JP2015033298A - Motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and accurately resolve an overload on a motor and a circuit without stopping rotation of the motor.SOLUTION: A motor control device includes: a current detection section 94 for detecting a current between a battery 80 and an inverter circuit 40; an overload criterion value output section 96 for outputting an overload criterion value; an overload determination section 98 for determining that a motor 52 is overloaded if a current value detected by the current detection section 94 is equal to or greater than the overload criterion value; a chip thermistor RT having one end fed with a voltage Vcc via a resistor R3 and the other end grounded, and having a resistance value varying with temperature; a bridge thermistor RTB connecting the one end of the chip thermistor RT and an output end of the overload criterion value output section 96, and having a resistance value varying with temperature; and a forced 500 rpm command section 88 for controlling a rotational speed of the motor 52 to a predetermined speed of 500 rpm if the overload determination section 98 determines that the motor 52 is overloaded.

Description

  The present invention relates to a motor control device.

  Among the motors, for example, a blower motor used for blowing air from a vehicle air conditioner stops the rotation of the blower motor if the blower motor is impeded by foreign matter such as dead leaves that enter from the outside of the vehicle and the blower motor load increases. Performs load protection control. By executing such overload protection, overheating of the blower motor control device circuit and the blower motor stator coil due to overload is prevented.

  FIG. 13 is a schematic diagram illustrating an example of a motor control device that determines a motor overload based on a current value between the inverter circuit 40 and the negative electrode of the battery 80. In FIG. 13, a current detection unit 94 is provided between the source of each of the inverters FETs 44 </ b> D, 44 </ b> E, and 44 </ b> F and the battery 80. The current detection unit 94 includes a shunt resistor 94A and an amplifier 94B that amplifies the detected current value by detecting the current value of the shunt resistor 94A. The signal output from the amplifier 94B is an overload determination unit 98 and an overcurrent determination. Are input to the unit 102.

  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, and the overload determination unit 98 compares the signal output from the amplifier 94B with the overcurrent determination value. The overload determination value output by the load determination value output unit 96 is compared. The signals output from the overcurrent determination unit 102 and the overload determination unit 98 are input to the OR circuit 130.

  The OR circuit 130 outputs a voltage correction unit 68 when the signal output from the amplifier 94B is determined to be greater than or equal to the overcurrent determination value by the overcurrent determination unit 102 or when the overload determination unit 98 determines greater than or equal to the overload determination value. A signal that forcibly stops the output of is output. As a result, when it is determined that the circuit is in an overload state or an overcurrent state, the rotation of the motor 52 can be stopped and the circuit can be prevented from being burned out.

  In addition, a filter for preventing foreign matters from entering is provided in the intake system of the vehicle air conditioner. However, since such a filter can become an intake resistance, the vehicle air conditioner may be used with the filter removed. When the filter of the intake system is removed, the air flow rate of the air conditioner increases, but the blower motor tends to maintain the same rotation by controlling the rotation speed, and therefore the blower motor tends to have a high torque (= high load).

  In addition, the blower motor cools circuits such as the motor control device with a part of the fan airflow, but if the airflow of the fan changes greatly with the filter of the intake system removed, a part of the airflow from the fan is reduced. It cannot be introduced to the cooling of the circuit, and the circuit is likely to overheat.

  When the load of the blower motor increases, the overload protection control for stopping the rotation of the blower motor is executed as described above in order to prevent overheating of the motor control device. However, in the situation where the filter of the intake system is removed and the blower motor is likely to over-rotate, the above-described overload protection control is frequently executed, and the smooth operation of the vehicle air conditioner cannot be expected. there were.

  Patent Document 1 discloses a motor that prevents overheating of a circuit by lowering the level of a motor rotation speed command signal when the temperature of a shunt resistor arranged in a path for supplying driving power to the motor reaches a predetermined temperature. An overload protection device for a drive system is disclosed.

