JP2016082780A - Motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an element of a circuit and a coil of a motor from being damaged when heat is stored in the element of the circuit and the coil of the motor caused by motor lock or the like.SOLUTION: A motor control device comprises: a current detection part 94 for outputting a signal corresponding to a current value between a battery 80 and an inverter circuit 40 which generates a voltage to be applied to a coil 14 of a motor 52; an overcurrent determination value output part 100 which outputs an overcurrent determination value for determining whether the motor 52 is in an overcurrent state; a thermistor RT which detects a temperature; a bridge resistor RB which connects an output terminal of the thermistor RT and an output terminal of the overcurrent determination value output part 100 in order to adjust the overcurrent determination value; an overcurrent determination part 102 which determines that the motor 52 is in the overcurrent state if a signal output by the current detection signal 94 is equal to or higher than the overcurrent determination value; and an FET driver 70 which stops electrification to the coil 14 if the overcurrent determination part 102 determines that the motor 52 is in the overcurrent state.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a motor control device.

  In blower motors (hereinafter abbreviated as “motors”) used to blow air conditioners for vehicles, the rotation of the motor is increased when the rotation of the fan is hindered by foreign matter such as dead leaves entering from the outside of the vehicle and the motor load increases. Perform overload protection control to reduce speed. By executing such overload protection, overheating of the motor control circuit and the motor stator coil due to overload is prevented.

  In Patent Document 1, a thermistor detects the temperature of a shunt resistor in which the amount of heat generation increases as the current value of the motor coil increases, and energization of the motor coil occurs when the temperature of the thermistor exceeds a predetermined value. An overload protection device for a motor drive system that suppresses noise is disclosed.

Japanese Patent No. 3801015

  However, the overload protection device of the motor drive system described in Patent Document 1 is such that the motor coil and the motor control device elements are overheated in the case of a motor lock in which the rotation of the motor is stopped as a result of foreign matter or the like interfering with the fan. There was a problem that it was easily damaged.

  When the motor is a brushless DC motor, a coil of the motor is provided around a rotor composed of a permanent magnet, and a so-called rotating magnetic field is generated by appropriately switching the polarity of a voltage applied to the coil. The rotor configured by the permanent magnet rotates following the rotating magnetic field generated in the coil, so that the motor operates. The motor control device switches the polarity of the voltage applied to the coil in accordance with the rotation of the rotor.

  However, when the rotation of the rotor is stopped by the motor lock, the polarity of the voltage applied to the motor coil is not switched and the voltage of the same polarity is continuously applied to the motor coil. Excessive current tends to flow through the generated control device elements and motor coils.

  The overload protection device for a motor drive system described in Patent Document 1 stops energization of the motor coil when the current of the motor coil becomes excessive and the temperature of the shunt resistance exceeds a predetermined value. To do. Then, after the energization is stopped, energization of the motor coil is resumed when the temperature of the shunt resistor falls below a predetermined value.

  A shunt resistor, which is made of a nickel-based alloy having relatively good thermal conductivity and has a small element volume, drops in temperature in a relatively short time if no current flows. However, elements other than the shunt resistor mounted on the motor coil and the motor control device board do not dissipate heat as easily as the shunt resistor when overheated by the motor lock.

  FIG. 11 is a schematic diagram illustrating an example of a temperature change of the element mounted on the substrate of the motor drive system when the motor lock occurs. In FIG. 11, the peak temperature rises due to the motor lock, and the temperature drop after the peak is due to the stop of energization of the motor coil. FIG. 11 shows a case where the motor lock is continued, and the stop and restart of energization to the motor coil are continuously performed a plurality of times.

  In FIG. 11, as the energization of the motor coil is repeatedly stopped and resumed, the temperature of the element when the energization of the motor coil is stopped tends to increase.

  As described above, the temperature increasing tendency of such elements occurs because, in the elements other than the shunt resistor mounted on the motor control device, the heat when overheated by the motor lock is not easily dissipated as much as the shunt resistor. . If the temperature of the shunt resistor is lowered and the energization of the motor coil is resumed before the heat of the elements other than the shunt resistor is sufficiently dissipated, heat is accumulated in the elements other than the shunt resistor and the motor coil. .

