JP2014181012A - On-vehicle load overheat preventive apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an on-vehicle heater overheat preventive apparatus which can prevent load overheat inexpensively without use of a thermistor.SOLUTION: A connection load 28 and a power source 30 are connected through an FET26, and the FET26 is controlled by ECU12. When the FET26 is driven in a predetermined duty ratio by PWM control of the periodic time, an FET26 taking a time for reaching the temperature at which an overheat protecting function operates and which is equal to the time for reaching a temperature for detection of overheat of the connection load 28 is selected.

Description

  The present invention relates to an on-vehicle load overheat prevention device for preventing overheating of a load such as a heater mounted on a vehicle.

  As shown in FIG. 5, a load such as a heater mounted on a vehicle includes a PCT (Positive Temperature Coefficient) thermistor 54 and a load 52 controlled by an ECU (Electronic Control Unit) 50. When the PTC thermistor 54 detects overheating, the resistance value increases greatly. Therefore, the energization current to the load 52 can be cut off, and abnormal overheating of the load can be prevented.

  Moreover, as a vehicle-mounted temperature control apparatus provided with the thermistor, the technique of patent document 1 is proposed, for example.

  In Patent Document 1, at least a current control element driven by a temperature signal of the thermistor and a thermistor disconnection protection circuit that interrupts a current flowing through the current control element when the thermistor is disconnected are provided, and a linear heating element is provided. This is a vehicle temperature controller that adjusts the temperature of the warmed product for the vehicle using the temperature signal of the thermistor. When an abnormally high voltage is superimposed on the power supply voltage of the vehicle-mounted temperature controlled object, the thermistor disconnection protection circuit is A vehicle-mounted temperature control device that is configured to operate in a pseudo manner for almost the same period as the superposition period is proposed.

Japanese Patent Laid-Open No. 2004-127591

  However, the above-described PCT thermistor used for overheating prevention is expensive and there is room for improvement because the heater drive system cannot be set inexpensively in the vehicle.

  The present invention has been made in consideration of the above facts, and an object of the present invention is to provide an in-vehicle heater overheat prevention device that can prevent overheating of a load at low cost without using a thermistor.

  In order to achieve the above-mentioned object, the invention according to claim 1 is mounted on an automobile and driven by power from a predetermined power source, and is connected between the load and the power source. A heat generation protection function that operates to cut off power supply from the power source to the load when a predetermined heat generation protection temperature is reached, and the load reaches a predetermined overheat temperature from the start of power supply to the load; Switching means for operating the heat protection function when a heat generation protection time corresponding to an arrival time until reaching the heat generation protection temperature has elapsed, and supplying the power of the power source to the load And a control means for controlling.

  According to the first aspect of the present invention, the load is mounted on the automobile and is driven by a predetermined power source. As the load, various heaters such as a seat heater and a steering heater may be applied, or other loads may be applied.

  The switching means is connected between the load and the power supply, and has an overheat cutoff function that operates to cut off the power supply from the power supply to the load when a predetermined overheat temperature is reached. That is, the power of the power source can be supplied to the load by switching by the switching means, and the power supply from the power source to the load is cut off when the predetermined heat generation protection temperature is reached, and the overheating of the switching means is prevented.

In addition, the switching means corresponds to the arrival time from the start of power supply to the load until the load reaches a predetermined overheat temperature, and the heat generation protection function is activated when the heat generation protection time that rises to the heat generation protection temperature has elapsed. It is like that. That is, since the arrival time until the load reaches the overheat temperature corresponds to the heat generation protection time until the heat generation protection function of the switching means is activated, the heat generation protection function of the switching means can prevent additional overheating. . Therefore, it is possible to prevent overheating of the load without using a thermistor. Note that, as in the invention according to claim 2, voltage detecting means for detecting the voltage of the power source and the temperature inside the vehicle are detected. And a temperature detection means, and the control means further controls the switching means so as to correct the deviation of the correspondence between the arrival time and the heat generation protection time based on the detection results of the voltage detection means and the temperature detection means. You may make it do. That is, even if the correspondence between the heat generation protection time when the heat generation protection function is activated and the arrival time is deviated depending on the voltage or the vehicle interior temperature, it can be corrected, so that the heat generation protection function of the switching means can reliably prevent the heat generation of the load. it can.

