It is a figure which shows the thermal radiation coefficient correction table showing the relationship between a coil raise temperature and a correction coefficient. It is a functional block diagram which shows the function structure of TVC. It is a flowchart which shows a motor overheat determination process. It is a flowchart which shows a drive ON / OFF hysteresis process. It is a flowchart which shows a thermal radiation energy calculation process. It is a flowchart which shows an input heat energy calculation process.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, an explanation will be given by taking as an example the case where the present invention is applied to a TVC (Trottle Valve Controller) that performs drive control of an electronic control valve (for example, an exhaust valve) used in an automobile or the like. However, the present invention is not limited to this, and the present invention can be applied to any device that controls a driving device that needs to prevent overheating with heat generation from a motor or the like.

  First, the TVC according to the present embodiment will be described. FIG. 1 is a block diagram showing a hardware configuration of a TVC and an electronic control valve according to the present embodiment. As shown in FIG. 1, the TVC 1 according to the present embodiment performs drive control of the electronic control valve 2 by performing a motor overheat determination process, which will be described later, and includes a CPU (Central Processing Unit) 101, IPD (Intelligent Power Device) 102. The TVC 1 includes a temperature sensor 103, a memory 104, an EEPROM (Electrically Erasable Programmable Read-Only Memory) 105, and a power supply control circuit 106. The TVC 1 includes a power supply circuit 107, a watchdog circuit 108, a power supply voltage detection circuit 109, an IGN (ignition) voltage detection circuit 110, and a CAN (controller area network) interface circuit 111.

  The CPU 101 is applied with a voltage of 2.5 V as a reference voltage, and controls the entire TVC1. The IPD 102 obtains a PWM pulse signal from the IPD drive duty obtained from the CPU 101 based on the voltage applied from the MOTOR BATT (motor battery), and applies the pulse voltage obtained from the PWM pulse signal to the coil 201. The motor 20 is driven by PWM control. The temperature sensor 103 detects the temperature of the IPD 102 and outputs the result to the CPU 101. The memory 104 is a volatile storage device in which various programs and temporary data are expanded, and the EEPROM 105 is a nonvolatile storage device that records an estimated coil temperature and the like described later.

  The power supply control circuit 106 is applied with an IGN voltage and a power supply voltage from a BATT (battery), and supplies power from the BATT to the power supply circuit 107. The power supply circuit 107 supplies stable power to the CPU 101. The power supply control circuit 106 is instructed by the CPU 101 even when the power supply of the system including the TVC 1 and the electronic control valve 2 is turned off, that is, when the ignition key switch is turned off (Key Off) and the IGN is turned off. The latch circuit supplies power to the CPU 101. The power supply control circuit 106 allows the CPU 101 to receive power until the estimated coil temperature is written to the EEPROM 105 even after the power is turned off. Note that the power supply circuit 107 is monitored by the watchdog circuit 108 for normal operation.

  The power supply voltage detection circuit 109 detects the voltage applied to the power supply circuit 107 and outputs the result to the CPU 101. The IGN voltage detection circuit 110 detects the IGN voltage applied to the power supply control circuit 106 and outputs the result to the CPU 101. Based on the detection result of the IGN voltage detection circuit 110, the CPU 101 determines whether the power is on or off.

  The CAN interface circuit 111 connects a host device (not shown) and the CPU 101, and the CPU 101 receives control drive duty, power ON / OFF, and the like from the host device through the CAN interface circuit 111, and executes appropriate processing. . For example, the CPU 101 is connected to an ECM (Engine Control Module) via the CAN interface circuit 111.

  As shown in FIG. 1, the electronic control valve 2 is a so-called butterfly valve that includes a motor 20 and that rotates a valve body (not shown) when the motor 20 is driven. The motor 20 includes a coil 201 and a TPS (Throttle Position Sensor) 202. The motor 20 is a torque motor that is driven by applying a pulse voltage controlled by the IPD 102 to the coil 201. The TPS 202 detects the angle of the valve body described above and outputs the detection result to the CPU 101. The motor 20 includes a coil 201.