Japanese Patent No. 3801015

  There is a correlation between the motor load and the current supplied to the motor, and the current supplied to the motor increases as the motor load increases. However, in the invention described in Patent Document 1, since the thermistor detects the heat generated in the shunt resistor by the current and determines the load of the motor, the load of the motor is determined by the magnitude of the current supplied to the motor. Compared to the case, there is a problem that quick determination is difficult. The invention described in Patent Document 1 also has a problem that it is difficult for the thermistor to be affected by temperature changes due to the amount of current in the motor winding, and it is difficult to accurately grasp the overheating state of the circuit.

  The present invention has been made in view of the above, and an object of the present invention is to provide a motor control device that can quickly and accurately eliminate an overload state of a motor and a circuit without stopping the rotation of the motor.

  In order to solve the above-mentioned problem, the motor control device according to claim 1, a current detection unit that detects a current flowing between a power source and an inverter circuit that generates a voltage to be applied to a coil of the motor, and the motor An overload determination value output means for outputting an overload determination value for determining whether or not an overload is present; and when the current value detected by the current detection means is equal to or greater than the overload determination value, the motor is overloaded. An overload judging means for judging that there is a thermistor having a characteristic in which a voltage is applied to one end via a resistor and the other end is grounded, and the resistance value decreases as the temperature rises, and a resistance increases as the temperature rises The value decreases, and the one end of the thermistor and the output end of the overload determination value output means are connected to output the output end of the overload determination value output means as the temperature rises. A temperature variable resistor that reduces the voltage of the overload determination value, and a rotation speed that performs control to reduce the rotation speed of the motor to a predetermined speed when the overload determination means determines that the motor is overloaded Control means.

  In this motor control device, the current detection means detects the current between the power supply and the inverter circuit. The overload determination means compares the current detected by the current detection means with a predetermined overload determination value to determine whether or not the motor is overloaded, so the heat generated by the current flowing through the circuit is detected by the thermistor. As compared with the case where the motor overload is detected and the motor is overloaded, the determination can be made quickly and accurately.

  Further, in this motor control device, as the circuit temperature rises, the temperature variable resistance and the resistance value of the thermistor decrease, whereby the voltage of the overload determination value is divided through the temperature variable resistance. As a result, the overload judgment value, which is the current value output by the overload judgment value output means, is also reduced. Therefore, when there is a possibility that the circuit is overheated, the motor overload is quickly detected based on the lower overload judgment value. The load can be determined.

  Further, in the case where there is a possibility that the circuit is overheated as described above, the motor control device determines whether the motor is overloaded quickly based on a lower overload determination value, and then the overload determination means If it is determined that, the motor is controlled to rotate at a predetermined rotational speed. With this control, it is possible to quickly and accurately eliminate the overload state of the motor and circuit without stopping the rotation of the motor.

  A motor control device according to a second aspect of the present invention is the motor control device according to the first aspect, further comprising a resistor connected in parallel to the temperature variable resistor.

  According to this motor control device, the resistance value of the temperature variable resistor can be increased in a low temperature range by relaxing the characteristic of the temperature variable resistor whose resistance value decreases due to temperature change by the resistor connected in parallel with the temperature variable resistor. It is suppressed. Thereby, the change in the voltage in the normal temperature range of the overload determination value output by the overload determination value output means is alleviated, and the product related to the motor control device can be accurately inspected in the normal temperature range.

  According to a third aspect of the present invention, in the motor control device according to the first or second aspect, the temperature variable resistor is a thermistor.

According to this motor control device, by using a thermistor whose resistance value decreases as the circuit temperature rises for the temperature variable resistor, the voltage of the overload judgment value output by the overload judgment value output means as the temperature rises Is divided through a temperature variable resistor. As a result, the overload judgment value, which is the current value output by the overload judgment value output means, is also reduced. Therefore, when there is a possibility that the circuit is overheated, the motor overload is quickly detected based on the lower overload judgment value. The load can be determined.

  According to a fourth aspect of the present invention, in the motor control device according to any one of the first to third aspects, an overcurrent determination value output means for outputting an overcurrent determination value exceeding the overload determination value, and the current detection Overcurrent determination means for determining that the motor is in an overcurrent state when the current value detected by the means is greater than or equal to the overcurrent determination value, and the rotational speed control means includes the overcurrent determination means. When it is determined that the motor is in an overcurrent state, the rotation of the motor is stopped for a predetermined time.