  In this case, the control means adjusts at least one of the duty ratio and the period of the pulse width modulation to correct the correspondence between the arrival time and the heat generation protection time, as in the invention described in claim 3. You may make it control a switching means. By controlling the switching means with the pulse width modulation method and adjusting the duty ratio and period of the pulse width modulation, the heat generation protection time of the switching means can be adjusted, so the load reaches the overheat temperature for the heat generation protection time It becomes possible to adjust to the arrival time until.

  Further, as in the invention described in claim 4, the control means further includes voltage detection means for detecting the voltage of the power source and temperature detection means for detecting the temperature inside the vehicle, and the control means includes the voltage detection means and the temperature. Based on the detection result of the detection means, the arrival time may be further predicted, and the switching means may be further controlled to stop the supply of power to the load when the predicted arrival time is reached. That is, if the voltage of the power supply and the temperature inside the vehicle are known, the arrival time until the load overheat temperature is reached can be predicted, so the arrival time is predicted, and the switching means is controlled when the predicted arrival time is reached to control the load Preventing overheating of the load by stopping the supply of power to As a result, in addition to preventing overheating of the hardware load using the heat generation protection function of the switching means, overheating prevention of the soft load is performed, so it is possible to reliably prevent overheating of the load by double fail safe. Can do. At this time, as in the invention described in claim 5, the control means predicts the arrival time as a time longer than the heat generation protection time during which the heat generation protection function is activated. Also good. That is, priority may be given to the prevention of overheating of the load by the heat generation protection function of the switching means, and the overheating prevention of the load by the software control means may be supplementarily performed.

  As described above, according to the present invention, the thermistor can be operated by using the switching means in which the heat generation protection function operates in the heat generation protection time corresponding to the arrival time until reaching the predetermined overheat temperature at which it is desired to detect overheating of the load. There is an effect that it is possible to provide an on-vehicle heater overheat prevention device that can prevent overheating of the load at low cost without using it.

It is a block diagram which shows the structure of the vehicle-mounted load overheat prevention apparatus which concerns on embodiment of this invention. (A) is a figure which shows the temperature of the connection load with respect to time passage when a connection load is driven by PWM control of a predetermined duty ratio and cycle, and (B) is PWM control of a predetermined duty ratio and cycle. It is a figure which shows the heat_generation | fever temperature of FET with respect to time passage when driving FET. It is a figure which shows an example of FET from which the time until it reaches heat generation protection detection temperature differs. It is a flowchart which shows an example of the flow of the process performed by ECU of the vehicle-mounted load overheat prevention apparatus which concerns on embodiment of this invention. It is a figure which shows the prior art example of the load which incorporated the PTC thermistor.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the on-vehicle load overheat prevention device according to the first embodiment of the present invention.

  As shown in FIG. 1, in the vehicle load overheat prevention device 10, an ECU (Electronic Control Unit) 12 is connected to a connection load 28, and the drive of the connection load 28 is controlled by the ECU 12.

  As the connection load 28, for example, various heaters such as a seat heater and a steering heater can be applied. Moreover, you may make it apply the load which needs to prevent overheating other than a heater. In the following, a case where a heater is applied as the connection load 28 will be described.

  As shown in FIG. 1, the ECU 12 includes a microcomputer in which a CPU 14, a ROM 16, a RAM 18, and an I / O (input / output interface) 20 are connected to a bus 19.

  The ROM 16 stores a program for controlling the drive of the connection load 28 and various data such as various tables and mathematical formulas. The program stored in the ROM 16 is expanded in the RAM 18 and executed by the CPU 14. The drive of the connection load 28 is controlled. In addition, as a program memorize | stored in ROM16, the connection load overheat prevention program mentioned later is memorize | stored as an example.

  A power supply monitoring unit 22 and a vehicle interior temperature monitoring unit 24 are connected to the I / O 20, and a connection load 28 is connected via an FET (Field effect transistor) 26.

  The power supply monitoring unit 22 monitors the voltage of the power supply 30 that supplies power to the CPU 14 and the connection load 28, and the vehicle interior temperature monitoring unit 24 monitors the vehicle interior temperature using a temperature sensor or the like.