  As a result, the element or motor coil may be damaged by the heat accumulated in the element or motor coil.

  The present invention has been made in view of the above, and provides a motor control device that prevents damage to circuit elements and motor coils when heat is accumulated in the circuit elements and motor coils due to motor lock or the like. The purpose is to do.

  In order to solve the above-mentioned problem, the motor control device according to claim 1, a current detection unit that outputs a signal corresponding to a current value between the power source and the motor, and a resistance value that changes with a temperature change. Including a temperature variable resistance element having temperature characteristics, a threshold value output unit that outputs a threshold value according to a change in the resistance value of the temperature variable resistance element, and a signal output from the current detection unit is equal to or greater than the threshold value, A rotation control unit that performs control to stop the rotation of the motor for a predetermined time.

  In the motor control device, the current detection unit detects a current between the power source and the motor and outputs a signal corresponding to the detected current value. The rotation control unit stops the motor as being in an overcurrent state when the signal output from the current detection unit is equal to or greater than a threshold value. Compared with the case where the thermistor detects the heat generated by the current flowing through the circuit and determines the overcurrent state of the motor, the motor can be stopped quickly, and damage to the motor coil and circuit elements can be prevented.

  In this motor control device, the threshold output unit outputs a threshold corresponding to a resistance value corresponding to the temperature of the temperature variable resistance element. Therefore, when heat is accumulated in the circuit element and the motor coil due to motor lock or the like, the overcurrent state is quickly detected and the rotation of the motor is stopped for a predetermined time. Damage to the motor coil can be prevented.

  The motor control device according to claim 2 is the motor control device according to claim 1, wherein the temperature variable resistance element has a temperature characteristic in which a resistance value decreases as the temperature rises, and the threshold output unit A threshold value that is lowered as the resistance value of the temperature variable resistance element decreases as the temperature increases is output.

  According to this motor control device, when the resistance value of the temperature variable resistance element decreases as the temperature rises, the threshold output unit outputs the threshold value reduced according to the resistance value of the temperature variable resistance element. As a result, when heat is accumulated in the circuit element and the motor coil due to motor lock or the like, the rotation of the motor can be quickly stopped based on a lower threshold.

  According to a third aspect of the present invention, in the motor control device according to the first aspect, the temperature variable resistance element has a temperature characteristic in which a resistance value increases with an increase in temperature, and the threshold value output unit increases with an increase in temperature. Then, a threshold value that is lowered as the resistance value of the temperature variable resistance element increases is output.

  According to this motor control device, when the resistance value of the temperature variable resistance element increases as the temperature rises, the threshold output unit outputs the threshold value lowered according to the resistance value of the temperature variable resistance element. As a result, when heat is accumulated in the circuit element and the motor coil due to motor lock or the like, the rotation of the motor can be quickly stopped based on a lower threshold.

It is the schematic which shows the structure of the motor unit using the motor control apparatus which concerns on embodiment of this invention. It is a figure which shows the outline of the motor control apparatus which concerns on embodiment of this invention. It is the schematic of the overcurrent determination value output part which is an example of a voltage dividing circuit. It is the schematic which shows the connection of the chip | tip thermistor and overcurrent determination value output part in embodiment of this invention. It is the schematic which shows the relationship between the electric current value in the bridge circuit of the chip | tip thermistor which concerns on embodiment of this invention, and an overcurrent determination value output part, a voltage value, and resistance value. It is a figure which shows an example of the change of the overcurrent threshold voltage corresponding to the change of the resistance value of bridge resistance in embodiment of this invention. It is a figure which shows an example of the change of the chip | tip thermistor voltage corresponding to the change of the resistance value of bridge resistance in embodiment of this invention. (A) is the schematic which showed an example of the change in the time series of the overcurrent threshold voltage in the motor control apparatus which concerns on embodiment of this invention, (B) concerns on embodiment of this invention. It is the schematic which showed an example of the change in the time series of the chip | tip thermistor voltage in a motor control apparatus. It is the schematic which showed an example of the temperature change of the temperature of the element of the motor control apparatus when the motor lock | rock arises in the motor control apparatus which concerns on embodiment of this invention. It is a flowchart which shows the overcurrent protection control in the motor control apparatus which concerns on embodiment of this invention. It is the schematic which showed an example of the temperature change of the temperature of the element mounted in the board | substrate of a motor drive system when a motor lock | rock occurs.