  Next, in order to facilitate understanding of the present embodiment, an outline of the motor overheat determination process performed by the TVC 1 will be described. The motor overheat determination process calculates an estimated coil temperature from the heat radiation energy of the motor 20 and the input heat energy to the coil 201, and determines whether to fail the motor 20 based on the estimated coil temperature. It is processing. In this motor overheat determination process, in this embodiment, the heat dissipation coefficient corrected by the correction value for increasing the estimated temperature of the motor 20 is used in calculating the heat dissipation energy. In other words, a heat dissipation coefficient set lower than the ideal value is used. The ideal value here is a value obtained from the temperature simulation processing result of the actual machine (such as the electronic control valve 2), and setting low means that the ideal value is lowered by a predetermined ratio. For example, when the heat dissipation coefficient is lowered by 10% (in the case of −10%), the actual temperature of the coil 201 increases by 1.5 ° C. in 320 seconds. Therefore, 10 to 20% of the ideal value is suitable as the predetermined ratio. From the above, the correction by the correction value for increasing the estimated temperature described above corresponds to subtracting 10 to 20% of the heat dissipation coefficient from the heat dissipation coefficient.

  Further, in the motor overheat determination process according to the present embodiment, it is determined whether or not to fail depending on whether or not the estimated coil temperature exceeds the upper limit temperature. This upper limit temperature is set based on an error in the coil 201, that is, an error in coil resistance. More specifically, the maximum value of the estimated coil temperature error derived from the coil resistance error in the coil 201 is a predetermined member provided in the motor 20 and a member whose upper limit temperature is lower than that of the coil 201. Is the value subtracted from the upper limit temperature of

  A coil bobbin or the like around which the coil 201 is wound is a resin member, but has a heat resistant temperature higher than that of the bearing. For example, in the present embodiment, the heat resistance temperature of the wire of the coil 201 is 180 ° C., but the heat resistance temperature of the bearing is 150 ° C. In this case, the upper limit temperature of the motor 20 is preferably 150 ° C. Here, an error may occur even in the estimated coil temperature, but the error is mainly caused by an error of the coil resistance of the coil 201. Therefore, it is preferable to consider the influence of the coil resistance error on the estimated coil temperature. For example, when the coil resistance is 0.75Ω ± 0.075Ω, the estimated coil temperature error due to this coil resistance error is about ± 5 ° C. For example, if the upper limit of the environmental temperature of the motor 20 is 108 ° C., the allowable temperature increase of the motor 20 is preferably 150 ° C.−108 ° C.−5 ° C. = 37 ° C.

  Further, in the motor overheat determination process according to the present embodiment, when the power is turned off, the current estimated coil temperature is stored in the EEPROM 105, and immediately after the power is turned on again, the estimated coil temperature is read and the estimated coil temperature is read out. It is determined whether to fail the motor 20 based on the coil temperature. Here, it is preferable to correct the read estimated coil temperature with a correction value for lowering the estimated coil temperature in consideration of the temperature at which the motor 20 decreases from the power OFF to the power ON.

  FIG. 2 is a diagram showing a coil temperature correction table showing the relationship between the coil lowering temperature and the IPD lowering temperature. As shown in FIG. 2, when the power is turned off, for example, if the IPD 102 is lowered by 11 ° C., the coil 201 is lowered by 16 ° C., and if the IPD 102 is lowered by 14 ° C., the coil 201 is lowered by 26 ° C. If the IPD lowering temperature is calculated from the difference between the temperature of the IPD 102 before the power is turned off and the temperature of the IPD 102 after the power is turned on based on this table, the lowering temperature of the coil 201 can be obtained. In the motor overheat determination process according to the present embodiment, the obtained reduced temperature is used as the correction value described above.