  As the FET 26, an FET with a heat generation protection function is applied, and when the FET 26 reaches a predetermined heat generation protection temperature, the energization to the connection load 28 is cut off. For example, since the voltage of the FET 26 increases with heat generation, the power supply from the power source 30 to the connection load 28 is interrupted by the voltage increase, thereby functioning as a heat generation protection function.

  In the present embodiment, when the FET 26 is driven by PWM (Pulse Width Modulation) control (pulse width modulation method) with a predetermined duty ratio and cycle, the time from the start of energization until the heat generation protection temperature is reached by the heat generation protection function. However, the FET 26 that substantially matches the time until the temperature at which the overload of the connection load 28 is desired to be detected is applied. That is, when the heat generation protection function of the FET 26 is activated, the temperature at which the overload of the connection load 28 is detected is reached. Therefore, the overheating of the connection load 28 can be prevented by the heat generation protection function of the FET 26.

  Here, a method of selecting the above-described FET 26 with a heat generation protection function will be described.

  The temperature of the connection load 28 is measured by driving the connection load 28 by PWM control with a predetermined duty ratio and cycle under the conditions of a predetermined vehicle interior temperature and a predetermined power supply voltage, and the temperature is shown in FIG. As described above, the time t1 from the start of energization until the temperature at which the overload of the connection load 28 is desired to be detected (for example, 60 ° C.) is measured.

  Similarly, the FET 26 is driven by PWM control with a predetermined duty ratio and cycle under conditions of a predetermined in-vehicle temperature and a predetermined power supply voltage, and the heat generation temperature of the FET 26 is measured, as shown in FIG. As described above, the time t2 from the start of energization until the temperature at which the overheat protection function operates (for example, 150 ° C.) is measured.

  The FET 26 has different heat generation temperatures such as A to C in FIG. 2B depending on the on-resistance and the package (the size of the FET 26, etc.), so that the FET 26 reaches a temperature at which overheating of the connection load 28 is desired to be detected. The FET 26 at time t2 until the temperature at which the overheat protection function is activated, which coincides with the time t1, is selected. As a result, the time t2 until the temperature at which the FET 26 overheat protection activation is activated can correspond to the time t1 until the temperature at which the overload of the connection load 28 is desired to be detected, so that the heat generation protection function of the FET 26 is used. By doing so, it is possible to prevent overheating of the connection load 28, and a PTC thermistor or the like becomes unnecessary.

  By the way, even if the FET 26 is selected as described above, when the power supply voltage or the vehicle interior temperature changes from the preconditions (the conditions of the vehicle interior temperature and the power supply voltage determined in advance), the connection load 28 is There is a difference between the heater time t1 and the FET 26 time t2.

  Therefore, in the present embodiment, the time t1 is adjusted by adjusting at least one of the duty ratio and the period when the FET 26 is driven by PWM control based on the monitoring results of the power supply voltage monitoring unit 22 and the in-vehicle temperature monitoring unit 24. And the time t2 are corrected.

  By adjusting at least one of the duty ratio and the period when the FET 26 is PWM-controlled, the load heat generation curve of the FET 26 changes as indicated by A to C in FIG. The time to reach (C) also varies. In the example of FIG. 3, the time until the heat generation protection detection temperature is reached changes from t2 to t4.

  Specifically, when the duty ratio is increased, the heat generation amount of the FET 26 is increased. When the duty ratio is decreased, the heat generation amount of the FET 26 is decreased. When the PWM cycle is shortened, the heat generation amount is increased. Since it decreases, the time t1 and the time t2 are matched by using this.

  For example, when the heater load heat generation time is greater than the FET heat generation time, since the FET 26 is mounted on a copper foil substrate and has better heat dissipation than the heater load, heat generation of the FET 26 can be suppressed by reducing the PWM control duty ratio. Thus, the heater load and the heat generation time of the FET 26 can be combined. Alternatively, since the switching loss of the FET 26 is reduced by delaying the PWM control cycle, the heat generation time of the FET 26 can be delayed and the heater load and the heat generation time of the FET 26 can be combined.