  FIG. 1 is a schematic diagram showing a configuration of a motor unit 10 using a motor control device 20 according to the present embodiment. The motor unit 10 according to the present embodiment in FIG. 1 is a so-called blower motor unit used for blowing air from a vehicle air conditioner as an example.

  The motor unit 10 according to the present embodiment relates to a three-phase motor having an outer rotor structure in which a rotor 12 is provided outside a stator 14. The stator 14 is an electromagnet in which a lead wire is wound around a core member, and constitutes three phases of a U phase, a V phase, and a W phase.

  Each of the U-phase, V-phase, and W-phase of the stator 14 generates a so-called rotating magnetic field by switching the polarity of the magnetic field generated by the electromagnet under the control of the motor control device 20 described later.

  A rotor magnet is provided inside the rotor 12 (not shown), and the rotor magnet rotates the rotor 12 by responding to the rotating magnetic field generated by the stator 14.

  The rotor 12 is provided with a shaft 16 and rotates integrally with the rotor 12. Although not shown in FIG. 1, in the present embodiment, the shaft 16 is provided with a multi-blade fan such as a so-called sirocco fan, and the multi-blade fan rotates together with the shaft 16, thereby blowing air in the vehicle air conditioner. It becomes possible.

  The stator 14 is attached to the motor control device 20 via the upper case 18. The motor control device 20 includes a substrate 22 of the motor control device 20 and a heat sink 24 that dissipates heat generated from elements on the substrate 22.

  A lower case 28 is attached to the motor unit 10 including the rotor 12, the stator 14, and the motor control device 20.

  FIG. 2 is a diagram schematically showing the motor control device 20 according to the present embodiment. The inverter circuit 40 shown in FIG. 2 switches the electric power supplied to the coil of the stator 14 of the motor 52 by FET (Field Effect Transistor). For example, the inverter FETs 44A and 44D switch the power supplied to the U-phase coil 14U, the inverter FETs 44B and 44E switch to the V-phase coil 14V, and the inverter FETs 44C and 44F switch the power supplied to the W-phase coil 14W.

  The drains of the inverters FETs 44A, 44B, and 44C are connected to the positive electrode of the on-vehicle battery 80 via the choke coil 82. The sources of the inverters FET 44D, 44E, and 44F are connected to the negative electrode of the battery 80.

  Further, on the board of the motor control device 20 of the present embodiment, in addition to the inverter circuit 40 described above, a comparator 54, an actual rotation number calculation unit 56, a command rotation number calculation unit 58, a standby circuit 60, a main power supply energization unit 62, an energization control drive waveform determination unit 64, a PI control unit 66, a voltage correction unit 68, an FET driver 70, and the like are mounted.

  A choke coil 82 and smoothing capacitors 84A and 84B are mounted on the substrate of the motor control device 20 of the present embodiment, and an air conditioner ECU (Electronic Control Unit) 78 and a battery 80 are connected. The choke coil 82 and the smoothing capacitors 84A and 84B together with the battery 80 constitute a substantially DC power source. The air conditioner ECU 78 is an electronic control unit for a vehicle air conditioner. When the user turns on the air conditioner by the air conditioner ECU 78, the motor 52 is operated under the control of the motor control device 20. When the user adjusts the air volume of the vehicle air conditioner, a signal for instructing the rotational speed of the motor 52 (rotor 12) is input via the air conditioner ECU 78.