  In the motor overheat determination process according to the present embodiment, the heat dissipation coefficient is calculated based on the heat dissipation coefficient by multiplying the heat dissipation coefficient by a correction coefficient corresponding to the estimated temperature rise of the coil 201. FIG. 3 is a diagram showing a heat dissipation coefficient correction table representing the relationship between the coil rising temperature and the correction coefficient. As shown in FIG. 3, the correction coefficient increases as the coil temperature rises. In the motor overheat determination process according to the present embodiment, the heat dissipation coefficient is multiplied by a correction coefficient corresponding to the estimated temperature increase of the coil 201 using this table. The estimated rise temperature is obtained by the difference between the latest estimated coil temperature and the previous estimated coil temperature. As described above, the motor overheat determination processing as described above is realized by each function that cooperates to realize hardware resources such as the memory 104 included in the TVC 1.

  Next, the functional configuration of the TVC 1 will be described. FIG. 4 is a functional block diagram showing the functional configuration of the TVC. As shown in FIG. 4, the TVC 1 includes a temperature calculation unit 301, a determination processing unit 302, a temperature storage unit 303, a temperature correction unit 304, and a drive control unit 305 as functions. Note that these functions are realized by cooperation of hardware resources provided in the TVC 1 such as the CPU 101 and the memory 104 described above.

  The temperature calculation unit 301 calculates heat radiation energy based on the heat radiation coefficient of the motor 20 corrected by the correction value for increasing the estimated temperature of the motor 20, and based on the drive duty or drive current for driving the motor 20. The input heat energy input to the coil 201 is calculated, and the estimated coil temperature is calculated based on the heat radiation energy and the input heat energy. Further, the temperature calculation unit 301 obtains an estimated increase temperature from the difference between the latest estimated coil temperature and the previous estimated coil temperature, calculates a correction coefficient from the estimated increase temperature based on the heat dissipation coefficient correction table, and calculates the heat dissipation energy. calculate.

  The determination processing unit 302 performs various determinations in the motor overheat determination process, such as determining whether the estimated coil temperature exceeds a preset upper limit temperature. When the stop of the motor 20 is instructed, the temperature storage unit 303 stores the estimated coil temperature and the temperature of the IPD 102 in the EEPROM 105. The temperature correction unit 304 reads the estimated coil temperature stored in the EEPROM 105 immediately after the motor 20 is stopped and started, and corrects the estimated coil temperature with a correction value for lowering the estimated coil temperature. Further, immediately after the motor 20 is stopped and started, the temperature correction unit 304 calculates a decrease temperature from the difference between the current temperature of the IPD 102 and the temperature of the IPD stored in the EEPROM 105, and based on the coil temperature correction table, A correction value for lowering the estimated coil temperature corresponding to the decreased temperature is calculated. When it is determined that the estimated coil temperature exceeds a preset upper limit temperature, the drive control unit 305 performs various drive controls of the motor 20 based on the drive duty and the drive current, such as fail control of the motor 20.

  Next, details of the motor overheat determination process by the TVC 1 will be described. FIG. 5 is a flowchart showing a motor overheat determination process according to the present embodiment. Note that the motor overheat determination processing in the present embodiment is executed for each sample (for example, every 5 msec), and is continuously executed until the power is turned off. Further, the motor overheat determination process is executed with the power-on as a trigger.

  First, as shown in FIG. 5, the temperature correction unit 304 reads the estimated coil temperature and the temperature of the IPD 102 stored in the EEPROM 105 by the temperature storage unit 303 when the power is turned off (S101), and performs the estimated coil temperature correction process (S101). S102).

  Here, the estimated coil temperature correction process will be described. First, the temperature correction unit 304 acquires the current temperature of the IPD 102 and subtracts the temperature from the temperature of the IPD 102 stored in the EEPROM 105. The temperature correction unit 304 obtains the coil lowering temperature corresponding to this result from the coil temperature correction table shown in FIG. 2, and subtracts it from the estimated coil temperature stored in the EEPROM 105, thereby obtaining an estimated coil temperature close to the actually measured value. obtain. Note that the estimated coil temperature may be stored in the EEPROM 105 by the temperature storage unit 303 after this processing.