  Further, when the heater load heat generation time is smaller than the FET heat generation time, the switching loss of the FET 26 is increased by increasing the PWM control period. Therefore, the heat generation time of the FET 26 can be shortened, and the heat generation of the heater load and the FET 26 is achieved. The time can be adjusted. Alternatively, by increasing the duty ratio of the PWM control, the heat generation amount of the FET 26 can be increased, and the heater load and the heat generation time of the FET 26 can be matched.

  However, the control for adjusting at least one of the duty ratio and the cycle needs to be measured in advance by changing the duty ratio and the cycle of the PWM control under various conditions of the power supply voltage and the in-vehicle temperature. The result is stored in the ROM 16 as a correspondence relationship such as a table or a mathematical formula, and is corrected based on the stored correspondence relationship. Thereby, it is possible to correct the difference between the time t1 and the time t2.

  Further, in the present embodiment, in addition to the hardware overheating prevention using the heat generation protection function of the FET 26, a function for preventing the connection load 28 from being overheated in software is provided. The function of preventing the connected load 28 from being overheated in software is realized by the above-described connected load overheat prevention program.

  Specifically, a time t1 until the temperature at which the overload of the connection load 28 is desired to be detected is predicted from the power supply voltage and the vehicle interior temperature. If the power supply voltage and the vehicle interior temperature are known, the time t1 until the temperature at which the overload of the connection load 28 is desired to be detected can be predicted from the duty ratio and cycle of the PWM control, so the time t1 is predicted and predicted. What is necessary is just to control FET26 which stops the drive of FET26 when time t1 passes. At this time, in the present embodiment, the driving of the FET 26 is not stopped when the predicted time t1 has elapsed, and the driving of the FET 26 is stopped when the time obtained by adding a predetermined value to the predicted time t1 has elapsed. To be controlled. As a result, hardware overheating prevention is preferentially performed, and soft overheating prevention is performed as fail safe for hardware overheating prevention. That is, in this embodiment, the hardware and software are double fail-safe.

  In the present embodiment, hardware overheating prevention (overheating prevention using the overheating protection function of the FET 26) is basically performed. Therefore, the overheating protection function of the FET 26 is prioritized and software overheating prevention is performed later. However, on the contrary, priority may be given to soft overheat prevention. In this case, the drive of the FET 26 may be controlled to stop when a time obtained by subtracting a predetermined value from the predicted time t1 has elapsed.

  Then, the effect | action of the vehicle-mounted load overheat prevention apparatus 10 which concerns on embodiment of this invention comprised as mentioned above is demonstrated. FIG. 4 is a flowchart showing an example of a flow of processing performed by the ECU 12 of the on-vehicle load overheat prevention device 10 according to the embodiment of the present invention. 4 is performed by executing the above-described connected load overheat prevention program, and starts when the heater of the connected load 28 is turned on and ends when the heater is turned off. Will be described.

  First, in step 100, the driving of the FET 26 is started and the time count-up is started, and the process proceeds to step 102. That is, when the FET 26 is driven with a predetermined duty ratio and a predetermined PWM control cycle, the voltage of the power supply 30 is applied to the heater as the connection load 28 and the heater is overheated. At the same time, the CPU 14 counts up the time for counting the time from the start of overheating.

  In step 102, the voltage of the power supply 30 monitored by the power supply voltage monitoring unit 22 is acquired, and the in-vehicle temperature monitored by the in-vehicle temperature monitoring unit 24 is acquired, and the process proceeds to step 104.

  In step 104, the CPU 14 determines whether or not it is necessary to correct the driving of the FET 26. The determination is based on whether the time t1 until the temperature at which the overload of the connection load 28 is desired to be detected is different from the time t2 until the heat generation protection temperature by the heat generation protection function of the FET 26 is deviated. If the determination is affirmative, the process proceeds to step 106. If the determination is negative, the process proceeds to step 108. More specifically, for example, it is determined whether or not the acquired power supply voltage or in-vehicle temperature is an environment in which the driving of the FET 26 needs to be corrected. That is, the determination is made using a table or mathematical expression (duty ratio or PWM control cycle for driving the FET 26 corresponding to the power supply voltage or the vehicle interior temperature) stored in advance in the ROM 16.