  In the present embodiment, the Hall element 12B detects the magnetic field of the sensor magnet 12A provided coaxially with the shaft 16. The comparator 54 is a device that converts the analog output of the Hall element 12 </ b> B into a digital signal, and the actual rotational speed calculation unit calculates the actual rotational speed of the rotor 12 based on the digital signal output from the comparator 54. The command rotation number calculation unit calculates a target rotation speed based on an instruction from the air conditioner ECU 78 or the like. In the present embodiment, the target rotation speed is approximately 1000 to 5000 rpm.

  The PI controller 66 changes the coil of the stator 14 when changing the actual rotational speed to the target rotational speed from the target rotational speed calculated by the command rotational speed calculator 58 and the actual rotational speed calculated by the actual rotational speed calculator 56. The voltage applied to is calculated by so-called PI control. The PI control unit 66 includes a deviation proportional unit 66P that calculates a voltage at the target rotational speed based on a proportional relationship between a deviation between the target rotational speed and the actual rotational speed and a deviation between the voltage at the target rotational speed and the voltage at the actual rotational speed. Including. Further, the PI control unit 66 includes a deviation integration unit 66I that eliminates the residual deviation by deviation integration when the residual deviation is generated only by the proportional relationship. The voltage correction unit 68 corrects the voltage applied to the coil of the stator 14 based on the calculation result by the PI control unit 66.

  The standby circuit 60 is a circuit that controls power supply from the battery 80 to each unit. The main power supply energization unit 62 turns on the power to the motor control device according to the control of the standby circuit 60. Further, the main power supply energizing unit 62 issues a command to the forced 500 rpm command unit 88 via the OR circuit 86 when the motor 52 is started, that is, when the motor 52 is rotated from a rotation speed of 0 rpm. The forced 500 rpm command unit 88 controls the command rotational speed calculation unit 58 so that the target rotational speed becomes 500 rpm at a predetermined time when the motor 52 is started, and the command rotational speed calculation unit 58 performs PI control on a signal related to 500 rpm. The data is output to the unit 66. The predetermined time is 500 to 1000 milliseconds as an example.

  After the predetermined time has elapsed, the control to the command rotational speed calculation unit 58 by the forced 500 rpm command unit is finished, and the command rotational speed calculation unit 58 outputs a signal related to the target rotational speed calculated based on an instruction from the air conditioner ECU 78. Output to the PI controller 66.

  When power is supplied via the standby circuit 60 and the main power supply energization unit 62, the energization control drive waveform determination unit 64 determines the position of the rotor 12 based on the digital signal output from the comparator 54, and determines the position of the rotor 12. Based on the target rotational speed calculated by the command rotational speed calculation unit 58, the drive waveform of the voltage applied to the coil of the stator 14 is determined.

  The FET driver 70 generates a PWM signal for controlling the switching of the inverter circuit 40 based on the drive waveform determined by the energization control drive waveform determination unit 64 and the voltage value corrected by the voltage correction unit 68 to generate an inverter. Output to the circuit 40.

  Further, on the substrate of the motor control device 20 according to the present embodiment, a chip thermistor that detects the temperature of the substrate as a resistance value is applied with a control voltage Vcc at one end via a resistor R3 and the other end grounded. RT is implemented. The chip thermistor RT used in this embodiment is an NTC (Negative Temperature Coefficient) thermistor whose resistance decreases with increasing temperature, and the resistance value of the chip thermistor RT decreases with increasing temperature. Note that a PTC (Positive Temperature Coefficient) thermistor whose resistance value increases as the temperature rises by using an inverting circuit together may be used.

  The chip thermistor RT and the resistor R3 form a kind of voltage dividing circuit, and a voltage that changes based on the resistance value of the chip thermistor RT is output from one end of the chip thermistor RT connected to the resistor R3. . The voltage output from one end of the chip thermistor RT is compared with the overheat determination value output from the overheat determination value output unit 104 in the overheat state determination unit 106, and the voltage output from one end of the chip thermistor RT is equal to or less than the overheat determination value. The command rotational speed calculation unit 58 is controlled so as to force the target rotational speed to 0 rpm. As described above, since the chip thermistor RT according to the present embodiment is a type in which the resistance decreases as the temperature rises, the chip thermistor that is also the output terminal of the voltage dividing circuit composed of the resistor R3 and the chip thermistor RT. The voltage output from one end of RT decreases as the temperature increases. The overheat state determination unit 106 determines that the circuit is overheated when the voltage output from one end of the chip thermistor RT is equal to or less than the overheat determination value. The overheat determination value varies depending on the element mounted on the substrate and the position of the chip thermistor RT.