  After the estimated coil temperature correction processing, the determination processing unit 302 performs drive ON / OFF hysteresis processing (S103). Here, the driving ON / OFF hysteresis processing will be described with reference to FIG. FIG. 6 is a flowchart showing drive ON / OFF hysteresis processing. First, the determination processing unit 302 acquires a preset upper limit temperature (upper limit temperature based on the above-described coil resistance error) (S201), and determines whether or not the fail flag is OFF (S202). The fail flag is information indicating whether or not fail control is currently being performed. When the fail flag is OFF (S202, YES), the determination processing unit 302 determines whether or not the estimated coil temperature exceeds the upper limit temperature (S203). When the estimated coil temperature exceeds the upper limit temperature (S203, YES), the determination processing unit 302 sets the fail flag to ON (S204), and the drive ON / OFF hysteresis process ends.

  On the other hand, when the estimated coil temperature does not exceed the upper limit temperature (S203, NO), the determination processing unit 302 maintains the fail flag OFF and ends the drive ON / OFF hysteresis processing. If the fail flag is not OFF in step S202 (S202, NO), the determination processing unit 302 determines whether or not the estimated coil temperature is equal to or lower than the return coil temperature (S205). When the estimated coil temperature is equal to or lower than the return coil temperature (S205, YES), the determination processing unit 302 sets the fail flag to OFF (S206), and ends the drive ON / OFF hysteresis process. On the other hand, when the estimated coil temperature is not equal to or lower than the return coil temperature (S205, YES), the determination processing unit 302 maintains the fail flag ON, and the drive ON / OFF hysteresis process ends.

  Returning to FIG. 5, after the drive ON / OFF hysteresis process, the determination processing unit 302 determines whether or not the fail flag is OFF (S104). When the fail flag is OFF (S104, YES), the drive control unit 305 gives the control drive duty from the host device to the IPD 102 as the IPD drive duty (S105), and proceeds to the next sample (S107). On the other hand, when the fail flag is ON (S104, NO), the drive control unit 305 performs fail control by notifying the host device of a coil overheat fail and giving the IPD drive duty to 0 (zero) to the IPD 102 ( S106), the process proceeds to the next sample (S107).

  Next, the temperature calculation unit 301 performs a heat dissipation energy calculation process (S108) and an input heat energy calculation process (S109), adds the calculated heat dissipation energy and the input heat energy, and performs a heat energy integration process. The estimated coil temperature at the current sample is calculated (S110). After the calculation, the process returns to step S103 and the drive ON / OFF hysteresis process is performed. Hereinafter, the heat radiation energy calculation process and the input heat energy calculation process will be described with reference to FIGS. 7 and 8.

  FIG. 7 is a flowchart showing the heat radiation energy calculation process. As shown in FIG. 7, first, the temperature calculation unit 301 integrates a preset heat dissipation coefficient (a heat dissipation coefficient set lower than the ideal value described above) and the estimated coil temperature at the previous sample (S301). ). After the integration, the temperature calculation unit 301 acquires a correction coefficient corresponding to the difference between the estimated coil temperature at the previous sample and the estimated coil temperature at the previous sample from the heat dissipation coefficient correction table (S302). After the acquisition, the temperature calculation unit 301 integrates the integration result and the correction coefficient again to calculate the heat radiation energy (S303), and the heat radiation energy calculation process ends.