  According to this motor control device, when the current detected by the current detection means is equal to or greater than the overcurrent determination value that is larger than the overload determination value, the motor is determined to be in a more critical overcurrent state than the overload state. To do. In the case of the determination, since the rotation of the motor is stopped for a predetermined time, the motor and the circuit can be prevented from being burned out.

It is the schematic which shows the structure of the motor unit using the motor control apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the outline of the motor control apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the temperature characteristic of the chip | tip thermistor used for the motor control apparatus which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the overload protection control in the motor control apparatus which concerns on the 1st Embodiment of this invention. It is the schematic which shows the connection of the chip | tip thermistor and the overload determination value output part in the 1st 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 the 1st Embodiment of this invention, and an overload determination value, a voltage value, and resistance value. It is a figure which shows an example of the change of the overload threshold voltage VP with respect to the chip | tip thermistor temperature in the 1st Embodiment of this invention. It is a figure which shows an example of the change of the chip | tip thermistor voltage VT with respect to the chip | tip thermistor temperature in the 1st Embodiment of this invention. It is a figure which shows the outline of the motor control apparatus which concerns on the 2nd Embodiment of this invention. (A) is the schematic which shows the connection of the chip thermistor and overload judgment value output part in 1st Embodiment, (B) is the chip thermistor and overload judgment value output part in 2nd Embodiment. It is the schematic which shows the connection. It is a figure which shows an example of the change of the overload threshold voltage VP with respect to the chip | tip thermistor temperature in the 2nd Embodiment of this invention. It is a figure which shows an example of the change of the chip | tip thermistor voltage VT with respect to the chip | tip thermistor temperature in the 2nd Embodiment of this invention. It is the schematic which shows an example of the motor control apparatus which determines the overload of a motor based on the electric current value between an inverter circuit and the negative electrode of a battery.

[First Embodiment]
FIG. 1 is a schematic diagram showing a configuration of a motor unit 10 using a motor control device 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 illustrating the motor control device 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. FIG. 3 is a diagram illustrating an example of temperature characteristics of the chip thermistor used in the motor control device according to the present embodiment. The chip thermistor RT used in the present embodiment is an NTC (Negative Temperature Coefficient) thermistor whose resistance decreases with increasing temperature, and as shown in FIG. 3, the resistance value of the chip thermistor RT increases with increasing temperature. Decrease. 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 resistance value 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. If the resistance value of the chip thermistor RT is equal to or less than the overheat determination value, the target rotational speed is forced. Therefore, the command rotational speed calculation unit 58 is controlled so as to achieve 0 rpm. As described above, the chip thermistor RT according to the present embodiment is a type in which the resistance decreases as the temperature rises. Therefore, the circuit is overheated when the resistance value indicated by the chip thermistor RT is equal to or lower than the overheat determination value. Is determined. The overheat determination value varies depending on the element mounted on the substrate, the position of the chip thermistor RT, and the like. As an example, it is the resistance value of the chip thermistor RT at 145 ° C.

  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 includes a shunt resistor 94A having a resistance value as small as about 0.2 mΩ to several Ω, and an amplifier 94B that detects the current value of the shunt resistor 94A and amplifies the detected current value. The signals are 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 current value that requires the rotation of the motor 52 to 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 on the right in FIG. 5 is used.

  After determining the overcurrent state and stopping the rotation of the motor 52, the application of voltage to the coil of the stator 14 is interrupted for a predetermined time to prevent the circuit from burning out. 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. If the state is repeated a predetermined number of times, it is determined that there is a high risk of circuit burnout, and the application of voltage again is stopped.

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

  In the present 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 overload determination value output unit 96 are connected via the bridge thermistor RTB. doing. The bridge thermistor RTB is an NTC thermistor of the same type as the chip thermistor RT, and its characteristics are as shown in FIG. An element other than the NTC thermistor may be used as long as the resistance value decreases as the temperature increases.