  In addition, a current detection unit 94 is provided between the source of each of the inverters FETs 44D, 44E, and 44F and the battery 80. The current detection unit 94 has a shunt resistor 94A having a resistance value of about 0.2 mΩ to several Ω, and an amplifier 94B that amplifies the potential difference between both ends of the shunt resistor 94A and outputs a voltage value proportional to the current of the shunt resistor 94A as a signal. The signal output from the amplifier 94B is input to the overload determination unit 98 and the overcurrent determination unit 102, respectively. The overcurrent determination unit 102 compares the signal output from the amplifier 94B with the overcurrent determination value output from the overcurrent determination value output unit 100. If the signal output from the amplifier 94B is greater than or equal to the overcurrent determination value, the overcurrent determination value is compulsory. Thus, by stopping the output of the voltage correction unit 68, the rotation of the motor 52 is stopped. The overload determination unit 98 compares the signal output from the amplifier 94B with the overload determination value output from the overload determination value output unit 96, and when the signal output from the amplifier 94B is equal to or greater than the overload determination value. Sends a command to the forced 500 rpm command section 88 via the OR circuit 86 to control the motor 52 to forcibly reduce the rotational speed of the motor 52 to a predetermined rotational speed of 500 rpm.

  In the present embodiment, the overcurrent determination value is a value that exceeds the overload determination value, and is a voltage value corresponding to a current for which the rotation of the motor 52 must be urgently stopped for circuit protection. Since the specific values of the overcurrent determination value and the overload determination value depend on the specifications of the motor 52, they are specifically determined for each motor specification through simulation and experiment at the time of design. Various circuit configurations of the overcurrent determination value output unit 100 and the overload determination value output unit 96 are conceivable. As an example, a voltage dividing circuit as shown in FIG. 3 is used.

  After determining the overcurrent state and stopping the rotation of the motor 52, the voltage application to the coil of the stator 14 is interrupted for a predetermined time to prevent the circuit from being damaged. The predetermined time is, for example, 100 milliseconds, and the application of voltage to the coil is interrupted for 100 milliseconds. Thereafter, the voltage application is resumed. If the overcurrent determination value is exceeded, the voltage application is interrupted again.

  Further, when it is determined that the motor is overloaded and the rotation speed of the motor 52 is set to 500 rpm, the rotation speed of the motor 52 is set to 500 rpm until the voltage value corresponding to the current detected by the current detection unit 94 falls below the overload determination value. Control. After the voltage value corresponding to the current detected by the current detector 94 falls below the overload determination value, the coil of the stator 14 is rotated so that the motor 52 rotates at the target rotational speed calculated by the command rotational speed calculator 58. Control the voltage to be applied.

  In this embodiment, a bridge circuit is configured in which the end (output end) of the chip thermistor RT to which the resistor R3 is connected and the output end of the overcurrent determination value output unit 100 are connected via the bridge resistor RB. Yes. As long as the bridge circuit can be configured, other connection means such as a conductor or a diode may be used in addition to the bridge resistor RB.

  FIG. 4 is a schematic diagram showing the connection between the chip thermistor RT and the overcurrent determination value output unit 100 in the present embodiment. The overcurrent determination value output unit 100 and the chip thermistor RT each constitute a voltage dividing circuit, and both voltage dividing circuits are connected by a bridge resistor RB.