  FIG. 8 is a flowchart showing the input heat energy calculation process. As shown in FIG. 8, the temperature calculation unit 301 integrates a predetermined copper temperature coefficient and the estimated coil temperature at the previous sample (S401), adds 1 to the integration result, and serves as a reference coil resistance ( For example, the coil resistance at the estimated coil temperature is calculated by multiplying the addition result by (coil resistance at 25 ° C.) (S402). After the calculation, the temperature calculation unit 301 performs absolute value processing on the IPD driving duty at the time of the previous sample, and calculates the control driving voltage by integrating the result and the power supply voltage (S403). After the calculation, the temperature calculation unit 301 calculates the control drive current by multiplying the control drive voltage by the coil resistance at the estimated coil temperature, and calculates the input power by integrating the control drive current and the control drive voltage (S404). . After the calculation, the temperature calculation unit 301 integrates the predetermined temperature increase coefficient and the input power, calculates the input heat energy (S405), and the input heat energy calculation process ends. Note that step S403 may be performed prior to steps S401 and S402.

  According to the present embodiment, the estimated coil temperature can be set higher than the actual temperature by using the heat dissipation coefficient set lower than the ideal value in calculating the heat dissipation energy. Therefore, the actual temperature of the motor 20 tends to decrease even when the drive recovery timing of the motor 20 after the determination of overheating of the motor 20 (after fail control) is early. Therefore, the change in the motor temperature after the determination of overheating of the motor 20 can be reduced without increasing, and motor overheating can be prevented.

  Further, according to the present embodiment, motor overheating can be prevented more accurately by setting the upper limit temperature based on the coil resistance error in the coil 201. Also, the estimated coil temperature when the power is turned off and the temperature of the IPD 102 are recorded, and the estimated coil temperature is a correction value for lowering the estimated coil temperature in consideration of the temperature at which the motor 20 decreases from the power supply OFF to the power supply ON. It is corrected. By correcting in this way, it is possible to calculate the estimated coil temperature more accurately and to reduce the performance of the motor 20 even when the power is turned off and on repeatedly. Further, the estimated coil temperature can be calculated more accurately by multiplying the heat dissipation coefficient by a correction coefficient corresponding to the estimated temperature rise of the coil 201 and calculating the heat dissipation energy based on the heat dissipation coefficient.

  In the present embodiment, it has been described that the estimated coil temperature in each sample is calculated while using the heat dissipation coefficient set lower than the ideal value. However, the present invention is not limited to this. For each of a plurality of samples, an ideal heat dissipation coefficient may be used as it is. By alternately lowering the heat dissipation coefficient in this way, it is possible to prevent the actual coil temperature from being excessively lowered.

  In the present embodiment, the correction value for lowering the estimated coil temperature is determined based on the coil temperature correction table. However, the present invention is not limited to this, and the correction value may be a fixed value.

  Further, in the present embodiment, it has been described that the estimated coil temperature and the temperature of the IPD 102 are written to the EEPROM 105 when the power is turned off. However, the present invention is not limited to this. You may make it write out suitably.

  In addition, by incorporating the various steps described in this embodiment into an existing TVC as an overheat prevention program, the above-described functions can be realized in the TVC.

  The present invention can be implemented in various other forms without departing from the gist or main features thereof. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is shown by the scope of claims, and is not restricted by the text of the specification. Moreover, all modifications, various improvements, substitutions and modifications belonging to the equivalent scope of the claims are all within the scope of the present invention.

  The overheat prevention device described in the claims corresponds to, for example, the TVC 1 in the above-described embodiment, and the drive device corresponds to, for example, the motor 20. Further, the calculation unit corresponds to, for example, the temperature calculation unit 301, and the determination unit corresponds to, for example, the determination processing unit 302. The control unit corresponds to the drive control unit 305, for example. The storage unit corresponds to the temperature storage unit 303, for example, and the correction unit corresponds to the temperature correction unit 304, for example. The estimated temperature corresponds to, for example, the estimated coil temperature, and the coil corresponds to, for example, the coil 201. The storage device corresponds to the EEPROM 105, for example. The intelligent power device corresponds to, for example, the IPD 102, and the predetermined member included in the motor corresponds to, for example, a bearing.