  FIG. 4 is a flowchart showing overload protection control in the motor control apparatus according to the present embodiment. The overload protection control is started when the overload determination unit 98 determines that the current value detected by the current detection unit 94 is equal to or higher than the overload determination value. In step 400, the rotation speed of the motor 52 is controlled to 500 rpm. In step 402, it is determined whether or not the current value detected by the current detection unit 94 in the overload determination unit 98 is equal to or greater than the overload determination value. If the determination is affirmative, the procedure is returned to step 400, and the control for setting the rotation speed of the motor 52 to 500 rpm is continued. If the determination in step 402 is negative, the overload protection control is terminated by controlling the rotational speed of the motor 52 to the target rotational speed in step 404.

  FIG. 5 is a schematic diagram showing the connection between the chip thermistor RT and the overload determination value output unit 96 in the present embodiment. The overload determination value output unit 96 includes resistors R1 and R2, and constitutes a voltage dividing circuit that outputs the control voltage Vcc as the overload threshold voltage VP. The chip thermistor RT is also a resistor whose resistance value changes with temperature, and forms a voltage dividing circuit that outputs the control voltage Vcc as the chip thermistor voltage VT together with the resistor R3. In the present embodiment, the voltage dividing circuits of both the overload determination value output unit 96 and the chip thermistor RT are connected by the bridge thermistor RTB.

The resistance values of the resistors shown in FIG. 5 are as follows as an example, except for the chip thermistor RT and the bridge thermistor RTB whose resistance values vary with temperature.
R1: 49.9kΩ
R2: 30.1kΩ
R3: 3.57k

FIG. 6 is a schematic diagram showing a relationship between a current value, a voltage value, and a resistance value in a bridge circuit between the chip thermistor RT and the overload determination value output unit 96 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 _{R T} of the chip thermistor RT, the resistance value of the bridge thermistor RTB 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 thermistor RTB is I _B , the current value of the current I3 flowing through the resistor R3 is I ₃ , and the voltage value of the overload threshold voltage VP Is V _P , and the voltage value of the chip thermistor voltage VT is V _T , the following equations (1) to (5) are derived.

Further, from FIG. _{7, I 3 = (Vcc-} V T) / R 3, I B = (V P -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. 7 is a diagram illustrating an example of a change in the overload threshold voltage VP with respect to the chip thermistor temperature in the present embodiment. Using the above formula (7), the overload threshold voltage VP is calculated with Vcc being 5V. Further, in FIG. 7, in place of the bridge thermistor RTB, when a bridge resistance having a resistance value of 10, 20, 30, 40, 50, 60, 70, 80, and 90 kΩ is mounted, and a resistance value infinite where the bridge resistance is not mounted. The overload threshold voltage VP calculated in each case is also shown.

  As shown in FIG. 7, when the bridge thermistor RTB or the bridge resistor is mounted, the overload threshold voltage VP is high and the temperature is high when the temperature is low, as compared to the infinite case where the bridge resistor is not mounted. At times, the overload threshold voltage VP becomes low. 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 overload determination value output unit 96 is likely to be divided to the chip thermistor RT side via the bridge thermistor RTB or the bridge resistance. The threshold voltage VP decreases.

  If the overload threshold voltage VP decreases, the overload determination value that is a current value also decreases, and the overload state can be determined more quickly. In particular, an overload often accompanies circuit overheating, so if the overload threshold voltage VP decreases when the temperature of the chip thermistor RT is high, the overload threshold voltage VP does not decrease at a high temperature more quickly. It is possible to quickly determine whether the circuit is burned out. In particular, when a bridge thermistor RTB is used for the bridge circuit, the voltage division becomes remarkable at an equilibrium temperature or higher at which the overload threshold voltage VP is the same as in the case of infinite without resistance, and the overload threshold voltage VP decreases rapidly. Therefore, the overload state of the motor 52 can be determined quickly.