The resistance values of the resistors shown in FIG. 4 are as follows as an example, except for the chip thermistor RT whose resistance value varies with temperature. Further, the bridge resistance RB is changed stepwise in the range of 10 to 90 kΩ as will be described later, and an optimum resistance value is selected in order to eliminate the overcurrent state.
R1: 49.9kΩ
R2: 30.1kΩ
R3: 3.57 kΩ
RB: 10 to 90 kΩ

FIG. 5 is a schematic diagram showing a relationship between a current value, a voltage value, and a resistance value in a bridge circuit between the NTC type chip thermistor RT and the overcurrent determination value output unit 100 according to the present embodiment. The resistance value of the resistor R1 _{R 1,} the resistance value of the resistor R2 _{R 2,} the resistance value of the resistor R3 _{R 3,} the resistance value of the chip thermistor RT _{R T,} the resistance value of the bridge resistor RB and _{R B.} The current value of the current I1 flowing through the resistor R1 is I ₁ , the current value of the current IB flowing through the bridge resistor RB is I _B , the current value of the current I3 flowing through the resistor R3 is I ₃ , and an overcurrent is an overcurrent determination value. the voltage value of the threshold voltage VO _{V o,} the voltage value of the chip thermistor voltage VT and _{V T,} the following equation (1) to (5) is derived.

Further, from FIG. _{5, I 3 = (Vcc-} V T) / R 3, I B = (V O -V T) / from _R is _B, and these _I 3, the _{I B} of the formula (5) When substituted, the following equation (6) is obtained.

From the above formula (6) and the above formulas (1) to (4), the following formulas (7) and (8) are obtained.

  FIG. 6 is a diagram illustrating an example of a change in the overcurrent threshold voltage VO corresponding to a change in the resistance value of the bridge resistor RB in the present embodiment. Using the above equation (7), Vcc is 5 V, the resistance value of the bridge resistor RB is 10, 20, 30, 40, 50, 60, 70, 80, 90 kΩ and the resistance value is infinite when the bridge resistor RB is not mounted. The overcurrent threshold voltage VO is calculated by changing each largely.

  As shown in FIG. 6, the overcurrent threshold voltage VO is high when the temperature of the chip thermistor RT is low, and it is excessive when the temperature of the chip thermistor RT is high, compared to the infinite case where the bridge resistor RB is not mounted. The current threshold voltage VO is lowered. The chip thermistor RT used in the present embodiment is an NTC thermistor whose resistance decreases with increasing temperature. Therefore, when the temperature of the circuit rises and the resistance value of the chip thermistor RT decreases, the voltage of the overcurrent determination value output unit 100 is easily divided to the chip thermistor RT side via the bridge resistor RB, and the overcurrent threshold voltage VO Decreases.

  If the overcurrent threshold voltage VO decreases, the overcurrent state can be determined more quickly. Since the overcurrent often accompanies overheating of the circuit, if the overcurrent threshold voltage VO decreases when the temperature of the chip thermistor RT is high, the overcurrent threshold voltage VO does not decrease at a high temperature more quickly than when the overcurrent threshold voltage VO does not decrease. The state can be determined and circuit damage can be prevented quickly.

  When the present embodiment is mounted on a vehicle air conditioner, the overcurrent threshold voltage VO at a safe temperature at which the circuit is not damaged or the like is obtained from the result or experiment of FIG. By selecting the bridge resistance, it is possible to determine overcurrent to prevent circuit damage. For example, if the safe temperature at which the circuit is not damaged is 140 ° C. and the overcurrent threshold voltage VO is 1.5 V or less at 140 ° C., the resistance value of the bridge resistor RB is 20 kΩ.

  FIG. 7 is a diagram showing an example of the change in the chip thermistor voltage VT corresponding to the change in the resistance value of the bridge resistor RB in the present embodiment, and is calculated using the above equation (8). As shown in FIG. 7, even if the value of the bridge resistor RB changes, the value of the chip thermistor voltage VT does not change greatly, and in the present embodiment in which the bridge circuit is configured, the circuit by the overheat state determination unit 106 is used. There is no hindrance in judging the overheating state.