  In step 106, the driving correction of the FET 26 is performed, and the routine proceeds to step 108. That is, based on the acquired power supply voltage and in-vehicle temperature, at least one of the duty ratio for driving the FET 26 and the PWM control cycle is changed. As a result, a deviation between the time t1 until the temperature at which the overload of the connection load 28 is desired to be detected and the time t2 until the heat generation protection temperature by the heat generation protection function of the FET 26 is reached is corrected. Therefore, it is possible to reliably prevent overheating of the connection load 28 by using the heat generation protection function of the FET 26.

  In step 108, based on the power supply voltage and the vehicle interior temperature acquired in step 102, the predicted heating time (time t1 until reaching the temperature at which it is desired to detect overheating of the connected load 28) is predicted, and the routine proceeds to step 110.

  In step 110, it is determined whether or not the predicted overheating time has been reached. If the determination is negative, the process returns to step 102 and the above processing is repeated. If the determination is affirmative, the process proceeds to step 112.

  In step 112, the driving of the FET 26 is stopped by the CPU 14, and the time count-up is reset, and the process proceeds to step 114. As a result, even when the heat generation protection function of the FET 26 is not activated due to a failure or the like, the driving of the FET 26 is stopped in software, so that it is possible to reliably prevent the connection load 28 from being overheated.

  In step 114, it is determined whether or not the driving of the FET 26 is resumed. The determination is made, for example, by determining whether or not a predetermined time has elapsed (time when the FET 26 and the connection load 28 are equal to or lower than a predetermined temperature), and waits until the determination is affirmed. By the way, a series of processing is returned, and the processing from step 100 is started again.

  As described above, in the in-vehicle load overheat prevention device 10 according to the present embodiment, until reaching the temperature at which the overheat protection function operates, which approximately coincides with the time t1 until the temperature at which the overload of the connection load 28 is desired to be detected is reached. By selecting the FET 26 at the time t2, the overload of the connection load 28 can be prevented using the heat generation protection function of the FET 26 without using an effective PTC thermistor or the like.

  Further, by executing the above processing, it is possible to prevent overheating of the connection load in terms of software in addition to the hardware overheating prevention by the heat generation protection function of the FET 26, so the connection load 28 can be overheated with double fail-safe. It can be surely prevented.

  In the above embodiment, an example of performing both hardware overheating prevention and software overheating prevention has been described. However, either one may be performed, but hardware overheating prevention is better. Since there is no software runaway and so on, the reliability is high. Therefore, when only one of them is performed, it is preferable to prevent hardware overheating.

10 On-vehicle load overheat prevention device 12 ECU
22 Power supply monitoring unit 24 Car interior temperature monitoring unit 26 FET
28 Connection load 30 Power supply

Claims (5)

A load mounted on an automobile and driven by power from a predetermined power source;
The load is connected between the load and the power source, and has a heat generation protection function that operates to cut off power supply from the power source to the load when a predetermined heat generation protection temperature is reached. Switching means in which the heat generation protection function is activated when a heat generation protection time corresponding to an arrival time from the start of power supply to the load reaching a predetermined overheat temperature and rising to the heat generation protection temperature has elapsed,
Control means for controlling the switching means to supply power of the power source to the load;
A vehicle load overheat prevention device comprising: Voltage detection means for detecting the voltage of the power supply; and temperature detection means for detecting the temperature inside the automobile;
The control means further controls the switching means so as to correct a corresponding deviation between the arrival time and the heat generation protection time based on detection results of the voltage detection means and the temperature detection means. The vehicle load overheat prevention device according to claim 1.   3. The control unit according to claim 2, wherein the control unit controls the switching unit to adjust a correspondence deviation between the arrival time and the heat generation protection time by adjusting at least one of a duty ratio and a period of pulse width modulation. In-vehicle load overheat prevention device. Voltage detection means for detecting the voltage of the power supply; and temperature detection means for detecting the temperature inside the automobile;
The control means further predicts the arrival time based on the detection results of the voltage detection means and the temperature detection means, and stops supplying power to the load when the predicted arrival time is reached. The in-vehicle load overheat prevention device according to any one of claims 1 to 3, further controlling the switching means.   The on-vehicle load overheat prevention device according to claim 4, wherein the control means predicts, as the arrival time, a time longer than the heat generation protection time during which the heat generation protection function is activated when the arrival time is predicted.

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