  FIG. 8 is a diagram showing an example of a change in the chip thermistor voltage VT with respect to the chip thermistor temperature in the present embodiment, and is calculated using the above equation (8). As shown in FIG. 8, even if the bridge thermistor RTB is mounted, the value of the chip thermistor voltage VT does not change greatly even if the value of the bridge resistance changes, and even in the present embodiment in which the bridge circuit is configured, There is no problem in the determination of the overheat state of the circuit by the overheat state determination unit 106.

  As described above, in the present embodiment, the overload determination value output unit 96 and the chip thermistor RT, each of which constitutes the voltage dividing circuit, are connected by the bridge thermistor RTB, so that an overload is likely to occur. When the temperature is high, the overload state can be quickly determined.

  Second Embodiment FIG. 9 is a diagram showing an outline of a motor control device according to a second embodiment of the present invention. In FIG. 9, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description of the same components as those in the first embodiment is omitted. The present embodiment is different from the first embodiment in that a parallel resistance RBP is provided in the bridge thermistor RTB.

  FIG. 10A is a schematic diagram showing the connection between the chip thermistor RT and the overload determination value output unit 96 in the first embodiment. The overload determination value output unit 96 and the chip thermistor RT each constitute a voltage dividing circuit, and both voltage dividing circuits are connected by a bridge thermistor RTB. FIG. 10B is a schematic diagram showing the connection between the chip thermistor RT and the overload determination value output unit 96 in the present embodiment. The overload judgment value output unit 96 and the chip thermistor RT constitute a voltage dividing circuit, and both voltage dividing circuits are connected by a bridge thermistor RTB, but are connected in parallel to the bridge thermistor RTB. A parallel resistor RBP is separately provided.

The resistance values of the resistors shown in FIG. 10A are the same as those shown in FIG. The resistance values of the resistors shown in FIG. 10B are as follows as an example, except for the chip thermistor RT and the bridge thermistor RTB whose resistance values change with temperature. Further, the parallel resistance RBP is changed stepwise in the range of 1 to 40 kΩ as described later, and an optimum resistance value is selected in order to eliminate the overload state.
R1: 49.9kΩ
R2: 30.1kΩ
R3: 3.57 kΩ
RBP: 1 to 40 kΩ

  In the present embodiment, the bridge thermistor RTB and the parallel resistor RBP are regarded as one combined resistor, and the overload threshold voltage VP and the chip thermistor voltage VT are calculated using the aforementioned equations (7) and (8).

  FIG. 11 is a diagram illustrating an example of a change in the overload threshold voltage VP corresponding to a change in the resistance value of the parallel resistor RBP in the present embodiment. In FIG. 11, the resistance value of the parallel resistor RBP is changed to 1, 5, 10, 15, 20, 25, 30, 35, 40 kΩ and the resistance value infinite when the parallel resistor RBP is not mounted, respectively, and the overload threshold voltage is changed. VP is calculated. In any case, the overload threshold voltage VP is lower in the high temperature range than the equilibrium temperature, which is the temperature at which the overload threshold voltage VP is the same as that without the bridge, compared to the case without the bridge without the bridge thermistor RTB. doing. Further, a difference is observed in the overload threshold voltage VP in a low temperature range below the equilibrium temperature. In the present embodiment, the parallel resistance RBP is connected in parallel to the bridge thermistor RTB, whereby the change in resistance value due to the temperature of the bridge thermistor RTB is suppressed by the parallel resistance RBP. As a result, the drop of the overload threshold voltage VP in the low temperature range below the equilibrium temperature is reduced compared to the case without the parallel resistor RBP. The drop in the overload threshold voltage VP in the low temperature region decreases as the resistance value of the parallel resistor RBP decreases.