  FIG. 8A is a schematic diagram illustrating an example of a time-series change of the overcurrent threshold voltage VO in the motor control device 20 according to the present embodiment, and FIG. 8B is a diagram illustrating the present embodiment. It is the schematic which showed an example of the change in the time series of the chip | tip thermistor voltage VT in the motor control apparatus 20 which concerns on.

  In FIG. 8A, a motor lock overcurrent threshold voltage 120, which is a time-series change of the overcurrent threshold voltage VO when a motor is locked due to foreign matter interfering with the fan or the like, is indicated by a solid line. Yes. In FIG. 8A, a normal overcurrent threshold voltage 122, which is a time-series change of the normal overcurrent threshold voltage VO in which motor lock has not occurred, is indicated by a broken line.

  When the circuit and the coil 14 are not overheated due to a motor lock or the like, the overcurrent threshold voltage VO is constant and does not change like the normal overcurrent threshold voltage 122 indicated by a broken line in FIG. . However, when the motor is locked, the overcurrent threshold voltage VO gradually decreases with time and converges to a constant value as the motor lock overcurrent threshold voltage 120 indicated by the solid line in FIG. I will do it.

  In the present embodiment, the overcurrent threshold voltage VO decreases as the chip thermistor temperature increases as shown in FIG. Further, as described above, in the motor lock state, since heat is easily accumulated in the elements and the coil 14 constituting the motor control device 20, the chip thermistor temperature also rises due to the accumulated heat. . As a result, when the motor lock is not released, the overcurrent threshold voltage 120 at the time of motor lock gradually decreases.

  In the present embodiment, the chip thermistor voltage VT also decreases as the chip thermistor temperature rises as shown in FIG. Therefore, in the motor lock state, the temperature of the chip thermistor rises due to the influence of the heat accumulated in the elements and the coil 14 constituting the motor control device 20, so as shown in FIG. The chip thermistor voltage VT decreases with time.

  In the present embodiment, when the chip thermistor voltage VT decreases, it is determined that the motor 52 or the circuit board is in a heated state, and energization to the coil 14 of the motor 52 is suppressed. Therefore, apart from the case where the overcurrent determination unit 102 determines that the overcurrent state occurs, the coil 14 of the motor 52 and the elements of the circuit board can be prevented from being damaged by heat.

  FIG. 9 is a schematic diagram illustrating an example of a temperature change of the element temperature of the motor control device 20 when the motor lock occurs at time t1 in the motor control device 20 according to the present embodiment. In FIG. 9, the element temperature 124 when the bridge resistor is mounted, which is the element temperature in the motor control device 20 according to the present embodiment, is indicated by a solid line. Also, in FIG. 9, unlike the present embodiment, the element temperature 126 at the time of non-mounting of the bridge resistance indicating the tendency of the temperature change of the element when the bridge resistance RB is not mounted is indicated by a broken line.

  As shown in FIG. 9, in the motor lock state, the element temperature 126 when the bridge resistor is not mounted shows a tendency to increase with time. When the bridge resistor is mounted, the element temperature 124 is repeatedly reduced from the peak maximum value to the minimum value and then to the peak maximum value again. Although the element temperature 124 at the time of mounting the bridge resistance shown in FIG. 9 is determined to be an overcurrent state when the maximum value is reached and the coil 14 is deenergized, the element temperature 124 is reduced to the minimum value. Since it has not been solved, it has repeatedly reached the maximum value again.

  When the motor lock is not released, the maximum value and the minimum value of the element temperature 124 when the bridge resistor is mounted are increased with time, but their increase rate is lower than the element temperature 126 when the bridge resistor is not mounted.