  DESCRIPTION OF SYMBOLS 1 TVC, 2 Electronic control valve, 8 Information processing apparatus, 9 Recording medium, 20 Motor, 101 CPU, 102 IPD, 103 Temperature sensor, 104 Memory, 105 EEPROM, 106 Power supply control circuit, 107 Power supply circuit, 108 Watchdog circuit, 109 power supply voltage detection circuit, 110 IGN voltage detection circuit, 111 CAN interface circuit, 301 temperature calculation unit, 302 determination processing unit, 303 temperature storage unit, 304 temperature correction unit, 305 drive control unit

Claims (9)

The heat dissipation coefficient of the drive device corrected with the correction value for increasing the estimated temperature of the drive device is multiplied by a correction coefficient corresponding to the estimated temperature rise of the coil provided in the drive device, and the heat dissipation energy is calculated based on the heat dissipation coefficient And calculating the input heat energy input to the drive device based on a drive duty or drive current for driving the drive device, and calculating the estimated temperature based on the heat radiation energy and the input heat energy. A calculation unit for calculating,
A determination unit that determines whether or not the estimated temperature exceeds a preset upper limit temperature;
An overheat prevention device comprising: a controller that performs fail control on the drive device when it is determined that the estimated temperature exceeds the upper limit temperature. The overheat prevention device according to claim 1, wherein the heat dissipation coefficient is a value obtained by lowering a heat dissipation coefficient obtained from a temperature simulation processing result in the drive device by a predetermined percentage. The overheat prevention device according to claim 1, wherein the upper limit temperature is set based on an error of coil resistance in a coil included in the drive device. The upper limit temperature is a value obtained by subtracting the maximum value of the estimated temperature error derived from the error of the coil resistance from the upper limit temperature of a member provided in the driving device and having an upper limit temperature lower than that of the coil. The overheat prevention device according to claim 3. A storage unit that stores the estimated temperature in a nonvolatile storage device when an instruction to stop the drive device is given;
Immediately after the drive device is stopped and started, a correction unit that reads the estimated temperature stored in the storage device and corrects it with a correction value for lowering the estimated temperature, and
The overheat prevention device according to any one of claims 1 to 4, wherein the determination unit determines whether or not the corrected estimated temperature exceeds the upper limit temperature. The storage unit stores, in the storage device, the temperature of an intelligent power device that drives and controls the drive device based on the drive duty or the drive current when an instruction to stop the drive device is given,
The correction unit calculates a decrease temperature from the difference between the current temperature of the intelligent power device and the temperature of the intelligent power device stored in the storage device immediately after the drive device is stopped and started, and the decrease The overheat prevention device according to claim 5, wherein a correction value for decreasing the estimated temperature is determined based on a temperature. The overheat prevention device according to claim 2, wherein the predetermined ratio is 10% or more and 20% or less. Overheat prevention device
The heat dissipation coefficient of the drive device corrected with the correction value for increasing the estimated temperature of the drive device is multiplied by a correction coefficient corresponding to the estimated temperature rise of the coil included in the drive device, and the heat dissipation energy is calculated based on the heat dissipation coefficient. And calculating the input heat energy input to the drive device based on the drive duty for driving the drive device, calculating the estimated temperature based on the heat radiation energy and the input heat energy,
Determining whether the estimated temperature exceeds a preset upper limit temperature,
An overheating prevention method of performing fail control on the drive device when it is determined that the estimated temperature exceeds the upper limit temperature. Computer
The heat dissipation coefficient of the drive device corrected with the correction value for increasing the estimated temperature of the drive device is multiplied by a correction coefficient corresponding to the estimated temperature rise of the coil provided in the drive device, and the heat dissipation energy is calculated based on the heat dissipation coefficient Calculation to calculate the input heat energy input to the drive device based on the drive duty for driving the drive device, and to calculate the estimated temperature based on the heat radiation energy and the input heat energy And
A determination unit that determines whether or not the estimated temperature exceeds a preset upper limit temperature;
When it is determined that the estimated temperature exceeds the upper limit temperature, an overheat prevention program for causing the drive device to function as a control unit that performs fail control.

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