  When the bridge thermistor RTB is mounted, the overload threshold voltage VP can be lowered in the high temperature range as in the first embodiment. However, in the low temperature range, the overload threshold voltage VP is higher than when the bridge thermistor RTB is not mounted. The overload threshold voltage VP becomes maximum when the chip thermistor temperature is 57 ° C., and starts to decrease when the temperature becomes lower than 57 ° C. Thus, if the overload threshold voltage VP has a characteristic that the value of the overload threshold voltage VP changes in response to a temperature change in a low temperature range below the equilibrium temperature, the overload threshold voltage VP is the ambient temperature when the product is inspected. May change and affect test results. In the present embodiment, since the drop of the overload threshold voltage VP in the low temperature range below the equilibrium temperature is suppressed, the risk of hindering product inspection in the low temperature range can be reduced. As an example, if the parallel resistance RBP is 20 kΩ, the change of the overload threshold voltage VP is reduced at 20 ± 20 ° C., and the influence of the ambient temperature in the inspection at the time of product shipment can be eliminated.

  FIG. 12 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 parallel resistor RBP in the present embodiment, and is calculated using the above equation (8). As shown in FIG. 12, even when the parallel resistor RBP is mounted, the value of the chip thermistor voltage VT is not greatly changed, and in this embodiment, the overheat state determination unit 106 has a problem in determining the overheat state of the circuit. Absent.

  As described above, in the present embodiment, by providing the parallel resistance RBP in the bridge thermistor RTB, the characteristics of the bridge thermistor RTB whose resistance value increases in the low temperature range are relaxed by the parallel resistance RBP, A drop in the load threshold voltage VP is suppressed. Therefore, the change in the overload threshold voltage VP in the low temperature region is less than in the case where the parallel resistor RBP is not mounted, and the influence on the inspection result due to the factory ambient temperature can be reduced in the inspection at the time of shipping the product.

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... Real rotation speed calculation section, 58... Command rotation speed calculation section, 60. Main power supply energization section, 64 ... energization control drive waveform determination section, 66 ... PI control section, 66I ... deviation integration section, 66P ... deviation proportional section, 68 ... voltage correction section, 70 ··Dora , 78 ... air conditioner ECU, 80 ... battery, 82 ... choke coil, 84A, 84B ... smoothing capacitor, 86 ... logical sum circuit, 88 ... forced 500rpm command section, 94 ..Current detection unit, 94A ... shunt resistor, 94B ... amplifier, 96 ... overload judgment value output unit, 98 ... overload judgment unit, 100 ... overcurrent judgment value output unit, DESCRIPTION OF SYMBOLS 102 ... Overcurrent determination part, 104 ... Overheat determination value output part, 106 ... Heating state determination part, 130 ... Logical sum circuit, R1, R2, R3 ... Resistance, RTB ... Bridge thermistor, RBP ... Parallel resistance, RT ... Chip thermistor, Vcc ... Control voltage, VP ... Overload threshold voltage, VT ... Chip thermistor voltage

Claims (4)

Current detection means for detecting a current flowing between the power source and an inverter circuit for generating a voltage to be applied to the motor coil;
Overload determination value output means for outputting an overload determination value for determining whether or not the motor is overloaded;
Overload determination means for determining that the motor is overloaded when the current value detected by the current detection means is greater than or equal to the overload determination value;
A thermistor having a characteristic that a voltage is applied to one end via a resistor and the other end is grounded, and the resistance value decreases as the temperature rises;
The resistance value decreases as the temperature rises, and the output of the overload determination value output means is connected as the temperature rises by connecting the one end of the thermistor and the output end of the overload determination value output means. A temperature variable resistor that lowers the voltage of the overload judgment value output by the end; and
A rotation speed control means for performing control to reduce the rotation speed of the motor to a predetermined speed when the overload determination means determines that the motor is overloaded;
A motor control device comprising:   The motor control device according to claim 1, further comprising a resistor connected in parallel to the temperature variable resistor.   The motor control device according to claim 1, wherein the temperature variable resistor is a thermistor. An overcurrent determination value output means for outputting an overcurrent determination value exceeding the overload determination value;
Overcurrent determination means for determining that the motor is in an overcurrent state when the current value detected by the current detection means is greater than or equal to the overcurrent determination value;
Further comprising
The rotation speed control means according to any one of claims 1 to 3, wherein when the overcurrent determination means determines that the motor is in an overcurrent state, the rotation speed control means stops the rotation of the motor for a predetermined time. Motor control device.