  As described above, in the present embodiment, the overcurrent threshold voltage VO decreases as the chip thermistor temperature increases. Therefore, when the motor lock occurs in the overheated state or the state close to the overheated state, the overcurrent threshold voltage VO is lowered, so that the power supply to the coil 14 can be quickly cut off, and the temperature rise of the elements and the like is suppressed. The

  FIG. 10 is a flowchart showing overcurrent protection control in the motor control device 20 according to the present embodiment. The overcurrent protection control is started when the overcurrent determination unit 102 determines that the signal output from the current detection unit 94 is equal to or greater than the overcurrent determination value. In step 400, the coil of the motor 52 is stopped in order to stop the rotation of the motor 52. 14 is stopped for a predetermined time. In step 402, the overcurrent determination unit 102 determines again whether the signal output from the current detection unit 94 is equal to or greater than the overcurrent determination value. If the determination is affirmative, the procedure returns to step 400, and energization of the coil 14 of the motor 52 is again stopped for a predetermined time. If the determination in step 402 is negative, the overcurrent protection control is terminated by controlling the rotational speed of the motor 52 to the target rotational speed in step 404.

  As described above, in the present embodiment, the temperature of the chip thermistor RT is increased by connecting the output terminal of the chip thermistor RT and the output terminal of the overcurrent determination value output unit 100 via the bridge resistor RB. Accordingly, the overcurrent threshold voltage VO output from the overcurrent determination value output unit 100 is decreased.

  As a result, in the case of motor lock, the rotation of the motor 52 can be quickly stopped, and overheating of the circuit elements of the motor control device 20 and the coil 14 of the motor 52 can be prevented.

DESCRIPTION OF SYMBOLS 10 ... Motor unit, 12 ... Rotor, 12A ... Sensor magnet, 12B ... Hall element, 14 ... Stator, 14U, 14V, 14W ... Coil, 16 ... Shaft, 18 ... Upper case, 20 ... Motor controller, 22 ... Substrate, 24 ... Heat sink, 28 ... Lower case, 40 ... Inverter circuit, 44A, 44B, 44C, 44D, 44E, 44F ... Inverter FET, 52 ... Motor, 54 ... Comparator, 56 ... Actual rotational speed calculation unit, 58 ... Command rotational speed Calculation unit, 60 ... standby circuit, 62 ... main power supply energization unit, 64 ... energization control drive waveform determination unit, 66 ... PI control unit, 66I ... deviation integration unit, 66P ... deviation proportional unit, 68 ... voltage correction unit, 70 ... FET driver, 78 ... air conditioner ECU, 80 ... battery, 82 ... choke coil, 84A, 84B ... smoothing capacitor, DESCRIPTION OF SYMBOLS 6 ... OR circuit, 88 ... Force 500rpm command part, 94 ... Current detection part, 94A ... Shunt resistance, 94B ... Amplifier, 96 ... Overload judgment value output part, 98 ... Overload judgment part, 100 ... Overcurrent judgment value Output unit 102 ... overcurrent determination unit 104 ... overheat determination value output unit 106 ... overheat state determination unit 120 ... overcurrent threshold voltage at motor lock, 122 ... overcurrent threshold voltage at normal time, 124 ... when bridge resistance is mounted Element temperature 126 ... Element temperature when no bridge resistance is mounted, R1, R2, R3, R3 ... Resistance, RB ... Bridge resistance, RT ... Chip thermistor, Vcc ... Control voltage, VO ... Overcurrent threshold voltage, VT ... Chip thermistor voltage

Claims (3)

A current detector that outputs a signal according to the current value between the power source and the motor;
A threshold output unit including a temperature variable resistance element having a temperature characteristic in which a resistance value changes with respect to a temperature change, and outputs a threshold according to a change in the resistance value of the temperature variable resistance element;
A rotation control unit that performs control to stop the rotation of the motor for a predetermined time when the signal output from the current detection unit is equal to or greater than the threshold;
A motor control device comprising: The temperature variable resistance element has a temperature characteristic in which the resistance value decreases as the temperature rises,
The motor control device according to claim 1, wherein the threshold value output unit outputs a threshold value that is lowered in accordance with a decrease in the resistance value of the temperature variable resistance element as the temperature rises. The temperature variable resistance element has a temperature characteristic in which a resistance value increases with an increase in temperature,
2. The motor control device according to claim 1, wherein the threshold output unit outputs a threshold that is lowered in accordance with an increase in a resistance value of the temperature variable resistance element as the temperature rises.